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+//clear//
+//Example 11.9:Gain and Phase Margins and their
+//associated cross over frequencies
+s =poly(0,'s'); // Define ss as polynomial variable
+//Create s transfer function in forward path
+F = syslin('c',[(4*(1+0.5*s))/(s*(1+2*s)*(1+0.05*s+(0.125*s)^2))])
+B = syslin('c',(1+0*s)/(1+0*s)) 
+OL = F*B;
+fmin = 0.01; // Min freq in Hz
+fmax = 10; // Max freq in Hz
+scf(1);
+//clf;
+// Plot frequency response of open loop transfer function 
+bode(OL,0.01,10); 
+// display gain and phase margin and cross over frequencies
+show_margins(OL);
+[gm,fr1] = g_margin(OL)
+[phm,fr2] = p_margin(OL)
+disp(gm,'gain margin in dB')
+disp(fr1,'gain cross over frequency in Hz')
+disp(phm,'phase margin in dB')
+disp(fr2,'phase cross over frequency in Hz')