Hello!
I have some general questions about deal.II. I am not sure if what I think
is correct. Thank you for your help!
i) Copy Trilinos::MPI::Vector
Consider using Trilinos to do MPI. Suppose the following vectors:
TrilinosWrappers::MPI::Vector distributed_sln_old (locally_owned_dofs,
mpi_communicator), distributed_sln_new (locally_owned_dofs,
mpi_communicator);
TrilinosWrappers::MPI::Vector locally_relevant_sln_with_ghost_old
(locally_owned_dofs, locally_relevant_dofs, mpi_communicator),
locally_relevant_sln_with_ghost_new (locally_owned_dofs,
locally_relevant_dofs, mpi_communicator); //this is the local vector with
ghost.
//Now we have four assignments:
locally_relevant_sln_with_ghost_new = distributed_sln_new; //This is
commonly seen in the tutorials. I assume the locally_owned_dofs are copied,
and the ghosts are properly updated.
distributed_sln_new = distributed_sln_old; //These two are all local
vectors, so it is just a copy operation.
locally_relevant_sln_with_ghost_new = locally_relevant_sln_with_ghost_old;
//This and the following one are rarely seen in the tutorials. Does this
mean the vector is exactly copied? i.e. both locally_owned_dofs and the
ghost_dofs are all copied?
distributed_sln_new = locally_relevant_sln_with_ghost_new; //Does this mean
the locally_owned_dofs are copied, while the ghosts are neglected?
ii) ConstraintMatrix::distribute() and Newton's method
In a Newton's method solver, we have:
version A:
//...get the new newton_update vector from solving the equation
constraints.distribute(newton_update);
new_sln = old_sln + alpha* newton_update;
version B:
//...get the new newton_update vector from solving the equation
new_sln = old_sln + alpha* newton_update;
constraints.distribute(new_sln);
In the tutorials it seems version A is more commonly used. However, it
seems to me that if there are inhomogeneous constraints, then only version
B is correct. Is it right? I don't know how the distribute() function is
implemented, but based on the documentation it seems version B is a more
logical and universal way.
iii) solve system with inhomogeneous constraints
I have a problem with inhomogeneous constraints. I did some tests and it
seems that sometimes the solver collapses due to convergence(?) while
sometimes it doesn't, for example depending on the mesh.
May I ask, with inhomogeneous constraints, do I need to, say, choose
different preconditioner, or providing the preconditioner with
AdditionalData?
Best,
Yiyang
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