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  • 1
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Notizen: Abstract: This paper considers an application of decision aiding for maritime operations, viz the design of an intelligent operator aid for dynamic route planning. The limitations of some existing methods are discussed and an Al approach is proposed that combines algorithmic and heuristic processing elements within an embedded system. The aid consists of three elements: a intelligent front end, a route planner and an explanation facility.
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  • 8
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Notizen: Abstract: Recent developments in a subarea of computer science called artificial intelligence have included the creation of expert systems that are capable of solving difficult applications problems which require expert knowledge for their solution. Such expert systems have been found to be useful in a number of applications (e.g. medicine, biochemistry and mineral exploration). In this paper the author presents an expert system for solving problems concerning income and transfer tax planning for individuals In developing this system, a theoretical structure and a set of decision rules were specified and then programmed into a rule-based system that had previously been used for medical diagnosis (Mycin [1]) Once the system was developed, its problem-solving capabilities were refined and verified by a panel of tax experts using a blind verification procedure. This verification step demonstrated that an expert system could be developed in that domain.
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  • 9
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Notizen: Abstract: The purpose of this paper is to design an expert system or an intelligent procedure' that purports to screen hazard potentials of environmental chemicals on the basis of structure-activity relationships in the study of chemical carcinogenesis, particularly with respect to analysing the current state of known structural information about chemical carcinogens and predicting the possible carcinogenicity of untested chemicals An analysis of a computerised database of known carcinogens (knowledge base) is being performed using the structure-activity trees in order to test the validity of the tree as a classification scheme (inference engine) and to evaluate trends or patterns that may exist between chemical structure and specificity for target tissue, route of administration, and animal species. Practical applications of the structure-activity tree depend on its eventual validation as a predictor of carcinogenic activity.
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  • 11
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Notizen: Abstract: Activities concerning expert systems in Japan are outlined. Expert systems are receiving increasing attention in Japan, together with fifth-generation computers. Rather than describing the details of individual systems, a variety of expert systems are briefly introduced with their aims and features.
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  • 14
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Notizen: Abstract: Analysis of the job shop scheduling domain has indicated that the crux of the scheduling problem is the determination and satisfaction of a large variety of constraints. Schedules are influenced by such diverse and conflicting factors as due date requirements, cost restrictions, production levels, machine capabilities and substitutability, alternative production processes, order characteristics, resource requirements, and resource availability. This paper describes ISIS, a scheduling system capable of incorporating all relevant constraints in the construction of job shop schedules. We examine both the representation of constraints within ISIS, and the manner in which these constraints are used in conducting a constraint-directed search for an acceptable schedule. The important issues relating to the relaxation of constraints are addressed. Finally, the interactive scheduling facilities provided by ISIS are considered.
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  • 15
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 16
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Notizen: Abstract: Log interpretation science is a controversial and rapidly changing domain. Designing interpretation models is a highly experimental process which involves trials with a computer program as an integral part of the design. Therefore conventional software engineering techniques, which require a complete specification of the problem before the program is written, are often not applicable or fail to produce high quality software. The development of expert systems has provided the techniques, tools, and capabilities to let us seek alternate methods to produce log interpretation software: exploratory programming environments and automatic programming systems. An exploratory programming environment combines the power of interactive graphics and programming tools to merge the design and programming tasks into a single process where model and program develop together. An automatic programming system will embody the knowledge of the programming process and of some log interpretation heuristics to produce log processing programs from interactive specifications expressed in familiar terms. These facilities will allow log interpretation model designers, who are non-computer specialists, to produce high quality software as the end result of a model design.
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  • 18
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 19
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 21
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 1 (1984), S. 0 
    ISSN: 1468-0394
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Informatik
    Materialart: Digitale Medien
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  • 22
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 16 (1983), S. 57-60 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract It is shown that a Thue system of the formT 1 = {(w,e)} is Church-Rosser if and only if there is a Thue systemT 2 that is Church-Rosser and is equivalent toT 1.
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 16 (1983), S. 133-157 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We associate to a maximal codeX on an alphabetA a dynamical system Ω; our main result proves that the property of unique decipherability implies that the partition of Ω associated to the letters ofA is a Bernoulli partition. Surprisingly it is possible to give two very different proofs of this result: the first one uses probability measures on monoids together with methods from automata theory; the other is based on results of entropy theory.
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  • 24
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 16 (1983), S. 233-249 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract In contrast to the case of a single dynamical system, the asymptotic stability of orbits of control systems cannot be characterized in terms of suitably defined Lyapunov functions. It is shown that the existence of Lyapunov functions corresponds to a stronger type of asymptotic stability, which is defined by introducing higher prolongations.
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  • 25
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 16 (1983), S. 191-231 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Several equivalence decision algorithms for classes of grammars, program schemes, transducers follow the general pattern of the Korenjak-Hopcroft algorithm for deciding the equivalence of simple deterministic grammars. An axiomatic framework is presented which points out the essence of the Korenjak-Hopcroft algorithm and applies to numerous situations.
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  • 26
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 16 (1983), S. 159-183 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Call a connected planar graphG legal if it has at least two nodes, no parallel edges or self-loops and at most two terminals (degree 1 nodes) and all terminals and degree 2 nodes are exterior. This class of graphs arose in connection with a two-dimensional generating system for modeling growth by binary cell division. Showing that any permitted pattern can be generated properly requires a matching or pairing lemma. The vertex set of a legal graph withn nodes can be split intop adjacent pairs ands singletons withs p, resulting in a matching which includes at least $$2\left[ {\frac{n}{3}} \right]$$ nodes. This bound is sharp in the sense that there are legal graphs for which this matching is maximum. The matching can be implemented by a linear time algorithm. A legal graph witht terminals and n≥4 nodes has a spanning tree with at most $$\left[ {\frac{{n - t}}{2}} \right] + t$$ terminals; this bound is sharp. Such a spanning tree can be constructed by an algorithm which operates in almost linear time.
