lgamma(3) — Subroutines

NAME

lgamma, gamma − Compute the logarithm of the gamma function

LIBRARY

Math Library (libm.a)

SYNOPSIS

#include <math.h>

double lgamma (double x);
float lgammaf (float x);

STANDARDS

Interfaces documented on this reference page conform to industry standards as follows:

lgamma(): XPG4

gamma(): XPG4

Refer to the standards(5) reference page for more information about industry standards and associated tags.

DESCRIPTION

The lgamma() and lgammaf() functions return the logarithm of the absolute value of gamma of x, or ln(|G(x)|), where G is the gamma function. The sign of gamma of x is returned in the external integer variable signgam. The x parameter cannot be 0 or a negative integer.

The gamma() function returns the natural log of the gamma function and so is functionally equivalent to lgamma(). Because of this, gamma() is marked TO BE WITHDRAWN in the X/Open Portability Guide, Revision 4 (XPG4).

The following table describes function behavior in response to exceptional arguments:

Function	Exceptional Argument	Routine Behavior
lgamma(), lgammaf()	\|x\| = infinity	Invalid argument
lgamma(), lgammaf()	x = 0, -1, -2, -3,...	Invalid argument
lgamma(), lgammaf()	x > lgamma_max_float	Overflow

The following table lists boundary values used by these functions: