说明：  Cell centered (LAPc) and cell edge (LAPe) algorithms were developed to solve the static neutron diffusion equation in 2D Cartesian geometry using Lagrange interpolation with the progressive polynomial approximation. Two benchmark problems were used to test the algorithms the two-group TWIGL problem and a one-group IAEA benchmark problem. The LAP algorithms showed to be more accurate than a finite difference method (FDM) and for about the same level of accuracy, the LAP numerical methods have an efficiency advantage because they have to solve for less number of unknowns. The LAP algorithms showed more sensitivity to the mesh size than what QUANDRY results showed. Even though the FDMs algorithm, for the calculation of keff, showed systematically to be less accurate than QUANDRY, LAPc, and that LAPe, it was the only one that did not produce negative flux in any location for all the mesh structures analyzed in the IAEA problem. Other variants of