Add derivative tally based k_eff search support for material perturbations #3690
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GuySten
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Jan 6, 2026
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GuySten
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This looks like a nice feature.
A better place for the examples should be in the openmc-notebooks repo though.
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The examples you added are nice but imo a better place for them should be in the openmc-notebooks repository.
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I suggest moving the criticality search tests into test_criticality_search.py file.
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Description
This PR extends the recently added Model.keff_search method for material input parameters by leveraging derivative tallies. It adds least-squares curve fitting over a combination of K_eff evaluations and its derivatives as an alternative method to GRSecant's curve fitting. We have observed considerable reduction in the required number of MC evaluations for some cases (reproducible using
test_tally_deriv_keff_search.py) which is consistent with the primary work by @smharper as reported here: https://dspace.mit.edu/bitstream/handle/1721.1/106690/969775837-MIT.pdfIt is an initial work on #980 and is related to: #3569, #2693.
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