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 │ MT-Unsafe 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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