<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<font face="Ubuntu">I tried <br>
</font><br>
<font face="Ubuntu"><font face="Ubuntu">-pc_type gamg
-pc_mg_cycle_type v -pc_gamg_agg_nsmooths 1 </font><font
face="Ubuntu">-mg_coarse_sub_pc_factor_shift_nonzero<br>
<br>
but I still get <br>
<br>
[0]PETSC ERROR: Detected zero pivot in LU factorization:<br>
see
<a class="moz-txt-link-freetext" href="http://www.mcs.anl.gov/petsc/documentation/faq.html#ZeroPivot">http://www.mcs.anl.gov/petsc/documentation/faq.html#ZeroPivot</a>!<br>
[0]PETSC ERROR: Zero pivot row 280 value 6.58999e-17 tolerance
2.22045e-14!<br>
[0]PETSC ERROR:
------------------------------------------------------------------------<br>
[0]PETSC ERROR: Petsc Release Version 3.3.0, Patch 3, Wed Aug 29
11:26:24 CDT 2012<br>
[0]PETSC ERROR: See docs/changes/index.html for recent updates.<br>
[0]PETSC ERROR: See docs/faq.html for hints about trouble
shooting.<br>
[0]PETSC ERROR: See docs/index.html for manual pages.<br>
[0]PETSC ERROR:
------------------------------------------------------------------------<br>
[0]PETSC ERROR: ./hit on a named nid21818 by Unknown Fri May 24
16:08:33 2013<br>
[0]PETSC ERROR: Libraries linked from<br>
[0]PETSC ERROR: Configure run at<br>
[0]PETSC ERROR: Configure options<br>
[0]PETSC ERROR:
------------------------------------------------------------------------<br>
[0]PETSC ERROR: MatPivotCheck_none() line 583 in
src/mat/impls/aij/seq//ptmp/skelly/petsc/3.3.03/cray_interlagos_build/real/src/include/petsc-private/matimpl.h<br>
[0]PETSC ERROR: MatPivotCheck() line 602 in
src/mat/impls/aij/seq//ptmp/skelly/petsc/3.3.03/cray_interlagos_build/real/src/include/petsc-private/matimpl.h<br>
[0]PETSC ERROR: MatLUFactorNumeric_SeqAIJ() line 585 in
src/mat/impls/aij/seq/aijfact.c<br>
[0]PETSC ERROR: MatLUFactorNumeric() line 2803 in
src/mat/interface/matrix.c<br>
[0]PETSC ERROR: PCSetUp_LU() line 160 in
src/ksp/pc/impls/factor/lu/lu.c<br>
[0]PETSC ERROR: PCSetUp() line 832 in
src/ksp/pc/interface/precon.c<br>
[0]PETSC ERROR: KSPSetUp() line 278 in
src/ksp/ksp/interface/itfunc.c<br>
[0]PETSC ERROR: PCSetUpOnBlocks_BJacobi_Singleblock() line 715
in src/ksp/pc/impls/bjacobi/bjacobi.c<br>
[0]PETSC ERROR: PCSetUpOnBlocks() line 865 in
src/ksp/pc/interface/precon.c<br>
[0]PETSC ERROR: KSPSetUpOnBlocks() line 154 in
src/ksp/ksp/interface/itfunc.c<br>
[0]PETSC ERROR: KSPSolve() line 403 in
src/ksp/ksp/interface/itfunc.c<br>
[0]PETSC ERROR: PCMGMCycle_Private() line 20 in
src/ksp/pc/impls/mg/mg.c<br>
[0]PETSC ERROR: PCMGMCycle_Private() line 49 in
src/ksp/pc/impls/mg/mg.c<br>
[0]PETSC ERROR: PCMGMCycle_Private() line 49 in
src/ksp/pc/impls/mg/mg.c<br>
[0]PETSC ERROR: PCMGMCycle_Private() line 49 in
src/ksp/pc/impls/mg/mg.c<br>
[0]PETSC ERROR: PCApply_MG() line 326 in
src/ksp/pc/impls/mg/mg.c<br>
[0]PETSC ERROR: PCApply() line 384 in
src/ksp/pc/interface/precon.c<br>
[0]PETSC ERROR: KSPSolve_CG() line 139 in
src/ksp/ksp/impls/cg/cg.c<br>
[0]PETSC ERROR: KSPSolve() line 446 in
src/ksp/ksp/interface/itfunc.c<br>
<br>
<br>
If instead I use <br>
<br>
</font>-pc_type gamg -pc_mg_cycle_type v -pc_gamg_agg_nsmooths 1
-mg_coarse_pc_type svd <br>
<br>
as Matthew suggested, I am told that there is an invalid argument.<br>
<br>
Michele<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
</font><font face="Ubuntu"><br>
