On the strong metric dimension of graph, king graph, and Km ⊙ Kn graph

Yuyun Mintarsih and Tri Atmojo Kusmayadi Department of Mathematics, Faculty of Mathematics and Natural Sciences, Universitas Sebelas Maret, Surakarta, Indonesia E-mail: [email protected], [email protected]

Abstract. Let G be a connected graph with a set of vertices V (G) and a set of edges E(G). The interval I[u, v] between u and v to be the collection of all vertices that belong to some shortest u-v path. A s ∈ V (G) is said to be strongly resolved for vertices u, v ∈ V (G) if v ∈ I[u, s] or u ∈ I[v, s]. A vertex set S ⊆ V (G) is a strong resolving set for G if every two distinct vertices of G are strongly resolved by some vertices of S. The strong metric dimension of G, denoted by sdim(G), is defined as the smallest cardinality of a strong resolving set. In this paper, we determine the strong metric dimension of an antiprism An graph, a king Km,n graph, and a Km ⊙ Kn graph. We obtain the strong metric dimension of an antiprim graph An are n for n odd and n + 1 for n even. The strong metric dimension of King graph Km,n is m + n − 1. The strong metric dimension of Km ⊙ Kn graph are n for m = 1, n ≥ 1 and mn − 1 for m ≥ 2, n ≥ 1.

1. Introduction The strong metric dimension was introduced by Seb¨oand Tannier [6] in 2004. Let G be a connected graph with a set of vertices V (G) and a set of edges E(G). Oelermann and Peters- Fransen [5] defined the interval I[u, v] between u and v to be the collection of all vertices that belong to some shortest u − v path. A vertex s ∈ S is said to strongly resolve two vertices u and v if u ∈ I[v, s] or v ∈ I[u, v]. A vertex set S of G is a strong resolving set for G if every two distinct vertices of G are strongly resolved by some vertices of S. The strong metric basis of G is a strong resolving set with minimal cardinality. The strong metric dimension of a graph G is defined as the cardinality of strong metric basis denoted by sdim(G). Some authors have investigated the strong metric dimension to some graph classes. Seb¨oand Tannier [6] observed the strong metric dimension of Kn, cycle graph Cn, and tree. Kratica et al. [2] observed the strong metric dimension of hamming graph Hn,k. At the same year, Kratica et al [3] determined the strong metric dimension of convex polytope Dn and Tn. Yi [8] determined that sdim(G) = 1 if only if G is path graph and sdim(G) = n−1 if only if G is complete graph. Kusmayadi et al. [4] determined the strong metric dimension of sunflower graph, t-fold , helm graph, and friendship graph. In this paper, we determine the strong metric dimension of an antiprism graph, a king graph, and a Km ⊙ Kn graph. 2. Main Results 2.1. Strong Metric Dimension Let G be a connected graph with a set of vertices V (G), a set of edges E(G), and S={s1, s2, . . . , sk} ∈ V (G). Oelermann and Peters-Fransen [5] defined the interval I[u, v] between u and v to be the collection of all vertices that belong to some shortest u − v path. A vertex s ∈ S is said to strongly resolve two vertices u and v if u ∈ I[v, s] or v ∈ I[u, s]. A vertex set S of G is a strong resolving set for G if every two distinct vertices of G are strongly resolved by some vertices of S. The strong metric basis of G is a strong resolving set with minimal cardinality. The strong metric dimension of a graph G is defined as the cardinality of strong metric basis denoted by sdim(G). We often make use of the following lemma and properties about strong metric dimension given by Kratica et al. [3]. Lemma 2.1 Let u, v ∈ V(G), u ≠ v, (i) d(w,v) ≤ d(u,v) for each w such that u w ∈ E(G), and (ii) d(u,w) ≤ d(u,v) for each w such that v w ∈ E(G). Then there does not exist vertex a ∈ V(G), a ≠ u,v that strongly resolves vertices u and v. Property 2.1 If S ⊂ V(G) is strong resolving set of graph G, then for every two vertices u, v ∈ V(G) satisfying conditions 1 and 2 of Lemma 2.1, obtained u ∈ S or v ∈ S. Property 2.2 If S ⊂ V(G) is strong resolving set of graph G, then for every two vertices u, v ∈ V(G) satisfying d(u, v) = diam(G), obtained u ∈ S or v ∈ S.

