# lgammal(3) [centos man page]

```LGAMMA(3)						     Linux Programmer's Manual							 LGAMMA(3)

NAME
lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam - log gamma function

SYNOPSIS
#include <math.h>

double lgamma(double x);
float lgammaf(float x);
long double lgammal(long double x);

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

extern int signgam;

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

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

The  lgamma()  function	returns  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  nega-
tive.

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

RETURN VALUE
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.

ERRORS
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.

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

BUGS
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)

COLOPHON
This  page is part of release 3.53 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.

2010-09-11								 LGAMMA(3)```

## Check Out this Related Man Page

```LGAMMA(3)						     Linux Programmer's Manual							 LGAMMA(3)

NAME
lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam - log gamma function

SYNOPSIS
#include <math.h>

double lgamma(double x);
float lgammaf(float x);
long double lgammal(long double x);

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

extern int signgam;

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

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

The  lgamma()  function	returns  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  nega-
tive.

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

RETURN VALUE
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.

ERRORS
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.

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

BUGS
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.