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MathGroup Archive 2000

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Re: RE: RE:Working Precision

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24071] Re: [mg24047] RE: [mg23928] RE:Working Precision
  • From: David Withoff <withoff at wolfram.com>
  • Date: Fri, 23 Jun 2000 02:26:40 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

> The only problem I have with the examples based on 
>  
>    x=1.11111111111111111111;
>    Do[x=2*x-x, {100}];
> 
> is that a message is never posted warning that the results are not reliable
> due to lose of precision in the value of (x). I suspect many users would
> want to know when arbitrary precision arithmetic gives results with very low
> precision.

It would be difficult (or impossible) to know when to post such a message.
The numerical error may be bigger than you had expected, but the result is
reliable and mathematically it is exactly what it should be.  The computer
has no way of knowing that you might have been surprised by it.  Almost
every area of mathematics contains potentially surprising things.

Dave Withoff
Wolfram Research


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