// my_pgamma - evaluate the distribution function of the gamma distribution
//             a demo of the R standalone math library
//
// Written in 2020 by Charles J. Geyer <geyer@umn.edu>
//
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to
// the public domain worldwide. This software is distributed without
// any warranty.
//
// See the CC0 Public Domain Dedication
// <http://creativecommons.org/publicdomain/zero/1.0/>.

#define MATHLIB_STANDALONE
#include <Rmath.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

int main(int argc, char *argv[])
{
    if (argc != 4) {
        fputs("Usage: my_pgamma x alpha beta\n"
            "where x is a real number and alpha and beta"
            " are postive real numbers\n"
            "the shape and scale parameters (respectively)\n", stderr);
        return EXIT_FAILURE;
    }

    double x, alpha, beta;

    if (sscanf(argv[1], "%lg", &x) != 1) {
        fputs("failed to read x\n", stderr);
        return EXIT_FAILURE;
    }

    if (sscanf(argv[2], "%lg", &alpha) != 1) {
        fputs("failed to read alpha\n", stderr);
        return EXIT_FAILURE;
    }

    if (sscanf(argv[3], "%lg", &beta) != 1) {
        fputs("failed to read beta\n", stderr);
        return EXIT_FAILURE;
    }

    double result = pgamma(x, alpha, beta, true, false);

    printf("pgamma(x, alpha, beta) = %g\n", result);

    return EXIT_SUCCESS;
}