gamma(3)                   Library Functions Manual                   gamma(3)

NAME
       gamma, gammaf, gammal - (logarithm of the) gamma function

LIBRARY
       Math library (libm, -lm)

SYNOPSIS
       #include <math.h>

       [[deprecated]] double gamma(double x);
       [[deprecated]] float gammaf(float x);
       [[deprecated]] long double gammal(long double x);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       gamma():
           _XOPEN_SOURCE
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       gammaf(), gammal():
           _XOPEN_SOURCE >= 600 || (_XOPEN_SOURCE && _ISOC99_SOURCE)
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 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 | MT-Unsafe race:signgam |
       |()                           |               |                        |
       +-----------------------------+---------------+------------------------+
STANDARDS
       None.

HISTORY
       SVID 2.

       Because of historical variations in behavior across systems, this
       function is not specified in any recent 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 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)

Linux man-pages 6.7               2023-10-31                          gamma(3)