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<div id="version" align=right><b>petsc-3.4.2 2013-07-02</b></div>
<A NAME="MatSeqBAIJSetPreallocation"><H1>MatSeqBAIJSetPreallocation</H1></A>
Sets the block size and expected nonzeros per row in the matrix. For good matrix assembly performance the user should preallocate the matrix storage by setting the parameter nz (or the array nnz). By setting these parameters accurately, performance during matrix assembly can be increased by more than a factor of 50.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscmat.h"
PetscErrorCode MatSeqBAIJSetPreallocation(Mat B,PetscInt bs,PetscInt nz,const PetscInt nnz[])
</PRE>
Collective on <A HREF="../Sys/MPI_Comm.html#MPI_Comm">MPI_Comm</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 matrix
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>bs </B></TD><TD>- size of block
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>nz </B></TD><TD>- number of block nonzeros per block row (same for all rows)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>nnz </B></TD><TD>- array containing the number of block nonzeros in the various block rows
(possibly different for each block row) or NULL
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Options Database Keys</FONT></H3>
<DT><B>-mat_no_unroll </B> -uses code that does not unroll the loops in the
block calculations (much slower)
<br>
<DT><B>-mat_block_size </B> -size of the blocks to use
<br>
<P>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
If the nnz parameter is given then the nz parameter is ignored
<P>
You can call <A HREF="../Mat/MatGetInfo.html#MatGetInfo">MatGetInfo</A>() to get information on how effective the preallocation was;
for example the fields mallocs,nz_allocated,nz_used,nz_unneeded;
You can also run with the option -info and look for messages with the string
malloc in them to see if additional memory allocation was needed.
<P>
The block AIJ format is fully compatible with standard Fortran 77
storage. That is, the stored row and column indices can begin at
either one (as in Fortran) or zero. See the users' manual for details.
<P>
Specify the preallocated storage with either nz or nnz (not both).
Set nz=<A HREF="../Sys/PETSC_DEFAULT.html#PETSC_DEFAULT">PETSC_DEFAULT</A> and nnz=NULL for PETSc to control dynamic memory
allocation. See the <A href="../../docs/manual.pdf#nameddest=ch_mat"><A HREF="../Mat/Mat.html#Mat">Mat</A> chapter of the users manual</A> for details.
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../Mat/MatCreate.html#MatCreate">MatCreate</A>(), <A HREF="../Mat/MatCreateSeqAIJ.html#MatCreateSeqAIJ">MatCreateSeqAIJ</A>(), <A HREF="../Mat/MatSetValues.html#MatSetValues">MatSetValues</A>(), <A HREF="../Mat/MatCreateBAIJ.html#MatCreateBAIJ">MatCreateBAIJ</A>(), <A HREF="../Mat/MatGetInfo.html#MatGetInfo">MatGetInfo</A>()
<BR><P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>intermediate
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/mat/impls/baij/seq/baij.c.html#MatSeqBAIJSetPreallocation">src/mat/impls/baij/seq/baij.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/mat/examples/tutorials/ex17.c.html">src/mat/examples/tutorials/ex17.c.html</A><BR>
<A HREF="../../../src/snes/examples/tutorials/ex48.c.html">src/snes/examples/tutorials/ex48.c.html</A><BR>
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