.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)

.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk

.\"     <mtk.manpages@gmail.com>

.\"

.\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)

.\" Distributed under GPL

.\" %%%LICENSE_END

.\"

.\" based on glibc infopages

.\"

.TH LGAMMA 3 2017-09-15 "" "Linux Programmer's Manual"

.SH NAME

lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam \-

log gamma function

.SH SYNOPSIS

.nf

.B #include <math.h>

.PP

.BI "double lgamma(double " x );

.BI "float lgammaf(float " x );

.BI "long double lgammal(long double " x );

.PP

.BI "double lgamma_r(double " x ", int *" signp );

.BI "float lgammaf_r(float " x ", int *" signp );

.BI "long double lgammal_r(long double " x ", int *" signp );

.PP

.BI "extern int " signgam ;

.fi

.PP

Link with \fI\-lm\fP.

.PP

.in -4n

Feature Test Macro Requirements for glibc (see

.BR feature_test_macros (7)):

.in

.PP

.ad l

.BR lgamma ():

.RS 4

_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE

    || /* Since glibc 2.19: */ _DEFAULT_SOURCE

    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

.RE

.br

.BR lgammaf (),

.BR lgammal ():

.RS 4

_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L

    || /* Since glibc 2.19: */ _DEFAULT_SOURCE

    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

.RE

.BR lgamma_r (),

.BR lgammaf_r (),

.BR lgammal_r ():

.RS 4

/* Since glibc 2.19: */ _DEFAULT_SOURCE

    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

.RE

.IR signgam :

.RS 4

_XOPEN_SOURCE

    || /* Since glibc 2.19: */ _DEFAULT_SOURCE

    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

.RE

.ad b

.SH DESCRIPTION

For the definition of the Gamma function, see

.BR tgamma (3).

.PP

The

.BR lgamma (),

.BR lgammaf (),

and

.BR lgammal ()

functions return the natural logarithm of

the absolute value of the Gamma function.

The sign of the Gamma function is returned in the

external integer

.I signgam

declared in

.IR <math.h> .

It is 1 when the Gamma function is positive or zero, \-1

when it is negative.

.PP

Since using a constant location

.I signgam

is not thread-safe, the functions

.BR lgamma_r (),

.BR lgammaf_r (),

and

.BR lgammal_r ()

have been introduced; they return the sign via the argument

.IR signp .

.SH RETURN VALUE

On success, these functions return the natural logarithm of Gamma(x).

.PP

If

.I x

is a NaN, a NaN is returned.

.PP

If

.I x

is 1 or 2, +0 is returned.

.PP

If

.I x

is positive infinity or negative infinity,

positive infinity is returned.

.PP

If

.I x

is a nonpositive integer,

a pole error occurs,

and the functions return

.RB + HUGE_VAL ,

.RB + HUGE_VALF ,

or

.RB + HUGE_VALL ,

respectively.

.PP

If the result overflows,

a range error occurs,

.\" e.g., lgamma(DBL_MAX)

and the functions return

.BR HUGE_VAL ,

.BR HUGE_VALF ,

or

.BR HUGE_VALL ,

respectively, with the correct mathematical sign.

.SH ERRORS

See

.BR math_error (7)

for information on how to determine whether an error has occurred

when calling these functions.

.PP

The following errors can occur:

.TP

Pole error: \fIx\fP is a nonpositive integer

.I errno

is set to

.BR ERANGE

(but see BUGS).

A divide-by-zero floating-point exception

.RB ( FE_DIVBYZERO )

is raised.

.TP

Range error: result overflow

.I errno

is set to

.BR ERANGE .

An overflow floating-point exception

.RB ( FE_OVERFLOW )

is raised.

.\" glibc (as at 2.8) also supports an inexact

.\" exception for various cases.

.SH CONFORMING TO

The

.BR lgamma ()

functions are specified in C99, POSIX.1-2001, and POSIX.1-2008.

.I signgam

is specified in POSIX.1-2001 and POSIX.1-2008, but not in C99.

The

.BR lgamma_r ()

functions are nonstandard, but present on several other systems.

.SH BUGS

In glibc 2.9 and earlier,

.\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6777

when a pole error occurs,

.I errno

is set to

.BR EDOM ;

instead of the POSIX-mandated

.BR ERANGE .

Since version 2.10, glibc does the right thing.

.SH SEE ALSO

.BR tgamma (3)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.