GAMMA(3M)                            SysV                            GAMMA(3M)



NAME
     gamma - log gamma function

SYNOPSIS
     #include <math.h>

     double gamma (x)
     double x;

     extern int signgam;

DESCRIPTION
                                                        oo -t x-1
     gamma returns ln(|G(x)|), where G(x) is defined as ^ e  t   dt.  The sign
     of G(x) is returned in the external integer signgam.
0  The argument x may
     not be a non-positive integer.

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

          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.

     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).