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  • 27
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 16 (1983), S. 185-188 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The class of readout maps of the early state space literature and the class of operators which are both causal and anticausal are compared. The first class is a subset of the second and is shown by example to be a proper subset. A characterization of the smaller class in terms of causality structure is presented. We denote this characterization by the term completely memoryless.
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 85-96 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A simple problem concerning evaluation of programs is shown to be nonelementary recursive. The problem is the following: Given an input-free programP (i.e. all variables are initially 0) without nested loops using only instructions of the formx ← 1, x ← x + y, $$x \leftarrow x\dot - y$$ ,do x... end, doesP output 0? This problem has time complexity $$2^{2^{ {\mathinner{\mkern2mu\raise1pt\hbox{.}\mkern2mu \raise4pt\hbox{.}\mkern2mu\raise7pt\hbox{.}\mkern1mu}} ^2 } } $$ }cn-levels for some constantc. Other results are presented which show how the complexity of the 0-evaluation problem changes when the nonlooping instructions are varied. For example, it is shown that 0-evaluation is PSPACE-complete even for the case when the nonlooping instructions are onlyx ← x + 1,if x = 0then y ←y $$y \leftarrow y\dot - 1$$ .
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  • 29
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 29-45 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The main result of this paper is a separation result: there is a positive integerk such that for all well-behaving functionst(n), there is a language accepted by a nondeterministic (multi-tape) Turing machine in timet(n) which cannot be accepting by any deterministic (multitape) Turing machine in timeO(t(n)) and simultaneously spaceo((t(n)) 1/k ). This implies, for example that for any positive integer,l,l ≠k, there is a language accepted by an l time bounded NDTM which cannot be accepted by a DTM in time and spaceO(n l ) andO((logn) l ′) respectively for anyl′. Such a result is not provable by direct diagonalization because we do not have time to “simulate and do the opposite". We devise a different method for accomplishing the result: We first use an alternating Turing machine to speed up the simulation of a time and space bounded DTM and then argue that if our separation result did not hold, every NDTM can itself be simulated faster by another NDTM producing a contradiction to the standard hierarchy results. Some other applications of this method are also presented.
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  • 30
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 97-133 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract In this paper we consider the problem of uniform asymptotic stabilization of neutral delay differential systems by a suitable choice of linear feedback law, where the controller is static and at timet 0 has full knowledge ofx(t 0) ∈ ℝ n as well asx(t 0 − d) for finitely many delays present in the system. Using complex analysis in several variables in a Banach algebra context we present a solution to this problem in the form of a sufficient condition for the existence of such a stabilizing feedback gain. This condition is a weak form of (algebraic) reachability together with a condition, which we call resolvability, on the solution of an associated algebraic Riccati equation. In the case of commensurable delays our results apply to neutral systems having aD-operator which is stable in the sense of Cruz and Hale. In the non-commensurate case, our results hold for systems with aD-operator satisfying a stronger condition on the spectrum of the evolution equation, which we call formal stability. A graphical criterion, in the spirit of the multi-dimensional Nyquist theory, is presented for formal stability ofD. We find these results especially interesting in light of recent work [39] which shows that, for a special class of systems, formal stability is necessary for stabilization by a feedback gain of the type considered here. This, in fact, gives a counterexample [39] to the well known condition of Pandolfi [40]. Included among our results is an extension to the neutral case of the result in [11] which states that if the pointwise Kronecker indices are constant then the system is feedback equivalent to a delay-free system. As corollaries to this result we obtain some existing results [33] on canonical forms for time-delay systems, and, in addition, exhibit a large class of systems which are resolvable.
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  • 31
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 159-166 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Sufficient conditions that a two-dimensional system with output is locally observable are presented. Known results depend on time derivatives of the output and the inverse function theorem. In some cases, no information is provided by these theories, and one must study observability by other methods. We dualize the observability problem to the controllability problem, and apply the deep results of Hermes on local controllability to prove a theorem concerning local observability.
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  • 32
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 199-215 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A wordw is called recurrent with respect to a substitution if any descendant of it can regeneratew itself by iterations of the substitution. The set of recurrent words with respect to a regular (resp. context free) substitution is a regular (resp. context free) language. The set of recurrent words which are the descendants of a single fixed word with respect to a context free substitution is context free.
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  • 33
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 263-277 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract It is known that nondeterministic polynomial time truth-table reducibility is exactly the same as nondeterministic polynomial time Turing reducibility. Here we study the standard nondeterministic reducibilities (conjunctive, bounded truth-table, bounded positive truth-table, and many-one) and show that each is a restriction of nondeterministic polynomial time Turing reducibility corresponding to acceptance modulo a set of “oracle conditions.” Then we show that the reduction classes of these reducibilities are classes of formal languages and as such have language theoretic characterization theorems. The same program is carried out for polynomial space.
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  • 34
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 279-291 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This paper deals with algebraic power series over a commutative semiringA. A characteristization result states that a power series is algebraic if and only if it is the behavior of a proper pushdown automaton. To achieve this result some topological concepts are needed to be able to solve linear equations over semirings.
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  • 35
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 351-356 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract In this paper a question of the controllability of nonlinear systems is considered. On the basis of theorems due to Graves, a new sufficient condition for local controllability is established.
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  • 36
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 217-241 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Crossed product algebras are proposed as a framework for the study of input-output properties of linear time-varying systems. It is shown that internally stable systems with bounded continuous coefficients have transfer operators in a crossed product and conversely, that the set of all such transfer operators is dense in a crossed product. It is also shown that crossed product algebras admit causal additive decompositions, and allow a generalized frequency-domain representation.
