Creating a new matrix of size A with columns n:n+56 and zeros

Hi everyone,

I have a 2464 by 2464 matrix A. I created matrix A1 with the first 56 columns of A using the following code:

A1=zeros(2464,2464);
A1(:,1:56)=A(:,1:56);

Does anyone know how I can create matrix A2 to A44 using a loop? where A2 would be

A2=zeros(2464,2464);
A2(:,57:112)=A(:,57:112);
etc.etc.

Thanks a lot in advance!

Answer 1

[Ameer Hamza]

Using variable names like A2, A3, A4, ... is never a good idea: https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval. Better to use cell array

A = rand(2464,2464);
A1 = repmat({zeros(2464,2464)}, 1, size(A, 2)/56);
for i=1:numel(A1)
    col_range = (56*(i-1)+1):(56*i);
    A1{i}(:, col_range) = A(:,col_range);
end

Access each group of 44 columns like this

A2{1}
A2{2}
..
A2{44}

[Ulrike Zijlstra]

Thanks a lot, the code works. It's just that I need to define the matrices of 2464 by 2464 of only zero excepts for those columns specified (also, I need to repeat this process for 14 different A matrices, so doing everything manually would just be too time consuming).

[Ameer Hamza]

Please check the updated answer. It does what you asked in the question. Can you explain more about 14 different A matrices? What are the names of the variables storing 14 matrices?

[Ulrike Zijlstra]

That's perfect, thank you so much.

I have a matrix for 14 different years. The actual names I'm using are d_Q01, d_Q02, ..., d_Q14. (I named my matrix A in my initial question to make the question more straightforward)

[Ameer Hamza]

Try something like this

d_Q = {d_Q01, d_Q02, d_Q03, d_Q04, d_Q05, d_Q06, d_Q07, ...
       d_Q08, d_Q09, d_Q10, d_Q11, d_Q12, d_Q13, d_Q13};

A1 = cell(1, numel(d_Q));
for k=1:numel(d_Q)
    A = d_Q{k};
    A1{k} = repmat({zeros(2464,2464)}, 1, size(A, 2)/56);
    for i=1:numel(A1{k})
        col_range = (56*(i-1)+1):(56*i);
        A1{k}{i}(:, col_range) = A(:,col_range);
    end
end

The output A1 is a nested cell array.