star-wf

commit 63b2eb872bc292e637a75e6919a2d8ab3024f295
parent ee5831cc6b1e53556cb2185446f53280c62b44c1
Author: Vincent Forest <vincent.forest@meso-star.com>
Date:   Wed,  6 Mar 2024 16:05:35 +0100

Correction and adjustment of the swf_H3d_eval function

The sign was wrong in the terms of the series. The evaluated error is
also updated: there's no need to calculate the relative error, since the
target error is 0.

Diffstat:
M
src/swf.h
 | 
2
+-
M
src/swf_H.c
 | 
10
+++++-----

2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/src/swf.h b/src/swf.h
@@ -40,7 +40,7 @@ struct swf_H_tabulate_args {
   double delta_x;
   struct mem_allocator* allocator; /* NULL <=> use default allocator */
 };
-#define SWF_H_TABULATE_ARGS_DEFAULT__ {1e-5, 3.88, 4e-5, NULL}
+#define SWF_H_TABULATE_ARGS_DEFAULT__ {0, 3.88, 1e-5, NULL}
 static const struct swf_H_tabulate_args SWF_H_TABULATE_ARGS_DEFAULT =
   SWF_H_TABULATE_ARGS_DEFAULT__;
 
diff --git a/src/swf_H.c b/src/swf_H.c
@@ -57,20 +57,20 @@ swf_H3d_eval(const double x)
 {
   double sign = -1; /* Sign of the term */
   double sum = 0; /* Sum */
-  double error = INF; /* Relative error */
+  double error = INF; /* Error */
   unsigned k = 1; /* Index of the term */
-  ASSERT(x < 0); /* Check pre-condition */
+  ASSERT(x >= 0); /* Check pre-condition */
 
   if(x == 0) return 0;
 
   do {
     const double t = PI*(double)k;
-    const double term =  sign * exp(-t*t*x);
+    const double term =  sign * exp(-(t*t)*x);
     const double sum_next = sum + term;
 
-    error = (sum_next - sum) / sum_next;
+    error = sum_next - sum;
     sum = sum_next;
-    sign *= sign;
+    sign *= -1;
   } while(error != 0 && ++k < UINT_MAX);
 
   return 1.0 + 2.0 * sum;