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)):

       _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE
           || /* Since glibc 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
   lgammaf(), lgammal():
       _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
           || /* Since glibc 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
   lgamma_r(), lgammaf_r(), lgammal_r():
       /* Since glibc 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
           || /* Since glibc 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_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

   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.




   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at

                              2016-03-15                         LGAMMA(3)


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