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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="MatMatMult"><H1>MatMatMult</H1></A>
Performs Matrix-Matrix Multiplication C=A*B.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscmat.h"
PetscErrorCode MatMatMult(Mat A,Mat B,MatReuse scall,PetscReal fill,Mat *C)
</PRE>
Neighbor-wise 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>A </B></TD><TD>- the left matrix
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>B </B></TD><TD>- the right matrix
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>scall </B></TD><TD>- either MAT_INITIAL_MATRIX or MAT_REUSE_MATRIX
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>fill </B></TD><TD>- expected fill as ratio of nnz(C)/(nnz(A) + nnz(B)), use <A HREF="../Sys/PETSC_DEFAULT.html#PETSC_DEFAULT">PETSC_DEFAULT</A> if you do not have a good estimate
if the result is a dense matrix this is irrelevent
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Output Parameters</FONT></H3>
<DT><B>C </B> -the product matrix
<br>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
Unless scall is MAT_REUSE_MATRIX C will be created.
<P>
MAT_REUSE_MATRIX can only be used if the matrices A and B have the same nonzero pattern as in the previous call
<P>
To determine the correct fill value, run with -info and search for the string "Fill ratio" to see the value
actually needed.
<P>
If you have many matrices with the same non-zero structure to multiply, you
should either
<pre>
1) use MAT_REUSE_MATRIX in all calls but the first or
</pre>
<pre>
2) call <A HREF="../Mat/MatMatMultSymbolic.html#MatMatMultSymbolic">MatMatMultSymbolic</A>() once and then <A HREF="../Mat/MatMatMultNumeric.html#MatMatMultNumeric">MatMatMultNumeric</A>() for each product needed
</pre>
In the special case where matrix B (and hence C) are dense you can create the correctly sized matrix C yourself and then call this routine
with MAT_REUSE_MATRIX, rather than first having <A HREF="../Mat/MatMatMult.html#MatMatMult">MatMatMult</A>() create it for you. You can NEVER do this if the matrix C is sparse.
<P>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../Mat/MatMatMultSymbolic.html#MatMatMultSymbolic">MatMatMultSymbolic</A>(), <A HREF="../Mat/MatMatMultNumeric.html#MatMatMultNumeric">MatMatMultNumeric</A>(), <A HREF="../Mat/MatTransposeMatMult.html#MatTransposeMatMult">MatTransposeMatMult</A>(), <A HREF="../Mat/MatMatTransposeMult.html#MatMatTransposeMult">MatMatTransposeMult</A>(), <A HREF="../Mat/MatPtAP.html#MatPtAP">MatPtAP</A>()
<BR><P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>intermediate
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/mat/interface/matrix.c.html#MatMatMult">src/mat/interface/matrix.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/ex70.c.html">src/snes/examples/tutorials/ex70.c.html</A><BR>
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