lgamma(3) — Linux manual page

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)

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Linux man-pages 6.9.1          2024-05-02                      lgamma(3)

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

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