Abstract
We solve an open problem, stated in 2008, about the feasibility of designing efficient algorithmic self-assembling systems which produce 2-dimensional colored patterns. More precisely, we show that the problem of finding the smallest tile assembly system which rectilinearly self-assembles an input pattern with 2 colors (i.e., 2-Pats) is \(\mathbf {NP}\)-hard. Of both theoretical and practical significance, the more general k-Pats problem has been studied in a series of papers which have shown k-Pats to be \(\mathbf {NP}\)-hard for \(k=60\), \(k=29\), and then \(k=11\). In this paper, we prove the fundamental conjecture that 2-Pats is \(\mathbf {NP}\)-hard, concluding this line of study. While most of our proof relies on standard mathematical proof techniques, one crucial lemma makes use of a computer-assisted proof, which is a relatively novel but increasingly utilized paradigm for deriving proofs for complex mathematical problems. This tool is especially powerful for attacking combinatorial problems, as exemplified by the proof for the four color theorem and the recent important advance on the Erdős discrepancy problem using computer programs. In this paper, these techniques will be brought to a new order of magnitude, computational tasks corresponding to one CPU-year. We massively parallelize our program, and provide a full proof of its correctness. Its source code is freely available online.
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Notes
http://self-assembly.net/wiki/index.php?title=2PATS-tileset-search (C++ version) and http://self-assembly.net/wiki/index.php?title=2PATS-search-ocaml (OCaml version).
The implementation is Open MPI: http://www.open-mpi.org.
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Acknowledgments
We thank Manuel Bertrand for his infinite patience and helpful assistance with setting up the server and helping debug our network and system problems, and Cécile Barbier, Eric Fede and Kai Poutrain for their assistance with software setup. We also thank anonymous referees for their valuable comments, especially about the relationship between M-Sat and SetCover, on the earlier version of this paper.
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This is a full version of [20].
This work is supported in part by the NSERC Discovery Grant R2824A01 and UWO Faculty of Science grant to L. K., NSF Grant CCF-1219274 to P.-È. M., NSF Grants CCF-1117672 and CCF-1422152 to M. J. P., Academy of Finland, Postdoctoral Researcher Grant 13266670/T30606, JST Program to Disseminate Tenure Tracking System, MEXT, Japan 6F36, and JSPS Grant-in-Aid for Research Activity Start-up No. 15H06212 to S. S.
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Kari, L., Kopecki, S., Meunier, PÉ. et al. Binary Pattern Tile Set Synthesis Is NP-Hard. Algorithmica 78, 1–46 (2017). https://doi.org/10.1007/s00453-016-0154-7
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DOI: https://doi.org/10.1007/s00453-016-0154-7