S-functions with ode45 in Matlab

Question

Gigi Dioda 2011-6-28

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Hi, all! I have a dynamical system written in an S-function and I want to simulate it in a Matlab loop. I use ode45 on the S-function and it seems to work (it runs with no errors). However it's not the result I was expecting. After that, I took the code from the S-function and plugged into a regular dx = f(t,x,u) function and when I applied ode45 to f, I got what I was looking for.

So, my question: what's wrong with applying ode45 to an S-function?

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Answer 1

Gigi Dioda 2011-6-28

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Ok, I solved it by creating a new function handle to the S-function.

Smth like:

f = @(t,x,u,params)SfunctionName(t,x,u,1,params{:});

[Tk,Xk] = ode45(f, [T(k) T(k+1)], x, options, U(k), params);

Best

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Answer 2

Arnaud Miege 2011-6-28

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You don't need to "apply" ode45 to an S-function since Simulink has its own solver. See Writing S-Functions in MATLAB in the documentation.

HTH,

Arnaud

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Gigi Dioda 2011-6-28

Thanks for the answer, Arnaud. However, I want to use the S-function in Matlab, without calling sim on a block comprising the S-function. Basically, I want to use the S-function in Matlab just as a regular ode in the form dx = f(t,x,u).

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