GAMMA(3M)                DOMAIN/IX SYS5                 GAMMA(3M)



NAME
     gamma - log gamma function

USAGE
     #include <math.h>

     double gamma (x)
     double x;
     extern int signgam;


DESCRIPTION
     Gamma returns ln(|Γ(x)|), where Γ(x) is defined as
     oo -t x-1
     ∫ e  t   dt.  The sign of Γ(x) is returned in the external
     0
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.

DIAGNOSTICS
     For non-negative integer arguments, gamma returns HUGE, sets
     errno to EDOM, and prints a SING error message on the stan-
     dard 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).

NOTE
     User programs that call this routine but do not link with
     libm.a will, instead, reference an older routine included in
     /lib/clib.  Support for the old (in clib) routines will be
     discontinued in a future release.  See intro(3M).

RELATED INFORMATION
     exp(3M), matherr(3M), values(5)





Printed 12/4/86                                           GAMMA-1