In this paper we study the problem of answering connectivity queries about a graph timeline. A graph timeline is a sequence of undirected graphs G1, . . . , Gt on a common set of vertices of size n such that each graph is obtained from the previous one by an addition or a deletion of a single edge. We present data structures, which preprocess the timeline and can answer the following queries: •...

We describe a simple way of partitioning a planar graph into three edge-disjoint forests in O(n log n) time, where n is the number of its vertices. We can use this partition in Kannan et al.‘s graph representation (1992) to label the planar graph vertices so that any two vertices’ adjacency can be tested locally by comparing their names in constant time.

Let G = (V,E) be an undirected graph and let S ⊆ V . The S-connectivity SG(u, v) of a pair of nodes u, v in G is the maximum number of uv-paths that no two of them have an edge or a node in S ∖ {u, v} in common. Edge-connectivity is the case S = ∅ and node-connectivity is the case S = V . Given a graph G = (V,E), an integer k, a subset T ⊆ V of terminals, and S ⊆ V , we consider the problem of ...

We prove that the game coloring number, and therefore the game chromatic number, of a planar graph is at most 18. This is a slight improvement of the current upper bound of 19. Perhaps more importantly, we bound the game coloring number of a graph G in terms of a new parameter r(G). We use this result to give very easy proofs of the best known upper bounds on game coloring number for forests, i...

Let G be a simple connected graph. The transmission of any vertex v of a graph G is defined as the sum of distances of a vertex v from all other vertices in a graph G. Then the distance signless Laplacian matrix of G is defined as D^{Q}(G)=D(G)+Tr(G), where D(G) denotes the distance matrix of graphs and Tr(G) is the diagonal matrix of vertex transmissions of G. For a given minimum dominating se...

it is necessary to generate the automorphism group of a chemical graph in computer-aidedstructure elucidation. an euclidean graph associated with a molecule is defined by a weightedgraph with adjacency matrix m = [dij], where for i≠j, dij is the euclidean distance between thenuclei i and j. in this matrix dii can be taken as zero if all the nuclei are equivalent. otherwise,one may introduce dif...

let $g$ be a simple graph of order $n$ and size $m$.the edge covering of $g$ is a set of edges such that every vertex of $g$ is incident to at least one edge of the set. the edge cover polynomial of $g$ is the polynomial$e(g,x)=sum_{i=rho(g)}^{m} e(g,i) x^{i}$,where $e(g,i)$ is the number of edge coverings of $g$ of size $i$, and$rho(g)$ is the edge covering number of $g$. in this paper we stud...

We investigate the connections between the complexity of a c.e. set, as calibrated by its strength as an oracle for Turing computations of functions in the Ershov hierarchy, and how strong reducibilities allows us to compute such sets. For example, we prove that a c.e. degree is totally ω-c.e. iff every set in it is weak truth-table reducible to a hypersimple, or ranked, set. We also show that ...

Let c : E(G) → [k] be an edge-coloring of a graph G, not necessarily proper. For each vertex v, let c̄(v) = (a1, . . . , ak), where ai is the number of edges incident to v with color i. Reorder c̄(v) for every v in G in nonincreasing order to obtain c∗(v), the color-blind partition of v. When c∗ induces a proper vertex coloring, that is, c∗(u) 6= c∗(v) for every edge uv in G, we say that c is col...

A simple set of trimethylene-substituted even, fully-π-bonded, non-alternant monocycles is shown to have several key features in common with acyclic, even alternant polyenes at the Hückel level. These non-alternant molecules provide a bridge between alternant and non-alternant hydrocarbons. This topic might serve as a useful addition to Hückel theory courses targeted at senior undergraduate stu...