We provide a polynomial algorithm that determines for any given undirected graph, positive integer k and various objective functions on the edges or on the degree sequences, as input, k edges that minimize the given objective function. The tractable objective functions include linear, sum of squares, etc. The source of our motivation and at the same time our main application is a subset of k ve...

Consider the following stochastic process on a graph: initially all vertices are uncovered and at each step cover the two vertices of a random edge. What is the expected number of steps required to cover all vertices of the graph? In this note we show that the mean cover time for a regular graph of N vertices is asymptotically (N log N)/2. Moreover, we compute the exact mean cover time for some...

We study a variation of the vertex cover problem where it is required that the graph induced by the vertex cover is connected. We prove that this problem is polynomial in chordal graphs, has a PTAS in planar graphs, is APX-hard in bipartite graphs and is 5/3-approximable in any class of graphs where the vertex cover problem is polynomial (in particular in bipartite graphs). Finally, dealing wit...

We study a variation of the vertex cover problem where it is required that the graph induced by the vertex cover is connected. We prove that this problem is polynomial in chordal graphs, has a PTAS in planar graphs, is APX-hard in bipartite graphs and is 5/3-approximable in any class of graphs where the vertex cover problem is polynomial (in particular in bipartite graphs).

We study generating functions for the number of involutions of length n avoiding (or containing exactly once) 132 and avoiding (or containing exactly once) an arbitrary permutation τ of length k. In several interesting cases these generating functions depend only on k and can be expressed via Chebyshev polynomials of the second kind. In particular, we show that involutions of length n avoiding ...

Many problems that are intractable for general graphs allow polynomial-time solutions for structured classes of graphs, such as planar graphs and graphs of bounded treewidth. In this paper, we demonstrate structural properties of larger classes of graphs and show how to exploit the properties to obtain algorithms. The classes considered are those formed by excluding as a minor a graph that can ...

The edge clique cover sum number (resp. edge clique partition sum number) of a graph G, denoted by scc(G) (resp. scp(G)), is defined as the smallest integer k for which there exists a collection of complete subgraphs of G, covering (resp. partitioning) all edges of G such that the sum of sizes of the cliques is at most k. By definition, scc(G) 5 scp(G). Also, it is known that for every graph G ...

In this paper, we introduce the b-bibranching problem in digraphs, which is a common generalization of the bibranching and b-branching problems. The bibranching problem, introduced by Schrijver (1982), is a common generalization of the branching and bipartite edge cover problems. Previous results on bibranchings include polynomial algorithms, a linear programming formulation with total dual int...

We examine the general problem of covering graphs by graphs: given a graph G, a collection P of graphs each on at most p vertices, and an integer r, is there a collection C of subgraphs of G, each belonging to P , such that the removal of the graphs in C from G creates a graph none of whose components have more than r vertices? We can also require that the graphs in C be disjoint (forming a “ma...

Szeged-like topological indices are well-studied distance-based molecular descriptors, which include, for example, the (edge-)Szeged index, (edge-)Mostar and (vertex-)PI index. For these indices, corresponding polynomials were also defined, i.e., polynomial, Mostar PI etc. It is well known that, by evaluating first derivative of such a polynomial at x=1, we obtain related The aim this paper to ...