Computing the local metric dimension of a graph from the local metric dimension of primary subgraphs

For an ordered subset W= w₁, w₂,?…?w_k of vertices and a vertex u in a connected graph G, the representation of u with respect to W is the ordered k-tuple r(u|W)=(d(u, w₁), d(u, w₂),?…?, d(u, w_k)), where d(x, y) represents the distance between the vertices x and y. The set W is a local metric generator for G if every two adjacent vertices of G have distinct representations. A minimum local metric generator is called a local metric basis for G and its cardinality the local metric dimension of G. We show that the computation of the local metric dimension of a graph with cut vertices is reduced to the computation of the local metric dimension of the so-called primary subgraphs. The main results are applied to specific constructions including bouquets of graphs, rooted product graphs, corona product graphs, block graphs and chain of graphs.     

Resolvability and the upper dimension of graphs

For an ordered set W = {w₁, w₂,…, w_k} of vertices and a vertex v in a connected graph G, the (metric) representation of v with respect to W is the k-vector r(v | W) = (d(v, w₁), d(v, w₂),…, d(v, w_k)), where d(x, y) represents the distance between the vertices x and y. The set W is a resolving set for G if distinct vertices of G have distinct representations. A new sharp lower bound for the dimension of a graph G in terms of its maximum degree is presented.

A resolving set of minimum cardinality is a basis for G and the number of vertices in a basis is its (metric) dimension dim(G). A resolving set S of G is a minimal resolving set if no proper subset of S is a resolving set. The maximum cardinality of a minimal resolving set is the upper dimension dim⁺(G). The resolving number res(G) of a connected graph G is the minimum k such that every k-set W of vertices of G is also a resolving set of G. Then 1 ≤ dim(G) ≤ dim⁺(G) ≤ res(G) ≤ n − 1 for every nontrivial connected graph G of order n. It is shown that dim⁺(G) = res(G) = n − 1 if and only if G = K_n, while dim⁺(G) = res(G) = 2 if and only if G is a path of order at least 4 or an odd cycle.

The resolving numbers and upper dimensions of some well-known graphs are determined. It is shown that for every pair a, b of integers with 2 ≤ a ≤ b, there exists a connected graph G with dim(G) = dim⁺(G) = a and res(G) = b. Also, for every positive integer N, there exists a connected graph G with res(G) − dim⁺(G) ≥ N and dim⁺(G) − dim(G) ≥ N.     

Computing minimal doubly resolving sets of graphs

In this paper we consider the minimal doubly resolving sets problem (MDRSP) of graphs. We prove that the problem is NP-hard and give its integer linear programming formulation. The problem is solved by a genetic algorithm (GA) that uses binary encoding and standard genetic operators adapted to the problem. Experimental results include three sets of ORLIB test instances: crew scheduling, pseudo-boolean and graph coloring. GA is also tested on theoretically challenging large-scale instances of hypercubes and Hamming graphs. Optimality of GA solutions on smaller size instances has been verified by total enumeration. For several larger instances optimality follows from the existing theoretical results. The GA results for MDRSP of hypercubes are used by a dynamic programming approach to obtain upper bounds for the metric dimension of large hypercubes up to 2⁹⁰$2^{90}$ nodes, that cannot be directly handled by the computer.     

Identification in the limit of categorial grammars

It is proved that for any k, the class of classical categorial grammars that assign at most k types to each symbol in the alphabet is learnable, in the Gold (1967) sense of identification in the limit from positive data. The proof crucially relies on the fact that the concept known as finite elasticity in the inductive inference literature is preserved under the inverse image of a finite-valued relation. The learning algorithm presented here incorporates Buszkowski and Penn's (1990) algorithm for determining categorial grammars from input consisting of functor-argument structures.     

On the partition dimension of a class of circulant graphs

For a vertex v   of a connected graph G(V,E)$G(V,E)$ and a subset S of V, the distance between a vertex v and S   is defined by d(v,S)=min{d(v,x):x∈S}$d(v,S)=\min \{d(v,x):x\in S\}$. For an ordered k  -partition π={_S1,_S2…_Sk}$\pi =\{S_1,S_2\dots S_k\}$ of V, the partition representation of v with respect to π is the k  -vector r(v|π)=(d(v,_S1),d(v,_S2)…d(v,_Sk))$r(v|\pi )=(d(v,S_1),d(v,S_2)\dots d(v,S_k))$. The k-partition π is a resolving partition if the k  -vectors r(v|π)$r(v|\pi )$, v∈V(G)$v\in V(G)$ are distinct. The minimum k for which there is a resolving k-partition of V is the partition dimension of G. Salman et al. [1] in their paper which appeared in Acta Mathematica Sinica, English Series   proved that partition dimension of a class of circulant graph G(n,±{1,2})$G(n,\pm \{1,2\})$, for all even n?6$n?6$ is four. In this paper we prove that it is three.     

