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 || _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
       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

       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.

SEE ALSO

       tgamma(3)

COLOPHON

       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)