std::lgamma

 

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Defined in header <cmath>
float       lgamma( float arg );		(since C++11)
double      lgamma( double arg );		(since C++11)
long double lgamma( long double arg );		(since C++11)
double      lgamma( Integral arg );		(since C++11)

Computes the natural logarithm of the absolute value of the gamma function of arg.

Parameters

arg

-

floating point value

Return value

The value of the logarithm of the gamma function of arg, that is log
e|∫∞
0targ-1
e^-t dt|.

If arg is a natural number, std::lgamma(arg) is the logarithm of the factorial of arg-1.

Exceptions

If arg is zero or a negative integer, pole error may occur and FE_INVALID or FE_DIVBYZERO may be raised.

If arg is too large, range error may occur and FE_OVERFLOW may be raised.

Notes

POSIX specification additionally requires that each execution of lgamma stores the sign of the gamma function of arg in the external variable signgam.

See also

tgamma (C++11)	gamma function (function)
C documentation for lgamma

External links

Weisstein, Eric W. "Log Gamma Function." From MathWorld--A Wolfram Web Resource.