C <math.h> - tgamma() Function

The C <math.h> tgamma() function returns gamma function of the argument. The gamma function of x is defined as:

Syntax

double tgamma  (double x);
float tgammaf (float x);
long double tgammal (long double x);              

Parameters

Return Value

• If no errors occur, returns gamma function of the argument.
• If a domain error occurs, an implementation-defined value (NaN where supported) is returned.
• If a pole error occurs, ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL is returned.
• If a range error due to overflow occurs, ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL is returned.
• If a range error due to underflow occurs, the correct value (after rounding) is returned.

Example:

The example below shows the usage of tgamma() function.

#include <stdio.h>
#include <math.h>
 
int main (){
  printf("tgamma(0.1): %lf\n", tgamma(0.1));
  printf("tgamma(1.5): %lf\n", tgamma(1.5));
  printf("tgamma(2.5): %lf\n", tgamma(2.5));
  printf("tgamma(-1.5): %lf\n", tgamma(-1.5));
  printf("tgamma(-2.5): %lf\n", tgamma(-2.5));
  return 0;
}

The output of the above code will be:

tgamma(0.1): 9.513508
tgamma(1.5): 0.886227
tgamma(2.5): 1.329340
tgamma(-1.5): 2.363272
tgamma(-2.5): -0.945309