Re^4: Fastest way to calculate hypergeometric distribution probabilities (i.e. BIG factorials)?


XP is just a number
	PerlMonks

Re^4: Fastest way to calculate hypergeometric distribution probabilities (i.e. BIG factorials)?

by tlm (Prior)

on Jun 16, 2005 at 00:56 UTC ( [id://467124]=note: print w/replies, xml )

Need Help??

in reply to Re^3: Fastest way to calculate hypergeometric distribution probabilities (i.e. BIG factorials)?
in thread Fastest way to calculate hypergeometric distribution probabilities (i.e. BIG factorials)?

Nice, but neither @log nor $next are necessary, and the whole thing can be given a functional interface, while transparently memoizing the results:

{
  my @ln_fact;
  BEGIN { $ln_fact[ 0 ] = 0; }

  sub ln_fact {
    # returns the natural log of the factorial

    my $n = shift;
    die "Invalid arg: $n" if $n < 0 or $n > int $n;
    $ln_fact[$_] = $ln_fact[$_-1] + log($_) for @ln_fact..$n;
    return $ln_fact[ $n ];
  }
}
[download]

the lowliest monk