'Array indices must be positive integers or logical values' error

I keep getting the 'Array indices must be positive integers or logical values' error specifically n=f(i).

f = (2000:100:3000);
l = length(f);
tt = zeros(1,1);
y = 4;

for i = i:l
    n = f(i);
    A = randn(n,n);
    b = rand(n,1);
    
    tic() 
    for j = 1:y %repeat nrep times for more precise timing
        [L,U] = lu(A);
        y = forwardsub(L,b);
        x = backsub(U,y);
    end
    tt(i) = toc()/y %average recorded time
    
end

[David Hill]

Should your for-loop be:

for i=1:l

Answer 1

[Raunak Gupta]

Hi,

The value of i is not initialized and you may start with some numerical value greater than zero at first. Otherwise n = f(i) return error because i is assigned as zero by default and in MATLAB, array indexing starts from 1. Even using logical value ‘true’ and ‘false’, the ‘false’ value will return an empty array instead of throwing an error. So you may try to initialize the looping variable.