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Matching random colored points with rectangles

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Abstract

Given \(n>0\), let \(S\subset [0,1]^2\) be a set of n points, chosen uniformly at random. Let \(R\cup B\) be a random partition, or coloring, of S in which each point of S is included in R uniformly at random with probability 1/2. We study the random variable M(n) equal to the number of points of S that are covered by the rectangles of a maximum strong matching of S with axis-aligned rectangles. The matching consists of closed axis-aligned rectangles that cover exactly two points of S of the same color, and is strong in the sense that all of its rectangles are pairwise disjoint. We prove that almost surely \(M(n)\ge 0.83\,n\) for n large enough. Our approach is based on modeling a deterministic greedy matching algorithm that runs over the random point set as a Markov chain.

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Acknowledgements

Author Corujo was supported by grants from the Université Paris-Dauphine (France) and the ITI IRMIA++. Author Flores-Peñaloza was supported by project PAPIIT IN120520 (UNAM, Mexico). Author Huemer was supported by projects PID2019-104129GB-I00/ MCIN/ AEI/ 10.13039/501100011033 and Gen. Cat. DGR 2021-SGR-00266. Author Pérez-Lantero was supported by projects CONICYT FONDECYT/Regular 1160543 (Chile), DICYT 041933PL Vicerrectoría de Investigación, Desarrollo e Innovación USACH (Chile), and Programa Regional STICAMSUD 19-STIC-02. Author Seara was supported by project PID2019-104129GB-I00/ MCIN/ AEI/ 10.13039/ 501100011033 and Gen. Cat. DGR 2021-SGR-00266.

Funding

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 734922.

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All authors contributed equally to the results of this manuscript. They also read and approved this final version.

Corresponding author

Correspondence to Pablo Pérez-Lantero.

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A preliminary version of this work appeared in WALCOM 2020, 14th International Conference and Workshop on Algorithms and Computation, Singapore (Corujo et al. 2020).

Bichromatic matching

Bichromatic matching

In this section, we present our results when matching red points with blue points. The Markov chain for this case consists of 20 states \(\{e_1,e_2,\ldots ,e_{20}\}\), and it is described in Fig. 9. Its transition matrix is showed in Fig. 8.

We have that \(f(e)=2\) for all \(e\in \{e_3,e_7,e_9,e_{10},e_{12},e_{17},e_{18},e_{19},e_{20}\}\), \(f(e_{11})=4\), and \(f(e)=0\) for every other state e. Furthermore, the stationary distribution \(s=(s_1,\ldots ,s_{20})\) satisfies

$$\begin{aligned}{} & {} s_3 ~=~ \frac{4694}{26397},~ s_7 ~=~ \frac{2560}{26397},~ s_9 ~=~ \frac{340}{26397},~ s_{10} ~=~ \frac{85}{2933},~ s_{11} ~=~ \frac{85}{8799}\\{} & {} s_{12} ~=~ \frac{340}{26397},~ s_{17} ~=~ \frac{340}{26397},~ s_{18} ~=~ \frac{68}{26397},~ s_{19} ~=~ \frac{68}{26397},~ s_{20} ~=~ \frac{68}{26397}. \end{aligned}$$

Then, we obtain

$$\begin{aligned} \alpha _3 ~{} & {} =~ 2(s_3+s_7+s_9+s_{10}+s_{17}+s_{18}+s_{19}+s_{20}) + 4s_{11} ~\nonumber \\{} & {} =~ \frac{19506}{26397} ~\approx ~ 0.738947608. \end{aligned}$$

By Theorem 1, taking \(\varepsilon =\alpha _3-0.7389>0\), for n large enough we have almost surely that at least \(0.7389\,n\) points can be matched (Fig. 9).

Fig. 8
figure 8

The transition matrix of the Markov chain for \(k=3\), when matching red points with blue points (Color figure online)

Fig. 9
figure 9

The table shows the 20 states of the Markov chain for \(k=3\), when matching red points with blue points. In the second column we show the first component of \(e_i\), and in the third column we show \(f(e_i)\). In the last column we show the neighborhood of \(e_i\) as pairs \((e_j,P_{i,j})\), where \(P_{i,j}\) is the transition probability from \(e_i\) to \(e_j\) (Color figure online)

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Corujo, J., Flores-Peñaloza, D., Huemer, C. et al. Matching random colored points with rectangles. J Comb Optim 45, 81 (2023). https://doi.org/10.1007/s10878-023-01010-z

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