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The development repository for the deal.II finite element library
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Teach FiniteElement how to fill MF::ShapeInfo #9544

Open kronbichler opened 4 years ago

kronbichler commented 4 years ago

The information for the tensor product information of certain FiniteElement classes is extracted in the struct internal::MatrixFreeFunctions::ShapeInfo from a given finite element object and a 1D quadrature formula. We do this by some dynamic cast magic in https://github.com/dealii/dealii/blob/1f3f4df3cd5e84a140e453b227608d5e83079789/include/deal.II/matrix_free/shape_info.templates.h#L103-L128 but this is not a real solution and does not scale if we want to support more elements (and I want to add some tensor product evaluators for RT and Nedelec with appropriate basis functions). The real solution is to add this as an interface to the FiniteElement classes and let them return tensor product information. I plan to do this in three steps:

What I want to discuss here before I start is the naming (any suggestions?) and how exactly we would like to set up the interface. One can think of this class/struct as a collection of arrays with evaluation of 1D shape functions along a 1D quadrature and for various combinations of faces/subfaces, so it is pretty low-level and a bit similar to the InternalDataBase objects in FiniteElement, but without the inheritance within the class.

peterrum commented 4 years ago

This is a good idea!

I guess then we can also eliminate this mess:

https://github.com/dealii/dealii/blob/1f3f4df3cd5e84a140e453b227608d5e83079789/source/multigrid/mg_transfer_internal.cc#L713-L722

and maybe part of this:

https://github.com/dealii/dealii/blob/1f3f4df3cd5e84a140e453b227608d5e83079789/source/multigrid/mg_transfer_internal.cc#L582-L640

peterrum commented 4 years ago

Move the include/deal.II/matrix_free/shape_info.{h,templates.h} files to the fe/ subfolder, extract it from the internal namespace and give it a proper name. I was thinking along the lines FiniteElementTensorProductInformation. I would put a template for the number type on this class but not the dimension as a tensor product element is in principle not restricted to a particular dimension.

I just wanted to suggest the same!

kronbichler commented 4 years ago

I guess then we can also eliminate this mess: [some ugly code in the multigrid transfer]

I hope that we can do; however, this means we need to add another field to the ShapeInfo class for the parent/child relation we use in GMG (which is useful information and cheap to obtain anyway).

peterrum commented 4 years ago

@kronbichler Let me know if I can do something or try something out. I have simply copied those two code snippets to my new transfer operators, but I am not happy with that...

I will have a look at my code maybe I find some additional requirements!

kronbichler commented 3 years ago

The evaluator side also relates to #7039 that should be generalized/restructured in one go.

peterrum commented 3 years ago

This PR will involve some time we don't have at the time. Adjusting the milestone.

kronbichler commented 1 year ago

In #14385 we noticed that the cases where we need special treatments, to be addressed by this PR, just keep increasing. I think we should aim for this effort before the next release.

peterrum commented 11 months ago

This is a place where this would be useful:

https://github.com/dealii/dealii/blob/e8f57130d069e153ff96e41d2086e394e89c1954/source/dofs/dof_accessor_set.cc#L253-L254

since we could replace the full matrix-vector product by sum factorization.