Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!decwrl!shelby!eos!eugene
From: eugene@eos.UUCP (Eugene Miya)
Newsgroups: comp.graphics
Subject: Re: Fractals, and Philosophy of Science (cellular automata for FD)
Message-ID: <5939@eos.UUCP>
Date: 9 Jan 90 07:56:31 GMT
References: <119.256E54C5@uscacm.UUCP> <1247@becker.UUCP> <9144@cbmvax.commodore.com> <6780@lindy.Stanford.EDU> <9215@cbmvax.commodore.com> <12707@phoenix.Princeton.EDU> <1990Jan6.122804.21949@jarvis.csri.toronto.edu> <6937@lindy.Stanford.EDU> <11638@csli.Stanford.ED
Reply-To: eugene@eos.UUCP (Eugene Miya)
Organization: NASA Ames Research Center, Calif.
Lines: 45

In article <11638@csli.Stanford.EDU> ceb@csli.Stanford.EDU (Charles Buckley) writes:
>In article <6937@lindy.Stanford.EDU> rick@hanauma.stanford.edu (Richard Ottolini) writes:
>   >(1) Cellular automata are a serious competitor to differential equations
>   >for modeling waves and fluids . . .
>   >(2) In computer graphics, quaternian transforms may be superior
>   >to homogeneous coordinates for modeling transformations.
>
>Well, not so fast:  
>1. the applications of cellular automata you cite are easily
>   relatable to differential equations, and anyway CA have
>   been respected for some time - the chief obstacle to their
>   use was simply a lack of hardware.

Not so fast.
CA appear fine for 2-D fluid dynamics.  They are less so for 3-D.  There are
2 reasons: 1) hardware, and 2) investment in existing PDE solvers.  A solution
does not necessarily consist of a visually based solution, such a some
type of single figure of merit, say Q.  CA's are kind of a fad, too, but
they need more work by serious scientists.

>2. Quaternia (singular: quaternion) have also been respectable for
>   quite some time - the chief obstacles to their widespread use were
>   a perceived obscurity and lack of perceived need, plus the fact
>   that much of the best work describing them was done in the Russian
>   hinterlands, and remained obscure due to societal chaos for many years.

I posted qhwc(1), the source code to a quaternion calculator developed by
Bill Burke [Williams's quaternion hoc calculator] some
time ago to comp.sources.misc a derivative of the hoc6 calculator
in Kernighan and Pike.  It handled complex arithmetic (obviously)
as well.  Two people expressed interest.  It was Bill's acknowledgement
that he had effectively learned lex and yacc.  Bill is in Gleick's Chaos book,
he uses quaternions for his cosmology and gravitation work.  He only asks
that the users of qhwc let him know (thru me, so if you are going to ask me
for a copy, I have to ask this) what they are using qhwc for:
i.e., graphics, astronomy [in one case, etc.].  Bill is the author of
"Applied Differential Geometry" and "Cosmology."

Another gross generalization from

--eugene miya, NASA Ames Research Center, eugene@aurora.arc.nasa.gov
  resident cynic at the Rock of Ages Home for Retired Hackers:
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  "If my mail does not reach you, please accept my apology."
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