# Seth Woolley's Man Viewer

## tgamma(3) - tgamma, tgammaf, tgammal, tgamma, tgammaf, tgammal - true gamma function - man 3 tgamma

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```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);

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 nonpositive integers.
For nonnegative integral m one has

Gamma(m+1) = m!

and, more generally, for all x:

Gamma(x+1) = x * Gamma(x)

For x < 0.5 one can use

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(7,n,1 builtins) errno to  zero  and  call  feclearex-
cept(FE_ALL_EXCEPT) before calling these functions. On return, if(3,n) errno
is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO |  FE_OVERFLOW  |
FE_UNDERFLOW) is non-zero, an error(8,n) has occurred.

A  range  error(8,n)  occurs if(3,n) x is too large.  A pole error(8,n) occurs if(3,n) x is
zero.  A domain error(8,n) (or a pole error(8,n)) occurs if(3,n) x is a negative inte-
ger.

CONFORMING TO
C99.