Index: /branches/eam_branches/ipp-20100823/psModules/src/imcombine/README
===================================================================
--- /branches/eam_branches/ipp-20100823/psModules/src/imcombine/README	(revision 29170)
+++ /branches/eam_branches/ipp-20100823/psModules/src/imcombine/README	(revision 29170)
@@ -0,0 +1,9 @@
+
+pmSubtractionEquation.v0.c
+
+  This version of the code includes the old-style form of the matrix
+  equations, in which the normalization and background were calculated
+  as part of the matrix inversion.  We've decided that this method is
+  too sensitive to errors in the normalization and no longer use this
+  approach.
+
Index: /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionEquation.c
===================================================================
--- /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionEquation.c	(revision 29169)
+++ /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionEquation.c	(revision 29170)
@@ -21,4 +21,6 @@
 //#define USE_WINDOW                      // Include weight (1/variance) in equation?
 
+# define PENALTY false
+# define MOMENTS (!PENALTY)
 
 //////////////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -170,13 +172,10 @@
 
 // Calculate the least-squares matrix and vector for dual convolution
-static bool calculateDualMatrixVector(psImage *matrix,	      // Least-squares matrix, updated
-                                      psVector *vector,	      // Least-squares vector, updated
+// XXX we could avoid calculating these values on successive passes *if* the stamp has not changed.
+static bool calculateDualMatrixVector(pmSubtractionStamp *stamp,	      // stamp of interest
                                       double normValue,	      // Normalisation, updated
-                                      const psKernel *image1, // Image 1
-                                      const psKernel *image2, // Image 2
+                                      double normValue2,      // Normalisation, updated
                                       const psKernel *weight,  // Weight image
                                       const psKernel *window,  // Window image
-                                      const psArray *convolutions1, // Convolutions of image 1 for each kernel
-                                      const psArray *convolutions2, // Convolutions of image 2 for each kernel
                                       const pmSubtractionKernels *kernels, // Kernels
                                       const psImage *polyValues, // Spatial polynomial values
@@ -184,13 +183,20 @@
                                       )
 {
-    int numKernels = kernels->num;                      // Number of kernels
-    int spatialOrder = kernels->spatialOrder;       // Order of spatial variation
+    int numKernels = kernels->num;			  // Number of kernels
+    int spatialOrder = kernels->spatialOrder;		  // Order of spatial variation
     int numPoly = PM_SUBTRACTION_POLYTERMS(spatialOrder); // Number of polynomial terms
     double poly[numPoly];                                 // Polynomial terms
     double poly2[numPoly][numPoly];                       // Polynomial-polynomial values
 
-    int numParams = numKernels * numPoly;  // Number of regular parameters
-    int numParams2 = numKernels * numPoly; // Number of additional parameters for dual
-    int numDual = numParams + numParams2;  // Total number of parameters for dual
+    int numParams = numKernels * numPoly;		  // Number of regular parameters
+    int numParams2 = numKernels * numPoly;	   // Number of additional parameters for dual
+    int numDual = numParams + numParams2;	   // Total number of parameters for dual
+
+    psImage *matrix = stamp->matrix;		   // Least-squares matrix, updated
+    psVector *vector = stamp->vector;		   // Least-squares vector, updated
+    psKernel *image1 = stamp->image1;		   // Image 1
+    psKernel *image2 = stamp->image2;		   // Image 2
+    psArray *convolutions1 = stamp->convolutions1; // Convolutions of image 1 for each kernel
+    psArray *convolutions2 = stamp->convolutions2; // Convolutions of image 2 for each kernel
 
     psAssert(matrix &&
@@ -199,4 +205,5 @@
              matrix->numRows == numDual,
              "Least-squares matrix is bad.");
+
     psAssert(vector &&
              vector->type.type == PS_TYPE_F64 &&
@@ -232,4 +239,13 @@
     // [kernel 0, x^n y^m][kernel 1 x^n y^m]...[kernel N, x^n y^m]
 
+    // for DUAL convolution analysis, we apply the normalization to I1 as follows:
+    // norm = I2 / I1
+    // 
+    // I1c = norm I1 + \Sum_i a_i norm I1 \cross k_i
+    // I2c =      I2 + \Sum_i b_i      I2 \cross k_i
+
+    // we cannot absorb the normalization into a_i until the analysis is complete, or the
+    // second moment terms are incorrectly calculated.
+
     for (int i = 0; i < numKernels; i++) {
         psKernel *iConv1 = convolutions1->data[i]; // Convolution 1 for index i
@@ -242,9 +258,14 @@
             double sumBB = 0.0;         // Sum of convolution products between image 2
             double sumAB = 0.0;         // Sum of convolution products across images 1 and 2
+
+	    double MxxAA = 0.0;
+	    double MyyAA = 0.0;
+	    double MxxBB = 0.0;
+	    double MyyBB = 0.0;
             for (int y = - footprint; y <= footprint; y++) {
                 for (int x = - footprint; x <= footprint; x++) {
-                    double aa = iConv1->kernel[y][x] * jConv1->kernel[y][x];
+                    double aa = iConv1->kernel[y][x] * jConv1->kernel[y][x] * PS_SQR(normValue);
                     double bb = iConv2->kernel[y][x] * jConv2->kernel[y][x];
-                    double ab = iConv1->kernel[y][x] * jConv2->kernel[y][x];
+                    double ab = iConv1->kernel[y][x] * jConv2->kernel[y][x] * normValue;
                     if (weight) {
                         float wtVal = weight->kernel[y][x];
@@ -262,6 +283,28 @@
                     sumBB += bb;
                     sumAB += ab;
-                }
-            }
+
+		    if (MOMENTS) {
+			MxxAA += x*x*aa;
+			MyyAA += y*y*aa;
+			MxxBB += x*x*bb;
+			MyyBB += y*y*bb;
+		    }
+                }
+            }
+
+	    if (MOMENTS) {
+		MxxAA /= stamp->normSquare1 * PS_SQR(normValue);
+		MyyAA /= stamp->normSquare1 * PS_SQR(normValue);
+		MxxBB /= stamp->normSquare2;
+		MyyBB /= stamp->normSquare2;
+	    }
+
+	    // XXX this makes the Chisq portion independent of the normalization and star flux
+	    // but may be mis-scaling between stars of different fluxes
+	    sumAA /= PS_SQR(stamp->normI2);
+	    sumAB /= PS_SQR(stamp->normI2);
+	    sumBB /= PS_SQR(stamp->normI2);
+
+	    // fprintf (stderr, "i,j : %d %d : M(xx,yy)(AA,BB) : %f %f %f %f\n", i, j, MxxAA, MyyAA, MxxBB, MyyBB);
 
             // Spatial variation of kernel coeffs
@@ -278,4 +321,31 @@
 		    matrix->data.F64[jIndex + numParams][iIndex + numParams] = bb;
 
+		    // add in second moments
+		    if (MOMENTS) {
+			matrix->data.F64[iIndex][jIndex] += kernels->penalty * MxxAA;
+			matrix->data.F64[iIndex][jIndex] += kernels->penalty * MyyAA;
+
+			matrix->data.F64[jIndex][iIndex] += kernels->penalty * MxxAA;
+			matrix->data.F64[jIndex][iIndex] += kernels->penalty * MyyAA;
+
+			matrix->data.F64[iIndex + numParams][jIndex + numParams] += kernels->penalty * MxxBB;
+			matrix->data.F64[iIndex + numParams][jIndex + numParams] += kernels->penalty * MyyBB;
+
+			matrix->data.F64[jIndex + numParams][iIndex + numParams] += kernels->penalty * MxxBB;
+			matrix->data.F64[jIndex + numParams][iIndex + numParams] += kernels->penalty * MyyBB;
+
+			// XXX this uses the single moments, first try
+			// matrix->data.F64[iIndex][jIndex] += kernels->penalty * stamp->MxxI1->data.F32[i]*stamp->MxxI1->data.F32[j];
+			// matrix->data.F64[iIndex][jIndex] += kernels->penalty * stamp->MyyI1->data.F32[i]*stamp->MyyI1->data.F32[j];
+			// 
+			// matrix->data.F64[jIndex][iIndex] += kernels->penalty * stamp->MxxI1->data.F32[i]*stamp->MxxI1->data.F32[j];
+			// matrix->data.F64[jIndex][iIndex] += kernels->penalty * stamp->MyyI1->data.F32[i]*stamp->MyyI1->data.F32[j];
+			// 
+			// matrix->data.F64[iIndex + numParams][jIndex + numParams] += kernels->penalty * stamp->MxxI2->data.F32[i]*stamp->MxxI2->data.F32[j];
+			// matrix->data.F64[iIndex + numParams][jIndex + numParams] += kernels->penalty * stamp->MyyI2->data.F32[i]*stamp->MyyI2->data.F32[j];
+			// 
+			// matrix->data.F64[jIndex + numParams][iIndex + numParams] += kernels->penalty * stamp->MxxI2->data.F32[i]*stamp->MxxI2->data.F32[j];
+			// matrix->data.F64[jIndex + numParams][iIndex + numParams] += kernels->penalty * stamp->MyyI2->data.F32[i]*stamp->MyyI2->data.F32[j];
+		    }
 		    matrix->data.F64[iIndex][jIndex + numParams] = ab;
 		    matrix->data.F64[jIndex + numParams][iIndex] = ab;
@@ -290,5 +360,5 @@
             for (int y = - footprint; y <= footprint; y++) {
                 for (int x = - footprint; x <= footprint; x++) {
-                    double ab = iConv1->kernel[y][x] * jConv2->kernel[y][x];
+                    double ab = iConv1->kernel[y][x] * jConv2->kernel[y][x] * normValue;
                     if (weight) {
                         ab *= weight->kernel[y][x];
@@ -301,4 +371,8 @@
             }
 
+	    // XXX this makes the Chisq portion independent of the normalization and star flux
+	    // but may be mis-scaling between stars of different fluxes
+	    sumAB /= PS_SQR(stamp->normI2);
+
             // Spatial variation of kernel coeffs
 	    for (int iTerm = 0, iIndex = i; iTerm < numPoly; iTerm++, iIndex += numKernels) {
@@ -315,4 +389,9 @@
         double sumAI1 = 0.0;            // Sum of A.I_1 products (for matrix, normalisation)
         double sumBI1 = 0.0;            // Sum of B.I_1 products (for matrix, normalisation)
+
+	double MxxAI1 = 0.0;
+	double MyyAI1 = 0.0;
+	double MxxBI2 = 0.0;
+	double MyyBI2 = 0.0;
         for (int y = - footprint; y <= footprint; y++) {
             for (int x = - footprint; x <= footprint; x++) {
@@ -322,8 +401,8 @@
                 float i2 = image2->kernel[y][x];
 
-                double ai2 = a * i2;
+                double ai2 = a * i2 * normValue;
                 double bi2 = b * i2;
-                double ai1 = a * i1;
-                double bi1 = b * i1;
+                double ai1 = a * i1 * PS_SQR(normValue);
+                double bi1 = b * i1 * normValue;
 
                 if (weight) {
@@ -345,6 +424,30 @@
                 sumAI1 += ai1;
                 sumBI1 += bi1;
-            }
-        }
+
+		if (MOMENTS) {
+		    MxxAI1 += x*x*ai1;
+		    MyyAI1 += y*y*ai1;
+		    MxxBI2 += x*x*bi2;
+		    MyyBI2 += y*y*bi2;
+		}
+            }
+        }
+
+	if (MOMENTS) {
+	    MxxAI1 /= stamp->normSquare1 * PS_SQR(normValue);
+	    MyyAI1 /= stamp->normSquare1 * PS_SQR(normValue);
+	    MxxBI2 /= stamp->normSquare2;
+	    MyyBI2 /= stamp->normSquare2;
+	}
+
+	// fprintf (stderr, "i : %d : M(xx,yy)(AI1,BI2) : %f %f %f %f\n", i, MxxAI1, MyyAI1, MxxBI2, MyyBI2);
+
+	// XXX this makes the Chisq portion independent of the normalization and star flux
+	// but may be mis-scaling between stars of different fluxes
+	sumAI1 /= PS_SQR(stamp->normI2);
+	sumBI1 /= PS_SQR(stamp->normI2);
+	sumAI2 /= PS_SQR(stamp->normI2);
+	sumBI2 /= PS_SQR(stamp->normI2);
+
         // Spatial variation
         for (int iTerm = 0, iIndex = i; iTerm < numPoly; iTerm++, iIndex += numKernels) {
@@ -353,6 +456,17 @@
             double ai1 = sumAI1 * poly[iTerm];
             double bi1 = sumBI1 * poly[iTerm];
-	    vector->data.F64[iIndex]             = ai2 - normValue * ai1;
-	    vector->data.F64[iIndex + numParams] = bi2 - normValue * bi1;
+	    vector->data.F64[iIndex]             = ai2 - ai1;
+	    vector->data.F64[iIndex + numParams] = bi2 - bi1;
+
+	    // fprintf (stderr, "i : %d : V(I1,I2) : %f %f\n", i, vector->data.F64[iIndex], vector->data.F64[iIndex + numParams]);
+
+	    // add in second moments
+	    if (MOMENTS) {
+		vector->data.F64[iIndex]             -= kernels->penalty * MxxAI1;
+		vector->data.F64[iIndex]             -= kernels->penalty * MyyAI1;
+
+		vector->data.F64[iIndex + numParams] -= kernels->penalty * MxxBI2;
+		vector->data.F64[iIndex + numParams] -= kernels->penalty * MyyBI2;
+	    }
         }
     }
@@ -414,9 +528,9 @@
                 // Contribution to chi^2: a_i^2 P_i
                 psAssert(isfinite(penalties1->data.F32[i]), "Invalid penalty");
-		fprintf (stderr, "penalty: %f + %f (%f * %f)\n", matrix->data.F64[index][index], normSquare1 * penalties1->data.F32[i], normSquare1, penalties1->data.F32[i]);
+		// fprintf (stderr, "penalty: %f + %f (%f * %f)\n", matrix->data.F64[index][index], normSquare1 * penalties1->data.F32[i], normSquare1, penalties1->data.F32[i]);
                 matrix->data.F64[index][index] += normSquare1 * penalties1->data.F32[i];
 
-		fprintf (stderr, "penalty: (x^%d y^%d fwhm %f) : %f + %f (%f * %f)\n", kernels->u->data.S32[index], kernels->v->data.S32[index], kernels->widths->data.F32[index], 
-			 matrix->data.F64[index + numParams][index + numParams], normSquare2 * penalties2->data.F32[i], normSquare2, penalties2->data.F32[i]);
+		// fprintf (stderr, "penalty: (x^%d y^%d fwhm %f) : %f + %f (%f * %f)\n", kernels->u->data.S32[index], kernels->v->data.S32[index], kernels->widths->data.F32[index], 
+		// matrix->data.F64[index + numParams][index + numParams], normSquare2 * penalties2->data.F32[i], normSquare2, penalties2->data.F32[i]);
 		matrix->data.F64[index + numParams][index + numParams] += normSquare2 * penalties2->data.F32[i];			     
 		// matrix[i][i] is ~ (k_i * I_1)(k_i * I_1)
@@ -484,4 +598,108 @@
 //////////////////////////////////////////////////////////////////////////////////////////////////////////////
 
