Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!uflorida!gatech!hubcap!Matthew From: mcvax!ivax.doc.imperial.ac.uk!mmh@uunet.UU.NET (Matthew Huntbach) Newsgroups: comp.parallel Subject: Re: Superlinear Message-ID: <3801@hubcap.UUCP> Date: 8 Dec 88 18:53:39 GMT Sender: fpst@hubcap.UUCP Lines: 32 Approved: parallel@hubcap.clemson.edu In article <3755@hubcap.UUCP>, robison@m.cs.uiuc.edu (Arch Robison) writes: > I'm looking for references (either pro or con) on the following claim: > > A p-processor parallel processor can never exhibit speedup > of greater than p. Depends on the algorithm. In parallel heuristic search superlinear speedup can happen easily. The reference I have to hand is: G-J.Li and B.W.Wah. How to cope with anomalies in parallel approximate branch-and-bound algorithms. In National Conference on Artificial Intelligence (AAAI-84) pp.212-215. though I think there was something in a recent CACM, possibly by the same authors. As a simple demonstration, suppose you are searching a tree with one branch which your heuristic tells you is promising, but which after a lot of computation (say 11 time units) does not yield a result, and another branch which your heuristic tells you is less promising but which does in fact yield a result after a small amount of computation (say 1 time unit). On a single processor you could search the whole large branch first before turning to the small branch and finding your solution: total time 12 units. With two processors you could assign one branch to each processor. Let us assume there is a time delay of one unit shipping the less promising branch to a remote processor, and a time delay of another unit getting the result back. You would still get you result in 3 units of time. So 2 processors give you a speedup of 4 Q.E.D.