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+//caption:stability_using_Nyquist_criterion
+//example 7.17.2
+//page 237
+clf();
+s=%s;
+s1=-s;
+disp("for K=1.25")
+g=(1.25*(s+1))/((s+0.5)*(s-2));
+g1=(1.25*(s1+1))/((s1+0.5)*(s1-2));
+GH=syslin('c',g);
+GH1=syslin('c',g1);
+nyquist(GH);
+nyquist(GH1);
+mtlb_axis([-1.5 0.2 -0.3 0.3]);
+xtitle('Nyquist plot of (10*(s-1))/((s+2)*(s+3));')
+figure;
+show_margins(GH,'nyquist')
+disp("since the point(-1+%i0) is  encircled clockwise by Nyquist plot ,so N=-1 and P=1(given)")
+N=-1;//no. of encirclement of -1+%i0 by G(s)H(s) plot anticlockwise
+P=1;//no. of poles of G(s)H(s) with positive real part
+Z=P-N;//np.of zeros of 1+G(s)H(s)=0 with positive real part
+disp(Z,"Z=")
+disp("as Z=2,there are two roots of closed loop characterstics eq having positive real part, hence system is unstable.")
+\ No newline at end of file
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