Changeset 463eb76e in sasview for sansmodels/src/sans/models/c_extensions/libmultifunc/libfunc.c

Timestamp:

Jul 25, 2011 3:43:34 PM (13 years ago)

Author:

Jae Cho <jhjcho@…>

Branches:

master, ESS_GUI, ESS_GUI_Docs, ESS_GUI_batch_fitting, ESS_GUI_bumps_abstraction, ESS_GUI_iss1116, ESS_GUI_iss879, ESS_GUI_iss959, ESS_GUI_opencl, ESS_GUI_ordering, ESS_GUI_sync_sascalc, costrafo411, magnetic_scatt, release-4.1.1, release-4.1.2, release-4.2.2, release_4.0.1, ticket-1009, ticket-1094-headless, ticket-1242-2d-resolution, ticket-1243, ticket-1249, ticket885, unittest-saveload

Children:

bc7bc839

Parents:

38155f7

Message:

implementation of pearlneckclace model: need utest and doc

File:

• sansmodels/src/sans/models/c_extensions/libmultifunc/libfunc.c (modified) (3 diffs)

sansmodels/src/sans/models/c_extensions/libmultifunc/libfunc.c

@@ +1 @@
+// by jcho
 #include <math.h>
 #include "libmultifunc/libfunc.h"
@@ -19 +20 @@
 
 // Used in pearl nec model
-//integral of sin(x)/x up to namx term nmax>10 looks fine.
-double Si(double x, int nmax )
+// Sine integral function: approximated within 1%!!!
+// integral of sin(x)/x up to namx term nmax=6 looks the best.
+double Si(double x)
 {
         int i;
+        int nmax=6;
         double out;
         long double power;
-        if (x > 5.0){
-                double pi = 4.0*atan(1.0);
-                return pi/2.0;
+        double pi = 4.0*atan(1.0);
+        if (x >= pi*6.2/4.0){
+
+                double out_sin = 0.0;
+                double out_cos = 0.0;
+                out = pi/2.0;
+                for (i=0; i<nmax-2; i+=1){
+                        out_cos += pow(-1.0, i) * (double)factorial(2*i) / pow(x, 2*i+1);
+                        out_sin += pow(-1.0, i) * (double)factorial(2*i+1) / pow(x, 2*i+2);
+                }
+                out -= cos(x) * out_cos;
+                out -= sin(x) * out_sin;
+                return out;
         }
         out = 0.0;
@@ -43 +56 @@
 }
 
-double sin_x(double x)
+double sinc(double x)
 {
         if (x==0){