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<div id="version" align=right><b>slepc-3.22.2 2024-12-02</b></div>
<div id="bugreport" align=right><a href="mailto:slepc-maint@upv.es?subject=Typo or Error in Documentation &body=Please describe the typo or error in the documentation: slepc-3.22.2 v3.22.2 docs/manualpages/EPS/EPSSetWhichEigenpairs.html "><small>Report Typos and Errors</small></a></div>
<H1>EPSSetWhichEigenpairs</H1>
Specifies which portion of the spectrum is to be sought.
<H3><FONT COLOR="#883300">Synopsis</FONT></H3>
<PRE>
#include "slepceps.h"
<A HREF="https://petsc.org/release/manualpages/Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> <A HREF="../EPS/EPSSetWhichEigenpairs.html#EPSSetWhichEigenpairs">EPSSetWhichEigenpairs</A>(<A HREF="../EPS/EPS.html#EPS">EPS</A> eps,<A HREF="../EPS/EPSWhich.html#EPSWhich">EPSWhich</A> which)
</PRE>
Logically Collective
<P>
<H3><FONT COLOR="#883300">Input Parameters</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>eps </B></TD><TD> - eigensolver context obtained from <A HREF="../EPS/EPSCreate.html#EPSCreate">EPSCreate</A>()
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>which </B></TD><TD> - the portion of the spectrum to be sought
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#883300">Options Database Keys</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-eps_largest_magnitude </B></TD><TD> - Sets largest eigenvalues in magnitude
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-eps_smallest_magnitude </B></TD><TD> - Sets smallest eigenvalues in magnitude
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-eps_largest_real </B></TD><TD> - Sets largest real parts
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-eps_smallest_real </B></TD><TD> - Sets smallest real parts
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-eps_largest_imaginary </B></TD><TD> - Sets largest imaginary parts
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-eps_smallest_imaginary </B></TD><TD> - Sets smallest imaginary parts
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-eps_target_magnitude </B></TD><TD> - Sets eigenvalues closest to target
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-eps_target_real </B></TD><TD> - Sets real parts closest to target
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-eps_target_imaginary </B></TD><TD> - Sets imaginary parts closest to target
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-eps_all </B></TD><TD> - Sets all eigenvalues in an interval or region
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#883300">Notes</FONT></H3>
The parameter 'which' can have one of these values
<P>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B><A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_LARGEST_MAGNITUDE</A> </B></TD><TD> - largest eigenvalues in magnitude (default)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B><A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_SMALLEST_MAGNITUDE</A> </B></TD><TD> - smallest eigenvalues in magnitude
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B><A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_LARGEST_REAL</A> </B></TD><TD> - largest real parts
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B><A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_SMALLEST_REAL</A> </B></TD><TD> - smallest real parts
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B><A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_LARGEST_IMAGINARY</A> </B></TD><TD> - largest imaginary parts
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B><A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_SMALLEST_IMAGINARY</A> </B></TD><TD> - smallest imaginary parts
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B><A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_TARGET_MAGNITUDE</A> </B></TD><TD> - eigenvalues closest to the target (in magnitude)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B><A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_TARGET_REAL</A> </B></TD><TD> - eigenvalues with real part closest to target
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B><A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_TARGET_IMAGINARY</A> </B></TD><TD> - eigenvalues with imaginary part closest to target
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B><A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_ALL</A> </B></TD><TD> - all eigenvalues contained in a given interval or region
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B><A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_WHICH_USER</A> </B></TD><TD> - user defined ordering set with <A HREF="../EPS/EPSSetEigenvalueComparison.html#EPSSetEigenvalueComparison">EPSSetEigenvalueComparison</A>()
</TD></TR></TABLE>
<P>
Not all eigensolvers implemented in <A HREF="../EPS/EPS.html#EPS">EPS</A> account for all the possible values
stated above. Also, some values make sense only for certain types of
problems. If SLEPc is compiled for real numbers <A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_LARGEST_IMAGINARY</A>
and <A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_SMALLEST_IMAGINARY</A> use the absolute value of the imaginary part
for eigenvalue selection.
