NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

CONFORMING TO

BUGS

SEE ALSO

COLOPHON

## NAME

## SYNOPSIS

## DESCRIPTION

## RETURN VALUE

## ERRORS

## CONFORMING TO

## BUGS

## SEE ALSO

## COLOPHON

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

CONFORMING TO

BUGS

SEE ALSO

COLOPHON

lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam − log gamma function

**#include
<math.h>**

**double
lgamma(double** *x***);
float lgammaf(float**

long double lgammal(long double

**double
lgamma_r(double** *x***, int ****signp***);
float lgammaf_r(float**

long double lgammal_r(long double

**extern
int** *signgam***;**

Link with
*−lm*.

Feature Test
Macro Requirements for glibc (see
**feature_test_macros**(7)):

**lgamma**():

_BSD_SOURCE || _SVID_SOURCE ||
_XOPEN_SOURCE || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;

or *cc -std=c99*

**lgammaf**(),
**lgammal**():

_BSD_SOURCE || _SVID_SOURCE ||
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;

or *cc -std=c99*

**lgamma_r**(),
**lgammaf_r**(), **lgammal_r**():

_BSD_SOURCE || _SVID_SOURCE

*signgam*:

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE

For the
definition of the Gamma function, see **tgamma**(3).

The
**lgamma**(), **lgammaf**(), and **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 *signgam* declared in
*<math.h>*. It is 1 when the Gamma function is
positive or zero, −1 when it is negative.

Since using a
constant location *signgam* is not thread-safe, the
functions **lgamma_r**(), **lgammaf_r**(), and
**lgammal_r**() have been introduced; they return the
sign via the argument *signp*.

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

If *x* is
a NaN, a NaN is returned.

If *x* is
1 or 2, +0 is returned.

If *x* is
positive infinity or negative infinity, positive infinity is
returned.

If *x* is
a nonpositive integer, a pole error occurs, and the
functions return +**HUGE_VAL**, +**HUGE_VALF**, or
+**HUGE_VALL**, respectively.

If the result
overflows, a range error occurs, and the functions return
**HUGE_VAL**, **HUGE_VALF**, or **HUGE_VALL**,
respectively, with the correct mathematical sign.

See
**math_error**(7) for information on how to determine
whether an error has occurred when calling these
functions.

The following
errors can occur:

Pole error: *x* is a nonpositive integer

*errno* is set to
**ERANGE** (but see BUGS). A divide-by-zero
floating-point exception (**FE_DIVBYZERO**) is
raised.

Range error: result overflow

*errno* is set to
**ERANGE**. An overflow floating-point exception
(**FE_OVERFLOW**) is raised.

The
**lgamma**() functions are specified in C99,
POSIX.1-2001, and POSIX.1-2008. *signgam* is specified
in POSIX.1-2001 and POSIX.1-2008, but not in C99. The
**lgamma_r**() functions are nonstandard, but present on
several other systems.

In glibc 2.9
and earlier, when a pole error occurs, *errno* is set
to **EDOM**; instead of the POSIX-mandated **ERANGE**.
Since version 2.10, glibc does the right thing.

**tgamma**(3)

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