+bool pmSubtractionCalculateMoments(
+    pmSubtractionKernels *kernels, // Kernels
+    pmSubtractionStampList *stamps)
+{
+    PM_ASSERT_SUBTRACTION_STAMP_LIST_NON_NULL(stamps, false);
+
+    // XXX skip this, right?
+    return true;
+
+    // these are only used by DUAL mode
+    if (kernels->mode != PM_SUBTRACTION_MODE_DUAL) return true;
+
+    psTimerStart("pmSubtractionCalculateMoments");
+
+    int footprint = stamps->footprint;  // Half-size of stamps
+
+    // Loop over each stamp and calculate its normalization factor 
+    for (int i = 0; i < stamps->num; i++) {
+        pmSubtractionStamp *stamp = stamps->stamps->data[i]; // Stamp of interest
+        if (stamp->status == PM_SUBTRACTION_STAMP_REJECTED) continue;
+        if (stamp->status == PM_SUBTRACTION_STAMP_NONE) continue;
+
+	pmSubtractionCalculateMomentsStamp(kernels, stamp, footprint, stamps->normWindow2, stamps->normWindow1);
+    }
+
+    psLogMsg("psModules.imcombine", PS_LOG_INFO, "Calculate moments: %f sec", psTimerClear("pmSubtractionCalculateMoments"));
+
+    return true;
+}
+
+bool pmSubtractionCalculateMomentsStamp(
+    pmSubtractionKernels *kernels, // Kernels
+    pmSubtractionStamp *stamp,		// stamp on which to save normalization)
+    int footprint,			// (Half-)Size of stamp
+    int normWindow1,			// Window (half-)size for normalisation measurement
+    int normWindow2			// Window (half-)size for normalisation measurement
+    )
+{
+    double Mxx, Myy;
+
+    int numKernels = kernels->num;
+
+    // Generate convolutions: these are generated once and saved
+    if (!pmSubtractionConvolveStamp(stamp, kernels, footprint)) {
+        psError(psErrorCodeLast(), false, "Unable to convolve stamp");
+        return false;
+    }
+
+    if (!stamp->MxxI1) {
+	stamp->MxxI1 = psVectorAlloc (numKernels, PS_TYPE_F32);
+    }
+    if (!stamp->MyyI1) {
+	stamp->MyyI1 = psVectorAlloc (numKernels, PS_TYPE_F32);
+    }
+    if (!stamp->MxxI2) {
+	stamp->MxxI2 = psVectorAlloc (numKernels, PS_TYPE_F32);
+    }
+    if (!stamp->MyyI2) {
+	stamp->MyyI2 = psVectorAlloc (numKernels, PS_TYPE_F32);
+    }
+
+    for (int i = 0; i < numKernels; i++) {
+        pmSubtractionCalculateMomentsKernel(&Mxx, &Myy, stamp->convolutions1->data[i], footprint, normWindow1);
+	stamp->MxxI1->data.F32[i] = Mxx / stamp->normI1;
+	stamp->MyyI1->data.F32[i] = Myy / stamp->normI1;
+        pmSubtractionCalculateMomentsKernel(&Mxx, &Myy, stamp->convolutions2->data[i], footprint, normWindow2);
+	stamp->MxxI2->data.F32[i] = Mxx / stamp->normI2;
+	stamp->MyyI2->data.F32[i] = Myy / stamp->normI2;
+    }
+
+    pmSubtractionCalculateMomentsKernel(&Mxx, &Myy, stamp->image1, footprint, normWindow1);
+    stamp->MxxI1raw = Mxx / stamp->normI1;
+    stamp->MyyI1raw = Myy / stamp->normI1;
+
+    pmSubtractionCalculateMomentsKernel(&Mxx, &Myy, stamp->image2, footprint, normWindow2);
+    stamp->MxxI2raw = Mxx / stamp->normI2;
+    stamp->MyyI2raw = Myy / stamp->normI2;
+
+    // fprintf (stderr, "Mxx I1: %f, Myy I1: %f, Mxx I2: %f, Myy I2: %f\n", stamp->MxxI1raw, stamp->MyyI1raw, stamp->MxxI2raw, stamp->MyyI2raw);
+
+    return true;
+}
+
+bool pmSubtractionCalculateMomentsKernel(double *Mxx, double *Myy, psKernel *image, int footprint, int window) {
+
+    double Sxx = 0.0;
+    double Syy = 0.0;
+    for (int y = - footprint; y <= footprint; y++) {
+        for (int x = - footprint; x <= footprint; x++) {
+            if (PS_SQR(x) + PS_SQR(y) > PS_SQR(window)) continue;
+
+            double flux = image->kernel[y][x];
+
+	    Sxx += PS_SQR(x) * flux;
+	    Syy += PS_SQR(y) * flux;
+        }
+    }
+    *Mxx = Sxx;
+    *Myy = Syy;
+    return true;
+}
+
+///---------
+
 bool pmSubtractionCalculateNormalization(
     pmSubtractionStampList *stamps,
@@ -493,4 +711,5 @@
 
     psVector *norms = psVectorAllocEmpty(stamps->num, PS_TYPE_F64); // Normalisations
+    psVector *norm2 = psVectorAllocEmpty(stamps->num, PS_TYPE_F64); // Normalisations
 
     int footprint = stamps->footprint;  // Half-size of stamps
@@ -510,4 +729,5 @@
 	}
 	psVectorAppend(norms, stamp->norm);
+	psVectorAppend(norm2, stamp->normSquare2 / stamp->normSquare1);
     }
 
@@ -517,12 +737,24 @@
 	psFree(stats);
 	psFree(norms);
+	psFree(norm2);
 	return false;
     }
     stamps->normValue = stats->robustMedian;
 
-    fprintf (stderr, "norm (1): %f\n", stamps->normValue);
+    psStatsInit(stats);
+    if (!psVectorStats(stats, norm2, NULL, NULL, 0)) {
+	psError(PM_ERR_DATA, false, "Unable to determine median normalisation");
+	psFree(stats);
+	psFree(norms);
+	psFree(norm2);
+	return false;
+    }
+    stamps->normValue2 = stats->robustMedian;
+
+    fprintf (stderr, "norm (1): %f (%f)\n", stamps->normValue, stamps->normValue2);
 
     psFree(stats);
     psFree(norms);
+    psFree(norm2);
 
     psLogMsg("psModules.imcombine", PS_LOG_INFO, "Calculate normalization: %f sec", psTimerClear("pmSubtractionCalculateNormalization"));
@@ -560,4 +792,6 @@
     }
     stamp->norm = normI2 / normI1;
+    stamp->normI1 = normI1;
+    stamp->normI2 = normI2;
     stamp->normSquare1 = normSquare1;
     stamp->normSquare2 = normSquare2;
@@ -675,7 +909,5 @@
         break;
       case PM_SUBTRACTION_MODE_DUAL:
-        status = calculateDualMatrixVector(stamp->matrix, stamp->vector, stamps->normValue, stamp->image1, stamp->image2,
-                                           weight, window, stamp->convolutions1, stamp->convolutions2,
-                                           kernels, polyValues, footprint);
+        status = calculateDualMatrixVector(stamp, stamps->normValue, stamps->normValue2, weight, window, kernels, polyValues, footprint);
         break;
       default:
@@ -924,5 +1156,7 @@
 #endif
 
-        calculatePenalty(sumMatrix, sumVector, kernels, normSquare1, normSquare2);
+	if (PENALTY) {
+	    calculatePenalty(sumMatrix, sumVector, kernels, normSquare1, normSquare2);
+	}
 
         psVector *solution = NULL;                       // Solution to equation!
@@ -930,5 +1164,5 @@
         psVectorInit(solution, 0);
 
-	solution = psMatrixSolveSVD(solution, sumMatrix, sumVector, 1e-6);
+	solution = psMatrixSolveSVD(solution, sumMatrix, sumVector, NAN);
 
 #if (1)
@@ -947,8 +1181,15 @@
         }
 
+	// for DUAL convolution analysis, we apply the normalization to I1 as follows:
+	// I1c = norm I1 + \Sum_i a_i norm I1 \cross k_i
+	// I2c =      I2 + \Sum_i b_i      I2 \cross k_i
+
+	// We absorb the normalization into a_i after the analysis is complete to be consistent
+	// with the SINGLE definitions of the convolutions
+
 	int numKernels = kernels->num;
 	for (int i = 0; i < numKernels * numSpatial; i++) {
-	    // XXX fprintf (stderr, "keep\n");
-	    kernels->solution1->data.F64[i] = solution->data.F64[i];
+	    // we solve for coefficients 
+	    kernels->solution1->data.F64[i] = solution->data.F64[i] * stamps->normValue;
 	    kernels->solution2->data.F64[i] = solution->data.F64[i + numSolution1];
 	}
Index: /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionEquation.h
===================================================================
--- /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionEquation.h	(revision 29169)
+++ /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionEquation.h	(revision 29170)
@@ -78,3 +78,17 @@
   );
 
