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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/PC/PCSPAISetBlockSize.html "><small>Report Typos and Errors</small></a></div>
<A NAME="PCSPAISetBlockSize"><H1>PCSPAISetBlockSize</H1></A>
set the block size for the SPAI preconditioner
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscpc.h"
<A HREF="../Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> <A HREF="../PC/PCSPAISetBlockSize.html#PCSPAISetBlockSize">PCSPAISetBlockSize</A>(<A HREF="../PC/PC.html#PC">PC</A> pc,int block_size1)
</PRE>
<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>pc </B></TD><TD>- the preconditioner
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>n </B></TD><TD>- block size (default 1)
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
A block
size of 1 treats A as a matrix of scalar elements. A
block size of s > 1 treats A as a matrix of sxs
blocks. A block size of 0 treats A as a matrix with
variable sized blocks, which are determined by
searching for dense square diagonal blocks in A.
This can be very effective for finite-element
matrices.
<P>
SPAI will convert A to block form, use a block
version of the preconditioner algorithm, and then
convert the result back to scalar form.
<P>
In many cases the a block-size parameter other than 1
can lead to very significant improvement in
performance.
<P>
<P>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../PC/PCSPAI.html#PCSPAI">PCSPAI</A>, <A HREF="../PC/PCSetType.html#PCSetType">PCSetType</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/ksp/pc/impls/spai/ispai.c.html#PCSPAISetBlockSize">src/ksp/pc/impls/spai/ispai.c</A>
<P><H3><FONT COLOR="CC3333">Implementations</FONT></H3><A HREF="../../../src/ksp/pc/impls/spai/ispai.c.html#PCSPAISetBlockSize_SPAI">PCSPAISetBlockSize_SPAI in src/ksp/pc/impls/spai/ispai.c</A><BR>
<BR><A HREF="./index.html">Index of all PC routines</A>
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