# Manual browser: lgamma(3)

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 LGAMMA(3) Library Functions Manual LGAMMA(3)

# NAME

lgamma, lgammaf, lgamma_r, lgammaf_r, gamma, gammaf, gamma_r, gammaf_r, tgamma, tgammaflog gamma function

# LIBRARY

Math Library (libm, -lm)

# SYNOPSIS

#include <math.h>

extern int signgam;

double
lgamma(double x);

float
lgammaf(float x);

double
lgamma_r(double x, int *sign);

float
lgammaf_r(float x, int *sign);

double
gamma(double x);

float
gammaf(float x);

double
gamma_r(double x, int *sign);

float
gammaf_r(float x, int *sign);

double
tgamma(double x);

float
tgammaf(float x);

# DESCRIPTION

lgamma(x) returns ln|Γ(x)|.

The external integer signgam returns the sign of Γ(x).

lgamma_r() is a reentrant interface that performs identically to lgamma(), differing in that the sign of Γ(x) is stored in the location pointed to by the sign argument and signgam is not modified.

The tgamma(x) and tgammaf(x) functions return Γ(x), with no effect on signgam.

gamma(), gammaf(), gamma_r(), and gammaf_r() are deprecated aliases for lgamma(), lgammaf(), lgamma_r(), and lgammaf_r(), respectively.

# IDIOSYNCRASIES

Do not use the expression “`signgam∗exp(lgamma(x))`” to compute g := Γ(x). Instead use a program like this (in C):

`lg = lgamma(x); g = signgam∗exp(lg);`

Only after lgamma() has returned can signgam be correct.

# RETURN VALUES

lgamma() returns appropriate values unless an argument is out of range. Overflow will occur for sufficiently large positive values, and non-positive integers. For large non-integer negative values, tgamma() will underflow. On the VAX, the reserved operator is returned, and errno is set to ERANGE.