function [res] = RR(X,Y,A,B,C,I,I1,I2)
% This function is used by Finite Element Method
% (Algorithm 12.5).
 res = R(X,Y)*(A(I,I1)+B(I,I1)*X+C(I,I1)*Y)*(A(I,I2)+B(I,I2)*X+C(I,I2)*Y);