[math] Fix TMath::Laplacian, add test and improve doxygen of finite difference methods#22823
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Test Results 23 files 23 suites 3d 3h 14m 47s ⏱️ For more details on these failures, see this check. Results for commit 8b399e5. ♻️ This comment has been updated with latest results. |
dpiparo
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ferdymercury
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Thanks a lot!
I'd suggest
- adding in the RelNotes of 6.38.x and 6.40.2 that using Laplacian lead to incorrect results.
- fix preexisting TMathTests to not exit 0 and multiply by four refvalues
The standard second-order central, backward and forward differences contained a mistake: a factor-of-4 error. See finite different coefficients here: https://en.wikipedia.org/wiki/Finite_difference_coefficient
Use a polynomial and its known derivatives to check the correctness of the finite difference methods.
The test failed without any consequences because it was always returning 0. Other "tests" in this file will need to be updated to check their outputs in the future. Furthermore: - The second derivatives are unstable with short, so remove it from the test. - The targets for the second derivatives were wrong by a factor 4; fix. - Due to rounding, finite differences on integers don't exactly hit the target. Allow a delta of 1.
ferdymercury
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Jul 16, 2026
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/backport to 6.40, 6.38 |
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Preparing to backport PR #22823 to branches 6.40 and 6.38 requested by hageboeck |
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Something went wrong when assigning the PR or setting labels @hageboeck please see the logs |
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Something went wrong when assigning the PR or setting labels @hageboeck please see the logs |
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This PR has been backported to |
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/backport to 6.36 |
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Preparing to backport PR #22823 to branch 6.36 requested by dpiparo |
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Note: Contains commits of #22809.
Here, the tests are added.