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<!-------- @HEADER
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! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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! Zoltan Toolkit for Load-balancing, Partitioning, Ordering and Coloring
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<HTML>
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<HEAD>
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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<META NAME="GENERATOR" CONTENT="Mozilla/4.04 [en] (X11; U; SunOS 5.6 sun4m) [Netscape]">
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<meta name="sandia.approval_type" content="formal">
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<meta name="sandia.approved" content="SAND2007-4748W">
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<meta name="author" content="Zoltan PI">
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<TITLE>Zoltan User's Guide: Refinement Tree Based Partition</TITLE>
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</HEAD>
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<BODY BGCOLOR="#FFFFFF">
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<div ALIGN=right><b><i><a href="ug.html">Zoltan User's Guide</a> | <a href="ug_alg_hypergraph.html">Next</a> | <a href="ug_alg_hsfc.html">Previous</a></i></b></div>
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<H2>
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<A NAME="REFTREE"></A>Refinement Tree Partitioning (REFTREE)</H2>
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The refinement tree based partitioning method is due to William Mitchell
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of the National Institute of Standards and Technology
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[<A HREF="ug_refs.html#reftree">Mitchell</A>].
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It is closely related to the Octree and Space-Filling Curve methods,
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except it uses the tree that represents the adaptive refinement process
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that created the grid. This tree is constructed through the tree-based
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query functions.
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<P>Each node of the refinement tree corresponds to an element that
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occurred during the grid refinement process. The first level of the tree
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(the children of the root of the tree) corresponds to the initial coarse
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grid, one tree node per initial element. It is assumed that the initial
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coarse grid does not change through the execution of the program, except
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that the local IDs, assignment of elements to processors, and weights
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can change. If any other aspect of the coarse grid changes, then the
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Zoltan structure should be destroyed and recreated.
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The children of a node in the
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tree correspond to the elements that were created when the corresponding
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element was refined. The children are ordered such that a traversal of
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the tree creates a space-filling curve within each initial element.
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If the initial elements can be ordered with a contiguous path through them,
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then the traversal creates a space-filling curve through all the elements.
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Each element has a designated "in" vertex and "out" vertex, with the out
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vertex of one element being the same as the in vertex of the next element
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in the path, in other words the path goes through a vertex to move from
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one element to the next (and does not go out the same vertex it came in).
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<P>The user may allow Zoltan to determine the order of the coarse grid
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elements, or may specify the order, which might be faster or produce a
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better path. If Zoltan determines the order, the user can select between
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an order that will produce connected parts, an order based on a Hilbert
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Space Filling Curve, or an order based on a Sierpinski Space Filling Curve.
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See the parameter REFTREE_INITPATH below. If the user provides the order, then
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the in/out vertices must also be supplied. Similarly, the
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user may specify the order and in/out vertices of the child elements, or
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allow Zoltan to determine them. If the user knows how to provide a good
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ordering for the children, this may be significantly faster than the default
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general algorithm. However, accelerated forms of the ordering algorithm
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are provided for certain types of refinement schemes and should be used in
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those cases.
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See <B><A HREF="ug_query_lb.html#ZOLTAN_CHILD_LIST_FN">ZOLTAN_CHILD_LIST_FN</A></B>.
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If the user always specifies the order, then the vertices and in/out vertices
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are not used and do not have to be provided.
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<P>Weights are assigned to the nodes of the tree. These weights need not be
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only on the leaves (the elements of the final grid), but can also be on
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interior nodes (for example, to represent work on coarse grids of a multigrid
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algorithm). The default weights are 1.0 at the leaves and 0.0 at the
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interior nodes, which produces a partition based on the number of elements
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in each part.
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An initial tree traversal is used to sum the weights, and a second traversal
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to cut the space-filling curve into appropriately-sized pieces and assign
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elements to parts. The number of parts is not necessarily equal
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to the number of processors.
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<P> The following limitations should be removed in the future.
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<LI>For multicomponent weights, only the first component is used.
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<LI>Heterogeneous architectures are not supported, in the sense that the
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computational load is equally divided over the processors. A vector of
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relative part sizes is used to determine the weight assigned to each
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part, but they are currently all equal. In the future they should
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be input to reflect heterogeneity.
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<p>
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Another limitation is that refinement tree partitioning has not been modified to work with
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64-bit global IDs. If 64-bit IDs are selected at configure time with either the
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<A HREF="ug_usage.html#Autotools">autotools</A> build or the
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<A HREF="ug_usage.html#CMake">CMake</A> build, the method will fail.
