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<div id="version" align=right><b>petsc-3.10.3 2018-12-18</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-3.10.3 v3.10.3 docs/manualpages/PC/PCASM.html "><small>Report Typos and Errors</small></a></div>
<A NAME="PCASM"><H1>PCASM</H1></A>
Use the (restricted) additive Schwarz method, each block is (approximately) solved with its own <A HREF="../KSP/KSP.html#KSP">KSP</A> object.
<H3><FONT COLOR="#CC3333">Options Database Keys</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_asm_blocks <blks> </B></TD><TD>- Sets total blocks
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_asm_overlap <ovl> </B></TD><TD>- Sets overlap
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_asm_type [basic,restrict,interpolate,none] </B></TD><TD>- Sets ASM type, default is restrict
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_asm_local_type [additive, multiplicative] </B></TD><TD>- Sets ASM type, default is additive
</TD></TR></TABLE>
<P>
IMPORTANT: If you run with, for example, 3 blocks on 1 processor or 3 blocks on 3 processors you
will get a different convergence rate due to the default option of -pc_asm_type restrict. Use
-pc_asm_type basic to use the standard ASM.
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
Each processor can have one or more blocks, but a block cannot be shared by more
than one processor. Use <A HREF="../PC/PCGASM.html#PCGASM">PCGASM</A> for subdomains shared by multiple processes. Defaults to one block per processor.
<P>
To set options on the solvers for each block append -sub_ to all the <A HREF="../KSP/KSP.html#KSP">KSP</A>, and <A HREF="../PC/PC.html#PC">PC</A>
options database keys. For example, -sub_pc_type ilu -sub_pc_factor_levels 1 -sub_ksp_type preonly
<P>
To set the options on the solvers separate for each block call <A HREF="../PC/PCASMGetSubKSP.html#PCASMGetSubKSP">PCASMGetSubKSP</A>()
and set the options directly on the resulting <A HREF="../KSP/KSP.html#KSP">KSP</A> object (you can access its <A HREF="../PC/PC.html#PC">PC</A>
with <A HREF="../KSP/KSPGetPC.html#KSPGetPC">KSPGetPC</A>())
<P>
<P>
<P>
<H3><FONT COLOR="#CC3333">References</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>1. </B></TD><TD>- M Dryja, OB Widlund, An additive variant of the Schwarz alternating method for the case of many subregions
Courant Institute, New York University Technical report
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>1. </B></TD><TD>- Barry Smith, Petter Bjorstad, and William Gropp, Domain Decompositions: Parallel Multilevel Methods for Elliptic Partial Differential Equations,
Cambridge University Press.
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../PC/PCCreate.html#PCCreate">PCCreate</A>(), <A HREF="../PC/PCSetType.html#PCSetType">PCSetType</A>(), <A HREF="../PC/PCType.html#PCType">PCType</A> (for list of available types), <A HREF="../PC/PC.html#PC">PC</A>,
<BR><A HREF="../PC/PCBJACOBI.html#PCBJACOBI">PCBJACOBI</A>, <A HREF="../PC/PCASMGetSubKSP.html#PCASMGetSubKSP">PCASMGetSubKSP</A>(), <A HREF="../PC/PCASMSetLocalSubdomains.html#PCASMSetLocalSubdomains">PCASMSetLocalSubdomains</A>(), <A HREF="../PC/PCASMType.html#PCASMType">PCASMType</A>, <A HREF="../PC/PCASMGetType.html#PCASMGetType">PCASMGetType</A>(), <A HREF="../PC/PCASMSetLocalType.html#PCASMSetLocalType">PCASMSetLocalType</A>(), <A HREF="../PC/PCASMGetLocalType.html#PCASMGetLocalType">PCASMGetLocalType</A>()
<A HREF="../PC/PCASMSetTotalSubdomains.html#PCASMSetTotalSubdomains">PCASMSetTotalSubdomains</A>(), PCSetModifySubmatrices(), <A HREF="../PC/PCASMSetOverlap.html#PCASMSetOverlap">PCASMSetOverlap</A>(), <A HREF="../PC/PCASMSetType.html#PCASMSetType">PCASMSetType</A>(), <A HREF="../PC/PCCompositeType.html#PCCompositeType">PCCompositeType</A>
<P>
<P><B></B><H3><FONT COLOR="#CC3333">Level</FONT></H3>beginner<BR>
<H3><FONT COLOR="#CC3333">Location</FONT></H3>
</B><A HREF="../../../src/ksp/pc/impls/asm/asm.c.html#PCASM">src/ksp/pc/impls/asm/asm.c</A>
<P><H3><FONT COLOR="#CC3333">Examples</FONT></H3>
<A HREF="../../../src/ksp/ksp/examples/tutorials/ex6.c.html">src/ksp/ksp/examples/tutorials/ex6.c.html</A><BR>
<A HREF="../../../src/ksp/ksp/examples/tutorials/ex8.c.html">src/ksp/ksp/examples/tutorials/ex8.c.html</A><BR>
<BR><A HREF="./index.html">Index of all PC routines</A>
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<BR><A HREF="../singleindex.html">Index of all manual pages</A>
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