Nametgamma, tgammaf, tgammal — true gamma function 
#include <math.h>
double
tgamma( 
double x) ; 
float
tgammaf( 
float x) ; 
long double
tgammal( 
long double x) ; 
Note  


Note  

Link with 
These functions calculate the Gamma function of x
.
The Gamma function is defined by
Gamma(x) = integral from 0 to infinity of t^(x−1) e^−t dt
It is defined for every real number except for nonpositive
integers. For nonnegative integral m
one has
Gamma(m+1) = m!
and, more generally, for all x
:
Gamma(x+1) = x * Gamma(x)
Furthermore, the following is valid for all values of
x
outside the
poles:
Gamma(x) * Gamma(1 − x) = PI / sin(PI * x)
On success, these functions return Gamma(x).
If x
is a NaN, a
NaN is returned.
If x
is positive
infinity, positive infinity is returned.
If x
is a negative
integer, or is negative infinity, a domain error occurs, and
a NaN is returned.
If the result overflows, a range error occurs, and the
functions return HUGE_VAL
,
HUGE_VALF
, or HUGE_VALL
, respectively, with the correct
mathematical sign.
If the result underflows, a range error occurs, and the functions return 0, with the correct mathematical sign.
If x
is −0
or +0, a pole error occurs, and the functions return
HUGE_VAL
, HUGE_VALF
, or HUGE_VALL
, respectively, with the same sign
as the 0.
See math_error(7) for information on how to determine whether an error has occurred when calling these functions.
The following errors can occur:
x
is a negative integer, or
negative infinityerrno
is set to
EDOM. An invalid
floatingpoint exception (FE_INVALID
) is raised (but see
BUGS).
x
is +0 or
−0errno
is set to
ERANGE. A dividebyzero
floatingpoint exception (FE_DIVBYZERO
) is raised.
errno
is set to
ERANGE. An overflow
floatingpoint exception (FE_OVERFLOW
) is raised.
glibc also gives the following error which is not specified in C99 or POSIX.12001.
An underflow floatingpoint exception (FE_UNDERFLOW
) is raised.
errno
is not set for
this case.
For an explanation of the terms used in this section, see attributes(7).
Interface  Attribute  Value 
tgamma (), tgammaf (), tgammal () 
Thread safety  MTSafe 
This function had to be called "true gamma function" since there is already a function gamma(3) that returns something else (see gamma(3) for details).
Before version 2.18, the glibc implementation of these
functions did not set errno
to
EDOM when x
is negative infinity.
In glibc versions 2.3.3 and earlier, an argument of +0 or
−0 incorrectly produced a domain error (errno
set to EDOM and an FE_INVALID
exception raised), rather than a
pole error.
This page is part of release 4.07 of the Linux manpages
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/.
Copyright 2002 Walter Harms (walter.harmsinformatik.unioldenburg.de) %%%LICENSE_START(GPL_NOVERSION_ONELINE) Distributed under GPL %%%LICENSE_END Based on glibc infopages and Copyright 2008, Linux Foundation, written by Michael Kerrisk <mtk.manpagesgmail.com> Modified 20041115, fixed error noted by Fabian Kreutz <kreutzdbs.unihannover.de> 