function R = hqr(H)
%
%  Algorithm 7.6
%
   R = H;  % transfer H to R
   n = size(H,1);  % get size
   for k = 1:n-1
      G = givensmat(R(k:k+1,k));
      R(k:k+1,:) = G*R(k:k+1,:);
   end