Hi, you are right such a function is unfortunately missing in deal.II. It has been on my TODO list for a long time but I didn't get around to implement it, since I haven't had to use DG for a while and in most of my applications I can move the BCs to the RHS.
Setting up the matrix is not particular difficult. You can take a look at our CFD code (https://github.com/exadg/exadg/blob/66a38ee6c0a03bbcc003ff4c19d94354face492b/include/exadg/operators/operator_base.cpp#L801-L827, https://github.com/exadg/exadg/blob/66a38ee6c0a03bbcc003ff4c19d94354face492b/include/exadg/operators/operator_base.cpp#L1681-L1967). Computing the diagonal is a bit more difficult. What the function in deal.II does is to compute a column of the element stiffness matrix and to apply right away the constraints without ever having to assemble the system matrix. I am not sure how much work is to extend the function so that it considers also face integrals; I think the logic should be similar. > think I will write new functions if there's no appropriate one. That would be great! Hope this help, Peter On Tuesday, 1 November 2022 at 13:25:09 UTC+1 yy.wayne wrote: > Maybe I should describe my question again. > > In short, to use Chebyshev smoother and solve mg coarse grid straightly, > we need *MatrixFreeTools::compute_diagonal and > MatrixFreeTools::compute_matrix,* respectively. > > However, for problems involve Robin boundary condition where integral is > required, those 2 function will not work(I think). That's because > FEFaceEvaluation should be included as well. > > I think I will write new functions if there's no appropriate one. Any > hint, especially on FEFaceEvaluation and multi-component MatrixFree > formulation is welcomed. > > 在2022年10月27日星期四 UTC+8 21:50:39<yy.wayne> 写道： > >> To write the boundary_integral in MatrixFree for step-29 is kind of >> confusing as well... >> For FEFaceEvaluation with 2 components(real and imaginary parts), whether >> a index correspond to src(alpha and beta) or basis function(phi_0 for phi >> and phi_1 for psi) is a problem. I cannot test this code yet due to the >> former question. >> [image: 20221027_1.png] >> [image: 20221027_2.png] >> >> 在2022年10月27日星期四 UTC+8 16:01:31<yy.wayne> 写道： >> >>> Hi there, >>> >>> I've been applying MatrixFree method to Step-29 where face integrals are >>> involved, different from step-37, step-75 and so on. Firstly I think loop() >>> instead of cell_loop() should be used. Secondly, similar to step-75, >>> Chebyshev smoother and a coarsest level matrix are needed in my code. In >>> step-75 we get diagonal vector by *MatrixFreeTools::compute_diagonal >>> and MatrixFreeTools::compute_matrix*. >>> >>> However, the face integral makes them different. Both two functions only >>> take cell_operations(FEEvaluation), not face_operations(FEFaceEvaluation). >>> My question is how to compute diagonal and matrix when my weak form has >>> face integrals terms (only boundary integral, no interface integral). >>> >> -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/2e80dd35-9e39-48c3-8494-7114bf8a18cdn%40googlegroups.com.
