Creating diagonal matrix from array of matrices in MATLAB

问题

I am interested how to create a diagonal matrix from an array of matrices. I created an array of matrices in MATLAB:

X<62x62x1000> it consists of 1000 matrices with dimensions 62x62

I want to create a matrix of dimensions 62000x62000 with 1000 sub matrices from array X along main diagonal.

Do you have any clue how to do this, except M=blkdiag(X(:,:,1), X(:,:,2), X(:,:,3)...) because that would be to much writing.

回答1:

A possible solution

M = kron(speye(1000),ones(62));
M(logical(M)) = X(:);

With kron a 62000*62000 sparse matrix M is created that contains 1000 blocks of ones on its diagonal, then replace ones with elements of X.

回答2:

You can flatten out your input matrix into a column vector using (:) indexing and then pass it to diag to place these elements along the diagonal of a new matrix.

result = diag(X(:))

This will order the elements along the diagonal in column-major order (the default for MATLAB). If you want a different ordering, you can use permute to re-order the dimensions prior to flattening.

It's important to note that your resulting matrix is going to be quite large. You could use spdiags instead to create a sparse diagonal matrix

spdiags(X(:), 0, numel(X), numel(X))

回答3:

A very controversial eval call can solve this very lazily, although I suspect there is a much better way to do this:

evalstring = ['M=blkdiag('];
for i = 1:999
    evalstring = [evalstring, 'X(:,:,', num2str(i),'),'];
end
evalstring = [evalstring, 'X(:,:,1000));'];
eval(evalstring);

来源：https://stackoverflow.com/questions/40614794/creating-diagonal-matrix-from-array-of-matrices-in-matlab