Middle-square method: Difference between revisions

Revision as of 11:48, 24 November 2006

Revision as of 14:10, 14 January 2007

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In [[mathematics]], the [[middle-square method]] is a method of generating [[pseudorandom number]]s. In practice it is not a good method, since its period is usually very short and it has some crippling weaknesses. The method was first suggested by [[John Von Neumann]] in 1946.

For example, toTo generate a sequence of ten-digit pseudorandom numbers, you would create a ten-digit starting value and square it. The middle ten digits of the result would be the next number in the sequence. You would then square that, and so on.

Clearly, for a generator of ''n''-digit numbers, the period can be no longer than 10^''n''. If the middle ten digits are all zeroes, the generator then outputs zeroes forever. If the first half of a number in the sequence is zeroes, the subsequent numbers will be decreasing to zero. While these runs of zero are easy to detect, they occur too frequently for this method to be of practical use.