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12
The FF planning system: Fast plan generation through heuristic search
 Journal of Artificial Intelligence Research
, 2001
"... We describe and evaluate the algorithmic techniques that are used in the FF planning system. Like the HSP system, FF relies on forward state space search, using a heuristic that estimates goal distances by ignoring delete lists. Unlike HSP's heuristic, our method does not assume facts to be independ ..."
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Cited by 599 (50 self)
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We describe and evaluate the algorithmic techniques that are used in the FF planning system. Like the HSP system, FF relies on forward state space search, using a heuristic that estimates goal distances by ignoring delete lists. Unlike HSP's heuristic, our method does not assume facts to be independent. We introduce a novel search strategy that combines Hillclimbing with systematic search, and we show how other powerful heuristic information can be extracted and used to prune the search space. FF was the most successful automatic planner at the recent AIPS2000 planning competition. We review the results of the competition, give data for other benchmark domains, and investigate the reasons for the runtime performance of FF compared to HSP.
Optimal linear arrangement of interval graphs
 in Proceedings of the 31st International Symposium on Mathematical Foundations of Computer Science (MFCS 2006
"... Abstract. We study the optimal linear arrangement (OLA) problem on interval graphs. Several linear layout problems that are NPhard on general graphs are solvable in polynomial time on interval graphs. We prove that, quite surprisingly, optimal linear arrangement of interval graphs is NPhard. The s ..."
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Cited by 5 (2 self)
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Abstract. We study the optimal linear arrangement (OLA) problem on interval graphs. Several linear layout problems that are NPhard on general graphs are solvable in polynomial time on interval graphs. We prove that, quite surprisingly, optimal linear arrangement of interval graphs is NPhard. The same result holds for permutation graphs. We present a lower bound and a simple and fast 2approximation algorithm based on any interval model of the input graph. 1
Layout Problems on Lattice Graphs
 Computing and Combinatorics, volume 1627 of Lecture Notes in Computer Science
, 1999
"... This work deals with bounds on the cost of layout problems for lattice graphs and random lattice graphs. Our main result in this paper is a convergence theorem for the optimal cost of the Minimum Linear Arrangement problem and the Minimum Sum Cut problem, for the case where the underlying graph is o ..."
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Cited by 4 (4 self)
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This work deals with bounds on the cost of layout problems for lattice graphs and random lattice graphs. Our main result in this paper is a convergence theorem for the optimal cost of the Minimum Linear Arrangement problem and the Minimum Sum Cut problem, for the case where the underlying graph is obtained through a subcritical site percolation process. This result can be viewed as an analogue of the Beardwood, Halton and Hammersley theorem for the Euclidian TSP. Finally we estimate empirically the value for the constant in the mentioned theorem. # This research was partially supported by ESPRIT LTR Project no. 20244  ALCOMIT, CICYT Project TIC971475CE, and CIRIT project 1997SGR00366. + Departament de Llenguatges i Sistemes Informatics. Universitat Politecnica de Catalunya. Campus Nord C6. c/ Jordi Girona 13. 08034 Barcelona (Spain). {diaz,jpetit,mjserna}@lsi.upc.es # Department of Mathematical Sciences, University of Durham, South Road, Durham DH1 3LE, England. Mathew.Penr...
Two Results on Linear Embeddings of Complete Binary Trees
 Theoretical Computer Science
, 1994
"... Given a binary tree T with n vertices, we want to embed T onto a given set A of n points on the line so as to minimize the total embedded edge length. Polynomial time algorithms for the two following special cases of this problem can be found in literature: (1) When T is arbitrary but A = f1 : : : n ..."
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Cited by 3 (0 self)
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Given a binary tree T with n vertices, we want to embed T onto a given set A of n points on the line so as to minimize the total embedded edge length. Polynomial time algorithms for the two following special cases of this problem can be found in literature: (1) When T is arbitrary but A = f1 : : : ng; (2) When T is a complete binary tree and A is arbitrary. To the best of our knowledge, the complexity of the general problem is open. In this paper we deal with case (2). Bern, Karloff, Raghavan and Schieber presented an algorithm for this case that runs in time O(n 5:76 ) and uses O(n 3:2 ) space. They also considered the naive embedding, which maps the root r of T into the middle point a of A, and then embeds, recursively, the left and right subtrees of r to the left and right of a, respectively. This is equivalent to embedding T from left to right according to the inorder traversal. They prove that this naive algorithm approximates the optimal solution within the factor of 3. Th...
Trianglefree subcubic graphs with minimum bipartite density
 J. Combin. Theory Ser. B
"... A graph is subcubic if its maximum degree is at most 3. The bipartite density of a graph G is max{ε(H)/ε(G) : H is a bipartite subgraph of G}, where ε(H) and ε(G) denote the numbers of edges in H and G, respectively. It is an NPhard problem to determine the bipartite density of any given trianglef ..."
