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<H2><A NAME="SECTION00071000000000000000">
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psb_cdall -- Allocates a communication descriptor</A>
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</H2>
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<P>
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<PRE>
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call psb_cdall(icontxt, desc_a, info,mg=mg,parts=parts)
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call psb_cdall(icontxt, desc_a, info,vg=vg,flag=flag)
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call psb_cdall(icontxt, desc_a, info,vl=vl,nl=nl,globalcheck=.true.)
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call psb_cdall(icontxt, desc_a, info,nl=nl)
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call psb_cdall(icontxt, desc_a, info,mg=mg,repl=.true.)
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</PRE>
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<P>
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This subroutine initializes the communication descriptor associated
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with an index space. One of the optional arguments
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<code>parts</code>, <code>vg</code>, <code>vl</code>, <code>nl</code> or <code>repl</code>
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must be specified, thereby choosing
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the specific initialization strategy.
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<DL>
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<DT><STRONG><B>On Entry </B></STRONG></DT>
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<DD>
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</DD>
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<DT><STRONG>Type:</STRONG></DT>
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<DD>Synchronous.
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</DD>
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<DT><STRONG>icontxt</STRONG></DT>
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<DD>the communication context.
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<BR>
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Scope:<B>global</B>.
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<BR>
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Type:<B>required</B>.
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<BR>
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Intent: <B>in</B>.
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<BR>
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Specified as: an integer value.
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</DD>
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<DT><STRONG>vg</STRONG></DT>
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<DD>Data allocation: each index <!-- MATH
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$i\in \{1\dots mg\}$
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-->
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<IMG
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WIDTH="98" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
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SRC="img86.png"
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ALT="$i\in \{1\dots mg\}$"> is allocated
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to process <IMG
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WIDTH="39" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
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SRC="img87.png"
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ALT="$vg(i)$">.
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<BR>
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Scope:<B>global</B>.
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<BR>
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Type:<B>optional</B>.
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<BR>
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Intent: <B>in</B>.
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<BR>
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Specified as: an integer array.
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</DD>
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<DT><STRONG>flag</STRONG></DT>
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<DD>Specifies whether entries in <IMG
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WIDTH="20" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
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SRC="img88.png"
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ALT="$vg$"> are zero- or one-based.
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<BR>
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Scope:<B>global</B>.
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<BR>
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Type:<B>optional</B>.
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<BR>
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Intent: <B>in</B>.
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<BR>
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Specified as: an integer value <IMG
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WIDTH="27" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
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SRC="img89.png"
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ALT="$0,1$">, default <IMG
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WIDTH="12" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
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SRC="img90.png"
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ALT="$0$">.
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<P>
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</DD>
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<DT><STRONG>mg</STRONG></DT>
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<DD>the (global) number of rows of the problem.
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<BR>
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Scope:<B>global</B>.
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<BR>
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Type:<B>optional</B>.
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<BR>
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Intent: <B>in</B>.
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<BR>
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Specified as: an integer value. It is required if <code>parts</code> or
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<code>repl</code> is specified, it is optional if <code>vg</code> is specified.
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</DD>
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<DT><STRONG>parts</STRONG></DT>
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<DD>the subroutine that defines the partitioning scheme.
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<BR>
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Scope:<B>global</B>.
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<BR>
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Type:<B>required</B>.
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<BR>
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Specified as: a subroutine.
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</DD>
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<DT><STRONG>vl</STRONG></DT>
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<DD>Data allocation: the set of global indices belonging to the
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calling process.
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<BR>
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Scope:<B>local</B>.
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<BR>
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Type:<B>optional</B>.
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<BR>
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Intent: <B>in</B>.
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<BR>
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Specified as: an integer array.
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</DD>
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<DT><STRONG>nl</STRONG></DT>
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<DD>Data allocation: in a generalized block-row distribution the
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number of indices belonging to the current process.
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<BR>
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Scope:<B>local</B>.
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<BR>
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Type:<B>optional</B>.
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<BR>
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Intent: <B>in</B>.
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<BR>
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Specified as: an integer value. May be specified together with
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<code>vl</code>.
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</DD>
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<DT><STRONG>repl</STRONG></DT>
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<DD>Data allocation: build a replicated index space (i.e. all
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processes own all indices).
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<BR>
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Scope:<B>global</B>.
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<BR>
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Type:<B>optional</B>.
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<BR>
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Intent: <B>in</B>.
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<BR>
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Specified as: the logical value <code>.true.</code>
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</DD>
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<DT><STRONG>globalcheck</STRONG></DT>
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<DD>Data allocation: do global checks on the local
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index lists <code>vl</code>
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<BR>
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Scope:<B>global</B>.
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<BR>
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Type:<B>optional</B>.
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<BR>
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Intent: <B>in</B>.
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<BR>
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Specified as: a logical value, default: <code>.true.</code>
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</DD>
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</DL>
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<P>
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<DL>
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<DT><STRONG><B>On Return</B></STRONG></DT>
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<DD>
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</DD>
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<DT><STRONG>desc_a</STRONG></DT>
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<DD>the communication descriptor.
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<BR>
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Scope:<B>local</B>.
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<BR>
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Type:<B>required</B>.
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<BR>
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Intent: <B>out</B>.
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<BR>
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Specified as: a structured data of type descdata<TT>psb_desc_type</TT>.
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</DD>
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<DT><STRONG>info</STRONG></DT>
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<DD>Error code.
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<BR>
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Scope: <B>local</B>
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<BR>
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Type: <B>required</B>
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<BR>
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Intent: <B>out</B>.
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<BR>
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An integer value; 0 means no error has been detected.
