design of decentralized critical observers for networks of finite state machines a formal method approach abstract motivated by safety critical applications in cyber physical systems in this paper we study the notion of critical observability and design of observers for networks of finite state machines fsms critical observability corresponds to the possibility of detecting if the current state of an fsm is in a given region of interest called set of critical states a critical observer detects on line the occurrence of critical states when a large scale network of fsms is considered the construction of such an observer is prohibitive because of the large computational effort needed we propose a decentralized architecture for critical observers of networks of fsms where on line detection of critical states is performed by local critical observers each associated with an fsm of the network which do not need to interact for the efficient design of decentralized critical observers we first extend on the fly algorithms traditionally used in the community of formal methods for the verification and control design of fsms we then extend to networks of fsms bisimulation theory traditionally given in the community of formal methods for single fsms the proposed techniques provide a remarkable computational complexity reduction as discussed throughout the paper and also demonstrated by means of illustrative examples

synthesis of inference based decentralized control for discrete event systems in our past work we presented a framework for the decentralized control of discrete event systems involving inferencing over ambiguities about the system state of various local decision makers using the knowledge of the self ambiguity and those of the others each local control decision is tagged with a certain ambiguity level level zero being the minimum and representing no ambiguity a global control decision is taken to be a winning local control decision i e one with a minimum ambiguity level for the existence of a decentralized supervisor so that for each controllable event the ambiguity levels of all winning disablement or enablement decisions are bounded by some number n such a supervisor is termed n inferring the notion of n inference observability was introduced when the given specification fails to satisfy the iv inference observability property an iv inferring supervisor achieving the entire specification does not exist we first show that the class of iv inference observable sublanguages is not closed under union implying that the supremal n inference observable sublanguage need not exist we next provide a technique for synthesizing an n inferring decentralized supervisor that achieves an n inference observable sublanguage of the specification the sublanguage achieved equals the specification language when the specification itself is iv inference observable a formula for the synthesized sublanguage is also presented for the special cases of n 0 and n 1 the proposed supervisor achieves the same language as those reported in 25 31 for n 0 and 32 for n 1 the synthesized supervisor is parameterized by n the parameter bounding the ambiguity level and as n is increased the supervisor becomes strictly more permissive in general thus a user can choose n based on the degree of permissiveness and the degree of computational complexity desired

modular strategies for recursive game graphs many problems in formal verification and program analysis can be formalized as computing winning strategies for two player games on graphs in this paper we focus on solving games in recursive game graphs which can model the control flow in sequential programs with recursive procedure calls while such games can be viewed as the pushdown games studied in the literature the natural notion of winning in our framework requires the strategies to be modular with only local memory that is resolution of choices within a module does not depend on the context in which the module is invoked but only on the history within the current invocation of the module while reachability in global pushdown games is known to be exptime complete we show reachability in modular games to be np complete we present a fixed point computation algorithm for solving modular games such that in the worst case the number of iterations is exponential in the total number of returned values from the modules if the strategy within a module does not depend on the global history but can remember the history of the past invocations of this module that is if memory is local but persistent we show that reachability becomes undecidable

polynomial time verification of diagnosability of partially observed discrete event systems the problem of verifying the properties of diagnosability and i diagnosability is considered we present new polynomial time algorithms for deciding diagnosability and i diagnosability these algorithms are based on the construction of a nondeterministic automaton called a verifier

edge based 3 d camera motion estimation with application to video coding two classes of algorithms for modeling camera motion in video sequences captured by a camera are proposed the first class can be applied when there is no camera translation and the motion of the camera can be adequately modeled by zoom pan and rotation parameters the second class is more general in that it can be applied when the camera is undergoing a translation motion as well as a rotation and zoom and pan this class uses seven parameters to describe the motion of the camera and requires the depth map to be known at the receiver the salient feature of both algorithms is that the camera motion is estimated using binary matching of the edges in successive frames the rate distortion characteristics of the algorithms are compared with that of the block matching algorithm and show that the former provide performance characteristics similar to those of the latter with reduced computational complexity

decentralized supervisory control with conditional decisions supervisor realization the strategy of decentralized supervisory control of discrete event systems using so called conditional decisions initiated in prior work is further investigated in this note specifically a constructive methodology for realizing supervisors that employ conditional decisions is developed this methodology is based on the construction of deterministic observers of nondeterministic automata that are built so as to track violations of c p and d a coobservability

