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+//Example 6.19
+//PID compensation design for spacecraft attitude control.
+
+xdel(winsid())//close all graphics Windows
+clear;
+clc;
+//------------------------------------------------------------------
+//System transfer function 
+s=poly(0,'s');
+G1=(0.9/s^2);
+G2=(2/(s+2));
+G=G1*G2;
+Gs=syslin('c',G);
+
+// PID controller parameters
+Td_inv=0.1;  //  Td_inv=1/Td=0.1
+Kd=1/Td_inv; //Kd=Td=Td_inv (derivative gain)
+
+Ti_inv=0.005;  //  Ti_inv=1/Ti=0.005
+Ki=Ti_inv; //Ki=Ti_inv (integral gain)
+
+Kp=0.05 //Kp (Proportional gain)
+
+D=Kp*(Kd*s+1)*(Ki/s+1); //PID Compensator
+
+Dsc=syslin('c',D);
+
+Ds=syslin('c',D/Kp); //PID Compensator with Kp=1 
+// Compensated system with Kp=1
+GDs=Gs*Ds;
+//PID compensated system Kp=0.05;
+GDsc=Gs*Dsc;
+//------------------------------------------------------------------
+//The bode plots
+bode([Gs;GDs;GDsc],0.01/2/%pi,100/2/%pi,...
+['G(s)';'D(s)G(s) with (Kp=1)';'D(s)G(s) with (Kp=0.05)'],"rad");
+exec .\fig_settings.sci; //custom script for setting figure properties
+title('Compensation for PID design','fontsize',3)
+
+//Phase margin of pid compensated system with Kp=0.05;
+[pm wcp]=p_margin(GDsc);
+
+//------------------------------------------------------------------
+//closed loop system
+//step response
+Gc=GDsc/(GDsc+1);
+figure;
+t=0:0.05:40;
+y=csim('step',t,Gc);
+plot(t,y,2)
+
+//Title, labels and grid to the figure
+exec .\fig_settings.sci; //custom script for setting figure properties
+title('Step response for PID compensation of spacecraft'...
+,'fontsize',3)
+xlabel('Time t (sec.)','fontsize',2)
+ylabel('$theta$','fontsize',2)
+//------------------------------------------------------------------
+//step disturbance response
+Gc=G1/((G1*G2*D)+1);
+Gcs=syslin('c',Gc);
+figure;
+t=0:0.5:1000;
+u=0.1*ones(1,length(t));
+y=csim(u,t,Gcs)
+plot(t,y,2)
+
+//Title, labels and grid to the figure
+exec .\fig_settings.sci; // custom script for setting figure properties
+title('Step disturbance response for PID compensation...
+ of spacecraft','fontsize',3)
+xlabel('Time t (sec.)','fontsize',2)
+ylabel('$theta$','fontsize',2)
+//------------------------------------------------------------------