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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 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() 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
       This  page  is  part of release 3.25 of the Linux man-pages project.  A description of the
       project,  and  information  about  reporting  bugs,  can  be  found   at   http://www.ker-
       nel.org/doc/man-pages/.

					    2008-08-05					LGAMMA(3)
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