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<div id="version" align=right><b>petsc-3.10.3 2018-12-18</b></div>
<div id="bugreport" align=right><a href="mailto:petsc-maint@mcs.anl.gov?subject=Typo or Error in Documentation &body=Please describe the typo or error in the documentation: petsc-3.10.3 v3.10.3 docs/manualpages/Mat/MatMatMult.html "><small>Report Typos and Errors</small></a></div>
<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>
<DT><B>C </B> -the product matrix
<br>
<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 either <A HREF="../Mat/MatReuse.html#MatReuse">MAT_INITIAL_MATRIX</A> or <A HREF="../Mat/MatMatMultSymbolic.html#MatMatMultSymbolic">MatMatMultSymbolic</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 either
<pre>
1) use <A HREF="../Mat/MatReuse.html#MatReuse">MAT_REUSE_MATRIX</A> 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 <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/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></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/examples/tutorials/ex70.c.html">src/snes/examples/tutorials/ex70.c.html</A><BR>
<P><H3><FONT COLOR="CC3333">Implementations</FONT></H3><A HREF="../../../src/mat/impls/aij/mpi/mpiaij.c.html#MatMatMult_MPIDense_MPIAIJ">MatMatMult_MPIDense_MPIAIJ in src/mat/impls/aij/mpi/mpiaij.c</A><BR>
<A HREF="../../../src/mat/impls/aij/mpi/mpimatmatmult.c.html#MatMatMult_MPIAIJ_MPIAIJ">MatMatMult_MPIAIJ_MPIAIJ in src/mat/impls/aij/mpi/mpimatmatmult.c</A><BR>
<A HREF="../../../src/mat/impls/aij/mpi/mpimatmatmult.c.html#MatMatMult_MPIAIJ_MPIDense">MatMatMult_MPIAIJ_MPIDense in src/mat/impls/aij/mpi/mpimatmatmult.c</A><BR>
<A HREF="../../../src/mat/impls/aij/seq/aij.c.html#MatMatMult_SeqDense_SeqAIJ">MatMatMult_SeqDense_SeqAIJ in src/mat/impls/aij/seq/aij.c</A><BR>
<A HREF="../../../src/mat/impls/aij/seq/aijmkl/aijmkl.c.html#MatMatMult_SeqAIJMKL_SeqAIJMKL_SpMV2">MatMatMult_SeqAIJMKL_SeqAIJMKL_SpMV2 in src/mat/impls/aij/seq/aijmkl/aijmkl.c</A><BR>
<A HREF="../../../src/mat/impls/aij/seq/matmatmult.c.html#MatMatMult_SeqAIJ_SeqAIJ">MatMatMult_SeqAIJ_SeqAIJ in src/mat/impls/aij/seq/matmatmult.c</A><BR>
<A HREF="../../../src/mat/impls/aij/seq/matmatmult.c.html#MatMatMult_SeqAIJ_SeqDense">MatMatMult_SeqAIJ_SeqDense in src/mat/impls/aij/seq/matmatmult.c</A><BR>
<A HREF="../../../src/mat/impls/aij/seq/matmatmult.c.html#MatMatMult_SeqAIJ_SeqAIJ_Combined">MatMatMult_SeqAIJ_SeqAIJ_Combined in src/mat/impls/aij/seq/matmatmult.c</A><BR>
<A HREF="../../../src/mat/impls/dense/mpi/mpidense.c.html#MatMatMult_MPIDense_MPIDense">MatMatMult_MPIDense_MPIDense in src/mat/impls/dense/mpi/mpidense.c</A><BR>
<A HREF="../../../src/mat/impls/dense/seq/dense.c.html#MatMatMult_SeqDense_SeqDense">MatMatMult_SeqDense_SeqDense in src/mat/impls/dense/seq/dense.c</A><BR>
<A HREF="../../../src/mat/impls/elemental/matelem.cxx.html#MatMatMult_Elemental">MatMatMult_Elemental in src/mat/impls/elemental/matelem.cxx</A><BR>
<A HREF="../../../src/mat/impls/hypre/mhypre.c.html#MatMatMult_HYPRE_HYPRE">MatMatMult_HYPRE_HYPRE in src/mat/impls/hypre/mhypre.c</A><BR>
<BR><A HREF="./index.html">Index of all Mat routines</A>
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