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.
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.
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.
46514608
A hybrid allocator
Dynamic memory management can make up to 30% of total program execution time. Object oriented languages like C++ allocate and free dynamic memory prolifically. Since computer memory is a limited resource its efficient utilization is required to minimize wastage and keep costs down. Memory management algorithms such as best fit seem to perform most efficiently in terms of space cost while simple segregated storage seems to minimize the time cost. There is a trade-off between time and space costs. We have developed a new general purpose hybrid algorithm that shows excellent performance with respect to both time and space in comparison to the Doug Lea version 2.7.0 dynamic memory allocator.
18001825
Architectural support for dynamic memory management
Recent advances in software engineering, such as graphical user interfaces and object-oriented programming, have caused applications to become more memory intensive. These applications tend to allocate dynamic memory prolifically. Moreover, automatic dynamic memory reclamation (garbage collection, GC) has become a popular feature in modern programming languages. As a result, the time consumed by dynamic storage management can be up to one-third of the program execution time. This illustrates the need for a high-performance memory management scheme. This paper presents a top-level design and evaluation of the proposed instruction extensions to facilitate heap management.
15172555
A tunable hybrid memory allocator
Dynamic memory management can make up to 60% of total program execution time. Object oriented languages such as C++ can use 20 times more memory than procedural languages like C. Bad memory management causes severe waste of memory, several times that actually needed, in programs. It can also cause degradation in performance. Many widely used allocators waste memory and/or CPU time. Since computer memory is an expensive and limited resource its efficient utilization is necessary. There cannot exist a memory allocator that will deliver best performance and least memory consumption for all programs and therefore easily tunable allocators are required. General purpose allocators that come with operating systems give less than optimal performance or memory consumption. An allocator with a few tunable parameters can be tailored to a program's needs for optimal performance and memory consumption. Our tunable hybrid allocator design shows 11-54% better performance and nearly equal memory consumption when compared to the well known Doug Lea allocator in seven benchmark programs.
1021056
A performance perspective on the Active Memory System
Abstract One major problem of using Java in real-time and embedded devices is the non-deterministic turnaround time of dynamic memory management systems (memory allocation and garbage collection). For the allocation, the non-determinism is often contributed by the time to perform searching, splitting, and coalescing. For the garbage collection, the turnaround time is usually determined by the size of the heap, the number of live objects, the number of object collected, and the amount of garbage collected. Even with the current state-of-the-art garbage collectors (generational and incremental schemes), they may or may not guarantee the worst-case latency. Moreover, such schemes often prolong overall garbage collection time. In this paper, the performance analysis of the proposed Active Memory Module (AMM) for embedded systems is presented. Unlike the software counterparts, the AMM can perform a memory allocation in a predictable and bounded fashion (14 cycles). Moreover, it can also yield a bounded sweeping time regardless of the number of live objects or heap size. By utilizing the proposed system, the overall speedup can be as high as 23% compared to the garbage collection system of the JDK 1.2.2 running in classic mode.
40774984
Performance enhancements to the Active Memory System
The Active Memory System - a garbage collected memory module - was introduced as a way to provide hardware support for garbage collection in embedded systems. The major component in the design was the Active Memory Processor (AMP) that utilized a set of bit-maps and a combinational circuit to perform mark-sweep garbage collection. The design can achieve constant time for both allocation and sweeping. In this paper two enhancements are made to the design of AMP so that it can perform one-bit reference counting that postpones the need to perform garbage collection. Moreover, a caching mechanism is also introduced to reduce the hardware cost of the design. The experimental results show that the proposed modification can reduce the number of garbage collection invocations by 76%. The speed-up in marking time can be as much as 5.81. With the caching mechanism, the hardware cost can be as small as 27 K gates and 6 KB of SRAM.