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<div id="version" align=right><b>petsc-3.14.5 2021-03-03</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"
<A HREF="../Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> <A HREF="../Mat/MatMatMult.html#MatMatMult">MatMatMult</A>(<A HREF="../Mat/Mat.html#Mat">Mat</A> A,<A HREF="../Mat/Mat.html#Mat">Mat</A> B,<A HREF="../Mat/MatReuse.html#MatReuse">MatReuse</A> scall,<A HREF="../Sys/PetscReal.html#PetscReal">PetscReal</A> fill,<A HREF="../Mat/Mat.html#Mat">Mat</A> *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 <A HREF="../Mat/MatReuse.html#MatReuse">MAT_INITIAL_MATRIX</A> or <A HREF="../Mat/MatReuse.html#MatReuse">MAT_REUSE_MATRIX</A>
</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>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>C </B></TD><TD>- the product matrix
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
Unless scall is <A HREF="../Mat/MatReuse.html#MatReuse">MAT_REUSE_MATRIX</A> C will be created.
<P>
<A HREF="../Mat/MatReuse.html#MatReuse">MAT_REUSE_MATRIX</A> can only be used if the matrices A and B have the same nonzero pattern as in the previous call and C was obtained from a previous
call to this function with <A HREF="../Mat/MatReuse.html#MatReuse">MAT_INITIAL_MATRIX</A>.
<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 use <A HREF="../Mat/MatProductCreate.html#MatProductCreate">MatProductCreate</A>()/<A HREF="../Mat/MatProductSymbolic.html#MatProductSymbolic">MatProductSymbolic</A>(C)/ReplaceMats(), and call <A HREF="../Mat/MatProductNumeric.html#MatProductNumeric">MatProductNumeric</A>() repeatedly.
<P>
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 <A HREF="../Mat/MatReuse.html#MatReuse">MAT_REUSE_MATRIX</A>, 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/MatTransposeMatMult.html#MatTransposeMatMult">MatTransposeMatMult</A>(), <A HREF="../Mat/MatMatTransposeMult.html#MatMatTransposeMult">MatMatTransposeMult</A>(), <A HREF="../Mat/MatPtAP.html#MatPtAP">MatPtAP</A>()
<BR><P><B></B><H3><FONT COLOR="#CC3333">Level</FONT></H3>intermediate<BR>
<H3><FONT COLOR="#CC3333">Location</FONT></H3>
</B><A HREF="../../../src/mat/interface/matrix.c.html#MatMatMult">src/mat/interface/matrix.c</A>
<P><H3><FONT COLOR="#CC3333">Examples</FONT></H3>
<A HREF="../../../src/snes/tutorials/ex70.c.html">src/snes/tutorials/ex70.c.html</A><BR>
<A HREF="../../../src/tao/pde_constrained/tutorials/elliptic.c.html">src/tao/pde_constrained/tutorials/elliptic.c.html</A><BR>
<A HREF="../../../src/tao/pde_constrained/tutorials/parabolic.c.html">src/tao/pde_constrained/tutorials/parabolic.c.html</A><BR>
<BR><A HREF="./index.html">Index of all Mat routines</A>
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