relative observability and coobservability of timed discrete event systems we study supervisory control of timed discrete event systems tdes under partial observation and propose new observability concepts effective for supervisor synthesis first we consider monolithic centralized supervisory control and introduce timed relative observability and timed relative weak observability the former concept extends our previous work to the timed case while the latter exploits choices of forcible events to preempt the clock event tick we prove that timed relative respectively weak observability is stronger than timed respectively weak observability weaker than normality and closed under set union hence there exists the supremal relatively respectively weakly observable sublanguage of a given language

on solvability of a decentralized supervisory control problem with communication we study a decentralized control problem of discrete event systems with communication we first give a general automata theoretic formalism that enables us to handle various types of communication including delay the decentralized control problem is shown to be undecidable under this formalism next we propose a semi decision procedure for computing finite state controllers to achieve a given specification in the sense of bisimilarity between the controlled system and a given specification using this procedure we prove decidability of the problem for two special cases one is the case in which the communication behavior is given as k bounded delay communication and the other is the case in which any cycle in the state transition diagram of the system contains an event observable by all controllers we also show a method for optimizing controllers based on a graph problem

supervisory control of a class of discrete event processes this paper studies the control of a class of discrete event processes i e processes that are discrete asynchronous and possibly nondeter ministic the controlled process is described as the generator of a formal language while the controller or supervisor is constructed from the grammar of a specified target language that incorporates the desired closed loop system behavior the existence problem for a supervisor is reduced to finding the largest controllable language contained in a given legal language two examples are provided

centralized and decentralized supervisory control of nondeterministic systems under partial observation in this paper we extend our earlier work on supervisory control of nondeterministic systems using prioritized synchronization as the mechanism of control and trajectory model as the modeling formalism by considering design of supervisors under partial observation we introduce the notion of observation compatible systems and show that prioritized synchronous composition psc of observation compatible systems can be used as a mechanism of control of nondeterministic systems under partial observation in presence of driven events necessary and sufficient conditions that depend on the trajectory model as opposed to the language model of the plant are obtained for the existence of centralized as well as decentralized supervision our work on centralized control shows that the results of the traditional supervisory control can be extended to the above setting provided that the supervisor is deterministic and the observation mask is projection type on the other hand our work on decentralized control is based on a new relation between controllability observability co observability and psc that we derive in this paper

matching sets of 3d line segments with application to polygonal arc matching in this paper we consider two sets of corresponding 3d line segments of equal length we derive a closed form solution for the coordinate transform rotation and translation that gives the best match between the two sets best in the sense of a least squares distance measure between the sets we use these results as the basis to construct efficient algorithms for solving other problems in computer vision specifically we address the problem of matching polygonal arcs that is the problem of finding a match between a short arc and a piece of long arc

deciding co observability is pspace complete in this note we reduce the deterministic finite state automata intersection problem to the problem of deciding co observability for regular languages using a polynomial time many one mapping this demonstrates that the problem of deciding co observability for languages marked by deterministic finite state automata is pspace complete we use a similar reduction to reduce the deterministic finite state automata intersection problem to deciding other versions of co observability introduced in a previous paper these results imply that the co observability of regular languages most likely cannot be decided in polynomial time unless we make further restrictions on the languages these results also show that deciding decentralized supervisor existence is pspace complete and therefore probably intractable

characterization of co observable languages and formulas for their super sublanguages we present fixed point based characterization of several classes of co observable languages that are of interest in the context of decentralized supervisory control of discrete event systems including c p spl or d a co observable languages c p co observable languages and d a co observable languages we also provide formulas for computing super sublanguages for each of these classes in cases where the class of co observable languages is not closed under intersection union we provide upper lower bound of the super sublanguage formula we present the computation of super sublanguages and also computation of their upper lower bounds has lead to the introduction of other classes of co observable languages namely strongly c p co observable languages strongly d a co observable languages locally observable languages and strongly locally observable languages fixed point based characterization of all the above language classes is also given and their closure under intersection union is investigated we also study whether the fixed point operator preserves prefix closure relative closure also called l sub m g closure and controllability

