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Re: Re: Looping

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96006] Re: [mg95991] Re: Looping
  • From: "David Park" <djmpark at comcast.net>
  • Date: Sun, 1 Feb 2009 04:40:00 -0500 (EST)
  • References: <glmt16$mqu$1@smc.vnet.net> <200901291056.FAA18117@smc.vnet.net> <glvk9h$e4d$1@smc.vnet.net> <17778064.1233403272879.JavaMail.root@m02>

And, in fact, I communicated privately with the poster who started this
thread and I think the problem was simply in the entry of his expression. He
used a Return before each term so instead of getting one expressions, he had
multiple lines, each containing one term! After fixing that everything
worked - instantaneously.

So actually it had nothing to do with the innards of Simplify.

David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/  


From: David Bailey [mailto:dave at removedbailey.co.uk] 


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!

David




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