27312959
Sorting a sequence of strong kings in a tournament
A king in a tournament is a player who beats any other player directly or indirectly. According to the existence of a king in every tournament, Wu and Sheng [Inform. Process. Lett. 79 (2001) 297-299] recently presented an algorithm for finding a sorted sequence of kings in a tournament of size n, i.e., a sequence of players u1, u2,....,un such that ui → ui+1 (ui beats ui+1) and ui is a king in the sub-tournament induced by {ui, ui+1,.....,un} for each i = 1, 2,....,n - 1. With each pair u,v of players in a tournament, let b(u,v) denote the number of third players used for u to beat v indirectly. Then, a king u is called a strong king if the following condition is fulfilled: if v → u then b(u, v) > b(v,u). In the sequel, we will show that the algorithm proposed by Wu and Sheng indeed generates a sorted sequence of strong kings, which is more restricted than the previous one.
29352440
Induced matchings in asteroidal triple-free graphs
An induced matching M of a graph G is a set of pairwise nonadjacent edges such that no two edges of M are joined by an edge in G. The problem of finding a maximum induced matching is known to be NP-hard even for bipartite graphs of maximum degree four. In this paper, we study the maximum induced matching problem on classes of graphs related to AT-free graphs. We first define a wider class of graphs called the line-asteroidal triple-free (LAT-free) graphs which contains AT-free graphs as a subclass. By examining the square of line graph of LAT-free graphs, we give a characterization of them and apply this for showing that the maximum induced matching problem and a generalization, called the maximum δ-separated matching problem, on LAT-free graphs can be solved in polynomial time. In fact, our result can be extended to the classes of graphs with bounded asteroidal index. Next, we propose a linear-time algorithm for finding a maximum induced matching in a bipartite permutation (bipartite AT-free) graph using the greedy approach. Moreover, we show that using the same technique the minimum chain subgraph cover problem on bipartite permutation graphs can be solved with the same time complexity.
9862925
Powers of Asteroidal Triple-free Graphs with Applications
An asteroidal triple is an independent set of three vertices in a graph such that every two of them are joined by a path avoiding the closed neighborhood of the third. Graphs without asteroidal triples are called AT-free graphs. In this paper, we show that every AT-free graph admits a vertex ordering that we call a 2-cocomparability ordering. The new suggested ordering generalizes the cocomparability ordering achievable for cocomparability graphs. According to the property of this ordering, we show that every proper power G (k ≥ 2) of an AT-free graph G is a cocomparability graph. Moreover, we demonstrate that our results can be exploited for algorithmic purposes on AT-free graphs.
13312657
Feedback vertex sets in star graphs
In a graph G = (V, E), a subset F ⊂ V(G) is a feedback vertex set of G if the subgraph induced by V(G) \ F is acyclic. In this paper, we propose an algorithm for finding a small feedback vertex set of a star graph. Indeed, our algorithm can derive an upper bound to the size of the feedback vertex set for star graphs. Also by applying the properties of regular graphs, a lower bound can easily be achieved for star graphs.
34947079
On the powers of graphs with bounded asteroidal number
Abstract For an undirected graph G =( V , E ), the kth power G k is the graph with the same vertex set as G such that two vertices are adjacent in G k if and only if their distance in G is at most k. A set of vertices A ⊆ V is an asteroidal set if for every vertex a ∈ A , the set A ⧹{ a } is contained in one connected component of G − N G [ a ], where N G [ a ] is the closed neighborhood of a in G. The asteroidal number of a graph G is the maximum cardinality of an asteroidal set in G. The class of graphs with asteroidal number at most s is denoted by A (s) . In this paper, we show that if G k ∈ A (s) for s ⩾2, then so is G k +1 . This generalizes a previous result for the family of AT-free graphs. Moreover, we consider the forbidden configurations for the powers of graphs with bounded asteroidal number. Based on these forbidden configurations, we show that every proper power of AT-free graphs is perfect.
