function acc=ComparePoly(x,y,dy,z)
% This compares the polynomials given by PolyHorn and EntPoly,
% which are the quintic polynomials having values and derivatives
% at three points given by x prescribed by the vectors y and dy.
% Outputs maximum difference between them over z

c=HermInt(x,y,dy);
Ip=Horner2(x,c,z);
Myp=EntPoly(z,x,y,dy);
plot(z,Ip-Myp);
acc = max(abs(Ip-Myp));