Index: trunk/ppSim/src/ppSimMakeGalaxies.c
===================================================================
--- trunk/ppSim/src/ppSimMakeGalaxies.c	(revision 34261)
+++ trunk/ppSim/src/ppSimMakeGalaxies.c	(revision 36079)
@@ -219,16 +219,25 @@
     }
 
+    // exponential
+    // f = I0 exp (sqrt(z)) (index = 1.0)
+
+    // f = I0 exp (-0.5*z) 
+
     if (isSersicType) {
 	// for a sersic model, 
-	float bn = 1.9992*index - 0.3271;
-	float Io = exp(bn);
+	// float bn = 1.9992*index - 0.3271;
+	// float Io = exp(bn);
 		    
 	// the integral of a Sersic has an analytical form as follows:
-	float logGamma = lgamma(2.0*index);
-	float bnFactor = pow(bn, 2.0*index);
-	float norm = 2.0 * M_PI * PS_SQR(galaxy->Rmaj) * index * Io * exp(logGamma) / bnFactor;
+	// float logGamma = lgamma(2.0*index);
+	// float bnFactor = pow(bn, 2.0*index);
+	// float norm = 2.0 * M_PI * PS_SQR(galaxy->Rmaj) * index * Io * exp(logGamma) / bnFactor;
 		    
+	// find the flux of a sersic with peak = 1.0:
+	float norm = pmSersicNorm (index);
+	float flux = 2.0 * M_PI * galaxy->Rmaj * galaxy->Rmin * norm;
+
 	// XXX probably should limit the allowed thinness of a galaxy
-	galaxy->peak = galaxy->flux / norm / (galaxy->Rmin / galaxy->Rmaj);
+	galaxy->peak = galaxy->flux / flux;
 	return true;
     }