lgamma(3)                  Library Functions Manual                  lgamma(3)

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

LIBRARY
       Math library (libm, -lm)

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;

   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 <= 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

       signgam:
           _XOPEN_SOURCE
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 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.

STANDARDS
       lgamma()
       lgammaf()
       lgammal()
              C11, POSIX.1-2008.

       signgam
              POSIX.1-2008.

       lgamma_r()
       lgammaf_r()
       lgammal_r()
              None.

HISTORY
       lgamma()
       lgammaf()
       lgammal()
              C99, POSIX.1-2001.

       signgam
              POSIX.1-2001.

       lgamma_r()
       lgammaf_r()
       lgammal_r()
              None.

BUGS
       In glibc 2.9 and earlier, when a pole error occurs, errno is set to
       EDOM; instead of the POSIX-mandated ERANGE.  Since glibc 2.10, glibc
       does the right thing.

SEE ALSO
       tgamma(3)

Linux man-pages 6.7               2023-10-31                         lgamma(3)