+bool pmSubtractionCalculateMoments(
+    pmSubtractionKernels *kernels, // Kernels
+    pmSubtractionStampList *stamps);
+
+bool pmSubtractionCalculateMomentsStamp(
+    pmSubtractionKernels *kernels, // Kernels
+    pmSubtractionStamp *stamp,		// stamp on which to save normalization)
+    int footprint,			// (Half-)Size of stamp
+    int normWindow1,			// Window (half-)size for normalisation measurement
+    int normWindow2			// Window (half-)size for normalisation measurement
+    );
+
+bool pmSubtractionCalculateMomentsKernel(double *Mxx, double *Myy, psKernel *image, int footprint, int window);
+
 #endif
Index: /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionEquation.v0.c
===================================================================
--- /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionEquation.v0.c	(revision 29170)
+++ /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionEquation.v0.c	(revision 29170)
@@ -0,0 +1,2238 @@
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <stdio.h>
+#include <string.h>
+#include <pslib.h>
+
+#include "pmErrorCodes.h"
+#include "pmSubtraction.h"
+#include "pmSubtractionKernels.h"
+#include "pmSubtractionStamps.h"
+#include "pmSubtractionThreads.h"
+
+#include "pmSubtractionEquation.h"
+#include "pmSubtractionVisual.h"
+
+//#define TESTING                         // TESTING output for debugging; may not work with threads!
+
+//#define USE_WEIGHT                      // Include weight (1/variance) in equation?
+//#define USE_WINDOW                      // Include weight (1/variance) in equation?
+
+
+//////////////////////////////////////////////////////////////////////////////////////////////////////////////
+// Private (file-static) functions
+//////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+// Calculate the least-squares matrix and vector
+static bool calculateMatrixVector(psImage *matrix, // Least-squares matrix, updated
+                                  psVector *vector, // Least-squares vector, updated
+                                  double *norm,     // Normalisation, updated
+                                  const psKernel *input, // Input image (target)
+                                  const psKernel *reference, // Reference image (convolution source)
+                                  const psKernel *weight,  // Weight image
+                                  const psKernel *window,  // Window image
+                                  const psArray *convolutions,         // Convolutions for each kernel
+                                  const pmSubtractionKernels *kernels, // Kernels
+                                  const psImage *polyValues, // Spatial polynomial values
+                                  int footprint, // (Half-)Size of stamp
+                                  int normWindow1, // Window (half-)size for normalisation measurement
+                                  int normWindow2, // Window (half-)size for normalisation measurement
+                                  const pmSubtractionEquationCalculationMode mode
+                                  )
+{
+    // (I - R * sum_i a_i k_i - g) (R * k_j) = 0
+    // I C_j = sum_i C_i C_j
+
+    // Background: C_i = 1.0
+    // Normalisation: C_i = R
+
+    int numKernels = kernels->num;                      // Number of kernels
+    int normIndex = PM_SUBTRACTION_INDEX_NORM(kernels); // Index for normalisation
+    int bgIndex = PM_SUBTRACTION_INDEX_BG(kernels); // Index in matrix for background
+    int spatialOrder = kernels->spatialOrder;       // Order of spatial variation
+    int numPoly = PM_SUBTRACTION_POLYTERMS(spatialOrder); // Number of polynomial terms
+    double poly[numPoly];                                 // Polynomial terms
+    double poly2[numPoly][numPoly];                       // Polynomial-polynomial values
+
+    // Evaluate polynomial-polynomial terms
+    // XXX we can skip this if we are not calculating kernel coeffs
+    for (int iyOrder = 0, iIndex = 0; iyOrder <= spatialOrder; iyOrder++) {
+        for (int ixOrder = 0; ixOrder <= spatialOrder - iyOrder; ixOrder++, iIndex++) {
+            double iPoly = polyValues->data.F64[iyOrder][ixOrder]; // Value of polynomial
+            poly[iIndex] = iPoly;
+            for (int jyOrder = 0, jIndex = 0; jyOrder <= spatialOrder; jyOrder++) {
+                for (int jxOrder = 0; jxOrder <= spatialOrder - jyOrder; jxOrder++, jIndex++) {
+                    double jPoly = polyValues->data.F64[jyOrder][jxOrder];
+                    poly2[iIndex][jIndex] = iPoly * jPoly;
+                }
+            }
+        }
+    }
+
+    // initialize the matrix and vector for NOP on all coeffs.  we only fill in the coeffs we
+    // choose to calculate
+    psImageInit(matrix, 0.0);
+    psVectorInit(vector, 1.0);
+    for (int i = 0; i < matrix->numCols; i++) {
+        matrix->data.F64[i][i] = 1.0;
+    }
+
+    // the order of the elements in the matrix and vector is:
+    // [kernel 0, x^0 y^0][kernel 1 x^0 y^0]...[kernel N, x^0 y^0]
+    // [kernel 0, x^1 y^0][kernel 1 x^1 y^0]...[kernel N, x^1 y^0]
+    // [kernel 0, x^n y^m][kernel 1 x^n y^m]...[kernel N, x^n y^m]
+    // normalization
+    // bg 0, bg 1, bg 2 (only 0 is currently used?)
+
+    for (int i = 0; i < numKernels; i++) {
+        psKernel *iConv = convolutions->data[i]; // Convolution for index i
+        for (int j = i; j < numKernels; j++) {
+            psKernel *jConv = convolutions->data[j]; // Convolution for index j
+
+            double sumCC = 0.0;         // Sum of convolution products
+            for (int y = - footprint; y <= footprint; y++) {
+                for (int x = - footprint; x <= footprint; x++) {
+                    double cc = iConv->kernel[y][x] * jConv->kernel[y][x];
+                    if (weight) {
+                        cc *= weight->kernel[y][x];
+                    }
+                    if (window) {
+                        cc *= window->kernel[y][x];
+                    }
+                    sumCC += cc;
+                }
+            }
+
+            // Spatial variation of kernel coeffs
+            if (mode & PM_SUBTRACTION_EQUATION_KERNELS) {
+                for (int iTerm = 0, iIndex = i; iTerm < numPoly; iTerm++, iIndex += numKernels) {
+                    for (int jTerm = 0, jIndex = j; jTerm < numPoly; jTerm++, jIndex += numKernels) {
+                        double value = sumCC * poly2[iTerm][jTerm];
+                        matrix->data.F64[iIndex][jIndex] = value;
+                        matrix->data.F64[jIndex][iIndex] = value;
+                    }
+                }
+            }
+        }
+
+        double sumRC = 0.0;             // Sum of the reference-convolution products
+        double sumIC = 0.0;             // Sum of the input-convolution products
+        double sumC = 0.0;              // Sum of the convolution
+        for (int y = - footprint; y <= footprint; y++) {
+            for (int x = - footprint; x <= footprint; x++) {
+                float conv = iConv->kernel[y][x];
+                float in = input->kernel[y][x];
+                float ref = reference->kernel[y][x];
+                double ic = in * conv;
+                double rc = ref * conv;
+                double c = conv;
+                if (weight) {
+                    float wtVal = weight->kernel[y][x];
+                    ic *= wtVal;
+                    rc *= wtVal;
+                    c *= wtVal;
+                }
+                if (window) {
+                    float winVal = window->kernel[y][x];
+                    ic *= winVal;
+                    rc *= winVal;
+                    c  *= winVal;
+                }
+                sumIC += ic;
+                sumRC += rc;
+                sumC += c;
+            }
+        }
+        // Spatial variation
+        for (int iTerm = 0, iIndex = i; iTerm < numPoly; iTerm++, iIndex += numKernels) {
+            double normTerm = sumRC * poly[iTerm];
+            double bgTerm = sumC * poly[iTerm];
+            if ((mode & PM_SUBTRACTION_EQUATION_NORM) && (mode & PM_SUBTRACTION_EQUATION_KERNELS)) {
+                matrix->data.F64[iIndex][normIndex] = normTerm;
+                matrix->data.F64[normIndex][iIndex] = normTerm;
+            }
+            if ((mode & PM_SUBTRACTION_EQUATION_BG) && (mode & PM_SUBTRACTION_EQUATION_KERNELS)) {
+                matrix->data.F64[iIndex][bgIndex] = bgTerm;
+                matrix->data.F64[bgIndex][iIndex] = bgTerm;
+            }
+            if (mode & PM_SUBTRACTION_EQUATION_KERNELS) {
+                vector->data.F64[iIndex] = sumIC * poly[iTerm];
+                if (!(mode & PM_SUBTRACTION_EQUATION_NORM)) {
+                    // subtract norm * sumRC * poly[iTerm]
+                    psAssert (kernels->solution1, "programming error: define solution first!");
+                    int normIndex = PM_SUBTRACTION_INDEX_NORM(kernels); // Index for normalisation
+                    double norm = fabs(kernels->solution1->data.F64[normIndex]);  // Normalisation
+                    vector->data.F64[iIndex] -= norm * normTerm;
+                }
+            }
+        }
+    }
+
+    double sumRR = 0.0;                 // Sum of the reference product
+    double sumIR = 0.0;                 // Sum of the input-reference product
+    double sum1 = 0.0;                  // Sum of the background
+    double sumR = 0.0;                  // Sum of the reference
+    double sumI = 0.0;                  // Sum of the input
+    double normI1 = 0.0, normI2 = 0.0;  // Sum of I_1 and I_2 within the normalisation window
+    for (int y = - footprint; y <= footprint; y++) {
+        for (int x = - footprint; x <= footprint; x++) {
+            double in = input->kernel[y][x];
+            double ref = reference->kernel[y][x];
+            double ir = in * ref;
+            double rr = PS_SQR(ref);
+            double one = 1.0;
+
+            if (PS_SQR(x) + PS_SQR(y) <= PS_SQR(normWindow1)) {
+                normI1 += ref;
+            }
+            if (PS_SQR(x) + PS_SQR(y) <= PS_SQR(normWindow2)) {
+                normI2 += in;
+            }
+
+            if (weight) {
+                float wtVal = weight->kernel[y][x];
+                rr *= wtVal;
+                ir *= wtVal;
+                in *= wtVal;
+                ref *= wtVal;
+                one *= wtVal;
+            }
+            if (window) {
+                float  winVal = window->kernel[y][x];
+                rr      *= winVal;
+                ir      *= winVal;
+                in      *= winVal;
+                ref *= winVal;
+                one *= winVal;
+            }
+            sumRR += rr;
+            sumIR += ir;
+            sumR += ref;
+            sumI += in;
+            sum1 += one;
+        }
+    }
+
+    *norm = normI2 / normI1;
+
+    fprintf (stderr, "normValue: %f %f %f\n", normI1, normI2, *norm);
+
+    if (mode & PM_SUBTRACTION_EQUATION_NORM) {
+        matrix->data.F64[normIndex][normIndex] = sumRR;
+        vector->data.F64[normIndex] = sumIR;
+        // subtract sum over kernels * kernel solution
+    }
+    if (mode & PM_SUBTRACTION_EQUATION_BG) {
+        matrix->data.F64[bgIndex][bgIndex] = sum1;
+        vector->data.F64[bgIndex] = sumI;
+    }
+    if ((mode & PM_SUBTRACTION_EQUATION_NORM) && (mode & PM_SUBTRACTION_EQUATION_BG)) {
+        matrix->data.F64[normIndex][bgIndex] = sumR;
+        matrix->data.F64[bgIndex][normIndex] = sumR;
+    }
+
+    // check for any NAN values in the result, skip if found:
+    for (int iy = 0; iy < matrix->numRows; iy++) {
+        for (int ix = 0; ix < matrix->numCols; ix++) {
+            if (!isfinite(matrix->data.F64[iy][ix])) {
+                fprintf (stderr, "WARNING: NAN in matrix\n");
+                return false;
+            }
+        }
+    }
+    for (int ix = 0; ix < vector->n; ix++) {
+        if (!isfinite(vector->data.F64[ix])) {
+            fprintf (stderr, "WARNING: NAN in vector\n");
+            return false;
+        }
+    }
+
+    return true;
+}
+
+
+// Calculate the least-squares matrix and vector for dual convolution
+static bool calculateDualMatrixVector(psImage *matrix, // Least-squares matrix, updated
+                                      psVector *vector, // Least-squares vector, updated
+                                      double *norm,     // Normalisation, updated
+                                      const psKernel *image1, // Image 1
+                                      const psKernel *image2, // Image 2
+                                      const psKernel *weight,  // Weight image
+                                      const psKernel *window,  // Window image
+                                      const psArray *convolutions1, // Convolutions of image 1 for each kernel
+                                      const psArray *convolutions2, // Convolutions of image 2 for each kernel
+                                      const pmSubtractionKernels *kernels, // Kernels
+                                      const psImage *polyValues, // Spatial polynomial values
+                                      int footprint, // (Half-)Size of stamp
+                                      int normWindow1, // Window (half-)size for normalisation measurement
+                                      int normWindow2, // Window (half-)size for normalisation measurement
+                                      const pmSubtractionEquationCalculationMode mode
+                                      )
+{
+    int numKernels = kernels->num;                      // Number of kernels
+    int normIndex = PM_SUBTRACTION_INDEX_NORM(kernels); // Index for normalisation
+    int bgIndex = PM_SUBTRACTION_INDEX_BG(kernels); // Index in matrix for background
+    int spatialOrder = kernels->spatialOrder;       // Order of spatial variation
+    int numPoly = PM_SUBTRACTION_POLYTERMS(spatialOrder); // Number of polynomial terms
+    double poly[numPoly];                                 // Polynomial terms
+    double poly2[numPoly][numPoly];                       // Polynomial-polynomial values
+
+    int numBackground = PM_SUBTRACTION_POLYTERMS(kernels->bgOrder); // Number of background terms
+    int numParams = numKernels * numPoly + 1 + numBackground;       // Number of regular parameters
+    int numParams2 = numKernels * numPoly;                          // Number of additional parameters for dual
+    int numDual = numParams + numParams2;                           // Total number of parameters for dual
+
+    psAssert(matrix &&
+             matrix->type.type == PS_TYPE_F64 &&
+             matrix->numCols == numDual &&
+             matrix->numRows == numDual,
+             "Least-squares matrix is bad.");
+    psAssert(vector &&
+             vector->type.type == PS_TYPE_F64 &&
+             vector->n == numDual,
+             "Least-squares vector is bad.");
+
+    // Evaluate polynomial-polynomial terms
+    for (int iyOrder = 0, iIndex = 0; iyOrder <= spatialOrder; iyOrder++) {
+        for (int ixOrder = 0; ixOrder <= spatialOrder - iyOrder; ixOrder++, iIndex++) {
+            double iPoly = polyValues->data.F64[iyOrder][ixOrder]; // Value of polynomial
+            poly[iIndex] = iPoly;
+            for (int jyOrder = 0, jIndex = 0; jyOrder <= spatialOrder; jyOrder++) {
+                for (int jxOrder = 0; jxOrder <= spatialOrder - jyOrder; jxOrder++, jIndex++) {
+                    double jPoly = polyValues->data.F64[jyOrder][jxOrder];
+                    poly2[iIndex][jIndex] = iPoly * jPoly;
+                }
+            }
+        }
+    }
+
+
+    // initialize the matrix and vector for NOP on all coeffs.  we only fill in the coeffs we
+    // choose to calculate
+    psImageInit(matrix, 0.0);
+    psVectorInit(vector, 1.0);
+    for (int i = 0; i < matrix->numCols; i++) {
+        matrix->data.F64[i][i] = 1.0;
+    }
+
+    for (int i = 0; i < numKernels; i++) {
+        psKernel *iConv1 = convolutions1->data[i]; // Convolution 1 for index i
+        psKernel *iConv2 = convolutions2->data[i]; // Convolution 2 for index i
+        for (int j = i; j < numKernels; j++) {
+            psKernel *jConv1 = convolutions1->data[j]; // Convolution 1 for index j
+            psKernel *jConv2 = convolutions2->data[j]; // Convolution 2 for index j
+
+            double sumAA = 0.0;         // Sum of convolution products between image 1
+            double sumBB = 0.0;         // Sum of convolution products between image 2
+            double sumAB = 0.0;         // Sum of convolution products across images 1 and 2
+            for (int y = - footprint; y <= footprint; y++) {
+                for (int x = - footprint; x <= footprint; x++) {
+                    double aa = iConv1->kernel[y][x] * jConv1->kernel[y][x];
+                    double bb = iConv2->kernel[y][x] * jConv2->kernel[y][x];
+                    double ab = iConv1->kernel[y][x] * jConv2->kernel[y][x];
+                    if (weight) {
+                        float wtVal = weight->kernel[y][x];
+                        aa *= wtVal;
+                        bb *= wtVal;
+                        ab *= wtVal;
+                    }
+                    if (window) {
+                        float wtVal = window->kernel[y][x];
+                        aa *= wtVal;
+                        bb *= wtVal;
+                        ab *= wtVal;
+                    }
+                    sumAA += aa;
+                    sumBB += bb;
+                    sumAB += ab;
+                }
+            }
+
+            // Spatial variation of kernel coeffs
+            if (mode & PM_SUBTRACTION_EQUATION_KERNELS) {
+                for (int iTerm = 0, iIndex = i; iTerm < numPoly; iTerm++, iIndex += numKernels) {
+                    for (int jTerm = 0, jIndex = j; jTerm < numPoly; jTerm++, jIndex += numKernels) {
+                        double aa = sumAA * poly2[iTerm][jTerm];
+                        double bb = sumBB * poly2[iTerm][jTerm];
+                        double ab = sumAB * poly2[iTerm][jTerm];
+
+                        matrix->data.F64[iIndex][jIndex] = aa;
+                        matrix->data.F64[jIndex][iIndex] = aa;
+
+                        matrix->data.F64[iIndex + numParams][jIndex + numParams] = bb;
+                        matrix->data.F64[jIndex + numParams][iIndex + numParams] = bb;
+
+                        matrix->data.F64[iIndex][jIndex + numParams] = ab;
+                        matrix->data.F64[jIndex + numParams][iIndex] = ab;
+                    }
+                }
+            }
+        }
+        for (int j = 0; j < i; j++) {
+            psKernel *jConv2 = convolutions2->data[j]; // Convolution 2 for index j
+            double sumAB = 0.0;         // Sum of convolution products for matrix C
+            for (int y = - footprint; y <= footprint; y++) {
+                for (int x = - footprint; x <= footprint; x++) {
+                    double ab = iConv1->kernel[y][x] * jConv2->kernel[y][x];
+                    if (weight) {
+                        ab *= weight->kernel[y][x];
+                    }
+                    if (window) {
+                        ab *= window->kernel[y][x];
+                    }
+                    sumAB += ab;
+                }
+            }
+
+            // Spatial variation of kernel coeffs
+            if (mode & PM_SUBTRACTION_EQUATION_KERNELS) {
+                for (int iTerm = 0, iIndex = i; iTerm < numPoly; iTerm++, iIndex += numKernels) {
+                    for (int jTerm = 0, jIndex = j; jTerm < numPoly; jTerm++, jIndex += numKernels) {
+                        double ab = sumAB * poly2[iTerm][jTerm];
+                        matrix->data.F64[iIndex][jIndex + numParams] = ab;
+                        matrix->data.F64[jIndex + numParams][iIndex] = ab;
+                    }
+                }
+            }
+        }
+
+        double sumAI2 = 0.0;            // Sum of A.I_2 products (for vector)
+        double sumBI2 = 0.0;            // Sum of B.I_2 products (for vector)
+        double sumAI1 = 0.0;            // Sum of A.I_1 products (for matrix, normalisation)
+        double sumA = 0.0;              // Sum of A (for matrix, background)
+        double sumBI1 = 0.0;            // Sum of B.I_1 products (for matrix, normalisation)
+        double sumB = 0.0;              // Sum of B products (for matrix, background)
+        double sumI2 = 0.0;             // Sum of I_2 (for vector, background)
+        for (int y = - footprint; y <= footprint; y++) {
+            for (int x = - footprint; x <= footprint; x++) {
+                double a = iConv1->kernel[y][x];
+                double b = iConv2->kernel[y][x];
+                float i1 = image1->kernel[y][x];
+                float i2 = image2->kernel[y][x];
+
+                double ai2 = a * i2;
+                double bi2 = b * i2;
+                double ai1 = a * i1;
+                double bi1 = b * i1;
+
+                if (weight) {
+                    float wtVal = weight->kernel[y][x];
+                    ai2 *= wtVal;
+                    bi2 *= wtVal;
+                    ai1 *= wtVal;
+                    bi1 *= wtVal;
+                    a *= wtVal;
+                    b *= wtVal;
+                    i2 *= wtVal;
+                }
+                if (window) {
+                    float wtVal = window->kernel[y][x];
+                    ai2 *= wtVal;
+                    bi2 *= wtVal;
+                    ai1 *= wtVal;
+                    bi1 *= wtVal;
+                    a *= wtVal;
+                    b *= wtVal;
+                    i2 *= wtVal;
+                }
+                sumAI2 += ai2;
+                sumBI2 += bi2;
+                sumAI1 += ai1;
+                sumA += a;
+                sumBI1 += bi1;
+                sumB += b;
+                sumI2 += i2;
+            }
+        }
+        // Spatial variation
+        for (int iTerm = 0, iIndex = i; iTerm < numPoly; iTerm++, iIndex += numKernels) {
+            double ai2 = sumAI2 * poly[iTerm];
+            double bi2 = sumBI2 * poly[iTerm];
+            double ai1 = sumAI1 * poly[iTerm];
+            double a   = sumA * poly[iTerm];
+            double bi1 = sumBI1 * poly[iTerm];
+            double b   = sumB * poly[iTerm];
+
+            if ((mode & PM_SUBTRACTION_EQUATION_NORM) && (mode & PM_SUBTRACTION_EQUATION_KERNELS)) {
+                matrix->data.F64[iIndex][normIndex] = ai1;
+                matrix->data.F64[normIndex][iIndex] = ai1;
+                matrix->data.F64[iIndex + numParams][normIndex] = bi1;
+                matrix->data.F64[normIndex][iIndex + numParams] = bi1;
+            }
+            if ((mode & PM_SUBTRACTION_EQUATION_BG) && (mode & PM_SUBTRACTION_EQUATION_KERNELS)) {
+                matrix->data.F64[iIndex][bgIndex] = a;
+                matrix->data.F64[bgIndex][iIndex] = a;
+                matrix->data.F64[iIndex + numParams][bgIndex] = b;
+                matrix->data.F64[bgIndex][iIndex + numParams] = b;
+            }
+            if (mode & PM_SUBTRACTION_EQUATION_KERNELS) {
+                vector->data.F64[iIndex] = ai2;
+                vector->data.F64[iIndex + numParams] = bi2;
+                if (!(mode & PM_SUBTRACTION_EQUATION_NORM)) {
+                    // subtract norm * sumRC * poly[iTerm]
+                    psAssert (kernels->solution1, "programming error: define solution first!");
+                    int normIndex = PM_SUBTRACTION_INDEX_NORM(kernels); // Index for normalisation
+                    double norm = fabs(kernels->solution1->data.F64[normIndex]);  // Normalisation
+                    vector->data.F64[iIndex] -= norm * ai1;
+                    vector->data.F64[iIndex + numParams] -= norm * bi1;
+                }
+            }
+        }
+    }
+
+    double sumI1 = 0.0;                 // Sum of I_1 (for matrix, background-normalisation)
+    double sumI1I1 = 0.0;               // Sum of I_1^2 (for matrix, normalisation-normalisation)
+    double sum1 = 0.0;                  // Sum of 1 (for matrix, background-background)
