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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="KSPSetDiagonalScale"><H1>KSPSetDiagonalScale</H1></A>
Tells <A HREF="../KSP/KSP.html#KSP">KSP</A> to symmetrically diagonally scale the system before solving. This actually CHANGES the matrix (and right hand side).
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscksp.h"
PetscErrorCode KSPSetDiagonalScale(KSP ksp,PetscBool scale)
</PRE>
Logically Collective on <A HREF="../KSP/KSP.html#KSP">KSP</A>
<P>
<H3><FONT COLOR="#CC3333">Input Parameter</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>ksp </B></TD><TD>- the <A HREF="../KSP/KSP.html#KSP">KSP</A> context
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>scale </B></TD><TD>- <A HREF="../Sys/PETSC_TRUE.html#PETSC_TRUE">PETSC_TRUE</A> or <A HREF="../Sys/PETSC_FALSE.html#PETSC_FALSE">PETSC_FALSE</A>
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Options Database Key</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-ksp_diagonal_scale </B></TD><TD>-
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-ksp_diagonal_scale_fix </B></TD><TD>- scale the matrix back AFTER the solve
</TD></TR></TABLE>
<P>
<P>
Notes: Scales the matrix by D^(-1/2) A D^(-1/2) [D^(1/2) x ] = D^(-1/2) b
where D_{ii} is 1/abs(A_{ii}) unless A_{ii} is zero and then it is 1.
<P>
BE CAREFUL with this routine: it actually scales the matrix and right
hand side that define the system. After the system is solved the matrix
and right hand side remain scaled unless you use <A HREF="../KSP/KSPSetDiagonalScaleFix.html#KSPSetDiagonalScaleFix">KSPSetDiagonalScaleFix</A>()
<P>
This should NOT be used within the <A HREF="../SNES/SNES.html#SNES">SNES</A> solves if you are using a line
search.
<P>
If you use this with the <A HREF="../PC/PCType.html#PCType">PCType</A> Eisenstat preconditioner than you can
use the <A HREF="../PC/PCEisenstatSetNoDiagonalScaling.html#PCEisenstatSetNoDiagonalScaling">PCEisenstatSetNoDiagonalScaling</A>() option, or -pc_eisenstat_no_diagonal_scaling
to save some unneeded, redundant flops.
<P>
<P>
<H3><FONT COLOR="#CC3333">Keywords</FONT></H3>
<A HREF="../KSP/KSP.html#KSP">KSP</A>, set, options, prefix, database
<BR>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../KSP/KSPGetDiagonalScale.html#KSPGetDiagonalScale">KSPGetDiagonalScale</A>(), <A HREF="../KSP/KSPSetDiagonalScaleFix.html#KSPSetDiagonalScaleFix">KSPSetDiagonalScaleFix</A>()
<BR><P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>intermediate
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/ksp/ksp/interface/itfunc.c.html#KSPSetDiagonalScale">src/ksp/ksp/interface/itfunc.c</A>
<BR><A HREF="./index.html">Index of all KSP routines</A>
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