lgamma(3)lgamma(3)NAME
lgamma, gamma - Compute the logarithm of the gamma function
SYNOPSIS
#include <math.h>
double lgamma(
double x ); float lgammaf(
float x ); long double lgammal(
long double x );
LIBRARY
Math Library (libm)
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards 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(), lgammaf(), and lgammal() 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marked TO BE WITHDRAWN in the X/Open Portability Guide, Revision 4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 excep‐
tional arguments:
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Function Exceptional Argument Routine Behavior
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lgamma(), lgammaf(), lgamma() |x| = infinity Invalid argument
lgamma(), lgammaf(), lgamma() x = 0, -1, -2, -3,... Invalid argument
lgamma(), lgammaf(), lgamma() x > lgamma_max_float Overflow
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The following table lists boundary values used by these functions:
──────────────────────────────────────────────────────────────────────────
Value Name Data Type Hexadecimal Value Decimal Value
──────────────────────────────────────────────────────────────────────────
lgamma_max_float S_FLOAT 7BC650F9 2.0594342e36
T_FLOAT 7F475ABDC501F55F 1.2812545499066958e305
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lgamma(3)