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

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

       #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)):

	   _POSIX_C_SOURCE >= 200112L;
	   or cc -std=c99
       lgammaf(), lgammal():
	   _POSIX_C_SOURCE >= 200112L;
	   or cc -std=c99
       lgamma_r(), lgammaf_r(), lgammal_r():

       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

       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.

       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

       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.

       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.


       This  page  is  part of release 3.55 of the Linux man-pages project.  A description of the
       project,    and	  information	 about	  reporting    bugs,	can    be    found     at

					    2010-09-11					LGAMMA(3)
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