Newsgroups: comp.parallel
From: Murray Cole <mic@dcs.ed.ac.uk>
Subject: Implied correctness of block-based parallel sorting
Organization: Department of Computer Science, University of Edinburgh
Date: 5 Sep 1995 14:41:38 GMT
Message-ID: <42hnj2$7gl@usenet.srv.cis.pitt.edu>

I'm putting together a course on parallel algorithms and have noticed
several quoted instances of the following:

  Given some comparison-exchange based parallel sorting algorithm operating 
  with one item per processor (i.e. p=n), derive a block based sorting 
  algorithm for p<n by 

  1. independently (in parallel) sorting the blocks assigned to each
     processor once, at the start.

  2. replacing each compare-exchange with a block merge-split (i.e. 
     merge the two sorted blocks and return lower and upper halves
     to the two processors)

It seems intuitive that this should always work (i.e. for any underlying
sorting algorithm on any machine model), but no one seems to state this
as an explicit result. Has anyone come across such a result? Is it true
at all?

Murray Cole.

