Large Matrices for solving linear systems

Can someone help me, I need to create the pentagonal matrix associated with the Laplace equation.. So -4 along the diagonal and 4 diagonals with 1’s. I want to be able to change the size, initially I was wanting N=33, hence 1024 x 1024.

Also an array with different values, I know I can do b=(ones(N-1)*(N-1),1) with ones or zeros, but is there a way to create a large array with different values.

I have codes for all my methods of solving linear systems, just cant create a matrix A

[Torsten]

You should think about whether it is necessary to form the matrix explicitly. If N gets larger, this may cause problems with available workspace.

Answer 1

[Steven Lord]

I think you may find this documentation example useful.

Answer 2

[KSSV]

N = 10 ;

A = diag(ones(N-2,1),-2)+diag(ones(N-1,1),-1)+4*diag(ones(N,1))+........
    diag(ones(N-1,1),1)+diag(ones(N-2,1),2) ;

[JJ]

thanks thins is similar to what I want but I need the specific pentagonal matrix associated with the discrete Laplace equation

Answer 3

[Walter Roberson]

spdiags() to create the A matrix .

There is no special way to create large dense matrices.

Answer 4

[Matt J]

values=[-4,1,1,1,1];
A=toeplitz([values(:), zeros(N-numel(values),1)  ]);