<br>
</font>
<div class="moz-cite-prefix">On 05/24/2013 01:04 PM, Matthew Knepley
wrote:<br>
</div>
<blockquote
cite="mid:CAMYG4G=o=cDjxto_YL2PTrF3m82-bCZrcRWd-tzmHcu+XA18+w@mail.gmail.com"
type="cite">
<div dir="ltr">On Fri, May 24, 2013 at 2:55 PM, Jed Brown <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:jedbrown@mcs.anl.gov" target="_blank">jedbrown@mcs.anl.gov</a>></span>
wrote:<br>
<div class="gmail_extra">
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="im">Michele Rosso <<a
moz-do-not-send="true" href="mailto:mrosso@uci.edu">mrosso@uci.edu</a>>
writes:<br>
<br>
> Hi Jed,<br>
><br>
> I followed your suggestion by using:<br>
><br>
> -pc_type gamg -pc_mg_cycle_type v
-pc_gamg_agg_nsmooths 1<br>
><br>
> This works perfectly if I have a non-singular
matrix. When instead I use<br>
> periodic conditions for my system ( I set the
nullspace removal<br>
> correctly ),<br>
> I receive an error saying a zero pivot is detected
in the LU<br>
> factorization. So, after some research, I found in
the mailinglist a fix :<br>
><br>
> -pc_type gamg -pc_mg_cycle_type v
-pc_gamg_agg_nsmooths 1<br>
> -mg_coarse_pc_factor_shift_nonzero<br>
<br>
</div>
It'll need to be -mg_coarse_sub_pc_factor_shift_nonzero<br>
<br>
With petsc-3.4 (which you should upgrade to), use<br>
-mg_coarse_sub_pc_factor_shift_type NONZERO<br>
<br>
The reason you need this "sub" prefix is that the code
always restricts<br>
using block Jacobi (usually localized so that all the
entries are in one<br>
block), before applying the direct coarse solver.</blockquote>
<div><br>
</div>
<div style="">I think this is less elegant than</div>
<div style=""><br>
</div>
<div style=""> -mg_coarse_pc_type svd</div>
<div style=""><br>
</div>
<div style="">
Matt</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="HOEnZb">
<div class="h5">
> Still I am receiving the following error<br>
><br>
><br>
> [0]PETSC ERROR: --------------------- Error
Message<br>
> ------------------------------------<br>
> [0]PETSC ERROR: Detected zero pivot in LU
factorization:<br>
> see <a moz-do-not-send="true"
href="http://www.mcs.anl.gov/petsc/documentation/faq.html#ZeroPivot"
target="_blank">http://www.mcs.anl.gov/petsc/documentation/faq.html#ZeroPivot</a>!<br>
> [0]PETSC ERROR: Zero pivot row 280 value
6.5908e-17 tolerance 2.22045e-14!<br>
> [0]PETSC ERROR:<br>
>
------------------------------------------------------------------------<br>
> [0]PETSC ERROR: Petsc Release Version 3.3.0,
Patch 3, Wed Aug 29<br>
> 11:26:24 CDT 2012<br>
> [0]PETSC ERROR: See docs/changes/index.html for
recent updates.<br>
> [0]PETSC ERROR: See docs/faq.html for hints about
trouble shooting.<br>
> [0]PETSC ERROR: See docs/index.html for manual
pages.<br>
> [0]PETSC ERROR:<br>
>
------------------------------------------------------------------------<br>
> [0]PETSC ERROR: ./hit on a named nid09458 by
Unknown Fri May 24<br>
> 14:40:48 2013<br>
> [0]PETSC ERROR: Libraries linked from<br>
> [0]PETSC ERROR: Configure run at<br>
> [0]PETSC ERROR: Configure options<br>
> [0]PETSC ERROR:<br>
>
------------------------------------------------------------------------<br>
> [0]PETSC ERROR: MatPivotCheck_none() line 583 in<br>
>
src/mat/impls/aij/seq//ptmp/skelly/petsc/3.3.03/cray_interlagos_build/real/src/include/petsc-private/matimpl.h<br>
