• Proceedings of the Korean Information Science Society Conference
• /
• 2003.04a
• /
• pp.881-883
• /
• 2003

하드웨어 검증과 모델 체킹 등의 분야에서, SAT(satisfiability problem)나 항진 명제 검사(tautology checking)는 매우 중요한 문제이다. 그러나 이들은 모두 NP-complete 문제이므로 그 복잡도가 매우 크다. 이를 해결하기 위해 여러 가지 연구가 이루어져 왔으며, 여러 효율적인 알고리즘이 존재한다. 이러한 알고리즘은 대부분 일반 표현식을 CNF(conjunctive normal form)로 바꾸어 입력 형식으로 사용한다. 이 논문에서는 일반 표현식을 입력으로 받아 DNF로 변환한 뒤 DNF의 특성을 이용하여 SAT를 검사하는 효율적인 방법을 제시한다.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.18 no.3
• /
• pp.339-347
• /
• 1993

The channel assignment problem in a mobile communication system is a NP-complete combinatorial optimization problem, in which the calculation time increases exponentially as the range of the problem is extended. This paper adapts a conventional Hopfield neural network model to the channel assignment problem to relieve the calculation time by means of the parallelism supplied from the neural network. In the simulation study, we checked the feasability of such a parallel method for the fixed channel assignment with uniform, and nouniform channel requirements, and for the dynamic channel assignment with considering continously varying channel requirements.

• Journal of the Korea Computer Industry Society
• /
• v.3 no.2
• /
• pp.185-190
• /
• 2002

As the TSP(Traveling Salesman Problem) belongs to the class of NP-complete problems, various techniques are required for finding optimum or near optimum solution to the TSP. This paper designs a distributed genetic algorithm in order to reduce the execution time and obtain more near optimal using multi-slave model for the TSP. Especially, distributed genetic algorithms with multiple populations are difficult to configure because they are controlled by many parameters that affect their efficiency and accuracy. Among other things, one must decide the number and the size of the populations (demes), the rate of migration, the frequency of migrations, and the destination of the migrants. In this paper, I develop random dynamic migration rate that controls the size and the frequency of migrations. In addition to this, I design new migration policy that selects the destination of the migrants among the slaves

• The Transactions of the Korea Information Processing Society
• /
• v.5 no.11
• /
• pp.2823-2834
• /
• 1998

This paper deals with the problem of one-to-one mapping of $2^n$ task modules of a parallel program to an n-dimensional hypercube multicomputer so as to minimize to total communication cost during the execution of the task. The problem of finding an optimal mapping has been proven to be NP-complete. We first propose a graph modification technique which transfers the mapping problem in a hypercube multicomputer into the problem of finding a set of maximum cutsets on a given task graph. Using the graph modification technique, we then propose a repeated mapping scheme which efficiently finds a one-to-one mapping of task modules to a hypercube multicomputer by repeatedly applying an existing bipartitioning algorithm on the modified graph. The repeated mapping scheme is shown to be highly effective on a number of test task graphs, it increasingly outperforms the greedy and recursive mapping algorithms as the number of processors increase. The proposed algorithm is shown to be very effective for regular graph, such as hypercube-isomorphic or 'almost' isomorphic graphs and meshes; it finds optimal mapping on almost all the regular task graphs considered.

• Journal of KIISE:Computer Systems and Theory
• /
• v.27 no.6
• /
• pp.608-618
• /
• 2000

We consider the problem of placing resources in a distributed computing system so that certain performance requirements may be met while minimizing the number of required resource copies, irrespective of node or link failures. To meet the requirements for high performance and high availability, minimum number of resource copies should be placed in such a way that each node has at least two copies on the node or its neighbor nodes. This is called the fault-tolerant resource placement problem in this paper. The structure of a parallel or a distributed computing system is represented by a graph. The fault-tolerant placement problem is first transformed into the problem of finding the smallest fault-tolerant dominating set in a graph. The dominating set problem is known to be NP-complete. In this paper, searching for the smallest fault-tolerant dominating set is formulated as a state-space search problem, which is then solved optimally with the well-known A* algorithm. To speed up the search, we derive heuristic information by analyzing the properties of fault-tolerant dominating sets. Some experimental results on various regular and random graphs show that the search time can be reduced dramatically using the heuristic information.

