Tridiagonal Matrix with subdiagonal and main diagonal is also matrix
11 views (last 30 days)
Show older comments
I have two matrices A and B. I want A to be main diagonal and B to be my subdiagonals. How do I create such a matrix? By the way sizes of A and B changes but they are square matrices.
Specifically, a1=4,b1=-1
A =diag(a1*ones(1,N-1)) + diag(b1*ones(1,N-2),1) + diag(b1*ones(1,N-2),-1)
B=(-1)*eye(N-1)
These are my A and B matrices. I need to define a (N-1)*(N-1) times (N-1)*(N-1) matrix . For example for N=1000 or N=5000 I should be able to change the N value.
14 Comments
Matt J
on 14 May 2021
I don't think so, but if you post a new question on it (ideally with a demo), others on the forum may have some thoughts.
Accepted Answer
More Answers (1)
Matt J
on 12 May 2021
Here's another way, probably much faster.
N=1000;
a1=4;b1=-1;
A =diag(a1*ones(1,N-1)) + diag(b1*ones(1,N-2),1) + diag(b1*ones(1,N-2),-1);
B=(-1)*eye(N-1);
E0=speye(N);
E1=E0(2:end,1:end-1);
E0=E0(1:end-1,1:end-1);
result=kron(E0,A) + kron(E1,B)+kron(E1.',B);
whos result
See Also
Categories
Find more on Performance and Memory in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!