I have a vector that I need to use to fill in the rows of a matrix. This vector will repeat over each row in the matrix except for the indices corresponding to the diagonals. Is there any way to do this without the need of a for loop?
MATLAB: Is there a way to fill a matrix around the diagonals
diagonalefficientlinear algebraMATLABmatrix
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You want to repeat that sequence on the main diagonal?
v = [4 1 0 1];A = diag(repmat(v,1,25));That is, use repmat to replicate the sequece 25 times. Then use diag to create the associated diagonal matrix.
If you wanted the matrix to be a sparse matrix, you would use spdiags to form the matrix.
v = [4;1;0;1];A = spdiags(repmat(v,25,1),0,100,100);In the second form, I used spdiags. We can visualize the matrix as created using spy.
spy(A)
A dot is shown for all non-zero elements. You can even visualize those zero elements on the diagonal, because no dots were shown there.
>> n = 5;>> toeplitz([2,-1,zeros(1,n-2)])ans = 2 -1 0 0 0 -1 2 -1 0 0 0 -1 2 -1 0 0 0 -1 2 -1 0 0 0 -1 2
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