The (i,i) part of the problem is probably a typo, can you ask for clarafication and report back? I don't see how that would be useful.
If they're expecting you to output 1 at J(i,j) if A(i,j)>0 and output 0 at J(i,j) if otherwise, then you could simply write;
A = [1,2,3;1,2,0;1,2,5];
J = check_positivity(A)
function [resulting_logical_matrix] = check_positivity(A)
resulting_logical_matrix = A>0; % this directly calculates the positivity of all elements
end
If they need you to output 1 at J(i,j) if A(i,i)>0 and output 0 at J(i,j) if otherwise, then you need too look at the diagonal elements of A only;
A = [1,2,3;1,2,0;1,2,5];
J = check_positivity(A)
function [resulting_matrix] = check_positivity(A)
[row1,col1] = size(A) ; % good practice to always use size() instead of length()
resulting_matrix = zeros(row1,col1); % good practice to always preallocate when possible
for ii1=1:row1
for ii2 = 1:col1
if A(ii1,ii1)>0 % if the diagonal element at that row is >0
resulting_matrix(ii1,ii2)=1; % elements in that row are 1
else % otherwise
resulting_matrix(ii1,ii2)=1; % elements in that row are 0
end
end
end
end
Hope this was helpful
