We study two optimization problems on simplicial complexes with homology over β€β, the minimum bounded chain problem: given a d-dimensional complex π¦ embedded in β^(d+1) and a null-homologous (d-1)-cycle C in π¦, find the minimum d-chain with boundary C, and the minimum homologous chain problem: given a (d+1)-manifold β³ and a d-chain D in β³, find the minimum d-chain homologous to D. We show strong hardness results for both problems even for small values of d; d = 2 for the former problem, and d=1 for the latter problem. We show that both problems are APX-hard, and hard to approximate within any constant factor assuming the unique games conjecture. On the positive side, we show that both problems are fixed-parameter tractable with respect to the size of the optimal solution. Moreover, we provide an O(β{log Ξ²_d})-approximation algorithm for the minimum bounded chain problem where Ξ²_d is the dth Betti number of π¦. Finally, we provide an O(β{log n_{d+1}})-approximation algorithm for the minimum homologous chain problem where n_{d+1} is the number of (d+1)-simplices in β³.
@InProceedings{borradaile_et_al:LIPIcs.SoCG.2020.21, author = {Borradaile, Glencora and Maxwell, William and Nayyeri, Amir}, title = {{Minimum Bounded Chains and Minimum Homologous Chains in Embedded Simplicial Complexes}}, booktitle = {36th International Symposium on Computational Geometry (SoCG 2020)}, pages = {21:1--21:15}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-143-6}, ISSN = {1868-8969}, year = {2020}, volume = {164}, editor = {Cabello, Sergio and Chen, Danny Z.}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2020.21}, URN = {urn:nbn:de:0030-drops-121799}, doi = {10.4230/LIPIcs.SoCG.2020.21}, annote = {Keywords: computational topology, algorithmic complexity, simplicial complexes} }
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