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One more thing you may wish to consider is using algorithms that do not rely on large integers. For example, instead of computing ncr( $n, $r ) ("n choose r") by the formula $n! / ($n! * ($n-$r)!), use the following approach:

sub ncr { my( $n, $r ) = @_; my( $i, $result ); + + $result = 1; for $i ( 1 .. $r ) { $result *= $n - $r + $i; $result /= $i; } return $result; } + + print "ncr( 6, 3 ) = ", ncr( 6, 3), "\n"; # ncr( 6, 3 ) = 20

That is, arrange your multiplications and divisions in such a way that at any given point of time you have an integer not much larger than the output.


In reply to Re: Fastest way to calculate hypergeometric distribution probabilities (i.e. BIG factorials)? by kaif
in thread Fastest way to calculate hypergeometric distribution probabilities (i.e. BIG factorials)? by Commander Salamander

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