An Optimal Multilevel technique for the DPN equations in cell-type geometries

The paper deals with the acceleration techniques that improve the solution of the DPn equations that are routinely used in APOLLO2 to accelerate the transport iterations for the Linear Surface (LS) characteristics method. Since for the LS method the basic cell geometrical unit can be very roughly discretized without penalizing the precision, we propose here a method that takes advantage of the very weak coupling between regions. This is done by using an optimal domain decomposition technique that reduces the computational effort. Further generalization to an arbitrary number of levels is also proposed and computational results on realistic cases are shown. (authors)