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original version by: Nikos Drakos, CBLU, University of Leeds
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* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan
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<B> Next:</B> <A NAME="tex2html278"
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HREF="node9.html">Data Structures and Classes</A>
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HREF="node7.html">User-defined index mappings</A>
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<H2><A NAME="SECTION00034000000000000000">
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Programming model</A>
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</H2>
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<P>
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The PSBLAS librarary is based on the Single Program Multiple Data
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(SPMD) programming model: each process participating in the
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computation performs the same actions on a chunk of data. Parallelism
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is thus data-driven.
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<P>
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Because of this structure, many subroutines coordinate their action
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across the various processes, thus providing an implicit
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synchronization point, and therefore <I>must</I> be
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called simultaneously by all processes participating in the
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computation. This is certainly true for the data allocation and
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assembly routines, for all the computational routines and for some of
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the tools routines.
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<P>
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However there are many cases where no synchronization, and indeed no
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communication among processes, is implied; for instance, all the routines in
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sec. <A HREF="node9.html#sec:datastruct">3</A> are only acting on the local data structures,
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and thus may be called independently. The most important case is that
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of the coefficient insertion routines: since the number of
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coefficients in the sparse and dense matrices varies among the
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processors, and since the user is free to choose an arbitrary order in
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builiding the matrix entries, these routines cannot imply a
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synchronization.
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<P>
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Throughout this user's guide each subroutine will be clearly indicated
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as:
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<DL>
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<DT><STRONG>Synchronous:</STRONG></DT>
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<DD>must be called simultaneously by all the
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processes in the relevant communication context;
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</DD>
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<DT><STRONG>Asynchronous:</STRONG></DT>
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<DD>may be called in a totally independent manner.
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</DD>
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</DL>
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<B> Next:</B> <A NAME="tex2html278"
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HREF="node9.html">Data Structures and Classes</A>
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<B> Up:</B> <A NAME="tex2html274"
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HREF="node3.html">General overview</A>
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<B> Previous:</B> <A NAME="tex2html270"
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HREF="node7.html">User-defined index mappings</A>
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HREF="node1.html">Contents</A></B>
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