gamma(3M)                         SDK R4.11                        gamma(3M)


NAME
       gamma, lgamma - log gamma function

SYNOPSIS
       cc [flag ...] file ...  -lm [library ...]

       #include <math.h>

       double gamma (double x);

       double lgamma (double x);

       extern int signgam;

DESCRIPTION
       gamma and lgamma return

              ln(||¯(x)|)

       where |¯(x) is defined as

              integral from 0 to oo of e^(-t)t^(x-1)dt

       The sign of |¯(x) is returned in the external integer signgam.  The
       argument x may not be a negative integer.

       The following C program fragment might be used to calculate |¯:

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

       where LNMAXDOUBLE is the least value that causes exp to return a
       range error, and is defined in the values.h header file.

DIAGNOSTICS
       For negative integer arguments, HUGE is returned and errno is set to
       EDOM.  A message indicating SING error is printed on the standard
       error output.  When the -Xa or -Xc compilation options are used, a
       divide by zero exception is raised.

       If the correct value would overflow, gamma and lgamma return HUGE and
       set errno to ERANGE.

       For each of these functions, if x is a quiet NaN, that value is
       returned.  If x is a signaling NaN, a quiet NaN is returned and an
       invalid operation exception is raised.  In either case, errno is set
       to EDOM, and a message indicating DOMAIN error is printed on the
       standard error output.

       When the -Xt compilation option is used, these error-handling
       procedures may be changed with the function matherr.

       When the -Xa or -Xc compilation options are used, HUGEVAL is
       returned instead of HUGE, and no error messages are printed.


SEE ALSO
       cc(1), exp(3M), matherr(3M), values(5), fpsetmask(3M).


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