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  • 37
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 243-261 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A new technique based on Kneser's theorem is introduced, to extend the topological method of Ważewski for Caratheodory systems. In this line an existence theorem for a general boundary value problem is obtained as an application, as well as some asymptotic properties for semi-linear systems.
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  • 38
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 293-318 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract In this paper we give necessary and sufficient conditions for a stationary finite Volterra series to have a linear (in the controls) analytic realization, which at the same time has a Hamiltonian structure. The result generalizes that for linear systems, where the condition is that the impulse response should be an odd function, and is expressed as a particular symmetry condition on the Volterra kernals. The relation between this problem and that of the inverse problem in Newtonian mechanics is explored. The finiteness of the Volterra series implies a nilpotence condition on a certain Lie algebra defined by the realization. The additional requirement that the system be Hamiltonian adds further structure to the classical representation of a nilpotent Lie algebra by lower triangular matrices.
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  • 39
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 319-333 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract It is shown that for a nonlinear regulator to be structurally stable in its response to step reference and disturbance signals, it is both necessary and sufficient for the controller to be of feedback type and to incorporate integrating action in each error channel. These results constitute an extension to nonlinear systems of the well-known method of “integral control” used in the design of linear regulators; and as such they provide an additional instance of the Internal Model Principle of control theory.
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  • 40
    Digitale Medien
    Digitale Medien
    Springer
    Theory of computing systems 17 (1984), S. 335-350 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This is the first of two papers concerned with the formulation of a continuous-time quantum-mechanical filter. Efforts focus on a quantum system with Hamiltonian of the formH 0+u(t)H 1, whereH 0 is the Hamiltonian of the undisturbed system,H 1 is a system observable which couples to an external classical field, andu(t) represents the time-varying signal impressed by this field. An important problem is to determine when and how the signalu(t) can be extracted from the time-development of the measured value of a suitable system observableC (invertibility problem). There exist certain quasiclassical observables such that the expected value and the measured value can be made to coincide. These are called quantum nondemolition observables. The invertibility problem is posed and solved for such observables. Since the physical quantum-mechanical system must be modelled as aninfinite-dimensional bilinear system, the domain issue for the operatorsH 0,H 1, andC becomes nontrivial. This technical matter is dealt with by invoking the concept of an analytic domain. An additional complication is that the output observableC is in general time-dependent.
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  • 41
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    Theory of computing systems 9 (1975), S. 132-141 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract When properly viewed, the transition rule of a cellular automaton becomes a mapF from a set to itself. The set may be made a probability space. Sufficient conditions are given to ensure thatF be measure-preserving and ergodic. Some geometric consequences of ergodicity are noted.
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  • 42
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    Theory of computing systems 9 (1975), S. 198-231 
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    Thema: Informatik
    Notizen: Abstract The top-down and bottom-up tree transducer are incomparable with respect to their transformation power. The difference between them is mainly caused by the different order in which they use the facilities of copying and nondeterminism. One can however define certain simple tree transformations, independent of the top-down/bottom-up distinction, such that each tree transformation, top-down or bottom-up, can be decomposed into a number of these simple transformations. This decomposition result is used to give simple proofs of composition results concerning bottom-up tree transformations. A new tree transformation model is introduced which generalizes both the top-down and the bottom-up tree transducer.
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  • 43
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    Theory of computing systems 9 (1975), S. 289-297 
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    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Several results concerning local contractions on uniform spaces are obtained and applied to yield some theorems on fixed and periodic points for local contractions on probabilistic metric spaces.
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  • 44
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    Theory of computing systems 9 (1975), S. 46-50 
    ISSN: 1433-0490
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    Thema: Informatik
    Notizen: Abstract LetG denote an infinite,σ-compact, locally compact topological group. In this paper a construction is given for a topological transformation groupH G with the Hilbert spaceL 2 (G × G) as a phase space such that any topological transformation group (G, X, π) can be embedded inH G , providedX is a separable metrizable space andπ is a bounded action. The class of such topological transformation groups contains all actions ofG on separable, metrizable, locally compact spaces.
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  • 45
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    Theory of computing systems 9 (1975), S. 83-94 
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    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
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  • 46
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    Theory of computing systems 9 (1975), S. 117-131 
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    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
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  • 47
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    Theory of computing systems 9 (1975), S. 159-189 
    ISSN: 1433-0490
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    Thema: Informatik
    Notizen: Abstract O. Hájek proved in his book “Dynamical Systems in the Plane” (Chapter III) that there isat most one abstract local dynamical system which is locally equivalent to, or equivalently an extension of, a given elementary dynamical system, and suggested a question of finding reasonable conditions on the latter for the existence ofat least one such abstract local dynamical system. An elementary dynamical systemμ is said to satisfy the “No-Intersection Axiom” and is called an abstract germ ifμ(x 1, t) = μ(x 2,t) impliesx 1 =x 2. We show thatμ is (uniquely) extendable to an abstract local dynamical system if and only ifμ is an abstract germ, and hence the question is completely answered. After introducing various kinds of isomorphisms of abstract germs and abstract local dynamical systems corresponding to those of continuous germs and continuous local dynamical systems, we obtain some sufficient conditions for extendability of isomorphisms and possibility of restriction of them, and thus establish the local determinacy of abstract local dynamical systems up to isomorphisms in some wider categories.
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  • 48
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    Theory of computing systems 10 (1976), S. 33-52 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The complexity of predicates on several classes of formal languages is studied. For finite automata, pushdown automata, and several classes of stack automata, every nontrivial predicate on the languages accepted by the 1-way devices requires as much time and space as the recognition problem for any language accepted by the corresponding 2-way devices. Moreover there are nontrivial predicates on the languages accepted by the 1-way devices such that is the accepted language of some corresponding one or two head 2-way device. Thus our lower bounds are fairly tight.
