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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="KSPComputeEigenvaluesExplicitly"><H1>KSPComputeEigenvaluesExplicitly</H1></A>
Computes all of the eigenvalues of the preconditioned operator using LAPACK.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscksp.h"
<A HREF="../Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> <A HREF="../KSP/KSPComputeEigenvaluesExplicitly.html#KSPComputeEigenvaluesExplicitly">KSPComputeEigenvaluesExplicitly</A>(<A HREF="../KSP/KSP.html#KSP">KSP</A> ksp,<A HREF="../Sys/PetscInt.html#PetscInt">PetscInt</A> nmax,<A HREF="../Sys/PetscReal.html#PetscReal">PetscReal</A> r[],<A HREF="../Sys/PetscReal.html#PetscReal">PetscReal</A> c[])
</PRE>
Collective on ksp
<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>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>n </B></TD><TD>- size of arrays r and c
</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>r </B></TD><TD>- real part of computed eigenvalues, provided by user with a dimension at least of n
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>c </B></TD><TD>- complex part of computed eigenvalues, provided by user with a dimension at least of n
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
This approach is very slow but will generally provide accurate eigenvalue
estimates. This routine explicitly forms a dense matrix representing
the preconditioned operator, and thus will run only for relatively small
problems, say n < 500.
<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 singular values at each iteration of the linear solve.
<P>
The preconditoner operator, rhs vector, solution vectors should be
set before this routine is called. i.e use <A HREF="../KSP/KSPSetOperators.html#KSPSetOperators">KSPSetOperators</A>(),<A HREF="../KSP/KSPSolve.html#KSPSolve">KSPSolve</A>() or
<A HREF="../KSP/KSPSetOperators.html#KSPSetOperators">KSPSetOperators</A>()
<P>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../KSP/KSPComputeEigenvalues.html#KSPComputeEigenvalues">KSPComputeEigenvalues</A>(), <A HREF="../KSP/KSPMonitorSingularValue.html#KSPMonitorSingularValue">KSPMonitorSingularValue</A>(), <A HREF="../KSP/KSPComputeExtremeSingularValues.html#KSPComputeExtremeSingularValues">KSPComputeExtremeSingularValues</A>(), <A HREF="../KSP/KSPSetOperators.html#KSPSetOperators">KSPSetOperators</A>(), <A HREF="../KSP/KSPSolve.html#KSPSolve">KSPSolve</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/eige.c.html#KSPComputeEigenvaluesExplicitly">src/ksp/ksp/interface/eige.c</A>
<BR><A HREF="./index.html">Index of all KSP routines</A>
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