<P>
The target is a scalar value provided with <A HREF="../EPS/EPSSetTarget.html#EPSSetTarget">EPSSetTarget</A>().
<P>
The criterion <A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_TARGET_IMAGINARY</A> is available only in case PETSc and
SLEPc have been built with complex scalars.
<P>
<A HREF="../EPS/EPSWhich.html#EPSWhich">EPS_ALL</A> is intended for use in combination with an interval (see
<A HREF="../EPS/EPSSetInterval.html#EPSSetInterval">EPSSetInterval</A>()), when all eigenvalues within the interval are requested,
or in the context of the CISS solver for computing all eigenvalues in a region.
In those cases, the number of eigenvalues is unknown, so the nev parameter
has a different sense, see <A HREF="../EPS/EPSSetDimensions.html#EPSSetDimensions">EPSSetDimensions</A>().
<P>
<P>
<H3><FONT COLOR="#883300">See Also</FONT></H3>
<A HREF="../EPS/EPSGetWhichEigenpairs.html#EPSGetWhichEigenpairs">EPSGetWhichEigenpairs</A>(), <A HREF="../EPS/EPSSetTarget.html#EPSSetTarget">EPSSetTarget</A>(), <A HREF="../EPS/EPSSetInterval.html#EPSSetInterval">EPSSetInterval</A>(),
<BR><A HREF="../EPS/EPSSetDimensions.html#EPSSetDimensions">EPSSetDimensions</A>(), <A HREF="../EPS/EPSSetEigenvalueComparison.html#EPSSetEigenvalueComparison">EPSSetEigenvalueComparison</A>(), <A HREF="../EPS/EPSWhich.html#EPSWhich">EPSWhich</A>
<P><B></B><H3><FONT COLOR="#883300">Level</FONT></H3>intermediate<BR>
<H3><FONT COLOR="#883300">Location</FONT></H3>
</B><A HREF="../../../src/eps/interface/epsopts.c.html#EPSSetWhichEigenpairs">src/eps/interface/epsopts.c</A>
<P><H3><FONT COLOR="#883300">Examples</FONT></H3>
<A HREF="../../../src/eps/tutorials/ex9.c.html">src/eps/tutorials/ex9.c</A><BR>
<A HREF="../../../src/eps/tutorials/ex10.c.html">src/eps/tutorials/ex10.c</A><BR>
<A HREF="../../../src/eps/tutorials/ex10f.F90.html">src/eps/tutorials/ex10f.F90</A><BR>
<A HREF="../../../src/eps/tutorials/ex11.c.html">src/eps/tutorials/ex11.c</A><BR>
<A HREF="../../../src/eps/tutorials/ex12.c.html">src/eps/tutorials/ex12.c</A><BR>
<A HREF="../../../src/eps/tutorials/ex19.c.html">src/eps/tutorials/ex19.c</A><BR>
<A HREF="../../../src/eps/tutorials/ex24.c.html">src/eps/tutorials/ex24.c</A><BR>
<A HREF="../../../src/eps/tutorials/ex25.c.html">src/eps/tutorials/ex25.c</A><BR>
<A HREF="../../../src/eps/tutorials/ex30.c.html">src/eps/tutorials/ex30.c</A><BR>
<A HREF="../../../src/eps/tutorials/ex35.c.html">src/eps/tutorials/ex35.c</A><BR>
<A HREF="../../../src/eps/tutorials/ex36.c.html">src/eps/tutorials/ex36.c</A><BR>
<BR><BR><A HREF="./index.html">Index of all EPS routines</A>
<BR><A HREF="../../../docs/manual.html">Table of Contents for all manual pages</A>
<BR><A HREF="../singleindex.html">Index of all manual pages</A>
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