Section (3) gamma

Linux manual pages Section 3  


gamma, gammaf, gammal — (logarithm of the) gamma function


#include <math.h>
double gamma( double x);
float gammaf( float x);
long double gammal( long double x);
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_XOPEN_SOURCE || /* Since glibc 2.19:
*/ _DEFAULT_SOURCE || /* Glibc versions <= 2.19:
gammaf(), gammal():
_XOPEN_SOURCE >= 600 || (_XOPEN_SOURCE && _ISOC99_SOURCE) || /* Since glibc 2.19:
*/ _DEFAULT_SOURCE || /* Glibc versions <= 2.19:
[Note] Note

Link with −lm.


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 computes the natural logarithm of the Gamma function.


See lgamma(3).


See lgamma(3).


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


Because of historical variations in behavior across systems, this function is not specified in any recent standard. It was documented in SVID 2.



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.


lgamma(3), signgam(3), tgamma(3)


This page is part of release 4.16 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−pages/.

  Copyright 2002 Walter Harms (

Distributed under GPL

Modified 2003-11-18, aeb: historical remarks