On 26/01/15 13:00, Jørgen Kvalsvik wrote:
Hi,
Hi,
Sorry about the delay. I was just going through my old e-mail and
noticed that I didn't see an answer to this question. I'll provide one
for the mailing list record, even it much time has passed since the
question was posed.
Can the Dirichlet and periodic facetypes alternate within the same
matrix, or are they mutually exclusive? If they are exclusive using a
vector of facevalues really doesn't make sense (nor does the switch).
These face types can definitely appear within the same problem. One
typical case would be an upscaling problem that uses periodic pressure
drop in one cardinal direction, for instance along the X axis, and a
constant pressure drop in another cardinal direction--for instance along
the Y axis. That might be a strange configuration from an end-user
application point of view, but it is nevertheless possible and we have
to allow for the situation.
The l2g values, are they contiguous?
No, they are not. Basically, L2G plays the role of the traditional
local-to-global mapping degrees of freedom in implementations of finite
element methods. In other words
l2g[i]
is the global identity of the i-th local degree of freedom.
In the periodic case, will some indices be encountered twice?
I'm not sure I understand the question. All indices may, and typically
will, be encountered multiple times in the assembly stage.
The
comments say a*(x0-x1) = a*(pd) etc with no reference to a, but implies
this should be computable with an assignment, not +=.
That comment outlines the type of the linear equation, or rather,
contribution, being assembled in the periodic case. In this case, 'a'
is a coefficient, 'x0', and 'x1', are degrees of freedom, and 'pd' is
the prescribed periodic pressure drop. We are specifically not talking
about C++ implementation at that point.
Finally, and if this has a good answer then ignore the three questions
above: is there a better way to formulate this in terms of matrix
operations? Right now it is quite hands-on update-individual-cells, but
I would like a more math-oriented algorithm. e.g. in the case of
dirichlet it basically reduces to finding diagonal segments of the
SharedFortranMatrix and assigning them to (maybe contiguous) diagonals
in S_.
Class IncompFlowSolverHybrid<> implements a fairly standard assembly of
a system of simultaneous linear equations with contributions for each
cell being sequentially added to the coefficient matrix and right hand
sides. The process is very much inspired by traditional finite-element
software. If there is a better approach, then I'd like to see it.
Sincerely,
--
Bård Skaflestad <[email protected]>
SINTEF ICT, Applied Mathematics
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