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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML3.2 EN">
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<TITLE>PetscSubcommCreate</TITLE>
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<A NAME="PetscSubcommCreate"><H1>PetscSubcommCreate</H1></A>
Create a <A HREF="../Sys/PetscSubcomm.html#PetscSubcomm">PetscSubcomm</A> context.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petsc.h"
#include "petscsys.h"
PetscErrorCode PETSCMAT_DLLEXPORT PetscSubcommCreate(MPI_Comm comm,PetscInt nsubcomm,PetscSubcomm *psubcomm)
</PRE>
Collective on <A HREF="../Sys/MPI_Comm.html#MPI_Comm">MPI_Comm</A>
<P>
<H3><FONT COLOR="#CC3333">Input Parameter</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B><A HREF="../Sys/comm.html#comm">comm</A> </B></TD><TD>- MPI communicator
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>nsubcomm </B></TD><TD>- the number of subcommunicators to be created
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Output Parameter</FONT></H3>
<DT><B>psubcomm </B> -location to store the <A HREF="../Sys/PetscSubcomm.html#PetscSubcomm">PetscSubcomm</A> context
<br>
<P>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
To avoid data scattering from subcomm back to original <A HREF="../Sys/comm.html#comm">comm</A>, we create subcommunicators
by iteratively taking a process into a subcommunicator.
Example: <A HREF="../Sys/size.html#size">size</A>=4, nsubcomm=(*psubcomm)->n=3
<H3><FONT COLOR="#CC3333">comm=(*psubcomm)->parent</FONT></H3>
<A HREF="../Sys/rank.html#rank">rank</A>: [0] [1] [2] [3]
color: 0 1 2 0
<P>
<H3><FONT COLOR="#CC3333">subcomm=(*psubcomm)->comm</FONT></H3>
subrank: [0] [0] [0] [1]
<P>
<H3><FONT COLOR="#CC3333">dupcomm=(*psubcomm)->dupparent</FONT></H3>
duprank: [0] [2] [3] [1]
<P>
Here, subcomm[color = 0] has subsize=2, owns process [0] and [3]
subcomm[color = 1] has subsize=1, owns process [1]
subcomm[color = 2] has subsize=1, owns process [2]
dupcomm has same number of processes as <A HREF="../Sys/comm.html#comm">comm</A>, and its duprank maps
<H3><FONT COLOR="#CC3333">processes in subcomm contiguously into a 1d array</FONT></H3>
duprank: [0] [1] [2] [3]
<A HREF="../Sys/rank.html#rank">rank</A>: [0] [3] [1] [2]
subcomm[0] subcomm[1] subcomm[2]
<P>
<P>
<H3><FONT COLOR="#CC3333">Keywords</FONT></H3>
communicator, create
<BR>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
PetscSubcommDestroy()
<BR><P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>advanced
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/sys/objects/subcomm.c.html#PetscSubcommCreate">src/sys/objects/subcomm.c</A>
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