coeff_dxx_m1 = RATIONAL(2.0,1.0)+RATIONAL(-3.0,1.0)*x;
      coeff_dxx_0 = RATIONAL(-5.0,1.0)+RATIONAL(9.0,1.0)*x;
      coeff_dxx_p1 = RATIONAL(-9.0,1.0)*x+RATIONAL(4.0,1.0);
      coeff_dxx_p2 = RATIONAL(-1.0,1.0)+RATIONAL(3.0,1.0)*x;