TGAMMA(3)

NAME
tgamma, tgammaf, tgammal - true gamma function

SYNOPSIS
#include <math.h>

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

DESCRIPTION
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 poles:

 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.

ERRORS
In order to check for errors, set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | 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 integer.

CONFORMING TO
C99.

SEE ALSO
gamma(3), lgamma(3)