Results 1  10
of
91
Complexity and Algorithms for Reasoning About Time: A GraphTheoretic Approach
, 1992
"... Temporal events are regarded here as intervals on a time line. This paper deals with problems in reasoning about such intervals when the precise topological relationship between them is unknown or only partially specified. This work unifies notions of interval algebras in artificial intelligence ..."
Abstract

Cited by 90 (11 self)
 Add to MetaCart
Temporal events are regarded here as intervals on a time line. This paper deals with problems in reasoning about such intervals when the precise topological relationship between them is unknown or only partially specified. This work unifies notions of interval algebras in artificial intelligence with those of interval orders and interval graphs in combinatorics. The satisfiability, minimal labeling, all solutions and all realizations problems are considered for temporal (interval) data. Several versions are investigated by restricting the possible interval relationships yielding different complexity results. We show that even when the temporal data comprises of subsets of relations based on intersection and precedence only, the satisfiability question is NPcomplete. On the positive side, we give efficient algorithms for several restrictions of the problem. In the process, the interval graph sandwich problem is introduced, and is shown to be NPcomplete. This problem is als...
Interval Routing Schemes
, 1998
"... Interval routing was introduced to reduce the size of routing tables: a router finds the direction where to forward a message by determining which interval contains the destination address of the message, each interval being associated to one particular direction. This way of implementing a routin ..."
Abstract

Cited by 29 (6 self)
 Add to MetaCart
Interval routing was introduced to reduce the size of routing tables: a router finds the direction where to forward a message by determining which interval contains the destination address of the message, each interval being associated to one particular direction. This way of implementing a routing function is quite attractive but very little is known about the topological properties that must satisfy a network to support an interval routing function with particular constraints (shortest paths, limited number of intervals associated to each direction, etc.). In this paper we investigate the study of the interval routing functions. In particular, we characterize the set of networks which support a linear or a linear strict interval routing function with only one interval per direction. We also derive practical tools to measure the efficiency of an interval routing function (number of intervals, length of the paths, etc.), and we describe large classes of networks which support optimal (linear) interval routing functions. Finally, we derive the main properties satisfied by the popular networks used to interconnect processors in a distributed memory parallel computer.
Efficient parallel algorithms for chordal graphs
"... We give the first efficient parallel algorithms for recognizing chordal graphs, finding a maximum clique and a maximum independent set in a chordal graph, finding an optimal coloring of a chordal graph, finding a breadthfirst search tree and a depthfirst search tree of a chordal graph, recognizing ..."
Abstract

Cited by 27 (0 self)
 Add to MetaCart
We give the first efficient parallel algorithms for recognizing chordal graphs, finding a maximum clique and a maximum independent set in a chordal graph, finding an optimal coloring of a chordal graph, finding a breadthfirst search tree and a depthfirst search tree of a chordal graph, recognizing interval graphs, and testing interval graphs for isomorphism. The key to our results is an efficient parallel algorithm for finding a perfect elimination ordering.
Optimization of Dynamic Hardware Reconfigurations
, 2001
"... Recent generations of Field Programmable Gate Arrays (FPGA) allow the dynamic reconfiguration of cells on the chip during runtime. For a given problem consisting of a set of tasks with computation requirements modeled by rectangles of cells, several optimization problems such as finding the array o ..."
Abstract

Cited by 23 (3 self)
 Add to MetaCart
Recent generations of Field Programmable Gate Arrays (FPGA) allow the dynamic reconfiguration of cells on the chip during runtime. For a given problem consisting of a set of tasks with computation requirements modeled by rectangles of cells, several optimization problems such as finding the array of minimal size to accomplish the tasks within a given time limit are considered. Existing approaches based on ILP formulations to solve these problems as multidimensional packing problems turn out not to be applicable for problem sizes of interest. Here, a breakthrough is achieved in solving these problems to optimality by using the new notion of packing classes. It allows a significant reduction of the search space such that problems of the above type may be solved exactly using a special branchandbound technique. We validate the usefulness of our method by providing computational results.
An Exact Algorithm for HigherDimensional Orthogonal Packing
 Operations Research
, 2006
"... Higherdimensional orthogonal packing problems have a wide range of practical applications, including packing, cutting, and scheduling. Combining the use of our data structure for characterizing feasible packings with our new classes of lower bounds, and other heuristics, we develop a twolevel tr ..."
Abstract

Cited by 22 (3 self)
 Add to MetaCart
Higherdimensional orthogonal packing problems have a wide range of practical applications, including packing, cutting, and scheduling. Combining the use of our data structure for characterizing feasible packings with our new classes of lower bounds, and other heuristics, we develop a twolevel tree search algorithm for solving higherdimensional packing problems to optimality. Computational results are reported, including optimal solutions for all twodimensional test problems from recent literature.
Fast and simple algorithms for recognizing chordal comparability graphs and interval graphs
 SIAM Journal on Computing
, 1999
"... Abstract. In this paper, we present a lineartime algorithm for substitution decomposition on chordal graphs. Based on this result, we develop a lineartime algorithm for transitive orientation on chordal comparability graphs, which reduces the complexity of chordal comparability recognition from O( ..."
Abstract

