GAMMA(3) Linux Programmer's Manual GAMMA(3)
gamma, gammaf, gammal - (logarithm of the) gamma function
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)):
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
These functions are deprecated: instead, use either the tgamma(3) or the lgamma(3) func-
tions, as appropriate.
For the definition of the Gamma function, see tgamma(3).
The libm in 4.4BSD and some versions of FreeBSD had a gamma() function that computes the
Gamma function, as one would expect.
Glibc has a gamma() function that is equivalent to lgamma(3) and computes the natural log-
arithm of the Gamma function.
Because of historical variations in behavior across systems, this function is not speci-
fied in any standard.
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
"At some time in the future the name gamma will be rehabilitated and used for the
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
lgamma(3), signgam(3), tgamma(3)
This page is part of release 3.53 of the Linux man-pages project. A description of the
project, and information about reporting bugs, can be found at
GNU 2008-08-05 GAMMA(3)