creating a repeating diagonal matrix

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Josue Lujan
Josue Lujan 2020-9-8
编辑： Muhammad Fiaz 2022-1-24
I'm trying to create a diagonal matrix with the following sequence on the main diagonal line where v is the vector v=[4,1,0,1] to get the following matrix
[4 0 0 0 0 0 0
0 1 0 0 0 0 0
0 0 0 0 0 0 0
0 0 0 1 0 0 0
0 0 0 0 4 0 ...]
but I want it to repeat the same sequence over an over again for a 100 by 100 matrix how would I be able to do this?

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John D'Errico
John D'Errico 2020-9-8
编辑：John D'Errico 2020-9-8
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.
  2 个评论
Josue Lujan
Josue Lujan 2020-9-8
yes i wanted to repeat the sequence on the main diaginal thank you!
Muhammad Fiaz
Muhammad Fiaz 2022-1-24
编辑：Muhammad Fiaz 2022-1-24
Can we repeat matrix is tri-diagnally?
e.g
[1 2 3 4]
I want to make it [1 2 0 0 0 0 ; 3 4 0 0 0 0 ; 0 0 1 2 0 0 ; 0 0 3 4 0 0 ; 0 0 0 0 1 2; 0 0 0 0 3 4]

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