  function Apr9()
% Note the smallest eignvalue of A is the largest eigenvalue of inv(A).
% So apply power method to inv(A).
% This requires matrix-vector products of the form y = inv(A)*x over and
% over. 
% Compute the Cholesky factorization A = GG' once. That is O(n).
% Then inside the power method loop, handle y = A\x via y = G'\(G\x)).