<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <!--Converted with LaTeX2HTML 2012 (1.2) original version by: Nikos Drakos, CBLU, University of Leeds * revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan * with significant contributions from: Jens Lippmann, Marek Rouchal, Martin Wilck and others --> <HTML> <HEAD> <TITLE>Descriptor data structure</TITLE> <META NAME="description" CONTENT="Descriptor data structure"> <META NAME="keywords" CONTENT="userhtml"> <META NAME="resource-type" CONTENT="document"> <META NAME="distribution" CONTENT="global"> <META NAME="Generator" CONTENT="LaTeX2HTML v2012"> <META HTTP-EQUIV="Content-Style-Type" CONTENT="text/css"> <LINK REL="STYLESHEET" HREF="userhtml.css"> <LINK REL="next" HREF="node22.html"> <LINK REL="previous" HREF="node9.html"> <LINK REL="up" HREF="node9.html"> <LINK REL="next" HREF="node11.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html344" HREF="node11.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next.png"></A> <A NAME="tex2html340" HREF="node9.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up.png"></A> <A NAME="tex2html334" HREF="node9.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="prev.png"></A> <A NAME="tex2html342" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="contents.png"></A> <BR> <B> Next:</B> <A NAME="tex2html345" HREF="node11.html">Descriptor Methods</A> <B> Up:</B> <A NAME="tex2html341" HREF="node9.html">Data Structures and Classes</A> <B> Previous:</B> <A NAME="tex2html335" HREF="node9.html">Data Structures and Classes</A> <B> <A NAME="tex2html343" HREF="node1.html">Contents</A></B> <BR> <BR> <!--End of Navigation Panel--> <H2><A NAME="SECTION00041000000000000000"></A> <A NAME="sec:desc"></A> <BR> Descriptor data structure </H2> All the general matrix informations and elements to be exchanged among processes are stored within a data structure of the type descdata<TT>psb_desc_type</TT>. Every structure of this type is associated with a discretization pattern and enables data communications and other operations that are necessary for implementing the various algorithms of interest to us. <P> The data structure itself <code>psb_desc_type</code> can be treated as an opaque object handled via the tools routines of Sec. <A HREF="node68.html#sec:toolsrout">6</A> or the query routines detailed below; nevertheless we include here a description for the curious reader. <P> First we describe the <code>psb_indx_map</code> type. This is a data structure that keeps track of a certain number of basic issues such as: <UL> <LI>The value of the communication/MPI context; </LI> <LI>The number of indices in the index space, i.e. global number of rows and columns of a sparse matrix; </LI> <LI>The local set of indices, including: <UL> <LI>The number of local indices (and local rows); </LI> <LI>The number of halo indices (and therefore local columns); </LI> <LI>The global indices corresponding to the local ones. </LI> </UL> </LI> </UL> There are many different schemes for storing these data; therefore there are a number of types extending the base one, and the descriptor structure holds a polymorphic object whose dynamic type can be any of the extended types. The methods associated with this data type answer the following queries: <UL> <LI>For a given set of local indices, find the corresponding indices in the global numbering; </LI> <LI>For a given set of global indices, find the corresponding indices in the local numbering, if any, or return an invalid </LI> <LI>Add a global index to the set of halo indices; </LI> <LI>Find the process owner of each member of a set of global indices. </LI> </UL> All methods but the last are purely local; the last method potentially requires communication among processes, and thus is a synchronous method. The choice of a specific dynamic type for the index map is made at the time the descriptor is initially allocated, according to the mode of initialization (see also <A HREF="node68.html#sec:toolsrout">6</A>). <P> The descriptor contents are as follows: <DL> <DT><STRONG><B>indxmap</B></STRONG></DT> <DD>A polymorphic variable of a type that is any extension of the indx_map type described above. <BR></DD> <DT><STRONG><B>halo_index</B></STRONG></DT> <DD>A list of the halo and boundary elements for the current process to be exchanged with other processes; for each processes with which it is necessary to communicate: <OL> <LI>Process identifier; </LI> <LI>Number of points to be received; </LI> <LI>Indices of points to be received; </LI> <LI>Number of points to be sent; </LI> <LI>Indices of points to be sent; </LI> </OL> The list may contain an arbitrary number of groups; its