tgamma, tgammaf, tgammal - true gamma function
#include <math.h>
double tgamma(double x);
float tgammaf(float x);
long double tgammal(long double x);Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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.