gamma

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():
           _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 com-
       putes 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 |
       +----------------------------+---------------+------------------------+
CONFORMING TO
       Because of historical variations in behavior across systems, this func-
       tion 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
       This page is part of release 4.15 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

GNU                               2017-09-15                          GAMMA(3)
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