gamma(3M)                                               gamma(3M)



NAME
     gamma - logs a 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.

STATUS MESSAGES AND VALUES
     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)









January 1992                                                    1