x035.h

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#pragma once

#include <gsl/gsl_deriv.h>
#include <gsl/gsl_math.h>
#include <stdio.h>

namespace nmx::apps::x035 {

double f(double x, void *params) {
    (void) (params); /* avoid unused parameter warning */
    return pow(x, 1.5);
}

inline void ex1() {
    gsl_function F;
    double result, abserr;

    F.function = &f;
    F.params = nullptr;

    printf("f(x) = x^(3/2)\n");

    gsl_deriv_central(&F, 2.0, 1e-8, &result, &abserr);
    printf("x = 2.0\n");
    printf("f'(x) = %.10f +/- %.10f\n", result, abserr);
    printf("exact = %.10f\n\n", 1.5 * sqrt(2.0));

    gsl_deriv_forward(&F, 0.0, 1e-8, &result, &abserr);
    printf("x = 0.0\n");
    printf("f'(x) = %.10f +/- %.10f\n", result, abserr);
    printf("exact = %.10f\n", 0.0);
}

} // namespace nmx::apps::x035