Run a simulink model from a nested function in matlab code and save data

Hello everyone!

I'm simulating an electric circuit model with Simulink/Simscape. I want to estimate the parameters of this circuit by comparing the real voltage (taken from measurements) with the simulated voltage. I measure the voltage with a voltage sensor and connect its output to a "To workspace". When I run the model with known values of the parameters, the vector V_sim is shown to the base workspace thanks to "To workspace" block.

My main problem is that in my code I use this nested function

function out = mySimulation(x)
assignin('base', 'R0', x(1));
assignin('base', 'R1', x(2));
assignin('base', 'R2', x(3));
assignin('base', 'R3', x(4));
assignin('base', 'C0', x(5));
assignin('base', 'C1', x(6));
assignin('base', 'C2', x(7));
assignin('base', 'C3', x(8));

out= sim('RC_3branch');
assignin('base', 'V_sim', V_sim);
end

The command "assignin('base', 'V_sim', V_sim);" allows the function to export "V_sim" from the local workspace to the base one.

I call the function "out=mySimulation(x)" in another nested function of the code that is my objective function, the one I want to minimize in order to define the right set of parameters. The function is:

 function y = objectiveFunction(x,V_real)
     out = mySimulation(x);
     y=  sum((V_sim - V_real).^2);
    end

My initial idea was to call "out=mySimulation(x)" that, since how it is defined, should give as output "V_sim" and the object function should measure sum((V_sim - V_real).^2).

This is not happening, when the code arrives at objectiveFunction, it stops running because it does not find any "V_sim" variables.

I fixed it in this way:

    function y = objectiveFunction(x,V_real)
    out = mySimulation(x);
    out= sim('RC_3branch');
    assignin('base', 'V_sim', V_sim);
    y=  (sum((V_sim - V_real).^2))./length(V_real);
    end

but I think it's just a waste of time because to me it seems it's redundant and makes the code less clear. Do you guys have any suggestions for a more intelligent solution?

Thank you very much!!

Answer 1

[Ishu]

Hi Irene,

When you simulate a model programmatically inside a function, logged data is returned in the workspace for the function. Further your code is returning the simulation results in a single output and are stored in variable “out”.

When simulation results are returned in a single output, the “SimulationOutput” object contains a variable for each To Workspace block in the model. Therefore, your results are stored in “out” variable and you access the “V_Sim” using the “out”.

You can access the data logged by a To Workspace block by following methods:

1. Using dot “.” Operator
2. Using get function

You can change the code in your mySimulation(x) function as:

out= sim('RC_3branch'); % stores your Simulation results in out                       

toWksData = get(out,"V_Sim"); % getting V_Sim from out

assignin("base","toWksData",toWksData);

For further information you can refer these documentations:

https://www.mathworks.com/help/simulink/slref/toworkspace.html

https://www.mathworks.com/help/simulink/slref/sim.html?s_tid=doc_ta

Hope it helps!