Index: trunk/psModules/src/objects/models/pmModel_SERSIC.c
===================================================================
--- trunk/psModules/src/objects/models/pmModel_SERSIC.c	(revision 14324)
+++ trunk/psModules/src/objects/models/pmModel_SERSIC.c	(revision 14325)
@@ -51,17 +51,25 @@
 
     psF32 f2 = pow(z,PAR[PM_PAR_7]);
-    psF32 f1 = exp(-z);
+    psF32 f1 = exp(-f2);
     psF32 z0 = PAR[PM_PAR_I0]*f1;
     psF32 f0 = PAR[PM_PAR_SKY] + z0;
 
+    assert (isfinite(f2));
+    assert (isfinite(f1));
+    assert (isfinite(z0));
+    assert (isfinite(f0));
+
     if (deriv != NULL) {
         psF32 *dPAR = deriv->data.F32;
 
-        // note difference from a pure gaussian: q = params->data.F32[PM_PAR_I0]*r
-	psF32 z1 = z0*PAR[PM_PAR_7]*pow(z,PAR[PM_PAR_7] - 1.0);
+	// gradient is infinite for z = 0; saturate at z = 0.01
+	psF32 z1 = (z < 0.01) ? z0*PAR[PM_PAR_7]*pow(0.01,PAR[PM_PAR_7] - 1.0) : z0*PAR[PM_PAR_7]*pow(z,PAR[PM_PAR_7] - 1.0);
 
         dPAR[PM_PAR_SKY]  = +1.0;
         dPAR[PM_PAR_I0]   = +f1;
         dPAR[PM_PAR_7]    = (z == 0.0) ? 0.0 : -z0*f2*log(z);
+
+	assert (isfinite(z1));
+	assert (isfinite(dPAR[PM_PAR_7]));
 
         dPAR[PM_PAR_XPOS] = +1.0*z1*(2.0*px/PAR[PM_PAR_SXX] + Y*PAR[PM_PAR_SXY]);
@@ -70,6 +78,7 @@
         dPAR[PM_PAR_SYY]  = +2.0*z1*py*py/PAR[PM_PAR_SYY];
         dPAR[PM_PAR_SXY]  = -1.0*z1*X*Y;
-    }
-    return(f);
+        dPAR[PM_PAR_SXY]  = -1.0*z1*X*Y;
+    }
+    return (f0);
 }
 
@@ -156,5 +165,5 @@
             break;
         case PM_PAR_7:
-            params_min =   0.1;
+            params_min =   0.25;
             break;
         default:
@@ -244,5 +253,5 @@
     PAR[PM_PAR_SYY]  = PS_MAX(0.5, M_SQRT2*shape.sy);
     PAR[PM_PAR_SXY]  = shape.sxy;
-    PAR[PM_PAR_7]    = 1.0;
+    PAR[PM_PAR_7]    = 0.5;
 
     return(true);
Index: trunk/psModules/src/objects/pmModelGroup.c
===================================================================
--- trunk/psModules/src/objects/pmModelGroup.c	(revision 14324)
+++ trunk/psModules/src/objects/pmModelGroup.c	(revision 14325)
@@ -6,6 +6,6 @@
  *  @author EAM, IfA
  *
- *  @version $Revision: 1.16 $ $Name: not supported by cvs2svn $
- *  @date $Date: 2007-07-20 00:27:59 $
+ *  @version $Revision: 1.17 $ $Name: not supported by cvs2svn $
+ *  @date $Date: 2007-07-20 00:31:43 $
  *
  *  Copyright 2004 Maui High Performance Computing Center, University of Hawaii
@@ -48,5 +48,5 @@
                                           {"PS_MODEL_PGAUSS",       7, pmModelFunc_PGAUSS,  pmModelFlux_PGAUSS,  pmModelRadius_PGAUSS,  pmModelLimits_PGAUSS,  pmModelGuess_PGAUSS, pmModelFromPSF_PGAUSS, pmModelFitStatus_PGAUSS},
                                           {"PS_MODEL_QGAUSS",       8, pmModelFunc_QGAUSS,  pmModelFlux_QGAUSS,  pmModelRadius_QGAUSS,  pmModelLimits_QGAUSS,  pmModelGuess_QGAUSS, pmModelFromPSF_QGAUSS, pmModelFitStatus_QGAUSS},
-                                          {"PS_MODEL_RGAUSS",       8, pmModelFunc_RGAUSS,  pmModelFlux_RGAUSS,  pmModelRadius_RGAUSS,  pmModelLimits_RGAUSS,  pmModelGuess_RGAUSS, pmModelFromPSF_RGAUSS, pmModelFitStatus_RGAUSS}
+                                          {"PS_MODEL_RGAUSS",       8, pmModelFunc_RGAUSS,  pmModelFlux_RGAUSS,  pmModelRadius_RGAUSS,  pmModelLimits_RGAUSS,  pmModelGuess_RGAUSS, pmModelFromPSF_RGAUSS, pmModelFitStatus_RGAUSS},
                                           {"PS_MODEL_SERSIC",       8, pmModelFunc_SERSIC,  pmModelFlux_SERSIC,  pmModelRadius_SERSIC,  pmModelLimits_SERSIC,  pmModelGuess_SERSIC, pmModelFromPSF_SERSIC, pmModelFitStatus_SERSIC}
                                       };