How to superimpose certain indices of two matrices.

Suppose I have matrices K^1 and K^2. I would like to construct a globla stiffness matrix such that wwe add certain indices to construct the globlal matrix. The color coating indicates the elements being added and their corresponding index in the global matrix. How would I do this in Matlab? How would I do it if I had more matices?

Answer 1

[Ameer Hamza]

For two matrices, try

K1 = rand(4);
K2 = rand(4);

Kg = zeros(6);
Kg(1:4, 1:4) = K1;
Kg(3:6, 3:6) = Kg(3:6, 3:6) + K2

For a general case

K1 = rand(4);
K2 = rand(4);
K3 = rand(4);
K4 = rand(4);

K = {K1, K2, K3, K4};
n = 2*numel(K)+2;
Kg = zeros(n);
Kg(1:4, 1:4) = K{1};
for i = 2:numel(K)
    Kg(2*i-1:2*i+2, 2*i-1:2*i+2) =  Kg(2*i-1:2*i+2, 2*i-1:2*i+2) + K{i};
end