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  • 49
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    Theory of computing systems 10 (1976), S. 53-67 
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    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A class of infinite dimensional linear systems over the binary field is introduced. Necessary and sufficient conditions for realizability by such systems are obtained. In particular, their input/output relations can be described by certain regular sets. An algebraic method is introduced to compute the generating functions of an example. Also bounds are placed on the complexity of the formal languages which can be recognised by these systems.
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  • 50
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    Theory of computing systems 10 (1976), S. 85-90 
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    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A new idea of perturbing Lyapunov functions is presented which permits one to discuss nonuniform properties of solutions of differential equations under weaker assumptions
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  • 51
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    Theory of computing systems 10 (1976), S. 69-75 
    ISSN: 1433-0490
    Schlagwort(e): nonlinear stochastic integral equation ; stochastic Hammerstein equation ; random solution ; almost surely continuous processes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A nonlinear stochastic integral equation of the Hammerstein type in the formx(t; ω) = h(t, x(t; ω)) + ∫ s k(t, s; ω)f(s, x(s; ω); ω)dμ(s) is studied wheret ∈ S, a measure space with certain properties,ω ∈ Ω, the supporting set of a probability measure space (Ω,A, P), and the integral is a Bochner integral. A random solution of the equation is defined to be an almost surely continuousm-dimensional vector-valued stochastic process onS which is bounded with probability one for eacht ∈ S and which satisfies the equation almost surely. Several theorems are proved which give conditions such that a unique random solution exists.
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  • 52
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    Theory of computing systems 10 (1976), S. 97-97 
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    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
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  • 53
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    Theory of computing systems 10 (1976), S. 91-96 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Dushnik and Miller defined the dimension of a partially ordered setX, DimX, as the minimum number of linear extensions ofX whose intersection is the partial ordering onX. The concept of dimension for a partially ordered set has applications to preference structures and the theory of measurement. Hiraguchi proved that DimX ≤ [|X|/2] when |X| ≥ 4. Bogart, Trotter, and Kimble gave a forbidden subposet characterization of Hiraguchi's inequality by constructing for eachn ≥ 2 the minimum collectionℬ n of posets such that if [|X|/2] =n ≥ 2, then DimX 〈 n unlessX contains one of the posets inℬ n . Recently Trotter gave a simple proof of Hiraguchi's inequality based on the following theorem. IfA is an antichain ofX and |X − A| =n ≥ 2, then DimX ≤ n. In this paper we give a forbidden subposet characterization of this last inequality.
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  • 54
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    Theory of computing systems 10 (1976), S. 99-127 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We present a data structure, based upon a hierarchically decomposed tree, which enables us to manipulate on-line a priority queue whose priorities are selected from the interval 1,⋯,n with a worst case processing time of $$\mathcal{O}$$ (log logn) per instruction. The structure can be used to obtain a mergeable heap whose time requirements are about as good. Full details are explained based upon an implementation of the structure in a PASCAL program contained in the paper.
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  • 55
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    Theory of computing systems 10 (1976), S. 169-180 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract In this paper we consider the system of bilinear forms which are defined by a product of two polynomials modulo a thirdP. We show that the number of multiplications depend on how the field of constants used in the algorithm splitsP. If $$P = \prod\nolimits_{i = 1}^k {P_i^{li} } $$ then 2 ·deg(P) − k multiplications are needed. (We assume thatP i is irreducible.)
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  • 56
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    Theory of computing systems 10 (1976), S. 129-167 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This paper explores the connections between two areas pioneered by Shannon: the transmission of information with a fidelity criterion, and the realization of Boolean functions by networks and formulae. We study three phenomena: 1. The effect of the relative number of O's and l's in a function's table on its complexity. 2. The effect of the number of unspecified entries in a partially specified function's table on its complexity. 3. The effect of the number of errors allowed in the realization of a function on its complexity. Our main result is a precise version of the following statement: The complexity of approximately realizing a partially specified Boolean function, in whose table a fractiond of the entries are unspecified and a fractionp of the specified entries are l'swith errors allowed in a fraction not more thane of the specified entries, is less by the factor (1 −d) [H(p) − H(e)] (whereH(z) = −z log2 z −(1 −z) log2 (1 −z) is the binary entropy function) than the complexity of exactly realizing an arbitrary fully specified Boolean function. We also give an intuitively appealing information-theoretic interpretation of the result.
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  • 57
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    Theory of computing systems 10 (1976), S. 181-191 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The problem of choosing a “best” program for a function presented by example is considered. General axioms for total complexity involving time and size measures are presented. For measures obeying the axioms, certain positive and negative results are obtained on the existence of effective algorithms for learning the best program.
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  • 58
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    Theory of computing systems 10 (1976), S. 193-210 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The inevitably poor utilization of storage by computed-access realizations of extendible rectangular arrays can be circumvented by storing such arrays by hashing. This paper studies the extent to which the same switch in storage strategy avoids the even worse utilization of storage by computed-access realizations of extendible ragged (i.e., nonrectangular) arrays. Unfortunately, the dramatic successes of the rectangular case do not carry over: any hashing scheme for extendible ragged arrays with storage demands very much smaller than those of computed-access realizations must suffer expected access time that is close to worst possible. On the other hand, one can obtain moderate savings in storage demands by hashing ragged arrays, together with sufferable access time. This last result issues from a general technique for trading increased access time for savings in storage. Even more striking savings are attainable if one restricts attention tofully-justified ragged arrays, whose raggedness is more regular than that of general ragged arrays. However, the overall impact of our results is that extendible ragged arrays do not succumb to the storage strategies that work efficiently on their rectangular counterparts.
