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Re: Octave ode45 vs. Matlab ode45


From: Torsten
Subject: Re: Octave ode45 vs. Matlab ode45
Date: Sat, 15 Jun 2013 10:27:31 +0200
User-agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130510 Thunderbird/17.0.6

On 14.06.2013 22:30, Jeff wrote:
> Yes, it looks like you're right. I tried changing the call to 
> [t, u1] = ode45(@(t,y) f(t,y,beta), [0,T], [u0; v0], options);
> 
> Now I'm getting the messages
> warning: Option "InitialStep" not set, new value 100.000000 is used
> warning: Option "MaxStep" not set, new value 100.000000 is used

ode45 gives you a warning when you have not configured the parameters
MaxStep, InitialStep, RelTol and AbsTol.

> I would expect the initial time to be the "InitialStep", but I guess
> not. But when I add
> options=odeset(options,'InitialStep',0);
> 
> to the initialization, it fails to run with this message
> error: Solving has not been successful. The iterative integration loop
> exited at time t = 0.000000 before endpoint at tend = 1000.000000 was
> reached. This may happen if the stepsize grows smaller than defined in
> vminstepsize. Try to reduce the value of "InitialStep" and/or "MaxStep"
> with the command "odeset".

InitialStep is not the first time instance the result is calculated for
but the first (initial) step size used by the solver.

Torsten



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