Changeset 71b751d in sasmodels for sasmodels/models/vesicle.c

Timestamp:

Aug 14, 2018 10:09:34 AM (6 years ago)

Author:

Paul Kienzle <pkienzle@…>

Branches:

master, core_shell_microgels, magnetic_model, ticket-1257-vesicle-product, ticket_1156, ticket_1265_superball, ticket_822_more_unit_tests

Children:

86aa992

Parents:

2f8cbb9

Message:

update remaining form factors to use Fq interface

File:

• sasmodels/models/vesicle.c (modified) (4 diffs)

sasmodels/models/vesicle.c

@@ -1 @@
-double form_volume(double radius, double thickness);
-
-double Iq(double q, 
-          double sld, double sld_solvent, double volfraction,
-          double radius, double thickness);
-
-double form_volume(double radius, double thickness)
+static double
+form_volume(double radius, double thickness)
 {
     //note that for the vesicle model, the volume is ONLY the shell volume
@@ -11 +6 @@
 }
 
-double Iq(double q,
+
+static void
+Fq(double q,
+    double *F1,
+    double *F2,
     double sld,
     double sld_solvent,
@@ -31 +30 @@
     vol = M_4PI_3*cube(radius);
     f = vol * sas_3j1x_x(q*radius) * contrast;
- 
+
     //now the shell. No volume normalization as this is done by the caller
     contrast = sld-sld_solvent;
@@ -37 +36 @@
     f += vol * sas_3j1x_x(q*(radius+thickness)) * contrast;
 
-    //rescale to [cm-1]. 
-    f2 = volfraction * f*f*1.0e-4;
-    
-    return f2;
+    //rescale to [cm-1].
+    // With volume fraction as part of the model in the dilute limit need
+    // to return F2 = Vf <fq^2>.  In order for beta approx. to work correctly
+    // need F1^2/F2 equal to <fq>^2 / <fq^2>.  By returning F1 = sqrt(Vf) <fq>
+    // and F2 = Vf <fq^2> both conditions are satisfied.
+    // Since Vf is the volume fraction of vesicles of all radii, it is
+    // constant when averaging F1 and F2 over radii and so pops out of the
+    // polydispersity loop, so it is safe to apply it inside the model
+    // (albeit conceptually ugly).
+    *F1 = 1e-2 * sqrt(volfraction) * f;
+    *F2 = 1.0e-4 * volfraction * f * f;
 }