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():
           _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  func-
       tions  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 math-
       ematical 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 float-
              ing-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
       This page is part of release 4.16 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/.



                                  2017-09-15                         LGAMMA(3)