gsl.c

#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);
//	int gsl_integration_qags (const gsl function * f, double a, double b, [Function] double epsabs, double epsrel, size t limit, gsl integration workspace * workspace, double * result, double * abserr)
	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;
}