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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="KSPComputeExtremeSingularValues"><H1>KSPComputeExtremeSingularValues</H1></A>
Computes the extreme singular values for the preconditioned operator. Called after or during <A HREF="../KSP/KSPSolve.html#KSPSolve">KSPSolve</A>().
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscksp.h"
#include "petscmat.h"
<A HREF="../Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> <A HREF="../KSP/KSPComputeExtremeSingularValues.html#KSPComputeExtremeSingularValues">KSPComputeExtremeSingularValues</A>(<A HREF="../KSP/KSP.html#KSP">KSP</A> ksp,<A HREF="../Sys/PetscReal.html#PetscReal">PetscReal</A> *emax,<A HREF="../Sys/PetscReal.html#PetscReal">PetscReal</A> *emin)
</PRE>
Not Collective
<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>- iterative context obtained from <A HREF="../KSP/KSPCreate.html#KSPCreate">KSPCreate</A>()
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Output Parameters</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>emin, emax </B></TD><TD>- extreme singular values
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Options Database Keys</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-ksp_view_singularvalues </B></TD><TD>- compute extreme singular values and print when <A HREF="../KSP/KSPSolve.html#KSPSolve">KSPSolve</A> completes.
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
One must call <A HREF="../KSP/KSPSetComputeSingularValues.html#KSPSetComputeSingularValues">KSPSetComputeSingularValues</A>() before calling <A HREF="../KSP/KSPSetUp.html#KSPSetUp">KSPSetUp</A>()
(or use the option -ksp_view_eigenvalues) in order for this routine to work correctly.
<P>
Many users may just want to use the monitoring routine
<A HREF="../KSP/KSPMonitorSingularValue.html#KSPMonitorSingularValue">KSPMonitorSingularValue</A>() (which can be set with option -ksp_monitor_singular_value)
to print the extreme singular values at each iteration of the linear solve.
<P>
Estimates of the smallest singular value may be very inaccurate, especially if the Krylov method has not converged.
The largest singular value is usually accurate to within a few percent if the method has converged, but is still not
intended for eigenanalysis.
<P>
Disable restarts if using <A HREF="../KSP/KSPGMRES.html#KSPGMRES">KSPGMRES</A>, otherwise this estimate will only be using those iterations after the last
restart. See <A HREF="../KSP/KSPGMRESSetRestart.html#KSPGMRESSetRestart">KSPGMRESSetRestart</A>() for more details.
<P>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../KSP/KSPSetComputeSingularValues.html#KSPSetComputeSingularValues">KSPSetComputeSingularValues</A>(), <A HREF="../KSP/KSPMonitorSingularValue.html#KSPMonitorSingularValue">KSPMonitorSingularValue</A>(), <A HREF="../KSP/KSPComputeEigenvalues.html#KSPComputeEigenvalues">KSPComputeEigenvalues</A>(), <A HREF="../KSP/KSP.html#KSP">KSP</A>
<BR><P><B></B><H3><FONT COLOR="#CC3333">Level</FONT></H3>advanced<BR>
<H3><FONT COLOR="#CC3333">Location</FONT></H3>
</B><A HREF="../../../src/ksp/ksp/interface/itfunc.c.html#KSPComputeExtremeSingularValues">src/ksp/ksp/interface/itfunc.c</A>
<P><H3><FONT COLOR="#CC3333">Examples</FONT></H3>
<A HREF="../../../src/ksp/ksp/tutorials/ex56.c.html">src/ksp/ksp/tutorials/ex56.c.html</A><BR>
<A HREF="../../../src/ksp/ksp/tutorials/ex59.c.html">src/ksp/ksp/tutorials/ex59.c.html</A><BR>
<P><H3><FONT COLOR="CC3333">Implementations</FONT></H3><A HREF="../../../src/ksp/ksp/impls/cg/cgeig.c.html#KSPComputeExtremeSingularValues_CG">KSPComputeExtremeSingularValues_CG in src/ksp/ksp/impls/cg/cgeig.c</A><BR>
<A HREF="../../../src/ksp/ksp/impls/fetidp/fetidp.c.html#KSPComputeExtremeSingularValues_FETIDP">KSPComputeExtremeSingularValues_FETIDP in src/ksp/ksp/impls/fetidp/fetidp.c</A><BR>
<A HREF="../../../src/ksp/ksp/impls/gmres/gmreig.c.html#KSPComputeExtremeSingularValues_GMRES">KSPComputeExtremeSingularValues_GMRES in src/ksp/ksp/impls/gmres/gmreig.c</A><BR>
<BR><A HREF="./index.html">Index of all KSP routines</A>
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