GAMMA(3) libc math functions GAMMA(3)NAME
gamma - logarithm of the gamma function
SYNOPSIS
#include <math.h>
double gamma (double x);
float gammaf (float x);
long double gammal (long double x);
DESCRIPTION
The gamma() functions exist for compatibility reasons. They are equivalent to lgamma() etc. Use these. Use of the name gamma() is confus-
ing, since these functions do not compute the Gamma function, but the natural logarithm of the Gamma function.
CONFORMING TO
Nonstandard. Compatible with previous mistakes.
SEE ALSO lgamma(3), signgam(3), tgamma(3)GNU 2002-08-10 GAMMA(3)

Check Out this Related Man Page

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():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
gammaf(), gammal():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
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 computes the natural logarithm of the Gamma function.
RETURN VALUE
See lgamma(3).
ERRORS
See lgamma(3).
CONFORMING TO
Because of historical variations in behavior across systems, this function is not specified in any standard.
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 3.27 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 2008-08-05 GAMMA(3)

Here is some javascript code that implements the Lanczos approximation to the gamma function (http://en.wikipedia.org/wiki/Lanczos_approximation):
<script type="text/javascript">
// Gamma approximation; coefficients used by the GNU Scientific Library
function gamma(z) {
var p = ;
if z... (2 Replies)