function [K,Wcg]=critif(G)
% 用于系統G的幅值穩定裕度和交角頻率

% Copyright 2000-2001 ECUST. 
%   $Revision: 1.1 $  $Date: 2001/12/21 13:08:44 $

G=tf(G);num=G.num{1};den=G.den{1};
AG=allmargin(G);Wcg=AG.GMFrequency;K=AG.GainMargin;