How can I resolve this 'Improper assignment with rectangular..' error while using Genetic Algorithm minimization (ga function)?

I am getting an error while using the ga() function with ub,lb,non-linear and integer constraints but no linear inequality/equality constraints.

The error is- "Improper assignment with rectangular empty matrix."

Here's the piece of my code- (EWPL and constraint are my functions which accept a single argument i.e. y. constraint returns C and Ceq=[])

    %SETTING THE INTEGER CONSTRAINTS ON ALL DECISION VARIABLES EXCEPT FOR y(1).
    for i=2:nvars
    intcon(i-1)=i;
    end

    %RESULT 
    f=@(y)EWPL(y);
    nonlcon=@(y)constraint(y);
    yopt=ga(f,nvars,[],[],[],[],lb,ub,nonlcon,intcon);

Interestingly, the error is totally different when I try to run the code some times. The error is in line 351 of ga() again but it's different.

Can anyone please tell me where I am going wrong? This is the very first time that I am using the genetic algorithm. Thanks :)

Answer 1

[Matt J]

The "user-supplied nonlinear constraint function" mentioned in the error message is your nonlcon function. Basically, constraint() is returning output that is bad in some way. You will probably have to use the debugger to trap this.

[Aakash Rajwani]

Yes, that was really the problem. It was inside the constraint function. It is a Chemical Engineering problem and as always, the part creating all the problems was the units of the quantities. Debugging it right now.

Thank you so very much for the help and time, Matt. I really appreciate it :)

Answer 2

[Alan Weiss]

There could be several problems here. One is that you set intcon wrong. If you want all variables except for the first to be integer-valued, then

 intcon = 2:nvars;

Another could be your nonlinear constraint function. Does it return two values, c and ceq? And is ceq = []? It should be.

Alan Weiss

MATLAB mathematical toolbox documentation

[Aakash Rajwani]

Yes, it returns two values. There were some bad values (NaN) being returned in C in the constraint function. I am debugging it right now. Thank you so much for your help :) I appreciate it.