**gamma**

**GAMMA(3)** Linux Programmer's Manual **GAMMA(3)**
NAME
gamma, gammaf, gammal - (logarithm of the) gamma function
SYNOPSIS
#include <math.h>
double gamma(double x);
float gammaf(float x);
long double gammal(long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see **feature_test_macros(7)**):
gamma():
_XOPEN_SOURCE
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
gammaf(), gammal():
_XOPEN_SOURCE >= 600 || (_XOPEN_SOURCE && _ISOC99_SOURCE)
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
These functions are deprecated: instead, use either the **tgamma(3)** or
the **lgamma(3)** functions, as appropriate.
For the definition of the Gamma function, see **tgamma(3)**.
*BSD version
The libm in 4.4BSD and some versions of FreeBSD had a gamma() function
that computes the Gamma function, as one would expect.
glibc version
Glibc has a gamma() function that is equivalent to **lgamma(3)** and com-
putes the natural logarithm of the Gamma function.
RETURN VALUE
See **lgamma(3)**.
ERRORS
See **lgamma(3)**.
ATTRIBUTES
For an explanation of the terms used in this section, see
**attributes(7)**.
+----------------------------+---------------+------------------------+
|Interface | Attribute | Value |
+----------------------------+---------------+------------------------+
|gamma(), gammaf(), gammal() | Thread safety | MT-Unsafe race:signgam |
+----------------------------+---------------+------------------------+
CONFORMING TO
Because of historical variations in behavior across systems, this func-
tion is not specified in any recent standard. It was documented in
SVID 2.
NOTES
History
4.2BSD had a gamma() that computed ln(|Gamma(|x|)|), leaving the sign
of Gamma(|x|) in the external integer signgam. In 4.3BSD the name was
changed to **lgamma(3)**, and the man page promises
"At some time in the future the name gamma will be rehabilitated
and used for the Gamma function"
This did indeed happen in 4.4BSD, where gamma() computes the Gamma
function (with no effect on signgam). However, this came too late, and
we now have **tgamma(3)**, the "true gamma" function.
SEE ALSO
**lgamma(3)**, **signgam(3)**, **tgamma(3)**
COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2017-09-15 **GAMMA(3)**

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