For a connected graph G, let ~-(G) be the set of all spanning trees of G and let nd(G) be the number of vertices of maximum degree in G. In this paper we show that if G is a cactus or a connected graph with p vertices and p + 1 edges, then the set {na(T) : T C ~-(G)) has at most one gap, that is, it is a set of consecutive integers or it is the union of two sets each of which consists of consec...

In this paper, we study the computational complexity and approximation complexity of the connected set-cover problem. We derive necessary and sufficient conditions for the connected set-cover problem to have a polynomial-time algorithm. We also present a sufficient condition for the existence of a (1 + ln δ)-approximation. In addition, one such (1 + ln δ)-approximation algorithm for this proble...

Given compact non-self-intersecting planar shapes, there are a pair of ambiguities characterized by topological (in-)equivalence. When shapes are topologically inequivalent, one shape can not be continuously morphed to the other as there is no bi-continuous map (homeomorphism) between them. Thus we cannot build an isomorphism between the shapes’ standard topology. Nevertheless, one can develop ...

Given a graphG, the k-dominating graph ofG, Dk(G), is defined to be the graph whose vertices correspond to the dominating sets of G that have cardinality at most k. Two vertices in Dk(G) are adjacent if and only if the corresponding dominating sets of G differ by either adding or deleting a single vertex. The graph Dk(G) aids in studying the reconfiguration problem for dominating sets. In parti...

A graph is said to be P 4-connected if for every partition of its vertex-set into two nonempty disjoint sets, some P 4 in the graph has vertices from both sets in the partition. A P 4-chain is a sequence of vertices such that every four consecutive ones induce a P 4. The main result of this work states that a graph is P 4-connected if and only if each pair of vertices is connected by a P 4-chai...

In this paper, we consider the problem of determining in polynomial time whether a given planar point set P of n points admits 4-connected triangulation. We propose a necessary and sufficient condition for recognizing P , and present an O(n) algorithm of constructing a 4-connected triangulation of P . Thus, our algorithm solves a longstanding open problem in computational geometry and geometric...

A graph G is a chordal-k-generalized split graph if G is chordal and there is a clique Q in G such that every connected component in G[V \ Q] has at most k vertices. Thus, chordal-1-generalized split graphs are exactly the split graphs. We characterize chordal-k-generalized split graphs by forbidden induced subgraphs. Moreover, we characterize a very special case of chordal-2-generalized split ...

Let k¿2; n=2+1; and let m0; : : : ; mk−1 each be a multiple of n. The graph Cm0×· · ·×Cmk−1 consists of isomorphic connected components, each of which is (n − 1)-regular and admits of a vertex partition into n smallest independent dominating sets. Accordingly, (independent) domination number of each connected component of this graph is equal to (1=n)th of the number of vertices in it. ? 2001 El...

Let G be a finite group and let k be a field of characteristic p. Given a finitely generated indecomposable non-projective kG-module M , we conjecture that if the Tate cohomology Ĥ ∗ (G, M) of G with coefficients in M is finitely generated over the Tate cohomology ring Ĥ ∗ (G, k), then the support variety VG(M) of M is equal to the entire maximal ideal spectrum VG(k). We prove various results w...

In the sequel, we suppose that p(l) = 2, p(2), p(3),... is the sequence of primes in ascending order. Let T be a rooted tree, r its root. The connected components of Tr are denoted by T, ,..., T,, where v is the degree of r. The graphs Tj ul,..., v) obviously are trees, which we transform into rooted trees by defining as the root of Tj the vertex of 7” which is adjacent to r in T. We now assign...