Subscript indices must either be real positive integers or logicals?

The below code is not able to execute due to the stated error in the line "U(i,:)=max(lb,U(i,:))" , but I really cant find any error.

tic
%%prob settings
lb=[-100 -100 ]; 
ub= [100 100 ];

%% parameters for differential evolution

np=10;
max=500;
%it=100;
cr=0.7;
F=0.8;
e=exp(1);
%x_ss=[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0];

%% START of DE

f=NaN(np,1);
fu=NaN(np,1);
d=length(lb);
U=NaN(np,d);
p= repmat(lb,np,1)+(repmat((ub-lb),np,1).*rand(np,d));

for i=1:np
    x=p(i,1);
    y=p(i,2);
    
    f(i)= -(20*exp(-0.2*sqrt((1/2)*(x^2+y^2))))+20+e-exp((1/2)*(cos(2*pi*x)+cos(2*pi*y)));
   
end

%% iteration loop

for it=1:max
    
    
    for i=1:np
       
        candidates=[1:i-1 i+1:np];
        idx= candidates(randperm(np-1,3));
        
        X1= p(idx(1),:);
        X2= p(idx(2),:);
        X3= p(idx(3),:);
        
        v= X1+F*(X2-X3);
        
        for j=1:d
            
            irand= randi(d,1);
            
            if (rand<=cr || j==irand)
                U(i,j)= v(j);
            else
                U(i,j)=p(i,j);
            end
        end
    end
    
    %% fitness function
    
    for i=1:np
        
        U(i,:)= min(ub,U(i,:));
        U(i,:)= max(lb,U(i,:));
        
    A=U(i,:);
    x=A(1); 
    y=A(2);
   
     fu(i)= -(20*exp(-0.2*sqrt((1/2)*(x^2+y^2))))+20+e-exp((1/2)*(cos(2*pi*x)+cos(2*pi*y)));
        
    A=p(i,:);
    x=A(1); 
    y=A(2);
    
    f(i)= -(20*exp(-0.2*sqrt((1/2)*(x^2+y^2))))+20+e-exp((1/2)*(cos(2*pi*x)+cos(2*pi*y)));
        
        if (fu(i)<f(i))
          
           p(i,:)= U(i,:);
          f(i)=fu(i);
        else 
            p(i,:)=p(i,:);
       
        end
        
    end
    
 
     
    
end
toc

[bestfitness ind]= min(f)
bestsol=p(ind,:)

 
    

Answer 1

[Chunru]

You define max as a variable

max=500;

However you intend to use max as a function in:

U(i,:)= max(lb,U(i,:));

Since max is defined as a variable (overwriting as a function), the above statement is trying to index to max as a scalar variable. This causes the error.

To correnct the error, change max (as a variable) into other names, for example:

NMax = 500;

You may also need to change the following line accordingly:

for it=1:max   % max==>NMax

Answer 2

[Image Analyst]

A thorough explanation is given in the FAQ:

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