8316302
List Homomorphisms and Circular Arc Graphs
G, H, and lists , a list homomorphism of G to Hwith respect to the listsL is a mapping , such that for all , and for all . The list homomorphism problem for a fixed graph H asks whether or not an input graph G together with lists , , admits a list homomorphism with respect to L. We have introduced the list homomorphism problem in an earlier paper, and proved there that for reflexive graphs H (that is, for graphs H in which every vertex has a loop), the problem is polynomial time solvable if H is an interval graph, and is NP-complete otherwise. Here we consider graphs H without loops, and find that the problem is closely related to circular arc graphs. We show that the list homomorphism problem is polynomial time solvable if the complement of H is a circular arc graph of clique covering number two, and is NP-complete otherwise. For the purposes of the proof we give a new characterization of circular arc graphs of clique covering number two, by the absence of a structure analogous to Gallai's asteroids. Both results point to a surprising similarity between interval graphs and the complements of circular arc graphs of clique covering number two.
10979198
Weakly Hamiltonian-connected ordinary multipartite tournaments
Abstract We characterize weakly Hamiltonian-connected ordinary multipartite tournaments. Our result generalizes such a characterization for tournaments by Thomassen and implies a polynomial algorithm to decide the existence of a Hamiltonian path connecting two given vertices in an ordinary multipartite tournament and finds one, if it exists.
14351696
A sufficient condition for a semicomplete multipartite digraph to be Hamiltonian
Abstract A multipartite tournament is an orientation of a complete k -partite graph for some k ⩾ 2. A factor of a digraph D is a collection of vertex disjoint cycles covering all the vertices of D . We show that there is no degree of strong connectivity which together with the existence of a factor will guarantee that a multipartite tournament is Hamiltonian. Our main result is a sufficient condition for a multipartite tournament to be Hamiltonian. We show that this condition is general enough to provide easy proofs of many existing results on paths and cycles in multipartite tournaments. Using this condition, we obtain a best possible lower bound on the length of a longest cycle in any strongly connected multipartite tournament.
4789976
In-Tournament Digraphs
Abstract In this paper we introduce a generalization of digraphs that are locally tournaments (and hence of tournaments). This is the class of in-tournament digraphs-the set of predecessors of every vertex induces a tournament. We show that many properties of local tournament digraphs can be extended even to in-tournament digraphs. For instance, any strongly connected in-tournament digraph has a directed hamiltonian cycle. We prove that the underlying graph of any in-tournament digraph is l-homotopic. We investigate the problem of which graphs are orientable as in-tournament digraphs and prove that any graph representable as an intersection subgraph of a unicyclic graph can be so oriented. It is shown that there is a polynomial algorithm for recognizing those graphs that can be oriented as in-tournament digraphs.
31025959
A Note on Spanning Local Tournaments in Locally Semicomplete Digraphs
We prove a result which implies that every k-connected locally semicomplete digraph which is not a semicomplete digraph must contain a k-connected spanning local tournament. This improves an earlier result of Guo and partially answers a question of Jackson and Thomassen.
43442956
Representation characterizations of chordal bipartite graphs
A bipartite graph is chordal bipartite if it does not contain an induced cycle of length at least six. We give three representation characterizations of chordal bipartite graphs. More precisely, we show that a bipartite graph is chordal bipartite if and only if the complement is the intersection graph of a family of pairwise compatible claws in a weighted hypercircle. (A hypercircle is a graph which consists of internally vertex disjoint paths between two distinguished vertices, and a claw in a hypercircle is a connected subgraph containing exactly one of the two distinguished vertices.) We also introduce two classes of bipartite graphs, both containing interval bigraphs and interval containment bigraphs. They are compatible subtree intersection bigraphs and compatible subtree containment bigraphs. We show that these two classes are identical to the class of chordal bipartite graphs.
16721854
Learning from labeled and unlabeled data on a directed graph
We propose a general framework for learning from labeled and unlabeled data on a directed graph in which the structure of the graph including the directionality of the edges is considered. The time complexity of the algorithm derived from this framework is nearly linear due to recently developed numerical techniques. In the absence of labeled instances, this framework can be utilized as a spectral clustering method for directed graphs, which generalizes the spectral clustering approach for undirected graphs. We have applied our framework to real-world web classification problems and obtained encouraging results.
14132755
Efficient Name Disambiguation for Large-Scale Databases
Name disambiguation can occur when one is seeking a list of publications of an author who has used different name variations and when there are multiple other authors with the same name. We present an efficient integrative framework for solving the name disambiguation problem: a blocking method retrieves candidate classes of authors with similar names and a clustering method, DBSCAN, clusters papers by author. The distance metric between papers used in DBSCAN is calculated by an online active selection support vector machine algorithm (LASVM), yielding a simpler model, lower test errors and faster prediction time than a standard SVM. We prove that by recasting transitivity as density reachability in DBSCAN, transitivity is guaranteed for core points. For evaluation, we manually annotated 3,355 papers yielding 490 authors and achieved 90.6% pairwise-F1. For scalability, authors in the entire CiteSeer dataset, over 700,000 papers, were readily disambiguated.
11615380
A sigma-delta modulation based BIST scheme for mixed-signal circuits
In this work, we present the analysis of a built-in self-test (BIST) scheme for mixed-signal circuits that is intended to provide on-chip stimulus generation and response analysis. Based on the sigma-delta modulation principle, the proposed scheme can produce high-quality stimuli and obtain accurate measurements without the need of precise analog circuitry. Numerical simulations are conducted to validate our idea and the results show that the scheme is a promising BIST approach for mixed-signal circuits.
806919
Using Learning to Facilitate the Evolution of Features for Recognizing Visual Concepts
This paper describes a hybrid methodology that integrates genetic algorithms (GAs) and decision tree learning in order to evolve useful subsets of discriminatory features for recognizing complex visual concepts. A GA is used to search the space of all possible subsets of a large set of candidate discrimination features. Candidate feature subsets are evaluated by using C4.5, a decision tree learning algorithm, to produce a decision tree based on the given features using a limited amount of training data. The classification performance of the resulting decision tree on unseen testing data is used as the fitness of the underlying feature subset. Experimental results are presented to show how increasing the amount of learning significantly improves feature set evolution for difficult visual recognition problems involving satellite and facial image data. In addition, we also report on the extent to which other more subtle aspects of the Baldwin effect are exhibited by the system.
27000200
An on-chip short-time interval measurement technique for testing high-speed communication links
In this paper, we present a BIST scheme for on-chip short-time interval measurement intended for characterizing the time-domain specifications, e.g., the rise/fall time of modern high-speed communication transceivers. To reduce hardware overhead, the proposed BIST technique uses the coherent under-sampling principle, and measures implicitly the time interval in a two-pass manner. Simulation results are shown to validate the proposed technique.