TGAMMA(3) libc math functions 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);
Compile with -std=c99; link with -lm.
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 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)
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() that returns something else.
ERRORS
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_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 inte‐
ger.
CONFORMING TO
C99.
SEE ALSOgamma(3), lgamma(3)GNU 2004-11-15 TGAMMA(3)