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</DD>
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</DL>
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<P>
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<FONT SIZE="+1"><B>Notes</B></FONT>
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<OL>
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<LI>One of the optional arguments <code>parts</code>, <code>vg</code>,
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<code>vl</code>, <code>nl</code> or <code>repl</code> must be specified, thereby choosing the
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initialization strategy as follows:
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<DL>
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<DT><STRONG>parts</STRONG></DT>
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<DD>In this case we have a subroutine specifying the mapping
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between global indices and process/local index pairs. If this
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optional argument is specified, then it is mandatory to
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specify the argument <code>mg</code> as well.
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The subroutine must conform to the following interface:
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<PRE>
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interface
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subroutine psb_parts(glob_index,mg,np,pv,nv)
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integer, intent (in) :: glob_index,np,mg
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integer, intent (out) :: nv, pv(*)
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end subroutine psb_parts
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end interface
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</PRE>
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The input arguments are:
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<DL>
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<DT><STRONG>glob_index</STRONG></DT>
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<DD>The global index to be mapped;
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</DD>
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<DT><STRONG>np</STRONG></DT>
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<DD>The number of processes in the mapping;
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</DD>
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<DT><STRONG>mg</STRONG></DT>
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<DD>The total number of global rows in the mapping;
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</DD>
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</DL>
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The output arguments are:
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<DL>
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<DT><STRONG>nv</STRONG></DT>
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<DD>The number of entries in <code>pv</code>;
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</DD>
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<DT><STRONG>pv</STRONG></DT>
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<DD>A vector containing the indices of the processes to
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which the global index should be assigend; each entry must satisfy
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<!-- MATH
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$0\le pv(i) < np$
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-->
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<IMG
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WIDTH="107" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
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SRC="img91.png"
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ALT="$0\le pv(i) < np$">; if <IMG
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WIDTH="51" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
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SRC="img92.png"
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ALT="$nv>1$"> we have an index assigned to multiple
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processes, i.e. we have an overlap among the subdomains.
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</DD>
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</DL>
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</DD>
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<DT><STRONG>vg</STRONG></DT>
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<DD>In this case the association between an index and a process
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is specified via an integer vector; the size of the index space is
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equal to the size of <code>vg</code>, and each index <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="$i$"> is assigned to
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the process <IMG
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WIDTH="39" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
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SRC="img87.png"
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ALT="$vg(i)$">. The vector <code>vg</code> must be identical on all
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calling processes; its entries may have the ranges <IMG
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WIDTH="94" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
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SRC="img93.png"
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ALT="$(0\dots np-1)$">
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or <IMG
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WIDTH="65" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
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SRC="img94.png"
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ALT="$(1\dots np)$"> according to the value of <code>flag</code>. Optionally,
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the user may specify <code>mg</code>, in
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which case the portion <code>vg(1:mg)</code> is used.
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</DD>
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<DT><STRONG>vl</STRONG></DT>
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<DD>In this case we are specifying the list of indices assigned
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to the current process; thus, the global problem size <IMG
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WIDTH="27" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
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SRC="img95.png"
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ALT="$mg$"> is given by
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the range of the aggregate of the individual vectors <code>vl</code> specified
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in the calling processes. If <code>globalcheck=.true.</code>
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the subroutine will check how many times each entry in the global
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index space <IMG
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WIDTH="70" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
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SRC="img96.png"
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ALT="$(1\dots mg)$"> is specified in the input lists
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<code>vl</code>, thus allowing for the presence of overlap in the input,
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and checking for ``orphan'' indices.
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If <code>globalcheck=.false.</code>, the subroutine will not check for
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overlap, and may be substantially faster, but
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the user is implicitly guaranteeing that there are neither orphan
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nor overlap indices. Optionally, the user may specify <code>nl</code>, in
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which case the portion <code>vl(1:nl)</code> is used.
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</DD>
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<DT><STRONG>nl</STRONG></DT>
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<DD>In this case we are implying a generalized row-block
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distribution in which each process <IMG
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WIDTH="13" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
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SRC="img97.png"
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ALT="$I$"> gets assigned a consecutive
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chunk of <IMG
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WIDTH="60" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
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SRC="img98.png"
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ALT="$N_I=nl$"> global indices.
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</DD>
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<DT><STRONG>repl</STRONG></DT>
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<DD>In this case we are asking to replicate all indices on
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all processes. This is a special purpose data allocation that is
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useful in the construction of some multilevel preconditioners.
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</DD>
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</DL>
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</LI>
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<LI>On exit from this routine the descriptor is in the build state
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</LI>
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</OL>
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<FONT SIZE="+1"><B>Notes</B></FONT>
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<OL>
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<LI>On exit from this routine the descriptor is in the build
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state.
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</LI>
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<LI>Calling the routine with <code>vg</code> or <code>parts</code> implies that
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every process will scan the entire index space to figure out the
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local indices.
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</LI>
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<LI>Overlapped indices are possible with both <code>parts</code> and
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<code>vl</code> invocations.
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</LI>
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<LI>When the subroutine is invoked with <code>vl</code> in
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conjunction with <code>globalcheck=.true.</code>, it will perform a scan
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of the index space to search for overlap or orphan indices.
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</LI>
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<LI>When the subroutine is invoked with <code>vl</code> in
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conjunction with <code>globalcheck=.false.</code>, no index space scan
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will take place. Thus it is the responsibility of the user to make
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sure that the indices specified in <code>vl</code> have neither orphans nor
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overlaps; if this assumption fails, results will be
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unpredictable.
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</LI>
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<LI>Orphan and overlap indices are
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impossible by construction when the subroutine is invoked with
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<code>nl</code> (alone), or <code>vg</code>.
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</LI>
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</OL>
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