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():
           _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
       signgam:
           _XOPEN_SOURCE
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

       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.

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, 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.

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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       information  about  reporting  bugs,  and  the  latest  version  of  this   page,   can   be   found   at
       https://www.kernel.org/doc/man-pages/.

                                                   2017-09-15                                          LGAMMA(3)