The purpose of this paper is to find solutions to the 1-median and 2-median problems on a tree network with grey parameters. Generally, the p-median problem asks for finding a set of p facilities on the vertices of a given tree such that the sum of weighted distances from vertices to the closest facility is minimized. First, the 1-median problem with grey weight of vertices and edge lengths is considered, and by showing some properties for this problem, a linear time algorithm is proposed. Then an edge deletion method with time complexity
S. L. Hakimi, Optimum locations of switching centers and the absolute centers and medians of a graph, Oper. Res., vol. 12, no. 3, pp. 450–459, 1964.
O. Kariv and S. L. Hakimi, An algorithmic approach to network location problems. I: The p-centers, SIAM J. Appl. Math., vol. 37, no. 3, pp. 513–538, 1979.
A. J. Goldman, Optimal center location in simple networks, Transp. Sci., vol. 5, no. 2, pp. 212–221, 1971.
P. B. Mirchandani and A. Oudjit, Localizing 2-medians on probabilistic and deterministic tree networks, Networks, vol. 10, no. 4, pp. 329–350, 1980.
B. Gavish and S. Sridhar, Computing the 2-median on tree networks in O(n lg n) time, Networks, vol. 26, no. 4, pp. 305–317, 1995.
A. Oudjit and M. F. Stallmann, Efficient algorithms for finding 2-medians of a tree, Networks, vol. 77, no. 3, pp. 383–402, 2021.
M. J. Canós, C. Ivorra, and V. Liern, An exact algorithm for the fuzzy p-median problem, Eur. J. Oper. Res., vol. 116, no. 1, pp. 80–86, 1999.
F. Taleshian, J. Fathali, and N. A. Taghi-Nezhad, Fuzzy majority algorithms for the 1-median and 2-median problems on a fuzzy tree, Fuzzy Information and Engineering, vol. 10, no. 2, pp. 225–248, 2018.
S. M. A. Nayeem and M. Pal, The p-center problem on fuzzy networks and reduction cost, Iranian Journal of Fuzzy Systems, vol. 5, pp. 1–26, 2008.
J. Fathali and A. Jamalian, Locating multiple facilities in convex sets with fuzzy data and block norms, Appl. Math., vol. 3, no. 12, pp. 1950–1958, 2012.
K. Yang, Y. K. Liu, and G. Q. Yang, Solving fuzzy p-hub center problem by genetic algorithm incorporating local search, Appl. Soft Comput., vol. 13, no. 5, pp. 2624–2632, 2013.
J. A. M. Pérez, J. M. M. Vega, and J. L. Verdegay, Fuzzy location problems on networks, Fuzzy Sets Syst., vol. 142, no. 3, pp. 393–405, 2004.
F. Taleshian and J. Fathali, A mathematical model for fuzzy p-median problem with fuzzy weights and variables, Adv. Oper. Res., vol. 2016, pp. 1–13, 2016.
F. Taleshian, J. Fathali, and N. A. Taghi-Nezhad, Finding the absolute and vertex center of a fuzzy tree, Transp. Lett., vol. 14, no. 6, pp. 591–599, 2022.
J. L. Deng, Control problems of grey systems, Syst. Contr. Lett., vol. 1, no. 5, pp. 288–294, 1982.
G. Huang, B. W. Baetz, and G. G. Patry, A grey linear programming approach for municipal solid waste management planning under uncertainty, Civ. Eng. Syst., vol. 9, no. 4, pp. 319–335, 1992.
G. H. Huang and R. D. Moore, Grey linear programming, its solving approach, and its application, Int. J. Syst. Sci., vol. 24, no. 1, pp. 159–172, 1993.
G. H. Huang, B. W. Baetz, and G. G. Patry, Grey fuzzy integer programming: An application to regional waste management planning under uncertainty, Socio Econ. Plan. Sci., vol. 29, no. 1, pp. 17–38, 1995.
Q. X. Li, The cover solution of grey linear programming, J. Grey Syst., vol. 19, pp. 309–320, 2007.
S. H. Nasseria, A. Yazdani, and D. Darvishi, A primal simplex algorithm for solving linear programming problem with grey cost coefficients, J. New Res. Math., vol. 1, no. 4, pp. 121–141, 2016.
H. Nasseri and D. Darvishi, Duality results on grey linear programming problems, J. Grey Syst., vol. 30, no. 3, pp. 127–142, 2018.
D. Darvishi and P. Babaei, Grey prediction in linear programming problems, Int. J. Appl. Oper. Res., vol. 9, pp. 11–18, 2019.
D. D. Salookolaei and S. H. Nasseri, A dual simplex method for grey linear programming problems based on duality results, Grey Syst. Theory Appl., vol. 10, no. 2, pp. 145–157, 2020.
D. Darvishi, S. Liu, and J. Y. L. Forrest, Grey linear programming: A survey on solving approaches and applications, Grey Syst. Theory Appl., vol. 11, no. 1, pp. 110–135, 2021.
J. Fathali, Grey median problem and vertex optimality, Stat., Optim. Inf. Comput., vol. 11, no. 3, pp. 670–676, 2023.
D. Darvishi, J. Forrest, and S. Liu, A comparative analysis of grey ranking approaches, Grey Syst. Theory Appl., vol. 9, no. 4, pp. 472–487, 2019.