end is marked by a -1. <BR> Specified as: an allocatable integer array of rank one. </DD> <DT><STRONG><B>ext_index</B></STRONG></DT> <DD>A list of element indices to be exchanged to implement the mapping between a base descriptor and a descriptor with overlap. </DD> <DT><STRONG><B>ovrlap_index</B></STRONG></DT> <DD>A list of the overlap elements for the current process, organized in groups like the previous vector: <OL> <LI>Process identifier; </LI> <LI>Number of points to be received; </LI> <LI>Indices of points to be received; </LI> <LI>Number of points to be sent; </LI> <LI>Indices of points to be sent; </LI> </OL> The list may contain an arbitrary number of groups; its end is marked by a -1. <BR> Specified as: an allocatable integer array of rank one. </DD> <DT><STRONG><B>ovr_mst_idx</B></STRONG></DT> <DD>A list to retrieve the value of each overlap element from the respective master process. <BR> Specified as: an allocatable integer array of rank one. </DD> <DT><STRONG><B>ovrlap_elem</B></STRONG></DT> <DD>For all overlap points belonging to th ecurrent process: <OL> <LI>Overlap point index; </LI> <LI>Number of processes sharing that overlap points; </LI> <LI>Index of a ``master'' process: </LI> </OL> Specified as: an allocatable integer array of rank two. </DD> <DT><STRONG><B>bnd_elem</B></STRONG></DT> <DD>A list of all boundary points, i.e. points that have a connection with other processes. </DD> </DL> The Fortran 2003 declaration for <code>psb_desc_type</code> structures is as follows: <DIV ALIGN="CENTER"><A NAME="fig:desctype"></A><A NAME="878"></A> <TABLE> <CAPTION ALIGN="BOTTOM"><STRONG>Figure 3:</STRONG> The PSBLAS defined data type that contains the communication descriptor.</CAPTION> <TR><TD> <DIV ALIGN="CENTER"> </DIV><TABLE WIDTH="90%"> <TR><TD> <PRE> type psb_desc_type class(psb_indx_map), allocatable :: indxmap integer, allocatable :: halo_index(:) integer, allocatable :: ext_index(:) integer, allocatable :: ovrlap_index(:) integer, allocatable :: ovrlap_elem(:,:) integer, allocatable :: ovr_mst_idx(:) integer, allocatable :: bnd_elem(:) end type psb_desc_type </PRE></TD></TR> </TABLE> <DIV ALIGN="CENTER"> </DIV></TD></TR> </TABLE> </DIV> <P> A communication descriptor associated with a sparse matrix has a state, which can take the following values: <DL> <DT><STRONG>Build:</STRONG></DT> <DD>State entered after the first allocation, and before the first assembly; in this state it is possible to add communication requirements among different processes. </DD> <DT><STRONG>Assembled:</STRONG></DT> <DD>State entered after the assembly; computations using the associated sparse matrix, such as matrix-vector products, are only possible in this state. </DD> </DL> <P> <BR><HR> <!--Table of Child-Links--> <A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A> <UL> <LI><A NAME="tex2html346" HREF="node11.html">Descriptor Methods</A> <LI><A NAME="tex2html347" HREF="node12.html">get_local_rows -- Get number of local rows</A> <LI><A NAME="tex2html348" HREF="node13.html">get_local_cols -- Get number of local cols</A> <LI><A NAME="tex2html349" HREF="node14.html">get_global_rows -- Get number of global rows</A> <LI><A NAME="tex2html350" HREF="node15.html">get_global_cols -- Get number of global cols</A> <LI><A NAME="tex2html351" HREF="node16.html">get_global_indices -- Get vector of global indices</A> <LI><A NAME="tex2html352" HREF="node17.html">get_context -- Get communication context</A> <LI><A NAME="tex2html353" HREF="node18.html">Clone -- clone current object</A> <LI><A NAME="tex2html354" HREF="node19.html">psb_cd_get_large_threshold -- Get threshold for index mapping switch</A> <LI><A NAME="tex2html355" HREF="node20.html">psb_cd_set_large_threshold -- Set threshold for index mapping switch</A> <LI><A NAME="tex2html356" HREF="node21.html">Named Constants</A> </UL> <!--End of Table of Child-Links--> <HR> <!--Navigation Panel--> <A NAME="tex2html344" HREF="node11.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next.png"></A> <A NAME="tex2html340" HREF="node9.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up.png"></A> <A NAME="tex2html334" HREF="node9.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="prev.png"></A> <A NAME="tex2html342" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="contents.png"></A> <BR> <B> Next:</B> <A NAME="tex2html345" HREF="node11.html">Descriptor Methods</A> <B> Up:</B> <A NAME="tex2html341" HREF="node9.html">Data Structures and Classes</A> <B> Previous:</B> <A NAME="tex2html335" HREF="node9.html">Data Structures and Classes</A> <B> <A NAME="tex2html343" HREF="node1.html">Contents</A></B> <!--End of Navigation Panel--> </BODY> </HTML>