function Apr23()
% Hc*sc = -gc so sc = -inv(Hc)gc 
% Taylor series: phi(xc+mu*sc) = phi(xc) + gc'(mu*sc) + O(mu^2)
%                              = phi(xc) - mu*(gc'*inv(Hc)*gc) + O(mu^2)
%
% Since (gc'*inv(Hc)*gc)>0 we can choose mu small enough so that 
%
%             - mu*(gc'*inv(Hc)*gc) + O(mu^2) < 0
