function [A] = Laplacian_mat(m, varargin)

% Square matrix
if nargin < 2
  n = m;
else
  % Rectangular matrix
  arg1 = varargin{1};
  n = arg1(1);
end;

% Create a partial Laplacian for one "row" of the grid
% approximation (Doesn't work for grid widths less than two)
z = sparse(zeros(1,n));
z(1) = 4;
z(2) = -1;
tridiag=kron(speye(m), toeplitz(z));

% Now generate the cell prototype for the offdiagonal elements
z = sparse(zeros(1,m));
z(2) = -1;
offdiag = toeplitz(z);

%create the discrete Laplacian
A=tridiag + kron(offdiag, speye(n));