Hi all,
I am brand new to deal.II, so please excuse me if this question has an
obvious answer.
So far, I am quite enjoying the library and working through the different
Step tutorials.
I've been working through Step-47 and in particular am trying to better
understand the MeshWorker class.
In particular, I'm interested in using MeshWorker::mesh_loop to compute a
norm--this norm has integrals of jumps and averages over interior cell
faces. I know there is already an example in Step-82 that does just this.
However, if I understand correctly, the logic used in that example becomes
more challenging when using local refinement (which I'm aiming towards).
But MeshWorker handles the logic quite seamlessly, and (if I'm not
mistaken) automatically does it in parallel (this is just a bonus).
As a consistency check, I decided to use the MeshWorker class to compute
the L2 norm of my solution and compare it against the result using:
(1) VectorTools::integrate_difference and
VectorTools::compute_global_error (to be clear, I integrated the difference
between my computed solution and the zero function)
and
(2) the method used in Step-82.
Note, the results from (1) and (2) agree with each other to 15 digits of
accuracy. However, the result from the MeshWorker method only agrees with
these two up to 6 digits of accuracy.
Is there any reason why this would be true?
To be clear, "the MeshWorker method" entails computing (the square root of)
u^T A u, where u is my computed solution and A is the matrix whose entries
correspond to the integrals of the i-th and j-th shape functions, assembled
with MeshWorker::mesh_loop.
(Happy to post my code if it helps resolve the query, but for now wanted to
keep the post relatively clean.)
Thank you very much in advance for the assistance--
Regards,
-Sean
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