Large Matrices for solving linear systems

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JJ
JJ 2018-12-3
回答： Steven Lord 2018-12-3
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
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Torsten
Torsten 2018-12-3
You should think about whether it is necessary to form the matrix explicitly. If N gets larger, this may cause problems with available workspace.

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Steven Lord
Steven Lord 2018-12-3
I think you may find this documentation example useful.

更多回答（3 个）

KSSV
KSSV 2018-12-3
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) ;
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JJ
JJ 2018-12-3
thanks thins is similar to what I want but I need the specific pentagonal matrix associated with the discrete Laplace equation

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Walter Roberson
Walter Roberson 2018-12-3
spdiags() to create the A matrix .
There is no special way to create large dense matrices.
Matt J
Matt J 2018-12-3
编辑：Matt J 2018-12-3
values=[-4,1,1,1,1];
A=toeplitz([values(:), zeros(N-numel(values),1) ]);

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