testgsl.cpp

//
// Copyright (c) 2011 Ronaldo Carpio
//                                     
// Permission to use, copy, modify, distribute and sell this software
// and its documentation for any purpose is hereby granted without fee,
// provided that the above copyright notice appear in all copies and   
// that both that copyright notice and this permission notice appear
// in supporting documentation.  The authors make no representations
// about the suitability of this software for any purpose.          
// It is provided "as is" without express or implied warranty.
//                                                            
  


#include <stdio.h>
#include <math.h>
#include <gsl/gsl_integration.h>

double f (double x, void * params) {
  double alpha = *(double *) params;
  double f = log(alpha*x) / sqrt(x);
  return f;
}

int
main (void)
{
  gsl_integration_workspace * w 
    = gsl_integration_workspace_alloc (1000);
  
  double result, error;
  double expected = -4.0;
  double alpha = 1.0;

  gsl_function F;
  F.function = &f;
  F.params = &alpha;

  gsl_integration_qags (&F, 0, 1, 0, 1e-7, 1000,
    w, &result, &error); 

  printf ("result= % .18f\n", result);
  printf ("exact result    = % .18f\n", expected);
  printf ("estimated error = % .18f\n", error);
  printf ("actual error    = % .18f\n", result - expected);
  printf ("intervals =  %d\n", w->size);

  gsl_integration_workspace_free (w);

  return 0;
}