How to use fsolve solution as its initial values for the next step size

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Ismaeel 2018-5-4

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评论： Walter Roberson 2018-5-5

Hi, I want to solve a system of nonlinear equations (having sine and cosine) inside a user-defined function in Simulink. It works well. However, the initial values I gave the solver for t=0 is no longer a good guess for the next step size of running the program. So my question is, how can I give the solver initial values equal to the solution for the previous step? Of course, at t=0, I have already set a vector of constant initial conditions. Note that if I connect the output of the block (solution of fsolve) as an input to the block (to be used as initial values for fsolve inside the block), there will be algebraic loop problem; consequently, the program stops. Any idea?

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Walter Roberson 2018-5-5

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Break the algebraic loop. See https://blogs.mathworks.com/simulink/2015/07/18/why-you-should-never-break-an-algebraic-loop-with-with-a-memory-block/

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Ismaeel 2018-5-5

Thanks. Yes, it is a MATLAB Function block. But sorry, I didn't get what you mean exactly by your question.

Walter Roberson 2018-5-5

See for example the discussion at https://www.mathworks.com/matlabcentral/answers/309929-using-persistent-vars-in-custom-simulink-matlab-function

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