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Document DESC%CNV method and MOLD arguments to CDASB and PREC%BUILD
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<!--Converted with LaTeX2HTML 2012 (1.2)
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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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* with significant contributions from:
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Jens Lippmann, Marek Rouchal, Martin Wilck and others -->
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<!--Converted with LaTeX2HTML 2017.2 (Released Jan 23, 2017) -->
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<HTML>
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<HEAD>
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<TITLE>Application structure</TITLE>
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@@ -13,7 +9,7 @@ original version by: Nikos Drakos, CBLU, University of Leeds
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@@ -25,30 +21,31 @@ original version by: Nikos Drakos, CBLU, University of Leeds
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<H2><A NAME="SECTION00033000000000000000"></A>
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@@ -63,10 +60,10 @@ library objects are created and exist with reference to a discretized
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space to which there corresponds an index space and a matrix sparsity
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pattern. As an example, consider a cell-centered finite-volume
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discretization of the Navier-Stokes equations on a simulation domain;
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the index space <IMG
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the index space <SPAN CLASS="MATH"><IMG
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WIDTH="46" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
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SRC="img15.png"
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ALT="$1\dots n$"> is isomorphic to the set of cell centers,
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ALT="$1\dots n$"></SPAN> is isomorphic to the set of cell centers,
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whereas the pattern of the associated linear system matrix is
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isomorphic to the adjacency graph imposed on the discretization mesh
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by the discretization stencil.
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@@ -74,70 +71,70 @@ by the discretization stencil.
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<P>
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Thus the first order of business is to establish an index space, and
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this is done with a call to <code>psb_cdall</code> in which we specify the
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size of the index space <IMG
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size of the index space <SPAN CLASS="MATH"><IMG
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WIDTH="13" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
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SRC="img16.png"
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ALT="$n$"> and the allocation of the elements of the
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ALT="$n$"></SPAN> and the allocation of the elements of the
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index space to the various processes making up the MPI (virtual)
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parallel machine.
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<P>
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The index space is partitioned among processes, and this creates a
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mapping from the ``global'' numbering <IMG
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mapping from the “global” numbering <SPAN CLASS="MATH"><IMG
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WIDTH="46" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
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SRC="img15.png"
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ALT="$1\dots n$"> to a numbering
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``local'' to each process; each process <IMG
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ALT="$1\dots n$"></SPAN> to a numbering
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“local” to each process; each process <SPAN CLASS="MATH"><IMG
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WIDTH="9" HEIGHT="17" ALIGN="BOTTOM" BORDER="0"
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SRC="img4.png"
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ALT="$i$"> will own a certain subset
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ALT="$i$"></SPAN> will own a certain subset
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<!-- MATH
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$1\dots n_{\hbox{row}_i}$
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-->
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<IMG
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<SPAN CLASS="MATH"><IMG
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WIDTH="77" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
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SRC="img17.png"
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ALT="$1\dots n_{\hbox{row}_i}$">, each element of which corresponds to a certain
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element of <IMG
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ALT="$1\dots n_{\hbox{row}_i}$"></SPAN>, each element of which corresponds to a certain
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element of <SPAN CLASS="MATH"><IMG
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WIDTH="46" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
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SRC="img15.png"
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ALT="$1\dots n$">. The user does not set explicitly this mapping;
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ALT="$1\dots n$"></SPAN>. The user does not set explicitly this mapping;
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when the application needs to indicate to which element of the index
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space a certain item is related, such as the row and column index of a
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matrix coefficient, it does so in the ``global'' numbering, and the
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library will translate into the appropriate ``local'' numbering.
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matrix coefficient, it does so in the “global” numbering, and the
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library will translate into the appropriate “local” numbering.
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<P>
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For a given index space <IMG
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For a given index space <SPAN CLASS="MATH"><IMG
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WIDTH="46" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
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SRC="img15.png"
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ALT="$1\dots n$"> there are many possible associated
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ALT="$1\dots n$"></SPAN> there are many possible associated
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topologies, i.e. many different discretization stencils; thus the
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description of the index space is not completed until the user has
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defined a sparsity pattern, either explicitly through <code>psb_cdins</code>
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or implicitly through <code>psb_spins</code>. The descriptor is finalized
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with a call to <code>psb_cdasb</code> and a sparse matrix with a call to
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<code>psb_spasb</code>. After <code>psb_cdasb</code> each process <IMG
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<code>psb_spasb</code>. After <code>psb_cdasb</code> each process <SPAN CLASS="MATH"><IMG
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WIDTH="9" HEIGHT="17" ALIGN="BOTTOM" BORDER="0"
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SRC="img4.png"
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ALT="$i$"> will have
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defined a set of ``halo'' (or ``ghost'') indices
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ALT="$i$"></SPAN> will have
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defined a set of “halo” (or “ghost”) indices
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<!-- MATH
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$n_{\hbox{row}_i}+1\dots n_{\hbox{col}_i}$
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-->
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<IMG
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<SPAN CLASS="MATH"><IMG
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WIDTH="130" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
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SRC="img18.png"
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ALT="$n_{\hbox{row}_i}+1\dots n_{\hbox{col}_i}$">, denoting elements of the index
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space that are <I>not</I> assigned to process <IMG
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ALT="$n_{\hbox{row}_i}+1\dots n_{\hbox{col}_i}$"></SPAN>, denoting elements of the index
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space that are <SPAN CLASS="textit">not</SPAN> assigned to process <SPAN CLASS="MATH"><IMG
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WIDTH="9" HEIGHT="17" ALIGN="BOTTOM" BORDER="0"
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SRC="img4.png"
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ALT="$i$">; however the
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ALT="$i$"></SPAN>; however the
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variables associated with them are needed to complete computations
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associated with the sparse matrix <IMG
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associated with the sparse matrix <SPAN CLASS="MATH"><IMG
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WIDTH="16" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
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SRC="img1.png"
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ALT="$A$">, and thus they have to be
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ALT="$A$"></SPAN>, and thus they have to be
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fetched from (neighbouring) processes. The descriptor of the index
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space is built exactly for the purpose of properly sequencing the
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communication steps required to achieve this objective.
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@@ -171,7 +168,7 @@ follows:
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</LI>
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<LI>Choose the preconditioner to be used with <code>prec%init</code> and
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build it with <code>prec%build</code><A NAME="tex2html5"
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HREF="footnode.html#foot278"><SUP>3</SUP></A>.
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HREF="footnode.html#foot278"><SUP><SPAN CLASS="arabic">3</SPAN></SUP></A>.
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</LI>
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<LI>Call the iterative method of choice, e.g. <code>psb_bicgstab</code>
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</LI>
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@@ -249,34 +246,35 @@ from optimal.
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<!--Table of Child-Links-->
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<LI><A NAME="tex2html266"
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<UL CLASS="ChildLinks">
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<LI><A NAME="tex2html267"
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HREF="node7.html">User-defined index mappings</A>
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