2.2. The Strong Metric Dimension of antiprism graph Baˇca [1] defined the antiprism graph An for n ≥ 3 is a 4- with 2n vertices and 4n edges. It consists of outer and inner Cn, while the two cycles connected by edges viui and viu1+i(mod n) for i = 1, 2, 3, . . . , n. The antiprism graph An can be depicted as in Figure 1.

Figure 1. Antiprism graph An

Lemma 2.2 For every integer n ≥ 3 and n odd, if S is a strong resolving set of antiprism graph An then | S | ≥ n.

Proof. We know that S is a strong resolving set of antiprism graph An. Suppose that S contains at most n - 1 vertices, then | S | < n. Let V1, V2 ⊂ V (An), with V1 = {u1, u2, . . . , un} and V2 = {v1, v2, . . . , vn}. Now, we define S1 = V1 ∩ S and S2 = V2 ∩ S. Without loss of generality, we may take | S1 | = p, p > 0 and | S2 | = q, q ≥ 0. Clearly p + q ≥ n, if not then there are two distinct vertices va and vb where va ∈ V1 \ S1 and vb ∈ V2 \ S2 such that for every s ∈ S, we obtain va ∈/ I[vb, s] and vb ∈/ I[va, s]. This contradicts with the supposition that S is a strong resolving set. Thus, | S | ≥ n. ⊓⊔

Lemma 2.3 For every integer n ≥ 3 and n odd, a set S = {u1, u2, . . . , un} is a strong resolving set of antiprism graph An.

Proof. For every integer i, j ∈ [1, n] with 1 ≤ i < j ≤ n, a vertex ui ∈ S which strongly resolves vi dan vj so that vj ∈ I[vi, uj]. Thus, S = {u1, u2, . . . , un} is a strong resolving set of antiprism graph An. ⊓⊔ Lemma 2.4 For every integer n ≥ 3 and n even, if S is a strong resolving set of antiprism graph An then | S | ≥ n+1.

Proof. We know that S is a strong resolving set of antiprism graph An. Suppose that S contains at most n vertices, then | S | < n + 1. Let V1, V2 ⊂ V (An), with V1 = {u1, u2, . . . , un} and V2 = {v1, v2, . . . , vn}. Now, we define S1 = V1 ∩ S and S2 = V2 ∩ S. Without loss of generality, we may take | S1 | = p, p ≥ 0 and | S2 | = q, q ≥ 0. Clearly p + q ≥ n + 1, if not then there are two distinct vertices va and vb where va ∈ V1 \ S1 and vb ∈ V2 \ S2 such that for every s ∈ S, we obtain va ∈/ I[vb, s] and vb ∈/ I[va, s]. This contradicts with the supposition that S is a strong resolving set. Thus, | S | ≥ n+1. ⊓⊔

Lemma 2.5 For every integer n ≥ 3 and n even, a set S = {u1, u2, . . . , u n , u n , v1, v2, . . . , v n } 2 2 +1 2 is a strong resolving set of antiprism graph An.

