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171.
黄迪明 《电子科技大学学报(社会科学版)》1996,(Z2)
介绍在Windows环境下用BorlandC++3.1开发的通用函数图形发生器的结构和功能,讨论了实现中的表达式求值算法和图形生成算法。FGG的主要特点是,对输入的任意一元、二元函数表达式可直接生成对应的二维和三维图形。FGG作为CAI写作工具的支撑软件,可用于CAI课件的开发及演示。 相似文献
172.
轴向电子注通过介质慢波系统,当波的相速略低于电子注的速度时就可产生相干的切伦可夫辐射,这一现象是一切行波管的基础。本文利用线性理论,通过自洽求解粒子连续性方程和相对论运动方程与麦克斯韦方程组,分析了薄环形相对论电子注介质切伦可夫脉塞的注波互作用,得到了完全描述其薄环形电子注作用的跳变条件,导出了描述其不稳定性的色散方程和注波互作用的同步条件,并求得了波增长率。 相似文献
173.
174.
The problems dealt with in this paper are generalizations of the set cover problem, min{cx | Ax b, x {0,1}n}, where c Q+n, A {0,1}m × n, b 1. The covering 0-1 integer program is the one, in this formulation, with arbitrary nonnegative entries of A and b, while the partial set cover problem requires only m–K constrains (or more) in Ax b to be satisfied when integer K is additionall specified. While many approximation algorithms have been recently developed for these problems and their special cases, using computationally rather expensive (albeit polynomial) LP-rounding (or SDP-rounding), we present a more efficient purely combinatorial algorithm and investigate its approximation capability for them. It will be shown that, when compared with the best performance known today and obtained by rounding methods, although its performance comes short in some special cases, it is at least equally good in general, extends for partial vertex cover, and improves for weighted multicover, partial set cover, and further generalizations. 相似文献
175.
Batch-Processing Scheduling with Setup Times 总被引:2,自引:0,他引:2
The problem is to minimize the total weighted completion time on a single batch-processing machine with setup times. The machine can process a batch of at most B jobs at one time, and the processing time of a batch is given by the longest processing time among the jobs in the batch. The setup time of a batch is given by the largest setup time among the jobs in the batch. This batch-processing problem reduces to the ordinary uni-processor scheduling problem when B = 1. In this paper we focus on the extreme case of B = +, i.e. a batch can contain any number of jobs. We present in this paper a polynomial-time approximation algorithm for the problem with a performance guarantee of 2. We further show that a special case of the problem can be solved in polynomial time. 相似文献
176.
Center and Distinguisher for Strings with Unbounded Alphabet 总被引:2,自引:0,他引:2
Consider two sets
and
of strings of length L with characters from an unbounded alphabet , i.e., the size of is not bounded by a constant and has to be taken into consideration as a parameter for input size. A closest string s* of
is a string that minimizes the maximum of Hamming1
distance(s, s*) over all string s : s
. In contrast, a farthest string t* from
maximizes the minimum of Hamming distance(t*,t) over all elements t: t
. A distinguisher of
from
is a string that is close to every string in
and far away from any string in
. We obtain polynomial time approximation schemes to settle the above problems. 相似文献
177.
Sorting by Reversals (SBR) is one of the most widely studied models of genome rearrangements in computational molecular biology. At present,
is the best known approximation ratio achievable in polynomial time for SBR. A very closely related problem, called Breakpoint Graph Decomposition (BGD), calls for a largest collection of edge disjoint cycles in a suitably-defined graph. It has been shown that for almost all instances SBR is equivalent to BGD, in the sense that any solution of the latter corresponds to a solution of the former having the same value. In this paper, we show how to improve the approximation ratio achievable in polynomial time for BGD, from the previously known
to
for any > 0. Combined with the results in (Caprara, Journal of Combinatorial Optimization, vol. 3, pp. 149–182, 1999b), this yields the same approximation guarantee for n! – O((n – 5)!) out of the n! instances of SBR on permutations with n elements. Our result uses the best known approximation algorithms for Stable Set on graphs with maximum degree 4 as well as for Set Packing where the maximum size of a set is 6. Any improvement in the ratio achieved by these approximation algorithms will yield an automatic improvement of our result. 相似文献
178.
Yoshiyuki Kusakari Daisuke Masubuchi Takao Nishizeki 《Journal of Combinatorial Optimization》2001,5(2):249-266
Let G = (V,E) be a plane graph with nonnegative edge weights, and let
be a family of k vertex sets
, called nets. Then a noncrossing Steiner forest for
in G is a set
of k trees
in G such that each tree
connects all vertices, called terminals, in net N
i, any two trees in
do not cross each other, and the sum of edge weights of all trees is minimum. In this paper we give an algorithm to find a noncrossing Steiner forest in a plane graph G for the case where all terminals in nets lie on any two of the face boundaries of G. The algorithm takes time
if G has n vertices and each net contains a bounded number of terminals. 相似文献
179.
数字签名技术的研究与探讨 总被引:2,自引:0,他引:2
李永新 《绍兴文理学院学报》2003,23(7):47-49
通过对对称加密体制、非对称加密体制以及Hash算法的分析,根据数字签名的要求,给出了一种具有防伪、防赖及保密的数字签名技术. 相似文献
180.
The problem of computing the strength and performing optimal reinforcement for an edge-weighted graph G(V, E, w) is well-studied. In this paper, we present fast (sequential linear time and parallel logarithmic time) on-line algorithms for optimally reinforcing the graph when the reinforcement material is available continuously on-line. These are the first on-line algorithms for this problem. We invest O(|V|3|E|log|V|) time (equivalent to (|V|) invocations of the fastest known algorithms for optimal reinforcement) in preprocessing the graph before the start of our algorithms. It is shown that the output of our on-line algorithms is as good as that of the off-line algorithms. Thus our algorithms are better than the fastest off-line algorithms in situations when a sequence of more than (|V|) reinforcement problems need to be solved. The key idea is to make use of ideas underlying the theory of Principal Partition of a Graph. Our ideas are easily generalized to the general setting of polymatroid functions. We also present a new efficient algorithm for computation of the Principal Sequence of a graph. 相似文献