Re: Octave ode45 vs. Matlab ode45

[Torsten]

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