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<div id="version" align=right><b>petsc-3.10.3 2018-12-18</b></div>
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<A NAME="PCGAMGSetThreshold"><H1>PCGAMGSetThreshold</H1></A>
Relative threshold to use for dropping edges in aggregation graph
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscpc.h"
<A HREF="../Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> <A HREF="../PC/PCGAMGSetThreshold.html#PCGAMGSetThreshold">PCGAMGSetThreshold</A>(<A HREF="../PC/PC.html#PC">PC</A> pc, <A HREF="../Sys/PetscReal.html#PetscReal">PetscReal</A> v[], <A HREF="../Sys/PetscInt.html#PetscInt">PetscInt</A> n)
</PRE>
Not 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>threshold </B></TD><TD>- the threshold value, 0.0 means keep all nonzero entries in the graph; negative means keep even zero entries in the graph
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Options Database Key</FONT></H3>
<DT><B>-pc_gamg_threshold <threshold></B> -
Notes:
Increasing the threshold decreases the rate of coarsening. Conversely reducing the threshold increases the rate of coarsening (aggressive coarsening) and thereby reduces the complexity of the coarse grids, and generally results in slower solver converge rates. Reducing coarse grid complexity reduced the complexity of Galerkin coarse grid construction considerably.
Before coarsening or aggregating the graph, GAMG removes small values from the graph with this threshold, and thus reducing the coupling in the graph and a different (perhaps better) coarser set of points.
<br>
<P>
<P>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../PC/PCGAMGFilterGraph.html#PCGAMGFilterGraph">PCGAMGFilterGraph</A>(), <A HREF="../PC/PCGAMGSetSquareGraph.html#PCGAMGSetSquareGraph">PCGAMGSetSquareGraph</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/gamg/gamg.c.html#PCGAMGSetThreshold">src/ksp/pc/impls/gamg/gamg.c</A>
<P><H3><FONT COLOR="CC3333">Implementations</FONT></H3><A HREF="../../../src/ksp/pc/impls/gamg/gamg.c.html#PCGAMGSetThreshold_GAMG">PCGAMGSetThreshold_GAMG in src/ksp/pc/impls/gamg/gamg.c</A><BR>
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