function [y,z]=dhorner(W,x)
  n=length(W) ;
  y=W(1) ;
  z=0;
  for i=2:n
    z=y+z.*x;
    y=y.*x+W(i);
  end
end

function[pn,err,k]=polnewton(W,p0,delta,max)
 for k=1:max
    [y,z]=dhorner(W,p0);
    pn=p0 - y / z;
    err=abs(pn - p0);
    p0=pn;
    if(err<delta)
        return;
    end
end

W=[2 -1]

polnewton(W, 1, 0.2, 100)

W=[2 -1 0]

polnewton(W, 1, 0.2, 100)

W=[1 -2 0 1]

polnewton(W, 0.5, 0.2, 100)