set simulink time step

I want to simulate a dynamics system 'mdl' using sim('mdl',parameters), and I want to get the simulation output at some specific time points, instead of time points determined by the ode solver. Is there any way that I can specify the time step of the simulink ode solver?

Like when using ode45, I can use ode45(odefun,tspan,y0) with tspan=0:0.1:1, can I still get simulation output at time points 0:0.1:1 with simulink?

Answer 1

[Kaustubha Govind]

For variable-step solvers, you can do this by setting the Output options parameter on the Import/Export Pane of the Configuration Parameters window to either 'Produce additional output' or 'Produce specified output only' and entering the time array in Output times.

[Hongkai Dai]

It can be done with fixed-step solvers. I set the ode to ode4 by using setSimulinkParam('Solver','ode4'), and specify the options.FixedStep=dt, then sim('mdl',options) will give me the output at the equally dt spaced time points with 4th order Runge-Kutta. I will try the output options for the varaible-step solvers, thanks a lot!

[Hongkai Dai]

Thanks for your help! Do you know how to set the output options to "Produce specified output only" through command line?

[Hongkai Dai]

Thanks, I have found out, I can specify option.OutputOption, and then pass sim('mdl',option)

Answer 2

[Fangjun Jiang]

Yes, certainly you can! Why don't you try it and see the results.

Use the MATLAB supplied "f14" model as an example, you can specify a time vector with variable time step and then run simulation. open the model and make it to output the simulation time "tout" and "yout" at Simulation>Configuration Parameters...>Data Import/Export

t=[0:0.01:5,5.1:0.1:10]';
sim('f14',t);
all(t==tout)
ans =
     1
>> size(tout)
ans =
   551     1
>> size(yout)
ans =
   551     2

[Hongkai Dai]

Thanks, I can set the FixedStep option to some number dt, then I have an equally spaced time points. But what if the time sequence is not equally spaced? Is there an option to be set?

[Kaustubha Govind]

I don't think that is possible with fixed-step solvers. However, if what you want is to only get output signal values at specified time-steps, you can choose the least common divisor of your desired steps as the solver fixed-step and then extract the desired points from the logged outputs.

[Fangjun Jiang]

See my edited answer above. I added an example with time vector with variable time step.

Answer 3

[Fangjun Jiang]

I guess a short answer to your question is YES. Since you already know how to use ode45(odefun,tspan,y0) with tspan=0:0.1:1, you can do the same with sim, sim('YouModelName',tspan) with tspan=0:0.1:1.

[Hongkai Dai]

Thanks a lot for your kind help! But Mathworks says such syntax are obsolete: http://www.mathworks.com/help/toolbox/simulink/ug/f11-61836.html#bsoh2ls. Anyway, your solution helps me a lot! Thanks!