首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到18条相似文献,搜索用时 140 毫秒
1.
逻辑函数的无冗余覆盖选择问题   总被引:1,自引:1,他引:0  
逻辑函数的最小化算法可分为两大步骤:产生本源蕴涵项和在这些蕴涵项中选择一个最小覆盖。人说后者比前者更加困难,这的确是事实。我们这里提出一个无冗余和选择一个最小覆盖的算法。给定函数f的一个本源覆盖G,首先将G分为三个子集:实质本源项子集E,完全冗余项子集R和相对冗余项子集P。然后在P中选择一个子集P^*,使P^*∪E为f的一个近似最小覆盖。很明显,后一项任务比前者要复杂得多。所以,我们的讨论侧重于后  相似文献   

2.
为进一步提高逻辑函数的化简速度,提出一种改进的Q-M逻辑函数化简方法。在迭代比较过程中设置2个权值以缩减可合并蕴涵项集合的大小,只对满足条件的蕴涵项进行合并处理,得到全部质蕴涵项。构造质蕴涵项与最小项关联图,利用启发式规则得到能蕴涵全部最小项的最少质蕴涵项集合,从而得到逻辑函数的最小覆盖,完成逻辑函数化简。实验结果表明,该算法能降低迭代次数,减少逻辑函数的化简时间。  相似文献   

3.
逻辑函数绝对最小覆盖的改进算法   总被引:4,自引:2,他引:2  
逻辑函数的绝对最小化算法存在的主要问题是运行时间过长和需要的存储空间过大。本文提出了一个从给定本源蕴涵项集合中抽出一个绝对最小覆盖的算法,而时间、空间的需求被大缩小了。  相似文献   

4.
用关键特征集对逻辑进行优化   总被引:3,自引:1,他引:2  
提出了一个两级逻辑优化的新算法,与通过函数质蕴涵集求解覆盖的传统算法不同,文中将求解逻辑函数的质蕴涵项与推导覆盖问题相结合,直接得出覆盖问题的解。算法的主要问题可以简化为:对于立方描述的单元,求解最小覆盖,在这个过程中又提出了一种改进的覆盖吸收算法,基于关键特征集合的选拔吸收算法,此算法不用求所有的立方,通过标准的测试例子与原来的Espresso算法作比较,对于大电路,在计算时间上,新算法有明显的改进。  相似文献   

5.
论文提出了EDA中易于计算机实现的逻辑函数优化方法,即在优化过程中引入删劣运算,用锐积运算求质蕴涵项,用选择提炼极值法求最小覆盖,并对循环函数进行处理的优化方法。设计了相应的组合逻辑电路逻辑综合优化程序,大量的测试证明了该方法的正确性和易于计算机实现的有效性。  相似文献   

6.
大变量逻辑函数最佳覆盖问题研究   总被引:2,自引:0,他引:2  
逻辑函数的最佳覆盖,一直是逻辑综合领域的关键环节。尤其是大变量逻辑函数最佳覆盖,对复杂的逻辑综合更为重要,但也更加困难。本文在对逻辑覆盖算法研究的基础上,提出了适合大变量逻辑函数最佳覆盖的Beister改进算法。经过大量算题的测试表明,改进的列覆盖算法在时间复杂度和选择效果方面均优于Beister算法。  相似文献   

7.
支持大规模变量集的最小覆盖迭代搜索算法   总被引:1,自引:0,他引:1  
两级逻辑综合中的多输出逻辑电路最小覆盖的求解是一个NP难解问题,在输出变量集合和质蕴含项集合规模较大的情况下,会出现空间需求过大、处理时间太长等问题,影响多输出最小覆盖求解的可行性.在精选法的基础上,提出一种多输出最小覆盖迭代求解算法.将一次性求解最小覆盖的模式转换为多次迭代逼近最优解的过程,使得在有限的时间和空间范围内获得尽可能优化的最小覆盖结果.同时,对影响算法复杂度的单输出到多输出函数的阵列合并、极值的选择这2个主要环节进行了改进,大幅度降低了多输出最小覆盖求解算法的时间和空间复杂度.  相似文献   

