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From: eugene@pioneer.arc.nasa.gov (Eugene N. Miya)
Newsgroups: comp.parallel
Subject: Re: parallel numerical algorithms
Message-ID: <1766@hubcap.UUCP>
Date: 27 May 88 20:06:17 GMT
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Approved: parallel@hubcap.clemson.edu

Remember what Alan Perlis said: A LISP Programmer knows the value of
everything, but the cost of nothing. ;-)

>In my world it is very simple.

Certainly, because you have probably simple problems.  This I assume.

>parallelism is when you do several things at
>once, at different places. Vector operations are usually executed in a
>pipeline. When the pipeline is filled every stage in it will execute in
>parallel. Thus vector operations provide a special form of parallelism.

I will give you an analogy about parallelism.  Imagine n cars being at a stop
light waiting for it to change.  The light turns green. One form of
parallelism is when you have a multilane road (too easy case) [the
undergrad concept of parallelism].
	= = = = = >  #
	= = = = = >  #
	= = = = = >  #
	= = = = = >  #
We assume no one decides to change langes.  Why we run run freeways at
99% efficiency at 65 MPH.
But it is also a form of parallelism when you have all the serially lined
drivers hit the gas SIMULTANEOUSLY.  You only trust that the car ahead
	= > = > = > = >  #
of you moves at the same rate.  What we have in REAL traffic
intersections is PIPELINING (some people call this temporal
	- > - > - > - >  #
parallelism, but it really isn't parallelism is some senses, you even call
it and vectorization "special cases").  The part of the problem comes
from these dependences (the car ahead of you).  If you are willing to
run into him (or thru him, to sacrifice consistency) fine, we have
chaotic relaxation algorithms.  Ah, but if life could be so easy.

Another gross generalization from

--eugene miya, NASA Ames Research Center, eugene@aurora.arc.nasa.gov
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