LRpoisson.c

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/*
 * Copyright    2019    R.K. Owen, Ph.D.
 * License      see lgpl.md (Gnu Lesser General Public License)
 */
#ifdef __cplusplus
extern "C" {
#endif

#include <math.h>
#include "libran.h"

/* int */
int LRi_poisson_RAN(LR_obj *o) {
        float zero = 0.0, one = 1.0, u, p = one;
        int kk = 0;
        if (isnan(o->q))
                o->q = expf(-o->p);

        do {
                do {
                        u = o->uf(o);
                } while (u == zero);
                kk++;
                p *= u;
        } while (p > o->q);

        return kk - 1;
}

float LRi_poisson_PDF(LR_obj *o, int x) {
        float zero = 0.0, one = 1.0, p = one;
        if (isnan(o->q))
                o->q = expf(- o->p);

        if (x < 0)      return zero;

        if (x == 0) {
                return o->q;
        } else {
                for (int nn = 1; nn <= x; nn++) {
                        p *= (o->p/nn);
                }
                return p * o->q;
        }
}

float LRi_poisson_CDF(LR_obj *o, int x) {
        float zero = 0.0, one = 1.0, p = one, s = one;
        if (isnan(o->q))
                o->q = expf(- o->p);

        if (x < 0)      return zero;

        if (x == 0) {
                return o->q;
        } else {
                for (int nn = 1; nn <= x; nn++) {
                        p *= (o->p/nn);
                        s += p;
                }
                return s * o->q;
        }
}

#ifdef __cplusplus
}
#endif