LGAMMA(3) MachTen Programmer’s Manual LGAMMA(3)

NAME
lgamma gamma - log gamma function, gamma function

SYNOPSIS
#include <math.h>

extern int signgam;

double
lgamma(double x)

double
gamma(double x)

DESCRIPTION _
Lgamma(x) returns ln|| (x)|.
_
The external integer signgam returns the sign of | (x).
_
Gamma(x) returns | (x), with no effect on signgam.

IDIOSYNCRASIES
D_ 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() has returned can signgam be correct.

For arguments in its range, gamma() is preferred, as for positive argu-
ments it is accurate to within one unit in the last place. Exponentia-
tion of lgamma() will lose up to 10 significant bits.

RETURN VALUES
Gamma() and lgamma() return appropriate values unless an argument is out
of range. Overflow will occur for sufficiently large positive values,
and non-positive integers. On the VAX, the reserved operator is re-
turned, and errno is set to ERANGE For large non-integer negative values,
gamma() will underflow.

SEE ALSO
math(3), infnan(3)

HISTORY
The lgamma function appeared in 4.3BSD. The gamma function appeared in
4.4BSD. The name gamma() was originally dedicated to the lgamma() func-
tion, so some old code may no longer be compatible.

4.3 Berkeley Distribution December 11, 1993 1