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Cited by 3 (2 self)
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A graph is subcubic if its maximum degree is at most 3. The bipartite density of a graph G is max{ε(H)/ε(G) : H is a bipartite subgraph of G}, where ε(H) and ε(G) denote the numbers of edges in H and G, respectively. It is an NPhard problem to determine the bipartite density of any given trianglefree cubic graph. Bondy and Locke gave a polynomial time algorithm which, given a trianglefree subcubic graph G, finds a bipartite subgraph of G with at least 4 5ε(G) edges; and showed that the Petersen graph and the dodecahedron are the only trianglefree cubic graphs with bipartite density 4 5. Bondy and Locke further conjectured that there are precisely seven trianglefree subcubic graphs with bipartite density 4 5. We prove this conjecture of Bondy and Locke. Our result will be used in a forthcoming paper to solve a problem of Bollobás and Scott related to judicious partitions.
Memetic algorithms for the MinLA problem
 Lecture Notes in Computer Science
"... Abstract. This paper presents a new Memetic Algorithm designed to compute near optimal solutions for the MinLA problem. It incorporates a highly specialized crossover operator, a fast MinLA heuristic used to create the initial population and a local search operator based on a fine tuned Simulated An ..."
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Cited by 2 (1 self)
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Abstract. This paper presents a new Memetic Algorithm designed to compute near optimal solutions for the MinLA problem. It incorporates a highly specialized crossover operator, a fast MinLA heuristic used to create the initial population and a local search operator based on a fine tuned Simulated Annealing algorithm. Its performance is investigated through extensive experimentation over well known benchmarks andcomparedwithotherstateoftheartalgorithms. Key words: Memetic Algorithms, Linear Arrangement, Heuristics. 1
Parallel Algorithms for the Minimum Cut and the Minimum Length Tree Layout Problems
, 1997
"... The minimum cut and minimum length linear arrangement problems usually occur in solving wiring problems and have a lot in common with job sequencing questions. Both problems are NPcomplete for general graphs and in P for trees. We present here two parallel algorithms for the CREW PRAM. The first so ..."
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Cited by 2 (1 self)
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The minimum cut and minimum length linear arrangement problems usually occur in solving wiring problems and have a lot in common with job sequencing questions. Both problems are NPcomplete for general graphs and in P for trees. We present here two parallel algorithms for the CREW PRAM. The first solves the minimum length linear arrangement problem for trees and the second solves the minimum cut arrangement for trees. We prove that the first problem belongs to NC for trees, and the second problem is in NC for bounded degree trees. To the best of our knowledge, these are the first parallel algorithms for the minimum length and the minimum cut linear arrangement problems. Keywords: Parallel algorithm, minimum length layout, minimum cut layout, parallel tree contraction, CREW PRAM. A preliminary version of this paper presented at COCOON'95. y This research was supported by the EEC ESPRIT Basic Research Project ALCOM II (contract no. 7141). The work of the third and the fifth author ...
Disseminating dependent data in wireless broadcast environments, Distributed Parallel Databases, available online
, 2007
"... Abstract In wireless mobile environments, data broadcasting is an effective approach to disseminate information to mobile clients. In some applications, the access pattern of all the data can be represented by a weighted DAG. In this paper, we explore how to efficiently generate the broadcast schedu ..."
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Abstract In wireless mobile environments, data broadcasting is an effective approach to disseminate information to mobile clients. In some applications, the access pattern of all the data can be represented by a weighted DAG. In this paper, we explore how to efficiently generate the broadcast schedule in a wireless environment for the data set having a weighted DAG access pattern. Such a broadcast schedule not only minimizes the access latency but also is a topological ordering of the DAG. Minimized access latency ensures the quality of service (QoS). We prove that it is NPhard to find an optimal broadcast schedule and provide some heuristics. After giving an analysis for these heuristics on the latency and complexity, we implement all the proposed heuristics to compare their performance. Keywords Data broadcasting. Latency. Directed acyclic graphs. NPhard. Access pattern 1
On Minimum Circular Arrangement
 Proc. 21st Annual Symposium on Theoretical Computer Science (STACS’04
, 2003
"... Abstract. Motivated by a scheduling problem encountered in multicast environments, we study a vertex labelling problem, called Minimum Circular Arrangement (MCA), that requires one to find an embedding of a given weighted directed graph into a discrete circle which minimizes the total weighted arc l ..."
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Abstract. Motivated by a scheduling problem encountered in multicast environments, we study a vertex labelling problem, called Minimum Circular Arrangement (MCA), that requires one to find an embedding of a given weighted directed graph into a discrete circle which minimizes the total weighted arc length. Its decision version is already known to be NPcomplete when restricted to sparse weighted instances. We prove that the decision version of even unweighted MCA is NPcomplete in case of sparse as well as dense graphs. We also consider complementary version of MCA, called MaxCA. We prove that it is MAXSNP[π] complete and, therefore, has no PTAS unless P=NP. A similar proof technique shows that MCA is MAXSNP[π]Hard and hence admits no PTAS as well. Then we prove a conditional lower bound of √ 2 − ɛ for MCA approximation under some hardness assumptions, and conclude with a PTAS for MCA on dense instances.