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<A NAME="PCICCSetShift"><H1>PCICCSetShift</H1></A>
specify whether to use Manteuffel shifting of ICC. If an ICC factorisation breaks down because of nonpositive pivots, adding sufficient identity to the diagonal will remedy this.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscpc.h"
int PCICCSetShift(PC pc,PetscTruth shift)
</PRE>
Manteuffel shifting for ICC uses a different algorithm than the ILU case.
Here we base the shift on the lack of diagonal dominance when a negative
pivot occurs.
<P>
<H3><FONT COLOR="#CC3333">Input parameters</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>pc </B></TD><TD>- the preconditioner context
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>shifting </B></TD><TD>- PETSC_TRUE to set shift else PETSC_FALSE
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Options Database Key</FONT></H3>
<DT><B>-pc_icc_shift </B> -Activate <A HREF="../PC/PCICCSetShift.html#PCICCSetShift">PCICCSetShift</A>()
<br>
<P>
<P>
<H3><FONT COLOR="#CC3333">Keywords</FONT></H3>
<A HREF="../PC/PC.html#PC">PC</A>, indefinite, factorization, incomplete, ICC
<BR>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../PC/PCILUSetShift.html#PCILUSetShift">PCILUSetShift</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/icc/icc.c.html#PCICCSetShift">src/ksp/pc/impls/icc/icc.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/pc/examples/tutorials/ex2.c.html">src/ksp/pc/examples/tutorials/ex2.c.html</A><BR>
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