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():
           _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

       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 func-
       tions 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

       Pole error: x is a nonpositive integer
              errno is set to ERANGE (but see BUGS).  A divide-by-zero  float-
              ing-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 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 3.54 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)
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