How to superimpose certain indices of two matrices.

Question

Missael Hernandez 2020-11-3

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https://ww2.mathworks.cn/matlabcentral/answers/634859-how-to-superimpose-certain-indices-of-two-matrices

回答： Ameer Hamza 2020-11-3

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?

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Answer 1

Ameer Hamza 2020-11-3

1
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https://ww2.mathworks.cn/matlabcentral/answers/634859-how-to-superimpose-certain-indices-of-two-matrices#answer_532539

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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