function A = qrstepW(A)

% one step of the QR iteration
% with Wilkinson shifting

[m,n]=size(A);
lambda = eig(A(n-1:n,n-1:n));
[m,i] = min( abs(lambda-A(n,n)) );
rho = lambda(i(1));
disp(['rho = ' num2str(rho)])
[Q,R]=qr(A-rho*eye(n,n));
A = R*Q + rho*eye(n,n);