Repeating entries of blkdiag

10 views (last 30 days)
SA
SA on 9 Nov 2020
Commented: SA on 10 Nov 2020
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

Accepted Answer

John D'Errico
John D'Errico on 9 Nov 2020
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
  1 Comment
SA
SA on 10 Nov 2020
It worked thanks a lot.
This my new code.
n = 4;
A = [ 6 2 0; 3 6 2; 0 3 6];
B = 7*eye(3);
BB = repmat({B},1,2);
BDiag = blkdiag(BB{:});
D = 4*eye(3);
DD = repmat({D},1,2);
DDiag = blkdiag(DD{:});
C = kron(eye(3),A);
C(1:end-(n-1),(n-1)+1:end) = C(1:end-(n-1),(n-1)+1:end) + BDiag;
C((n-1)+1:end,1:end-(n-1)) = C((n-1)+1:end,1:end-(n-1)) + DDiag;

Sign in to comment.

More Answers (0)

Categories

Find more on Creating and Concatenating Matrices in Help Center and File Exchange

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!