Doublesum

2012 4 15
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Suppose I have matrix with elements M(i,j,k) and I want to sum all the elements corresponding to a fixed k, how might I achieve that? In other words I would like to sum over two of the indices. Thank you.

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Jan
Jan 2012-4-15

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M = randn(10,10,3); % Arbitrary test data
P = M(:, :, 2); % Get submatrix, 3rd dimension is 2
P = P(:); % Reshape submatrix to a column vector
S = sum(P); % Sum over all elements of P

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Brooke
Brooke 2012-4-15
Thank you, Jan! Would you mind explaining what each line of code you have written means?
Jan
Jan 2012-4-15
I've added comments. The basics of Matlab are explained in the Getting Started chapters of the documentation.
Brooke
Brooke 2012-4-15
Thank you very much! :)

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