+    double sumI2 = 0.0;                 // Sum of I_2 (for vector, background)
+    double sumI1I2 = 0.0;               // Sum of I_1.I_2 (for vector, normalisation)
+    double normI1 = 0.0, normI2 = 0.0;  // Sum of I_1 and I_2 within the normalisation window
+    for (int y = - footprint; y <= footprint; y++) {
+        for (int x = - footprint; x <= footprint; x++) {
+            double i1 = image1->kernel[y][x];
+            double i2 = image2->kernel[y][x];
+
+            double i1i1 = i1 * i1;
+            double one = 1.0;
+            double i1i2 = i1 * i2;
+
+            if (PS_SQR(x) + PS_SQR(y) <= PS_SQR(normWindow1)) {
+                normI1 += i1;
+            }
+            if (PS_SQR(x) + PS_SQR(y) <= PS_SQR(normWindow2)) {
+                normI2 += i2;
+            }
+
+            if (weight) {
+                float wtVal = weight->kernel[y][x];
+                i1 *= wtVal;
+                i1i1 *= wtVal;
+                one *= wtVal;
+                i2 *= wtVal;
+                i1i2 *= wtVal;
+            }
+            if (window) {
+                float wtVal = window->kernel[y][x];
+                i1 *= wtVal;
+                i1i1 *= wtVal;
+                one *= wtVal;
+                i2 *= wtVal;
+                i1i2 *= wtVal;
+            }
+            sumI1 += i1;
+            sumI1I1 += i1i1;
+            sum1 += one;
+            sumI2 += i2;
+            sumI1I2 += i1i2;
+        }
+    }
+
+    *norm = normI2 / normI1;
+    fprintf (stderr, "normValue: %f %f %f\n", normI1, normI2, *norm);
+
+    if (mode & PM_SUBTRACTION_EQUATION_NORM) {
+        matrix->data.F64[normIndex][normIndex] = sumI1I1;
+        vector->data.F64[normIndex] = sumI1I2;
+    }
+    if (mode & PM_SUBTRACTION_EQUATION_BG) {
+        matrix->data.F64[bgIndex][bgIndex] = sum1;
+        vector->data.F64[bgIndex] = sumI2;
+    }
+    if ((mode & PM_SUBTRACTION_EQUATION_NORM) && (mode & PM_SUBTRACTION_EQUATION_BG)) {
+        matrix->data.F64[bgIndex][normIndex] = sumI1;
+        matrix->data.F64[normIndex][bgIndex] = sumI1;
+    }
+
+    // check for any NAN values in the result, skip if found:
+    for (int iy = 0; iy < matrix->numRows; iy++) {
+        for (int ix = 0; ix < matrix->numCols; ix++) {
+            if (!isfinite(matrix->data.F64[iy][ix])) {
+                fprintf (stderr, "WARNING: NAN in matrix\n");
+                return false;
+            }
+        }
+    }
+    for (int ix = 0; ix < vector->n; ix++) {
+        if (!isfinite(vector->data.F64[ix])) {
+            fprintf (stderr, "WARNING: NAN in vector\n");
+            return false;
+        }
+    }
+
+
+    return true;
+}
+
+#if 1
+// Add in penalty term to least-squares vector
+bool calculatePenalty(psImage *matrix,                     // Matrix to which to add in penalty term
+		      psVector *vector,                    // Vector to which to add in penalty term
+		      const pmSubtractionKernels *kernels, // Kernel parameters
+		      float norm                           // Normalisation
+  )
+{
+    if (kernels->penalty == 0.0) {
+        return true;
+    }
+
+    psVector *penalties1 = kernels->penalties1; // Penalties for each kernel component (input)
+    psVector *penalties2 = kernels->penalties2; // Penalties for each kernel component (ref)
+
+    int spatialOrder = kernels->spatialOrder; // Order of spatial variations
+    int numKernels = kernels->num; // Number of kernel components
+    int numSpatial = PM_SUBTRACTION_POLYTERMS(spatialOrder); // Number of spatial variations
+    int numParams = numKernels * numSpatial;                 // Number of kernel parameters
+
+    // order is :
+    // [p_0,x_0,y_0 p_1,x_0,y_0, p_2,x_0,y_0]
+    // [p_0,x_1,y_0 p_1,x_1,y_0, p_2,x_1,y_0]
+    // [p_0,x_0,y_1 p_1,x_0,y_1, p_2,x_0,y_1]
+    // [norm]
+    // [bg]
+    // [q_0,x_0,y_0 q_1,x_0,y_0, q_2,x_0,y_0]
+    // [q_0,x_1,y_0 q_1,x_1,y_0, q_2,x_1,y_0]
+    // [q_0,x_0,y_1 q_1,x_0,y_1, q_2,x_0,y_1]
+
+    for (int i = 0; i < numKernels; i++) {
+        for (int yOrder = 0, index = i; yOrder <= spatialOrder; yOrder++) {
+            for (int xOrder = 0; xOrder <= spatialOrder - yOrder; xOrder++, index += numKernels) {
+                // Contribution to chi^2: a_i^2 P_i
+                psAssert(isfinite(penalties1->data.F32[i]), "Invalid penalty");
+		fprintf (stderr, "penalty: %f + %f (%f * %f)\n", matrix->data.F64[index][index], norm * penalties1->data.F32[i], norm, penalties1->data.F32[i]);
+                matrix->data.F64[index][index] += norm * penalties1->data.F32[i];
+                if (kernels->mode == PM_SUBTRACTION_MODE_DUAL) {
+		    fprintf (stderr, "penalty: (x^%d y^%d fwhm %f) : %f + %f (%f * %f)\n", kernels->u->data.S32[index], kernels->v->data.S32[index], kernels->widths->data.F32[index], 
+			     matrix->data.F64[index + numParams + 2][index + numParams + 2], norm * penalties2->data.F32[i], norm, penalties2->data.F32[i]);
+		    matrix->data.F64[index + numParams + 2][index + numParams + 2] += norm * penalties2->data.F32[i];			     
+                    // matrix[i][i] is ~ (k_i * I_1)(k_i * I_1)
+                    // penalties scale with second moments
+                    //
+                }
+            }
+        }
+    }
+
+    return true;
+}
+# endif
+
+//////////////////////////////////////////////////////////////////////////////////////////////////////////////
+// Semi-public functions
+// XXX We might like to define these functions as "extern inline" but gcc currently doesn't handle this in c99
+// mode.  See http://gcc.gnu.org/ml/gcc/2006-11/msg00006.html
+//////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+// Calculate the value of a polynomial, specified by coefficients and polynomial values
+double p_pmSubtractionCalculatePolynomial(const psVector *coeff, // Coefficients
+                                          const psImage *polyValues, // Polynomial values
+                                          int order, // Order of polynomials
+                                          int index, // Index at which to begin
+                                          int step // Step between subsequent indices
+                                          )
+{
+    double sum = 0.0;                   // Value of the polynomial sum
+    for (int yOrder = 0; yOrder <= order; yOrder++) {
+        for (int xOrder = 0; xOrder <= order - yOrder; xOrder++, index += step) {
+
+            assert(index < coeff->n);
+
+            sum += coeff->data.F64[index] * polyValues->data.F64[yOrder][xOrder];
+        }
+    }
+    return sum;
+}
+
+double p_pmSubtractionSolutionCoeff(const pmSubtractionKernels *kernels, const psImage *polyValues,
+                                    int index, bool wantDual)
+{
+#if 0
+    // This is probably in a tight loop, so don't check inputs
+    PM_ASSERT_SUBTRACTION_KERNELS_NON_NULL(kernels, NAN);
+    PM_ASSERT_SUBTRACTION_KERNELS_SOLUTION(kernels, NAN);
+    PS_ASSERT_IMAGE_NON_NULL(polyValues, NAN);
+    PS_ASSERT_INT_POSITIVE(index, NAN);
+#endif
+
+    psVector *solution = wantDual ? kernels->solution2 : kernels->solution1; // Solution vector
+    return p_pmSubtractionCalculatePolynomial(solution, polyValues, kernels->spatialOrder, index,
+                                              kernels->num);
+}
+
+double p_pmSubtractionSolutionNorm(const pmSubtractionKernels *kernels)
+{
+#if 0
+    // This is probably in a tight loop, so don't check inputs
+    PM_ASSERT_SUBTRACTION_KERNELS_NON_NULL(kernels, NAN);
+    PM_ASSERT_SUBTRACTION_KERNELS_SOLUTION(kernels, NAN);
+    PS_ASSERT_IMAGE_NON_NULL(polyValues, NAN);
+#endif
+
+    int normIndex = PM_SUBTRACTION_INDEX_NORM(kernels); // Index for normalisation
+    return kernels->solution1->data.F64[normIndex];
+}
+
+double p_pmSubtractionSolutionBackground(const pmSubtractionKernels *kernels,
+                                                const psImage *polyValues)
+{
+#if 0
+    // This is probably in a tight loop, so don't check inputs
+    PM_ASSERT_SUBTRACTION_KERNELS_NON_NULL(kernels, NAN);
+    PM_ASSERT_SUBTRACTION_KERNELS_SOLUTION(kernels, NAN);
+    PS_ASSERT_IMAGE_NON_NULL(polyValues, NAN);
+#endif
+
+    int bgIndex = PM_SUBTRACTION_INDEX_BG(kernels); // Index for background
+    return p_pmSubtractionCalculatePolynomial(kernels->solution1, polyValues, kernels->bgOrder, bgIndex, 1);
+}
+
+//////////////////////////////////////////////////////////////////////////////////////////////////////////////
+// Public functions
+//////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+bool pmSubtractionCalculateEquationThread(psThreadJob *job)
+{
+    PS_ASSERT_THREAD_JOB_NON_NULL(job, false);
+
+    pmSubtractionStampList *stamps = job->args->data[0]; // List of stamps
+    pmSubtractionKernels *kernels = job->args->data[1]; // Kernels
+    int index = PS_SCALAR_VALUE(job->args->data[2], S32); // Stamp index
+    pmSubtractionEquationCalculationMode mode  = PS_SCALAR_VALUE(job->args->data[3], S32); // calculation model
+
+    return pmSubtractionCalculateEquationStamp(stamps, kernels, index, mode);
+}
+
+bool pmSubtractionCalculateEquationStamp(pmSubtractionStampList *stamps, pmSubtractionKernels *kernels,
+                                         int index, const pmSubtractionEquationCalculationMode mode)
+{
+    PM_ASSERT_SUBTRACTION_STAMP_LIST_NON_NULL(stamps, false);
+    PM_ASSERT_SUBTRACTION_KERNELS_NON_NULL(kernels, false);
+    PS_ASSERT_INT_NONNEGATIVE(index, false);
+    PS_ASSERT_INT_LESS_THAN(index, stamps->num, false);
+
+    int footprint = stamps->footprint;  // Half-size of stamps
+    int spatialOrder = kernels->spatialOrder; // Maximum order of spatial variation
+    int numKernels = kernels->num;      // Number of kernel basis functions
+    int numSpatial = PM_SUBTRACTION_POLYTERMS(spatialOrder); // Number of spatial variations
+    int numBackground = PM_SUBTRACTION_POLYTERMS(kernels->bgOrder); // Number of background terms
+
+    // numKernels is the number of unique kernel images (one for each Gaussian modified by a specific polynomial).
+    // = \sum_i^N_Gaussians [(order + 1) * (order + 2) / 2], eg for 1 Gauss and 1st order, numKernels = 3
+
+    // Total number of parameters to solve for: coefficient of each kernel basis function, multipled by the
+    // number of coefficients for the spatial polynomial, normalisation and a constant background offset.
+    int numParams = numKernels * numSpatial + 1 + numBackground;
+    if (kernels->mode == PM_SUBTRACTION_MODE_DUAL) {
+        // An additional image is convolved
+        numParams += numKernels * numSpatial;
+    }
+
+    pmSubtractionStamp *stamp = stamps->stamps->data[index]; // Stamp of interest
+    psAssert(stamp->status == PM_SUBTRACTION_STAMP_CALCULATE, "We only operate on stamps with this state.");
+
+    // Generate convolutions: these are generated once and saved
+    if (!pmSubtractionConvolveStamp(stamp, kernels, footprint)) {
+        psError(psErrorCodeLast(), false, "Unable to convolve stamp %d.", index);
+        return NULL;
+    }
+
+#ifdef TESTING
+    for (int j = 0; j < numKernels; j++) {
+        if (stamp->convolutions1) {
+            psString convName = NULL;
+            psStringAppend(&convName, "conv1_%03d_%03d.fits", index, j);
+            psFits *fits = psFitsOpen(convName, "w");
+            psFree(convName);
+            psKernel *conv = stamp->convolutions1->data[j];
+            psFitsWriteImage(fits, NULL, conv->image, 0, NULL);
+            psFitsClose(fits);
+        }
+
+        if (stamp->convolutions2) {
+            psString convName = NULL;
+            psStringAppend(&convName, "conv2_%03d_%03d.fits", index, j);
+            psFits *fits = psFitsOpen(convName, "w");
+            psFree(convName);
+            psKernel *conv = stamp->convolutions2->data[j];
+            psFitsWriteImage(fits, NULL, conv->image, 0, NULL);
+            psFitsClose(fits);
+        }
+    }
+#endif
+
+    // XXX visualize the set of convolved stamps
+
+    psImage *polyValues = p_pmSubtractionPolynomial(NULL, spatialOrder,
+                                                    stamp->xNorm, stamp->yNorm); // Polynomial terms
+
+    bool new = stamp->vector ? false : true; // Is this a new run?
+    if (new) {
+        stamp->matrix = psImageAlloc(numParams, numParams, PS_TYPE_F64);
+        stamp->vector = psVectorAlloc(numParams, PS_TYPE_F64);
+    }
+#ifdef TESTING
+    psImageInit(stamp->matrix, NAN);
+    psVectorInit(stamp->vector, NAN);
+#endif
+
+    bool status;                    // Status of least-squares matrix/vector calculation
+
+    psKernel *weight = NULL;
+    psKernel *window = NULL;
+
+#ifdef USE_WEIGHT
+    weight = stamp->weight;
+#endif
+#ifdef USE_WINDOW
+    window = stamps->window;
+#endif
+
+    switch (kernels->mode) {
+      case PM_SUBTRACTION_MODE_1:
+        status = calculateMatrixVector(stamp->matrix, stamp->vector, &stamp->norm, stamp->image2, stamp->image1,
+                                       weight, window, stamp->convolutions1, kernels,
+                                       polyValues, footprint, stamps->normWindow1, stamps->normWindow2, mode);
+        break;
+      case PM_SUBTRACTION_MODE_2:
+        status = calculateMatrixVector(stamp->matrix, stamp->vector, &stamp->norm, stamp->image1, stamp->image2,
+                                       weight, window, stamp->convolutions2, kernels,
+                                       polyValues, footprint, stamps->normWindow2, stamps->normWindow1, mode);
+        break;
+      case PM_SUBTRACTION_MODE_DUAL:
+        status = calculateDualMatrixVector(stamp->matrix, stamp->vector, &stamp->norm,
+                                           stamp->image1, stamp->image2,
+                                           weight, window, stamp->convolutions1, stamp->convolutions2,
+                                           kernels, polyValues, footprint, stamps->normWindow1, stamps->normWindow2, mode);
+        break;
+      default:
+        psAbort("Unsupported subtraction mode: %x", kernels->mode);
+    }
+
+    if (!status) {
+        stamp->status = PM_SUBTRACTION_STAMP_REJECTED;
+        psWarning("Rejecting stamp %d (%d,%d) because of bad equation",
+                  index, (int)(stamp->x - 0.5), (int)(stamp->y - 0.5));
+    } else {
+        stamp->status = PM_SUBTRACTION_STAMP_USED;
+    }
+
+#ifdef TESTING
+    {
+        psString matrixName = NULL;
+        psStringAppend(&matrixName, "matrix_%d.fits", index);
+        psFits *matrixFile = psFitsOpen(matrixName, "w");
+        psFree(matrixName);
+        psFitsWriteImage(matrixFile, NULL, stamp->matrix, 0, NULL);
+        psFitsClose(matrixFile);
+
+        matrixName = NULL;
+        psStringAppend(&matrixName, "vector_%d.fits", index);
+        psImage *dummy = psImageAlloc(stamp->vector->n, 1, PS_TYPE_F64);
+        memcpy(dummy->data.F64[0], stamp->vector->data.F64,
+               PSELEMTYPE_SIZEOF(PS_TYPE_F64) * stamp->vector->n);
+        matrixFile = psFitsOpen(matrixName, "w");
+        psFree(matrixName);
+        psFitsWriteImage(matrixFile, NULL, dummy, 0, NULL);
+        psFree(dummy);
+        psFitsClose(matrixFile);
+    }
+#endif
+
+    psFree(polyValues);
+
+    return true;
+}
+
+bool pmSubtractionCalculateEquation(pmSubtractionStampList *stamps, pmSubtractionKernels *kernels,
+                                    const pmSubtractionEquationCalculationMode mode)
+{
+    PM_ASSERT_SUBTRACTION_STAMP_LIST_NON_NULL(stamps, false);
+    PM_ASSERT_SUBTRACTION_KERNELS_NON_NULL(kernels, false);
+
+    psTimerStart("pmSubtractionCalculateEquation");
+
+    // We iterate over each stamp, allocate the matrix and vectors if
+    // necessary, and then calculate those matrix/vectors.
+    for (int i = 0; i < stamps->num; i++) {
+        pmSubtractionStamp *stamp = stamps->stamps->data[i]; // Stamp of interest
+        if (stamp->status != PM_SUBTRACTION_STAMP_CALCULATE) {
+            continue;
+        }
+
+        if ((stamp->x <= 0.0) && (stamp->y <= 0.0)) {
+            psAbort ("bad stamp");
+        }
+        if (!isfinite(stamp->x) && !isfinite(stamp->y)) {
+            psAbort ("bad stamp");
+        }
+
+        if (pmSubtractionThreaded()) {
+            psThreadJob *job = psThreadJobAlloc("PSMODULES_SUBTRACTION_CALCULATE_EQUATION");
+            psArrayAdd(job->args, 1, stamps);
+            psArrayAdd(job->args, 1, (pmSubtractionKernels*)kernels); // Casting away const to put on array
+            PS_ARRAY_ADD_SCALAR(job->args, i, PS_TYPE_S32);
+            PS_ARRAY_ADD_SCALAR(job->args, mode, PS_TYPE_S32);
+            if (!psThreadJobAddPending(job)) {
+                return false;
+            }
+        } else {
+            pmSubtractionCalculateEquationStamp(stamps, kernels, i, mode);
+        }
+    }
+
+    if (!psThreadPoolWait(true)) {
+        psError(psErrorCodeLast(), false, "Error waiting for threads.");
+        return false;
+    }
+
+    pmSubtractionVisualPlotLeastSquares(stamps);
+    pmSubtractionVisualShowKernels((pmSubtractionKernels  *)kernels);
+    pmSubtractionVisualShowBasis(stamps);
+
+    psLogMsg("psModules.imcombine", PS_LOG_INFO, "Calculate equation: %f sec",
+             psTimerClear("pmSubtractionCalculateEquation"));
+
+
+    return true;
+}
+
+// private functions used on pmSubtractionSolveEquation
+bool psVectorWriteFile (char *filename, const psVector *vector);
+bool psFitsWriteImageSimple (char *filename, psImage *image, psMetadata *header);
+
+psImage *p_pmSubSolve_wUt (psVector *w, psImage *U);
+psImage *p_pmSubSolve_VwUt (psImage *V, psImage *wUt);
+
+bool p_pmSubSolve_SetWeights (psVector *wApply, psVector *w, psVector *wMask);
+
+bool p_pmSubSolve_UtB (psVector **UtB, psImage *U, psVector *B);
+bool p_pmSubSolve_wUtB (psVector **wUtB, psVector *w, psVector *UtB);
+bool p_pmSubSolve_VwUtB (psVector **VwUtB, psImage *V, psVector *wUtB);
+
+bool p_pmSubSolve_Ax (psVector **B, psImage *A, psVector *x);
+bool p_pmSubSolve_VdV (double *value, psVector *x, psVector *y);
+bool p_pmSubSolve_y2 (double *y2, pmSubtractionKernels *kernels, const pmSubtractionStampList *stamps);
+
+psImage *p_pmSubSolve_Xvar (psImage *V, psVector *w);
+
+double p_pmSubSolve_ChiSquare (pmSubtractionKernels *kernels, const pmSubtractionStampList *stamps);
+
+bool pmSubtractionSolveEquation(pmSubtractionKernels *kernels,
+                                const pmSubtractionStampList *stamps,
+                                const pmSubtractionEquationCalculationMode mode)
+{
+    PM_ASSERT_SUBTRACTION_KERNELS_NON_NULL(kernels, false);
+    PM_ASSERT_SUBTRACTION_STAMP_LIST_NON_NULL(stamps, false);
+
+    // Check inputs
+    int numKernels = kernels->num;      // Number of kernel basis functions
+    int numSpatial = PM_SUBTRACTION_POLYTERMS(kernels->spatialOrder); // Number of spatial variations
+    int numBackground = PM_SUBTRACTION_POLYTERMS(kernels->bgOrder); // Number of background terms
+    int numParams = numKernels * numSpatial + 1 + numBackground;    // Number of parameters being solved for
+    int numSolution1 = numParams, numSolution2 = 0;                 // Number of parameters for each solution
+    if (kernels->mode == PM_SUBTRACTION_MODE_DUAL) {
+        // An additional image is convolved
+        numSolution2 = numKernels * numSpatial;
+        numParams += numSolution2;
+    }
+
+    for (int i = 0; i < stamps->num; i++) {
+        pmSubtractionStamp *stamp = stamps->stamps->data[i]; // Stamp of interest
+        PS_ASSERT_PTR_NON_NULL(stamp, false);
+        if (stamp->status != PM_SUBTRACTION_STAMP_USED) {
+            continue;
+        }
+
+        PS_ASSERT_VECTOR_NON_NULL(stamp->vector, false);
+        PS_ASSERT_VECTOR_SIZE(stamp->vector, (long)numParams, false);
+        PS_ASSERT_VECTOR_TYPE(stamp->vector, PS_TYPE_F64, false);
+        PS_ASSERT_IMAGE_NON_NULL(stamp->matrix, false);
+        PS_ASSERT_IMAGE_SIZE(stamp->matrix, numParams, numParams, false);
+        PS_ASSERT_IMAGE_TYPE(stamp->matrix, PS_TYPE_F64, false);
+    }
+
+    psString ds9name = NULL;            // Filename for ds9 region file
+    static int ds9num = 0;              // File number for ds9 region file
+    psStringAppend(&ds9name, "stamps_solution_%d.ds9", ds9num);
+    FILE *ds9 = pmSubtractionStampsFile(stamps, ds9name, "solution stamps");
+    psFree(ds9name);
+    ds9num++;
+
+    if (kernels->mode != PM_SUBTRACTION_MODE_DUAL) {
+        // Accumulate the least-squares matricies and vectors
+        psImage *sumMatrix = psImageAlloc(numParams, numParams, PS_TYPE_F64); // Combined matrix
+        psVector *sumVector = psVectorAlloc(numParams, PS_TYPE_F64); // Combined vector
+        psVectorInit(sumVector, 0.0);
+        psImageInit(sumMatrix, 0.0);
+
+        psVector *norms = psVectorAllocEmpty(stamps->num, PS_TYPE_F64); // Normalisations
+
+        int numStamps = 0;              // Number of good stamps
+        for (int i = 0; i < stamps->num; i++) {
+            pmSubtractionStamp *stamp = stamps->stamps->data[i]; // Stamp of interest
+            if (stamp->status == PM_SUBTRACTION_STAMP_USED) {
+		
+                (void)psBinaryOp(sumMatrix, sumMatrix, "+", stamp->matrix);
+                (void)psBinaryOp(sumVector, sumVector, "+", stamp->vector);
+
+                psVectorAppend(norms, stamp->norm);
+
+                pmSubtractionStampPrint(ds9, stamp->x, stamp->y, stamps->footprint, "green");
+                numStamps++;
+            } else if (stamp->status == PM_SUBTRACTION_STAMP_REJECTED) {
+                pmSubtractionStampPrint(ds9, stamp->x, stamp->y, stamps->footprint, "red");
+            }
+        }
+
+#if 0
+        int bgIndex = PM_SUBTRACTION_INDEX_BG(kernels); // Index for background
+        calculatePenalty(sumMatrix, sumVector, kernels, sumMatrix->data.F64[bgIndex][bgIndex]);
+#endif
+
+        psVector *solution = NULL;                       // Solution to equation!
+        solution = psVectorAlloc(numParams, PS_TYPE_F64);
+        psVectorInit(solution, 0);
+
+#if 0
+        // Regular, straight-forward solution
+        solution = psMatrixSolveSVD(solution, sumMatrix, sumVector, NAN);
+#else
+        {
+            // Solve normalisation and background separately
+            int normIndex = PM_SUBTRACTION_INDEX_NORM(kernels); // Index for normalisation
+            int bgIndex = PM_SUBTRACTION_INDEX_BG(kernels); // Index for background
+
+            psStats *stats = psStatsAlloc(PS_STAT_ROBUST_MEDIAN); // Statistics for norm
+            if (!psVectorStats(stats, norms, NULL, NULL, 0)) {
+                psError(PM_ERR_DATA, false, "Unable to determine median normalisation");
+                psFree(stats);
+                psFree(sumMatrix);
+                psFree(sumVector);
+                psFree(norms);
+                return false;
+            }
+
+            // double normValue = 1.0;
+            double normValue = stats->robustMedian;
+            // double bgValue = 0.0;
+
+            psFree(stats);
+
+#ifdef TESTING
+            fprintf(stderr, "Norm: %lf\n", normValue);
+#endif
+            // Solve kernel components
+            for (int i = 0; i < numSolution1; i++) {
+                sumVector->data.F64[i] -= normValue * sumMatrix->data.F64[normIndex][i];
+
+                sumMatrix->data.F64[i][normIndex] = 0.0;
+                sumMatrix->data.F64[normIndex][i] = 0.0;
+            }
+            sumVector->data.F64[bgIndex] -= normValue * sumMatrix->data.F64[normIndex][bgIndex];
+            sumMatrix->data.F64[bgIndex][normIndex] = 0.0;
+            sumMatrix->data.F64[normIndex][bgIndex] = 0.0;
+
+            sumMatrix->data.F64[normIndex][normIndex] = 1.0;
+            sumVector->data.F64[normIndex] = 0.0;
+
+            solution = psMatrixSolveSVD(solution, sumMatrix, sumVector, NAN);
+
+            solution->data.F64[normIndex] = normValue;
+        }
+# endif
+
+#if (1)
+        for (int i = 0; i < solution->n; i++) {
+            fprintf(stderr, "Single solution %d: %lf\n", i, solution->data.F64[i]);
+        }
+#endif
+
+        if (!kernels->solution1) {