Proof. We prove that for every two distinct vertices u, v ∈ V (An)\S, u ≠ v there exists a vertex s ∈ S which strongly resolves u and v. There are three possible pairs of vertices. n n ̸ (i) A pair of vertices (ui, uj) with i, j = 2 + 2, 2 + 3, . . . , n, i = j. ∈ n For every integer i, j [ 2 + 2, n] with i < j, we obtain the shortest ui - u1 path: ui, ui+1, . . . , uj, . . . , un, u1. Thus, uj ∈ I[ui, u1]. n n ̸ (ii) A pair of vertices (vi, vj) with i, j = 2 + 1, 2 + 2, . . . , n, i = j. ∈ n For every integer i, j [ 2 + 1, n] with i < j, we obtain the shortest vi - v1 path: vi, vi+1, . . . , vj, . . . , vn, v1. Thus, vj ∈ I[vi, v1]. n n n n (iii) A pair of vertices (ui, vj) with i = 2 + 2, 2 + 3, . . . , n dan j = 2 + 1, 2 + 2, . . . , n. ∈ n ∈ n ≤ For every integer i [ 2 + 2, n] and j [ 2 + 1, n] with i j, we obtain the shortest ui - v1 ∈ ∈ n path: ui, vi, . . . , vj, ..., vn, v1. Thus, vj I[ui, v1]. Then, for every integer i [ 2 +2, n] and n j ∈ [ + 1, n] with i > j, we obtain the shortest ui - v n path: ui, vi−1, . . . , vj, . . . , v n , v n . 2 2 2 +1 2 Thus, vj ∈ I[ui,v n ]. 2 From every possible pairs of vertices, there exists a vertex s ∈ S which strongly resolves u, v ∈ V (Km,n) \ S. Thus, S is a strong resolving set of antiprism graph An. ⊓⊔

Theorem 2.1 Let An be the antiprism{ graph with n ≥ 3, then n, n odd; sdim(A ) = n n + 1, n even.

Proof. Let An be an antiprism graph with n ≥ 3 and a set of vertices V (An) = {u1, u2, ..., un, v1, v2, ..., vn}. We divide the proof into two cases according to the values of n. (i) For n odd. By using Lemma 2.3, a set S = {u1, u2, . . . , un} is a strong resolving set of antiprism graph An. According to Lemma 2.2, | S |≥ n so that S is a strong metric basis of antiprism graph An. Hence, sdim(An) = n. (ii) For n even. By using Lemma 2.5, a set S = {u1, u2, . . . , u n , v1, v2, . . . , v n } is a strong resolving set of 2 +1 2 antiprism graph An. According to Lemma 2.4, | S |≥ n so that S is a strong metric basis of antiprism graph An. Hence, sdim(An) = n + 1. ⊓⊔

2.3. The Strong Metric Dimension of King Graph Weisstein [7] defined the king graph Km,n for m, n ≥ 2 is the graph with mn vertices in which each vertex represents a square in an m × n chessboard, and each edge corresponds to a legal move by king.The king graph Km,n can be depicted as in Figure 2.

Figure 2. King graph Km,n

Lemma 2.6 For every integer m,n ≥ 2, if S is a strong resolving set of king graph Km,n then | S | ≥ m+n-1.

Proof. We know that S is a strong resolving set of king graph Km,n. Suppose that S contains at most m + n − 2 vertices, then | S | < m + n − 1. Let V1,V2 ⊂ V (An), with { 1 1 1 2 3 m} { 2 2 2 3 3 3 m m m} V1 = v1, v2, . . . , vn, v1, v1, . . . , v1 and V2 = v2, v3, . . . , vn, v2, v3, . . . , vn, . . . , v2 , v3 , vn . Now, we define S1 = V1 ∩ S and S2 = V2 ∩ S. Without loss of generality, we may take | S1 | = p, p > 0 and | S2 | = q, q ≥ 0. Clearly p + q ≥ m + n − 1, if not then there are two distinct vertices va and vb where va ∈ V1 \ S1 and vb ∈ V2 \ S2 such that for every s ∈ S, we obtain va ∈/ I[vb, s] and vb ∈/ I[va, s]. This contradicts with the supposition that S is a strong resolving set. Thus, | S | ≥ m+n-1. ⊓⊔ ≥ { 1 1 1 2 3 m} Lemma 2.7 For every integer m,n 2, a set S = v1, v2, . . . , vn, v1, v1, . . . , v1 is a strong resolving set of king graph Km,n.

