1 files changed, 47 insertions, 0 deletions
diff --git a/gsl-1.9/doc/examples/sum.c b/gsl-1.9/doc/examples/sum.c
new file mode 100644
index 0000000..c0237ea
--- /dev/null
+++ b/gsl-1.9/doc/examples/sum.c
@@ -0,0 +1,47 @@
+#include <stdio.h>
+#include <gsl/gsl_math.h>
+#include <gsl/gsl_sum.h>
+
+#define N 20
+
+int
+main (void)
+{
+  double t[N];
+  double sum_accel, err;
+  double sum = 0;
+  int n;
+  
+  gsl_sum_levin_u_workspace * w 
+    = gsl_sum_levin_u_alloc (N);
+
+  const double zeta_2 = M_PI * M_PI / 6.0;
+  
+  /* terms for zeta(2) = \sum_{n=1}^{\infty} 1/n^2 */
+
+  for (n = 0; n < N; n++)
+    {
+      double np1 = n + 1.0;
+      t[n] = 1.0 / (np1 * np1);
+      sum += t[n];
+    }
+  
+  gsl_sum_levin_u_accel (t, N, w, &sum_accel, &err);
+
+  printf ("term-by-term sum = % .16f using %d terms\n", 
+          sum, N);
+
+  printf ("term-by-term sum = % .16f using %d terms\n", 
+          w->sum_plain, w->terms_used);
+
+  printf ("exact value      = % .16f\n", zeta_2);
+  printf ("accelerated sum  = % .16f using %d terms\n", 
+          sum_accel, w->terms_used);
+
+  printf ("estimated error  = % .16f\n", err);
+  printf ("actual error     = % .16f\n", 
+          sum_accel - zeta_2);
+
+  gsl_sum_levin_u_free (w);
+  return 0;
+}