Directed Graph
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This paper deals with approximating feedback sets in directed graphs. We consider two related problems: the weighted feedback vertex set (FVS) problem, and the weighted feedback edge set (FES) problem. In the {FVS} (resp. FES) problem,... more
We study approximation hardness of the Minimum Dominating Set problem and its variants in undirected and directed graphs. Using a similar result obtained by Trevisan for Minimum Set Cover we prove the first explicit approximation lower... more
Normalization is the most exercised technique for the analysis of relational databases. It aims at creating a set of relational tables with minimum data redundancy that preserve consistency and facilitate correct insertion, deletion, and... more
We show that the number of acyclic directed graphs with n labeled vertices is equal to the number of nxn (0, 1)-matrices whose eigenvalues are positive real numbers.
We propose a unified description of the known forces. We formulate a quantum relativistic spacetime as a (directed) graph of causal arrows with indefinite Hilbert metric, whose physical meaning is given. The simplest graph whose quantum... more
Since the web is always developing, and users' needs are constantly changing, organisations in recent decades have increasingly focused on developing information and communication technologies (ICTs). To introduce new... more
Brauer’s centerlizer algebras have a basis consisting of undirected graphs. Signed Brauer’s algebras have a basis consisting of directed graphs, which generalizes Brauer’s algebras. In this paper, we compute a complete set of matrix units... more
Consider a network \(\mathcal{N}\) =(G, c, τ) whereG=(N, A) is a directed graph andc ij andτ ij , respectively, denote the capacity and the transmission time of arc (i, j) ∈A. The quickest flow problem is then to determine for a given... more
We propose shortest path algorithms that use A* search in combination with a new graph-theoretic lower-bounding technique based on landmarks and the triangle inequality. Our algorithms compute optimal shortest paths and work on any... more
The interconnections of agriculture and energy markets have increased through the rise in the new biofuel agribusinesses and the oil-ethanol-corn linkages. The question is whether these linkages have a causal structure by which oil prices... more