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  • 59
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    Theory of computing systems 10 (1976), S. 229-237 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A languageL has theprefix property if for allx, y ∈ L, eitherx is a prefix ofy ory is a prefix ofx. It is shown that for certain classes of languages, if a language in the class has the prefix property, then it is a regular set. The results provide new distinctions between classes as well as new profs of previously known distinctions.
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  • 60
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    Theory of computing systems 10 (1976), S. 211-228 
    ISSN: 1433-0490
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    Thema: Informatik
    Notizen: Abstract We considered some of the important unsolved problems in the theory of computation concerning the relationship between deterministic and nondeterministic computations, and between tape and time bounded computations. For each such problem we find an equivalent problem concerning two-way deterministic pushdown automaton languages.
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  • 61
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    Theory of computing systems 10 (1976), S. 239-251 
    ISSN: 1433-0490
    Schlagwort(e): Pebble game ; Register allocation ; Space bounds ; Turing machines
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We study a one-person game played by placing pebbles, according to certain rules, on the vertices of a directed graph. In [3] it was shown that for each graph withn vertices and maximum in-degreed, there is a pebbling strategy which requires at mostc(d) n/logn pebbles. Here we show that this bound is tight to within a constant factor. We also analyze a variety of pebbling algorithms, including one which achieves the 0(n/logn) bound.
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  • 62
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    Theory of computing systems 10 (1976), S. 259-261 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract It is shown that a symbolic flow with infinite phase groupT is point transitive ifT is abelian.
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  • 63
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    Theory of computing systems 10 (1976), S. 253-258 
    ISSN: 1433-0490
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    Thema: Informatik
    Notizen: Abstract We prove that every strictly bounded language with a semilinear Parikh mapping is an EDTOL language, and use the main proofargument to establish that all finite intersections of bounded context-free languages, and also the complements of these intersections, are EDTOL languages.
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  • 64
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    Theory of computing systems 10 (1976), S. 263-284 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract In the theory of finite dimensional linear systems, it is well known that every input-output map that can be realized by one such system can also be realized by a system which is “minimal”, i.e. both controllable and observable. Moreover, the minimal realization of a given map is unique up to isomorphism. It is shown here that similar results hold for the class of all systems whose state space is a real analytic manifold, whose dynamics is given by a family of complete real analytic vector fields, and whose output is an arbitrary real analytic function on the state space.
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  • 65
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    Theory of computing systems 10 (1976), S. 285-287 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We show that the set of pointsG on then-dimensional manifold, for which the set of attainability is open, is open itself and that ifx andy are points in the same connected component ofG then their sets of attainability,A(x) andA(y) are equal.
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  • 66
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    Theory of computing systems 10 (1976), S. 289-303 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Top-down tree transducers with regular look-ahead are introduced. It is shown how these can be decomposed and composed, and how this leads to closure properties of surface sets and tree transformation languages. Particular attention is paid to deterministic tree transducers.
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    Theory of computing systems 10 (1976), S. 305-321 
    ISSN: 1433-0490
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    Thema: Informatik
    Notizen: Abstract A procedure for comparing language operations is formulated and used to study some general algebraic properties of such operations as well as the interrelationships of some specific well known operations. The comparison scheme is used to partition the family of all language operations into a collection of equivalence classes that forms an upper semilattice, When full semi-AFL operations are used as a basis of comparison, the Min and Max operations are shown to be in the same class as relative complementation and reside above the class containing Kleene closure. This gives the result that any complementation closed full semi-AFL is a full AFL closed under Min and Max.
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    Theory of computing systems 10 (1976), S. 337-343 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The rudimentary relations, defined by Smullyan (1961), are known to contain the contextfree languages. It is shown here that the one-way stack languages and their complements are also rudimentary.
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  • 69
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    Theory of computing systems 10 (1976), S. 323-336 
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    Thema: Informatik
    Notizen: Abstract A property of the truth table of a symmetric Boolean function is given from which one can infer a lower bound on the minimal number of 2-ary Boolean operations that are necessary to compute the function. For certain functions ofn arguments, lower bounds between roughly 2n and 5n/2 can be obtained. In particular, for eachm ≥ 3, a lower bound of 5n/2 −O(1) is established for the function ofn arguments that assumes the value 1 iff the number of arguments equal to 1 is a multiple ofm. Fixingm = 4, this lower bound is the best possible to within an additive constant.
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    Theory of computing systems 10 (1976), S. 345-361 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Homomorphic simplification is one way of defining valid simplication of deterministic models. To allow the use of similar techniques for probabilistic systems, we introduce the concept of an ergodic machine. An ergodic machine is a specification for a deterministic system and it represents and associated probabilistic system when viewed properly. The probabilistic features arise by using an ergodic transformation on a “hidden” partial state space. An ergodic transformation can be thought of as an ideal random number generator. In this paper, we develop the concepts of ergodic machines necessary for faithfully representing probabilistic systems and make connections to markov chains and pseudo random number generators.
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    Theory of computing systems 10 (1976), S. 387-400 
    ISSN: 1433-0490
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    Thema: Informatik
    Notizen: Abstract The transition ruleF of a cellular automaton may sometimes be regarded as a “rule of growth” of a crystal from a “seed”ω. A study is made of the iteratesω,Fω,F 2 ω⋯.For certain one-dimensional growth rules, the limiting “shapes” of the crystals are computed, and an asymptotic formula for the size of the crystal as a function of time is obtained.
