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<A NAME="PetscCommDuplicate"><H1>PetscCommDuplicate</H1></A>
Duplicates the communicator only if it is not already a PETSc communicator.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscsys.h"
PetscErrorCode PetscCommDuplicate(MPI_Comm comm_in,MPI_Comm *comm_out,PetscMPIInt* first_tag)
</PRE>
Collective on <A HREF="../Sys/MPI_Comm.html#MPI_Comm">MPI_Comm</A>
<P>
<H3><FONT COLOR="#CC3333">Input Parameters</FONT></H3>
<DT><B>comm_in </B> -Input communicator
<br>
<P>
<H3><FONT COLOR="#CC3333">Output Parameters</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>comm_out </B></TD><TD>- Output communicator. May be comm_in.
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>first_tag </B></TD><TD>- Tag available that has not already been used with this communicator (you may
pass in <A HREF="../Sys/PETSC_NULL.html#PETSC_NULL">PETSC_NULL</A> if you do not need a tag)
</TD></TR></TABLE>
<P>
PETSc communicators are just regular MPI communicators that keep track of which
tags have been used to prevent tag conflict. If you pass a non-PETSc communicator into
a PETSc creation routine it will attach a private communicator for use in the objects communications.
The internal <A HREF="../Sys/MPI_Comm.html#MPI_Comm">MPI_Comm</A> is used to perform all the MPI calls for PETSc, the outer <A HREF="../Sys/MPI_Comm.html#MPI_Comm">MPI_Comm</A> is a user
level <A HREF="../Sys/MPI_Comm.html#MPI_Comm">MPI_Comm</A> that may be performing communication for the user or other library and so <A HREF="../IS/IS.html#IS">IS</A> NOT used by PETSc.
<P>
<P>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../Sys/PetscObjectGetNewTag.html#PetscObjectGetNewTag">PetscObjectGetNewTag</A>(), <A HREF="../Sys/PetscCommGetNewTag.html#PetscCommGetNewTag">PetscCommGetNewTag</A>(), <A HREF="../Sys/PetscCommDestroy.html#PetscCommDestroy">PetscCommDestroy</A>()
<BR><P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>developer
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/sys/objects/tagm.c.html#PetscCommDuplicate">src/sys/objects/tagm.c</A>
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