Abstract
We discuss recent positive experiences applying convex feasibility algorithms of Douglas–Rachford type to highly combinatorial and far from convex problems.
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Notes
Here indices are understood modulo N. That is, C N+1:=C 1.
In this context, “feasibility” and “satisfiability” can be used interchangeably.
See http://carma.newcastle.edu.au/DRmethods/comb-opt/2cycle.html for an animated version.
Also known as McMahon Squares in honour of the great English combinatorialist, Percy MacMahon, who examined them nearly a century ago.
Pulkit Bansal did this as a 2010 NSERC summer student with Heinz Bauschke and Xianfu Wang.
Japanese, being based on ideograms, does not lead itself to anagrams, crosswords or other word puzzles; this in part explains why so many good numeric and combinatoric games originate in Japan.
top1465: http://magictour.free.fr/top1465
Gordon Royle: http://school.maths.uwa.edu.au/~gordon/sudokumin.php
reglib-1.3: http://hodoku.sourceforge.net/en/libs.php
ksudoku16/25: http://carma.newcastle.edu.au/DRmethods/comb-opt/
Gurobi Sudoku model: http://www.gurobi.com/documentation/5.5/example-tour/node155
Schaad’s web-based solver: https://people.ok.ubc.ca/bauschke/Jason/
For the five solutions: http://carma.newcastle.edu.au/DRmethods/comb-opt/nasty_nonunique.txt
If x n is the current iterate, x ∗ the solution, and m=max n ∥P D x n −x ∗∥, ∥P D x n −x ∗∥/m is plotted against n.
QR (quick response) codes are two-dimensional bar codes originally designed for use in the Japanese automobile industry. Their data is typically encoded in either numerical, alphanumerical, or binary formats.
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Acknowledgements
We wish to thank Heinz Bauschke, Russell Luke, Ian Searston and Brailey Sims for many useful insights. We would also like to thank the anonymous referee for their helpful suggestions. Example 2.1 was provided by Brailey Sims.
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Communicated by Michel Théra.
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Aragón Artacho, F.J., Borwein, J.M. & Tam, M.K. Recent Results on Douglas–Rachford Methods for Combinatorial Optimization Problems. J Optim Theory Appl 163, 1–30 (2014). https://doi.org/10.1007/s10957-013-0488-0
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DOI: https://doi.org/10.1007/s10957-013-0488-0