lgamma - log gamma function

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SYNOPSIS

#include <math.h>

extern int signgam;

double lgamma(x)
double x;

DESCRIPTION

lgamma() returns

ln|\(*G(x)|
where
\(*G(x) = \(is0\(iftx-1e-tdt
for x > 0 and
\(*G(x) = \(*p/(\(*G(1-x)sin(\(*px))
for x < 1.

The external integer signgam returns the sign of \(*G(x).

IDIOSYNCRASIES

Do not use the expression signgam*exp(lgamma(x)) to compute `g := \(*G(x)'. Instead compute lgamma() first:

lg = lgamma(x); g = signgam*exp(lg);

only after lgamma() has returned can signgam be correct. Note: \(*G(x) must overflow when x is large enough, underflow when -x is large enough, and generate a division by zero exception at the singularities x a nonpositive integer. In addition, lgamma() may also set errno and call matherr.3m

SEE ALSO

Created by unroff & hp-tools. © somebody (See intro for details). All Rights Reserved. Last modified 11/5/97