This note describes our submission to the 2023 PACE Challenge on the computation of twin-width. Our solver Hydra Prime combines modular decomposition with a collection of upper- and lower-bound algorithms, which are alternatingly applied on the prime graphs resulting from the modular decomposition. We introduce two novel approaches which contributed to the solver’s winning performance in the Exact Track: timeline encoding and hydra decomposition. Timeline encoding is a new data structure for computing the width of a given contraction sequence, enabling faster local search; the hydra decomposition is an iterative refinement strategy featuring a small vertex separator.
@InProceedings{mizutani_et_al:LIPIcs.IPEC.2023.36, author = {Mizutani, Yosuke and Dursteler, David and Sullivan, Blair D.}, title = {{PACE Solver Description: Hydra Prime}}, booktitle = {18th International Symposium on Parameterized and Exact Computation (IPEC 2023)}, pages = {36:1--36:5}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-305-8}, ISSN = {1868-8969}, year = {2023}, volume = {285}, editor = {Misra, Neeldhara and Wahlstr\"{o}m, Magnus}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2023.36}, URN = {urn:nbn:de:0030-drops-194552}, doi = {10.4230/LIPIcs.IPEC.2023.36}, annote = {Keywords: Twin-width, PACE 2023} }
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