Array indices must be positive integers or logical values. Error in WCA (line 44) pop(i).cos​t=objectiv​e_function​(pop(i).po​sition); I am getting this issue while I am running the code of distribution load flow analysis

I have attached two files in this questions, the objective is to call the fx file in BackawardFarwardNew_28bus.m to implement the WCA !!, could you please tell how to integrate or what is the issue i am facing here, its quite urgent..!!

for i=1:Npop

pop(i).position=LB+(UB-LB).*rand(1,nvars);

pop(i).cost=objective_function(pop(i).position);

this is the 44th line of water cycle algorithm where i got the error

[AR Hithesh]

thank you for answering

Answer 1

[Walter Roberson]

In BackwardFarwardNew_28bus.m you have

objective_function = min(P_l);
[Xmin,Fmin,NFEs,Elapsed_Time]=WCA(objective_function,LB,UB,nvars,Npop,Nsr,dmax,max_it)

so you are taking min() of something and passingå it in as objective_function .

What is that thing, P_l ? Well, you have

   for i=size(LD,1):-1:1
        c=[];
        P_l = [];
        e=[];
        [c e]=find(LD(:,2:3)==LD(i,3));
        if size(c,1)-1==0
            IB(LD(i,1))=I(LD(i,3));
            x = LD(:,4);
            P_l = real(((IB(LD(i,1)))^2).*x)
        else
             IB(LD(i,1))=I(LD(i,3))+sum(IB(LD(c,1)))-IB(LD(i,1));
             x =LD(:,4);
                P_l = real(((IB(LD(i,1)))^2).*x)
        end

    end

That runs a loop (backwards), and every iteration of the loop it resets all of P_l to empty, and then it sets P_l to P_l = real(((IB(LD(i,1)))^2).*x) where x = LD(:,4); looks like a column vector. So P_l appears that it will be a column vector after the for loop. With the .* operator, it is most likely numeric, but at the moment we cannot rule out symbolic or even something more strange such as transfer function.

So what is IB ?

    IB=zeros(size(LD,1),1);

That is numeric, as was most likely.

So, you loop backwards over the rows of LD, and each time you overwrite all of P_l with a numeric vector. Then afterwards you take min() of the numeric vector, giving a numeric scalar result. And you pass that numeric scalar result into WCA.

What does WCA do with it?

% Water Cycle Algorithm (WCA) (Standard Version)
% This code is prepared for single objective function (minimization), unconstrained, and continuous problems.

so WCA is expecting to minimize a function. Most likely the first parameter,

function [Xmin,Fmin,NFEs,Elapsed_Time]=WCA(objective_function,LB,UB,nvars,Npop,Nsr,dmax,max_it)

objective_function. But you passed a numeric scalar into that position.

    pop(i).cost=objective_function(pop(i).position);

objective_function is a numeric scalar. The only valid indices for it are scalar true, any number of false, and any number of numeric 1 . But

   pop(i).position=LB+(UB-LB).*rand(1,nvars);

That is not going to be true, false, or 1.

You need to review your BackwardFarwardNew_28bus.m and figure out what it is that you want to minimize. You need to be passing in a function handle, and the function handle has to expect to receive (in the context of your code) a vector of length 6, and the function handle has to return a scalar numeric value.