Initial Step ODE45 not working
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Francesco Fortunato
on 20 Oct 2018
Commented: Walter Roberson
on 21 Oct 2018
I am using an ode45 with options but my time vector still doesn't have the 1st step as I defined. I should have t=[0 5 15 25 35...] But I have t=[0 10 20 30...]
tspan=[1 10000]
options = odeset('NormControl','on','RelTol',simul.RelTol,'AbsTol',simul.AbsTol,'InitialStep',5,'Refine',1,'stats','off','MaxStep',MaxStp,'OutputFcn',@IntegrationFcn);
[ t , y ] = ode45( @dy , tspan , y_0 , options );
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Accepted Answer
Walter Roberson
on 21 Oct 2018
When you pass in a tspan that has two elements then ode45 will automatically pick times to evaluate at as needed to maintain accuracy.
You can pass a vector of times instead. ode45 will output for those times. It will continue to evaluate at whichever points it wants to maintain accuracy, but it will calculate for the times given and report only for those.
2 Comments
Walter Roberson
on 21 Oct 2018
Right. But you would want tspan starting from zero in most conditions, as the first element of tspan tells it the time at which the boundary conditions apply. So for example,
tspan = [0 5 10:10:10000];
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