nbinomial.c

#include "nbinomial.h"
#include <float.h>
#include <math.h>

double liknorm_nbinomial_log_partition(const double theta)
{
    return theta > -log(DBL_MAX) ? -log1p(-exp(theta)) : 0;
}

double liknorm_nbinomial_log_partition_fderivative(const double theta)
{
    return theta > -log(DBL_MAX) ? theta - log1p(-exp(theta)) : theta;
}

void liknorm_nbinomial_log_partition_derivatives(const double theta, double *b0,
                                         double *logb1, double *logb2)
{
    if (theta > -log(DBL_MAX))
    {
        double log1p_ = log1p(-exp(theta));
        *b0 = -log1p_;
        *logb1 = theta - log1p_;
        *logb2 = theta - 2 * log1p_;
    }
    else
    {
        *b0 = 0;
        *logb1 = theta;
        *logb2 = theta;
    }
}