[petsc-users] Applying Multi-Point-Constraints with SNES

[Hongrui Yu]

Thanks Matt. To clarify, were you referring to the following section in DMPlexCreateBoxMesh_Tensor_SFC_Periodicity_Private()?

 

  PetscCall(DMPlexSetIsoperiodicFaceSF(dm, sfper));

 

  PetscScalar t[4][4] = {{0}};

  t[0][0]             = 1;

  t[1][1]             = 1;

  t[2][2]             = 1;

  t[3][3]             = 1;

  for (PetscInt i = 0; i < dim; i++)

    if (periodicity[i] == DM_BOUNDARY_PERIODIC) t[i][3] = upper[i] - lower[i];

  PetscCall(DMPlexSetIsoperiodicFaceTransform(dm, &t[0][0]));

 

In my understanding, DMPlexSetIsoperiodicFaceSF() defines the points where the constrains exists. The constrains are specified in t matrix and set by calling DMPlexSetIsoperiodicFaceTransform(). Is this correct?

 

Does constraints set by this also apply to non-displacement DoFs? Our application is of phase-field fracture in elasticity so we have a scalar DoF on each vertices in addition to displacement field. In other words, the section has two fields, where displacement field has 2 DoFs and phase-field has 1 DoF.

 

Thanks,

Hongrui

 

From: Matthew Knepley <knepley at gmail.com> 
Sent: Thursday, July 6, 2023 3:34 PM
To: Hongrui Yu <yuhongrui at utexas.edu>
Cc: petsc-users at mcs.anl.gov
Subject: Re: [petsc-users] Applying Multi-Point-Constraints with SNES

 

On Thu, Jul 6, 2023 at 3:40 PM Hongrui Yu <yuhongrui at utexas.edu <mailto:yuhongrui at utexas.edu> > wrote:

Hello PETSc users,

 

In our Finite Element application we would like to apply Multi-Point-Constraints to some vertices. In these Multi-Point-Constraints we force certain DoF in the following nodes to be the same as those in controlling nodes. We use DMPlex to store our mesh. I’m wondering what would be a good way to implement this together with SNES? Or is there an example that does similar thing?

 

There is a simple thing that Jed implemented call "isoperiodicity" in plexsfc.c, and you can see

him using it to define a periodic box in

 

  DMPlexCreateBoxMesh_Tensor_SFC_Periodicity_Private()

 

You could use exactly this to define an affine relation between two dofs.

 

Currently both right-hand-side and solution vectors in out application are created using DMCreateGlobalVec(). And we tried (unsuccessfully) to modify solution within FormRHS or FormJacobian routines but the solution vector seems to be read-only (for good reason). Is there a way to tell SNES about these constraints? Or perhaps one can somehow create a vector with only a subset of the DoFs (the actual “unknowns”)?

 

Doing it as above will eliminate the constrained unknowns from the SNES automatically, so this will not be a concern.

 

  Thanks,

 

     Matt

 

Thank you in advance for any help or advice!

 

Hongrui

 




 

-- 

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

 

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/> 

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