lgammaf

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



NAME
       lgamma - 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);

DESCRIPTION
       The Gamma function is defined by

        Gamma(x) = integral from 0 to infinity of t^(x-1) e^-t dt

       It  is  defined  for every real number except for nonpositive integers.
       For nonnegative integral m one has

        Gamma(m+1) = m!

       and, more generally, for all x:

        Gamma(x+1) = x * Gamma(x)

       For x < 0.5 one can use

        Gamma(x) * Gamma(1-x) = PI/sin(PI*x)

       The lgamma() function returns 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() etc. have been introduced; they return this  sign  via
       the parameter signp.

       For  nonpositive  integer  values of x, lgamma() returns HUGE_VAL, sets
       errno to ERANGE and raises  the  zero  divide  exception.   (Similarly,
       lgammaf() returns HUGE_VALF and lgammal() returns HUGE_VALL.)

ERRORS
       An  application  wishing to check for error situations should set errno
       to zero and  call  feclearexcept(FE_ALL_EXCEPT)  before  calling  these
       functions. On return, if errno is non-zero or fetestexcept(FE_INVALID |
       FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero,  an  error  has
       occurred.

       ERANGE Invalid argument - nonpositive integer value of x.

CONFORMING TO
       C99, SVID 3, BSD 4.3

SEE ALSO
       tgamma(3)



                                  2002-08-10                         LGAMMA(3)