'\" t
.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
.\"
.\" SPDX-License-Identifier: GPL-1.0-or-later
.\"
.\" Modified 2003-11-18, aeb: historical remarks
.\"
.TH gamma 3 2023-03-30 "Linux man-pages 6.04"
.SH NAME
gamma, gammaf, gammal \- (logarithm of the) gamma function
.SH LIBRARY
Math library
.RI ( libm ", " \-lm )
.SH SYNOPSIS
.nf
.B #include <math.h>
.PP
.BI "[[deprecated]] double gamma(double " x ");"
.BI "[[deprecated]] float gammaf(float " x ");"
.BI "[[deprecated]] long double gammal(long double " x ");"
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR gamma ():
.nf
    _XOPEN_SOURCE
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.PP
.BR gammaf (),
.BR gammal ():
.nf
    _XOPEN_SOURCE >= 600 || (_XOPEN_SOURCE && _ISOC99_SOURCE)
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.SH DESCRIPTION
These functions are deprecated: instead, use either the
.BR tgamma (3)
or the
.BR lgamma (3)
functions, as appropriate.
.PP
For the definition of the Gamma function, see
.BR tgamma (3).
.SS *BSD version
The libm in 4.4BSD and some versions of FreeBSD had a
.BR gamma ()
function that computes the Gamma function, as one would expect.
.SS glibc version
glibc has a
.BR gamma ()
function that is equivalent to
.BR lgamma (3)
and computes the natural logarithm of the Gamma function.
.SH RETURN VALUE
See
.BR lgamma (3).
.SH ERRORS
See
.BR lgamma (3).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR gamma (),
.BR gammaf (),
.BR gammal ()
T}	Thread safety	MT-Unsafe race:signgam
.TE
.hy
.ad
.sp 1
.SH STANDARDS
None.
.SH HISTORY
SVID 2.
.PP
Because of historical variations in behavior across systems,
this function is not specified in any recent standard.
.PP
4.2BSD had a
.BR gamma ()
that computed
.RI ln(|Gamma(| x |)|),
leaving the sign of
.RI Gamma(| x |)
in the external integer
.IR signgam .
In 4.3BSD the name was changed to
.BR lgamma (3),
and the man page promises
.PP
.in +4n
"At some time in the future the name gamma will be rehabilitated
and used for the Gamma function"
.in
.PP
This did indeed happen in 4.4BSD, where
.BR gamma ()
computes the Gamma function (with no effect on
.IR signgam ).
However, this came too late, and we now have
.BR tgamma (3),
the "true gamma" function.
.\" The FreeBSD man page says about gamma() that it is like lgamma()
.\" except that is does not set signgam.
.\" Also, that 4.4BSD has a gamma() that computes the true gamma function.
.SH SEE ALSO
.BR lgamma (3),
.BR signgam (3),
.BR tgamma (3)