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Re: Help with ODE solver

From: John W. Eaton
Subject: Re: Help with ODE solver
Date: Thu, 12 Sep 2002 12:32:24 -0500

On 12-Sep-2002, Martin Senator <address@hidden> wrote:

| I don't know the value of time at which a component of the dependent
| variable hits its critical value until the integration tells me (usually
| one component changes sign, and I have to interpolate to find the time at
| which this occurs and then restart the integration using the new right
| hand side).

That is a somewhat different problem.  You really need the ODE solver
to take care of that detail for you too.  In the current CVS sources
(and therefore the next 2.1.x snapshot) I have included a DAE solver
based on DASSL that has root solving capability.  The Octave function
is called dasrt and allows you to specify a function to say when to

In this case you are right, you will have to break the solution up
into pieces based on the times that dasrt returns control to you when
a stopping condition is met.

Although dasrt is based on a DAE solver, there should be no problem
calling it with a set of equations that have no algebraic equations
mixed in.


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