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<TITLE>MatSNESMFSetFunctionError</TITLE>
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<A NAME="MatSNESMFSetFunctionError"><H1>MatSNESMFSetFunctionError</H1></A>
Sets the error_rel for the approximation of matrix-vector products using finite differences.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscsnes.h"
int MatSNESMFSetFunctionError(Mat mat,PetscReal error)
</PRE>
Collective on <A HREF="../Mat/Mat.html#Mat">Mat</A>
<P>
<H3><FONT COLOR="#CC3333">Input Parameters</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>mat </B></TD><TD>- the matrix free matrix created via <A HREF="../SNESMF/MatCreateSNESMF.html#MatCreateSNESMF">MatCreateSNESMF</A>()
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>error_rel </B></TD><TD>- relative error (should be set to the square root of
the relative error in the function evaluations)
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Options Database Keys</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-snes_mf_err <error_rel> </B></TD><TD>- Sets error_rel
</TD></TR>
<P>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
The default matrix-free matrix-vector product routine computes
<PRE>
F'(u)*a = [F(u+h*a) - F(u)]/h where
h = error_rel*u'a/||a||^2 if |u'a| > umin*||a||_{1}
= error_rel*umin*sign(u'a)*||a||_{1}/||a||^2 else
</PRE>
<P>
<H3><FONT COLOR="#CC3333">Keywords</FONT></H3>
<A HREF="../SNES/SNES.html#SNES">SNES</A>, matrix-free, parameters
<BR>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../SNESMF/MatCreateSNESMF.html#MatCreateSNESMF">MatCreateSNESMF</A>(),<A HREF="../SNESMF/MatSNESMFGetH.html#MatSNESMFGetH">MatSNESMFGetH</A>(),
<BR><A HREF="../SNESMF/MatSNESMFSetHHistory.html#MatSNESMFSetHHistory">MatSNESMFSetHHistory</A>(), <A HREF="../SNESMF/MatSNESMFResetHHistory.html#MatSNESMFResetHHistory">MatSNESMFResetHHistory</A>(),
MatSNESMFKSPMonitor()
<P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>advanced
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/snes/mf/snesmfj.c.html#MatSNESMFSetFunctionError">src/snes/mf/snesmfj.c</A>
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