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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GNU                                                2017-09-15                                           GAMMA(3)