Proof. We prove that for every two distinct vertices u, v ∈ V (Km,n)\S, u ≠ v there exists a vertex s ∈ S which strongly resolves u and v. There are three possible pairs of vertices. p p (i) A pair of vertices (vk, vl ) with p = 2, 3, . . . , m and k, l = 2, 3, . . . , n. ∈ ∈ p p For every integer p [2, m] and k, l [2, n] with k < l, we obtain the shortest vl - v1 path: p p p p p p ∈ p p vl , vl−1, . . . , vk, . . . , v2, v1. Thus, vk I[vl , v1]. i j (ii) A pair of vertices (vq, vq) with i, j = 2, 3, . . . , m and q = 2, 3, . . . , n. ∈ ∈ j 1 For every integer i, j [2, m], q [2, n] with i < j, we obtain the shortest vq - vq path: j j−1 i 2 1 i ∈ j 1 vq, vq , . . . , vq, . . . , vq , vq . Thus, vq I[vq, vq ]. i j (iii) A pair of vertices (vk, vl ) with i, j = 2, 3, . . . , m and k, l = 2, 3, . . . , n. ∈ ∈ j For every integer i, j [2, m], k, l [1, n] with i < j dan k < l, we obtain the shortest vl - 1 j j−1 j−1 j−1 j−2 i i−1 2 1 i ∈ j 1 vk path: vl , vl−1 , vl−1 , . . . , vk , vk , . . . , vk, vk , . . . , vk, vk. Thus, vk I[vl , vk]. From every possible pairs of vertices, there exists a vertex s ∈ S which strongly resolves u, v ∈ V (Km,n)\S. Thus S is a strong resolving set of king graph Km,n. ⊓⊔

Theorem 2.2 Let Km,n be the king graph with m, n ≥ 2, then sdim(Km,n) = m + n − 1. { 1 1 1 2 3 m} Proof. By using Lemma 2.7, a set S = v1, v2, . . . , vn, v1, v1, . . . , v1 is a strong resolving set of king graph Km,n. According to Lemma 2.6, | S |≥ m + n − 1 so that S is a strong metric basis of king graph Km,n. Hence, sdim(Km,n) = m + n − 1. ⊓⊔

2.4. The Strong Metric Dimension of Km ⊙ Kn Graph The corona product Km ⊙ Kn graph is graph obtained from Km and Kn by taking one copy th of Km and n copies of Kn and joining by an edge each vertex from i -copy of Kn with the th i -vertex of Km. The Km ⊙ Kn can be depicted as in Figure 3. v 1,1 v 1,n v 1,2

v v m v 1,3 v ,2 1,4 2,n v v m,3 v 2,4 v 1 m,1 v v 2,1 2 v v m m, n vm v ,4 2,3 v 2,2 v v 3 4,3 v v 3,4 v 4 4,2 v n v v 3, 4,4 3,3

v v 4,1 v v 3,1 4,n 3,2

Figure 3. Km ⊙ Kn Graph

Lemma 2.8 For every integer m ≥ 2 and n ≥ 1, if S is a strong resolving set of Km ⊙ Kn graph then | S | ≥ mn-1.

Proof. Let us consider a pair of vertices (vi,k, vj,l) for i, j ∈ [1, m], k, l ∈ [1, n] satisfying both of the conditions of Lemma 2.1. According to Property 2.1, we obtain vi,k ∈ S or vj,l ∈ S. It means that S contains one vertex from distinct sets X = { vi,k, vj,l } with i, j = 1, 2, ..., m and k, l = 1, 2, . . . , n. The minimum number of vertices from distinct sets X is mn − 1. Therefore, | S | ≥ mn − 1. ⊓⊔

Lemma 2.9 For every integer m ≥ 2 and n ≥ 1, a set S = {v1,1, v1,2, ..., v1,n−1, v1,n, v2,1, v2,2, ..., v2,n−1, v2,n, . . . , vm,1, vm,2, . . . , vm,n−1} is a strong resolving set of Km ⊙ Kn graph. Proof. For every integer i ∈ [1, m−1], we obtain the shortest vm,n - vi,k path: vm,n, vm, vi, vi,k. So that vi,k strongly resolves a pair of vertices (vi, vm,n). Thus, vi ∈ I[vm,n, vi,k]. For a pair of vertices (vi, vj) with i, j ∈ [1, m] and i ≠ j, we obtain the shortest vi - vj,l path: vi, vj, vj,l. So that vj,l strongly resolves a pair of vertices (vi, vj). Thus, vj ∈ I[vi, vj,l]. Therefore S = {v1,1, v1,2, . . . , v1,n−1, v1,n, v2,1, v2,2, . . . , v2,n−1, v2,n, . . . , vm,1, vm,2, . . . , vm,n−1} is a strong resolving set of Km⊙Kn graph. ⊓⊔

Theorem 2.3 Let Km ⊙ Kn graph with m,{ n ≥ 1, then n, m = 1, n ≥ 1; sdim(K ⊙ K ) = m n mn − 1, m ≥ 2, n ≥ 1.

