“…Besides, the BCFD method can guarantee the mass conservation and result in a symmetric positive definite system, compared with a saddle-point system generated by the classical mixed element method [34]. Therefore, the BCFD method is more efficient and widely used for modeling of flow model [37,58], convection-diffusion model [52], and even time-fractional model [17,22,23,51]. Recently, Shi et al [40] proposed a compact BCFD method for the elliptic and parabolic problems, which further improves the spatial accuracy from second-order to fourth-order.…”