“…However, these methods have some critical drawbacks, such as, being difficult to be implemented to complex geometries, or often requiring a lot of computation time to achieve high precision even for simple problems. Another kind of methods is based on solving set of discretized partial differential equations of the RTE, including discrete ordinates methods (DOM) [12,13], finite volume method (FVM) [14], finite element method (FEM) [15], spectral element method [16] and meshless or meshfree methods [3,4,[17][18][19][20][21], which have obvious advantages, such as high efficiency and excellent flexibility to deal with multidimensional complex geometries. In recent years, considerable effort has been dedicated to develop these partial differential equation discretization based methods.…”