gamma(3M)                                               gamma(3M)



     NAME
          gamma - log gamma function

     SYNOPSIS
          #include <math.h>

          extern int signgam;

          double gamma (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(|(x)|),
          where (x) is defined as

               oo
                 e-ttx-1dt.
               0
          The sign of (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
          :

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

          where LNMAXDOUBLE 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 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).









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