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    Theory of computing systems 10 (1976), S. 363-385 
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    Thema: Informatik
    Notizen: Abstract In this paper we study real linear dynamical systems $$\dot x = Fx + Gu,y = Hx,x \in R^n $$ = state space,u ∈ R m = input space,y ∈ R p = output space, under the equivalence relation induced by base change in state space; or in other words we study triples of matrices with real coefficients (F, G, H) of sizesn × n, n × m, p × n respectively, under the action(F, G, H.) →(TFT −1,TG, HT −1) ofGL n (R), the group of invertible realn × n matrices. One of the central questions studied is: “do there exist continuous canonical forms for this equivalence relation?”. After various trivial obstructions to the existence of such forms have been removed the answer is very roughly: no ifm ≥ 2, p ≥ 2, yes ifm = 1, orp = 1. For a precise statement cf. theorem 1.7. Existence or nonexistence of continuous canonical forms is related to the existence of a universal family of real linear dynamical systems. More precisely continuous canonical forms exist if such a universal family exists and if the underlying vector bundle of this family is the trivial vector bundle. In the case studied we show that a universal family in the appropriate sense does exist. The methods used are purely (differential) topological and in particular do not involve any algebraic geometry. There is a corresponding algebraic theory over any fieldk instead ofR which is the subject of part III of this series of papers.
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  • 73
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    Theory of computing systems 11 (1977), S. 1-8 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Stimulated by the work of Hartmanis and Berman [5], we study the question of the existence of a tally languageL inNP such thatL is inP if and only ifP = NP. The method used is applicable to questions regarding the comparison of a wide range of pairs of classes of formal languages specified by machines whose computational resources are bounded in time or space.
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    Theory of computing systems 11 (1977), S. 77-84 
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    Thema: Informatik
    Notizen: Abstract A fixed point theorem for random nonlinear contraction mappings is proven. The random nonlinear contraction principle is then used to study the existence and uniqueness of solutions for a class of random nonlinear integral equations.
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    Theory of computing systems 11 (1977), S. 9-28 
    ISSN: 1433-0490
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    Thema: Informatik
    Notizen: Abstract A context-free language is said to be simple if it is accepted by a single-state deterministic pushdown store acceptor that operates in real-time and accepts by empty store. While the problem remains open of deciding whether or not the language accepted by a deterministic pushdown store acceptor is simple, it is shown that this problem is equivalent to another problem in schemata theory. This question is that of determining whether or not a monadic recursion scheme has a strongly equivalent free scheme.
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    Theory of computing systems 11 (1977), S. 29-46 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Most of the operations of interest in language theory arecontinuous in a certain technical sense. For such operations, there always exist infinite sets of languages that areindependent in the sense that no language in such a set can be generated from the other languages in the set by the operations in question.
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    Theory of computing systems 11 (1977), S. 85-85 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
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  • 78
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    Theory of computing systems 11 (1977), S. 47-60 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Controlled partition grammars (CPGs) were designed to apply to certain needs of linguists. General CPGs generate exactly all context-sensitive languages. CPGs have two parameters:size andindex. The partition index of CPGs can be bounded by two, while CPGs with partition index one generate exactly the class of context-free languages. The size (of the partition blocks) of CPGs can be bounded by two, while CPGs of size one generate a class of languages properly contained in the class of contextsensitive languages. If one can eliminate recursive productions of the formA→B in a CPG then deterministic and nondeterministic lba's are equivalent.
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  • 79
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    Theory of computing systems 11 (1977), S. 87-109 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The realtime one-state deterministic pushdown automata with jumps define the family of deterministic languages. A simplified regularity test for deterministic languages can be derived from this fact.
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  • 80
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    Theory of computing systems 11 (1977), S. 111-146 
    ISSN: 1433-0490
    Schlagwort(e): palindrome ; real-time ; Turing machine ; language recognition ; repetition ; reversal ; string-matching ; pattern-matching ; periodicity ; predictability condition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Real-time multitape Turing machine algorithms are presented for recognizing the languages {wxyxz∈Σ*:|w|=r|x,|z| =t|x|} and {wxyx R z ∈Σ*:|w|=r|x,|z| =t|x|} for fixedr, s, andt and for string-matching with “forced mismatches.”
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  • 81
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    Theory of computing systems 11 (1977), S. 147-155 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Define a cylinder to be a family of languages which is closed under inverse homomorphisms and intersection with regular sets. A number of well-known families of languages are cylinders: —CFL, the family of context-free languages, is a principal cylinder, i.e. the smallest cylinder containing a languageL O described in [6]. —the family of deterministic context-free languages is proved to be a nonprincipal cylinder in [7]. —the family of unambiguous context-free languages is a cylinder: to prove that it is not principal seems to be a very hard problem. In this paper we prove that Lin, the family of linear context-free languages, is a nonprincipal cylinder. This is achieved in the standard way by exhibiting a sequence of languages Sn, n∈N, such that Lin is the union of all the principal cylinders generated by these languages and is not the union of any finite number of these cylinders. This leaves open the problem raised by Sheila Greibach of whether there exists a languageL such that every linear context-free language is the image ofL in some inverse gsm mapping.
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  • 82
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    Theory of computing systems 12 (1978), S. 59-72 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Doubly-indexed dynamical systems provide a state space realization of two-dimensional filters which includes previous state models. Algebraic criteria for testing structural properties (reachability, observability, internal stability) are introduced.
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  • 83
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    Theory of computing systems 12 (1978), S. 133-149 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A realization problem for a class of linear hereditary systems is formulated and “state space” representations are constructed from inputoutput relations. The resulting hereditary models are shown to be Euclidean controllable, and comparisons are made between these hereditary realizations and other recently developed theories.
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  • 84
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    Theory of computing systems 12 (1978), S. 205-211 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We show the existence of a single interpretation for which no flowchart produces the same results as a particular recursion scheme.
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  • 85
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    Theory of computing systems 12 (1978), S. 151-173 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A data space is a mathematical model for virtual machines as they arise in programming. It consists of a set of objects (states), a set of descriptors, and a control. In this general framework, formal definitions of both fixed-depth and variable-depth indirect addressing are developed. The former definition serves as a model for simple hardware spaces, whereas the latter has applications in the realm of higher-level programming.
