tgamma
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   Defined in header <math.h>
   | 
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|   float       tgammaf( float arg );  | 
(since C99) | |
|   double      tgamma( double arg );  | 
(since C99) | |
|   long double tgammal( long double arg );  | 
(since C99) | |
Computes the gamma function of arg.
Contents | 
[edit] Parameters
| arg | - | floating point value | 
[edit] Return value
The value of the gamma function of arg, that is ∫∞
0targ-1
 e-t dt.
If arg is a natural number, tgamma(arg) is the factorial of arg-1.
[edit] Exceptions
If arg is negative, domain error may occur and FE_INVALID may be raised.
If arg is zero, pole error may occur and FE_DIVBYZERO may be raised.
If arg is too large, range error may occur and FE_OVERFLOW may be raised.
If arg is too small, range error may occur and FE_UNDERFLOW may be raised.
[edit] Notes
Many implementations calculate the exact integer-domain factorial if the argument is a sufficiently small integer.
[edit] Example
| This section is incomplete Reason: no example  | 
[edit] See also
|    (C99)  | 
   natural logarithm of the gamma function   (function)  | 
|   C++ documentation for tgamma 
 | |
[edit] External links
Weisstein, Eric W. "Gamma Function." From MathWorld--A Wolfram Web Resource.