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<A NAME="KSPChebychevSetEstimateEigenvalues"><H1>KSPChebychevSetEstimateEigenvalues</H1></A>
Automatically estimate the eigenvalues to use for Chebychev
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscksp.h"
PetscErrorCode KSPChebychevSetEstimateEigenvalues(KSP ksp,PetscReal a,PetscReal b,PetscReal c,PetscReal d)
</PRE>
Logically Collective on <A HREF="../KSP/KSP.html#KSP">KSP</A>
<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>ksp </B></TD><TD>- the Krylov space context
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>a </B></TD><TD>- multiple of min eigenvalue estimate to use for min Chebychev bound (or <A HREF="../Sys/PETSC_DECIDE.html#PETSC_DECIDE">PETSC_DECIDE</A>)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>b </B></TD><TD>- multiple of max eigenvalue estimate to use for min Chebychev bound (or <A HREF="../Sys/PETSC_DECIDE.html#PETSC_DECIDE">PETSC_DECIDE</A>)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>c </B></TD><TD>- multiple of min eigenvalue estimate to use for max Chebychev bound (or <A HREF="../Sys/PETSC_DECIDE.html#PETSC_DECIDE">PETSC_DECIDE</A>)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>d </B></TD><TD>- multiple of max eigenvalue estimate to use for max Chebychev bound (or <A HREF="../Sys/PETSC_DECIDE.html#PETSC_DECIDE">PETSC_DECIDE</A>)
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Options Database</FONT></H3>
<DT><B>-ksp_chebychev_estimate_eigenvalues a,b,c,d</B> -
Notes:
The Chebychev bounds are estimated using
<br>
<PRE>
minbound = a*minest + b*maxest
maxbound = c*minest + d*maxest
</PRE>
The default configuration targets the upper part of the spectrum for use as a multigrid smoother, so only the maximum eigenvalue estimate is used.
The minimum eigenvalue estimate obtained by Krylov iteration is typically not accurate until the method has converged.
<P>
If 0.0 is passed for all transform arguments (a,b,c,d), eigenvalue estimation is disabled.
<P>
<P>
<H3><FONT COLOR="#CC3333">Keywords</FONT></H3>
<A HREF="../KSP/KSP.html#KSP">KSP</A>, Chebyshev, set, eigenvalues
<BR><P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>intermediate
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/ksp/ksp/impls/cheby/cheby.c.html#KSPChebychevSetEstimateEigenvalues">src/ksp/ksp/impls/cheby/cheby.c</A>
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