LGAMMA(3) BSD Library Functions Manual LGAMMA(3)NAMElgamma gamma — log gamma function, gamma function
SYNOPSIS
#include <math.h>
extern int signgam;
double
lgamma(double x);
double
gamma(double x);
DESCRIPTIONLgamma(x) returns ln|Γ(x)|.
The external integer signgam returns the sign of Γ(x).
Gamma(x) returns Γ(x), with no effect on signgam.
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.
For arguments in its range, gamma() is preferred, as for positive argu‐
ments it is accurate to within one unit in the last place. Exponentia‐
tion of lgamma() will lose up to 10 significant bits.
RETURN VALUESGamma() and lgamma() return 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 For large non-integer negative val‐
ues, gamma() will underflow.
SEE ALSOmath(3), infnan(3)HISTORY
The lgamma function appeared in 4.3BSD. The gamma function appeared in
4.4BSD. The name gamma() was originally dedicated to the lgamma() func‐
tion, so some old code may no longer be compatible.
4.3 Berkeley Distribution December 11, 1993 4.3 Berkeley Distribution
