gsl_histogram_get_range(hist, 0, &x_min, ¬_used);
range = not_used - x_min;
gsl_histogram_get_range(hist, bins - 1, ¬_used, &x_max);
gsl_histogram_get_range(hist, 0, &x_min, ¬_used);
range = not_used - x_min;
gsl_histogram_get_range(hist, bins - 1, ¬_used, &x_max);