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<p>Hi everyone,<br>
<br>
I'm joining this discussion because we're testing a simple way to
simplify the current object naming and configuration system in
PETSc.<br>
<br>
The solution we're testing uses the same philosophy as the option
database keys: a "default" database.<br>
<br>
We're creating a "default" PetscObjectList that gives access to a
global list of pairs: <string, PetscObjectList>.<br>
<br>
With this, we can simply "name" and add all our PetscObjects to
it.<br>
<br>
At run time, we create an option that holds the name of the
PetscObject to be passed as a parameter to whatever we want to
configure.<br>
<br>
For example, let's say you want to pass an optional matrix named
"preSchur" to a specific PC. It could be configured like this:<br>
<br>
Mat MyMat;<br>
PetscObjectSetName(MyMat, "preSchur");<br>
PetscObjectListAdd(gGlobalList, "preSchur", (PetscObject)MyMat);
/* Here MyMat is made available into the global object list with
the key "preSchur" */<br>
<br>
Then, in a PC, you can retrieve the matrix by using both the
options database keys and the objects database. For example, if a
PC looks for options like:<br>
<br>
-pc_fieldsplit_schur_precondition user<br>
-pc_fieldsplit_schur_precondition_user_mat preSchur<br>
</p>
<p>It just needs to look if the key
"pc_fieldsplit_schur_precondition_user_mat" has been set, and if
so, retrieve the value, which is the name of the matrix to be
retrieved from the global list.<br>
<br>
With this approach, all PCs, KSPs, and other objects can be given
objects at setup time (or later) with proper naming of the options
and objects.<br>
<br>
Some key features of this approach include:<br>
<br>
- If a user misspells an option, it will be visible in the unused
options.<br>
- Any new options to any PC or KSP do not need a new function to
use them; just a new option key is needed.<br>
- All software that uses PETSc as a library can have a very
"light" interface to it: just name all objects and let users
"configure" them!<br>
- This is almost the same idea as "composing objects," which is
already used in many places in PETSc. It's simpler to use and
really relaxes the constraints on "when" you can configure a PC.</p>
<p>I think this is a promising approach to simplifying the object
naming and configuration system in PETSc. I'm interested in
hearing your feedback.<br>
<br>
Thanks,<br>
</p>
<p>Eric</p>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">On 2023-07-13 13:44, Matthew Knepley
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAMYG4G=Z=iSN+i8p5cQxcOUGqf4u=7aU_YqVjX2b_SBYpJYi_w@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">
<div dir="ltr">On Thu, Jul 13, 2023 at 5:33 AM Pierre Jolivet
<<a href="mailto:pierre.jolivet@lip6.fr"
moz-do-not-send="true" class="moz-txt-link-freetext">pierre.jolivet@lip6.fr</a>>
wrote:<br>
</div>
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div>Dear Nicolas,<br>
<div><br>
<blockquote type="cite">
<div>On 13 Jul 2023, at 10:17 AM, TARDIEU Nicolas <<a
href="mailto:nicolas.tardieu@edf.fr"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">nicolas.tardieu@edf.fr</a>>
wrote:</div>
<br>
<div>
<div
style="font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none;font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt">Dear
Pierre,</div>
<div
style="font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none;font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt"><br>
</div>
<div
style="font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none;font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt">You
are absolutely right. I was using a
--with-debugging=0 (aka release) install and this
is definitely an error.<br>
Once I used my debug install, I found the way to
fix my problem. The solution is in the attached
script: I first need to extract the correct block
from the PC operator's MatNest and then append the
null space to it.</div>
<div
style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none">
<div
style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt">Anyway
this is a bit tricky...</div>
</div>
</div>
</blockquote>
<div><br>
</div>
<div>Yep, it’s the same with all “nested” solvers,
fieldsplit, ASM, MG, you name it.</div>
<div>You first need the initial PCSetUp() so that the
bare minimum is put in place, then you have to fetch
things yourself and adapt it to your needs.</div>
<div>We had a similar discussion with the MEF++ people
last week, there is currently no way around this,
AFAIK.</div>
</div>
</div>
</blockquote>
<div><br>
</div>
<div>Actually, I hated this as well, so I built a way around
it _if_ you are using a DM to define the problem. Then</div>
<div>you can set a "nullspace constructor" to make it if the
field you are talking about is ever extracted. You
use DMSetNullSpaceConstructor(). I do this in SNES ex62 and
ex69, and other examples.</div>
<div><br>
</div>
<div> Thanks,</div>
<div><br>
</div>
