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fp coeff_dxx_m1_m1, coeff_dxx_0_m1, coeff_dxx_p1_m1, coeff_dxx_m1_0, coeff_dxx_0_0, coeff_dxx_p1_0, coeff_dxx_m1_p1, coeff_dxx_0_p1, coeff_dxx_p1_p1;