NAME
lgamma, lgammaf,
lgamma_r, lgammaf_r,
gamma, gammaf,
gamma_r, gammaf_r,
tgamma, tgammaf —
log gamma function
LIBRARY
library “libm”
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
HISTORY
The lgamma function appeared in
4.3BSD. The tgamma()
function appeared in NetBSD 6.0.