+            kernels->solution1 = psVectorAlloc(sumVector->n, PS_TYPE_F64);
+            psVectorInit(kernels->solution1, 0.0);
+        }
+
+        // only update the solutions that we chose to calculate:
+        if (mode & PM_SUBTRACTION_EQUATION_NORM) {
+            int normIndex = PM_SUBTRACTION_INDEX_NORM(kernels); // Index for normalisation
+            kernels->solution1->data.F64[normIndex] = solution->data.F64[normIndex];
+        }
+        if (mode & PM_SUBTRACTION_EQUATION_BG) {
+            int bgIndex = PM_SUBTRACTION_INDEX_BG(kernels); // Index in matrix for background
+            kernels->solution1->data.F64[bgIndex] = solution->data.F64[bgIndex];
+        }
+        if (mode & PM_SUBTRACTION_EQUATION_KERNELS) {
+            int numKernels = kernels->num;
+            int spatialOrder = kernels->spatialOrder;       // Order of spatial variation
+            int numPoly = PM_SUBTRACTION_POLYTERMS(spatialOrder); // Number of polynomial terms
+            for (int i = 0; i < numKernels * numPoly; i++) {
+                kernels->solution1->data.F64[i] = solution->data.F64[i];
+            }
+        }
+
+        psFree(norms);
+        psFree(solution);
+        psFree(sumVector);
+        psFree(sumMatrix);
+
+#ifdef TESTING
+        // XXX double-check for NAN in data:
+        for (int ix = 0; ix < kernels->solution1->n; ix++) {
+            if (!isfinite(kernels->solution1->data.F64[ix])) {
+                fprintf (stderr, "WARNING: NAN in vector\n");
+            }
+        }
+#endif
+
+    } else {
+        // Dual convolution solution
+
+        // Accumulation of stamp matrices/vectors
+        psImage *sumMatrix = psImageAlloc(numParams, numParams, PS_TYPE_F64);
+        psVector *sumVector = psVectorAlloc(numParams, PS_TYPE_F64);
+        psImageInit(sumMatrix, 0.0);
+        psVectorInit(sumVector, 0.0);
+
+        psVector *norms = psVectorAllocEmpty(stamps->num, PS_TYPE_F64); // Normalisations
+
+        int numStamps = 0;              // Number of good stamps
+        for (int i = 0; i < stamps->num; i++) {
+            pmSubtractionStamp *stamp = stamps->stamps->data[i]; // Stamp of interest
+            if (stamp->status == PM_SUBTRACTION_STAMP_USED) {
+                (void)psBinaryOp(sumMatrix, sumMatrix, "+", stamp->matrix);
+                (void)psBinaryOp(sumVector, sumVector, "+", stamp->vector);
+
+                psVectorAppend(norms, stamp->norm);
+
+                pmSubtractionStampPrint(ds9, stamp->x, stamp->y, stamps->footprint, "green");
+                numStamps++;
+            }
+        }
+
+#if 0
+	psImage *save = psImageCopy(NULL, sumMatrix, PS_TYPE_F32);
+        psFitsWriteImageSimple ("sumMatrix.fits", save, NULL);
+        psVectorWriteFile("sumVector.dat", sumVector);
+	psFree (save);
+#endif
+
+#if 1
+        // int bgIndex = PM_SUBTRACTION_INDEX_BG(kernels); // Index for background
+        // calculatePenalty(sumMatrix, sumVector, kernels, sumMatrix->data.F64[bgIndex][bgIndex]);
+
+        int normIndex = PM_SUBTRACTION_INDEX_NORM(kernels); // Index for normalisation
+        calculatePenalty(sumMatrix, sumVector, kernels, sumMatrix->data.F64[normIndex][normIndex] / 100.0);
+#endif
+
+        psVector *solution = NULL;                       // Solution to equation!
+        solution = psVectorAlloc(numParams, PS_TYPE_F64);
+        psVectorInit(solution, 0);
+
+#if 0
+        // Regular, straight-forward solution
+        solution = psMatrixSolveSVD(solution, sumMatrix, sumVector, NAN);
+#else
+        {
+            // Solve normalisation and background separately
+            int normIndex = PM_SUBTRACTION_INDEX_NORM(kernels); // Index for normalisation
+            int bgIndex = PM_SUBTRACTION_INDEX_BG(kernels); // Index for background
+
+#if 0
+            psImage *normMatrix = psImageAlloc(2, 2, PS_TYPE_F64);
+            psVector *normVector = psVectorAlloc(2, PS_TYPE_F64);
+
+            normMatrix->data.F64[0][0] = sumMatrix->data.F64[normIndex][normIndex];
+            normMatrix->data.F64[1][1] = sumMatrix->data.F64[bgIndex][bgIndex];
+            normMatrix->data.F64[0][1] = normMatrix->data.F64[1][0] = sumMatrix->data.F64[normIndex][bgIndex];
+
+            normVector->data.F64[0] = sumVector->data.F64[normIndex];
+            normVector->data.F64[1] = sumVector->data.F64[bgIndex];
+
+            psVector *normSolution = psMatrixSolveSVD(NULL, normMatrix, normVector, NAN);
+
+            double normValue = normSolution->data.F64[0];
+            double bgValue = normSolution->data.F64[1];
+
+            psFree(normMatrix);
+            psFree(normVector);
+            psFree(normSolution);
+#endif
+
+            psStats *stats = psStatsAlloc(PS_STAT_ROBUST_MEDIAN); // Statistics for norm
+            if (!psVectorStats(stats, norms, NULL, NULL, 0)) {
+                psError(PM_ERR_DATA, false, "Unable to determine median normalisation");
+                psFree(stats);
+                psFree(sumMatrix);
+                psFree(sumVector);
+                psFree(norms);
+                return false;
+            }
+
+            double normValue = stats->robustMedian;
+
+            psFree(stats);
+
+#ifdef TESTING
+            fprintf(stderr, "Norm: %lf\n", normValue);
+#endif
+
+            // Solve kernel components
+            for (int i = 0; i < numSolution2; i++) {
+                sumVector->data.F64[i] -= normValue * sumMatrix->data.F64[normIndex][i];
+                sumVector->data.F64[i + numSolution1] -= normValue * sumMatrix->data.F64[normIndex][i + numSolution1];
+
+                sumMatrix->data.F64[i][normIndex] = 0.0;
+                sumMatrix->data.F64[normIndex][i] = 0.0;
+
+                sumMatrix->data.F64[i + numSolution1][normIndex] = 0.0;
+                sumMatrix->data.F64[normIndex][i + numSolution1] = 0.0;
+            }
+            sumVector->data.F64[bgIndex] -= normValue * sumMatrix->data.F64[normIndex][bgIndex];
+            sumMatrix->data.F64[bgIndex][normIndex] = 0.0;
+            sumMatrix->data.F64[normIndex][bgIndex] = 0.0;
+
+            sumMatrix->data.F64[normIndex][normIndex] = 1.0;
+
+            sumVector->data.F64[normIndex] = 0.0;
+
+// save the matrix and vector after the NULLs have been set
+#if 0
+	    psImage *save = psImageCopy(NULL, sumMatrix, PS_TYPE_F32);
+	    psFitsWriteImageSimple ("sumMatrix.fits", save, NULL);
+	    psVectorWriteFile("sumVector.dat", sumVector);
+	    psFree (save);
+#endif
+
+	    solution = psMatrixSolveSVD(solution, sumMatrix, sumVector, 1e-6);
+	    // solution = psMatrixSolveSVD(solution, sumMatrix, sumVector, 3e-4);
+	    // psVectorCopy (solution, sumVector, PS_TYPE_F64);
+            // psMatrixGJSolve(sumMatrix, solution);
+            solution->data.F64[normIndex] = normValue;
+        }
+#endif
+
+
+#if (1)
+        for (int i = 0; i < solution->n; i++) {
+            fprintf(stderr, "Dual solution %d: %lf\n", i, solution->data.F64[i]);
+        }
+#endif
+
+        psFree(sumMatrix);
+        psFree(sumVector);
+
+        psFree(norms);
+
+        if (!kernels->solution1) {
+            kernels->solution1 = psVectorAlloc(numSolution1, PS_TYPE_F64);
+            psVectorInit (kernels->solution1, 0.0);
+        }
+        if (!kernels->solution2) {
+            kernels->solution2 = psVectorAlloc(numSolution2, PS_TYPE_F64);
+            psVectorInit (kernels->solution2, 0.0);
+        }
+
+        // only update the solutions that we chose to calculate:
+        if (mode & PM_SUBTRACTION_EQUATION_NORM) {
+            int normIndex = PM_SUBTRACTION_INDEX_NORM(kernels); // Index for normalisation
+            kernels->solution1->data.F64[normIndex] = solution->data.F64[normIndex];
+        }
+        if (mode & PM_SUBTRACTION_EQUATION_BG) {
+            int bgIndex = PM_SUBTRACTION_INDEX_BG(kernels); // Index in matrix for background
+            kernels->solution1->data.F64[bgIndex] = solution->data.F64[bgIndex];
+        }
+        if (mode & PM_SUBTRACTION_EQUATION_KERNELS) {
+            int numKernels = kernels->num;
+            for (int i = 0; i < numKernels * numSpatial; i++) {
+                // XXX fprintf (stderr, "keep\n");
+                kernels->solution1->data.F64[i] = solution->data.F64[i];
+                kernels->solution2->data.F64[i] = solution->data.F64[i + numSolution1];
+            }
+        }
+
+
+        memcpy(kernels->solution1->data.F64, solution->data.F64,
+               numSolution1 * PSELEMTYPE_SIZEOF(PS_TYPE_F64));
+        memcpy(kernels->solution2->data.F64, &solution->data.F64[numSolution1],
+               numSolution2 * PSELEMTYPE_SIZEOF(PS_TYPE_F64));
+
+        psFree(solution);
+
+    }
+
+    if (ds9) {
+        fclose(ds9);
+    }
+
+    if (psTraceGetLevel("psModules.imcombine") >= 7) {
+        for (int i = 0; i < kernels->solution1->n; i++) {
+            psTrace("psModules.imcombine", 7, "Solution 1 %d: %f\n", i, kernels->solution1->data.F64[i]);
+        }
+        if (kernels->mode == PM_SUBTRACTION_MODE_DUAL) {
+            for (int i = 0; i < kernels->solution2->n; i++) {
+                psTrace("psModules.imcombine", 7, "Solution 2 %d: %f\n", i, kernels->solution2->data.F64[i]);
+            }
+        }
+     }
+
+    // pmSubtractionVisualPlotLeastSquares((pmSubtractionStampList *) stamps); //casting away const
+    return true;
+}
+
+// measure some useful stats on the stamp residuals:
+// fResSigma : the residual stdev / total flux
+// fResOuter : the residual fabs / total flux for R > 2 pix
+// fResTotal : the residual fabs / total flux for R > 0 pix
+bool pmSubtractionResidualStats(psVector *fResSigma, psVector *fResOuter, psVector *fResTotal, psKernel *target, psKernel *source, psKernel *residual, double norm, int footprint) {
+
+    float sum = 0.0;
+    float peak = 0.0;
+    for (int y = - footprint; y <= footprint; y++) {
+        for (int x = - footprint; x <= footprint; x++) {
+            sum += 0.5*(target->kernel[y][x] + source->kernel[y][x] * norm);
+            peak = PS_MAX(peak, 0.5*(target->kernel[y][x] + source->kernel[y][x] * norm));
+        }
+    }
+
+    // init counters
+    int npix = 0;
+    float dflux1 = 0.0;
+    float dflux2 = 0.0;
+    float dOuter = 0.0;
+    float dTotal = 0.0;
+
+    for (int y = - footprint; y <= footprint; y++) {
+        for (int x = - footprint; x <= footprint; x++) {
+            dflux1 += residual->kernel[y][x];
+            dflux2 += PS_SQR(residual->kernel[y][x]);
+            dTotal += fabs(residual->kernel[y][x]);
+	    if (hypot(x,y) > 2.0) {
+	      dOuter += fabs(residual->kernel[y][x]);
+	    }
+            npix ++;
+        }
+    }
+    float sigma = sqrt(dflux2 / npix - PS_SQR(dflux1/npix));
+    if (!isfinite(sum))  return false;
+    if (!isfinite(peak)) return false;
+    if (!isfinite(dOuter)) return false;
+    if (!isfinite(dTotal)) return false;
+
+    fprintf (stderr, "sum: %f, peak: %f, sigma: %f, fsigma: %f, fmax: %f, fmin: %f\n", sum, peak, sigma, sigma/sum, dOuter/sum, dTotal/sum);
+    psVectorAppend(fResSigma, sigma/sum);
+    psVectorAppend(fResOuter, dOuter/sum);
+    psVectorAppend(fResTotal, dTotal/sum);
+    return true;
+}
+
+psVector *pmSubtractionCalculateDeviations(pmSubtractionStampList *stamps,
+                                           pmSubtractionKernels *kernels)
+{
+    PM_ASSERT_SUBTRACTION_STAMP_LIST_NON_NULL(stamps, NULL);
+    PM_ASSERT_SUBTRACTION_KERNELS_NON_NULL(kernels, NULL);
+    PM_ASSERT_SUBTRACTION_KERNELS_SOLUTION(kernels, NULL);
+
+    psVector *deviations = psVectorAlloc(stamps->num, PS_TYPE_F32); // Mean deviation for stamps
+    int footprint = stamps->footprint; // Half-size of stamps
+    long numPixels = PS_SQR(2 * footprint + 1); // Number of pixels in footprint
+    double devNorm = 1.0 / (double)numPixels; // Normalisation for deviations
+    int numKernels = kernels->num;      // Number of kernels
+
+    psImage *polyValues = NULL;         // Polynomial values
+    psKernel *residual = psKernelAlloc(-footprint, footprint, -footprint, footprint); // Residual image
+
+    // set up holding images for the visualization
+    pmSubtractionVisualShowFitInit (stamps);
+
+    psVector *fResSigma = psVectorAllocEmpty(stamps->num, PS_TYPE_F32);
+    psVector *fResOuter = psVectorAllocEmpty(stamps->num, PS_TYPE_F32);
+    psVector *fResTotal = psVectorAllocEmpty(stamps->num, PS_TYPE_F32);
+
+    // we want to save the residual images for the 9 brightest stamps.
+    // identify the 9 brightest stamps
+    psVector *keepStamps  = psVectorAlloc(stamps->num, PS_TYPE_S32);
+    psVectorInit (keepStamps, 0);
+    {
+        psVector *flux  = psVectorAlloc(stamps->num, PS_TYPE_F32);
+        psVectorInit (flux, 0.0);
+
+        for (int i = 0; i < stamps->num; i++) {
+            pmSubtractionStamp *stamp = stamps->stamps->data[i];
+            if (!isfinite(stamp->flux)) continue;
+            flux->data.F32[i] = stamp->flux;
+        }
+
+        psVector *index = psVectorSortIndex(NULL, flux);
+        for (int i = 0; (i < stamps->num) && (i < 9); i++) {
+            int n = stamps->num - i - 1;
+            keepStamps->data.S32[index->data.S32[n]] = 1;
+        }
+        psFree (flux);
+        psFree (index);
+
+        // this function is called multiple times in the iteration, but
+        // we only know after the interation is done if we will try again.
+        // therefore we must save the sample each time, and blow away the old one
+        // if it exists.
+        psFree (kernels->sampleStamps);
+        kernels->sampleStamps = psArrayAllocEmpty(9);
+    }
+
+    psString log = psStringCopy("Deviations:\n");               // Log message with deviations
+    for (int i = 0; i < stamps->num; i++) {
+        pmSubtractionStamp *stamp = stamps->stamps->data[i]; // The stamp of interest
+        if (stamp->status != PM_SUBTRACTION_STAMP_USED) {
+            deviations->data.F32[i] = NAN;
+            continue;
+        }
+
+        // Calculate coefficients of the kernel basis functions
+        polyValues = p_pmSubtractionPolynomial(polyValues, kernels->spatialOrder, stamp->xNorm, stamp->yNorm);
+        double norm = p_pmSubtractionSolutionNorm(kernels); // Normalisation
+        double background = p_pmSubtractionSolutionBackground(kernels, polyValues);// Difference in background
+
+        // Calculate residuals
+        psKernel *weight = stamp->weight; // Weight postage stamp
+        psImageInit(residual->image, 0.0);
+        if (kernels->mode != PM_SUBTRACTION_MODE_DUAL) {
+            psKernel *target;           // Target postage stamp
+            psKernel *source;           // Source postage stamp
+            psArray *convolutions;      // Convolution postage stamps for each kernel basis function
+            switch (kernels->mode) {
+              case PM_SUBTRACTION_MODE_1:
+                target = stamp->image2;
+                source = stamp->image1;
+                convolutions = stamp->convolutions1;
+
+                // Having convolved image1 and changed its normalisation, we need to renormalise the residual
+                // so that it is on the scale of image1.
+                psImage *image = pmSubtractionKernelImage(kernels, stamp->xNorm, stamp->yNorm,
+                                                          false); // Kernel image
+                if (!image) {
+                    psError(psErrorCodeLast(), false, "Unable to generate image of kernel.");
+                    return false;
+                }
+                double sumKernel = 0;   // Sum of kernel, for normalising residual
+                int size = kernels->size; // Half-size of kernel
+                int fullSize = 2 * size + 1; // Full size of kernel
+                for (int y = 0; y < fullSize; y++) {
+                    for (int x = 0; x < fullSize; x++) {
+                        sumKernel += image->data.F32[y][x];
+                    }
+                }
+                psFree(image);
+                devNorm = 1.0 / sumKernel / numPixels;
+                break;
+              case PM_SUBTRACTION_MODE_2:
+                target = stamp->image1;
+                source = stamp->image2;
+                convolutions = stamp->convolutions2;
+                break;
+              default:
+                psAbort("Unsupported subtraction mode: %x", kernels->mode);
+            }
+
+            for (int j = 0; j < numKernels; j++) {
+                psKernel *convolution = convolutions->data[j]; // Convolution
+                double coefficient = p_pmSubtractionSolutionCoeff(kernels, polyValues, j,
+                                                                  false); // Coefficient
+                for (int y = - footprint; y <= footprint; y++) {
+                    for (int x = - footprint; x <= footprint; x++) {
+                        residual->kernel[y][x] += convolution->kernel[y][x] * coefficient;
+                    }
+                }
+            }
+
+            // XXX visualize the target, source, convolution and residual
+            pmSubtractionVisualShowFitAddStamp (target, source, residual, background, norm, i);
+
+            for (int y = - footprint; y <= footprint; y++) {
+                for (int x = - footprint; x <= footprint; x++) {
+                    residual->kernel[y][x] += background + source->kernel[y][x] * norm - target->kernel[y][x];
+                }
+            }
+
+            if (keepStamps->data.S32[i]) {
+                psImage *sample = psImageCopy(NULL, residual->image, PS_TYPE_F32);
+                psArrayAdd (kernels->sampleStamps, 9, sample);
+                psFree (sample);
+            }
+
+            pmSubtractionResidualStats(fResSigma, fResOuter, fResTotal, target, source, residual, norm, footprint);
+
+        } else {
+            // Dual convolution
+            psArray *convolutions1 = stamp->convolutions1; // Convolutions of the first image
+            psArray *convolutions2 = stamp->convolutions2; // Convolutions of the second image
+            psKernel *image1 = stamp->image1; // The first image
+            psKernel *image2 = stamp->image2; // The second image
+
+            for (int j = 0; j < numKernels; j++) {
+                psKernel *conv1 = convolutions1->data[j]; // Convolution of first image
+                psKernel *conv2 = convolutions2->data[j]; // Convolution of second image
+                double coeff1 = p_pmSubtractionSolutionCoeff(kernels, polyValues, j, false); // Coefficient 1
+                double coeff2 = p_pmSubtractionSolutionCoeff(kernels, polyValues, j, true); // Coefficient 2
+
+                for (int y = - footprint; y <= footprint; y++) {
+                    for (int x = - footprint; x <= footprint; x++) {
+                        residual->kernel[y][x] += conv2->kernel[y][x] * coeff2 + conv1->kernel[y][x] * coeff1;
+                    }
+                }
+            }
+
+            // XXX visualize the target, source, convolution and residual
+            pmSubtractionVisualShowFitAddStamp (image2, image1, residual, background, norm, i);
+
+            for (int y = - footprint; y <= footprint; y++) {
+                for (int x = - footprint; x <= footprint; x++) {
+                    residual->kernel[y][x] += background + image1->kernel[y][x] * norm - image2->kernel[y][x];
+                }
+            }
+            if (keepStamps->data.S32[i]) {
+                psImage *sample = psImageCopy(NULL, residual->image, PS_TYPE_F32);
+                psArrayAdd (kernels->sampleStamps, 9, sample);
+                psFree (sample);
+            }
+
+            pmSubtractionResidualStats(fResSigma, fResOuter, fResTotal, image1, image2, residual, norm, footprint);
+        }
+
+        double deviation = 0.0;         // Sum of differences
+        for (int y = - footprint; y <= footprint; y++) {
+            for (int x = - footprint; x <= footprint; x++) {
+                double dev = PS_SQR(residual->kernel[y][x]) * weight->kernel[y][x];
+                deviation += dev;
+#ifdef TESTING
+                residual->kernel[y][x] = dev;
+#endif
+            }
+        }
+        deviations->data.F32[i] = devNorm * deviation;
+        psTrace("psModules.imcombine", 5, "Deviation for stamp %d (%d,%d): %f\n",
+                i, (int)(stamp->x - 0.5), (int)(stamp->y - 0.5), deviations->data.F32[i]);
+        psStringAppend(&log, "Stamp %d (%d,%d): %f\n",
+                       i, (int)(stamp->x - 0.5), (int)(stamp->y - 0.5), deviations->data.F32[i]);
+        if (!isfinite(deviations->data.F32[i])) {
+            stamp->status = PM_SUBTRACTION_STAMP_REJECTED;
+            psTrace("psModules.imcombine", 5,
+                    "Rejecting stamp %d (%d,%d) because of non-finite deviation\n",
+                    i, (int)(stamp->x - 0.5), (int)(stamp->y - 0.5));
+            continue;
+        }
+
+#ifdef TESTING
+        {
+            psString filename = NULL;
+            psStringAppend(&filename, "resid_%03d.fits", i);
+            psFits *fits = psFitsOpen(filename, "w");
+            psFree(filename);
+            psFitsWriteImage(fits, NULL, residual->image, 0, NULL);
+            psFitsClose(fits);
+        }
+        if (stamp->image1) {
+            psString filename = NULL;
+            psStringAppend(&filename, "stamp_image1_%03d.fits", i);
+            psFits *fits = psFitsOpen(filename, "w");
+            psFree(filename);
+            psFitsWriteImage(fits, NULL, stamp->image1->image, 0, NULL);
+            psFitsClose(fits);
+        }
+        if (stamp->image2) {
+            psString filename = NULL;
+            psStringAppend(&filename, "stamp_image2_%03d.fits", i);
+            psFits *fits = psFitsOpen(filename, "w");
+            psFree(filename);
+            psFitsWriteImage(fits, NULL, stamp->image2->image, 0, NULL);
+            psFitsClose(fits);
+        }
+        if (stamp->weight) {
+            psString filename = NULL;
+            psStringAppend(&filename, "stamp_weight_%03d.fits", i);
+            psFits *fits = psFitsOpen(filename, "w");
+            psFree(filename);
+            psFitsWriteImage(fits, NULL, stamp->weight->image, 0, NULL);
+            psFitsClose(fits);
+        }
+#endif
+
+    }
+
+    psFree(keepStamps);
+
+    psLogMsg("psModules.imcombine", PS_LOG_DETAIL, "%s", log);
+    psFree(log);
+
+    // calculate and report the normalization and background for the image center
+    {
+        polyValues = p_pmSubtractionPolynomial(polyValues, kernels->spatialOrder, 0.0, 0.0);
+        double norm = p_pmSubtractionSolutionNorm(kernels); // Normalisation
+        double background = p_pmSubtractionSolutionBackground(kernels, polyValues);// Difference in background
+        psLogMsg("psModules.imcombine", PS_LOG_INFO, "normalization: %f, background: %f", norm, background);
+
+        pmSubtractionVisualShowFit(norm);
+        pmSubtractionVisualPlotFit(kernels);
+
+        psStats *stats = psStatsAlloc(PS_STAT_ROBUST_MEDIAN | PS_STAT_ROBUST_STDEV);
+        psVectorStats (stats, fResSigma, NULL, NULL, 0);
+        kernels->fResSigmaMean  = stats->robustMedian;
+        kernels->fResSigmaStdev = stats->robustStdev;
+
+        psStatsInit (stats);
+        psVectorStats (stats, fResOuter, NULL, NULL, 0);
+        kernels->fResOuterMean  = stats->robustMedian;
+        kernels->fResOuterStdev = stats->robustStdev;
+
+        psStatsInit (stats);
+        psVectorStats (stats, fResTotal, NULL, NULL, 0);
+        kernels->fResTotalMean  = stats->robustMedian;
+        kernels->fResTotalStdev = stats->robustStdev;
+
+        // XXX save these values somewhere
+        psLogMsg("psModules.imcombine", PS_LOG_INFO, "fResSigma: %f +/- %f, fResOuter: %f +/- %f, fResTotal: %f +/- %f",
+                 kernels->fResSigmaMean, kernels->fResSigmaStdev,
+                 kernels->fResOuterMean, kernels->fResOuterStdev,
+                 kernels->fResTotalMean, kernels->fResTotalStdev);
+
+        psFree (fResSigma);
+        psFree (fResOuter);
+        psFree (fResTotal);
+        psFree (stats);
+    }
+
+    psFree(residual);
+    psFree(polyValues);
+
+    return deviations;
+}
+
