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<div id="version" align=right><b>petsc-3.4.2 2013-07-02</b></div>
<A NAME="PCGASM"><H1>PCGASM</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_gasm_total_block_count <n> </B></TD><TD>- Sets total number of local subdomains (known as blocks) to be distributed among processors
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_gasm_view_subdomains </B></TD><TD>- activates the printing of subdomain indices in <A HREF="../PC/PCView.html#PCView">PCView</A>(), -ksp_view or -snes_view
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_gasm_print_subdomains </B></TD><TD>- activates the printing of subdomain indices in <A HREF="../PC/PCSetUp.html#PCSetUp">PCSetUp</A>()
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_gasm_overlap <ovl> </B></TD><TD>- Sets overlap by which to (automatically) extend local subdomains
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_gasm_type [basic,restrict,interpolate,none] </B></TD><TD>- Sets GASM type
</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_gasm_type restrict. Use
-pc_gasm_type basic to use the standard GASM.
<P>
Notes: Each processor can have one or more blocks, but a block cannot be shared by more
than one processor. 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/PCGASMGetSubKSP.html#PCGASMGetSubKSP">PCGASMGetSubKSP</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>
<P>
<H3><FONT COLOR="#CC3333">References</FONT></H3>
An additive variant of the Schwarz alternating method for the case of many subregions
M Dryja, OB Widlund - Courant Institute, New York University Technical report
<P>
Domain Decompositions: Parallel Multilevel Methods for Elliptic Partial Differential Equations,
Barry Smith, Petter Bjorstad, and William Gropp, Cambridge University Press, ISBN 0-521-49589-X.
<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/PCGASMGetSubKSP.html#PCGASMGetSubKSP">PCGASMGetSubKSP</A>(), <A HREF="../PC/PCGASMSetSubdomains.html#PCGASMSetSubdomains">PCGASMSetSubdomains</A>(),
<A HREF="../PC/PCGASMSetTotalSubdomains.html#PCGASMSetTotalSubdomains">PCGASMSetTotalSubdomains</A>(), PCSetModifySubmatrices(), <A HREF="../PC/PCGASMSetOverlap.html#PCGASMSetOverlap">PCGASMSetOverlap</A>(), <A HREF="../PC/PCGASMSetType.html#PCGASMSetType">PCGASMSetType</A>()
<P>
<P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>beginner
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/ksp/pc/impls/gasm/gasm.c.html#PCGASM">src/ksp/pc/impls/gasm/gasm.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/ex8g.c.html">src/ksp/ksp/examples/tutorials/ex8g.c.html</A><BR>
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