fmincon returns wrong length

Hi! I have a large Simulink- Modell in which I want to optimize two PI- controllers. My variables are x_1... x_4 such as:

 x = [Kp_1 Ti_1 Kp_2 Ti_2];
 [x,f,eflag,output] = fmincon(@fun,x0,[],[],[],[],lb,ub,@mynlconst,opts);

In my nonlinear constrains I added 20 constrains, for example:

 function [c,ceq] = mynlconst(x)
 ceq = [];
 set_param(char([SimName '/CF/Kp_1']), 'Gain', 'x(1)');
 set_param(char([SimName '/CF/Ti_1']), 'Gain', 'x(2)');
 % Same for x(3) and x(4)

 opts = simset('DstWorkspace','current','SrcWorkspace','base');
 sim(SimName,Tend,opts);

 c(1) = max(yout(:,1)) - MaxPX;
 c(2) = -min(yout(:,1)) - MinPX;
 c(3) = max(yout(:,3)) - MaxTX;
 c(4) = -min(yout(:,3)) - MinTX;
 c(5) = max(yout(:,5)) - MaxHX;
 c(6) = -min(yout(:,5)) - MinHX;
      |
 c(20)= ...;

yout is a matrix from Simulink with the size (130,variables). As constrains I've used the max, min of the vector.

My optimazion function fun (To keep it simple I just wrote the necessary parts):

 function y = fun(x)
 set_param(char([SimName '/CF/Kp_1']), 'Gain', 'x(1)');
 set_param(char([SimName '/CF/Ti_1']), 'Gain', 'x(2)');
 % Same for x(3) and x(4)

 opts = simset('DstWorkspace','current','SrcWorkspace','base');
 sim(SimName,Tend,opts);
 y = e'*e; % e= error, imput of controller

Somehow I get a vector x length 130, my Sample lengh :( I just want a optimized variable x legnth 4.

Any suggestions?

Thank you!

Answer 1

[Alan Weiss]

What is your x0 input to fmincon? The returned solution x has the same size as x0.

Alan Weiss

MATLAB mathematical toolbox documentation

[K0ertis]

x0 has the length 4.

 x0= [-10 500 -100 1500];

[Alan Weiss]

I don't know what is going on. Then again, I don't know anything about Simulink. I suggest that you run the debugger to see how fmincon is returning an x of the wrong size, something that I have never before seen.

I also noticed that you seem to use the variable opts for two different things: fmincon options and Simulink options. Perhaps you should use options with different names for these two uses.

Alan Weiss

MATLAB mathematical toolbox documentation

[K0ertis]

Did I wrote my functions in the correct form? For example mynlynconst: by writing 20 nonlinear constraints in this form?

Thank you

[K0ertis]

Just found out that i overwrote x in my Simulink Modell. Thank you for your help!