complexity of infimal observable superlanguages the infimal prefix closed controllable and observable superlanguage plays an essential role in the relationship between controllability observability and co observability the central notions of supervisory control theory existing algorithms for its computation are exponential and it is not known whether a polynomial algorithm exists we answer the question by studying the state complexity of this language state complexity of a language is the number of states of its minimal deterministic finite automaton dfa for a language with state complexity n we show that the upper bound state complexity on the infimal prefix closed and observable superlanguage is 2 n 1 and that this bound is asymptotically tight hence there is no algorithm computing a dfa of the infimal prefix closed and observable superlanguage in polynomial time our construction shows that such a dfa can be computed in time o 2 n the construction involves nondeterministic finite automata nfas and a computation of the supremal prefix closed sublanguage we study the computation of supremal prefix closed sublanguages and show that there is no polynomial time algorithm computing an nfa of the supremal prefix closed sublanguage of a language given as an nfa even if the language is unary

characterizing intransitive noninterference for 3 domain security policies with observability this note introduces a new algorithmic approach to the problem of checking the property of intransitive noninterference ini using discrete event systems dess tools and concepts ini property is widely used in formal verification of security problems in computer systems and protocols the approach consists of two phases first a new property called ip observability observability based on a purge function is introduced to capture ini we prove that a system satisfies ini if and only if it is ip observable second a relation between ip observability and p observability observability as used in des is established by transforming the automaton modeling a system protocol into an automaton where p observability and hence ip observability can be determined this allows us to check ini by checking p observability which can be done efficiently our approach can be used for all systems protocols with three domains or levels which is sufficient for most noninterference problems for cryptographic protocols and systems

brief paper formulae relating controllability observability and co observability we present formulae relating controllability observability and co observability arising in the context of supervisory control of discrete event systems given a discrete event plant g with event set e uncontrollable event set e u i and observation mask m i of the ith supervisor we first show that the infimal prefix closed l g i e u i controllable and l g e u i m i co observable superlanguage equals the intersection taken over all i s of the infimal prefix closed l g e u i controllable and l g m i observable superlanguage next we show that the infimal prefix closed and e m observable superlanguage computation preserves e e u controllability these results can be used to compute individual supervisors in the decentralized control setting

decentralized state feedback control of discrete event systems abstract in this paper we consider decentralized state feedback control of discrete event systems with a global control specification given by a predicate in this framework instead of a global state feedback each local state feedback controls a part of the system according to local information so that global behaviors satisfy the global control specification we introduce the notion of n observability of predicates and present necessary and sufficient conditions for the existence of a decentralized state feedback which achieves the global control specification

relative observability of discrete event systems and its supremal sublanguages we identify a new observability concept called relative observability in supervisory control of discrete event systems under partial observation a fixed ambient language is given relative to which observability is tested relative observability is stronger than observability but enjoys the important property that it is preserved under set union hence there exists the supremal relatively observable sublanguage of a given language relative observability is weaker than normality and thus yields when combined with controllability a generally larger controlled behavior in particular no constraint is imposed that only observable controllable events may be disabled we design new algorithms which compute the supremal relatively observable and controllable sublanguage of a given language which is generally larger than the normal counterpart we demonstrate the new observability concept and algorithms with a guideway and an agv example

hierarchical generalized hough transforms and line segment based generalized hough transforms abstract generalized hough transforms are fast point pattern matching algorithms which have applications in image processing two extensions to generalized hough transforms are described the first allows for matching hierarchically organized point patterns an example concerning image registration using hierarchical point patterns is described the second extension concerns matching patterns of simple geometric objects such as line segments rather than patterns of points

undecidability in decentralized supervision abstract it is well known that supervisor synthesis problems involving partial observations generally have high computational complexity but was only recently shown in the preliminary version of this article that the solvability of decentralized supervisor synthesis problems may be undecidable even in cases where all pertinent languages are represented as finite automata the result is established by reduction from the halting problem for turing machines alternative proofs discovered independently by other authors employ a reduction from post s correspondence problem

decentralized control of discrete event systems with bounded or unbounded delay communication we introduce problems of decentralized control with delayed communication where delays are either unbounded or bounded by a given constant k in the k bounded delay model between the transmission of a message and its reception the plant can execute at most k events in the unbounded delay model the plant can execute any number of events between transmission and reception we show that our framework yields an infinite hierarchy of control problems where the containments are strict cc is the set of control problems solvable with a single controller centralized case and dcc sub k respectively dcuc dc is the set of problems solvable with two controllers in a k bounded delay network respectively in an unbounded delay network without communication the hierarchy is a result of the following property controllers which work in a given network will also work in a less nondeterministic network this property does not hold when nonblockingness is introduced checking the existence of controllers in the unbounded delay case or in the case without communication are undecidable problems however a related decentralized observation problem with bounded delay communication is decidable