> [0]PETSC ERROR: MatPivotCheck() line 602 in<br>
>
src/mat/impls/aij/seq//ptmp/skelly/petsc/3.3.03/cray_interlagos_build/real/src/include/petsc-private/matimpl.h<br>
> [0]PETSC ERROR: MatLUFactorNumeric_SeqAIJ() line
585 in<br>
> src/mat/impls/aij/seq/aijfact.c<br>
> [0]PETSC ERROR: MatLUFactorNumeric() line 2803 in
src/mat/interface/matrix.c<br>
> [0]PETSC ERROR: PCSetUp_LU() line 160 in
src/ksp/pc/impls/factor/lu/lu.c<br>
> [0]PETSC ERROR: PCSetUp() line 832 in
src/ksp/pc/interface/precon.c<br>
> [0]PETSC ERROR: KSPSetUp() line 278 in
src/ksp/ksp/interface/itfunc.c<br>
> [0]PETSC ERROR:
PCSetUpOnBlocks_BJacobi_Singleblock() line 715 in<br>
> src/ksp/pc/impls/bjacobi/bjacobi.c<br>
> [0]PETSC ERROR: PCSetUpOnBlocks() line 865 in
src/ksp/pc/interface/precon.c<br>
> [0]PETSC ERROR: KSPSetUpOnBlocks() line 154 in<br>
> src/ksp/ksp/interface/itfunc.c<br>
> [0]PETSC ERROR: KSPSolve() line 403 in
src/ksp/ksp/interface/itfunc.c<br>
> [0]PETSC ERROR: PCMGMCycle_Private() line 20 in
src/ksp/pc/impls/mg/mg.c<br>
> [0]PETSC ERROR: PCMGMCycle_Private() line 49 in
src/ksp/pc/impls/mg/mg.c<br>
> [0]PETSC ERROR: PCMGMCycle_Private() line 49 in
src/ksp/pc/impls/mg/mg.c<br>
> [0]PETSC ERROR: PCMGMCycle_Private() line 49 in
src/ksp/pc/impls/mg/mg.c<br>
> [0]PETSC ERROR: PCApply_MG() line 326 in
src/ksp/pc/impls/mg/mg.c<br>
> [0]PETSC ERROR: PCApply() line 384 in
src/ksp/pc/interface/precon.c<br>
> [0]PETSC ERROR: KSPSolve_CG() line 139 in
src/ksp/ksp/impls/cg/cg.c<br>
> [0]PETSC ERROR: KSPSolve() line 446 in
src/ksp/ksp/interface/itfunc.c<br>
><br>
> What could the reason be?<br>
> Thank you,<br>
><br>
> Michele<br>
><br>
><br>
><br>
> On 05/17/2013 07:35 PM, Michele Rosso wrote:<br>
>> Thank you very much. I will try and let you
know.<br>
>><br>
>> Michele<br>
>><br>
>> On 05/17/2013 07:01 PM, Jed Brown wrote:<br>
>>> Michele Rosso<<a
moz-do-not-send="true" href="mailto:mrosso@uci.edu">mrosso@uci.edu</a>>
writes:<br>
>>><br>
>>>> I noticed that the problem appears
even if I use CG with the default<br>
>>>> preconditioner: commenting KSPSetDM()
solves the problem.<br>
>>> Okay, this issue can't show up if you use
SNES, but it's a consequence<br>
>>> of making geometric multigrid work with a
pure KSP interface. You can<br>
>>> either use KSPSetComputeOperators() to
put your assembly in a function<br>
>>> (which will also be called on coarse
levels if you use -pc_type mg<br>
>>> without Galerkin coarse operators) or you
can can provide the Jacobian<br>
>>> using KSPSetOperators() as usual, but
also call KSPSetDMActive() so that<br>
>>> the DM is not used for computing/updating
the Jacobian.<br>
>>><br>
>>> The logic is cleaner in petsc-3.4 and I
think it just does the right<br>
>>> thing in your case.<br>
>>><br>
>>>> So basically without a proper grid
(it seems no grid with an even<br>
>>>> numbers of nodes qualifies) and with
my own system matrix, I cannot use<br>
>>>> any type of multigrid<br>
>>>> pre-conditioner?<br>
>>> You can use all the AMG methods without
setting a DM.<br>
>>><br>
>><br>
</div>
</div>
</blockquote>
</div>
<br>
<br clear="all">
<div><br>
</div>
-- <br>
What most experimenters take for granted before they begin
their experiments is infinitely more interesting than any
results to which their experiments lead.<br>
-- Norbert Wiener
</div>
</div>
</blockquote>
<br>
</body>
</html>