NAME

lgamma, lgammaf, lgamma_r, lgammaf_r, gamma, gammaf, gamma_r, gammaf_r - log gamma function

LIBRARY

Math Library (libm, -lm)

SYNOPSIS



extern int signgam;



double lgamma(double x)

float lgammaf(float x)

double lgamma_r(double x, int *sign)

float lgammaf_r(float x, int *sign)

double gamma(double x)

float gammaf(float x)

double gamma_r(double x, int *sign)

float gammaf_r(float x, int *sign)

DESCRIPTION

lgamma(x) returns ln|(x)|.

The external integer signgam returns the sign of (x).

lgamma_r() is a reentrant interface that performs identically to lgamma(), differing in that the sign of (x) is stored in the location pointed to by the sign argument and signgam is not modified.

IDIOSYNCRASIES

Do not use the expression ``signgam*exp(lgamma(x))'' to compute g := (x). Instead use a program like this (in C):
lg = lgamma(x); g = signgam*exp(lg);

Only after lgamma() has returned can signgam be correct.

RETURN VALUES

lgamma() returns appropriate values unless an argument is out of range. Overflow will occur for sufficiently large positive values, and non-positive integers. On the VAX, the reserved operator is returned, and errno is set to ERANGE.

SEE ALSO

math(3)

HISTORY

The lgamma function appeared in 4.3BSD.