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 <[email protected]>
Sent: Thursday, July 6, 2023 3:34 PM
To: Hongrui Yu <[email protected]>
Cc: [email protected]
Subject: Re: [petsc-users] Applying Multi-Point-Constraints with SNES
On Thu, Jul 6, 2023 at 3:40 PM Hongrui Yu <[email protected]
<mailto:[email protected]> > 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/>
