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+//caption:gain_margin_and_phase_margin
+//example 11_22
+//page 493
+s=%s;
+g=((2*(s+0.25))/(s^2*(s+1)*(s+0.5)));
+G=syslin('c',g)
+fmin=0.1; 
+fmax=100; 
+bode(G, fmin, fmax) 
+[gm,freqGM]=g_margin(G);
+[pm,freqPM]=p_margin(G);
+show_margins(G);
+disp(gm,"gain_margin=");
+disp((freqGM*2*%pi),"gain_margin_freq=");
+disp(pm,"phase_margin=");
+disp((freqPM*2*%pi),"phase_margin_freq=");
+show_margins(G);
+disp("since gain and phase margin are both negative so system is unstable")