1. • Let T = (V, E) be a tree and let D =< d1, . . . , dk > denote the set of demands. We reduce the prize-collecting steiner forest problem on trees to the minimum weighted vertex cover problem. We make a bipartite graph H = (V ′, E ′) where for each edge e ∈ E we put a vertex pe in V ′ and also for every di ∈ D we put a vertex qi in V ′. We put an edge between pe and qi iff the edge e is on t...

We present a deterministic algorithm that given a tree T with n vertices, a starting vertex v and a slackness parameter ǫ > 0, estimates within an additive error of ǫ the cover and return time, namely, the expected time it takes a simple random walk that starts at v to visit all vertices of T and return to v. The running time of our algorithm is polynomial in n/ǫ, and hence remains polynomial i...

The topological index of a graph G is a numeric quantity related to G which is invariant under automorphisms of G. The vertex PI polynomial is defined as PIv (G)  euv nu (e)  nv (e). Then Omega polynomial (G,x) for counting qoc strips in G is defined as (G,x) = cm(G,c)xc with m(G,c) being the number of strips of length c. In this paper, a new infinite class of fullerenes is constructed. ...

The optimal path cover problem is to find a minimum number of vertex disjoint paths which together cover all the vertices of the graph. Finding an optimal path cover for an arbitrary graph is known to be NP-complete [3]. However, polynornial-time algorithms exist for trees [4], cacti [4] and for interval graphs [9]. The solution presented in [2] For circular-arc graphs is known to be wrong. In ...

1 Approximation Algorithms Any known algorithm that finds the solution to an NP-hard optimization problem has exponential running time. However, sometimes polynomial time algorithms exist which find a " good " solution instead of an optimum solution. Given a minimization problem and an approximation algorithm, we can evaluate the algorithm as follows. First, we find a lower bound on the optimum...

The cover polynomial C(D) = C(D;x, y) of a digraph D is a twovariable polynomial whose coefficients are determined by the number of vertex coverings of D by directed paths and cycles. Just as for the Tutte polynomial for undirected graphs (cf. [11, 16]), various properties of D can be read off from the values of C(D;x, y). For example, for an n-vertex digraph D, C(D; 1, 0) is the number of Hami...

let g be a simple graph and (g,) denotes the number of proper vertex colourings of gwith at most  colours, which is for a fixed graph g , a polynomial in  , which is called thechromatic polynomial of g . using the chromatic polynomial of some specific graphs, weobtain the chromatic polynomials of some nanostars.

The cover time is the expected time it takes a simple random walk to cover all vertices of a graph. It arises in numerous questions related to the behaviour of random walks on graphs. Despite the fact that it can be approximated with arbitrary precision by a simple polynomial time Monte-Carlo algorithm which simulates the random walk, it is not known whether the cover time of a graph can be com...

We consider a scenario of distributed service installation in privately owned networks. Our model is a non-cooperative vertex cover game for k players. Each player owns a set of edges in a graph G and strives to cover each edge by an incident vertex. Vertices have costs and must be purchased to be available for the cover. Vertex costs can be shared arbitrarily by players. Once a vertex is bough...