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15
The power of team exploration: Two robots can learn unlabeled directed graphs
 In Proceedings of the Thirty Fifth Annual Symposium on Foundations of Computer Science
, 1994
"... We show that two cooperating robots can learn exactly any stronglyconnected directed graph with n indistinguishable nodes in expected tame polynomial in n. We introduce a new type of homing sequence for two robots which helps the robots recognize certain previouslyseen nodes. We then present an ..."
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Cited by 68 (5 self)
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We show that two cooperating robots can learn exactly any stronglyconnected directed graph with n indistinguishable nodes in expected tame polynomial in n. We introduce a new type of homing sequence for two robots which helps the robots recognize certain previouslyseen nodes. We then present an algorithm in which the robots learn the graph and the homing sequence simultaneously by wandering actively through the graph. Unlike most previous learning results usang homing sequences, our algorithm does not require a teacher to provide counterexamples. Furthermore, the algorithm can use efficiently any additional information available that distinguishes nodes. We also present an algorithm in which the robots learn by taking random walks. The rate at which a random walk converges to the stationary distribution is characterized by the conductance of the graph. Our randomwalk algorithm learns in expected time polynomial in n and in the inverse of the conductance and is more eficient than the homingsequence algorithm for highconductance graphs. 1
Characterizing Diagnoses
, 1988
"... Most approaches to modelbased diagnosis describe a diagnosis for a system as a set of failing components that explains the symptoms. In order to characterize the typically very large number of diagnoses, usually only the minimal such sets of failing components are represented. This method of charac ..."
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Cited by 38 (4 self)
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Most approaches to modelbased diagnosis describe a diagnosis for a system as a set of failing components that explains the symptoms. In order to characterize the typically very large number of diagnoses, usually only the minimal such sets of failing components are represented. This method of characterizing all diagnoses is inadequate in general, in part because not every superset of the faulty components of a diagnosis necessarily provides a diagnosis. In this paper we analyze the notion of diagnosis in depth exploiting the notions of implicate/implicant and prime implicate/implicant. We use these notions to propose two alternative approaches for addressing the inadequacy of the concept of minimal diagnosis. First, we propose a new concept, that of kernel diagnosis, which is free of the problems of minimal diagnosis. Second, we propose to restrict the axioms used to describe the system to ensure that the concept of minimal diagnosis is adequate.
On detecting global predicates in distributed computations
 In Proceedings of the 21st IEEE International Conference on Distributed Computing Systems (ICDCS
, 2001
"... Monitoring of global predicates is a fundamental problem in asynchronous distributed systems. This problem arises in various contexts such as design, testing and debugging, and faulttolerance of distributed programs. In this paper, we establish that the problem of determining whether there exists a ..."
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Cited by 22 (11 self)
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Monitoring of global predicates is a fundamental problem in asynchronous distributed systems. This problem arises in various contexts such as design, testing and debugging, and faulttolerance of distributed programs. In this paper, we establish that the problem of determining whether there exists a consistent cut of a computation that satisfies a predicate in ¡CNF, ¡£¢¥ ¤ , in which no two clauses contain variables from the same process is NPcomplete in general. A polynomialtime algorithm to find the consistent cut, if it exists, that satisfies the predicate for special cases is provided. We also give algorithms albeit exponential that can be used to achieve an exponential reduction in time over existing techniques for solving the general version. Furthermore, we present an algorithm to determine whether there exists a consistent cut of a computation for which the ¦¨§�©�¦���©�������©�¦� � sum exactly equals some constant ¡, where each ¦� � is an integer variable on process �¨� such that it is incremented or decremented by at most one at each step. As a corollary, any symmetric global predicate on boolean variables such as absence of simple majority and exclusiveor of local predicates can now be detected. Additionally, the problem is proved to be NPcomplete if each ¦� � can be changed by an arbitrary amount at each step. Our results solve the previously open problems in predicate detection proposed in [7] and bridge the wide gap between the known tractability and intractability results that existed until now. 1.
Testing protocols modeled as FSMs with timing parameters
, 1999
"... An optimization method is introduced for generating minimumlength test sequences taking into account timing constraints for FSM models of communication protocols. Due to active timers in many of today's protocols, the number of consecutive selfloops that can be traversed in a given state before a ..."
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Cited by 12 (7 self)
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An optimization method is introduced for generating minimumlength test sequences taking into account timing constraints for FSM models of communication protocols. Due to active timers in many of today's protocols, the number of consecutive selfloops that can be traversed in a given state before a timeout occurs is limited. A test sequence that does not consider timing constraints will likely be unrealizable in a test laboratory, thereby potentially resulting in the incorrect failing Z. of valid implementations or, vice versa . The solution uses a series of augmentations for a protocol's directed graph representation. The resulting test sequence is proven to be of minimumlength while not exceeding the tolerable limit of consecutive selfloops at each state. Although UIO sequences are used for state verification method, the results also are applicable to test generation that uses distinguishing or characterizing sequences.
Design Error Diagnosis in Sequential Circuits
 Proc. Correct Hardware Design and Verification Methods, CHARME'95, Lecture
, 1995
"... . We present a new diagnostic algorithm for localising design errors in sequential circuits. The specification and the implementation may have different number of state variables, and different state encoding. The algorithm is based on the new concept of possible next states describing the possible ..."
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Cited by 11 (4 self)
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. We present a new diagnostic algorithm for localising design errors in sequential circuits. The specification and the implementation may have different number of state variables, and different state encoding. The algorithm is based on the new concept of possible next states describing the possible states of the circuit due to the existence of the error. Results obtained on benchmark circuits show that the error is always found, with an execution time proportional to the product of the circuit size, and the length of the test sequences used. 1 Introduction Although automated design tools are routinely used for digital circuits synthesis, manual changes are still being done to improve the performance, to obtain more compact structures, or to carry on small specification changes; doing so, the insertion of an unintentional error is very likely to happen. Another source of design errors is the presence of software bugs in the automated design and optimization tools. Therefore, formal ve...
