The figure shows a graph with six vertices, and a representation of this graph as an intersection graph of rectangles (two-dimensional boxes). This graph cannot be represented as an intersection graph of boxes in any lower dimension, so its boxicity is two.
Many graph problems can be solved or approximated more efficiently for graphs with bounded boxicity than they can for other graphs; for instance, the maximum clique problem can be solved in polynomial time for graphs with bounded boxicity. For some other graph problems, an efficient solution or approximation can be found if a low-dimensional box representation is known. However, finding such a representation may be difficult:
it is NP-complete to test whether the boxicity of a given graph is at most some given value K, even for K = 2.
Chandran, Francis & Sivadasan (2010) describe algorithms for finding representations of arbitrary graphs as intersection graphs of boxes, with a dimension that is within a logarithmic factor of the maximum degree of the graph; this result provides an upper bound on the graph's boxicity.
E.g., see Chandran, Francis & Sivadasan (2010) and Chandran & Sivadasan (2007). - Chandran, L. Sunil; Francis, Mathew C.; Sivadasan, Naveen (2010), "Geometric representation of graphs in low dimension using axis parallel boxes", Algorithmica, 56 (2): 129–140, arXiv:cs.DM/0605013, doi:10.1007/s00453-008-9163-5, MR 2576537, S2CID 17838951 https://arxiv.org/abs/cs.DM/0605013
Scheinerman (1984). - Scheinerman, E. R. (1984), Intersection Classes and Multiple Intersection Parameters, Ph. D thesis, Princeton University https://archive.org/details/intersection-classes-and-multi
Thomassen (1986). - Thomassen, Carsten (1986), "Interval representations of planar graphs", Journal of Combinatorial Theory, Series B, 40: 9–20, doi:10.1016/0095-8956(86)90061-4 https://doi.org/10.1016%2F0095-8956%2886%2990061-4
Bellantoni et al. (1993). - Bellantoni, Stephen J.; Ben-Arroyo Hartman, Irith; Przytycka, Teresa; Whitesides, Sue (1993), "Grid intersection graphs and boxicity", Discrete Mathematics, 114 (1–3): 41–49, doi:10.1016/0012-365X(93)90354-V https://doi.org/10.1016%2F0012-365X%2893%2990354-V
Chandran, Francis & Sivadasan (2010) observe that this follows from the fact that these graphs have a polynomial number of maximal cliques, i.e., the class of graphs with bounded boxicity is said to have few cliques. An explicit box representation is not needed to list all maximal cliques efficiently. - Chandran, L. Sunil; Francis, Mathew C.; Sivadasan, Naveen (2010), "Geometric representation of graphs in low dimension using axis parallel boxes", Algorithmica, 56 (2): 129–140, arXiv:cs.DM/0605013, doi:10.1007/s00453-008-9163-5, MR 2576537, S2CID 17838951 https://arxiv.org/abs/cs.DM/0605013
See, e.g., Agarwal, van Kreveld & Suri (1998) and Berman et al. (2001) for approximations to the maximum independent set for intersection graphs of rectangles, and Chlebík & Chlebíková (2005) for results on hardness of approximation of these problems in higher dimensions. - Agarwal, Pankaj K.; van Kreveld, Marc; Suri, Subhash (1998), "Label placement by maximum independent set in rectangles", Computational Geometry Theory and Applications, 11 (3–4): 209–218, doi:10.1016/S0925-7721(98)00028-5, hdl:1874/18908, S2CID 2381363 https://doi.org/10.1016%2FS0925-7721%2898%2900028-5
Cozzens (1981) shows that computing the boxicity is NP-complete; Yannakakis (1982) shows that even checking whether the boxicity is at most 3 is NP-hard; finally Kratochvil (1994) showed that recognising boxicity 2 is NP-hard. - Cozzens, M. B. (1981), Higher and Multidimensional Analogues of Interval Graphs, Ph.D. thesis, Rutgers University
Adiga, Chitnis & Saurabh (2010). - Adiga, Abhijin; Chitnis, Rajesh; Saurabh, Saket (2010), "Parameterized algorithms for boxicity", Algorithms and Computation: 21st International Symposium, ISAAC 2010, Jeju Island, Korea, December 15-17, 2010, Proceedings, Part I (PDF), Lecture Notes in Computer Science, vol. 6506, pp. 366–377, doi:10.1007/978-3-642-17517-6_33, ISBN 978-3-642-17516-9, archived from the original (PDF) on 2017-08-30, retrieved 2018-01-22 https://web.archive.org/web/20170830050212/http://www.wisdom.weizmann.ac.il/~chitnis/fptBoxicity.pdf
Chandran & Sivadasan (2007, Theorem 14) - Chandran, L. Sunil; Sivadasan, Naveen (2007), "Boxicity and treewidth", Journal of Combinatorial Theory, Series B, 97 (5): 733–744, arXiv:math.CO/0505544, doi:10.1016/j.jctb.2006.12.004, S2CID 9854207 https://arxiv.org/abs/math.CO/0505544
Chandran, Francis & Sivadasan (2010) - Chandran, L. Sunil; Francis, Mathew C.; Sivadasan, Naveen (2010), "Geometric representation of graphs in low dimension using axis parallel boxes", Algorithmica, 56 (2): 129–140, arXiv:cs.DM/0605013, doi:10.1007/s00453-008-9163-5, MR 2576537, S2CID 17838951 https://arxiv.org/abs/cs.DM/0605013
Esperet (2016) - Esperet, Louis (2016), "Boxicity and topological invariants", European Journal of Combinatorics, 51: 495–499, arXiv:1503.05765, doi:10.1016/j.ejc.2015.07.020, S2CID 5548385 https://arxiv.org/abs/1503.05765
Adiga, Chandran & Mathew (2014) - Adiga, Abhijin; Chandran, L. Sunil; Mathew, Rogers (2014), "Cubicity, Degeneracy, and Crossing Number", European Journal of Combinatorics, 35: 2–12, arXiv:1105.5225, doi:10.1016/j.ejc.2013.06.021, S2CID 2069078 https://arxiv.org/abs/1105.5225
Esperet & Wiechert (2018) - Esperet, Louis; Wiechert, Veit (2018), "Boxicity, poset dimension, and excluded minors", Electronic Journal of Combinatorics, 25 (4): #P4.51, arXiv:1804.00850, doi:10.37236/7787, S2CID 119148637 http://www.combinatorics.org/ojs/index.php/eljc/article/view/v25i4p51
Esperet (2016) - Esperet, Louis (2016), "Boxicity and topological invariants", European Journal of Combinatorics, 51: 495–499, arXiv:1503.05765, doi:10.1016/j.ejc.2015.07.020, S2CID 5548385 https://arxiv.org/abs/1503.05765