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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="MatCreateMFFD"><H1>MatCreateMFFD</H1></A>
Creates a matrix-free matrix. See also <A HREF="../SNES/MatCreateSNESMF.html#MatCreateSNESMF">MatCreateSNESMF</A>()
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscmat.h"
PetscErrorCode MatCreateMFFD(MPI_Comm comm,PetscInt m,PetscInt n,PetscInt M,PetscInt N,Mat *J)
</PRE>
Collective on <A HREF="../Vec/Vec.html#Vec">Vec</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>comm </B></TD><TD>- MPI communicator
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>m </B></TD><TD>- number of local rows (or <A HREF="../Sys/PETSC_DECIDE.html#PETSC_DECIDE">PETSC_DECIDE</A> to have calculated if M is given)
This value should be the same as the local size used in creating the
y vector for the matrix-vector product y = Ax.
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>n </B></TD><TD>- This value should be the same as the local size used in creating the
x vector for the matrix-vector product y = Ax. (or <A HREF="../Sys/PETSC_DECIDE.html#PETSC_DECIDE">PETSC_DECIDE</A> to have
calculated if N is given) For square matrices n is almost always m.
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>M </B></TD><TD>- number of global rows (or <A HREF="../Sys/PETSC_DETERMINE.html#PETSC_DETERMINE">PETSC_DETERMINE</A> to have calculated if m is given)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>N </B></TD><TD>- number of global columns (or <A HREF="../Sys/PETSC_DETERMINE.html#PETSC_DETERMINE">PETSC_DETERMINE</A> to have calculated if n is given)
</TD></TR></TABLE>
<P>
<P>
<H3><FONT COLOR="#CC3333">Output Parameter</FONT></H3>
<DT><B>J </B> -the matrix-free matrix
<br>
<P>
Options Database Keys: call <A HREF="../Mat/MatSetFromOptions.html#MatSetFromOptions">MatSetFromOptions</A>() to trigger these
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-mat_mffd_type </B></TD><TD>- wp or ds (see <A HREF="../Mat/MATMFFD_WP.html#MATMFFD_WP">MATMFFD_WP</A> or <A HREF="../Mat/MATMFFD_DS.html#MATMFFD_DS">MATMFFD_DS</A>)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-mat_mffd_err </B></TD><TD>- square root of estimated relative error in function evaluation
</TD></TR></TABLE>
<DT><B>-mat_mffd_period </B> -how often h is recomputed, defaults to 1, everytime
<br>
</TABLE>
<P>
<P>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
The matrix-free matrix context merely contains the function pointers
and work space for performing finite difference approximations of
Jacobian-vector products, F'(u)*a,
<P>
The default code uses the following approach to compute h
<P>
<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 otherwise
where
error_rel = square root of relative error in function evaluation
umin = minimum iterate parameter
</PRE>
<P>
You can call <A HREF="../SNES/SNESSetJacobian.html#SNESSetJacobian">SNESSetJacobian</A>() with <A HREF="../SNES/MatMFFDComputeJacobian.html#MatMFFDComputeJacobian">MatMFFDComputeJacobian</A>() if you are using matrix and not a different
preconditioner matrix
<P>
The user can set the error_rel via <A HREF="../Mat/MatMFFDSetFunctionError.html#MatMFFDSetFunctionError">MatMFFDSetFunctionError</A>() and
umin via <A HREF="../Mat/MatMFFDDSSetUmin.html#MatMFFDDSSetUmin">MatMFFDDSSetUmin</A>(); see Users-Manual: ch_snes for details.
<P>
The user should call <A HREF="../Mat/MatDestroy.html#MatDestroy">MatDestroy</A>() when finished with the matrix-free
matrix context.
<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>-mat_mffd_err <error_rel> </B></TD><TD>- Sets error_rel
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-mat_mffd_unim <umin> </B></TD><TD>- Sets umin (for default PETSc routine that computes h only)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-mat_mffd_check_positivity</B></TD><TD>-
</TD></TR></TABLE>
<H3><FONT COLOR="#CC3333">Keywords</FONT></H3>
default, matrix-free, create, matrix
<BR>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../Mat/MatDestroy.html#MatDestroy">MatDestroy</A>(), <A HREF="../Mat/MatMFFDSetFunctionError.html#MatMFFDSetFunctionError">MatMFFDSetFunctionError</A>(), <A HREF="../Mat/MatMFFDDSSetUmin.html#MatMFFDDSSetUmin">MatMFFDDSSetUmin</A>(), <A HREF="../Mat/MatMFFDSetFunction.html#MatMFFDSetFunction">MatMFFDSetFunction</A>()
<BR><A HREF="../Mat/MatMFFDSetHHistory.html#MatMFFDSetHHistory">MatMFFDSetHHistory</A>(), <A HREF="../Mat/MatMFFDResetHHistory.html#MatMFFDResetHHistory">MatMFFDResetHHistory</A>(), <A HREF="../SNES/MatCreateSNESMF.html#MatCreateSNESMF">MatCreateSNESMF</A>(),
<A HREF="../Mat/MatMFFDGetH.html#MatMFFDGetH">MatMFFDGetH</A>(), <A HREF="../Mat/MatMFFDRegister.html#MatMFFDRegister">MatMFFDRegister</A>(), <A HREF="../SNES/MatMFFDComputeJacobian.html#MatMFFDComputeJacobian">MatMFFDComputeJacobian</A>()
<P>
<P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>advanced
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/mat/impls/mffd/mffd.c.html#MatCreateMFFD">src/mat/impls/mffd/mffd.c</A>
<BR><A HREF="./index.html">Index of all Mat routines</A>
<BR><A HREF="../../index.html">Table of Contents for all manual pages</A>
<BR><A HREF="../singleindex.html">Index of all manual pages</A>
<P><H3><FONT COLOR="#CC3333">Examples</FONT></H3>
<A HREF="../../../src/snes/examples/tutorials/ex22.c.html">src/snes/examples/tutorials/ex22.c.html</A><BR>
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