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<div id="version" align=right><b>petsc-3.4.2 2013-07-02</b></div>
<A NAME="PetscThreadReductionBegin"><H1>PetscThreadReductionBegin</H1></A>
Initiates a threaded reduction and returns a reduction object to be passed to <A HREF="../PetscThreadComm/PetscThreadCommRunKernel.html#PetscThreadCommRunKernel">PetscThreadCommRunKernel</A>
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscthreadcomm.h"
PetscErrorCode PetscThreadReductionBegin(MPI_Comm comm,PetscThreadCommReductionOp op, PetscDataType type,PetscInt nreds,PetscThreadCommReduction *redout)
</PRE>
<H3><FONT COLOR="#CC3333">Input Parameters</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>comm </B></TD><TD>- the MPI comm
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>op </B></TD><TD>- the reduction operation
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>type </B></TD><TD>- the data type for reduction
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>nreds </B></TD><TD>- Number of reductions
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Output Parameters</FONT></H3>
<DT><B>redout </B> -the reduction context
<br>
<P>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
See include/petscthreadcomm.h for the available reduction operations
<P>
To be called from the main thread before calling <A HREF="../PetscThreadComm/PetscThreadCommRunKernel.html#PetscThreadCommRunKernel">PetscThreadCommRunKernel</A>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
PetscThreadCommReductionKernelPost(), PetscThreadCommReductionKernelEnd(), PetscThreadCommReductionEnd()
<BR><P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>developer
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/sys/threadcomm/interface/threadcommred.c.html#PetscThreadReductionBegin">src/sys/threadcomm/interface/threadcommred.c</A>
<BR><A HREF="./index.html">Index of all PetscThreadComm routines</A>
<BR><A HREF="../../index.html">Table of Contents for all manual pages</A>
<BR><A HREF="../singleindex.html">Index of all manual pages</A>
<P><H3><FONT COLOR="#CC3333">Examples</FONT></H3>
<A HREF="../../../src/sys/threadcomm/examples/tutorials/ex3.c.html">src/sys/threadcomm/examples/tutorials/ex3.c.html</A><BR>
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