create sparse diagonal system from 3d matrix in matlab

To create a sparse diagonal system from a 3D matrix in MATLAB, you can extract the diagonals from the 3D matrix and use them to form a sparse diagonal matrix. Here's how you can achieve it:

main.m
% Sample 3D matrix
A = rand(4, 4, 3);

% Extract diagonals
diags = cellfun(@(x) diag(x), mat2cell(A, size(A, 1), size(A, 2), ones(1, size(A, 3))), 'UniformOutput', false);

% Create sparse diagonal matrix
B = sparse(blkdiag(diags{:}));
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In this example, A is a sample 3D matrix. We extract the diagonals from each 2D slice of the 3D matrix using cellfun. Then, we use blkdiag to concatenate these diagonals into a single matrix, and finally use sparse to convert it into a sparse diagonal matrix.

Please note that the size of the resulting sparse matrix B will depend on the dimensions of the original 3D matrix A. Adjust the code accordingly to fit your specific use case.