[petsc-users] Options database in petsc4py

[SCOTTO Alexandre]

Hello Matthew,

I was indeed wondering if there was a clean way to match a given set of options to a specific KSP instance. Does the following makes sense:

1.       Associate a given a KSP instance a unique string, e.g. “toto” and call ksp_1.setOptionsPrefix(“toto”)

2.       Create an option database with corresponding prefix: options = Options(“toto_ksp_”)

3.       Then a call to ksp_1.setFromOptions() will only consider entrees in the option database starting with “toto”

Regards,
Alexandre.

De : Matthew Knepley <knepley at gmail.com>
Envoyé : lundi 27 octobre 2025 11:27
À : SCOTTO Alexandre <alexandre.scotto at irt-saintexupery.com>
Cc : petsc-users at mcs.anl.gov
Objet : Re: [petsc-users] Options database in petsc4py

On Mon, Oct 27, 2025 at 10:24 AM SCOTTO Alexandre via petsc-users <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>> wrote:
Dear PETSc Community,

In my developments, I am managing possibly several KSP solvers with options handled by the Options database. During my tests, I encountered the following behavior:

Code:
options = PETSc.Options("ksp_")
options.setValue("atol", 7e-8)
options.view()

options.clear()
options.view()

Output:
#PETSc Option Table entries:
-ksp_atol 7e-08 # (source: code)
#End of PETSc Option Table entries

#PETSc Option Table entries:
-ksp_atol 7e-08 # (source: code)
#End of PETSc Option Table entries

It seems that the clear() method does not really clear the Option database. To ensure that the several KSP I deal with are set with their own options (without getting options from a KSP previously set), the only way I found was to explicitly call the delValue() method for all the option keys passed:


1.       Iterate over a dictionary of options and use setValue(name, value)

2.       Set the KSP with option database: KSP.setFromOptions()

3.       Iterate over a the keys of the dictionary and use delValue(name) to effectively clear the option database.

Does it seem normal to you, is there something I am missing out?

That for pointing out this bug.

However, I don't think I would manage options this way. We normally give each separate solver a new _prefix_, meaning a string that prefaces all its options. That way they do not collide.

  Thanks,

     Matt

Regards,
Alexandre Scotto.


--
What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
-- Norbert Wiener

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