gamma(3M)                                               gamma(3M)



NAME
     gamma, lgamma - log gamma function

SYNOPSIS
     #include <math.h>

     double gamma (x)
     double x;

     double lgamma (x)
     double x;

     extern int signgam;

DESCRIPTION
     GAMMA returns ln ( |GAMMA(x)| ), where GAMMA(x) is defined
     as Integral [0, infinity] (e**(-t) * t**(x-t)) dt.  The sign
     of GAMMA(x) is returned in the external integer signgam.
     The argument x may not be a non-positive integer.

     The following C program fragment might be used to calculate
     gamma(x):

          if ((y = gamma(x)) > LN_MAXDOUBLE)
               error();
          y = signgam * exp(y);

     where LN_MAXDOUBLE is the least value that causes exp(3M) to
     return a range error, and is defined in the <values.h>
     header file.

DIAGNOSTICS
     For non-negative integer arguments HUGEVAL is returned, and
     errno is set to EDOM.  A message indicating SING error is
     printed on the standard error output.

     If the correct value would overflow, gamma returns HUGEVAL
     and sets errno to ERANGE.

     These error-handling procedures may be changed with the
     function matherr(3M).

SEE ALSO
     exp(3M), matherr(3M), values(5).











Page 1                        CX/UX Programmer's Reference Manual