Comment 3 for bug 1077912
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| Martin Sandve Alnæs (martinal) wrote Re: Incorrect DirichletBC behaviour with assemble_system | #3 |
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(Get the code!)
The zero rows is only a symptom of the underlying bug. Looking at the sparsity pattern of B you can see there are dramatic changes between setting enable_bug=1/0, so this is not an assemble_system specific issue.
If DirichletBC with method=topological only applies to dofs on the boundary, then the markers in the interior facets should not matter. However they do get used, causing the boundary condition to be applied to interior dofs as well as boundary dofs in the enable_bug=1 case in the provided code.
While this may very well be useful for some situations, it is contrary to the description in the documentation as quoted, and contrary to the name "boundary conditions".
The problem could be limited to for example DBC on subspaces of mixed elements, at least I failed to simplify it to a pure scalar case.