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<div id="version" align=right><b>petsc-3.7.5 2017-01-01</b></div>
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<A NAME="PCASMSetOverlap"><H1>PCASMSetOverlap</H1></A>
Sets the overlap between a pair of subdomains for the additive Schwarz preconditioner. Either all or no processors in the <A HREF="../PC/PC.html#PC">PC</A> communicator must call this routine. If <A HREF="../Mat/MatIncreaseOverlap.html#MatIncreaseOverlap">MatIncreaseOverlap</A> is used, use option -mat_increase_overlap when the problem size large.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscpc.h"
PetscErrorCode PCASMSetOverlap(PC pc,PetscInt ovl)
</PRE>
Logically Collective on <A HREF="../PC/PC.html#PC">PC</A>
<P>
<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>pc </B></TD><TD>- the preconditioner context
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>ovl </B></TD><TD>- the amount of overlap between subdomains (ovl >= 0, default value = 1)
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Options Database Key</FONT></H3>
<DT><B>-pc_asm_overlap <ovl> </B> -Sets overlap
<br>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
By default the ASM preconditioner uses 1 block per processor. To use
multiple blocks per perocessor, see <A HREF="../PC/PCASMSetTotalSubdomains.html#PCASMSetTotalSubdomains">PCASMSetTotalSubdomains</A>() and
<A HREF="../PC/PCASMSetLocalSubdomains.html#PCASMSetLocalSubdomains">PCASMSetLocalSubdomains</A>() (and the option -pc_asm_blocks <blks>).
<P>
The overlap defaults to 1, so if one desires that no additional
overlap be computed beyond what may have been set with a call to
<A HREF="../PC/PCASMSetTotalSubdomains.html#PCASMSetTotalSubdomains">PCASMSetTotalSubdomains</A>() or <A HREF="../PC/PCASMSetLocalSubdomains.html#PCASMSetLocalSubdomains">PCASMSetLocalSubdomains</A>(), then ovl
must be set to be 0. In particular, if one does not explicitly set
the subdomains an application code, then all overlap would be computed
internally by PETSc, and using an overlap of 0 would result in an ASM
variant that is equivalent to the block Jacobi preconditioner.
<P>
Note that one can define initial index sets with any overlap via
<A HREF="../PC/PCASMSetTotalSubdomains.html#PCASMSetTotalSubdomains">PCASMSetTotalSubdomains</A>() or <A HREF="../PC/PCASMSetLocalSubdomains.html#PCASMSetLocalSubdomains">PCASMSetLocalSubdomains</A>(); the routine
<A HREF="../PC/PCASMSetOverlap.html#PCASMSetOverlap">PCASMSetOverlap</A>() merely allows PETSc to extend that overlap further
if desired.
<P>
<P>
<H3><FONT COLOR="#CC3333">Keywords</FONT></H3>
<A HREF="../PC/PC.html#PC">PC</A>, ASM, set, overlap
<BR>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../PC/PCASMSetTotalSubdomains.html#PCASMSetTotalSubdomains">PCASMSetTotalSubdomains</A>(), <A HREF="../PC/PCASMSetLocalSubdomains.html#PCASMSetLocalSubdomains">PCASMSetLocalSubdomains</A>(), <A HREF="../PC/PCASMGetSubKSP.html#PCASMGetSubKSP">PCASMGetSubKSP</A>(),
<BR><A HREF="../PC/PCASMCreateSubdomains2D.html#PCASMCreateSubdomains2D">PCASMCreateSubdomains2D</A>(), <A HREF="../PC/PCASMGetLocalSubdomains.html#PCASMGetLocalSubdomains">PCASMGetLocalSubdomains</A>()
<P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>intermediate
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/ksp/pc/impls/asm/asm.c.html#PCASMSetOverlap">src/ksp/pc/impls/asm/asm.c</A>
<BR><A HREF="./index.html">Index of all PC 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/ksp/ksp/examples/tutorials/ex8.c.html">src/ksp/ksp/examples/tutorials/ex8.c.html</A><BR>
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