i got error at the line"strea​m(j).Posit​ion=stream​(j).Positi​on+2.*rand​(1).*(sea.​Position-s​tream(j).P​osition);" in Subscript indices must either be real positive integers or logicals. please help me.

for i=1:Npop
    pop(i).Position=LB+(UB-LB).*rand;
    pop(i).Cost=objective_function(pop(i).Position);
end

[pop, F]=NonDominatedSorting(pop);  % Non-dominated sorting
pop=CalcCrowdingDistance(pop,F);   % Calculate crowding distance
pop=SortPopulation(pop);     % Sort population
%------------- Forming Sea, Rivers, and Streams  --------------------------
sea=pop(1);
river=pop(2:Nsr);
stream=pop(Nsr+1:end);

cs=[sea.CrowdingDistance';[river.CrowdingDistance]';stream(1).CrowdingDistance];

f=0;
if length(unique(cs))~=1
    CN=cs-max(cs);
else
    CN=cs;
    f=1;
end

NS=round(abs(CN/(sum(CN)+eps))*N_stream);

if f~=1
    NS(end)=[];
end
NS=sort(NS,'descend');
% ------------------------- Modification on NS -----------------------
i=Nsr;
while sum(NS)>N_stream
    if NS(i)>1
        NS(i)=NS(i)-1;
    else
        i=i-1;
    end
end

i=1;
while sum(NS)<N_stream
    NS(i)=NS(i)+1;
end

if find(NS==0)
    index=find(NS==0);
    for i=1:size(index,1)
        while NS(index(i))==0
            NS(index(i))=NS(index(i))+round(NS(i)/6);
            NS(i)=NS(i)-round(NS(i)/6);
        end
    end
end

NS=sort(NS,'descend');
NB=NS(2:end);
FF=zeros(max_it,numel(sea.Cost));
for i=1:max_it
    %---------- Moving stream to sea---------------------------------------
    for j=1:NS(1)
        stream(j).Position=stream(j).Position+2.*rand(1).*(sea.Position-stream(j).Position);

          stream(j).Position=min(stream(j).Position,UB);
          stream(j).Position=max(stream(j).Position,LB);

[KSSV]

How we can test the code without knowing any inputs? Any ways check the value of j it is either 0 or negative that's why error poped out.