LGAMMA(3) BSD Library Functions Manual LGAMMA(3)NAME
lgamma, lgammaf, lgamma_r, lgammaf_r, gamma, gammaf, gamma_r, gammaf_r —
log gamma function
LIBRARY
Math Library (libm, -lm)
SYNOPSIS
#include <math.h>
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);
DESCRIPTIONlgamma(x) returns ln|Γ(x)|.
The external integer signgam returns the sign of Γ(x).
lgamma_r() is a reentrant interface that performs identically to
lgamma(), differing in that the sign of Γ(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 := Γ(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 VALUESlgamma() returns appropriate values unless an argument is out of range.
Overflow will occur for sufficiently large positive values, and non-posi‐
tive integers. On the VAX, the reserved operator is returned, and errno
is set to ERANGE.
SEE ALSOmath(3)HISTORY
The lgamma function appeared in 4.3BSD.
BSD December 3, 1992 BSD
