#include <math.h>double lgamma(double x); float lgammaf(float x); long double lgammal(long double x);double lgamma_r(double x, int *signp); float lgammaf_r(float x, int *signp); long double lgammal_r(long double x, int *signp);extern int signgam;

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99

lgammaf(),
lgammal():

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99

lgamma_r(),
lgammaf_r(),
lgammal_r():

_BSD_SOURCE || _SVID_SOURCE

signgam:

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE

DESCRIPTION

For the definition of the Gamma function, see
tgamma(3).

The
lgamma()
function returns the natural logarithm of
the absolute value of the Gamma function.
The sign of the Gamma function is returned in the
external integer signgam declared in
<math.h>.
It is 1 when the Gamma function is positive or zero, -1
when it is negative.

Since using a constant location
signgam
is not thread-safe, the functions
lgamma_r()
etc. have
been introduced; they return the sign via the argument
signp.

RETURN VALUE

On success, these functions return the natural logarithm of Gamma(x).

If
x
is a NaN, a NaN is returned.

If
x
is 1 or 2, +0 is returned.

If
x
is positive infinity or negative infinity,
positive infinity is returned.

If
x
is a nonpositive integer,
a pole error occurs,
and the functions return
+HUGE_VAL,
+HUGE_VALF,
or
+HUGE_VALL,
respectively.

If the result overflows,
a range error occurs,
and the functions return
HUGE_VAL,
HUGE_VALF,
or
HUGE_VALL,
respectively, with the correct mathematical sign.

ERRORS

See
math_error(7)
for information on how to determine whether an error has occurred
when calling these functions.

The following errors can occur:

Pole error: x is a nonpositive integer

errno
is set to
ERANGE
(but see BUGS).
A divide-by-zero floating-point exception
(FE_DIVBYZERO)
is raised.

Range error: result overflow

errno
is set to
ERANGE.
An overflow floating-point exception
(FE_OVERFLOW)
is raised.

CONFORMING TO

The
lgamma()
functions are specified in C99 and POSIX.1-2001.
signgam
is specified in POSIX.1-2001, but not in C99.
The
lgamma_r()
functions are nonstandard, but present on several other systems.

BUGS

In glibc 2.9 and earlier,
when a pole error occurs,
errno
is set to
EDOM;
instead of the POSIX-mandated
ERANGE.
Since version 2.10, glibc does the right thing.

This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.