gamma(3M)                                               gamma(3M)



     NAME
          gamma - log gamma function

     SYNOPSIS
          #include <math.h>

          extern int signgam;

          doublegamma(x)
          double x;

     DESCRIPTION
          gamma returns the natural log of gamma as a function of the
          absolute value of a given value.  gamma returns ln(|Γ(x)|),
          where Γ(x) is defined as

               oo
                  -t x-1
               ∫ e  t   dt.

               0

          The sign of Γ(x) is returned in the external integer
          signgam.  The argument x may not be a nonpositive integer.

          The following C program fragment might be used to calculate
          Γ:

             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.

     RETURN VALUE
          For non-negative integer arguments HUGE 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 HUGE 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).









     April, 1990                                                     1