lgamma, lgammaf, lgammal

Article
06/05/2017

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Determines the natural logarithm of the absolute value of the gamma function of the specified value.

Syntax

double lgamma(  
   double x  
);  
  
float lgamma(  
   float x  
); //C++ only  
  
long double lgamma(  
   long double x  
); //C++ only  
  
float lgammaf(  
   float x  
);  
  
long double lgammal(  
   long double x  
);

Parameters

[in] x
The value to compute.

Return Value

If successful, return the natural logarithm of the absolute value of the gamma function of x.

Issue	Return
`x` = NaN	NaN
`x` = ±0	+INFINITY
`x`= negative integer	+INFINITY
±INFINITY	+INFINITY
pole error	+HUGE_VAL, +HUGE_VALF, or +HUGE_VALL
overflow range error	±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL

Errors are reported as specified in _matherr.

Remarks

Because C++ allows overloading, you can call overloads of lgamma that take and return float and long double types. In a C program, lgamma always takes and returns a double.

If x is a rational number, this function returns the logarithm of the factorial of (x-1).

Requirements

Function	C header	C++ header
`lgamma`, `lgammaf`, `lgammal`	<math.h>	<cmath>

For additional compatibility information, see Compatibility.