4458929
Including Biological Literature Improves Homology Search
Annotating the tremendous amount of sequence information being generated requires accurate automated methods for recognizing homology. Although sequence similarity is only one of many indicators of evolutionary homology, it is often the only one used. Here we find that supplementing sequence similarity with information from biomedical literature is successful in increasing the accuracy of homology search results. We modified the PSI-BLAST algorithm to use literature similarity in each iteration of its database search. The modified algorithm is evaluated and compared to standard PSI-BLAST in searching for homologous proteins. The performance of the modified algorithm achieved 32% recall with 95% precision, while the original one achieved 33% recall with 84% precision; the literature similarity requirement preserved the sensitive characteristic of the PSI-BLAST algorithm while improving the precision.
1050294
Towards pairing Java applications on SMT processors
This paper investigates various issues of pairing Java applications for multithreaded execution on Intel's hyper-threading Pentium 4 processor. We first quantify the overall performance of multiprogrammed Java applications using a metric called combined speedup. Using the performance counters provided by the Pentium 4, we then quantitatively evaluate the performance of underneath micro-architecture components and their implications to the combined speedup. A statistical model is proposed to analyze the collected data. This novel approach reveals that trace cache is the major factor determining the pairing performance. In particular, we find that the trace cache miss rates of Java applications can be utilized to predict the combined speedups. Three new scheduling strategies are proposed based on these observations and then evaluated. The experimental results show that the proposed strategies have better performance than the conventional round-robin scheduling scheme. Overall, our best strategy enables a reduction in execution time of 10.5% over the serial execution, comparing with a reduction of 5.92% achieved by the round-robin scheduling. The improvement will be increasingly significant on future SMT processors.
9345376
Finding recently frequent itemsets adaptively over online transactional data streams,
A data stream is a massive unbounded sequence of data elements continuously generated at a rapid rate. Consequently, the knowledge embedded in a data stream is more likely to be changed as time goes by. Identifying the recent change of a data stream, especially for an online data stream, can provide valuable information for the analysis of the data stream. However, most of mining algorithms or frequency approximation algorithms over a data stream do not differentiate the information of recently generated data elements from the obsolete information of old data elements which may be no longer useful or possibly invalid at present. Therefore, they are not able to extract the recent change of information in a data stream adaptively. This paper proposes a data mining method for finding recently frequent itemsets adaptively over an online transactional data stream. The effect of old transactions on the current mining result of a data steam is diminished by decaying the old occurrences of each itemset as time goes by. Furthermore, several optimization techniques are devised to minimize processing time as well as memory usage. Finally, the performance of the proposed method is analyzed by a series of experiments to identify its various characteristics.
43225887
DMMX: Dynamic memory management extensions
Dynamic memory management allows programmers to be more productive and increases system reliability and functionality. However, software algorithms for memory management are slow and non-deterministic. It is well known that object-oriented applications tend to be dynamic memory intensive. This has led programmers to eschew dynamic memory allocation for many real-time and embedded systems. Instead, programmers using Java or C++ as a development language frequently decide to allocate memory statically instead of dynamically. In this paper, we present the design of a bitmap-based memory allocator implemented primarily in combinational logic to allocate memory in a small, predictable amount of time. It works in conjunction with an application-specific instruction-set extension called the dynamic memory management extension (DMMX). Allocation is done through a complete binary tree of combinational logic, which allows constant-time object creation. The garbage collection algorithm is mark sweep, where the sweeping phase can be accomplished in constant time. This hardware scheme can greatly improve the speed and predictability of dynamic memory management. The proposed DMMX is an add-on approach, which allows easy integration into any CPU, hardware-implemented Java virtual machine, or processor in memory.
42765958
Design and evaluation of a submesh allocation scheme for two-dimensional mesh-connected parallel computers
This paper presents the design and evaluation of a novel submesh allocation algorithm called the Optimized Buddy System which is derived from conventional binary buddy system. Our scheme is made feasible by using a bit-map to represent the status of the processors. The proposed scheme can be mapped into hardware directly to take the advantage of the speed of a pure combinational-logic implementation. Although the buddy system may allocate a submesh that is much larger than the requested size, the logic that finds a free submesh can be augmented by a "bit-flipper" to relinquish the unused portion at the end of the submesh. This effectively eliminates internal fragmentation. The hardware complexity of proposed scheme (i.e. and-gate tree, or-gate tree and bit-flipper) is O(m/spl times/n), where m/spl times/n is the total number of the processors. The unique blind spot issue of proposed system is also investigated. Simulation results show that the allocation efficiency of the proposed scheme is similar to the one that uses best-fit approach.