GAMMA
Section: Linux Programmer's Manual (3)
Updated: 20170915
Page Index
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 computes 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  MTUnsafe race:signgam

CONFORMING TO
Because of historical variations in behavior across systems,
this function 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
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