+// we are supplied U, not Ut; w represents a diagonal matrix (also, we apply 1/w instead of w)
+psImage *p_pmSubSolve_wUt (psVector *w, psImage *U) {
+
+    psAssert (w->n == U->numCols, "w and U dimensions do not match");
+
+    // wUt has dimensions transposed relative to Ut.
+    psImage *wUt = psImageAlloc (U->numRows, U->numCols, PS_TYPE_F64);
+    psImageInit (wUt, 0.0);
+
+    for (int i = 0; i < wUt->numCols; i++) {
+        for (int j = 0; j < wUt->numRows; j++) {
+            if (!isfinite(w->data.F64[j])) continue;
+            if (w->data.F64[j] == 0.0) continue;
+            wUt->data.F64[j][i] = U->data.F64[i][j] / w->data.F64[j];
+        }
+    }
+    return wUt;
+}
+
+// XXX this is just standard matrix multiplication: use psMatrixMultiply?
+psImage *p_pmSubSolve_VwUt (psImage *V, psImage *wUt) {
+
+    psAssert (V->numCols == wUt->numRows, "matrix dimensions do not match");
+
+    psImage *Ainv = psImageAlloc (wUt->numCols, V->numRows, PS_TYPE_F64);
+
+    for (int i = 0; i < Ainv->numCols; i++) {
+        for (int j = 0; j < Ainv->numRows; j++) {
+            double sum = 0.0;
+            for (int k = 0; k < V->numCols; k++) {
+                sum += V->data.F64[j][k] * wUt->data.F64[k][i];
+            }
+            Ainv->data.F64[j][i] = sum;
+        }
+    }
+    return Ainv;
+}
+
+// we are supplied U, not Ut
+bool p_pmSubSolve_UtB (psVector **UtB, psImage *U, psVector *B) {
+
+    psAssert (U->numRows == B->n, "U and B dimensions do not match");
+
+    UtB[0] = psVectorRecycle (UtB[0], U->numCols, PS_TYPE_F64);
+
+    for (int i = 0; i < U->numCols; i++) {
+        double sum = 0.0;
+        for (int j = 0; j < U->numRows; j++) {
+            sum += B->data.F64[j] * U->data.F64[j][i];
+        }
+        UtB[0]->data.F64[i] = sum;
+    }
+    return true;
+}
+
+// w is diagonal
+bool p_pmSubSolve_wUtB (psVector **wUtB, psVector *w, psVector *UtB) {
+
+    psAssert (w->n == UtB->n, "w and UtB dimensions do not match");
+
+    // wUt has dimensions transposed relative to Ut.
+    wUtB[0] = psVectorRecycle (wUtB[0], w->n, PS_TYPE_F64);
+    psVectorInit (wUtB[0], 0.0);
+
+    for (int i = 0; i < w->n; i++) {
+        if (!isfinite(w->data.F64[i])) continue;
+        if (w->data.F64[i] == 0.0) continue;
+        wUtB[0]->data.F64[i] = UtB->data.F64[i] / w->data.F64[i];
+    }
+    return true;
+}
+
+// this is basically matrix * vector
+bool p_pmSubSolve_VwUtB (psVector **VwUtB, psImage *V, psVector *wUtB) {
+
+    psAssert (V->numCols == wUtB->n, "V and wUtB dimensions do not match");
+
+    VwUtB[0] = psVectorRecycle (*VwUtB, V->numRows, PS_TYPE_F64);
+
+    for (int j = 0; j < V->numRows; j++) {
+        double sum = 0.0;
+        for (int i = 0; i < V->numCols; i++) {
+            sum += V->data.F64[j][i] * wUtB->data.F64[i];
+        }
+        VwUtB[0]->data.F64[j] = sum;
+    }
+    return true;
+}
+
+// this is basically matrix * vector
+bool p_pmSubSolve_Ax (psVector **B, psImage *A, psVector *x) {
+
+    psAssert (A->numCols == x->n, "A and x dimensions do not match");
+
+    B[0] = psVectorRecycle (*B, A->numRows, PS_TYPE_F64);
+
+    for (int j = 0; j < A->numRows; j++) {
+        double sum = 0.0;
+        for (int i = 0; i < A->numCols; i++) {
+            sum += A->data.F64[j][i] * x->data.F64[i];
+        }
+        B[0]->data.F64[j] = sum;
+    }
+    return true;
+}
+
+// this is basically Vector * vector
+bool p_pmSubSolve_VdV (double *value, psVector *x, psVector *y) {
+
+    psAssert (x->n == y->n, "x and y dimensions do not match");
+
+    double sum = 0.0;
+    for (int i = 0; i < x->n; i++) {
+        sum += x->data.F64[i] * y->data.F64[i];
+    }
+    *value = sum;
+    return true;
+}
+
+bool p_pmSubSolve_y2 (double *y2, pmSubtractionKernels *kernels, const pmSubtractionStampList *stamps) {
+
+    int footprint = stamps->footprint; // Half-size of stamps
+
+    double sum = 0.0;
+    for (int i = 0; i < stamps->num; i++) {
+
+        pmSubtractionStamp *stamp = stamps->stamps->data[i];
+        if (stamp->status != PM_SUBTRACTION_STAMP_USED) continue;
+
+        psKernel *weight = NULL;
+        psKernel *window = NULL;
+        psKernel *input = NULL;
+
+#ifdef USE_WEIGHT
+        weight = stamp->weight;
+#endif
+#ifdef USE_WINDOW
+        window = stamps->window;
+#endif
+
+        switch (kernels->mode) {
+            // MODE_1 : convolve image 1 to match image 2 (and vice versa)
+          case PM_SUBTRACTION_MODE_1:
+            input = stamp->image2;
+            break;
+          case PM_SUBTRACTION_MODE_2:
+            input = stamp->image1;
+            break;
+          default:
+            psAbort ("programming error");
+        }
+
+        for (int y = - footprint; y <= footprint; y++) {
+            for (int x = - footprint; x <= footprint; x++) {
+                double in = input->kernel[y][x];
+                double value = in*in;
+                if (weight) {
+                    float wtVal = weight->kernel[y][x];
+                    value *= wtVal;
+                }
+                if (window) {
+                    float  winVal = window->kernel[y][x];
+                    value *= winVal;
+                }
+                sum += value;
+            }
+        }
+    }
+    *y2 = sum;
+    return true;
+}
+
+double p_pmSubSolve_ChiSquare (pmSubtractionKernels *kernels, const pmSubtractionStampList *stamps) {
+
+    int footprint = stamps->footprint; // Half-size of stamps
+    int numKernels = kernels->num;      // Number of kernels
+
+    double sum = 0.0;
+
+    psKernel *residual = psKernelAlloc(-footprint, footprint, -footprint, footprint); // Residual image
+    psImageInit(residual->image, 0.0);
+
+    psImage *polyValues = NULL;         // Polynomial values
+
+    for (int i = 0; i < stamps->num; i++) {
+
+        pmSubtractionStamp *stamp = stamps->stamps->data[i];
+        if (stamp->status != PM_SUBTRACTION_STAMP_USED) continue;
+
+        psKernel *weight = NULL;
+        psKernel *window = NULL;
+        psKernel *target = NULL;
+        psKernel *source = NULL;
+
+        psArray *convolutions = NULL;
+
+#ifdef USE_WEIGHT
+        weight = stamp->weight;
+#endif
+#ifdef USE_WINDOW
+        window = stamps->window;
+#endif
+
+        switch (kernels->mode) {
+            // MODE_1 : convolve image 1 to match image 2 (and vice versa)
+          case PM_SUBTRACTION_MODE_1:
+            target = stamp->image2;
+            source = stamp->image1;
+            convolutions = stamp->convolutions1;
+            break;
+          case PM_SUBTRACTION_MODE_2:
+            target = stamp->image1;
+            source = stamp->image2;
+            convolutions = stamp->convolutions2;
+            break;
+          default:
+            psAbort ("programming error");
+        }
+
+        // Calculate coefficients of the kernel basis functions
+        polyValues = p_pmSubtractionPolynomial(polyValues, kernels->spatialOrder, stamp->xNorm, stamp->yNorm);
+        double norm = p_pmSubtractionSolutionNorm(kernels); // Normalisation
+        double background = p_pmSubtractionSolutionBackground(kernels, polyValues);// Difference in background
+
+        psImageInit(residual->image, 0.0);
+        for (int j = 0; j < numKernels; j++) {
+            psKernel *convolution = convolutions->data[j]; // Convolution
+            double coefficient = p_pmSubtractionSolutionCoeff(kernels, polyValues, j, false); // Coefficient
+            for (int y = - footprint; y <= footprint; y++) {
+                for (int x = - footprint; x <= footprint; x++) {
+                    residual->kernel[y][x] -= convolution->kernel[y][x] * coefficient;
+                }
+            }
+        }
+
+        for (int y = - footprint; y <= footprint; y++) {
+            for (int x = - footprint; x <= footprint; x++) {
+                double resid = target->kernel[y][x] - background - source->kernel[y][x] * norm + residual->kernel[y][x];
+                double value = PS_SQR(resid);
+                if (weight) {
+                    float wtVal = weight->kernel[y][x];
+                    value *= wtVal;
+                }
+                if (window) {
+                    float  winVal = window->kernel[y][x];
+                    value *= winVal;
+                }
+                sum += value;
+            }
+        }
+    }
+    psFree (polyValues);
+    psFree (residual);
+
+    return sum;
+}
+
+bool p_pmSubSolve_SetWeights (psVector *wApply, psVector *w, psVector *wMask) {
+
+    for (int i = 0; i < w->n; i++) {
+        wApply->data.F64[i] = wMask->data.U8[i] ? 0.0 : w->data.F64[i];
+    }
+    return true;
+}
+
+// we are supplied V and w; w represents a diagonal matrix (also, we apply 1/w instead of w)
+psImage *p_pmSubSolve_Xvar (psImage *V, psVector *w) {
+
+    psAssert (w->n == V->numCols, "w and U dimensions do not match");
+
+    psImage *Vn = psImageAlloc (V->numCols, V->numRows, PS_TYPE_F64);
+    psImageInit (Vn, 0.0);
+
+    // generate Vn = V * w^{-1}
+    for (int j = 0; j < Vn->numRows; j++) {
+        for (int i = 0; i < Vn->numCols; i++) {
+            if (!isfinite(w->data.F64[i])) continue;
+            if (w->data.F64[i] == 0.0) continue;
+            Vn->data.F64[j][i] = V->data.F64[j][i] / w->data.F64[i];
+        }
+    }
+
+    psImage *Xvar = psImageAlloc (V->numCols, V->numRows, PS_TYPE_F64);
+    psImageInit (Xvar, 0.0);
+
+    // generate Xvar = Vn * Vn^T
+    for (int j = 0; j < Vn->numRows; j++) {
+        for (int i = 0; i < Vn->numCols; i++) {
+            double sum = 0.0;
+            for (int k = 0; k < Vn->numCols; k++) {
+                sum += Vn->data.F64[k][i]*Vn->data.F64[k][j];
+            }
+            Xvar->data.F64[j][i] = sum;
+        }
+    }
+    return Xvar;
+}
+
+// I get confused by the index values between the image vs matrix usage:  In terms
+// of the elements of an image A(x,y) = A->data.F64[y][x] = A_x,y, a matrix
+// multiplication is: A_k,j * B_i,k = C_i,j
+
+
+bool psFitsWriteImageSimple (char *filename, psImage *image, psMetadata *header) {
+
+    psFits *fits = psFitsOpen(filename, "w");
+    psFitsWriteImage(fits, header, image, 0, NULL);
+    psFitsClose(fits);
+
+    return true;
+}
+
+bool psVectorWriteFile (char *filename, const psVector *vector) {
+
+    FILE *f = fopen (filename, "w");
+    int fd = fileno(f);
+    p_psVectorPrint (fd, vector, "unnamed");
+    fclose (f);
+
+    return true;
+}
+
+
+# if 0
+
+#ifdef TESTING
+        psFitsWriteImageSimple("A.fits", sumMatrix, NULL);
+        psVectorWriteFile ("B.dat", sumVector);
+#endif
+
+# define SVD_ANALYSIS 0
+# define COEFF_SIG 0.0
+# define SVD_TOL 0.0
+
+        // Use SVD to determine the kernel coeffs (and validate)
+        if (SVD_ANALYSIS) {
+
+            // We have sumVector and sumMatrix.  we are trying to solve the following equation:
+            // sumMatrix * x = sumVector.
+
+            // we can use any standard matrix inversion to solve this.  However, the basis
+            // functions in general have substantial correlation, so that the solution may be
+            // somewhat poorly determined or unstable.  If not numerically ill-conditioned, the
+            // system of equations may be statistically ill-conditioned.  Noise in the image
+            // will drive insignificant, but correlated, terms in the solution.  To avoid these
+            // problems, we can use SVD to identify numerically unconstrained values and to
+            // avoid statistically badly determined value.
+
+            // A = sumMatrix, B = sumVector
+            // SVD: A = U w V^T  -> A^{-1} = V (1/w) U^T
+            // x = V (1/w) (U^T B)
+            // \sigma_x = sqrt(diag(A^{-1}))
+            // solve for x and A^{-1} to get x & dx
+            // identify the elements of (1/w) that are nan (1/0.0) -> set to 0.0
+            // identify the elements of x that are insignificant (x / dx < 1.0? < 0.5?) -> set to 0.0
+
+            // If I use the SVD trick to re-condition the matrix, I need to break out the
+            // kernel and normalization terms from the background term.
+            // XXX is this true?  or was this due to an error in the analysis?
+
+            int bgIndex = PM_SUBTRACTION_INDEX_BG(kernels); // Index in matrix for background
+
+            // now pull out the kernel elements into their own square matrix
+            psImage  *kernelMatrix = psImageAlloc  (sumMatrix->numCols - 1, sumMatrix->numRows - 1, PS_TYPE_F64);
+            psVector *kernelVector = psVectorAlloc (sumMatrix->numCols - 1, PS_TYPE_F64);
+
+            for (int ix = 0, kx = 0; ix < sumMatrix->numCols; ix++) {
+                if (ix == bgIndex) continue;
+                for (int iy = 0, ky = 0; iy < sumMatrix->numRows; iy++) {
+                    if (iy == bgIndex) continue;
+                    kernelMatrix->data.F64[ky][kx] = sumMatrix->data.F64[iy][ix];
+                    ky++;
+                }
+                kernelVector->data.F64[kx] = sumVector->data.F64[ix];
+                kx++;
+            }
+
+            psImage *U = NULL;
+            psImage *V = NULL;
+            psVector *w = NULL;
+            if (!psMatrixSVD (&U, &w, &V, kernelMatrix)) {
+                psError(psErrorCodeLast(), false, "failed to perform SVD on sumMatrix\n");
+                return NULL;
+            }
+
+            // calculate A_inverse:
+            // Ainv = V * w * U^T
+            psImage *wUt  = p_pmSubSolve_wUt (w, U);
+            psImage *Ainv = p_pmSubSolve_VwUt (V, wUt);
+            psImage *Xvar = NULL;
+            psFree (wUt);
+
+# ifdef TESTING
+            // kernel terms:
+            for (int i = 0; i < w->n; i++) {
+                fprintf (stderr, "w: %f\n", w->data.F64[i]);
+            }
+# endif
+            // loop over w adding in more and more of the values until chisquare is no longer
+            // dropping significantly.
+            // XXX this does not seem to work very well: we seem to need all terms even for
+            // simple cases...
+
+            psVector *Xsvd = NULL;
+            {
+                psVector *Ax = NULL;
+                psVector *UtB = NULL;
+                psVector *wUtB = NULL;
+
+                psVector *wApply = psVectorAlloc(w->n, PS_TYPE_F64);
+                psVector *wMask = psVectorAlloc(w->n, PS_TYPE_U8);
+                psVectorInit (wMask, 1); // start by masking everything
+
+                double chiSquareLast = NAN;
+                int maxWeight = 0;
+
+                double Axx, Bx, y2;
+
+                // XXX this is an attempt to exclude insignificant modes.
+                // it was not successful with the ISIS kernel set: removing even
+                // the least significant mode leaves additional ringing / noise
+                // because the terms are so coupled.
+                for (int k = 0; false && (k < w->n); k++) {
+
+                    // unmask the k-th weight
+                    wMask->data.U8[k] = 0;
+                    p_pmSubSolve_SetWeights(wApply, w, wMask);
+
+                    // solve for x:
+                    // x = V * w * (U^T * B)
+                    p_pmSubSolve_UtB (&UtB, U, kernelVector);
+                    p_pmSubSolve_wUtB (&wUtB, wApply, UtB);
+                    p_pmSubSolve_VwUtB (&Xsvd, V, wUtB);
+
+                    // chi-square for this system of equations:
+                    // chi-square = sum over terms of: (Ax - B)*x - b*x - y^2
+                    // y^2 = \sum_stamps \sum_pixels input->kernel[y][x]^2
+                    p_pmSubSolve_Ax (&Ax, kernelMatrix, Xsvd);
+                    p_pmSubSolve_VdV (&Axx, Ax, Xsvd);
+                    p_pmSubSolve_VdV (&Bx, kernelVector, Xsvd);
+                    p_pmSubSolve_y2 (&y2, kernels, stamps);
+
+                    // apparently, this works (compare with the brute force value below
+                    double chiSquare = Axx - 2.0*Bx + y2;
+                    double deltaChi = (k == 0) ? chiSquare : chiSquareLast - chiSquare;
+                    chiSquareLast = chiSquare;
+
+                    // fprintf (stderr, "chi square = %f, delta: %f\n", chiSquare, deltaChi);
+                    if (k && !maxWeight && (deltaChi < 1.0)) {
+                        maxWeight = k;
+                    }
+                }
+
+                // keep all terms or we get extra ringing
+                maxWeight = w->n;
+                psVectorInit (wMask, 1);
+                for (int k = 0; k < maxWeight; k++) {
+                    wMask->data.U8[k] = 0;
+                }
+                p_pmSubSolve_SetWeights(wApply, w, wMask);
+
+                // solve for x:
+                // x = V * w * (U^T * B)
+                p_pmSubSolve_UtB (&UtB, U, kernelVector);
+                p_pmSubSolve_wUtB (&wUtB, wApply, UtB);
+                p_pmSubSolve_VwUtB (&Xsvd, V, wUtB);
+
+                // chi-square for this system of equations:
+                // chi-square = sum over terms of: (Ax - B)*x - b*x - y^2
+                // y^2 = \sum_stamps \sum_pixels input->kernel[y][x]^2
+                p_pmSubSolve_Ax (&Ax, kernelMatrix, Xsvd);
+                p_pmSubSolve_VdV (&Axx, Ax, Xsvd);
+                p_pmSubSolve_VdV (&Bx, kernelVector, Xsvd);
+                p_pmSubSolve_y2 (&y2, kernels, stamps);
+
+                // apparently, this works (compare with the brute force value below
+                double chiSquare = Axx - 2.0*Bx + y2;
+                psLogMsg ("psModules.imcombine", PS_LOG_INFO, "model kernel with %d terms; chi square = %f\n", maxWeight, chiSquare);
+
+                // re-calculate A^{-1} to get new variances:
+                // Ainv = V * w * U^T
+                // XXX since we keep all terms, this is identical to Ainv
+                psImage *wUt  = p_pmSubSolve_wUt (wApply, U);
+                Xvar = p_pmSubSolve_VwUt (V, wUt);
+                psFree (wUt);
+
+                psFree (Ax);
+                psFree (UtB);
+                psFree (wUtB);
+                psFree (wApply);
+                psFree (wMask);
+            }
+
+            // copy the kernel solutions to the full solution vector:
+            solution = psVectorAlloc(sumVector->n, PS_TYPE_F64);
+            solutionErr = psVectorAlloc(sumVector->n, PS_TYPE_F64);
+
+            for (int ix = 0, kx = 0; ix < sumVector->n; ix++) {
+                if (ix == bgIndex) {
+                    solution->data.F64[ix] = 0;
+                    solutionErr->data.F64[ix] = 0.001;
+                    continue;
+                }
+                solutionErr->data.F64[ix] = sqrt(Ainv->data.F64[kx][kx]);
+                solution->data.F64[ix] = Xsvd->data.F64[kx];
+                kx++;
+            }
+
+            psFree (kernelMatrix);
+            psFree (kernelVector);
+
+            psFree (U);
+            psFree (V);
+            psFree (w);
+
+            psFree (Ainv);
+            psFree (Xsvd);
+        } else {
+            psVector *permutation = NULL;       // Permutation vector, required for LU decomposition
+            psImage *luMatrix = psMatrixLUDecomposition(NULL, &permutation, sumMatrix);
+            if (!luMatrix) {
+                psError(PM_ERR_DATA, true, "LU Decomposition of least-squares matrix failed.\n");
+                psFree(solution);
+                psFree(sumVector);
+                psFree(sumMatrix);
+                psFree(luMatrix);
+                psFree(permutation);
+                return NULL;
+            }
+
+            solution = psMatrixLUSolution(NULL, luMatrix, sumVector, permutation);
+            psFree(luMatrix);
+            psFree(permutation);
+            if (!solution) {
+                psError(PM_ERR_DATA, true, "Failed to solve the least-squares system.\n");
+                psFree(solution);
+                psFree(sumVector);
+                psFree(sumMatrix);
+                return NULL;
+            }
+
+            // XXX LUD does not provide A^{-1}?  fake the error for now
+            solutionErr = psVectorAlloc(sumVector->n, PS_TYPE_F64);
+            for (int ix = 0; ix < sumVector->n; ix++) {
+                solutionErr->data.F64[ix] = 0.1*solution->data.F64[ix];
+            }
+        }
+
+        if (!kernels->solution1) {
+            kernels->solution1 = psVectorAlloc (sumVector->n, PS_TYPE_F64);
+            psVectorInit (kernels->solution1, 0.0);
+        }
+
+        // only update the solutions that we chose to calculate:
+        if (mode & PM_SUBTRACTION_EQUATION_NORM) {
+            int normIndex = PM_SUBTRACTION_INDEX_NORM(kernels); // Index for normalisation
+            kernels->solution1->data.F64[normIndex] = solution->data.F64[normIndex];
+        }
+        if (mode & PM_SUBTRACTION_EQUATION_BG) {
+            int bgIndex = PM_SUBTRACTION_INDEX_BG(kernels); // Index in matrix for background
+            kernels->solution1->data.F64[bgIndex] = solution->data.F64[bgIndex];
+        }
+        if (mode & PM_SUBTRACTION_EQUATION_KERNELS) {
+            int numKernels = kernels->num;
+            int spatialOrder = kernels->spatialOrder;       // Order of spatial variation
+            int numPoly = PM_SUBTRACTION_POLYTERMS(spatialOrder); // Number of polynomial terms
+            for (int i = 0; i < numKernels * numPoly; i++) {
+                // XXX fprintf (stderr, "%f +/- %f (%f) -> ", solution->data.F64[i], solutionErr->data.F64[i], fabs(solution->data.F64[i]/solutionErr->data.F64[i]));
+                if (fabs(solution->data.F64[i] / solutionErr->data.F64[i]) < COEFF_SIG) {
+                    // XXX fprintf (stderr, "drop\n");
+                    kernels->solution1->data.F64[i] = 0.0;
+                } else {
+                    // XXX fprintf (stderr, "keep\n");
+                    kernels->solution1->data.F64[i] = solution->data.F64[i];
+                }
+            }
+        }
+        // double chiSquare = p_pmSubSolve_ChiSquare (kernels, stamps);
+        // fprintf (stderr, "chi square Brute = %f\n", chiSquare);
+
+        psFree(solution);
+        psFree(sumVector);
+        psFree(sumMatrix);
+# endif
+
+#ifdef TESTING
+              // XXX double-check for NAN in data:
+                for (int iy = 0; iy < stamp->matrix->numRows; iy++) {
+                    for (int ix = 0; ix < stamp->matrix->numCols; ix++) {
+                        if (!isfinite(stamp->matrix->data.F64[iy][ix])) {
+                            fprintf (stderr, "WARNING: NAN in matrix\n");
+                        }
+                    }
+                }
+                for (int ix = 0; ix < stamp->vector->n; ix++) {
+                    if (!isfinite(stamp->vector->data.F64[ix])) {
+                        fprintf (stderr, "WARNING: NAN in vector\n");
+                    }
+                }
+#endif
+
+#ifdef TESTING
+        for (int ix = 0; ix < sumVector->n; ix++) {
+            if (!isfinite(sumVector->data.F64[ix])) {
+                fprintf (stderr, "WARNING: NAN in vector\n");
+            }
+        }
+#endif
+
+#ifdef TESTING
+        for (int ix = 0; ix < sumVector->n; ix++) {
+            if (!isfinite(sumVector->data.F64[ix])) {
+                fprintf (stderr, "WARNING: NAN in vector\n");
+            }
+        }
+        {
+            psImage *inverse = psMatrixInvert(NULL, sumMatrix, NULL);
+            psFitsWriteImageSimple("matrixInv.fits", inverse, NULL);
+            psFree(inverse);
+        }
+        {
+            psImage *X = psMatrixInvert(NULL, sumMatrix, NULL);
+            psImage *Xt = psMatrixTranspose(NULL, X);
+            psImage *XtX = psMatrixMultiply(NULL, Xt, X);
+            psFitsWriteImageSimple("matrixErr.fits", XtX, NULL);
+            psFree(X);
+            psFree(Xt);
+            psFree(XtX);
+        }
+#endif
+
Index: /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionMatch.c
===================================================================
--- /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionMatch.c	(revision 29169)
+++ /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionMatch.c	(revision 29170)
@@ -710,4 +710,12 @@
                 }
 
