From 05465025316ba921b7e0072e707c1b52201eec49 Mon Sep 17 00:00:00 2001 From: Wolfgang Bangerth Date: Tue, 13 Oct 2015 08:35:35 -0500 Subject: [PATCH] Add something to the documentation. --- doc/doxygen/headers/distributed.h | 29 ++++++++++++++++++++++++++++- 1 file changed, 28 insertions(+), 1 deletion(-) diff --git a/doc/doxygen/headers/distributed.h b/doc/doxygen/headers/distributed.h index 89c2cf7cce..af2dc1c964 100644 --- a/doc/doxygen/headers/distributed.h +++ b/doc/doxygen/headers/distributed.h @@ -1,6 +1,6 @@ // --------------------------------------------------------------------- // -// Copyright (C) 2009 - 2014 by the deal.II authors +// Copyright (C) 2009 - 2015 by the deal.II authors // // This file is part of the deal.II library. // @@ -132,6 +132,33 @@ * i.e. from the overlap of the turquoise, green, yellow and red * areas, disregarding the blue areas. * + * @note The decomposition of this "real" mesh into the pieces stored + * by each processes is provided by the p4est + * library. p4est stores the complete mesh in a distributed data structure + * called a parallel forest (thus the name). A parallel forest consists of + * quad-trees (in 2d) or oct-trees (in 3d) originating in each + * coarse mesh cell and representing the refinement structure + * from parent cells to their four (in 2d) or eight (in 3d) + * children. Internally, this parallel forest is represented by + * a (distributed) linear array of cells that corresponds to a + * depth-first traverse of each tree, and each process then stores + * a contiguous section of this linear array of cells. This results + * in partitions such as the one shown above that are not optimal + * in the sense that they do not minimize the length of the + * interface between subdomains (and consequently do not minimize + * the amount of communication) but that in practice are very + * good and can be manipulated with exceedingly fast algorithms. + * The efficiency of storing and manipulating cells in this way + * therefore often outweighs the loss in optimality of communication. + * (The individual subdomains resulting from this method of + * partitioning may also sometimes consist of disconnected + * parts, such as shown at the top right. However, it can be + * proven that each subdomain consists of at most two disconnected + * pieces; see C. Burstedde, T. Isaac: "Morton curve segments produce + * no more than two distinct face-connected subdomains", + *