“…Generally, there are two approaches to determine the value of k; one is to directly set it as the true number of clusters (Yu et al, 2018;Zhao et al, 2021;Liu et al, 2022;Wu and Ma, 2022); The other approach is applicable to the case where the true number of clusters is unknown, in which the variation range of k is determined firstly, and the k corresponding to the optimal value of an index (Silhouette index, Dunn index, Davies-Bouldin index, etc.) can be chosen as the optimal number of clusters (Gao et al, 2019;Acharya et al, 2020;López-Cortés et al, 2020;Zhang et al, 2022). In this paper, we adopt the first approach, and the number of clusters k is selected according to Table 1.…”