38611039
Vertex Ranking of Asteroidal Triple-Free Graphs
We present an efficient algorithm for computing the vertex ranking number of an asteroidal triple-free graph. Its running time is bounded by a polynomial in the number of vertices and the number of minimal separators of the input graph.
15615911
Time-varying shortest path problems with constraints
The shortest path problem is considered with yet another extension. The transit times b(x,y,u) and the arc costs c(x,y,u) on arc (x,y) vary as a function of the departure time u at the beginning vertex of the arc. The problem considered is to find the shortest path between a pair of nodes such that the total traverse time is lesser than some specified value T. Waiting times at nodes are considered as decision variables in this paper as well. Three variations of the problem are analyzed in which the waiting times are allowed to be arbitrary, the waiting times are zero and the waiting time has an upper bound at each vertex. Algorithms are also discussed to solve the problem. Some of the applications of the problem are encountered in communication networks and freight delivery problems. Suppose that some freight is to be sent from one city to another in a network before a deadline T. Different types of freight services with different costs and transit times are available between the two cities. An optimal solution would have to specify the route as well as the waiting times of the freight at each city so that the overall cost is minimum. A dynamic programming approach is used to compute the shortest path from the origin node to the destination node. Three cases are considered for the waiting times and an algorithm is suggested for each of those cases. This problem is obviously an NP-Complete problem as it is more difficult to solve than a problem with constant transit times and arc costs such as the previous problem which is NP-Complete. Some definitions: Waiting time w(x i) at a vertex x i is a nonnegative integer with an upper bound U x >= 0. Let P be a path from vertex x 1 to x r. The departure time T(x i) at a vertex x i can be expressed as below: T(x 1) = w(x 1) The departure time for all other vertices on the path can be expressed recursively as : The time of path P is defined as T(x r) where x r is the final node on the path..
16381803
Upper and lower bounds for graph-diameter problems with application to record allocation
This paper studies three graph problems with parameters n, the number of nodes, e, the number of edges, and k, the diameter of the graph. Given any two of these three parameters, the problem is to construct a directed graph which minimizes or maximizes the third. The first problem has its origin in a recent study of record allocation in a paged computer system. It is shown how to construct graphs that are optimal for all three problems in some cases and are asymptotically optimal for other cases. The solution of the second problem answers a question raised by Berge in “The Theory of Graphs and its Application,” 1962.
6074974
Vertex Ranking of Asteroidal Triple-Free Graphs
We present an efficient algorithm for computing the vertex ranking number of an asteroidal triple-free graph. Its running time is bounded by a polynomial in the number of vertices and the number of minimal separators of the input graph.
43443657
A note on visibility graphs
Abstract Given a set S = {s1, s2,…, sn} of vertical line segments, s1, sj see each other if there is a horizontal line segment which intersects them, but does not intersect any other line segment between them. A visibility graph G of vertices {v1, v2,…, vn} is put into a one-to-one correspondence with S, such that si corresponds to v1, and edge {vi, vj} exists in G iff si, sj see each other. We prove that any visibility graph G is ipo-triangular, that is, it can be transformed into a planar multigraph with all triangular finite faces, by successive duplications of existing edges of G. Conversely we prove that any ipo-triangular graph is a visibility graph for some set S.
46500499
Minimum Fill-in on Circle and Circular-Arc Graphs
We present two algorithms solving the minimum fill-in problem on circle graphs and on circular-arc graphs in timeO(n3).
47450428
An Algorithm to Compact a VLSI Symbolic Layout with Mixed Constraints
A popular algorithm to compact VLSI symbolic layout is to use a graph algorithm similar to finding the "longest path" in a network. The algorithm assumes that the spacing constraints on the mask elements are of the lower bound type. However, to enable the user to have close control over the compaction result, a desired symbolic layout system should allow the user to add either the equality or the upper bound constraints on selected pairs of mask elements as well. This paper proposes an algorithm which uses a graph-theoretic approach to solve efficiently the compaction problem with mixed constraints.
37608950
Efficient Heuristics for Orientation Metric and Euclidean Steiner Tree Problems
AbstractWe consider Steiner minimum trees (SMT) in the plane, where only orientations with angle
$${\sigma }$$
 , 0 ≤ i ≤ σ − 1 and σ an integer, are allowed. The orientations define a metric, called the orientation metric, λσ, in a natural way. In particular, λ2 metric is the rectilinear metric and the Euclidean metric can beregarded as λ∞ metric. In this paper, we provide a method to find an optimal λσ SMT for 3 or 4 points by analyzing the topology of λσ SMT's in great details. Utilizing these results and based on the idea of loop detection first proposed in Chao and Hsu, IEEE Trans. CAD, vol. 13, no. 3, pp. 303–309, 1994, we further develop an O(n2) time heuristic for the general λσ SMT problem, including the Euclidean metric. Experiments performed on publicly available benchmark data for 12 different metrics, plus the Euclidean metric, demonstrate the efficiency of our algorithms and the quality of our results.
654791
An image signature for any kind of image
We describe an algorithm for computing an image signature, suitable for first-stage screening for duplicate images. Our signature relies on the relative brightness of image regions, and is generally applicable to photographs, text documents, and line art. We give experimental results on the sensitivity and robustness of signatures for actual image collections, and also results on the robustness of signatures under transformations such as resizing, rescanning, and compression.
29097074
Analysis on the Session Life Time Distribution of Gnutella
1310783
Design, Implementation, and Experimentation on Mobile Agent Security for Electronic Commerce Applications
In this paper, a Shopping Information Agent System (SIAS) is built based on mobile agent technology. It sends out agents to di erent hosts in an electronic marketplace. The agents collect and report information such as prices and availabilities about products speci ed by users. Snapshots of the system in use are shown. Security is a major problem of mobile agent systems, especially when money transactions are concerned. Possible security attacks by malicious hosts to agents in SIAS are discussed, and a solution to prevent these attacks is presented. Finally, security of the solution is analyzed, and the performance overhead introduced is