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LGAMMA
Section: Linux Programmer's Manual (3)
Updated: 20150419
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NAME
lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam 
log gamma function
SYNOPSIS
#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;
Link with lm.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
lgamma():

_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(),
lgammaf(),
and
lgammal()
functions return 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 threadsafe, the functions
lgamma_r(),
lgammaf_r(),
and
lgammal_r()
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 dividebyzero floatingpoint exception
(FE_DIVBYZERO)
is raised.
 Range error: result overflow

errno
is set to
ERANGE.
An overflow floatingpoint exception
(FE_OVERFLOW)
is raised.
CONFORMING TO
The
lgamma()
functions are specified in C99, POSIX.12001, and POSIX.12008.
signgam
is specified in POSIX.12001 and POSIX.12008, 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 POSIXmandated
ERANGE.
Since version 2.10, glibc does the right thing.
SEE ALSO
tgamma(3)
COLOPHON
This page is part of release 4.04 of the Linux
manpages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
http://www.kernel.org/doc/manpages/.
Index
 NAME

 SYNOPSIS

 DESCRIPTION

 RETURN VALUE

 ERRORS

 CONFORMING TO

 BUGS

 SEE ALSO

 COLOPHON

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