On 5/30/24 09:55, Najwa Alshehri wrote:
The problem arises when comparing the inf-sup constants obtained using Matlab
and dealii (solving on the same mesh ):
1. Matlab: Using the "eig" solver, the inf-sup constant decays to zero as the
mesh is refined.
2. deal.II: Using the "ArpackSolver", the inf-sup constant is bounded away
from zero.
The discrepancy is puzzling, as both methods should give consistent results.
To illustrate this issue, I have attached a figure comparing the two results
and included in this post the two data files obtained from Matlab and deal.II.
I would greatly appreciate any insights or suggestions on what might be
causing the discrepancy.
Najwa:
my first question would be if your matrices are the same. If they are not,
then you should not expect eigenvalues to be the same. So what happens if you
output the relevant matrices from both codes on, say, a 2x2 mesh? On a coarse
enough mesh, you can often even compute the matrix by hand on a piece of paper
within half an hour, so that if the matrices you output are different, you can
figure out which one is right and which one is not.
Best
W.
--
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Wolfgang Bangerth email: bange...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/
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