Doublesum

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.

Answer 1

[Jan]

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

[Brooke]

Thank you, Jan! Would you mind explaining what each line of code you have written means?

[Jan]

I've added comments. The basics of Matlab are explained in the Getting Started chapters of the documentation.

[Brooke]

Thank you very much! :)