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+//Example 7.21
+// Symmetric root locus (SRL) for servo speed control
+
+xdel(winsid())//close all graphics Windows
+clear;
+clc;
+//------------------------------------------------------------------
+//Transfer function model of the given system
+a=1.5;//assume
+s=poly(0,'s');
+nums=1;
+dens=s+a;
+num_s=1;
+den_s=-s+a;
+G0s=syslin('c',nums/dens); //G0(s)
+G0_s=syslin('c',num_s/den_s); //G0(-s)
+
+evans(G0s)
+evans(G0_s)
+zoom_rect([-3 -0.1 3 0.1])
+f=gca();
+f.x_location = "origin"
+f.y_location = "origin"
+xset("color",2);
+h=legend('');
+h.visible = "off"
+
+//Title, labels and grid to the figure
+exec .\fig_settings.sci; // custom script for setting figure properties
+title('Symmetric root locus for a first order system','fontsize',3);
+//------------------------------------------------------------------
+//Root locus design
+//rho>0; choose rho=2
+rho=2;
+//optimal pole p=-sqrt(a^2+rho)
+p=-sqrt(a^2+rho)
+sig=real(p);
+omega=imag(p);
+plot(sig,omega,'ro')
+xstring(-2.5,0.02,["pole location at";"$\rho=2$"])
+xarrows([-2.2;-2.07],[0.02;0.002],-1.5,1)
+//------------------------------------------------------------------