8.
部分四值逻辑中Sheffer函数的判定   总被引:1,自引:0,他引:1       下载免费PDF全文
多值逻辑是指一切逻辑值的取值数大于2的逻辑。Sheffer函数的判定问题是多值逻辑完备性理论中的一个重要问题,此问题的解决依赖于定出多值逻辑函数集中所有准完备集的最小覆盖。在深入研究部分四值逻辑中Sheffer函数的基础上,根据部分四值逻辑中准完备集的最小覆盖,给出了一个部分四值逻辑中Sheffer函数的判定算法。此算法能够判定任意一个函数是不是部分四值逻辑中的Sheffer函数。  相似文献   

9.
本文介绍一个将任意布尔函数最小化的算法。其方法与先前首先求得全部质蕴涵项然后确定最小覆盖的方法不同。这个算法为了获得接近最小的积之和的实现,运用一组条件来选择质蕴涵项。并把它推广到多输出和不完全规定函数的情况。所提出的算法的主要特点是求解同一问题所化费的机器时间比用其它的算法少。如果只要求结果是较少的乘积项时,MINI算法对于输入、输出数目多的布尔函数可以给出较好的结果。这个算法也适合于寻求内部按积之和实现的大的布尔函数的可编程序阵列(PLA)的解。  相似文献   

10.
用精选法求布尔函数的最小化解时,传统的作法是先求出质覆盖Z,然后从Z中挑选必要质蕴涵项。本文提出的E算法在勿需求出质覆盖的情况下,就可以判断出多输出二值布尔函数的一个质蕴涵项是否是必要质蕴涵项,从而节省计算机的存储空间和运算时间。  相似文献   

11.
A method of determination of all the minimal prime implicant covers of switching functions by utilizing their connected cover term matrices is suggested in the paper. The method presented is an extension of the technique suggested by the authors in a previous paper (Choudhury and Das 1964). When majority of the prime implicants of a switching function will occur in more than two different columns of the cover table, it is shown that the determination of all the minimal prime implicant covers can often be greatly facilitated by initially dividing the cover table into more than two suitable sub-tables.  相似文献   

12.

A new method for obtaining a two-level collective minimal cover for a set of incompletely-specified switching functions $S=\{f_1,f_2,\ldots,f_n\}$ is presented. The method relies on the introduction of a single auxiliary function F whose subfunctions (restrictions) with respect to some additional auxiliary variables $y_1,y_2,\ldots,y_{n-1}$ are certain members of S . The complete sum of F has full information on the multiple-output prime implicants (MOPIs) of the set of functions S . A particularly constrained minimal cover for F contains only labeled versions of some paramount prime implicants (PPIs) of S and can be used to construct a multiple-output minimal cover for S . The present method can proceed by map, algebraic or tabular techniques, though only the map version is presented herein. This version employs a single map whose construction avoids the ANDing operations needed in the classical method, and whose size is almost one half the total size of the maps used by the classical method, and whose entries can be variable as well as constant. The minimization process is a direct two-step technique that avoids constructing the set of all PPIs as it produces only these PPIs needed in the minimal cover. Details of the method are carefully explained and illustrated via a typical example.  相似文献   

13.
邱建林  王波  刘维富 《计算机工程》2007,33(17):57-59,62
在对Espresso算法进行分析改进的基础上,提出了一种基于全域识别的多输入多输出逻辑函数实质本源项、完全冗余项和相对冗余项生成算法,该算法通过对基于积项表示的多输入多输出逻辑函数的余因子计算来进行全域判断,根据全域判断结果来识别实质本源项、完全冗余项和相对冗余项,从而构成实质本源项集合、完全冗余项集合和相对冗余项集合.对基于二级SOP型的多输入多输出逻辑函数设计了多输入多输出逻辑函数优化识别软件系统,允许的最大输入变量数为128、最大输出变量数为256、最大输入输出变量总和为300、最大输入积项数为20 000.软件系统在Pentium 1.8GHz、512MB内存的计算机上通过了Benchmark例题的测试.  相似文献   

