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Re: Looping

  • To: mathgroup at
  • Subject: [mg95991] Re: Looping
  • From: David Bailey <dave at>
  • Date: Sat, 31 Jan 2009 06:44:01 -0500 (EST)
  • References: <glmt16$mqu$> <> <glvk9h$e4d$>

Andrzej Kozlowski wrote:

> I doubt very much that they they ever get "stuck" in the way you  
> describe. Both Simplify and FullSimplify make use of algebraic  
> algorithms some of which have very high complexity (e.g. exponential  
> or even double exponential in the number of variables). 
> Andrzej Kozlowski

I was responding to a user who tells us he has left a calculation 
running for 3 days! He hadn't used TimeConstraint when he started the 
thing off, so it could not help him until he killed the process.

I have certainly had Simplify and FullSimplify get 'stuck' - though I 
have never waited 3 days for a possible answer (and I am yet to 
encounter this problem with 7.0, but I have not tried)!

In situations like this - which often spread over a lot of memory - the 
computer ends up swapping memory pages to/from disk, which slows the 
actual calculation to a crawl.

I would have thought I replied with the obvious practical advice, and 
that the word 'stuck' is sufficiently vague and informal as not to 
require a paragraph of mathematical caveats!


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