Demo multimesh-poisson has spikes
The solution computed by the demo multimesh-poisson has spikes in the solution that shouldn't be there. Missing or wrong stabilization?
Concerns both the Python and C++ version of the demos (which should be identical).
Comments (5)
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reporter -
I've done the following:
- I checked the formulation and it's the same as the one I've used previously.
- I ran the demo with geometry debugging and didn't encounter any errors.
- I increased \beta and I got a larger spike!
I need to think about this one a bit more.
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The dof causing the spike is fully covered by the upper mesh. The current implementation is using
GenericMatrix.ident_zeros
to eliminate such dofs, making it sensitive to round-off errors from the inclusion/exclusion calculations. This is what happened here - the roundoff errors were marginally larger than the threshold value which isDOLFIN_EPS
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Yes, there's missing correct scaling by some sort of a row norm.
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reporter - changed status to resolved
Resolved by Magne (improved stabilization parameters/terms).
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Solution as seen from below at step 6.