The Forbidden Projections of Unate Functions
 Discrete Applied Mathematics
, 1997
"... We characterize the forbidden projections of unate Boolean functions. Forbidden projections are analogous to forbidden graph minors. Unate functions have been studied in switching theory and in computational learning theory. 1 Introduction A major topic in graph and matroid theory has been the chara ..."
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Cited by 8 (1 self)
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We characterize the forbidden projections of unate Boolean functions. Forbidden projections are analogous to forbidden graph minors. Unate functions have been studied in switching theory and in computational learning theory. 1 Introduction A major topic in graph and matroid theory has been the characterization of classes of graphs and matroids by forbidden minors (see, e.g., [9]). Analogously, it is possible to characterize some classes of Boolean functions by forbidden projections. A minor of a graph is formed by contraction and deletion of a subset of the edges in the graph. A projection of a Boolean function is formed by taking a subset of the input variables of the function and fixing each of them to either 0 or 1. Surprisingly, despite the interest in graph and matroid minors, there has been almost no work on forbidden projections. One exception is the work of Seymour [8], who has characterized certain classes of clutters by forbidden clutter minors. A clutter is a collection of s...
Compiling devices and processes
 Presented at 4th International Workshop on Qualitative Physics
, 1990
"... This paperpresents anewapproach for exploiting Truth Maintenance Systems(TMSs in which the inference engine can convey locality in its knowledge to the TMS. This approach is ideally suited for systems which reason about the physical world because much of knowledge is inherently local, i.e., the cons ..."
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Cited by 5 (0 self)
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This paperpresents anewapproach for exploiting Truth Maintenance Systems(TMSs in which the inference engine can convey locality in its knowledge to the TMS. This approach is ideally suited for systems which reason about the physical world because much of knowledge is inherently local, i.e., the constraints for a particular component or process usually only interact with constraints of physically adjacent components and processes. The new TMSs operate with a set of arbitrary propositional formulae and use general Boolean Constraint Propagation(BCP) to answer queries about whether a particular literal follows from the formulae. Our TMS exploits the observation that if propositional formulae are converted to their prime implicates, then BCP is both efficient and logically complete. This observation allows the problem solver to influence the degree of completeness oftheTMS by controllinghowmany prime implicates are constructed. This control is exerted by using the locality in the original task to guide which combinations of formulae should be reduced to their prime implicates. We show that conveying locality to the TMS is an important strategy for qualitative physics problem solvers. For example, at a minimum formulae corresponding to a single component (or commonly occurring combinations) model should be compiled into prime implicates in order to minimize runtime cost. When confluence models are used, the results of using ourTMS subsume those of the qualitative reasolution rule. This approach has been implemented and tested both within AssumptionBased Truth Maintenance Systems and LogicBased Truth Maintenance Systems. 1
Storage Optimization by Replacing Some FlipFlops with Latches
, 1996
"... Conventionally, when a synchronous sequential circuit is synthesized, storage units are implemented in either edgetriggered flipflops or levelsensitive latches, but not both, depending on the clocking scheme (one or twophase) used. We propose that, in the former case, some of the flipflops can ..."
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Cited by 3 (0 self)
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Conventionally, when a synchronous sequential circuit is synthesized, storage units are implemented in either edgetriggered flipflops or levelsensitive latches, but not both, depending on the clocking scheme (one or twophase) used. We propose that, in the former case, some of the flipflops can be replaced with latches. Since a latch is generally smaller, faster and less powerconsuming than a flipflop, this replacement leads to improvements in circuit area, performance and power consumption. Whether a flipflop can be replaced with a latch depends on not only its structural context but also its temporal behavior. In this paper, we first present conditions under which a straightforward replacement can be made; then, we propose two retimingbased transformations that increase the number of replaceable flipflops. We have implemented the proposed idea in a software called FF2Latch. Experimental results on a set of controldominated circuits from the highlevel synthesis benchmark set [1] show that a large number of the flipflops can be replaced with latches. Up to 22% reduction in the circuit area and up to 73% reduction in the power consumption have been achieved.
On Test Derivation from Partial Specifications
, 2000
"... The paper addresses the problem of test derivation from partially defined specifications. A specification is modeled by an Input/Output FSM such that transitions from some states on some inputs are not specified (a partial FSM). ..."
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Cited by 2 (1 self)
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The paper addresses the problem of test derivation from partially defined specifications. A specification is modeled by an Input/Output FSM such that transitions from some states on some inputs are not specified (a partial FSM).
The existence of synchronizing word and Cerny Conjecture for some finite automata
 Second Haifa Workshop on Graph Theory, Combinatorics and Algorithms
, 2002
"... Abstract The word of transition semigroup of an automaton is called synchronizing (recurrent, reset) if the word sent all states of the automaton on a unique state. We prove that the existence of sink state in the transition graph of deterministic complete automata is equivalent to existence of sync ..."
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Cited by 2 (0 self)
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Abstract The word of transition semigroup of an automaton is called synchronizing (recurrent, reset) if the word sent all states of the automaton on a unique state. We prove that the existence of sink state in the transition graph of deterministic complete automata is equivalent to existence of synchronizing word for automata accepting starfree languages, for locally testable, locally threshold testable and piecewise testable automata. An upper bound on the length of shortest synchronizing word is found for all considered automata. Some important properties of locally threshold testable automata are established.