+		// step 0b : calculate the moments, pass along to the next steps via stamps->normValue
+		// XXX this step is now skipped -- delete
+                psTrace("psModules.imcombine", 3, "Calculating normalization...\n");
+                if (!pmSubtractionCalculateMoments(kernels, stamps)) {
+                    psError(psErrorCodeLast(), false, "Unable to calculate least-squares equation.");
+                    goto MATCH_ERROR;
+                }
+
                 // step 1: generate the elements of the matrix equation Ax = B
                 psTrace("psModules.imcombine", 3, "Calculating kernel equations...\n");
Index: /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionStamps.c
===================================================================
--- /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionStamps.c	(revision 29169)
+++ /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionStamps.c	(revision 29170)
@@ -344,6 +344,18 @@
     stamp->vector = NULL;
     stamp->norm = NAN;
+    stamp->normI1 = NAN;
+    stamp->normI2 = NAN;
     stamp->normSquare1 = NAN;
     stamp->normSquare2 = NAN;
+
+    stamp->MxxI1 = NULL;
+    stamp->MyyI1 = NULL;
+    stamp->MxxI2 = NULL;
+    stamp->MyyI2 = NULL;
+
+    stamp->MxxI1raw = NAN;
+    stamp->MyyI1raw = NAN;
+    stamp->MxxI2raw = NAN;
+    stamp->MyyI2raw = NAN;
 
