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   <div id="version" align=right><b>slepc-3.14.2 2021-02-01</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-3.14.2 v3.14.2 docs/manualpages/PEP/PEPSetEigenvalueComparison.html "><small>Report Typos and Errors</small></a></div>
<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" 
PetscErrorCode <A HREF="../PEP/PEPSetEigenvalueComparison.html#PEPSetEigenvalueComparison">PEPSetEigenvalueComparison</A>(<A HREF="../PEP/PEP.html#PEP">PEP</A> pep,PetscErrorCode (*func)(PetscScalar,PetscScalar,PetscScalar,PetscScalar,PetscInt*,void*),void* ctx)
</PRE>
Logically Collective on pep
<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>func </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 func</FONT></H3>
<pre>
  func(PetscScalar ar,PetscScalar ai,PetscScalar br,PetscScalar bi,PetscInt *res,void *ctx)
</pre>
<P>
<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><FONT COLOR="#883300">Location: </FONT></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.html</A><BR>
<BR><A HREF="./index.html">Index of all PEP routines</A>
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