pose determination from line to plane correspondences existence condition and closed form solutions a class of pose determination problems in which the sensory data are lines and the corresponding reference data are planes is discussed the lines considered are different from edge lines in that they are not the intersection of boundary faces of the object the author describes a polynomial approach that does not require a priori knowledge about the object location closed form solutions for orthogonal parallel and coplanar feature configurations of critical importance in real applications are derived findings concerning the necessary and sufficient conditions under which the line to plane pose determination problem can be solved are described

on deadlock free modular supervisory control of discrete event systems in this paper the problem of synthesizing deadlock free modular supervisors for discrete event systems is discussed by introducing the d invariant relation between a pair of supervisors it is shown that when the control objective is described in terms of intersection of two languages a necessary and sufficient condition for the modular supervisor to be deadlock free is that this pair of subsupervisors satisfies a d invariant relation a procedure for synthesizing the deadlock free modular supervisor is presented some issues concerning deadlock free modular supervisory control are also discussed

generalized differentiation and fixed points sets behaviors with respect to fisher convergence abstract we study the stability of a new concept of generalized differentiation for set valued mappings involving positively homogeneous maps with respect to a variational convergence deriving from the proximal topology this notion of convergence well suited for set valued mappings allows us as well to establish the continuous dependence of fixed points sets of set valued contractions

comments on polynomial time verification of decentralized diagnosability of discrete event systems versus decentralized failure diagnosis of discrete event systems complexity clarification an article on codiagnosability verification of discrete event systems was reported by moreira et al claiming an improvement in complexity over a paper by qiu and kumar this note clarifies an oversight in the complexity analysis of moreira et al s paper further the results of moreira et al s paper were obtained in a more restricted setting of projection masks in contrast to the more general non projection masks allowed in qiu and kumar s paper which was overlooked finally in the special case when the projection masks are used the complexity of qiu and kumar s paper is lower compared to the non projection masks case and equals the corrected complexity of moreira et al s paper

rigid motion and structure from several sets of parallel lines in a monocular image sequence abstract an image line is a very reliable feature in the feature based structure from motion sfm problem it has at least three advantages 1 it is not easily affected by occlusion 2 it can achieve subpixel accuracy 3 the correspondence problem is easier and less ambiguous although some generalized sfm algorithms using image line features have been recently developed they usually suffer from high error sensitivity and large matrix size besides in order to make their estimations more robust many line correspondences much more than the least requirement in theory are usually needed these shortages are not beneficial for practical use because many sets of parallel lines are frequently encountered in an artificial 3d environment and can be easily identified we try to utilize these identified parallel lines to simplify the generalized sfm problem and improve the performance of parameter estimation a fast and reliable algorithm is proposed in our paper both computer generated and real world images are tested and several satisfactory results have been obtained in addition its error sensitivity and data degeneracy will be discussed

maximal matching of 3 d points for multiple object motion estimation abstract determining the relative motion position between an observer and its environment is an important problem in computer vision a major task is to find corresponding object features in this paper an efficient algorithm for matching 3 d points of multiple rigid objects is presented the point matching algorithm determines the correspondence by initiating a pairing of a triplet of noncollinear sensed points with a triplet of reference points and searching for new pairs of corresponding points one at a time using local distance and angular constraints the pairing of each subsequent sensed point with a reference point is determined if the tetrahedron formed by the sensed point and the initial triplet is congruent to that formed by the corresponding reference points only simple computations are required in the algorithm global consistency of the pairings found by the algorithm is ensured without using model tests the algorithm can be easily extended to incorporate other geometrical or non geometrical object attributes to further prune the matching results of running the algorithm on synthetic and real data are given