14.
城市环境信息系统数据库设计及最小覆盖算法   总被引:3,自引:0,他引:3  
本文设计了城市环境信息系统(CEIS)数据库,并探讨了该数据库的三范式问题,最后提出了数据库函数依赖的最小覆盖,解决了数据库的冗余问题。  相似文献   

15.
A Cartesian product network is obtained by applying the cross operation on two graphs. We study the problem of constructing the maximum number of edge-disjoint spanning trees (abbreviated to EDSTs) in Cartesian product networks. Let G=(V/sub G/, E/sub G/) be a graph having n/sub 1/ EDSTs and F=(V/sub F/, E/sub F/) be a graph having n/sub 2/ EDSTs. Two methods are proposed for constructing EDSTs in the Cartesian product of G and F, denoted by G/spl times/F. The graph G has t/sub 1/=|E/sub G/|/spl middot/n/sub 1/(|V/sub G/|-1) more edges than that are necessary for constructing n/sub 1/ EDSTs in it, and the graph F has t2=|E/sub F/'-n/sub 2/(|V/sub F/|-1) more edges than that are necessary for constructing n/sub 2/ EDSTs in it. By assuming that t/sub 1//spl ges/n/sub 1/ and t/sub 2//spl ges/n/sub 2/, our first construction shows that n/sub 1/+n/sub 2/ EDSTS can be constructed in G/spl times/F. Our second construction does not need any assumption and it constructs n/sub 1/+n/sub 2/-1 EDSTs in G/spl times/F. By applying the proposed methods, it is easy to construct the maximum numbers of EDSTs in many important Cartesian product networks, such as hypercubes, tori, generalized hypercubes, mesh connected trees, and hyper Petersen networks.  相似文献   

16.
Having a database design that avoids redundant information and update anomalies is the main goal of normalization techniques. Ideally, data as well as constraints should be preserved. However, this is not always achievable: while BCNF eliminates all redundancies, it may not preserve constraints, and 3NF, which achieves dependency preservation, may not always eliminate all redundancies. Our first goal is to investigate how much redundancy 3NF tolerates in order to achieve dependency preservation. We apply an information-theoretic measure and show that only prime attributes admit redundant information in 3NF, but their information content may be arbitrarily low. Then we study the possibility of achieving both redundancy elimination and dependency preservation by a hierarchical representation of relational data in XML. We provide a characterization of cases when an XML normal form called XNF guarantees both. Finally, we deal with dependency preservation in XML and show that like in the relational case, normalizing XML documents to achieve non-redundant data can result in losing constraints.  相似文献   

17.
This paper concludes the discussion we began in the last two issues of CRYPTOLOGIA. A typical message receiver using an RSA public key cryptosystem believes that the secret nontrivial factors p and q of his public coding modulus m are primes. But he need not know that p or q are prime, or even square free. We give a few examples below. In some of them the “RSA public key cryptosystem” based on integers P and Q erroneously thought both to be prime works perfectly, but is more vulnerable to a cryptanalytic attack of the type G. J. Simmons and J. N. Norris [7] have suggested. In other cases these cryptosystems malfunction in an obvious fashion likely to be apprehended quickly by the message receiver. After the examples we prove all the results in I and II except a few which, like Theorems 1.1, 1.2 and 1.3, are obvious corollaries of other results in those papers.  相似文献   

18.
We examine the computational power of modular counting, where the modulus m is not a prime power, in the setting of polynomials in Boolean variables over Z m . In particular, we say that a polynomial P weakly represents a Boolean function f (both have n variables) if for any inputs x and y in {0,1}n, we have whenever . Barrington et al. (1994) investigated the minimal degree of a polynomial representing the OR function in this way, proving an upper bound of O(n 1/ r ) (where r is the number of distinct primes dividing m) and a lower bound of . Here, we show a lower bound of when m is a product of two primes and in general. While many lower bounds are known for a much stronger form of representation of a function by a polynomial (Barrington et al. 1994, Tsai 1996), very little is known using this liberal (and, we argue, more natural) definition. While the degree is known to be for the generalized inner product because of its high communication complexity (Grolmusz 1995), our bound is the best known for any function of low communication complexity and any modulus not a prime power. received 29 September 1994  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号