• Proceedings of the Korean Information Science Society Conference
• /
• 2002.04b
• /
• pp.283-285
• /
• 2002

강의시간표 문제(Lecture timetabling Problem)는 일주일을 기본으로 하는 특정 시간대 별로 학생(Course-class), 교수, 그리고 강의실과 같은 자원에 대한 스케줄링 문제로서 각각의 자원에 대하여 적절한 조합으로 제약조건들 사이의 충돌을 최소화하여 자원을 배치하는 할당문제이다. 강의시간표 문제는 수천 명 학생들에 대하여 개개인의 시간표를 작성해야 하므로 기하급수적으로 증가하는 탐색공간에 대하여 최악의 경우 탐색 시간이 지수적으로 증가하는 NP-complete Problem이다. 이러한 거대하고 복잡한 강의시간표 문제는 계층적으로 분할하여 기능별로 처리하면서 제약조건을 협상하도록 하는 각 모듈 단위의 에이전트를 구성하므로 좀 더 작고 단순한 문제로 변환될 수 있다. 본 논문에서는 방대한 탐색 공간과 과잉-제약조건(Over-constraint)문제의 하나인 강의시간표 작성 문제를 분산제약조건 만족 문제 특성을 이용하고 다중 에이전트 구조를 사용하여 해결하는 강의시간표 자동화 시스템 설계를 제안한다.

• The Transactions of the Korea Information Processing Society
• /
• v.5 no.9
• /
• pp.2302-2311
• /
• 1998

The problem of scheduling general packet traffic on WDM optical interconnection networks is NP-complete, It is known that the list scheduling is a good approximation algurithm fur this problem, The resulting list schedules vary depending on the order of transmitters considered to be placed on each time slot We propose an improvement of the list scheduling that tries different orders of transmitters to obtain shorter schedule lengths, Genetic algorithms are used to explore various orders of transmitters.

• Journal of KIISE:Information Networking
• /
• v.28 no.4
• /
• pp.657-664
• /
• 2001

In our predecessor paper(Part I)[13], we introduced a graph that represents the crosstalk relationship among multicast connections in the photonic Banyan-type switching network, and found the upper bound on the degree of it. In this paper(Part II), we consider the number of routing rounds(i.e., scheduling length) required for SE(switching element)-disjoint multicasting in photonic Banyan-type switching networks. Unfortunately, the problem to find an optimal scheduling length is NP-complete thus, we propose an approximation algorithm that gives its scheduling length is always within double of the upper bound on the optimal length. We also study the scheduling length on the Iink-disjoint(i.e., nonblocking) multicasting. Various nonblocking Banyan-type multicasting networks are found under the scheduling lengths.

• The KIPS Transactions:PartA
• /
• v.13A no.2 s.99
• /
• pp.163-170
• /
• 2006

Most scheduling problems including DAG(Directed Acyclic Graph)-based are known to be NP-complete, so many heuristic-based scheduling algorithms have been researched. HEFT and CPOP are such algorithms which have been devised to be effective in heterogeneous environment. We proposed, in the previous research, three scheduling algorithms which are effective in realistic global heterogeneous environment: CPOC, eCPOPC and eCPOP. In this paper, the heuristics which are used in the above five algorithms will be systematically analyzed. Those algorithms will be also studied experimentally using various benchmarks. Experimental results show that the eCPOC generates better schedules than any other algorithms and the heuristics which are used in the proposed algorithms are effective in the global heterogeneous environment.

• Journal of the Institute of Electronics Engineers of Korea CI
• /
• v.41 no.2
• /
• pp.9-22
• /
• 2004

This paper presents a parallel genetic algorithm for the Multi-disk data allocation problem an NP-complete problem. This problem is to find a method to distribute a Binary Cartesian Product File on disk-arrays to maximize parallel disk I/O accesses. A Sequential Genetic Algorithm(SGA), DAGA, has been proposed and showed the superiority to the other proposed methods, but it has been observed that DAGA consumes considerably lengthy simulation time. In this paper, a parallel version of DAGA(ParaDAGA) is proposed. The ParaDAGA is a 2-dimension torus-based Parallel Genetic Algorithm(PGA) and it is based on a distributed population structure. The ParaDAGA has been implemented on the parallel computer simulated on a single processor platform. Through the simulation, we study the impact of varying ParaDAGA parameters and compare the quality of solution derived by ParaDAGA and DAGA. Comparing the quality of solutions, ParaDAGA is superior to DAGA in all cases of configurations in less simulation time.