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Re: GSoC 2016 project idea - implementation of ode15s


From: Richard Crozier
Subject: Re: GSoC 2016 project idea - implementation of ode15s
Date: Sun, 6 Mar 2016 11:31:26 +0000
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On 05/03/16 19:52, Sebastian Schöps wrote:
Richard Crozier wrote
The closest equivalent solver in odepkg is probably
ode5r and, at least for the problems I solve this is much slower because
the number of steps taken to solve the problem is far smaller with ode15s.

Is your right-hand-side smoot enough? If yes, both ode15s and ode5r should
have similar performance, both are accurate up to 5th order. however single
step methods tend to use more function evaluations. if this is the
bottleneck, then you might go better with odebdi (nonetheless we should get
an ode15s for octave...)

Seb.



Well, my process for choosing ode15s was this: try ode45, was really slow, try ode15s, worked well. This should give you an idea of my knowledge of the underlying numerical workings of the solvers. However, this is also pretty much how ML recommend you choose one. My process for choosing ode5r was pretty similar, although I think this might be the only stiff solver, or possibly was when I first chose it. It gave best performance of the odepkg solvers.

I'm solving a transient simulation of a three-phase generator attached to a resistive load, so an inductive circuit with inductive coupling between circuits.

As far as I can tell odebdi is an implicit solver for which you need the initial derivatives, I don't know these.

Thanks for the help and pointing me to possibly new solvers.

I also think in general having an ode15s for octave is desirable anyway.

Richard



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