%% Sparse Laplacian Operator Matrix
% This example visualizes a sparse Laplacian operator matrix.
% The matrix representation of the discrete Laplacian operator on a two-dimensional, n-by- n grid is a n*n-by- n*n sparse matrix. There are at most five nonzero elements in each row or column. You can generate the matrix as the Kronecker product of one-dimensional difference operators. In this example n = 5.

n = 5;
I = speye(n,n);
E = sparse(2:n,1:n-1,1,n,n);
D = E+E'-2*I;
A = kron(D,I)+kron(I,D);

%
% Visualize the sparsity pattern with spy.

spy(A,'k')

% Copyright 2015 The MathWorks, Inc.