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<div id="version" align=right><b>petsc-3.7.5 2017-01-01</b></div>
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<A NAME="MatMFFDComputeJacobian"><H1>MatMFFDComputeJacobian</H1></A>
Tells the matrix-free Jacobian object the new location at which Jacobian matrix vector products will be computed at, i.e. J(x) * a. The x is obtained from the <A HREF="../SNES/SNES.html#SNES">SNES</A> object (using <A HREF="../SNES/SNESGetSolution.html#SNESGetSolution">SNESGetSolution</A>()).
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscsnes.h"
#include "petscdm.h"
PetscErrorCode MatMFFDComputeJacobian(SNES snes,Vec x,Mat jac,Mat B,void *dummy)
</PRE>
Logically Collective on <A HREF="../SNES/SNES.html#SNES">SNES</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>snes </B></TD><TD>- the nonlinear solver context
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>x </B></TD><TD>- the point at which the Jacobian vector products will be performed
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>jac </B></TD><TD>- the matrix-free Jacobian object
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>B </B></TD><TD>- either the same as jac or another matrix type (ignored)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>flag </B></TD><TD>- not relevent for matrix-free form
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>dummy </B></TD><TD>- the user context (ignored)
</TD></TR></TABLE>
<P>
<P>
<H3><FONT COLOR="#CC3333">Warning</FONT></H3>
If <A HREF="../Mat/MatMFFDSetBase.html#MatMFFDSetBase">MatMFFDSetBase</A>() is ever called on jac then this routine will NO longer get
the x from the <A HREF="../SNES/SNES.html#SNES">SNES</A> object and <A HREF="../Mat/MatMFFDSetBase.html#MatMFFDSetBase">MatMFFDSetBase</A>() must from that point on be used to
change the base vector x.
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
This can be passed into <A HREF="../SNES/SNESSetJacobian.html#SNESSetJacobian">SNESSetJacobian</A>() as the Jacobian evaluation function argument
when using a completely matrix-free solver,
that is the B matrix is also the same matrix operator. This is used when you select
-snes_mf but rarely used directly by users. (All this routine does is call <A HREF="../Mat/MatAssemblyBegin.html#MatAssemblyBegin">MatAssemblyBegin</A>/End() on
the <A HREF="../Mat/Mat.html#Mat">Mat</A> jac.)
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../Mat/MatMFFDGetH.html#MatMFFDGetH">MatMFFDGetH</A>(), <A HREF="../SNES/MatCreateSNESMF.html#MatCreateSNESMF">MatCreateSNESMF</A>(), <A HREF="../Mat/MatCreateMFFD.html#MatCreateMFFD">MatCreateMFFD</A>(), <A HREF="../Mat/MATMFFD.html#MATMFFD">MATMFFD</A>,
<BR><A HREF="../Mat/MatMFFDSetHHistory.html#MatMFFDSetHHistory">MatMFFDSetHHistory</A>(), <A HREF="../Mat/MatMFFDSetFunctionError.html#MatMFFDSetFunctionError">MatMFFDSetFunctionError</A>(), <A HREF="../Mat/MatCreateMFFD.html#MatCreateMFFD">MatCreateMFFD</A>(), <A HREF="../SNES/SNESSetJacobian.html#SNESSetJacobian">SNESSetJacobian</A>()
<P>
<P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>developer
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/snes/mf/snesmfj.c.html#MatMFFDComputeJacobian">src/snes/mf/snesmfj.c</A>
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