Abstract
In a random intersection graph \(G_{n,m,p}\), each of n vertices selects a random subset of a set of m labels by including each label independently with probability p and edges are drawn between vertices that have at least one label in common. Among other applications, such graphs have been used to model social networks, in which individuals correspond to vertices and various features (e.g. ideas, interests) correspond to labels; individuals sharing at least one common feature are connected and this is abstracted by edges in random intersection graphs. In this paper, we consider the problem of finding maximum cliques when the input graph is \(G_{n,m,p}\). Current algorithms for this problem are successful with high probability only for relatively sparse instances, leaving the dense case mostly unexplored. We present a spectral algorithm for finding large cliques that processes vertices according to respective values in the second largest eigenvector of the adjacency matrix of induced subgraphs of the input graph corresponding to common neighbors of small cliques. Leveraging on the Single Label Clique Theorem from [16], we were able to construct random instances, without the need to externally plant a large clique in the input graph. In particular, we used label choices to determine the maximum clique and then concealed label information by just giving the adjacency matrix of \(G_{n, m, p}\) as input to the algorithm. Our experimental evaluation showed that our spectral algorithm clearly outperforms existing polynomial time algorithms, both with respect to the failure probability and the approximation guarantee metrics, especially in the dense regime, thus suggesting that spectral properties of random intersection graphs may be also used to construct efficient algorithms for other NP-hard graph theoretical problems as well.
Christoforos Raptopoulos was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers” (Project Number: 704).
Paul Spirakis was supported by the NeST initiative of the EEE and CS of the University of Liverpool and by the EPSRC grant EP/P02002X/1.
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7 Appendix
7 Appendix
1.1 7.1 Greedy-Clique Algorithm
The pseudocode of the GREEDY-CLIQUE Algorithm from [5] is shown below.
1.2 7.2 Mono-Clique Algorithm
The pseudocode of the MONO-CLIQUE Algorithm from [5] is shown below.
1.3 7.3 Maximum-Clique Algorithm
The pseudocode of the Maximum-Clique Algorithm from [2] is shown below.
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Christodoulou, F., Nikoletseas, S., Raptopoulos, C., Spirakis, P.G. (2023). A Spectral Algorithm for Finding Maximum Cliques in Dense Random Intersection Graphs. In: Gąsieniec, L. (eds) SOFSEM 2023: Theory and Practice of Computer Science. SOFSEM 2023. Lecture Notes in Computer Science, vol 13878. Springer, Cham. https://doi.org/10.1007/978-3-031-23101-8_2
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