lgamma(3) — Linux manual page


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

           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       lgammaf(), lgammal():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       lgamma_r(), lgammaf_r(), lgammal_r():
           /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc <= 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

       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,

       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


COLOPHON         top

       This page is part of release 5.13 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

                               2021-03-22                      LGAMMA(3)

Pages that refer to this page: gamma(3)tgamma(3)