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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,[mg=mg,flag=flag])
call psb_cdall(icontxt, desc_a, info,vl=vl,[nl=nl,globalcheck=.true.,lidx=lidx])
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. 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="$vg(i)$">.
<BR>
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.
<BR>
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="12" HEIGHT="14" 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, it is optional if <code>vg</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 
  <IMG
 WIDTH="66" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img87.png"
 ALT="$vl(1:nl)$"> belonging to the calling process. 
<BR>
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. 
<BR>
Scope:<B>local</B>.
<BR>
Type:<B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer value. May be specified together with
<code>vl</code>. 
</DD>
<DT><STRONG>repl</STRONG></DT>
<DD>Data allocation: build a replicated index space 
  (i.e. all processes own all indices).
<BR>
Scope:<B>global</B>.
<BR>
Type:<B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: the logical value <code>.true.</code>
</DD>
<DT><STRONG>globalcheck</STRONG></DT>
<DD>Data allocation: do global checks on the local
  index lists <code>vl</code>
<BR>
Scope:<B>global</B>.
<BR>
Type:<B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: a logical value, default: <code>.true.</code>
</DD>
<DT><STRONG>lidx</STRONG></DT>
<DD>Data allocation: the set of local  indices 
  <IMG
 WIDTH="80" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img88.png"
 ALT="$lidx(1:nl)$"> to be assigned to the global indices <IMG
 WIDTH="18" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
 SRC="img89.png"
 ALT="$vl$">. 
<BR>
Scope:<B>local</B>.
<BR>
Type:<B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer array. 
</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>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
  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 containing 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="img90.png"
 ALT="$0\le pv(i) &lt; np$">; if <IMG
 WIDTH="51" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
 SRC="img91.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  <code>vg(1:mg)</code>; 
  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 assigned to 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="93" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img92.png"
 ALT="$(0\dots np-1)$">
  or <IMG
 WIDTH="66" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img93.png"
 ALT="$(1\dots np)$"> according to the value of <code>flag</code>.  
  The size <IMG
 WIDTH="26" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
 SRC="img94.png"
 ALT="$mg$"> may be  specified via the optional argument <code>mg</code>;
  the default is to use the entire vector <code>vg</code>, thus having
  <code>mg=size(vg)</code>. 
</DD>
<DT><STRONG>vl</STRONG></DT>
<DD>In this case we are specifying the list of indices
  <code>vl(1:nl)</code> assigned   to the current process; thus, the global
  problem size <IMG
 WIDTH="26" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
 SRC="img94.png"
 ALT="$mg$"> is given by 
  the range of the aggregate of the individual vectors <code>vl</code> specified
  in the calling processes. The size may be specified via the optional
  argument <code>nl</code>; the default is to use the entire vector
  <code>vl</code>, thus having   <code>nl=size(vl)</code>.  
  If <code>globalcheck=.true.</code>   the subroutine will check how many
  times  each entry in the global   index   space <IMG
 WIDTH="71" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img95.png"
 ALT="$(1\dots mg)$"> is
  specified in the input lists   <code>vl</code>, thus allowing for the
  presence of overlap in the input,   and checking for ``orphan''
  indices.    If <code>globalcheck=.false.</code>, the subroutine will not
  check for   overlap, and may be significantly faster, but   the user
  is implicitly guaranteeing that there are neither orphan   nor
  overlap indices.  
</DD>
<DT><STRONG>lidx</STRONG></DT>
<DD>The optional argument <code>lidx</code> is available for
  those cases in which the user has already established a
  global-to-local mapping; if it is specified, each  index in
  <code>vl(i)</code> will be mapped to the corresponding local index
  <code>lidx(i)</code>. When specifying the argument <code>lidx</code> the user
  would also likely employ <code>lidx</code> in calls to <code>psb_cdins</code>
  and <code>local</code> in calls to <code>psb_spins</code> and <code>psb_geins</code>;
  see also sec.&nbsp;<A HREF="node7.html#sec:usermaps">2.3.1</A>. 
</DD>
<DT><STRONG>nl</STRONG></DT>
<DD>If this argument is specified alone (i.e. without <code>vl</code>)
  the  result is  a generalized row-block   distribution in which each
  process <IMG
 WIDTH="12" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
 SRC="img96.png"
 ALT="$I$"> gets assigned a consecutive   chunk of <IMG
 WIDTH="60" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
 SRC="img97.png"
 ALT="$N_I=nl$"> global
  indices. 
</DD>
<DT><STRONG>repl</STRONG></DT>
<DD>This arguments specifies 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>
<LI>Calling the routine with <code>vg</code> or <code>parts</code> implies that
  every process will scan the entire index space to figure out the
  local indices.
</LI>
<LI>Overlapped indices are possible with both <code>parts</code> and
  <code>vl</code> invocations.
</LI>
<LI>When the subroutine is invoked with <code>vl</code> in
  conjunction with <code>globalcheck=.true.</code>, it will perform a scan
  of the index   space to search for overlap or orphan indices.
</LI>
<LI>When the subroutine is invoked with <code>vl</code> in
  conjunction with <code>globalcheck=.false.</code>, no index space scan
  will take place. Thus it is the responsibility of the user to make
  sure that the indices specified in <code>vl</code> have neither orphans nor
  overlaps; if this assumption fails, results will be 
  unpredictable. 
</LI>
<LI>Orphan and overlap indices are
  impossible by construction when the subroutine is invoked with
  <code>nl</code> (alone),  or <code>vg</code>.
</LI>
</OL>

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