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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 <= 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 │
       └───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴────────────────────────┘

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 lgam‐
       ma(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)

GNU                                                                            2021-03-22                                                                       GAMMA(3)