GAMMA(3) Linux Programmers 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)):
gamma(), gammaf(), gammal(): _BSD_SOURCE || _SVID_SOURCE ||
For the definition of the Gamma function, see tgamma(3).
4.4BSD and FreeBSD libm have a gamma() function that computes the Gamma
function, as one would expect.
Glibc has a gamma() function that is equivalent to lgamma(3) and com
putes the natural logarithm of the Gamma function. (This is for com
patibility reasons only. Dont use this function.)
4.2BSD. Compatible with previous mistakes.
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 3.05 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/.
GNU 2007-07-26 GAMMA(3)