Question

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How to concatenate a number to a variable name in MATLAB?

Hi everyone, as the title, i’d like to learn if anyone knows how, in Matlab, create ‘n’ matrices in a loop.

Like this:

for (i=1:n)

p_i = P(i, :);
q_i = Q(i, :);

A_i = [p_i, p_i', q_i];
end

Matlab, of course, rewrites n times on the matrix A_i, but i would like to have n matrices of ‘i’ index.

Thank you in advance, have a good day!!

Answer 1

You could concatenate everything into a 3D array:

A_i = zeros(D1,D2,n);  % D1 and D2 are the dimensions of the 2D arrays
for i = 1:n
    p_i = P(i,:);
    q_i = Q(i,:);
    A_i(:,:,i) = [p_i, p_i', q_i];
end

If you genuinely want n distinct matrices, then you will need a cell array. Your code would become something like:

A_i = cell(1,n);
for i = 1:n
    p_i = P(i,:);
    q_i = Q(i,:);
    A_i{i} = [p_i, p_i', q_i];
end

Note that you should carefully consider which would suit your needs the best. The only real advantage of a cell array is that it allows each element to be a different data-type, or a different-sized array. A 3D array has several advantages over a cell array of 2D arrays (you can sum over it, reshape it, slice 3D sub-chunks out of it, etc. etc.).