a branch and bound approach for the design of decentralized supervisors in petri net models the paper addresses the design of compact and maximally permissive decentralized supervisors for petri nets based on generalized mutual exclusion constraints decentralization constraints are formulated with respect to the net transitions instructing each local supervisor to detect and disable transitions of its own control site only a solution is characterized in terms of the states it allows and its feasibility is assessed by means of two separate tests one checking the required behavioral properties e g liveness reversibility and controllability of the induced reachability subgraph and the other ensuring the existence of a decentralized supervisor enforcing exactly the considered set of allowed states the second test employs an integer linear programming formulation maximal permissivity is ensured by efficiently exploring the solution space using a branch and bound method that operates on the reachable states particular emphasis is posed on the obtainment of the controllability property both in the structural and the behavioral interpretation

supervisory control of discrete event systems with distinguishers this paper deals with two relevant aspects of the supervisory control problem scp of discrete event systems des the degree of difficulty faced when modeling specifications to be fulfilled by the system under control and the computational complexity of the synthesis procedure the presented approach consists in refining the set of events of a des model into a new set each refinement is properly chosen to identify a particular instance of the original event in the system which may simplify the modeling of specifications a map named distinguisher is then proposed to establish the relationship between strings of the original and refined alphabets it is initially shown that using a refined set of events to solve a scp directly leads to the optimal control solution yet without providing computational advantages in synthesis with respect to the nonrefined method then we propose the use of outer approximations for the refined des model as a way to reduce the cost of synthesis while preserving controllability least restrictiveness and nonblocking of the control solution two examples of manufacturing systems illustrate our results

the hierarchical lattices of a finite machine the concept of dynamical consistency is introduced to define a high level transition function for an arbitrary partition of the state space of a finite input state machine m the existence of a dynamically consistent transition from a partition member xi to a member xj corresponds to the existence for every state x in xi of some x dependent control sequence which takes that state directly into xj this paper analyses what are termed in block controllable partition machines and between block controllable partition machines and establishes the existence of the associated in block controllable hierarchical lattice ibcp m it is shown that any partition machine in ibcp m is between block controllable if and only if the base machine m is controllable this setting allows the specification of state to state control trajectories of m to be decomposed into high level and low level components

using the orientation of fragmentary 3d edge segments for polyhedral object recognition several constraints are developed which impose consistency between model edge and sensed edge fragment geometries in order to collapse the search space in matching 3d edge data to 3d edge models the constraints have been demonstrated on error prone synthetic edge data and on 3d edge data obtained by stereo processing an important feature of the constraints is their ability to attach sign labels to the sensed edge fragments during matching providing consistency of edge directions between the model and data this feature progressively increases the power of the constraints and assists in finding the transformation between model and sensor spaces

modular control of discrete event systems with coalgebra modular supervisory control of discrete event systems where the overall system is a synchronous parallel product of subsystems is considered the main results of this paper are formulations of sufficient conditions for the compatibility between the synchronous product and various operations stemming from supervisory control as supervised product and supremal controllable sublanguages these results are generalized to the case of modules with partial observations e g modular computation of supremal normal sublanguages is studied coalgebraic techniques based on the coinduction proof principle are used in our main results sufficient conditions are derived for modular to equal global control synthesis an algorithmic procedure for checking the new conditions is proposed and the computational benefit of the modular approach is discussed and illustrated by comparing the time complexity of modular and monolithic computation

the hierarchical control of st finite state machines this paper follows caines and wei 1995 where a new notion of state aggregation for finite machines was introduced via the concept of the dynamical consistency dc relation between the blocks of states in any given state space partition this formulation results in a definition of high level dynamics on the finite partition machine m whose states correspond to the given partition elements this paper treats the more general case of st systems where there is a preferred sense of flow from a set of source states s to a set of target states t which is to be achieved by hierarchical control a generalisation of the theory of caines and wei to st systems is given which includes the generalisation of the notions of dynamical consistency in block controllability and hierarchical feedback control on the associated hierarchical lattices

optimal sensor selection for discrete event systems with partial observation for discrete event systems under partial observation we study the problem of selection of an optimal set of sensors that can provide sufficient yet minimal events observation information the sufficiency of the observed information is captured as the fulfillment of a desired formal property selection of sensors can be viewed as a selection of an observation mask and also of an equivalence class of events a sensor set is called optimal if any coarser selection of the corresponding equivalence class of events results in some significant loss of the events observation information we study an optimal selection of sensors over the set of general nonprojection observation masks we show that this problem is np hard in general for mask monotonic properties we present a top down and a bottom up algorithm each of polynomial complexity we show that observerness is not mask monotonic we show that the computational complexity can be further improved if the property is preserved under the projection via an intermediary observation mask that is an observer our results are obtained in a general setting so that they can be adapted for an optimal selection of sensors for a variety of applications

