On 2/14/23 07:15, 'yy.wayne' via deal.II User Group wrote:
The weak problem I'm solving is <curl u, curl u> + <div u, div u> -
k^2<u, u> = RHS, which is vector Maxwell wave equation (for nodal basis).
[...]
1) Is it reasonable the diagonal computed by MatrixFree operator with
compute_normal_flux() has negative entries?
The diagonal entries of the matrix, for this bilinear form, are
integrals of the form
A_ii = \int (curl phi_i)*(curl phi_i) + (div phi_i)*(div phi_i)
- k^2 phi_i * phi_i
In other words, A_ii is a sum of squares, but one of the squares is
negative. If k is small, the sum may still be positive, but for sure if
k is large, the diagonal entries of A will be negative.
Best
W.
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Wolfgang Bangerth email: bange...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/
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