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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 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).

     allbox;  lbw27 lb lb l l l.  Interface Attribute Value T{ gamma(), gam-
     maf(), gammal() T}   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.