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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="MatGetOrdering"><H1>MatGetOrdering</H1></A>
Gets a reordering for a matrix to reduce fill or to improve numerical stability of LU factorization.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscmat.h"
PetscErrorCode MatGetOrdering(Mat mat,MatOrderingType type,IS *rperm,IS *cperm)
</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
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>type </B></TD><TD>- type of reordering, one of the following:
</TD></TR></TABLE>
<pre>
MATORDERINGNATURAL - Natural
</pre>
<pre>
MATORDERINGND - Nested Dissection
</pre>
<pre>
MATORDERING1WD - One-way Dissection
</pre>
<pre>
MATORDERINGRCM - Reverse Cuthill-McKee
</pre>
<pre>
MATORDERINGQMD - Quotient Minimum Degree
</pre>
<P>
<H3><FONT COLOR="#CC3333">Output Parameters</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>rperm </B></TD><TD>- row permutation indices
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>cperm </B></TD><TD>- column permutation indices
</TD></TR></TABLE>
<P>
<P>
<H3><FONT COLOR="#CC3333">Options Database Key</FONT></H3>
<DT><B>-mat_view_ordering draw </B> -plots matrix nonzero structure in new ordering
<br>
<P>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
This DOES NOT actually reorder the matrix; it merely returns two index sets
that define a reordering. This is usually not used directly, rather use the
options <A HREF="../PC/PCFactorSetMatOrderingType.html#PCFactorSetMatOrderingType">PCFactorSetMatOrderingType</A>()
<P>
The user can define additional orderings; see <A HREF="../MatOrderings/MatOrderingRegister.html#MatOrderingRegister">MatOrderingRegister</A>().
<P>
These are generally only implemented for sequential sparse matrices.
<P>
The external packages that PETSc can use for direct factorization such as SuperLU do not accept orderings provided by
this call.
<P>
<P>
<H3><FONT COLOR="#CC3333">Keywords</FONT></H3>
matrix, set, ordering, factorization, direct, ILU, LU,
<BR>fill, reordering, natural, Nested Dissection,
One-way Dissection, Cholesky, Reverse Cuthill-McKee,
Quotient Minimum Degree
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../MatOrderings/MatOrderingRegister.html#MatOrderingRegister">MatOrderingRegister</A>(), <A HREF="../PC/PCFactorSetMatOrderingType.html#PCFactorSetMatOrderingType">PCFactorSetMatOrderingType</A>()
<BR><P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>intermediate
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/mat/order/sorder.c.html#MatGetOrdering">src/mat/order/sorder.c</A>
<BR><A HREF="./index.html">Index of all MatOrderings 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/mat/examples/tutorials/ex1.c.html">src/mat/examples/tutorials/ex1.c.html</A><BR>
<A HREF="../../../src/ksp/ksp/examples/tutorials/ex18.c.html">src/ksp/ksp/examples/tutorials/ex18.c.html</A><BR>
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