NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | BUGS | SEE ALSO | COLOPHON

LGAMMA(3)                 Linux Programmer's Manual                LGAMMA(3)

NAME         top

       lgamma,  lgammaf,  lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam -
       log gamma function

SYNOPSIS         top

       #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         top

       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         top

       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         top

       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         top

       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         top

       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         top

       tgamma(3)

COLOPHON         top

       This page is part of release 4.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

                                 2016-03-15                        LGAMMA(3)