Abstract
It is known that there exist 4-regular, 1-tough graphs which are non-hamiltonian. The smallest such graph known has \(n=18\) nodes and was found by Bauer et al., who conjectured that all 4-regular, 1-tough graphs with \(n\le 17\) are hamiltonian. They in fact proved that this is true for \(n\le 15\), but left open the possibility of non-hamiltonian graphs of 16 or 17 nodes. By using ILP for modeling a counterexample, and then finding out that the model has no solutions, we give an algorithmic proof that their conjecture was indeed correct.
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This research has been carried out in the framework of the departmental research project ICON: Innovative Combinatorial Optimization in Networks, Department of Mathematics, Computer Science and Physics (PRID 2017–2018), University of Udine, Italy.
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Lancia, G., Pippia, E., Rinaldi, F. (2020). Using Integer Programming to Search for Counterexamples: A Case Study. In: Kononov, A., Khachay, M., Kalyagin, V., Pardalos, P. (eds) Mathematical Optimization Theory and Operations Research. MOTOR 2020. Lecture Notes in Computer Science(), vol 12095. Springer, Cham. https://doi.org/10.1007/978-3-030-49988-4_5
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