Strong product of factor-critical graphs

Strong product G ₁? G ₂ of two graphs G ₁ and G ₂ has a vertex set V(G ₁)×V(G ₂) and two vertices (u ₁, v ₁) and (u ₂, v ₂) are adjacent whenever u ₁=u ₂ and v ₁ is adjacent to v ₂ or u ₁ is adjacent to u ₂ and v ₁=v ₂, or u ₁ is adjacent to u ₂ and v ₁ is adjacent to v ₂. We investigate the factor-criticality of G ₁? G ₂ and obtain the following. Let G ₁ and G ₂ be connected m-factor-critical and n-factor-critical graphs, respectively. Then i. if m? 0, n=0, |V(G ₁)|? 2m+2 and |V(G ₂)|? 4, then G ₁? G ₂ is (2m+2)-factor-critical;

ii. if n=1, |V(G ₁)|? 2m+3 and either m? 3 or |V(G ₂)|? 5, then G ₁? G ₂ is (2m+4??)-factor-critical, where ?=0 if m is even, otherwise ?=1;

iii. if m+2 ? |V(G ₁)|? 2m+2, or n+2? |V(G ₂)|? 2n+2, then G ₁? G ₂ is mn-factor-critical;

iv. if |V(G ₁)|? 2m+3 and |V(G ₂)|? 2n+3, then G ₁? G ₂ is (mn?min{[3m/2]₂, [3n/2]₂})-factor-critical.

     

The differential of the strong product graphs

Let G=(V, E) be a graph of order n and let B(D) be the set of vertices in V ? D that have a neighbour in the set D. The differential of a set D is defined as ? (D)=|B(D)|?|D| and the differential of a graph to equal the maximum value of ?(D) for any subset D of V. In this paper we obtain several tight bounds for the differential of strong product graphs. In particular, we investigate the relationship between the differential of this type of product graphs and various parameters in the factors of the product.     

Local colourings of Cartesian product graphs

A local colouring of a graph G is a function c: V(G)→? such that for each S ? V(G), 2≤|S|≤3, there exist u, v∈S with |c(u)?c(v)| at least the number of edges in the subgraph induced by S. The maximum colour assigned by c is the value χ_?(c) of c, and the local chromatic number of G is χ_?(G)=min {χ_?(c): c is a local colouring of G}. In this note the local chromatic number is determined for Cartesian products G □ H, where G and GH are 3-colourable graphs. This result in part corrects an error from Omoomi and Pourmiri [On the local colourings of graphs, Ars Combin. 86 (2008), pp. 147–159]. It is also proved that if G and H are graphs such that χ(G)≤? χ_?(H)/2 ?, then χ_?(G □ H)≤χ_?(H)+1.     

Fault diameter of Cartesian product graphs

The (k−1)-fault diameter Dk(G) of a k-connected graph G is the maximum diameter of G−F for any F⊂V(G) with |F|<k. Krishnamoorthy and Krishnamurthy first proposed this concept and gave Dκ(G₁)+κ(G₂)(G₁×G₂)?Dκ(G₁)(G₁)+Dκ(G₂)(G₂) when κ(G₁×G₂)=κ(G₁)+κ(G₂), where κ(G) is the connectivity of G. This paper gives a counterexample to this bound and establishes Dk₁+k₂(G₁×G₂)?Dk₁(G₁)+Dk₂(G₂)+1 for any ki-connected graph Gi and ki?1 for i=1,2.     

On the computation of the gap metric

This paper deals with the computation of the gap metric introduced by Zames and El-Sakkary [17]. It is shown that the gap between two systems (P₁, P₂) is precisely the maximum of the two expressions for (i, j) equal to (1, 2) and (2, 1), and (N_i, D_i) being normalized right coprine factorizations of P_i, I = 1, 2, in the sense of Vidyasagar [12]. This expression is computable using well-known techniques from interpolation theory.     

On edge connectivity of direct products of graphs

Let λ(G) be the edge connectivity of G. The direct product of graphs G and H is the graph with vertex set V(G×H)=V(G)×V(H), where two vertices (u₁,v₁) and (u₂,v₂) are adjacent in G×H if u₁u₂∈E(G) and v₁v₂∈E(H). We prove that λ(G×Kn)=min{n(n−1)λ(G),(n−1)δ(G)} for every nontrivial graph G and n?3. We also prove that for almost every pair of graphs G and H with n vertices and edge probability p, G×H is k-connected, where k=O(²(n/logn)).     

公理化的矩阵半张量积

本文给出矩阵半张量积的一个公理化框架, 它包括矩阵–矩阵半张量积、矩阵–向量半张量积和向量–向量半张量积. 首先, 对目前通用的各类矩阵半张量积的基本性质与应用做一个综述性的回顾. 然后, 介绍一种新近出现的矩阵半张量积, 即保维数矩阵半张量积. 跟普通矩阵乘法一样, 它是多功能的, 即它可同时实现矩阵–矩阵乘积、矩阵–向量乘积和向量–向量乘积这3种功能. 最后, 本文介绍保维数矩阵半张量积的一些代数性质, 包括非方矩阵的Cayley-Hamilton定理, 非方矩阵的特征值、特征向量等.     

A note on the sendograph metric of fuzzy numbers

In this paper, by studying the attainable properties of sendograph metric in fuzzy number space, we generalize Monotone convergence theorem and Nested theorem of intervals from the space of real numbers to the space of fuzzy numbers.     

几类特殊矩阵的Hadmard积

广义H-矩阵的理论在许多实际问题的研究中有着非常重要的作用,如偏微分方程数值求解中出现的线性方程组的块迭代法的收敛性问题。讨论了广义M-矩阵的Hadmard积还是广义M-矩阵,广义H-矩阵的Hadmard积还是广义H-矩阵。改进了线性方程组的广义迭代方法及其应用。