NAME
lgamma,
lgammaf,
lgamma_r,
lgammaf_r,
gamma,
gammaf,
gamma_r,
gammaf_r,
tgamma,
tgammaf —
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);
double
tgamma(
double
x);
float
tgammaf(
float
x);
DESCRIPTION
lgamma(
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.
The
tgamma(
x) and
tgammaf(
x) functions return Γ(x),
with no effect on
signgam.
gamma(),
gammaf(),
gamma_r(), and
gammaf_r() are deprecated
aliases for
lgamma(),
lgammaf(),
lgamma_r(), and
lgammaf_r(), respectively.
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 VALUES
lgamma() returns appropriate values unless an argument is out
of range. Overflow will occur for sufficiently large positive values, and
non-positive integers. For large non-integer negative values,
tgamma() will underflow. 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. The
tgamma() function
appeared in
NetBSD 6.0.