[Critical] Fix CN implementation of radially varying magnetic diffusion #346
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feathern
changed the title
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This PR is safe to accept now. I also added the changelog file as discussed. |
orvedahl
approved these changes
Dec 3, 2021
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The benchmarks, as well as most users, run with diffusion coefficients (nu, kappa, eta) that are constant in radius. Because of this, a bug in the code has gone unnoticed for a very long time. The diffusive terms are evolved using the semi-implicit Crank-Nicholson method, which is effectively an average of the forward and backward Euler methods. A magnetic diffusion term for the A-potential equation, namely dA/dr*deta/dr was being evolved without the explicit contribution from the CN scheme (i.e., the forward Euler component). This PR fixes the issue.
Please do not accept this PR just yet. I would like to hear from Rene about how we might automatically manage release notes before this is fully accepted.