Coupled P_N-DP_N method for solving the neutron transport equation of planar geometry

One of the difficulties in spherical harmonics (P_N) method is to deal with the discontinuity of neutron flux near interfaces or void boundaries. To solve this problem, Yvon proposed the expansion of the spherical harmonics over each half of the angular range, thus yielding the double spherical harmonics (DP_N) method. The purpose of this study is to combine the P_N method and the DP_N method to solve the time-independent isotropic neutron transport equation in one-dimensional planar geometry. Numerical results from several test problems are presented to demonstrate that great improvements in accuracy can be obtained using this coupled P_N-DP_N method.