GAMMA(3M)            INTERACTIVE UNIX System            GAMMA(3M)



          NAME
               gamma - log gamma function

          SYNOPSIS
               #include <math.h>

               double gamma (x)
               double x;

               extern int signgam;

          DESCRIPTION
               delim $$ The gamma function returns $ln ( | GAMMA ( ^ x ) |
               )$, where $GAMMA ( ^ x )$ is defined as $int from 0 to inf e
               sup { - t } t sup { x - 1 } dt$.  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
               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.

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

          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 [e.g. gamma (-5.0)].

               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).













          Rev. C Software Development Set                            Page 1