     return stamp;
Index: /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionStamps.h
===================================================================
--- /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionStamps.h	(revision 29169)
+++ /branches/eam_branches/ipp-20100823/psModules/src/imcombine/pmSubtractionStamps.h	(revision 29170)
@@ -26,4 +26,5 @@
     float normFrac;                     ///< Fraction of flux in window for normalisation window
     float normValue;			///< calculated normalization
+    float normValue2;			///< calculated normalization
     psKernel *window1;                  ///< window function generated from ensemble of stamps (input 1)
     psKernel *window2;                  ///< window function generated from ensemble of stamps (input 2)
@@ -86,7 +87,17 @@
     psVector *vector;                   ///< Least-squares vector, or NULL
     double norm;                        ///< Normalisation difference
+    double normI1;                       ///< Sum(flux) for image 1
+    double normI2;                       ///< Sum(flux) for image 2
     double normSquare1;                 ///< Sum(flux^2) for image 1 (used for penalty)
     double normSquare2;                 ///< Sum(flux^2) for image 2 (used for penalty)
     pmSubtractionStampStatus status;    ///< Status of stamp
+    psVector *MxxI1;			///< second moments of convolution images
+    psVector *MyyI1;			///< second moments of convolution images
+    psVector *MxxI2;			///< second moments of convolution images
+    psVector *MyyI2;			///< second moments of convolution images
+    double MxxI1raw;
+    double MyyI1raw;
+    double MxxI2raw;
+    double MyyI2raw;
 } pmSubtractionStamp;
 
