lib/poisson_pdf.c


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// Poisson Pdf
//
// poisson_pdf
//
// Poisson probability density
//
// 
//
// Inputs:    1
// Outputs:   1
// Constants: 1


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

typedef struct {
    fp_t lambda;
} ts_poisson_pdf_params_t;

ts_parameter_t const ts_poisson_pdf_p = { .n_inputs = 1, .n_outputs = 1, .n_constants = 1, .params_size = sizeof(ts_poisson_pdf_params_t) };

uint_t ts_poisson_pdf_offset( ts_constant_t const *c )
{
	( void )c;
	return ( 0 );
}

int ts_poisson_pdf(
	fp_t * const *y, uint_t y_n,
	fp_t const * const *x, uint_t x_n,
	uint_t n, ts_constant_t const *c
)
{
	TS_PROLOGUE( ts_poisson_pdf_p );
	if ( !c ) return -1;
	fp_t lambda = ((ts_poisson_pdf_params_t const *)c)->lambda;
	if (lambda < 0.0 || isnan(lambda) || isinf(lambda)) return -1;
	for( uint_t i = 0; i < n; ++i )
	{
		fp_t k_val = x[0][i];
		if( k_val < 0 ) { y[0][i] = 0; continue; }
		uint_t k = (uint_t)k_val;
		y[0][i] = pow( lambda, k ) * exp( -lambda ) / tgamma( k + 1.0 );
	}
	return 0;
}