function y = per(cs,x)

if (cs==1)

  p1 = -1.8636e-007;
  p2 = 1.3651e-005;
  p3 = -0.00038707;
  p4 = 0.005055;
  p5 = -0.02464;
  p6 = -0.05627;
  p7 = 0.67805;

y = p1.*x.^6 + p2.*x.^5 + p3.*x.^4 + p4.*x.^3 + p5.*x.^2 + p6.*x.^1 + p7; 
 
end

if (cs==2) 

  p1 = -5.0692e-007;
  p2 = 3.7424e-005;
  p3 = -0.0011104;
  p4 = 0.016522;
  p5 = -0.12082;
  p6 = 0.2939;
  p7 = 0.59118;
  
  y = p1.*x.^6 + p2.*x.^5 + p3.*x.^4 + p4.*x.^3 + p5.*x.^2 + p6.*x.^1 + p7; 


   
end

if (cs==3)
    
     p1 = -3.6305e-005;
  p2 = 0.0017444;
  p3 = -0.024901;
  p4 = 0.044283;
  p5 = 0.92058;

 y = p1.*x.^4 + p2.*x.^3 + p3.*x.^2 + p4.*x.^1 + p5; 

 
end

if (cs==4) 
    
    
  p1 = -2.2288e-007;
  p2 = 1.3595e-005;
  p3 = -0.00030003;
  p4 = 0.0030644;
  p5 = -0.019477;
  p6 = 0.061419;
  p7 = 0.93221;
  
y = p1.*x.^6 + p2.*x.^5 + p3.*x.^4 + p4.*x.^3 + p5.*x.^2 + p6.*x.^1 + p7; 



end

  index=find(x<2);
  y(index)=1;