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  • 86
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    Theory of computing systems 12 (1978), S. 233-252 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Strict interpretations of grammar forms are studied with respect to parsing, ambiguity, and decidability for intersection and containment. In particular, a parsing procedure for an arbitrary strict interpretation grammar is given which is based on a given parsing method for the master grammar. Time and space bounds on the new procedure are then obtained. Each ambiguous interpretation grammar of an unambiguous grammar form can be converted to an equivalent unambiguous interpretation of the same grammar form. Unambiguity is always decidable for strict interpretation grammars of unambiguous grammar forms. Also, for languages obtained from “compatible” strict interpretations of an unambiguous grammar form, the following problems are solvable: empty intersection, finite intersection, containment, and equality.
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  • 87
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    Theory of computing systems 12 (1978), S. 271-279 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Given a Hilbert spaceH, letH 1 andH 2 be two arbitrary subspaces. The problem of finding all minimal splitting subspaces ofH with respect toH 1 andH 2 is solved. This result is applied to the stochastic realization problem. Each minimal stochastic realization of a given vector processy defines a family of state spaces. It is shown that these families are precisely those families of minimal splitting subspaces (with respect to the past and the future ofy) which satisfy a certain growth condition.
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  • 88
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    Theory of computing systems 12 (1978), S. 297-324 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A grammar formF defines via a so-calledinterpretation mechanism, a family of languages (F). In this paper we establish that for many grammar formsF, (the family of context-free languages) implies (F)= RE (the family of recursively enumerable sets). We conjecture that this is also true in general. Because of this, it seems necessary to use restricted interpretations for non context-free grammar forms, a form giving then rise to a family We compare the obvious alternatives for restricting interpretations and focus attention on two promising alternatives, Q (F) and st(F) and their combination Q, st(F). Using st-interpretations, surprising families can be generated and strong normal form results can be obtained. Closure results and decidability results are also given. UnderQ, st-interpretation, it is possible to characterize a number of well-known families of languages between CF and RE, including the families of EOL, ETOL, matrix and scattered context languages.
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  • 89
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    Theory of computing systems 12 (1978), S. 371-393 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A universal input is an inputu with the property that, whenever two states give rise to a different output for some input, then they give rise to a different output foru. For an observable system,u is universal if the initial state can be reconstructed from the knowledge of the output foru. It is shown that, for continuous-time analytic systems, analytic universal inputs exist, and that, in the class ofC ∞ inputs, universality is a generic property. Stronger results are proved for polynomial systems.
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  • 90
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    Theory of computing systems 12 (1978), S. 361-370 
    ISSN: 1433-0490
    Schlagwort(e): Nonlinear systems ; controllability ; reachable set ; vector bundle
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Consider the nonlinear system $$\dot x(t) = f(x(t)) + \sum\limits_{i = 1}^m {u_i (t)g_i (x(t)), x(0) = x_0 \in M}$$ whereM is aC ∞ realn-dimensional manifold,f, g 1,⋯.,g m areC ∞ vector fields onM, andu 1 ,..,u m are real-valued controls. Ifm=n−1 andf, g 1 ,⋯,g m are linearly independent, then the system is called a hypersurface system, and necessary and sufficient conditions for controllability are known. For a generalm, 1 ≤m ≤n−1, and arbitraryC ∞ vector fields,f, g 1 ,⋯,g m , assume that the Lie algebra generated byf, g 1 ,⋯,g m and by taking successive Lie brackets of these vector fields is a vector bundle with constant fiber (vector space) dimensionp onM. By Chow's Theorem there exists a maximalC ∞ realp-dimensional submanifoldS ofM containingx 0 with the generated bundle as its tangent bundle. It is known that the reachable set fromx 0 must contain an open set inS. The largest open subsetU ofS which is reachable fromx 0 is called the region of reachability fromx 0. IfO is an open subset ofS which is reachable fromx 0,S we find necessary conditions and sufficient conditions on the boundary ofO inS so thatO = U. Best results are obtained when it is assumed that the Lie algebra generated byg 1,⋯,g m and their Lie brackets is a vector bundle onM.
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  • 91
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    Theory of computing systems 13 (1979), S. 1-27 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This paper presents a formulation, within the framework of initial algebra semantics, of Knuthian semantic systems (K-systems) which contain both synthesized and inherited attributes. The approach is based on viewing the semantics of a derivation tree of a context-free grammar as a set of values, called an attribute valuation, assigned to the attributes of all its nodes. Any tree's attribute valuation which is consistent with the semantic rules of the K-system may be chosen as the semantics of that derivation tree. The set of attribute valuations of a given tree is organized as a complete partially ordered set such that the semantic rules define a continuous transformation on this set. The least fixpoint of this transformation is chosen as the semantics of a given derivation tree. The mapping from derivation trees to their least fixpoint semantics is a homomorphism between certain algebras. Thus, the semantics of a K-system is an application of the Initial Algebra Semantics Principle of Goguen and Thatcher. This formulation permits a precise definition of K-systems, and generalizes Knuth's original formulation by defining the meaning of recursive (circular) semantic specifications. The algebraic formulation of K-systems is applied to proving the equivalence of K-systems having the same underlying grammar. Such proofs may require verifying that a K-system possesses certain properties and to this end, a principle of structural induction on many-sorted algebras is formulated, justified, and applied.
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  • 92
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    Theory of computing systems 13 (1979), S. 55-65 
    ISSN: 1433-0490
    Schlagwort(e): p-selective sets ; tally languages ; polynomial time reducibility
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The notion ofp-selective sets, and tally languages, are used to study polynomial time reducibilities onNP. P-selectivity has the property that a setA belongs to the classP if and only if bothĀ ≤ m p A andA isp-selective. We prove that for every tally language set inNP there exists a polynomial time equivalent set inNP that isp-selective. From this result it follows that if NEXT ≠ DEXT, then polynomial time Turing and many-one reducibilities differ onNP.
