#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 = α

  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       = %zu\n", w->size);

  gsl_integration_workspace_free (w);

  return 0;

}