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<TITLE>PCFactorSetUseDropTolerance</TITLE>
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<A NAME="PCFactorSetUseDropTolerance"><H1>PCFactorSetUseDropTolerance</H1></A>
The preconditioner will use an ILU based on a drop tolerance.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscpc.h"
PetscErrorCode PETSCKSP_DLLEXPORT PCFactorSetUseDropTolerance(PC pc,PetscReal dt,PetscReal dtcol,PetscInt maxrowcount)
</PRE>
Collective on <A HREF="../PC/PC.html#PC">PC</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>pc </B></TD><TD>- the preconditioner context
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>dt </B></TD><TD>- the drop tolerance, try from 1.e-10 to .1
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>dtcol </B></TD><TD>- tolerance for column pivot, good values [0.1 to 0.01]
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>maxrowcount </B></TD><TD>- the max number of nonzeros allowed in a row, best value
depends on the number of nonzeros in row of original matrix
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Options Database Key</FONT></H3>
<DT><B>-pc_factor_use_drop_tolerance <dt,dtcol,maxrowcount> </B> -Sets drop tolerance
<br>
<P>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
This uses the iludt() code of Saad's SPARSKIT package
<P>
There are NO default values for the 3 parameters, you must set them with reasonable values for your
matrix. We don't know how to compute reasonable values.
<P>
<H3><FONT COLOR="#CC3333">Keywords</FONT></H3>
<A HREF="../PC/PC.html#PC">PC</A>, levels, reordering, factorization, incomplete, ILU
<BR><P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>intermediate
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/ksp/pc/impls/factor/ilu/ilu.c.html#PCFactorSetUseDropTolerance">src/ksp/pc/impls/factor/ilu/ilu.c</A>
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