GAMMA(3M-SVR4)      RISC/os Reference Manual       GAMMA(3M-SVR4)



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(|Γ(x)|)

     where Γ(x) is defined as

          oo -t x-1
          ∫ e  t   dt
          0
     The sign of Γ(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-positive 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 and lgamma return
     HUGE and set errno to ERANGE.

     Except when the -Xc compilation option is used, these
     error-handling procedures may be changed with the function
     matherr.  When the -Xa or -Xc compilation options are used,



                        Printed 11/19/92                   Page 1

GAMMA(3M-SVR4)      RISC/os Reference Manual       GAMMA(3M-SVR4)



     HUGE_VAL is returned instead of HUGE and no error messages
     are printed.





















































 Page 2                 Printed 11/19/92