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<H2><A NAME="SECTION00071000000000000000">
psb_cdall -- Allocates a communication descriptor</A>
</H2>

<P>
<PRE>
call psb_cdall(icontxt, desc_a, info,mg=mg,parts=parts)
call psb_cdall(icontxt, desc_a, info,vg=vg,flag=flag)
call psb_cdall(icontxt, desc_a, info,vl=vl)
call psb_cdall(icontxt, desc_a, info,nl=nl)
call psb_cdall(icontxt, desc_a, info,mg=mg,repl=.true.)
</PRE>

<P>
This subroutine initializes the communication descriptor associated
with an index space. Exactly one of the  optional arguments
<code>parts</code>, <code>vg</code>, <code>vl</code>, <code>nl</code>  or <code>repl</code> 
must be specified, thereby choosing
the specific initialization strategy:
<DL>
<DT><STRONG><B>On Entry </B></STRONG></DT>
<DD>
</DD>
<DT><STRONG>Type:</STRONG></DT>
<DD>Synchronous.
</DD>
<DT><STRONG>icontxt</STRONG></DT>
<DD>the communication context.
<BR>
Scope:<B>global</B>.
<BR>
Type:<B>required</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer value.
</DD>
<DT><STRONG>vg</STRONG></DT>
<DD>Data allocation: each index <!-- MATH
 $i\in \{1\dots mg\}$
 -->
<IMG
 WIDTH="98" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img82.png"
 ALT="$i\in \{1\dots mg\}$"> is allocated
  to process <IMG
 WIDTH="39" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img83.png"
 ALT="$vg(i)$">.
Scope:<B>global</B>.
<BR>
Type:<B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer array. 
</DD>
<DT><STRONG>flag</STRONG></DT>
<DD>Specifies whether entries in <IMG
 WIDTH="20" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
 SRC="img84.png"
 ALT="$vg$"> are zero- or one-based.
Scope:<B>global</B>.
<BR>
Type:<B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer value <IMG
 WIDTH="27" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
 SRC="img85.png"
 ALT="$0,1$">, default <IMG
 WIDTH="11" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
 SRC="img86.png"
 ALT="$0$">.

<P>
</DD>
<DT><STRONG>mg</STRONG></DT>
<DD>the (global) number of rows of the problem.
<BR>
Scope:<B>global</B>.
<BR>
Type:<B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer value. It is required if <code>parts</code> or
<code>repl</code> is specified. 
</DD>
<DT><STRONG>parts</STRONG></DT>
<DD>the subroutine that defines the partitioning scheme.
<BR>
Scope:<B>global</B>.
<BR>
Type:<B>required</B>.
<BR>
Specified as: a subroutine. 
</DD>
<DT><STRONG>vl</STRONG></DT>
<DD>Data allocation: the set of global indices belonging to the
  calling process. 
Scope:<B>local</B>.
<BR>
Type:<B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer array. 
</DD>
<DT><STRONG>nl</STRONG></DT>
<DD>Data allocation: in a generalized block-row distribution the
  number of indices belonging to the current process. 
Scope:<B>local</B>.
<BR>
Type:<B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer value. 
</DD>
<DT><STRONG>repl</STRONG></DT>
<DD>Data allocation: build a replicated index space (i.e. all
  processes own all indices).
Scope:<B>global</B>.
<BR>
Type:<B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: the logical value <code>.true.</code>
</DD>
</DL>

<P>
<DL>
<DT><STRONG><B>On Return</B></STRONG></DT>
<DD>
</DD>
<DT><STRONG>desc_a</STRONG></DT>
<DD>the communication descriptor.
<BR>
Scope:<B>local</B>.
<BR>
Type:<B>required</B>.
<BR>
Intent: <B>out</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>Exactly one of the optional arguments  <code>parts</code>, <code>vg</code>,
  <code>vl</code>, <code>nl</code>  must be specified, thereby choosing the
  initialization   strategy as follows:
<DL>
<DT><STRONG>parts</STRONG></DT>
<DD>In this case we have a subroutine specifying the mapping
  between global indices and process/local index pairs. If this
  optional argument   is specified, then it is mandatory to 
  specify the argument <code>mg</code> as well.  
  The subroutine must conform to the following interface: 
<PRE>
  interface 
     subroutine psb_parts(glob_index,mg,np,pv,nv)
       integer, intent (in)  :: glob_index,np,mg
       integer, intent (out) :: nv, pv(*)
     end subroutine psb_parts
  end interface
</PRE>
  The input arguments are:
  <DL>
<DT><STRONG>glob_index</STRONG></DT>
<DD>The global index to be mapped;
    
</DD>
<DT><STRONG>np</STRONG></DT>
<DD>The number of processes in the mapping;
    
</DD>
<DT><STRONG>mg</STRONG></DT>
<DD>The total number of global rows in the mapping;
  
</DD>
</DL>
  The output arguments are:
  <DL>
<DT><STRONG>nv</STRONG></DT>
<DD>The number of entries in <code>pv</code>;
    
</DD>
<DT><STRONG>pv</STRONG></DT>
<DD>A vector containint the indices of the processes to
    which the global index should be assigend; each entry must satisfy
    <!-- MATH
 $0\le pv(i) < np$
 -->
<IMG
 WIDTH="106" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img87.png"
 ALT="$0\le pv(i) &lt; np$">; if <IMG
 WIDTH="51" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
 SRC="img88.png"
 ALT="$nv&gt;1$"> we have an index assigned to multiple
    processes, i.e. we have an overlap among the subdomains.
  
</DD>
</DL>
</DD>
<DT><STRONG>vg</STRONG></DT>
<DD>In this case the association between an index and a process
  is specified via an integer vector; the size of the index space is
  equal to the size of <code>vg</code>, and each index <IMG
 WIDTH="10" HEIGHT="17" ALIGN="BOTTOM" BORDER="0"
 SRC="img3.png"
 ALT="$i$"> is assigned to
  the process <IMG
 WIDTH="39" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img83.png"
 ALT="$vg(i)$">. The vector <code>vg</code> must be identical on all
  calling processes; its entries may have the ranges <IMG
 WIDTH="94" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img89.png"
 ALT="$(0\dots np-1)$">
  or <IMG
 WIDTH="65" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img90.png"
 ALT="$(1\dots np)$"> according to the value of <code>flag</code>.
</DD>
<DT><STRONG>vl</STRONG></DT>
<DD>In this case we are specifying the list of indices assigned
  to the current process; thus, the global problem size <IMG
 WIDTH="27" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
 SRC="img91.png"
 ALT="$mg$"> is given by
  the sum of the sizes of the individual vectors <code>vl</code> specified
  on the calling processes. The subroutine will check that each entry
  in the global index space <IMG
 WIDTH="70" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img92.png"
 ALT="$(1\dots mg)$"> is specified exactly once. 
</DD>
<DT><STRONG>nl</STRONG></DT>
<DD>In this case we are implying a generalized row-block
  distribution in which each process <IMG
 WIDTH="13" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
 SRC="img93.png"
 ALT="$I$"> gets assigned a consecutive
  chunk of <IMG
 WIDTH="59" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
 SRC="img94.png"
 ALT="$N_I=nl$"> global indices.
</DD>
<DT><STRONG>repl</STRONG></DT>
<DD>In this case we are asking to replicate all indices on
  all processes. This is a special purpose data allocation that is
  useful in the construction of some multilevel preconditioners.
</DD>
</DL>
</LI>
<LI>On exit from this routine the descriptor is in the build state
</LI>
</OL>

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