function V=F(x,y)
      t1 = x^2;
      t3 = y^2;
      t10 = (3+t1+t3)^2;
      t13 = -(-9+3*t1-3*t3+2*x-2*x*y)/t10;
      
      t1 = x^2;
      t2 = y^2;
      t8 = (3+t1+t2)^2;
      t11 = -(3+t1-t2+2*y+6*x*y)/t8;
      V = [t13,t11]';
end