We examine the complexity of maximising fitness via local search on valued constraint satisfaction problems (VCSPs). We consider two kinds of local ascents: (1) steepest ascents, where each step changes the domain that produces a maximal increase in fitness; and (2) ≺-ordered ascents, where - of the domains with available fitness increasing changes - each step changes the ≺-minimal domain. We provide a general padding argument to simulate any ordered ascent by a steepest ascent. We construct a VCSP that is a path of binary constraints between alternating 2-state and 3-state domains with exponentially long ordered ascents. We apply our padding argument to this VCSP to obtain a Boolean VCSP that has a constraint (hyper)graph of arity 5 and pathwidth 4 with exponential steepest ascents. This is an improvement on the previous best known construction for long steepest ascents, which had arity 8 and pathwidth 7.
@InProceedings{kaznatcheev_et_al:LIPIcs.CP.2024.17, author = {Kaznatcheev, Artem and van Marle, Melle}, title = {{Exponential Steepest Ascent from Valued Constraint Graphs of Pathwidth Four}}, booktitle = {30th International Conference on Principles and Practice of Constraint Programming (CP 2024)}, pages = {17:1--17:16}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-336-2}, ISSN = {1868-8969}, year = {2024}, volume = {307}, editor = {Shaw, Paul}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CP.2024.17}, URN = {urn:nbn:de:0030-drops-207021}, doi = {10.4230/LIPIcs.CP.2024.17}, annote = {Keywords: valued constraint satisfaction problem, steepest ascent, local search, bounded treewidth, intractability} }
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