Department of Computer Science | Institute of Theoretical Computer Science

Theory of Combinatorial Algorithms

Prof. Emo Welzl

abstract It has been known for 30 years that pseudorandom number generators in the class of \emph{linear congruential generators} (LCG) exhibit strong and predictable regularities. A widely used generator in this class is \texttt{drand48}. While the regularity is not problematic in most applications, I show that it can produce very misleading results in testing geometric algorithms that involve determinant computations. By presenting scenarios where LCG behave `nonrandom' (sometimes in a spectacular way), I want to raise awareness for possible problems with LCG and pseudorandom numbers in general.

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