control of networked discrete event systems dealing with communication delays and losses in this paper we investigate supervisory control of networked discrete event systems such systems are now widely used in practice the key feature of a networked discrete event system is communication delays and losses in observation and control without addressing communication delays and losses in networked systems no control will be effective we propose to use some special observation mappings to deal with observation delays and losses based on these mappings we define network observability we also consider control delays and losses in networked discrete event systems and define network controllability we show that these definitions capture precisely the requirements on effective supervisory control in networked discrete event systems in the sense that a networked supervisor exists if and only if both network controllability and network observability are satisfied

decentralized control of discrete event systems using prioritized composition with exclusion a necessary and sufficient condition for decentralized control of discrete event systems via prioritized composition with exclusion pcx is provided pcx was extended from prioritized synchronous composition psc in order to model various boolean modes of decision fusion by allowing the exclusivity of participation in system interactions a notion of pcx coobservability is introduced that captures the nature of pcx based decision fusion and a testing algorithm with polynomial complexity in the states of plant and specification is presented the result is extended for multiple supervisors with multiple exclusivity sets based on an extended pcx definition

localizing overlapping parts by searching the interpretation tree this paper discusses how local measurements of positions and surface normals may be used to identify and locate overlapping objects the objects are modeled as polyhedra or polygons having up to six degrees of positional freedom relative to the sensors the approach operates by examining all hypotheses about pairings between sensed data and object surfaces and efficiently discarding inconsistent ones by using local constraints on distances between faces angles between face normals and angles relative to the surface normals of vectors between sensed points the method described here is an extension of a method for recognition and localization of nonoverlapping parts previously described in 18 and 15

dual computation of projective shape and camera positions from multiple images given multiple image data from a set of points in 3d there are two fundamental questions that can be addressed what is the structure of the set of points in 3d what are the positions of the cameras relative to the points in this paper we show that for projective views and with structure and position defined projectively these problems are dual because they can be solved using constraint equations where space points and camera positions occur in a reciprocal way more specifically by using canonical projective reference frames for all points in space and images the imaging of point sets in space by multiple cameras can be captured by constraint relations involving three different kinds of parameters only coordinates of 1 space points 2 camera positions 3 image points the duality implies that the problem of computing camera positions fromp points in q views can be solved with the same algorithm as the problem of directly reconstructing q 4 points in p 4 views this unifies different approaches to projective reconstruction methods based on external calibration and direct methods exploiting constraints that exist between shape and image invariants

verification complexity of a class of observational properties for modular discrete events systems abstract a modular discrete event system is modeled by a set of module automata running synchronously in this paper we investigate the complexity of the verification problems of three different properties diagnosability predictability and detectability for partially observed modular discrete event systems we first show that deciding diagnosability for modular discrete event systems is pspace complete when the number of modules is unbounded then we show that deciding predictability and detectability for modular discrete event systems are both pspace hard problems these results reveal that in order to verify these properties for the complete system exploring the state space of the monolithic model may be unavoidable in the worst case

an inverse mapping theorem for h differentiable set valued maps taking advantage of recent developments in the theory of generalized differentiation we present an inverse mapping theorem for set valued maps and prove its stability under small linear perturbations using variational convergences of set valued mappings we present as well an approximate version of our inverse theorem

think globally act locally decentralized supervisory control decentralized supervisory control is investigated by considering problem formulations that model systems whose specifications are given as global constraints but whose solution is described by local controllers a necessary and sufficient condition is given for the existence of a solution to the problem of finding decentralized supervisors that ensure that the behavior of the closed loop system lies in a given range where the range of behavior can be described by regular languages it can be effectively tested whether the decentralized control problem is solvable in this case a procedure is given to compute the associated supervisors

