nf_gammaFunctions.cc File Reference

#include "nf_specialFunctions.h"

Go to the source code of this file.

Macros
#define	MAXGAM   171.624376956302725
#define	MAXSTIR   143.01608
#define	MAXLGM   2.556348e305

Functions
double	nf_gammaFunction (double x, nfu_status *status)
double	nf_logGammaFunction (double x, nfu_status *status)

Macro Definition Documentation

MAXGAM

#define MAXGAM   171.624376956302725

Definition at line 93 of file nf_gammaFunctions.cc.

MAXLGM

#define MAXLGM   2.556348e305

Definition at line 201 of file nf_gammaFunctions.cc.

MAXSTIR

#define MAXSTIR   143.01608

Definition at line 99 of file nf_gammaFunctions.cc.

Function Documentation

nf_gammaFunction()

double nf_gammaFunction	(	double	x,
		nfu_status *	status )

Definition at line 126 of file nf_gammaFunctions.cc.

                                                        {
 
    double p, q, z;
    int i, sgngam = 1;
 
    *status = nfu_badInput;
    if( !isfinite( x ) ) return( x );
    *status = nfu_Okay;
 
    q = fabs( x );
 
    if( q > 33.0 ) {
        if( x < 0.0 ) {
            p = floor( q );
            if( p == q ) goto goverf;
            i = (int) p;
            if( ( i & 1 ) == 0 ) sgngam = -1;
            z = q - p;
            if( z > 0.5 ) {
                p += 1.0;
                z = q - p;
            }
            z = q * sin( M_PI * z );
            if( z == 0.0 ) goto goverf;
            z = M_PI / ( fabs( z ) * stirf( q, status ) );
        }
        else {
            z = stirf( x, status );
        }
        return( sgngam * z );
    }
 
    z = 1.0;
    while( x >= 3.0 ) {
        x -= 1.0;
        z *= x;
    } // Loop checking, 11.06.2015, T. Koi
 
    while( x < 0.0 ) {
        if( x > -1.E-9 ) goto small;
        z /= x;
        x += 1.0;
    } // Loop checking, 11.06.2015, T. Koi
 
    while( x < 2.0 ) {
        if( x < 1.e-9 ) goto small;
        z /= x;
        x += 1.0;
    } // Loop checking, 11.06.2015, T. Koi
 
    if( x == 2.0 ) return( z );
 
    x -= 2.0;
    p = nf_polevl( x, P, 6 );
    q = nf_polevl( x, Q, 7 );
    return( z * p / q );
 
small:
    if( x == 0.0 ) goto goverf;
    return( z / ( ( 1.0 + 0.5772156649015329 * x ) * x ) );
 
goverf:
    return( sgngam * DBL_MAX );
}

Referenced by nf_incompleteGammaFunction(), and nf_incompleteGammaFunctionComplementary().

nf_logGammaFunction()

double nf_logGammaFunction	(	double	x,
		nfu_status *	status )

Definition at line 206 of file nf_gammaFunctions.cc.

                                                           {
/* Logarithm of gamma function */
 
    int sgngam;
 
    *status = nfu_badInput;
    if( !isfinite( x ) ) return( x );
    *status = nfu_Okay;
    return( lgam( x, &sgngam, status ) );
}