Hello Matt,
I am sorry that I have not replied before now.
I think that the reason you did not understand the question was that the
question was silly but I'll try to explain my thought process anyway.
If you have a periodic boundary condition then when you construct a
matrix to be used by a KSP it can address the ghost points corresponding
to the periodic boundaries. So, I wondered if when you have ghosted
boundary conditions you could refer to those ghosted points too when
constructing the matrix. This led on to the question of how those values
would be obtained when the linear solver came to be executed.
At this point I expect you are asking why on earth I would want to do
that and I do not have an adequate response.
I am sorry I wasted your time and thanks for your help,
David
On 18/02/2020 20:23, Matthew Knepley wrote:
On Tue, Feb 18, 2020 at 10:23 AM SCOTT David <[email protected]
<mailto:[email protected]>> wrote:
Hello Matt,
Thanks for the quick response.
Sorry to be dense but I want the ghost(ed) values to be used by
KSPSolve where the KSP has an associated DM. I can, of course
create a local vector using DMGetLocalVector and then populate the
ghosted locations but I do not know how to get the KSPSolve to use
these values in the way that automatically generated periodic,
ghost values would be.
Let me try and understand. We normally distinguish between
global vectors and local vectors. Global vectors, used in the solver,
describe the entire space. Local vectors, used in assembly, describe
overlapping patches of the space. The ghost values would only be used
in assembly, not in the solver, since they help make the correct
value, but have no equation associated with themselves. Am I
misunderstanding something?
Thanks,
Matt
Thanks,
David
On 18/02/2020 12:42, Matthew Knepley wrote:
On Tue, Feb 18, 2020 at 6:03 AM David Scott
<[email protected] <mailto:[email protected]>> wrote:
Hello,
I wish to solve a channel flow problem with different boundary
conditions. In the streamwise direction I may have periodic or
inlet/outlet BCs. I would like to make my code for the two
cases as
similar as possible. If I use DM_BOUNDARY_PERIODIC then when
performing
a linear solve the ghost values will be set automatically.
For the
inlet/outlet case can I use DM_BOUNDARY_GHOSTED instead and
somehow
arrange for values that I specify to be placed in the ghost
locations?
Yes, that is the intent.
Thanks,
Matt
Thanks,
David
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What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which
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