Re: NDSolve is really slow in version 8 but not 7
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- Subject: [mg126067] Re: NDSolve is really slow in version 8 but not 7
- From: A Retey <awnl at gmx-topmail.de>
- Date: Sat, 14 Apr 2012 03:12:12 -0400 (EDT)
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> I'm using NDSolve to solve a set of roughly 40 first order
> differential equations. It takes about 10 seconds in version 7 but
> more like 850 in version 8. Does anyone know why this might be and
> how I can speed things up?
> Also for one scenario I'm getting the error
> NDSolve::"ndsz" : ""At "\[NoBreak]t\[NoBreak]" ==
> "\[NoBreak]39.77534338386624`\[NoBreak]", step size is \ effectively
> zero; singularity or stiff system suspected."
> I realise its difficult to help without me giving an example but its
> a bit tricky to do so. Are there any standard tricks I could try?
I have seen things like that in some cases. Usually the reason was that
the newer version was choosing a different Method than the older version
did. So what you could try would be to find out which Method was chosen
with version 7 and then explicitly set that Method in version 8. I found
that usually then version 8 is even somewhat faster.
Unfortunately it's not a trivial task to determine which Method was
used, but there has been a discussion about that either in this group or
on stack exchange. I remember that Oliver Ruebenkoenig was making some
valuable contributions to that discussion, so you might want to include
his name in a search.
There is a chance that those choices are changed for good reasons, so
you'd have to make sure that the result will in fact be correct when
using the faster method...
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