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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="PCEisenstatGetOmega"><H1>PCEisenstatGetOmega</H1></A>
Gets the SSOR relaxation coefficient, omega, to use with Eisenstat's trick (where omega = 1.0 by default).
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscpc.h"
PetscErrorCode PCEisenstatGetOmega(PC pc,PetscReal *omega)
</PRE>
Logically Collective on <A HREF="../PC/PC.html#PC">PC</A>
<P>
<H3><FONT COLOR="#CC3333">Input Parameter</FONT></H3>
<DT><B>pc </B> -the preconditioner context
<br>
<P>
<H3><FONT COLOR="#CC3333">Output Parameter</FONT></H3>
<DT><B>omega </B> -relaxation coefficient (0 < omega < 2)
<br>
<P>
<H3><FONT COLOR="#CC3333">Options Database Key</FONT></H3>
<DT><B>-pc_eisenstat_omega <omega> </B> -Sets omega
<br>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
The Eisenstat trick implementation of SSOR requires about 50% of the
usual amount of floating point operations used for SSOR + Krylov method;
however, the preconditioned problem must be solved with both left
and right preconditioning.
<P>
To use SSOR without the Eisenstat trick, employ the <A HREF="../PC/PCSOR.html#PCSOR">PCSOR</A> preconditioner,
which can be chosen with the database options
<pre>
-pc_type sor -pc_sor_symmetric
</pre>
<P>
<P>
<H3><FONT COLOR="#CC3333">Keywords</FONT></H3>
<A HREF="../PC/PC.html#PC">PC</A>, Eisenstat, set, SOR, SSOR, relaxation, omega
<BR>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../PC/PCSORGetOmega.html#PCSORGetOmega">PCSORGetOmega</A>(), <A HREF="../PC/PCEisenstatSetOmega.html#PCEisenstatSetOmega">PCEisenstatSetOmega</A>()
<BR><P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>intermediate
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/ksp/pc/impls/eisens/eisen.c.html#PCEisenstatGetOmega">src/ksp/pc/impls/eisens/eisen.c</A>
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