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  • 93
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    Theory of computing systems 13 (1979), S. 95-104 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This paper concerns a constructive adaptation of the classical Borel-Cantelli lemma which allows us to solve such decomposition problems as: when does there exist an infinite object that is decomposable into infinitely many parts that are maximally complex? A constructive proof is supplied of the key theorem and its degree is characterized. For completeness a classical (i.e., nonconstructive) proof is also provided.
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  • 94
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    Theory of computing systems 13 (1979), S. 181-186 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We show the undecidability of the universe problem for two restricted classes of nondeterministic one-counter machines. These classes are among the simplest known for which the universe problem can be shown unsolvable.
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  • 95
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    Theory of computing systems 13 (1979), S. 105-130 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Adata encoding is a formal counterpart of the “translation of a logical data structure into a physical storage structure". In this paper, both kinds of structures are represented by graphs; and an encoding is a type of embedding of the guest (logical structure) graph in the host (physical structure) graph. Thecost of an encoding is the average amount that the edges of the guest graph are stretched as they are replaced by paths in the host graph via the encoding; this “average” is weighted by an assignment of probabilities to the edges of the guest graph (called ausage pattern) that weights the edges according to their anticipated frequencies of traversals. This paper continues the study begun in [13] of encodings of data structures in the leaves of complete trees. The major thrust of the paper is to show that tree-hosts do not accommodate tree-like guests as congenially as they do array-like guests. Specifically, we study two encodings of tree-guests in tree-hosts, and three usage patterns for the guests. One of these usage patterns can be accommodated with cost independent of the size of the guest by one of the encodings but not by the other; the second usage pattern engenders the complementary situation; and the third usage pattern resists size-independent cost not only on the part of the two encodings studied here but also on the part ofany encoding of trees into trees. We do, however, find a third encoding of trees in trees whose cost relative to this intransigent usage pattern is exponentially smaller than the costs of our two encodings and is, in fact, optimal in rate of growth. Motivated by the demonstrated weaknesses of trees as hosts in data encodings, we introduce a new tree-like storage structure called adree; and we show that drees are quite congenial hosts for array-like and tree-like (and dree-like) guests. Throughout the paper, demonstrations of size-independence in the costs of encodings are accompanied by proofs of the (asympotic) near-optimality of the attained costs.
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  • 96
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    Theory of computing systems 13 (1979), S. 219-236 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We extend to non deterministic recursive program schemes the methods and results which permit definition of the semantics of such schemes in the deterministic case. Under natural hypothesis the set of finite and infinite trees generated by a scheme is proved to be the greatest fixed point of the functional mapping usually attached to this scheme.
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  • 97
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    Theory of computing systems 13 (1979), S. 255-273 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This paper places the work of H. Walter on classification of grammars and languages via topology in a more general framework and provides short proofs of his main results. Also, it is proved that every grammar is topologically equivalent to one in normal form, that the discrete topology can be realized on every context-free language, and that a language is finite if and only if every topology on it can be realized as one of the topologies proposed by Walter. In addition, a new and straightforward approach is provided to yield the necessary background results, on divisibility and cancellation in categories of derivations, due to D. Benson and G. Hotz.
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  • 98
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    Theory of computing systems 13 (1979), S. 283-299 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We consider relativizing the constructions of Cook in [4] characterizing space-bounded auxiliary pushdown automata in terms of timebounded computers. LetS(n) ≥ logn be a measurable space bound. LetDT A[NTA] be the class of setsS such that there exists a machineM such thatM with oracleA recognizes the setS andM is a deterministic [nondeterministic] oracle Turing machine acceptor that runs in time 2 cS(n) for some constantc. LetDB i A [NB i A ] be the class of setsS such that there exists a machineM such thatM with oracleA recognizes the setS andM is a deterministic [non-deterministic] oracle Turing machine acceptor with auxiliary pushdown that runs in spaceS(n) and never queries the oracle about strings longer than:S(n) ifi = 1, 2 cS(n) for some constantc, ifi = 2, + ∞ ifi = 3. Then we prove the following results: These contrast with Cook's (unrelativized) result:DT = NB = DB.
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  • 99
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    Theory of computing systems 13 (1979), S. 301-322 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The problem of minimizing the depth of formulas by equivalence preserving transformations is formalized in a general algebraic setting. For a particular algebraic system ∑0 specific methods of a dynamic programming nature are developed for proving lower bounds on depth. Such lower bounds for ∑0 automatically imply the same results for the systems of (i) arithmetic computations with addition and multiplication only, and (ii) computations over finite languages using union and concatenation. The specific lower bounds obtained are (i) depth 2n−o(n) for the permanent, (ii) depth (0.25+o(1))log2 n for the symmetric polynomials and (iii) depth 1.16logn for a problem of formula sizen.
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    Theory of computing systems 13 (1979), S. 361-376 
    ISSN: 1433-0490
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract LetM be a connected real-analytic 2-dimensional manifold. Consider the system $$\dot x(t) = f(x(t)) + u(t)g(x(t)),x(0) = x_0 \in M,$$ (t) = f(x(t)) + u(t)g(x(t)),x(0) =x 0 ∈ M, wheref andg are real-analytic vector fields onM which are linearly independent at some point ofM, andu is a real-valued control. Sufficient conditions on the vector fieldsf andg are given so that the system is controllable fromx 0. Suppose that every nontrivial integral curve ofg has a pointp wheref andg are linearly dependent,g(p) is nonzero, and that the Lie bracket [f,g] andg are linearly independent atp. Then the system is controllable (with the possible exception of a closed, nowhere dense set which is not reachable) from any pointx 0 such that the vector space dimension of the Lie algebraL A generated byf,g and successive Lie brackets is 2 atx 0.
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