Invalid coarse mappings in multigrid #614
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nfehn
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Dec 1, 2023
This was referenced Dec 1, 2023
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With deal.II PR dealii/dealii#16317, an assert is now triggered in matrix_free/mapping_info.templates.h. |
Great! Thanks for checking! |
kronbichler
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Dec 4, 2023
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For the
poisson/sinetest case, I added a new "boundary-layer" manifold (typical of CFD applications to resolve turbulent boundary layers around bodies), which is described analytically by atanh()function in wall-normal direction and adealii::ChartManifold, and approximated in the numerical simulation by a quadratic mapping.Then, using our default multigrid implementation with the same mapping degree on all h-levels (equivalent to the fine level mapping degree), will lead to invalid Jacobians on coarser multigrid levels, which is shown by the present test case. For the chosen parameters and the chosen grid stretch factor, refine level 2 (set in the input.json file) leads to a valid mapping on the fine grid (level 2), while coarser grids (level 1) have an invalid mapping.
The present PR proposes a test case that fails on purpose. Potential solutions to this problem are to be addressed by upcoming PRs.