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<H2><A NAME="SECTION00081000000000000000">
psb_init -- Initializes PSBLAS parallel environment</A>
</H2>

<P>
<PRE>
call psb_init(icontxt, np, basectxt, ids)
</PRE>

<P>
This subroutine initializes the PSBLAS parallel environment, defining
a virtual parallel machine.
<DL>
<DT><STRONG>Type:</STRONG></DT>
<DD>Synchronous.
</DD>
<DT><STRONG><B>On Entry </B></STRONG></DT>
<DD>
</DD>
<DT><STRONG>np</STRONG></DT>
<DD>Number of processes in the PSBLAS virtual parallel machine.
<BR>
Scope: <B>global</B>.
<BR>
Type: <B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer value.  Default: use all available processes.
</DD>
<DT><STRONG>basectxt</STRONG></DT>
<DD>the initial communication context. The new context
  will be defined from the processes participating in the initial one.
<BR>
Scope: <B>global</B>.
<BR>
Type: <B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer value.  Default: use MPI_COMM_WORLD.
</DD>
<DT><STRONG>ids</STRONG></DT>
<DD>Identities of the processes to use for the new context; the
  argument is ignored when <code>np</code> is not specified. This allows the
  processes in the new environment to be in an order different from the
  original one.
<BR>
Scope: <B>global</B>.
<BR>
Type: <B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: an integer array.  Default: use the indices <IMG
 WIDTH="94" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
 SRC="img89.png"
 ALT="$(0\dots np-1)$">.  
</DD>
</DL>

<P>
<DL>
<DT><STRONG><B>On Return</B></STRONG></DT>
<DD>
</DD>
<DT><STRONG>icontxt</STRONG></DT>
<DD>the communication context identifying the virtual
  parallel machine. Note that this is always a duplicate of
  <code>basectxt</code>, so that library communications are completely
  separated from other communication operations.
<BR>
Scope: <B>global</B>.
<BR>
Type: <B>required</B>.
<BR>
Intent: <B>out</B>.
<BR>
Specified as: an integer variable.
</DD>
</DL>

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

<OL>
<LI>A call to this routine must precede any other PSBLAS call. 
</LI>
<LI>It is an error to specify a value for <IMG
 WIDTH="22" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
 SRC="img117.png"
 ALT="$np$"> greater than the
  number of processes available in the underlying base parallel
  environment. 
</LI>
</OL>

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