TGAMMA(3) Linux Programmer's Manual TGAMMA(3)
tgamma, tgammaf, tgammal - true gamma function
double tgamma(double x);
float tgammaf(float x);
long double tgammal(long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
tgamma(), tgammaf(), tgammal(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE;
or cc -std=c99
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 non-positive integers.
For non-negative 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
Gamma(x) * Gamma(1 - x) = PI / sin(PI * x)
This function returns the value of the Gamma function for the argument
x. It had to be called "true gamma function" since there is already a
function gamma(3) that returns something else.
In order to check for errors, set errno to zero and call feclearex-
cept(FE_ALL_EXCEPT) before calling these functions. On return, if
errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVER-
FLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
A range error occurs if x is too large. A pole error occurs if x is
zero. A domain error (or a pole error) occurs if x is a negative inte-
This page is part of release 3.05 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
GNU 2007-07-26 TGAMMA(3)