Matrix form

6 次查看（过去 30 天）
Feruz
Feruz 2011-12-8
Hi,
I have a question about make a matrix which has form of
Let say I have
cel = spdiags(ones(N,1),1,N,N) - spdiags(ones(N,1),-1,N,N);
N is size in a sense that matrix size is N^3 by N^3, and first N by N part, and then N^2 by N^2 part and then N^3 by N^3 matrices super-diagonals are 1 and -1, main diagonal is 0. I hope it makes sense!
So NxN zero main diag, and from N+1,N+1 starts again same matrix till N^2xN^2, then from N^2+1,N^2+1 starts again same matrix till N^3xN^3
I have tried with kron function, which is obvious function to use, i.e.
full(kron(speye(N),cel))
but unable to create very same matrix
Let say I have this scheme in 3D, boundary conditions are zero on the boundary
(u_i,j,k+1 - u_i,j,k-1)/(2*h) => which gives my matrix A
and I have vector u = [u_111,u_112,u_121,u_122,u_211,u_212,u_221,u_222] then I have Au = b where b is any vector size of 8...
Thanks in advance!

请先登录，再回答此问题。

回答（1 个）

Andrei Bobrov
Andrei Bobrov 2011-12-8
s = N.^(1:3);
bs = arrayfun(@(x)spdiags(ones(x,1)*[-1 1],[-1 1],x,x),s,'un',0);
out = blkdiag(bs{:});
  1 个评论
Feruz
Feruz 2011-12-8
Thank you for reply,
But I guess I did explain it not the way I should...
Let say I have this scheme in 3D, boundary conditions are zero on the boundary
(u_i,j,k+1 - u_i,j,k-1)/(2*h) => which gives my matrix A
and I have vector u = [u_111,u_112,u_121,u_122,u_211,u_212,u_221,u_222] then I have Au = b
where b is any vector size of 8...

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Resizing and Reshaping Matrices 的更多信息

标签

Community Treasure Hunt

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

Start Hunting!

Translated by