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From: ags@seaman.cc.purdue.edu (Dave Seaman)
Newsgroups: comp.sys.handhelds
Subject: Re: Interestring Property of HP-* Calculators
Keywords: 48SX,COS
Message-ID: <15670@mentor.cc.purdue.edu>
Date: 25 Oct 90 15:09:23 GMT
References: <2821@uc.msc.umn.edu> <15610@mentor.cc.purdue.edu> <2830@uc.msc.umn.edu>
Sender: news@mentor.cc.purdue.edu
Reply-To: ags@seaman.cc.purdue.edu (Dave Seaman)
Organization: Purdue University
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In article <2830@uc.msc.umn.edu> fin@norge.unet.umn.edu (Craig A. Finseth) writes:
>I think that you missed the point.  I know perfectly well about how
>fixed point arithmetic works and about fixed points of functions.
>That was the preface.  The obvservation was that COS(x) had a fixed
>point but ACOS(x) did not.

Actually, the observation was (quoting from 2821@uc.msc.umn.edu):

>Obviously, the ACOS algorithm has a different fixed point if, indeed,
>it has one at all.  The Solver reports a sign reversal for:
>
>	'ACOS(X)=X'
>
>at, oddly  enough, .9998447741531.

The fact that you thought there might be a different fixed point, plus the fact
that you seemed to be surprised at the apparent coincidence that the sign
reversal occurred at precisely the right value, led me to believe that you
might not understand the mathematical properties of your example.  That is what
I tried to explain.

--
Dave Seaman	  					
ags@seaman.cc.purdue.edu