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Man Pages


Manual Reference Pages  -  LGAMMAF (3)

NAME

lgamma, lgamma_r, lgammaf, lgammaf_r, lgammal, lgammal_r, gamma, gamma_r, gammaf, gammaf_r, tgamma, tgammaf - 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 long double lgammal long double x long double lgammal_r long double 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 long double tgamma double x float tgammaf float x

DESCRIPTION

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

The tgamma x and tgammaf x functions return |_(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 := |_(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, gammaf, gammal, gamma_r, gammaf_r, gammal_r, lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, and lgammal_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

The lgamma, lgammaf, lgammal, tgamma, and tgammaf functions are expected to conform to -isoC-99.

HISTORY

The lgamma function appeared in BSD 4.3 . The gamma function appeared in BSD 4.4 as a function which computed |_(x). This version was used in
.Fx 1.1 . The name gamma was originally dedicated to the lgamma function, and that usage was restored by switching to Sun’s fdlibm in
.Fx 1.1.5 . The tgamma function appeared in
.Fx 5.0 .
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