Add a Python implementation of the mixed Poisson example

This example program does the same as poisson-mfem.cc, but using the Python interface. The only difference is the type of the stiffness matrix. The C++ example uses a 2x2 matrix of BCRSMatrix objects, but that is not easy to replicate in Python unless we start writing Python bindings for dune-istl. This new Python example uses a single flat matrix instead.

This is currently a snapshot only, and far from working. In particular, it needs the Raviart-Thomas bindings from !440 (merged), and lots of other fixes.

added 51 commits

• 2ffea8dc...6cafc0bd - 48 commits from branch master
• 9f37fc46 - Modernize poisson-mfem.cc a tiny bit
• 54d4bc4e - Add a Python implementation of the mixed Poisson example
• b9ed6556 - WIP: poisson pq2.py

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added 3 commits

• e82f72e0 - [python][bugfix] Do not capture reference to temporary
• e1cd09f1 - [python] HACK: Deactivate interpolation from array<bool>
• 6cd4c0d3 - [python] Partially fix poisson-mfem.py example

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• 0c22b3d4 - [python][examples] Avoid warning due to implicit conversion of 1-dim vector to scalar

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• 371fe6b2 - Ensure proper type range type in contravariant Piola-transfomation
• 4400bd66 - Fix typo

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• 4400bd66...125baf28 - 4 commits from branch master
• 1712bd62 - Modernize Poisson examples a tiny bit
• cbce504c - Add a Python implementation of the mixed Poisson example
• bb476615 - WIP: poisson pq2.py
• 7cb7374c - Ensure proper type range type in contravariant Piola-transfomation

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added 3 commits

• 6fb401f0 - [python][examples] Implement boundary marking in poissson-mfem
• 92f832d2 - [python][examples] Fix boundary indicator functions in poisson-mfem
• 04fa1350 - [python][examples] Incorporate constraints in poisson-mfem

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added 13 commits

• 04fa1350...03dc66b6 - 5 commits from branch master
• 6bd14a8f - Modernize Poisson examples a tiny bit
• d5225afd - Add a Python implementation of the mixed Poisson example
• 636b8792 - WIP: poisson pq2.py
• cde6d6dc - [python][examples] Implement boundary marking in poissson-mfem
• a8494a8e - [python][examples] Fix boundary indicator functions in poisson-mfem
• b4fe4712 - [python][examples] Incorporate constraints in poisson-mfem
• 8d7255a0 - poisson-mfem.cc: Remove bogus comment
• cfbe66e8 - [python] Use new method LocalView::element()

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added 2 commits

• 64157b6c - [python][examples] Implement nonzero flux-BC for poisson-mfem
• e5dd7fa4 - [python][examples] Adjust to modified C++ version of poisson-mfem

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I implemented non-zero flux BC for the poisson-mfem example and modified this example according to !463 (merged).

The flux BC are now use a manually provided normal field instead of the so far missing bindings for FaceNormalGridFunction.

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• e5dd7fa4...2f917b12 - 16 commits from branch master
• a245ea95 - Modernize Poisson examples a tiny bit
• 3bde530f - [python] Export Tree::finiteElement as a method
• ff79a401 - [python][examples] Add a Python implementation of the mixed Poisson example
• 9039bd86 - WIP: poisson pq2.py

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Thanks. This collided with some of my own changes. Had to force-push.

added 2 commits

• d603d7dc - [python][examples] Add a Python implementation of the mixed Poisson example
• f0d1db08 - WIP: poisson pq2.py

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added 5 commits

• 666c1f41 - Fix a typo
• 92ef0e5d - Modernize Poisson examples a tiny bit
• fda53973 - [python] Export Tree::finiteElement as a method
• dbdab59e - [python][examples] Add a Python implementation of the mixed Poisson example
• f0e38e50 - [python][examples] Implement Python version of poisson-pq2.cc example

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added 3 commits

• 9066c295 - [python][examples] Add a Python implementation of the mixed Poisson example
• 98c17ede - [python][examples] Implement Python version of poisson-pq2.cc example
• 35c34659 - [python] Remove test 'pypoisson'

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added 2 commits

• 1d2cf2f3 - [python][examples] Implement Python version of poisson-pq2.cc example
• 65724bda - [python] Remove test 'pypoisson'

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marked this merge request as ready

enabled an automatic merge when the pipeline for 65724bda succeeds

aborted the automatic merge because source branch was updated

added 4 commits

• 94e77f31 - [python] Export Tree::finiteElement as a method
• 68050a2d - [python][examples] Add a Python implementation of the mixed Poisson example
• ec7a2365 - [python][examples] Implement Python version of poisson-pq2.cc example
• 9df7fba5 - [python] Remove test 'pypoisson'

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