Proof. Suppose Km ⊙ Kn graph with m, n, k ≥ 1 and a set of vertices V (Km ⊙ Kn)={v1, v2, ..., vm, v1,1, v1,2, ..., v1,n, v2,1, v2,2, ..., v2,n, ..., vm,1, vm,2, . . . , vm,n}. We divide the proof into two cases according to the values of m and n. (i) For m = 1 and n ≥ 1. ∼ By using characterization Yi [8], sdim(G) = n−1 if only if G = K , so that sdim(K ⊙K ) = ∼ n 1 n n because K1 ⊙ Kn = Kn+1 then strong resolving set of K1 ⊙ Kn graph has n element. Hence sdim(K1 ⊙ Kn) = n. (ii) For m ≥ 2 and n ≥ 1. By using Lemma 2.9 a set S = {v1,1, v1,2, . . . , v1,n−1, v1,n, v2,1, v2,2, . . . , v2,n−1, v2,n, . . . , vm,1, vm,2, . . . , vm,n−1} is a strong resolving set of Km⊙Kn graph. According to Lemma 2.8, | S |≥ mn−1 so that S is a strong metric basis of Km⊙Kn graph. Hence sdim(Km⊙Kn) = mn−1. ⊓⊔

3. Conclusion According to the discussion above, it can be concluded that the strong metric dimension of an antiprism graph, a king graph, and a Km ⊙ Kn graph are as stated in Theorem 2.1, Theorem 2.2, and Theorem 2.3 respectively. k Open Problem: Determine the strong metric dimension of a Km ⊙ Kn graph.

4. Acknowledgement The authors gratefully acknowledge the support from Department of Mathematics, Faculty of Mathematics and Natural Sciences, Universitas Sebelas Maret, Surakarta. Then, we wish to thank the referees for their suggestions and references, which helped to improve the paper.

References [1] Baˇca, M., F. Bashir, and A. Semaniˇcov´a, Face Antimagic Labeling of , Util. Math 84 (2011), 209–224. [2] Kratica, J., V. Kovaˇcevi´c-Vujˇci´c,and M. Cangalovi´c,ˇ Minimal Doubly Resolving Sets and The The Strong Metric Dimension of Hamming Graphs, Applicable Analysis and Discrete Mathematics 6 (2012), 63–71. [3] Kratica, J., V. Kovaˇcevi´c-Vujˇci´c,and M. Cangalovi´c,ˇ Minimal Doubly Resolving Sets and The The Strong Metric Dimension of Some Comvex Polytope, Applied Mathematics and Computation 218 (2012), 9790– 9801. [4] Kusmayadi, T. A., S. Kuntari, D. Rahmadi, and F. A. Lathifah, On The Strong Metric Dimension of Some Related Wheel Graph, Far East Journal of Mathematical Sciences (FJMS) 99 (2016), no. 9, 1325–1334. [5] Oelermann, O. and J. Peters-Fransen, The Strong Metric Dimension of Graphs and Digraphs, Discrete Applied Mathematics 155 (2007), 356–364. [6] Seb¨o,A. and E. Tannier, On Metric Generators of Graph, Mathematics and Operations Research 29(2) (2004), 383–393. [7] Weisstein, E. W., King Graph, From MathWorld-A Wolfram Web Resource, http://mathworld.wolfram.com/KingGraph.html. [8] Yi, E., On Strong Metric Dimension Graphs and Their Complements, Acta Mathematica Sinica 29(8) (2013), 1479–1492.