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<H2><A NAME="SECTION00076000000000000000">
psb_cdbldext -- Build an extended  communication
  descriptor</A>
</H2>

<P>
<PRE>
call psb_cdbldext(a,desc_a,nl,desc_out, info, extype)
</PRE>

<P>
This subroutine builds an extended communication descriptor, based on
the input descriptor <code>desc_a</code> and on the stencil specified
through the input sparse matrix <code>a</code>. 
<DL>
<DT><STRONG>Type:</STRONG></DT>
<DD>Synchronous.
</DD>
<DT><STRONG><B>On Entry</B></STRONG></DT>
<DD>
</DD>
<DT><STRONG>a</STRONG></DT>
<DD>A sparse matrix
Scope:<B>local</B>.
<BR>
Type:<B>required</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: a structured data type.
</DD>
<DT><STRONG>desc_a</STRONG></DT>
<DD>the communication descriptor.
<BR>
Scope:<B>local</B>.
<BR>
Type:<B>required</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: a structured data of type spdata<TT>psb_Tspmat_type</TT>.
</DD>
<DT><STRONG>nl</STRONG></DT>
<DD>the number of additional layers desired.
<BR>
Scope:<B>global</B>.
<BR>
Type:<B>required</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer value <IMG
 WIDTH="47" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
 SRC="img99.png"
 ALT="$nl\ge 0$">. 
</DD>
<DT><STRONG>extype</STRONG></DT>
<DD>the kind of estension required.
<BR>
Scope:<B>global</B>.
<BR>
Type:<B>optional </B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer value
<code>psb_ovt_xhal_</code>, <code>psb_ovt_asov_</code>, default: <code>psb_ovt_xhal_</code>

<P>
</DD>
</DL>

<P>
<DL>
<DT><STRONG><B>On Return</B></STRONG></DT>
<DD>
</DD>
<DT><STRONG>desc_out</STRONG></DT>
<DD>the extended communication descriptor.
<BR>
Scope:<B>local</B>.
<BR>
Type:<B>required</B>.
<BR>
Intent: <B>inout</B>.
<BR>
Specified as: a structured data of type descdata<TT>psb_desc_type</TT>.
</DD>
<DT><STRONG>info</STRONG></DT>
<DD>Error code.
<BR>
Scope: <B>local</B> 
<BR>
Type: <B>required</B> 
<BR>
Intent: <B>out</B>.
<BR>
An integer value; 0 means no error has been detected. 
</DD>
</DL>

<P>
<FONT SIZE="+1"><B>Notes</B></FONT>

<OL>
<LI>Specifying <code>psb_ovt_xhal_</code> for the <code>extype</code> argument
  the user will obtain a descriptor for a domain partition in which
  the additional layers are fetched as part of an (extended) halo;
  however the index-to-process mapping is identical to that of the
  base descriptor;
</LI>
<LI>Specifying <code>psb_ovt_asov_</code> for the <code>extype</code> argument
  the user will obtain a descriptor with an overlapped decomposition:
  the additional layer is aggregated to  the local subdomain (and thus
  is an overlap), and a new halo extending beyond the last additional
  layer is formed. 
</LI>
</OL>

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