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<div id="version" align=right><b>slepc-3.22.2 2024-12-02</b></div>
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<H1>PEPSetEigenvalueComparison</H1>
Specifies the eigenvalue comparison function when <A HREF="../PEP/PEPSetWhichEigenpairs.html#PEPSetWhichEigenpairs">PEPSetWhichEigenpairs</A>() is set to <A HREF="../PEP/PEPWhich.html#PEPWhich">PEP_WHICH_USER</A>.
<H3><FONT COLOR="#883300">Synopsis</FONT></H3>
<PRE>
#include "slepcpep.h"
<A HREF="https://petsc.org/release/manualpages/Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> <A HREF="../PEP/PEPSetEigenvalueComparison.html#PEPSetEigenvalueComparison">PEPSetEigenvalueComparison</A>(<A HREF="../PEP/PEP.html#PEP">PEP</A> pep,<A HREF="https://petsc.org/release/manualpages/Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> (*comp)(<A HREF="https://petsc.org/release/manualpages/Sys/PetscScalar.html#PetscScalar">PetscScalar</A> ar,<A HREF="https://petsc.org/release/manualpages/Sys/PetscScalar.html#PetscScalar">PetscScalar</A> ai,<A HREF="https://petsc.org/release/manualpages/Sys/PetscScalar.html#PetscScalar">PetscScalar</A> br,<A HREF="https://petsc.org/release/manualpages/Sys/PetscScalar.html#PetscScalar">PetscScalar</A> bi,<A HREF="https://petsc.org/release/manualpages/Sys/PetscInt.html#PetscInt">PetscInt</A> *res,void *ctx),void* ctx)
</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>pep </B></TD><TD> - eigensolver context obtained from <A HREF="../PEP/PEPCreate.html#PEPCreate">PEPCreate</A>()
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>comp </B></TD><TD> - a pointer to the comparison function
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>ctx </B></TD><TD> - a context pointer (the last parameter to the comparison function)
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#883300">Calling sequence of comp</FONT></H3>
<pre>
<A HREF="https://petsc.org/release/manualpages/Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> comp(<A HREF="https://petsc.org/release/manualpages/Sys/PetscScalar.html#PetscScalar">PetscScalar</A> ar,<A HREF="https://petsc.org/release/manualpages/Sys/PetscScalar.html#PetscScalar">PetscScalar</A> ai,<A HREF="https://petsc.org/release/manualpages/Sys/PetscScalar.html#PetscScalar">PetscScalar</A> br,<A HREF="https://petsc.org/release/manualpages/Sys/PetscScalar.html#PetscScalar">PetscScalar</A> bi,<A HREF="https://petsc.org/release/manualpages/Sys/PetscInt.html#PetscInt">PetscInt</A> *res,void *ctx)
</pre>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>ar </B></TD><TD> - real part of the 1st eigenvalue
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>ai </B></TD><TD> - imaginary part of the 1st eigenvalue
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>br </B></TD><TD> - real part of the 2nd eigenvalue
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>bi </B></TD><TD> - imaginary part of the 2nd eigenvalue
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>res </B></TD><TD> - result of comparison
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>ctx </B></TD><TD> - optional context, as set by <A HREF="../PEP/PEPSetEigenvalueComparison.html#PEPSetEigenvalueComparison">PEPSetEigenvalueComparison</A>()
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#883300">Note</FONT></H3>
The returning parameter 'res' can be
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>negative </B></TD><TD> - if the 1st eigenvalue is preferred to the 2st one
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>zero </B></TD><TD> - if both eigenvalues are equally preferred
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>positive </B></TD><TD> - if the 2st eigenvalue is preferred to the 1st one
</TD></TR></TABLE>
<P>
<P>
<H3><FONT COLOR="#883300">See Also</FONT></H3>
<A HREF="../PEP/PEPSetWhichEigenpairs.html#PEPSetWhichEigenpairs">PEPSetWhichEigenpairs</A>(), <A HREF="../PEP/PEPWhich.html#PEPWhich">PEPWhich</A>
<BR><P><B></B><H3><FONT COLOR="#883300">Level</FONT></H3>advanced<BR>
<H3><FONT COLOR="#883300">Location</FONT></H3>
</B><A HREF="../../../src/pep/interface/pepopts.c.html#PEPSetEigenvalueComparison">src/pep/interface/pepopts.c</A>
<P><H3><FONT COLOR="#883300">Examples</FONT></H3>
<A HREF="../../../src/pep/tutorials/nlevp/pdde_stability.c.html">src/pep/tutorials/nlevp/pdde_stability.c</A><BR>
<BR><BR><A HREF="./index.html">Index of all PEP routines</A>
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