gamma(3M)                UNIX System V(Math Libraries)                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(|Γ~(x)|)

      where Γ~(x) is defined as
            oo
            ∫ e-ttx-1dt
            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)) > 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.

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




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