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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

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       description  of  the project, and information about reporting bugs, can
       be found at http://man7.org/linux/man-pages/.

                                  2010-09-11                         LGAMMA(3)