[petsc-users] R: Two SNES on the same DM not working

[Matteo Semplice]

Dear Barry,

     sorry for jumping into this.


I am wondering if your reply is related to DMDA or to DM in general. I 
have at least one code where I do something similar to what Samuele did 
in his sample code: create a DMPlex, create a section on this DMPlex, 
create two SNES solving for Vecs defined on that same section and attach 
to each of them a different SNESFunction and SNESJacobian (one solves a 
predictor and the other is a corrector). Everything seems fine, but I am 
wondering if that code is somewhat weak and should be changed by 
DMCloning the plex as you suggested to Samuele.


Thanks

     Matteo


On 06/11/2025 07:49, Samuele Ferri wrote:
>
> 	
> sale987 at live.com sembra simile a un utente che in precedenza ti ha 
> inviato un messaggio di posta elettronica, ma potrebbe non essere lo 
> stesso. Scopri perché potrebbe trattarsi di un rischio 
> <https://urldefense.us/v3/__https://aka.ms/LearnAboutSenderIdentification__;!!G_uCfscf7eWS!d2x1h3Pt9OqhfeBcqW8pR0dbGy3bRw6bM-p0DxGAaY0CXWkqH3lpsuXiob9mOqfsy-aRVJXUig3819n2CWpYyFn4FDaTAWRxNDXZsA$ >
> 	
>
> Dear Barry,
>
> thank you for your reply. Now everything works fine.
>
> Best regards
> Samuele
> ------------------------------------------------------------------------
> *Da:* Barry Smith <bsmith at petsc.dev>
> *Inviato:* mercoledì 5 novembre 2025 15:47
> *A:* Samuele Ferri <sale987 at live.com>
> *Cc:* petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>
> *Oggetto:* Re: [petsc-users] Two SNES on the same DM not working
>
>    This is not supported. Duplicate your DM.
>
>> On Nov 5, 2025, at 9:17 AM, Samuele Ferri <sale987 at live.com> wrote:
>>
>> Dear petsc users,
>>
>> in petsc version 3.24, I'm trying to create two snes over the same 
>> DM, but with different functions and jacobians. Despite making 
>> different calls to SNESSetFunction it happens the second snes uses 
>> the same function of the first.
>> Can you help me finding the problem, please?
>>
>> Here below there is a minimal working example showing the issue:
>>
>> static char help[] = "Test SNES.\n";
>> #include <petscsys.h>
>> #include <petscdmda.h>
>> #include <petscsnes.h>
>>
>> PetscErrorCode Jac_1(SNES/snes/, Vec/x/, Mat/J/, Mat/B/, void *){
>>     PetscFunctionBegin;
>>     printf("Jac 1\n");
>>     PetscFunctionReturn(PETSC_SUCCESS);
>> }
>>
>> PetscErrorCode Function_1(SNES/snes/, Vec/x/, Vec/f/, void *){
>>     PetscFunctionBegin;
>>     printf("Function 1\n");
>>     PetscFunctionReturn(PETSC_SUCCESS);
>> }
>>
>> PetscErrorCode Jac_2(SNES/snes/, Vec/x/, Mat/J/, Mat/B/, void *){
>>     PetscFunctionBegin;
>>     printf("Jac 2\n");
>>     PetscFunctionReturn(PETSC_SUCCESS);
>> }
>>
>> PetscErrorCode Function_2(SNES/snes/, Vec/x/, Vec/f/, void *){
>>     PetscFunctionBegin;
>>     printf("Function 2\n");
>>     PetscFunctionReturn(PETSC_SUCCESS);
>> }
>>
>> int main(int/argc/, char **/argv/) {
>>
>>     PetscFunctionBeginUser;
>>     PetscCall(PetscInitialize(&/argc/, &/argv/, NULL, help));
>>
>>     DM dm;
>>     PetscCall(DMDACreate1d(PETSC_COMM_WORLD, DM_BOUNDARY_NONE, 100, 
>> 1, 1, NULL, &dm));
>>     PetscCall(DMSetFromOptions(dm));
>>     PetscCall(DMSetUp(dm));
>>
>>     SNES snes1, snes2;
>>     Vec r1,r2;
>>     Mat J1, J2;
>>
>>     PetscCall(DMCreateGlobalVector(dm, &r1));
>>     PetscCall(DMCreateGlobalVector(dm, &r2))
>>     PetscCall(DMCreateMatrix(dm, &J1));
>>     PetscCall(DMCreateMatrix(dm, &J2));
>>
>>     PetscCall(SNESCreate(PETSC_COMM_WORLD, &snes1));
>>     PetscCall(SNESCreate(PETSC_COMM_WORLD, &snes2));
>>     PetscCall(SNESSetType(snes1, SNESNEWTONLS));
>>     PetscCall(SNESSetType(snes2, SNESNEWTONLS));
>>     PetscCall(SNESSetFromOptions(snes1));
>>     PetscCall(SNESSetFromOptions(snes2));
>>     PetscCall(SNESSetFunction(snes1, r1, Function_1, NULL));
>>     PetscCall(SNESSetFunction(snes2, r2, Function_2, NULL));
>>     PetscCall(SNESSetJacobian(snes1, J1, J1, Jac_1, NULL));
>>     PetscCall(SNESSetJacobian(snes2, J2, J2, Jac_2, NULL));
>>     PetscCall(SNESSetDM(snes1, dm));
>>     PetscCall(SNESSetDM(snes2, dm));
>>
>>     PetscCall(SNESSolve(snes1, NULL, NULL));
>>     PetscCall(SNESSolve(snes2, NULL, NULL));
>>
>>     printf("snes1 %p; snes2 %p\n", snes1, snes2);
>>
>>     SNESFunctionFn *p;
>>     PetscCall(SNESGetFunction(snes1, NULL, &p, NULL));
>>     printf("snes1: pointer %p, true function %p\n", *p, Function_1);
>>     PetscCall(SNESGetFunction(snes2, NULL, &p, NULL));
>>     printf("snes2: pointer %p, true function %p\n", *p, Function_2);
>>     PetscCall(PetscFinalize());
>>     PetscFunctionReturn(PETSC_SUCCESS);
>> }
>
-- 
Prof. Matteo Semplice
Università degli Studi dell’Insubria
Dipartimento di Scienza e Alta Tecnologia – DiSAT
Professore Associato
Via Valleggio, 11 – 22100 Como (CO) – Italia
tel.: +39 031 2386316
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