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<BR>
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<BR>
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<TABLE WIDTH="100%" NOSAVE >
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<TR>
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<TD VALIGN=TOP><B>Method String:</B></TD>
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<TD><B>REFTREE</B></TD>
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</TR>
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<TR>
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<TD><B>Parameters:</B></TD>
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<TD></TD>
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</TR>
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<TR>
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<TD VALIGN=TOP> <I>REFTREE_HASH_SIZE</I></TD>
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<TD> The size of the hash table to map from global IDs to refinement tree
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nodes. Larger values require more memory but may reduce search time.</TD>
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</TR>
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<TR>
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<TD VALIGN=TOP><B>Default:</B></TD>
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<TD></TD>
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</TR>
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<TR>
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<TD></TD>
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<TD><I>REFTREE_HASH_SIZE</I> = 16384</TD>
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</TR>
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<TD></TD>
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</TR>
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<TR>
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<TD VALIGN=TOP> <I>REFTREE_INITPATH</I></TD>
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<TD>
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Determines the method for finding an order of the elements in the initial
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grid. </BR>
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"SIERPINSKI" uses a Sierpinski Space Filling Curve and is most appropriate
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for grids consisting of triangles. It is currently limited to 2D. </BR>
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"HILBERT" uses a Hilbert Space Filling Curve and is most appropriate for grids
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consisting of quadralaterals or hexahedra. </BR>
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"CONNECTED" attempts to produce connected parts (guaranteed for triangles
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and tetrahedra), however they tend to be stringy, i.e., less compact than the
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SFC methods. It is most appropriate when connected parts are required. </BR>
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An invalid character string will invoke the default method.
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</TD>
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</TR>
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<TR>
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<TD VALIGN=TOP><B>Default:</B></TD>
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<TD></TD>
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</TR>
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<TR>
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<TD></TD>
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<TD><I>REFTREE_INITPATH</I> = "SIERPINSKI" if the grid contains only triangles</BR>
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<I>REFTREE_INITPATH</I> = "HILBERT" otherwise
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</BR></BR>
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<I>NOTE:</I> In Zoltan versions 1.53 and earlier the default was "CONNECTED".
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To reproduce old results, use <I>REFTREE_INITPATH</I> = "CONNECTED".
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</TD>
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</TR>
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<TR>
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<TD VALIGN=TOP><B>Required Query Functions:</B></TD>
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<TD></TD>
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</TR>
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<TR>
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<TD></TD>
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<TD><B><A HREF="ug_query_lb.html#ZOLTAN_NUM_COARSE_OBJ_FN">ZOLTAN_NUM_COARSE_OBJ_FN</A></B></TD>
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</TR>
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<TR>
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<TD></TD>
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<TD><B><A HREF="ug_query_lb.html#ZOLTAN_COARSE_OBJ_LIST_FN">ZOLTAN_COARSE_OBJ_LIST_FN</A></B>
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or <B><A HREF="ug_query_lb.html#ZOLTAN_FIRST_COARSE_OBJ_FN">ZOLTAN_FIRST_COARSE_OBJ_FN</A></B>/<B><A HREF="ug_query_lb.html#ZOLTAN_NEXT_COARSE_OBJ_FN">ZOLTAN_NEXT_COARSE_OBJ_FN</A></B>
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pair
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</TD>
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</TR>
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<TR>
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<TD></TD>
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<TD><B><A HREF="ug_query_lb.html#ZOLTAN_NUM_CHILD_FN">ZOLTAN_NUM_CHILD_FN</A></B></TD>
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</TR>
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<TR>
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<TD></TD>
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<TD><B><A HREF="ug_query_lb.html#ZOLTAN_CHILD_LIST_FN">ZOLTAN_CHILD_LIST_FN</A></B></TD>
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</TR>
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<TR>
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<TD></TD>
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<TD><B><A HREF="ug_query_lb.html#ZOLTAN_CHILD_WEIGHT_FN">ZOLTAN_CHILD_WEIGHT_FN</A></B></TD>
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</TR>
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<TR>
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<TD></TD>
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<TD>The following functions are needed only if the order of the initial
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elements will be determined by a space filling curve method:</TD>
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</TR>
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<TR>
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<TD></TD>
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<TD><B><A HREF="ug_query_lb.html#ZOLTAN_NUM_GEOM_FN">ZOLTAN_NUM_GEOM_FN</A></B></TD>
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</TR>
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<TR>
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<TD></TD>
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<TD>
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<B><A HREF="ug_query_lb.html#ZOLTAN_GEOM_MULTI_FN">ZOLTAN_GEOM_MULTI_FN</A></B><B>
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or
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<B><A HREF="ug_query_lb.html#ZOLTAN_GEOM_FN">ZOLTAN_GEOM_FN</A></B>
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</TD>
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</TR>
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<TR>
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</TABLE>
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<P>
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<HR WIDTH="100%">[<A HREF="ug.html">Table of Contents</A> |
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<A HREF="ug_alg_hypergraph.html">Next: Hypergraph Partitioning</A>
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| <A HREF="ug_alg_hsfc.html">Previous: Hilbert Space-Filling
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Curve Partitioning</A> | <a href="https://www.sandia.gov/general/privacy-security/index.html">Privacy and Security</a>]
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