<div> Matt</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div>
<div>
<div>Thanks,</div>
<div>Pierre</div>
<br>
<blockquote type="cite">
<div>
<div
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<div id="m_3582794520278951836Signature">
<div name="divtagdefaultwrapper"
style="font-family:Calibri,Arial,Helvetica,sans-serif;margin:0px">
<div style="margin:0px"><font size="3"
face="Calibri,sans-serif">Regards,<span> </span></font></div>
<div style="margin:0px"><font
face="Calibri,sans-serif"><font size="3">Nicolas<br>
<br>
</font></font></div>
</div>
</div>
</div>
<hr
style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none;display:inline-block;width:867.297px"><span
style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none;float:none;display:inline"></span>
<div id="m_3582794520278951836divRplyFwdMsg"
dir="ltr"
style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none"><font
style="font-size:11pt" face="Calibri,
sans-serif"><b>De :</b><span> </span><a
href="mailto:pierre.jolivet@lip6.fr"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">pierre.jolivet@lip6.fr</a>
<<a href="mailto:pierre.jolivet@lip6.fr"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">pierre.jolivet@lip6.fr</a>><br>
<b>Envoyé :</b><span> </span>mercredi 12 juillet
2023 19:52<br>
<b>À :</b><span> </span>TARDIEU Nicolas <<a
href="mailto:nicolas.tardieu@edf.fr"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">nicolas.tardieu@edf.fr</a>><br>
<b>Cc :</b><span> </span><a
href="mailto:petsc-users@mcs.anl.gov"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">petsc-users@mcs.anl.gov</a>
<<a href="mailto:petsc-users@mcs.anl.gov"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">petsc-users@mcs.anl.gov</a>><br>
<b>Objet :</b><span> </span>Re: [petsc-users]
Near null space for a fieldsplit in petsc4py</font>
<div> </div>
</div>
<div
style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none"><font
size="2"><span style="font-size:11pt">
<div><br>
> On 12 Jul 2023, at 6:04 PM, TARDIEU
Nicolas via petsc-users <<a
href="mailto:petsc-users@mcs.anl.gov"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">petsc-users@mcs.anl.gov</a>>
wrote:<br>
><span> </span><br>
> Dear PETSc team,<br>
><span> </span><br>
> In the attached example, I set up a
block pc for a saddle-point problem in
petsc4py. The IS define the unknowns, namely
some physical quantity (phys) and a Lagrange
multiplier (lags).<br>
> I would like to attach a near null
space to the physical block, in order to get
the best performance from an AMG pc.<span> </span><br>
> I have been trying hard, attaching it
to the initial block, to the IS but no
matter what I am doing, when it comes to
"ksp_view", no near null space is attached
to the matrix.<br>
><span> </span><br>
> Could you please help me figure out
what I am doing wrong ?<br>
<br>
Are you using a double-precision 32-bit
integers real build of PETSc?<br>
Is it --with-debugging=0?<br>
Because with my debug build, I get the
following error (thus explaining why it’s
not attached to the KSP).<br>
Traceback (most recent call last):<br>
File
"/Volumes/Data/Downloads/test/test_NullSpace.py",
line 35, in <module><br>
ns = NullSpace().create(True, [v],
comm=comm)<br>
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^<br>
File "petsc4py/PETSc/Mat.pyx", line 5611,
in petsc4py.PETSc.NullSpace.create<br>
petsc4py.PETSc.Error: error code 62<br>
[0] MatNullSpaceCreate() at
/Volumes/Data/repositories/petsc/src/mat/interface/matnull.c:249<br>
[0] Invalid argument<br>
[0] Vector 0 must have 2-norm of 1.0, it is
22.3159<br>
<br>
Furthermore, if you set yourself the
constant vector in the near null-space, then
the first argument of create() must be
False, otherwise, you’ll have twice the same
vector, and you’ll end up with another error
(the vectors in the near null-space must be
orthonormal).<br>
If things still don’t work after those
couple of fixes, please feel free to send an
up-to-date reproducer.<br>
<br>
Thanks,<br>
Pierre<br>
<br>
> Thanks,<br>
> Nicolas<br>
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<span
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</blockquote>
</div>
<br>
</div>
</blockquote>
</div>
<br clear="all">
<div><br>
</div>
<span class="gmail_signature_prefix">-- </span><br>
<div dir="ltr" class="gmail_signature">
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<div>
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<div>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><br>
</div>
<div><a href="http://www.cse.buffalo.edu/~knepley/"
target="_blank" moz-do-not-send="true">https://www.cse.buffalo.edu/~knepley/</a><br>
</div>
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</div>
</div>
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</div>
</div>
</div>
</blockquote>
<pre class="moz-signature" cols="72">--
Eric Chamberland, ing., M. Ing
Professionnel de recherche
GIREF/Université Laval
(418) 656-2131 poste 41 22 42</pre>
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