Dear all!
To verify my MatrixFree implementation, I compared its application to the
classical matrix-vector multiplication (call it matrix *A*).
This is done by computing the matrix *M* of the operator *MF* by applying
it to all unit-vectors.
However, when I compute the diagonal in the same way as LaplaceOperator
does it (copied it), I get values different from the assembled diagonal
once I have hanging nodes.
This error only occurs in the compute_diagonal function, i.e surprisingly
*M* == *A, *but A(i,i) != compute_diagonal(i) (if hanging nodes are present)
My test-case starts with a 2x2 grid and refines one cell; apart from
hanging node constraints no other constraints are active.
Some more details:
Constraints: (these look suspicious as well, shouldn't there be 4
constrained dofs instead of 2?)
5 4: 0.5
5 8: 0.5
7 6: 0.5
7 8: 0.5
Error occurs at (ignoring 5 and 7, since they are constrained)
dof | M, A | diag
4 | 1.5 | 2.0
6 | 1.5 | 2.0
8 | 2.8 | 4.0
I will provide a mwe tomorrow, but maybe someone else has an idea already.
Thanks
Daniel
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