A set <em>W</em> is called a local resolving of <em>G</em> if the distance <em>u</em> and <em>v</em> to some elements are distinct for every two adjacent vertices in <em>G</em>. The metric dimension minimum cardinality connected graph split <em>V</em>(<em>G</em>) can be partitioned into subsets <em>V</e...

We investigate the properties of chordal graphs that follow from the well-known fact that chordal graphs admit tree representations. In particular, we study the structure of reduced clique graphs which are graphs that canonically capture all tree representations of chordal graphs. We propose a novel decomposition of reduced clique graphs based on two operations: edge contraction and removal of ...

A dominating set D in a graph is a subset of its vertex set such that each vertex is either in D or has a neighbour in D. In this paper, we are interested in an output-sensitive enumeration algorithm of (inclusionwise) minimal dominating sets in graphs, called Dom problem. It was known that this problem can be polynomially reduced to the well known Transversal problem in hypergraphs. We show th...

A vertex set D in a finite undirected graph G is an efficient dominating set (e.d.s. for short) of G if every vertex of G is dominated by exactly one vertex of D. The Efficient Domination (ED) problem, which asks for the existence of an e.d.s. in G, is known to be NP-complete even for very restricted graph classes such as for 2P3-free chordal graphs while it is solvable in polynomial time for P...

A graph G is matching-decyclable if it has a matching M such that G−M is acyclic. Deciding whether G is matching-decyclable is an NPcomplete problem even if G is 2-connected, planar, and subcubic. In this work we present characterizations of matching-decyclability in the following classes: chordal graphs, split graphs, distance-hereditary graphs, cographs, and Hamiltonian subcubic graphs. All t...

A tree t-spanner T in a graph G is a spanning tree of G such that the distance in T between every pair of vertices is at most t times their distance in G. The TREE t-SPANNER problem asks whether a graph admits a tree t-spanner, given t. We substantially strengthen the hardness result of Cai and Corneil (SIAM J. Discrete Math. 8 (1995) 359–387) by showing that, for any t¿ 4, TREE t-SPANNER is NP...

We provide polynomial-time algorithms for counting the number of perfect matchings and the number of matchings in chain graphs, cochain graphs, and threshold graphs. These algorithms are based on newly developed subdivision schemes that we call a recursive decomposition. On the other hand, we show the #P-completeness for counting the number of perfect matchings in chordal graphs, split graphs a...