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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/PCSOR.html "><small>Report Typos and Errors</small></a></div>
<A NAME="PCSOR"><H1>PCSOR</H1></A>
(S)SOR (successive over relaxation, Gauss-Seidel) preconditioning
<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_sor_symmetric </B></TD><TD>- Activates symmetric version
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_sor_backward </B></TD><TD>- Activates backward version
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_sor_forward </B></TD><TD>- Activates forward version
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_sor_local_forward </B></TD><TD>- Activates local forward version
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_sor_local_symmetric </B></TD><TD>- Activates local symmetric version (default version)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_sor_local_backward </B></TD><TD>- Activates local backward version
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_sor_omega <omega> </B></TD><TD>- Sets omega
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_sor_diagonal_shift <shift> </B></TD><TD>- shift the diagonal entries; useful if the matrix has zeros on the diagonal
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_sor_its <its> </B></TD><TD>- Sets number of iterations (default 1)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_sor_lits <lits> </B></TD><TD>- Sets number of local iterations (default 1)
</TD></TR></TABLE>
<P>
<P>
<P>
Notes: Only implemented for the AIJ and SeqBAIJ matrix formats.
Not a true parallel SOR, in parallel this implementation corresponds to block
Jacobi with SOR on each block.
<P>
For AIJ matrix if a diagonal entry is zero (and the diagonal shift is zero) then by default the inverse of that
zero will be used and hence the <A HREF="../KSP/KSPSolve.html#KSPSolve">KSPSolve</A>() will terminate with KSP_DIVERGED_NANORIF. If the option
<A HREF="../KSP/KSPSetErrorIfNotConverged.html#KSPSetErrorIfNotConverged">KSPSetErrorIfNotConverged</A>() or -ksp_error_if_not_converged the code will terminate as soon as it detects the
zero pivot.
<P>
For SeqBAIJ matrices this implements point-block SOR, but the omega, its, lits options are not supported.
<P>
For SeqBAIJ the diagonal blocks are inverted using dense LU with partial pivoting. If a zero pivot is detected
the computation is stopped with an error
<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/PCSORSetIterations.html#PCSORSetIterations">PCSORSetIterations</A>(), <A HREF="../PC/PCSORSetSymmetric.html#PCSORSetSymmetric">PCSORSetSymmetric</A>(), <A HREF="../PC/PCSORSetOmega.html#PCSORSetOmega">PCSORSetOmega</A>(), <A HREF="../PC/PCEISENSTAT.html#PCEISENSTAT">PCEISENSTAT</A>
<P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>beginner
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/ksp/pc/impls/sor/sor.c.html#PCSOR">src/ksp/pc/impls/sor/sor.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/ex21f.F.html">src/ksp/ksp/examples/tutorials/ex21f.F.html</A><BR>
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