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<div id="version" align=right><b>petsc-3.7.5 2017-01-01</b></div>
<div id="bugreport" align=right><a href="mailto:petsc-maint@mcs.anl.gov?subject=Typo or Error in Documentation &body=Please describe the typo or error in the documentation: petsc-3.7.5 v3.7.5 docs/manualpages/Vec/VecSetOption.html "><small>Report Typos and Errors</small></a></div>
<A NAME="VecSetOption"><H1>VecSetOption</H1></A>
Sets an option for controling a vector's behavior.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscvec.h"
PetscErrorCode VecSetOption(Vec x,VecOption op,PetscBool flag)
</PRE>
Collective on <A HREF="../Vec/Vec.html#Vec">Vec</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>x </B></TD><TD>- the vector
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>op </B></TD><TD>- the option
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>flag </B></TD><TD>- turn the option on or off
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Supported Options</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>VEC_IGNORE_OFF_PROC_ENTRIES, which causes <A HREF="../Vec/VecSetValues.html#VecSetValues">VecSetValues</A>() to ignore</B></TD><TD>- entries destined to be stored on a separate processor. This can be used
to eliminate the global reduction in the VecAssemblyXXXX() if you know
that you have only used <A HREF="../Vec/VecSetValues.html#VecSetValues">VecSetValues</A>() to set local elements
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>VEC_IGNORE_NEGATIVE_INDICES, which means you can pass negative indices</B></TD><TD>- in ix in calls to <A HREF="../Vec/VecSetValues.html#VecSetValues">VecSetValues</A>() or <A HREF="../Vec/VecGetValues.html#VecGetValues">VecGetValues</A>(). These rows are simply
ignored.
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>VEC_SUBSET_OFF_PROC_ENTRIES, which causes <A HREF="../Vec/VecAssemblyBegin.html#VecAssemblyBegin">VecAssemblyBegin</A>() to assume that the off</B></TD><TD>- process
entries will always be a subset (possibly equal) of the off-process entries set on the
first assembly. This reuses the communication pattern, thus avoiding a global reduction.
Subsequent assemblies setting off-process values should use the same <A HREF="../Sys/InsertMode.html#InsertMode">InsertMode</A> as the
first assembly.
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Developer Note</FONT></H3>
The <A HREF="../Sys/InsertMode.html#InsertMode">InsertMode</A> restriction could be removed by packing the stash messages out of place.
<P>
<P>
<P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>intermediate
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/vec/vec/interface/vector.c.html#VecSetOption">src/vec/vec/interface/vector.c</A>
<BR><A HREF="./index.html">Index of all Vec routines</A>
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