function exercise11task3

A = [2 1 0 ; 1 3 -1 ; 0 -1 1];
a = sort(eig(A));

N=50;
error_eig = [];
error_subdiag = [];

for k = 1:N
    [Q,R] = qr(A);
    A = R*Q;
    error_eig = [error_eig , norm(sort(diag(A))-a)];
    error_subdiag = [error_subdiag , norm(diag(A,-1))];
end
diag(A)
semilogy(1:N,error_eig,'r',1:N,error_subdiag,'b')
legend('error in the eigenvalues', 'error in the subdiagonal entries')