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

[Samuele Ferri]

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);
}

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