Path: news.io.com!news.fc.net!news3.net99.net!news.cais.net!uunet!in2.uu.net! + tank.news.pipex.net!pipex!lyra.csx.cam.ac.uk!nmm1 From: nmm1@cus.cam.ac.uk (Nick Maclaren) Newsgroups: comp.arch.arithmetic Subject: Re: Psuedo Random Numbers Date: 14 Oct 1995 21:15:23 GMT Organization: University of Cambridge, England Lines: 26 Message-ID: <45p99b$am@lyra.csx.cam.ac.uk> References: <44vm6r$1q5@bug.rahul.net>+ <4593t4$2nm0@b.stat.purdue.edu> NNTP-Posting-Host: bootes.cus.cam.ac.uk In article , Arthur Chance wrote: >In article <4593t4$2nm0@b.stat.purdue.edu> hrubin@b.stat.purdue.edu (Herman Rub in) writes: >> The period is essentially unimprtant. A Tausworthe generator like >> x[n] = x[n-460] + x[n-607] has period 2^(s-1)*(2^607 -1), where s >> is the word length; this is in integer arithmetic. This class of >> procedures are now known to have drawbacks. > >Could you explain that last sentence? I tend to use that style of RNG >as a convenient and easily programmed workhorse, so if there are >problems with it, I'd like to be aware of them. See M. Luescher, Computer Physics Communications, 79 (1994) p. 100. The problems have been known for many years (see Knuth), but previously to Luescher nobody had succeeded in describing them coherently. I had a heuristic argument about their failings back in the 1980s, but could never tighten it enough to publish in any worthwhile journal. It was VERY heuristic! Nick Maclaren, University of Cambridge Computer Laboratory, New Museums Site, Pembroke Street, Cambridge CB2 3QG, England. Email: nmm1@cam.ac.uk Tel.: +44 1223 334761 Fax: +44 1223 334679