Hi, rnrnthis is done by a 4D vector (iC, iX, iY, iZ) in the 3D case. Ic is the cuboid number shich is assigned to an mpi process. The class load balancer is handling the map and the class cuboid geometry is handling the 4D <-> 3D map. However, in the upcomming release (beginng of March) this shoul be much clearer since.rnrnMathias