
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;
Link with lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
lgamma(): _BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE  _ISOC99_SOURCE; or cc std=c99
lgammaf(), lgammal(): _BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 600 
_ISOC99_SOURCE; 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
negative.
Since using a constant location signgam is not threadsafe, 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 dividebyzero floatingpoint exception
(FE_DIVBYZERO) is raised.
Range error: result overflow
errno is set to ERANGE. An overflow floatingpoint exception (FE_OVERFLOW) is
raised.
CONFORMING TO
The lgamma() functions are specified in C99 and POSIX.12001. signgam is specified in
POSIX.12001, but not in C99. The lgamma_r() functions are nonstandard, but present on
several other systems.
BUGS
For a pole error, errno is set to EDOM; POSIX.1 says it should be set to ERANGE.
SEE ALSO
tgamma(3)
COLOPHON
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project, and information about reporting bugs, can be found at http://www.ker
nel.org/doc/manpages/.
20080805 LGAMMA(3) 
