NAME

gamma − log gamma function

SYNOPSIS

#include <math.h>

double gamma (x)
double x;

extern int signgam;

DESCRIPTION

gamma returns ln(|Γ( x)|), where Γ( 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)) > LN_MAXDOUBLE)
error();
y = signgam ∗ exp(y);

where LN_MAXDOUBLE is the least value that causes exp(3M) to return a range error, and is defined in the <values.h> header file. 

SEE ALSO

exp(3M), matherr(3M), values(5)

DIAGNOSTICS

For non-negative integer arguments HUGE is returned, and errno is set to EDOM.  A message indicating SING error is printed on the standard error output. 

If the correct value would overflow, gamma returns HUGE and sets errno to ERANGE. 

These error-handling procedures may be changed with the function matherr(3M).

September 02, 1992