inference based ambiguity management in decentralized decision making decentralized control of discrete event systems decentralized decision making requires the interaction of various local decision makers in order to arrive at a global decision limited sensing capabilities at each local site can create ambiguities in a decision making process at each local site we argue that such ambiguities are of differing gradations we propose a framework for decentralized decision making applied to decentralized control in particular that allows computation of such ambiguity gradations and utilizes their knowledge in arriving at a global decision each local decision is tagged with a certain grade or level of ambiguity with zero being the minimum ambiguity level a global decision is taken to be the same as a ldquowinningrdquo local decision i e one having the minimum level of ambiguity the computation of an ambiguity level for a local decision requires an assessment of the self ambiguities as well as the ambiguities of the others and an inference based upon such knowledge for the existence of a decentralized supervisor so that for each controllable event the ambiguity levels of all winning disablement or enablement decisions are bounded by some number n such a supervisor is termed n inferring the notion of n inference observability is introduced we show that the conjunctive and permissive c p v disjunctive and antipermissive d a co observability is the same as the zero inference observability whereas the conditional c p v d a co observability is the same as the unity inference observability we also present examples of higher order inference observable languages our framework does not require the existence of any a priori partition of the controllable events into permissive antipermissive sets nor does it require a global control computation based on conjunction disjunction of local decisions exhibiting that our ambiguity based approach is more efficient

on the supermal controllable sublanguage of a given language the concept of controllable language has been shown to play a basic role in the existence theory of supervisory controls for discrete event processes in this paper the supremal controllable sublanguage s of a given language l is characterized as the largest fixpoint of a monotone operator omega in the case where the languages involved are regular it is shown that the fixpoint s can be computed as the limit of the finite sequence k j given by k j 1 omega k j k 0 l an effective computational algorithm is developed and three examples are provided for illustration

np completeness of sensor selection problems arising in partially observed discrete event systems we consider the three properties of diagnosability normality and observability of discrete event systems in each case we consider the problem of finding an observable event set with minimum cardinality such that the property under consideration holds we prove that these search problems are computationally hard by showing that the corresponding decision problems are np complete

spatial planning a configuration space approach this paper presents algorithms for computing constraints on the position of an object due to the presence of ther objects this problem arises in applications that require choosing how to arrange or how to move objects without collisions the approach presented here is based on characterizing the position and orientation of an object as a single point in a configuration space in which each coordinate represents a degree of freedom in the position or orientation of the object the configurations forbidden to this object due to the presence of other objects can then be characterized as regions in the configuration space called configuration space obstacles the paper presents algorithms for computing these configuration space obstacles when the objects are polygons or polyhedra

the infimal prefix closed and observable superlanguage of given language abstract the supervisory control of discrete event systems under partial observation is examined in particular the condition of observability needed to solve the two main existing problems is investigated a fixed point characterization of observability is given and is shown to yield an effective test for observability where the system under consideration is specified by regular languages a formula for the infimal prefix closed observable superlanguage of a given language is presented where the system is specified by regular languages the formula for the infimal observable language is effectively computable

matching 3 d line segments with applications to multiple object motion estimation a two stage algorithm for matching line segments using three dimensional data is presented in the first stage a tree search based on the orientation of the line segments is applied to establish potential matches the sign ambiguity of line segments is fixed by a simple congruency constraint in the second stage a hough clustering technique based on the position of line segments is applied to verify potential matches any paired line segments of a match that cannot be brought to overlap by the translation determined by the clustering are removed from the match unlike previous methods this algorithm combats noise more effectively and ensures the global consistency of a match while the original motivation for the algorithm is multiple object motion estimation from stereo image sequences the algorithm can also be applied to other domains such as object recognition and object model construction from multiple views

fuzzy discrete event systems under fuzzy observability and a test algorithm in order to more effectively cope with the real world problems of vagueness impreciseness and subjectivity fuzzy discrete event systems fdess were proposed recently notably fdess have been applied to biomedical control for human immunodeficiency virus hiv acquired immune deficiency syndrome aids treatment planning and sensory information processing for robotic control qiu independently developed supervisory control theory of fdess we note that the controllability of events in qiu s work is fuzzy but the observability of events is crisp and the observability of events in cao and ying s work is also crisp although the controllability is not completely crisp since the controllable events can be disabled with any degrees motivated by the necessity to consider the situation that the events may be observed or controlled with some membership degrees in this paper we establish the supervisory control theory of fdess with partial observations in which both the observability and controllability of events are fuzzy instead we formalize the notions of fuzzy controllability condition and fuzzy observability condition in addition controllability and observability theorem of fdess is set up in a more generic framework in particular we present a detailed computing flow to verify whether the controllability and observability conditions hold thus this result can decide the existence of supervisors also we use this computing method to check the existence of supervisors in the controllability and observability theorem of classical discrete event systems dess which is a new method and different from classical case a number of examples are elaborated on to illustrate the presented results

