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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/PC/PCMG.html "><small>Report Typos and Errors</small></a></div>
<A NAME="PCMG"><H1>PCMG</H1></A>
Use multigrid preconditioning. This preconditioner requires you provide additional information about the coarser grid matrices and restriction/interpolation operators. 
<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_mg_levels &lt;nlevels&gt; </B></TD><TD>- number of levels including finest
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_mg_cycle_type &lt;v,w&gt; </B></TD><TD>- 
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_mg_smoothup &lt;n&gt; </B></TD><TD>- number of smoothing steps after interpolation
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_mg_smoothdown &lt;n&gt; </B></TD><TD>- number of smoothing steps before applying restriction operator
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_mg_type &lt;additive,multiplicative,full,kaskade&gt; </B></TD><TD>- multiplicative is the default
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_mg_log </B></TD><TD>- log information about time spent on each level of the solver
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_mg_galerkin </B></TD><TD>- use Galerkin process to compute coarser operators, i.e. Acoarse = R A R'
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_mg_multiplicative_cycles </B></TD><TD>- number of cycles to use as the preconditioner (defaults to 1)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_mg_dump_matlab </B></TD><TD>- dumps the matrices for each level and the restriction/interpolation matrices
to the Socket viewer for reading from MATLAB.
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_mg_dump_binary </B></TD><TD>- dumps the matrices for each level and the restriction/interpolation matrices
to the binary output file called binaryoutput
</TD></TR></TABLE>
<P>
Notes: If one uses a Krylov method such GMRES or CG as the smoother than one must use <A HREF="../KSP/KSPFGMRES.html#KSPFGMRES">KSPFGMRES</A>, KSPGCG, or <A HREF="../KSP/KSPRICHARDSON.html#KSPRICHARDSON">KSPRICHARDSON</A> as the outer Krylov method
<P>
When run with a single level the smoother options are used on that level NOT the coarse grid solver options
<P>

<P>
<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>, <A HREF="../PC/PCMGType.html#PCMGType">PCMGType</A>, <A HREF="../PC/PCEXOTIC.html#PCEXOTIC">PCEXOTIC</A>, <A HREF="../PC/PCGAMG.html#PCGAMG">PCGAMG</A>, <A HREF="../PC/PCML.html#PCML">PCML</A>, <A HREF="../PC/PCHYPRE.html#PCHYPRE">PCHYPRE</A>
<BR><A HREF="../PC/PCMGSetLevels.html#PCMGSetLevels">PCMGSetLevels</A>(), <A HREF="../PC/PCMGGetLevels.html#PCMGGetLevels">PCMGGetLevels</A>(), <A HREF="../PC/PCMGSetType.html#PCMGSetType">PCMGSetType</A>(), <A HREF="../PC/PCMGSetCycleType.html#PCMGSetCycleType">PCMGSetCycleType</A>(), <A HREF="../PC/PCMGSetNumberSmoothDown.html#PCMGSetNumberSmoothDown">PCMGSetNumberSmoothDown</A>(),
<A HREF="../PC/PCMGSetNumberSmoothUp.html#PCMGSetNumberSmoothUp">PCMGSetNumberSmoothUp</A>(), <A HREF="../PC/PCMGGetCoarseSolve.html#PCMGGetCoarseSolve">PCMGGetCoarseSolve</A>(), <A HREF="../PC/PCMGSetResidual.html#PCMGSetResidual">PCMGSetResidual</A>(), <A HREF="../PC/PCMGSetInterpolation.html#PCMGSetInterpolation">PCMGSetInterpolation</A>(),
<A HREF="../PC/PCMGSetRestriction.html#PCMGSetRestriction">PCMGSetRestriction</A>(), <A HREF="../PC/PCMGGetSmoother.html#PCMGGetSmoother">PCMGGetSmoother</A>(), <A HREF="../PC/PCMGGetSmootherUp.html#PCMGGetSmootherUp">PCMGGetSmootherUp</A>(), <A HREF="../PC/PCMGGetSmootherDown.html#PCMGGetSmootherDown">PCMGGetSmootherDown</A>(),
PCMGSetCycleTypeOnLevel(), <A HREF="../PC/PCMGSetRhs.html#PCMGSetRhs">PCMGSetRhs</A>(), <A HREF="../PC/PCMGSetX.html#PCMGSetX">PCMGSetX</A>(), <A HREF="../PC/PCMGSetR.html#PCMGSetR">PCMGSetR</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/mg/mg.c.html#PCMG">src/ksp/pc/impls/mg/mg.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/ex42.c.html">src/ksp/ksp/examples/tutorials/ex42.c.html</A><BR>
<A HREF="../../../src/snes/examples/tutorials/ex12.c.html">src/snes/examples/tutorials/ex12.c.html</A><BR>
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