% m10_QRfact.m - QR factorisation

    A = zeros(7,3)
    A(:) = (1:21).^2
    [Q,R] = qr(A,0)
    norm(A(:,1))
    norm(A(:,2))
    norm(R(:,2))
    Q'*Q
    Q*Q'
    rank(ans)

    A = randn(1e4,1e3);
    tic, [Q,R] = qr(A,0); toc
    max(max(abs(  Q'*Q - eye(1e3)  )))