gamma(3M)               LIBRARY FUNCTIONS               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)|)

     whereoo
|
~~(x) is defined as
          ∫ 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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