Why this piece of code gives error?

CostFunction='fun4sn0';
nPop=120;
nVar=4;%nVar=1000;
nPop_Initial=nPop;
nPop_Final=30;

MaxNFE=3e3;
MaxIter0=ceil(MaxNFE/((nPop_Initial+nPop_Final)/2));   % Approximate Maximum Iterations

Cr=0.5;

xmin=[0 0 0 0];
xmax=[10 10 pi pi];

%%%%%%%%%%%

NFE=0;
Gbest.Position=[];
Gbest.Cost=inf;
BestCosts=nan(1,MaxIter0);
nfe=BestCosts;

for i=1:nPop
    Velocity(i,:)=zeros(1,nVar); %#ok<*SAGROW>
    Position(i,:)=xmin+(xmax-xmin).*rand(1,nVar);
   Cost(i)=CostFunction(Position(i,:));
    PbestPosition(i,:)=Position(i,:);
    PbestCost(i)=Cost(i);
    PbestVel(i,:)=Velocity(i,:);
    
    if PbestCost(i)<Gbest.Cost
        Gbest.Position=PbestPosition(i,:);
        Gbest.Cost=PbestCost(i);
        Gbest.Velocity= PbestVel(i,:);
    end
end

[Jon]

what error does it give, please cut and paste entire error message

[Sadiq Akbar]

Thank you very much dear Jon for your response. It gives the following error:

Subscript indices must either be real positive integers or logicals.

Error in WGA1 (line 37)

Cost(i)=CostFunction(Position(i,:));

Answer 1

[Steven Lord]

Either make your CostFunction variable a function handle to the fun4sn0 function (which is the approach I'd prefer):

CostFunction= @fun4sn0;

or use feval to evaluate the function by name.

Cost(i) = feval(CostFunction, Position(i, :));

Both of these assume that your function returns a scalar, since you're assigning its output into one element of the Cost variable.

[Sadiq Akbar]

Thanks a lot dear Steven Lord this solved my problem.

[Image Analyst]

@Steven Lord messing with function handles and feval() seems like a roundabout way to do it. Is that better than just calling the function directly like I suggested?

Cost(i) = fun4sn0(Position(i,:));

[Steven Lord]

@Image Analyst That is another option, and is the easiest if you want to hard-code the cost function. I think that particular name put me in "this is likely going to be used in some form of optimization" mode and in that case (the "function function" scenario, see ode45, fminsearch, fzero, integral, etc.) to keep the code as a general purpose solver you wouldn't want to hard-code the function.

Answer 2

[Image Analyst]

CostFunction is a character array, not an actual function. Did you mean

Cost(i) = fun4sn0(Position(i,:));

instead of

Cost(i)=CostFunction(Position(i,:));

Thorough discussion of the error in the FAQ:

https://matlab.fandom.com/wiki/FAQ#.22Subscript_indices_must_either_be_real_positive_integers_or_logicals..22

[Sadiq Akbar]

Also thanks a lot dear Image Analyst.