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<div id="version" align=right><b>petsc-3.14.5 2021-03-03</b></div>
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<A NAME="PCFieldSplitSetGKBNu"><H1>PCFieldSplitSetGKBNu</H1></A>
Sets the scalar value nu >= 0 in the transformation H = A00 + nu*A01*A01' of the (1,1) block in the Golub-Kahan bidiagonalization preconditioner.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscpc.h"
<A HREF="../Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> <A HREF="../PC/PCFieldSplitSetGKBNu.html#PCFieldSplitSetGKBNu">PCFieldSplitSetGKBNu</A>(<A HREF="../PC/PC.html#PC">PC</A> pc,<A HREF="../Sys/PetscReal.html#PetscReal">PetscReal</A> nu)
</PRE>
Collective on <A HREF="../PC/PC.html#PC">PC</A>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
This shift is in general done to obtain better convergence properties for the outer loop of the algorithm. This is often achieved by chosing nu sufficiently big. However,
if nu is chosen too big, the matrix H might be badly conditioned and the solution of the linear system Hx = b in the inner loop gets difficult. It is therefore
necessary to find a good balance in between the convergence of the inner and outer loop.
<P>
For nu = 0, no shift is done. In this case A00 has to be positive definite. The matrix N in [Ar13] is then chosen as identity.
<P>
[Ar13] Generalized Golub-Kahan bidiagonalization and stopping criteria, SIAM J. Matrix Anal. Appl., Vol. 34, No. 2, pp. 571-592, 2013.
<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>nu </B></TD><TD>- the shift parameter
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Options Database</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-pc_fieldsplit_gkb_nu </B></TD><TD>- default is 1
</TD></TR></TABLE>
<P>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../PC/PCFIELDSPLIT.html#PCFIELDSPLIT">PCFIELDSPLIT</A>, <A HREF="../PC/PCFieldSplitSetGKBDelay.html#PCFieldSplitSetGKBDelay">PCFieldSplitSetGKBDelay</A>(), <A HREF="../PC/PCFieldSplitSetGKBTol.html#PCFieldSplitSetGKBTol">PCFieldSplitSetGKBTol</A>(), <A HREF="../PC/PCFieldSplitSetGKBMaxit.html#PCFieldSplitSetGKBMaxit">PCFieldSplitSetGKBMaxit</A>()
<BR><P><B></B><H3><FONT COLOR="#CC3333">Level</FONT></H3>intermediate<BR>
<H3><FONT COLOR="#CC3333">Location</FONT></H3>
</B><A HREF="../../../src/ksp/pc/impls/fieldsplit/fieldsplit.c.html#PCFieldSplitSetGKBNu">src/ksp/pc/impls/fieldsplit/fieldsplit.c</A>
<P><H3><FONT COLOR="CC3333">Implementations</FONT></H3><A HREF="../../../src/ksp/pc/impls/fieldsplit/fieldsplit.c.html#PCFieldSplitSetGKBNu_FieldSplit">PCFieldSplitSetGKBNu_FieldSplit in src/ksp/pc/impls/fieldsplit/fieldsplit.c</A><BR>
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