GAMMA(3M)                            SysV                            GAMMA(3M)



NAME
     gamma, lgamma - log gamma function

SYNOPSIS
     #include <math.h>

     double gamma (x)
     double x;

     double lgamma (x)
     double x;

     extern int signgam;

DESCRIPTION
     The gamma and lgamma functions return the logarithm of the absolute value
     of the gamma of x, where the gamma of x is defined as:

          $int from 0 to inf e sup { - t } t sup { x - 1 } dt$

     The names lgamma and gamma are different names for the same function. The
     sign of the gamma of x is stored in the external integer variable
     signgam. The x argument cannot be a nonpositive integer. The gamma of x
     is defined over the reals, except the nonpositive integers.  Do not use
     the expression

          g = signgam * exp (lgamma (x))

     to compute

          g = gamma (x)

     Instead, use the following sequence:

          lg = lgamma (x);
          g = signgam * exp (lg);

     This is because the C language does not specify evaluation order, and
     signgam is modified by the call to the lgamma function.

DIAGNOSTICS
     For non-negative integer arguments HUGE_VAL is returned, and errno is set
     to EDOM.  If x is NaN, NaN is returned.  A message indicating SING error
     is printed on the standard error output.

     If the correct value would overflow, HUGE_VAL is returned and errno is
     set to ERANGE.

     These error-handling procedures may be changed with the function
     matherr(3M).

SEE ALSO
     exp(3M isnan(3C) matherr(3M)