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%chap4_7f1.m 
function [u]=chap4_7f1(u1,u2,u3) 
global s 
persistent errori error_1 
 
ts=0.001; 
if u3==0 
   errori=0; 
   error_1=0; 
end    
 
s=3             %Selecting Signal Type 
if s==1         %Step Signal 
   kp=0.4; 
   ki=0.0; 
   kd=0.28; 
elseif s==2     %Sine Signal 
   kp=40; 
   ki=0.0; 
   kd=0.28; 
elseif s==3     %Square Wave Signal 
   kp=0; 
   ki=0.0; 
   kd=0.28; 
end 
error=u2; 
errord=(error-error_1)/ts; 
errori=errori+error*ts; 
 
u=kp*error+kd*errord+ki*errori; 
error_1=error;