MATLAB: ODE solvers and multiple tspans

ode113ode23tbode45tspan

I have a model which i use one of the odesolvers to simulate. I would like to do a comparison of the results so that I can determine the differences between the solvers. Since you do not have control of the time steps chosen be the mode I thought the way to do this would be to choose a tspan with more that two entries and run the calculation.

This seems to work for ode113 and ode45 but not for ode23tb. does anyone know why ode23tb seems to ignore the tspan I am providing?

Best Answer

I have found the problem,

I was calling the function with

sol = ode45(@myfun,[0:1:12],[0 1 1],options);

and expecting the tspan values to appear in sol.x

however if you call the function

[x,y] = ode45(@myfun,[0:1:12],[0 1 1],options);

all ode solvers behave the same with x being equal to tspan. I think it must of been coincidence that the values were appearing in ode45 and ode113 sol.x vector.

Related Solutions

MATLAB: Ode45 and sol structure – different results

If you look separately at ‘sol.x’, it only has 19 points. If you want to get all the results from your deval call, do this:

[~,SXINT] = deval(sol,zv);

Note that any vector will do in place of ‘zv’ here, providing the values are within the limits of your original tspan vector.

MATLAB: Faster than ODE45

ode23tb is more efficient for cruder tolerances, so make sure you use odeset to set the tolerances appropriately. RelTol and AbsTol are the settings to look at. (The defaults are 1e-3 and 1e-6, respectively.)

Also, ode23tb is for stiff systems. I assume you've already established that this is the case. If not, ode23 will be more efficient (again, setting RelTol and/or AbsTol appropriately).

opts = odeset('AbsTol',1e-3);
[t,y]=ode23tb(@Gi,[0.000001;a],[1,0],opts);

Creates a structure opts that contains the option settings, then passes that into ode23tb.

Best Answer

Related Solutions

MATLAB: Ode45 and sol structure – different results

MATLAB: Faster than ODE45

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