On Mon, 12 Jan 2015, David Knezevic wrote:
> I'm solving a series of PDEs with different non-zero Dirichlet boundary
> conditions. I'm using the DirichletBoundary functionality, and for each
> solve in the series I currently do this via the following steps:
>
> - Remove all existing DirichletBoundaries via
> get_dof_map().remove_dirichlet_boundary
> - Add the new DirichletBoundary objects (for the same set of boundaries as
> before)
> - Call EquationSystems::reinit() to reinitialize the dof constraints
> - Perform the solve
>
> This works fine, but the call to EquationSystems::reinit() is somewhat
> inefficient for me because it clobbers the PETSc matrix data so that PETSc
> doesn't let me reuse the preconditioner from one solve to the next.
>
> I'm not changing the mesh and I'm constraining the same set of dofs on each
> solve, so I was wondering if there's a way to just recompute the
> constraints without calling EquationSystems::reinit() ? I wonder if it
> would be sufficient for me to pick out a couple of the relevant commands
> from EquationSystems::reinit, like:
>
> sys.get_dof_map().create_dof_constraints(_mesh, sys.time);
> sys.get_dof_map().process_constraints(_mesh);
This has been (buried a ways down) on my TODO list for quite a while;
we definitely need to have some kind of "reinit_constraints()" method
to do just that more efficiently; it's ludicrous to redo every
DofObject and matrix just to change a few constraint right hand sides,
and I've got one case where the wasted reinit() calls are something
like 20% of runtime.
I believe a complete implementation would look like:
System::reinit_constraints() {
sys.get_dof_map().create_dof_constraints(_mesh, sys.time);
sys.user_constrain();
sys.get_dof_map().process_constraints(_mesh);
sys.get_dof_map().prepare_send_list();
}
The user_constrain() should be a no-op in your case. The
prepare_send_list() might be a bit of overhead for our use cases, but
I didn't see it show up in profiling, and it would be nice to leave it
in for use in e.g. contact problems where communication details may
depend on what ended up constrained by what.
Would you give that a try and give back to me?
Copying Paul so he'll be aware of upcoming GRINS changes if this
works, plus Nick so he'll be relieved to find out someone's finally
fixing this junk.
Thanks,
---
Roy
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