How can I optimize function output by tuning 3 input parameters?

I want to optimize a non-linear output (Pressures) by finding the best 3 input parameters (Kp,Kd,Ki).

An optimized output is a constrained output.

Attached an example for unconstrained output for the input (0.0001,0.0008,0.000002). Thats not optimized.

• I have tried using fminimax. It did not go well because Preasures is a long scalar vector (1x300) while the input is 3 scalars.
• I have tried using live editor optimization tool. It did not go well because I have 3 parameters to tune in order to find the best output.
• Unfortunately I do not know the system transfer function so I can not use the tune controller.

Thanks in advance.

function [Pressures] = myFunc(Kp,Kd,Ki)
    for i = 1:500
        ...
    end
end

Answer 1

[Bjorn Gustavsson]

You'll have to modify (at least for simplicity) your function to something like this:

function [Pressures] = myFunc(KpKdKi)
    Kp = KpKdKi(1);
    Kd = KpKdKi(2);
    Ki = KpKdKi(3);
    for i = 1:500
        ...
    end
end

Then you can use fminimax or some of the other optimization-functions. The important point is to combine all the input parameters into one array - that is the format the optimization-tools expect things to have.

HTH

[Yossef Yossefi]

First of all, thank you for your answer.

Second, you are right. I have tried changing the input to a raw vector of 3 scalars. It did not help me to get an optimized output. I might have not used the function fminimax correctly.

I have tried the following code. I get an error 'not enough input argument'.

KpKdKi = [Kp, Kd, Ki];
x = fminimax(mainProgram,KpKdKi) ;

function [Pressures] = myFunc(KpKdKi)
    Kp = KpKdKi(1);
    Kd = KpKdKi(2);
    Ki = KpKdKi(3);
    for i = 1:500
        ...
    end
end

[Bjorn Gustavsson]

In that version you try to optimize a function mainProgramme. You want to run fminimax on myFunc. I'd do something like this:

KpKdKi_best = fminimax(@(pars) myFunc(pars),KpKdKi);

In that call to fminimax a function-handle is used, this is a preferable way of doing this.

HTH

[Yossef Yossefi]

Ok I see, it worked.

Thank you very much :)

[Bjorn Gustavsson]

My pleasure.