NAME

gamma − log gamma function

SYNOPSIS

#include <math.h>

extern int signgam;

long float gamma (x)
long float x;

DESCRIPTION

Gamma returns ln(|Γ( x)|), whereΓ( x) is defined as ∞∫0e−ttx−1dt.  The sign of Γ( x)is returned in the external integer signgam. The argument x may not be a non-positive integer. 

The following C program fragment might be used to calculate Γ:

if ((y = gamma(x)) > LOGHUGE)
error();
y = signgam ∗ exp(y);

where LOGHUGE is the least value that causes exp(3M) to return a range error.

DIAGNOSTICS

Gamma checks its input for the illegal values Nan and ∞, raising a floating point exception with the type codes INVALID_OP_A, and INVALID_OP_F2, respecively.  Non-positive integer arguments cause a floating point exception to be raised with the type code DOMAIN_ERROR.

A floating point exception with the type OVERFL is raised if the input value would cause gamma to overflow. 

In all cases, the operation is MATH, and the global function identifier _mathfunc_id is set to GAMMA. 

SEE ALSO

exp(3M), fpsigset(3C). 

Version 2.5  —  April 22, 1987