the computational complexity of decentralized discrete event control problems computational complexity results are obtained for decentralized discrete event control problems these results generalize the earlier work of tsitsiklis 1989 who showed that for a special class of centralized supervisory control problems under partial observation there is an algorithm for determining in polynomial time whether or not a solution exists the negative complexity results associated with tsitsiklis work also carry over to the decentralized case so that solution existence for the more general class is not decidable in polynomial time nor does there exist a polynomial time algorithm for producing supervisor solutions when such solutions exist

decentralized supervisory control with intersection based architecture we investigate a new decentralized control architecture called intersection based architecture we propose a decentralized control protocol under this architecture called state estimator intersection based protocol sei protocol where each local supervisor sends its state estimate to the fusion sites and these sites take the intersection of these estimates in order to make a control decision the necessary and sufficient conditions for the achievability of the specification under this protocol is provided this condition is termed as state estimator intersection based coobservability sei coobservability a polynomial time algorithm for the verification of sei coobservability is provided we show that the languages that can be achieved under the sei protocol are incomparable with languages that can be achieved under existing architectures

observability and decentralized control of fuzzy discrete event systems fuzzy discrete event systems as a generalization of crisp discrete event systems have been introduced in order that it is possible to effectively represent uncertainty imprecision and vagueness arising from the dynamic of systems a fuzzy discrete event system has been modeled by a fuzzy automaton its behavior is described in terms of the fuzzy language generated by the automaton in this paper we are concerned with the supervisory control problem for fuzzy discrete event systems with partial observation observability normality and co observability of crisp languages are extended to fuzzy languages it is shown that the observability together with controllability of the desired fuzzy language is a necessary and sufficient condition for the existence of a partially observable fuzzy supervisor when a decentralized solution is desired it is proved that there exist local fuzzy supervisors if and only if the fuzzy language to be synthesized is controllable and co observable moreover the infimal controllable and observable fuzzy superlanguage and the supremal controllable and normal fuzzy sublanguage are also discussed simple examples are provided to illustrate the theoretical development

on codiagnosability and coobservability with dynamic observations codiagnosability and coobservability in discrete event systems where observations are dynamic are considered instead of having a fixed set of observable events the observation of an event is dynamic trace dependent in this paper a procedure is developed to transform the problem of coobservability to the problem of codiagnosability in the context of dynamic observations this proves that problems of coobservability are transformable to problems of codiagnosability and enables us to leverage the large literature available for codiagnosability to solve problems of coobservability furthermore in the case of dynamic observations the known polynomial complexity tests for the property of codiagnosability based on verifier automata with fixed observable event set s are no longer directly applicable a new testing procedure is developed that can handle transition based dynamic observations and remains of polynomial complexity in the state space of the system this new testing procedure employs a covering of the state space of the system based on cluster automata which enhances its computational efficiency based on cluster automata a new type of verifier automaton is built called the c verifier for verification of codiagnosability as an application of the above mentioned transformation the c verifier becomes a unified method for verifying both codiagnosability and coobservability

minimizing the cardinality of an events set for supervisors of discrete event dynamical systems in this paper we study sufficient observation and work spaces for supervisors of a class of discrete event dynamical systems deds we use finite state automata to model a deds the finite automata generates a formal language defined over the set of events in the deds a supervisor is a feedback system that observes a generated trace of events and dynamically disables or enables a subset of controllable events such that the closed loop system behaves as desired we model the desired behavior of the deds by a sublanguage defined over the set of events a sufficient observation space is a collection of events whose observation by a supervisor is enough to realize a given desired behavior a sufficient work space is a sufficient observation space such that the control action of the supervisor is limited to only the controllable elements of the work space we construct algorithms to evaluate a sufficient work or observation space the reduction of work or observation spaces results in reducing the number of event detectors communication and command channels between the supervisor and the plant

formulas for calculating supremal controllable and normal sublanguages abstract supremal controllable and normal sublanguages have been shown to play an important role in supervisor synthesis in this paper we discuss the computation of supremal controllable and normal sublanguages we derive formulas for both supremal controllable sublanguages and supremal normal sublanguages when the languages involved are closed as a result those languages can be computed without applying recursive algorithms we also discuss those aspects of these formulas