[petsc-users] fortran interface to snes matrix-free jacobian

[Barry Smith]

> On Dec 20, 2023, at 11:44 AM, Yi Hu <y.hu at mpie.de> wrote:
> 
> Dear Jed,
> 
> Thanks for your reply. I have an analytical one to implement.
> 
> Best, Yi
> 
> -----Original Message-----
> From: Jed Brown <jed at jedbrown.org> 
> Sent: Wednesday, December 20, 2023 5:40 PM
> To: Yi Hu <y.hu at mpie.de>; petsc-users at mcs.anl.gov
> Subject: Re: [petsc-users] fortran interface to snes matrix-free jacobian
> 
> Are you wanting an analytic matrix-free operator or one created for you based on finite differencing? If the latter, just use -snes_mf or -snes_mf_operator.
> 
> https://petsc.org/release/manual/snes/#jacobian-evaluation
> 
> Yi Hu <y.hu at mpie.de> writes:
> 
>> Dear PETSc team,
>> 
>> My  solution scheme relies on a matrix-free jacobian in the SNES solver. I saw the useful C interface like MatCreateSNESMF(), DMSNESCreateJacobianMF(). I am wondering if you have the fortran equivalence?

   You can use DMSNESCreateJacobianMF() (MatCreateSNESMF is not appropriate when you are providing the operation).
     
   
>> 
>> I think for my problem in the main program I need to do DMDASNESsetJacobianLocal(DM, INSERT_VALUES, myJacobian, ctx, err_petsc). Then in myJacobian() subroutine I have to create the operator from DMSNESCreateJacobianMF(), and register my own MATOP_MULT from MatShellSetOperation(). Am I correct?

Not exactly. Do not use DMDASNESsetJacobianLocal() use DMSNESCreateJacobianMF() to create a Mat J where you create the SNES and use SNESSetJacobian()  and pass the J matrix in along with myJacobian().

>> 
>> Are these fortran subroutines available? I saw an example in ts module 
>> as ex22f_mf.F90 which behaves similar as what I would like to do. Because I would like to use ngmres, I then need to stay in the SNES.
>> 
>> Thanks for your help.
>> 
>> Best wishes,
>> Yi
>> 
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> Stay up to date and follow us on LinkedIn, Twitter and YouTube.
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> Max-Planck-Institut für Eisenforschung GmbH
> Max-Planck-Straße 1
> D-40237 Düsseldorf
> 
> Handelsregister B 2533 
> Amtsgericht Düsseldorf
> 
> Geschäftsführung
> Prof. Dr. Gerhard Dehm
> Prof. Dr. Jörg Neugebauer
> Prof. Dr. Dierk Raabe
> Dr. Kai de Weldige
> 
> Ust.-Id.-Nr.: DE 11 93 58 514 
> Steuernummer: 105 5891 1000
> 
> 
> Please consider that invitations and e-mails of our institute are 
> only valid if they end with …@mpie.de. 
> If you are not sure of the validity please contact rco at mpie.de
> 
> Bitte beachten Sie, dass Einladungen zu Veranstaltungen und E-Mails
> aus unserem Haus nur mit der Endung …@mpie.de gültig sind. 
> In Zweifelsfällen wenden Sie sich bitte an rco at mpie.de
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