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LGAMMA (3) | C library functions | Unix Manual Pages | :man

NAME

lgamma, lgamma_r, lgammaf, lgammaf_r, gamma, gamma_r, gammaf, gammaf_r, tgamma - log gamma functions, gamma function

CONTENTS

Library
Synopsis
Description
Idiosyncrasies
Return Values
See Also
Standards
History

LIBRARY


.Lb libm

SYNOPSIS


.In math.h extern int signgam;

double lgamma "double x" double lgamma_r "double x" "int *signgamp" float lgammaf "float x" float lgammaf_r "float x" "int *signgamp" double gamma "double x" double gamma_r "double x" "int *signgamp" float gammaf "float x" float gammaf_r "float x" "int *signgamp" double tgamma "double x"

DESCRIPTION

lgamma x and lgammaf x return ln||_(x)| where
|_(x) = I00oo0 tx-10 e-t0 dt for x > 0 and
|_(x) = pi/(|_(1-x)sin(pix)) for x < 1.

return ln||_(x)|.

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

lgamma_r x signgamp and lgammaf_r x signgamp provide the same functionality as lgamma x and lgammaf x but the caller must provide an integer to store the sign of |_(x).

gamma, gammaf, gamma_r, and gammaf_r are deprecated aliases for lgamma, lgammaf, lgamma_r, and lgammaf_r, respectively. tgamma x returns |_(x), with no effect on signgam.

IDIOSYNCRASIES

Do not use the expression "signgam*exp(lgamma(x))" to compute g := |_(x). Instead use a program like this (in C):
lg = lgamma(x); g = signgam*exp(lg);

Only after lgamma or lgammaf has returned can signgam be correct.

For arguments in its range, tgamma is preferred, as for positive arguments it is accurate to within one unit in the last place. Exponentiation of lgamma will lose up to 10 significant bits.

RETURN VALUES

gamma, gamma_r, gammaf, gammaf_r, lgamma, lgamma_r, lgammaf, and lgammaf_r return 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.

SEE ALSO

math(3)

STANDARDS

HISTORY


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