Cited by 18 (3 self)
 Add to MetaCart
Abstract. In this paper, we present a lineartime algorithm for substitution decomposition on chordal graphs. Based on this result, we develop a lineartime algorithm for transitive orientation on chordal comparability graphs, which reduces the complexity of chordal comparability recognition from O(n 2)toO(n+m). We also devise a simple lineartime algorithm for interval graph recognition where no complicated data structure is involved. Key words. chordal graph, triangulated graph, interval graph, analysis of algorithms, graph theory, substitution decomposition, modular decomposition, cyclefree poset, transitive orientation, graph partitioning, cardinality lexicographic ordering, graph recognition
On moredimensional packing III: Exact Algorithms
, 2000
"... Moredimensional orthogonal packing problems have a wide range of practical applications, including packing, cutting, and scheduling. Combining the use of our data structure for characterizing feasible packings with our new classes of lower bounds, and other heuristics, we develop a twolevel tree s ..."
Abstract

Cited by 16 (6 self)
 Add to MetaCart
Moredimensional orthogonal packing problems have a wide range of practical applications, including packing, cutting, and scheduling. Combining the use of our data structure for characterizing feasible packings with our new classes of lower bounds, and other heuristics, we develop a twolevel tree search algorithm for solving moredimensional packing problems to optimality. Computational results are reported, including optimal solutions for all twodimensional test problems from recent literature. This is the third in a series of three articles describing new approaches to moredimensional packing.
The Mutual Exclusion Scheduling Problem for Permutation and Comparability Graphs
, 1998
"... In this paper, we consider the mutual exclusion scheduling problem for comparability graphs. Given an undirected graph G and a fixed constant m, the problem is to find a minimum coloring of G such that each color is used at most m times. The complexity of this problem for comparability graphs was me ..."
Abstract

Cited by 13 (1 self)
 Add to MetaCart
In this paper, we consider the mutual exclusion scheduling problem for comparability graphs. Given an undirected graph G and a fixed constant m, the problem is to find a minimum coloring of G such that each color is used at most m times. The complexity of this problem for comparability graphs was mentioned as an open problem by MÃ¶hring (1985) and for permutation graphs (a subclass of comparability graphs) as an open problem by Lonc (1991). We prove that this problem is already NPcomplete for permutation graphs and for each fixed constant m >= 6.
A Compendium of Problems Complete for Symmetric Logarithmic Space
 Computational Complexity
, 1996
"... . The paper's main contributions are a compendium of problems that are complete for symmetric logarithmic space (SL), a collection of material relating to SL, a list of open problems, and an extension to the number of problems known to be SLcomplete. Complete problems are one method of studyin ..."
Abstract

Cited by 13 (0 self)
 Add to MetaCart
. The paper's main contributions are a compendium of problems that are complete for symmetric logarithmic space (SL), a collection of material relating to SL, a list of open problems, and an extension to the number of problems known to be SLcomplete. Complete problems are one method of studying SL, a class for which programming is nonintuitive. Our exposition helps make the class SL less mysterious and more accessible to other researchers. Key words. Completeness, SL, space complexity, symmetric logarithmic space. Subject classifications. 68Q17. 1. Introduction In this paper we describe problems that are logarithmic space manyone complete for symmetric logarithmic space (SL). Our hope in collecting these problems and extending this list is that more insight can be gained about the relationships between the complexity classes deterministic logarithmic space (DL), SL, and nondeterministic logarithmic space (NL). The symmetric Turing machine model introduced by Lewis & Papadimitriou ...
Finding Minimum Height Elimination Trees For Interval Graphs In Polynomial Time
 BIT
, 1994
"... . The elimination tree plays an important role in many aspects of sparse matrix factorization. The height of the elimination tree presents a rough, but usually effective, measure of the time needed to perform parallel elimination. Finding orderings that produce low elimination trees is therefore im ..."
Abstract

Cited by 13 (2 self)
 Add to MetaCart
. The elimination tree plays an important role in many aspects of sparse matrix factorization. The height of the elimination tree presents a rough, but usually effective, measure of the time needed to perform parallel elimination. Finding orderings that produce low elimination trees is therefore important. As the problem of finding minimum height elimination tree orderings is NPhard, it is interesting to concentrate on limited classes of graphs and find minimum height elimination trees for these efficiently. In this paper, we use clique trees to find an efficient algorithm for interval graphs which make an important subclass of chordal graphs. We first illustrate this method through an algorithm that finds minimum height elimination trees for chordal graphs. This algorithm, although of exponential time complexity, is conceptionally simple and leads to a polynomialtime algorithm for finding minimum height elimination trees for interval graphs. AMS subject classifications: 05C50, 65F...