lgamma(3M)

NAME | SYNOPSIS | DESCRIPTION | IDIOSYNCRASIES | RETURN VALUES | ATTRIBUTES | SEE ALSO | NOTES

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)|

where

|~(x) = integral from 0 to +[infin ] of pow(t, x-1)*exp(-t) dt for x > 0

and

|~(x) = Pi/(|~(1-x)sin(pi*x)) for x < 0

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

gamma(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);

signgam will only be correct after lgamma has returned.

For arguments within its range, gamma is preferable , 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.

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only -

The lgamma function is not thread safe.

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RETURN VALUES

The gamma and lgamma functions return appropriate values unless an argument is out of range. Overflow will occur for sufficiently large positive values, and non-positive integers. In this case, infinity is returned, errno is set to ERANGE , and a system-dependent notification is performed. For large non-integer negative values, gamma will underflow.

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Evolving

SEE ALSO

math(3M) , infnan(3M)

NOTES

Due to signgam being a global variable, this routine is not reentrant.

ChorusOS 4.0  Last Revised December 1999

NAME | SYNOPSIS | DESCRIPTION | IDIOSYNCRASIES | RETURN VALUES | ATTRIBUTES | SEE ALSO | NOTES