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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 non-positive 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  func-
       tions.

       The following errors can occur:

       Pole error: x is a non-positive 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 non-standard, 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 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



                                  2008-08-05                         LGAMMA(3)