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<div id="version" align=right><b>slepc-3.22.2 2024-12-02</b></div>
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<H1>EPSSetTrueResidual</H1>
Specifies if the solver must compute the true residual explicitly or not.
<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/EPSSetTrueResidual.html#EPSSetTrueResidual">EPSSetTrueResidual</A>(<A HREF="../EPS/EPS.html#EPS">EPS</A> eps,<A HREF="https://petsc.org/release/manualpages/Sys/PetscBool.html#PetscBool">PetscBool</A> trueres)
</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> - the eigensolver context
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>trueres </B></TD><TD> - whether true residuals are required or not
</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_true_residual <boolean> </B></TD><TD> - Sets/resets the boolean flag 'trueres'
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#883300">Notes</FONT></H3>
If the user sets trueres=<A HREF="https://petsc.org/release/manualpages/Sys/PETSC_TRUE.html#PETSC_TRUE">PETSC_TRUE</A> then the solver explicitly computes
the true residual for each eigenpair approximation, and uses it for
convergence testing. Computing the residual is usually an expensive
operation. Some solvers (e.g., Krylov solvers) can avoid this computation
by using a cheap estimate of the residual norm, but this may sometimes
give inaccurate results (especially if a spectral transform is being
used). On the contrary, preconditioned eigensolvers (e.g., Davidson solvers)
do rely on computing the true residual, so this option is irrelevant for them.
<P>
<P>
<H3><FONT COLOR="#883300">See Also</FONT></H3>
<A HREF="../EPS/EPSGetTrueResidual.html#EPSGetTrueResidual">EPSGetTrueResidual</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/eps/interface/epsopts.c.html#EPSSetTrueResidual">src/eps/interface/epsopts.c</A>
<BR><BR><A HREF="./index.html">Index of all EPS routines</A>
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