MATLAB: Repeating entries of blkdiag

blkdiag

I created a block tridiagonal matrix sysytem using the code below.
n = 4;
A = [ 6 2 0; 3 6 2; 0 3 6];
B = 7*eye(3);
D =  4*eye(3)
C = kron(eye(3),A);
C(1:end-(n-1),(n-1)+1:end) = C(1:end-(n-1),(n-1)+1:end) + blkdiag(B,B);
C((n-1)+1:end,1:end-(n-1)) = C(1:end-(n-1),(n-1)+1:end) + blkdiag(D,D);
How do i avoid typing B or D twice in blkdiag? Is there a function that can repeat B or D twice or more without having to type B or D twice or more in case my A is a huge matrix?
Thanks

Best Answer

B = ones(2);
BB = repmat({B},1,5);
BDiag = blkdiag(BB{:});
spy(BDiag)
Create a cell array. Then use blkdiak properly, by turning the cell array into a comma separated list. BB{:} does that. Thus...
BB{:}
ans = 2×2
     1     1
     1     1

ans = 2×2
     1     1
     1     1

ans = 2×2
     1     1
     1     1

ans = 2×2
     1     1
     1     1

ans = 2×2
     1     1
     1     1

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