In the last decade, with the development of multi-core workstations, the availability of GPGPU-en... more In the last decade, with the development of multi-core workstations, the availability of GPGPU-enhanced systems and the access to Grid platforms and supercomputers worldwide, Parallel Programming reached mainstream programming and appeared as a key issue in order to use in an efficient manner the computing power at hand. Search methods and combinatorial optimization techniques are not isolated from this phenomenon, as bigger computing power means the ability to attack more complex combinatorial problems. In the last years some experiments have been done to extend to parallel execution search methods such as Constraint Programming or SAT solving (Boolean satisfiability), and combinatorial optimization methods such as Local Search, Meta-heuristics and Brand & Bound. However these works have mostly been done for shared memory multi-core systems (i.e. with a few cores) or for small PC clusters (a few machines). The next challenge is to devise efficient techniques and algorithms for massively parallel computers with tens or hundreds of thousands of cores in the form of heterogeneous hybrid systems based on both multi-core processors and GPUs. We would like to provide a cross-community forum for researchers working on search methods (Constraint Solving, Artificial Intelligence, Logic Programming, SAT solving, etc.), combinatorial optimization methods (metaheuristics, local search, tabu search, evolutionary algorithms, ant colony optimization, particle swarm optimization, memetic algorithms, and other types of algorithms) and High Performance Computing (Grids, large PC clusters, massively parallel computers, GPGPUs) in order to tackle the challenge of efficient implementations on all kinds of parallel hardware: multi-core, GPU-based or heterogeneous massively parallel systems. This meeting is designed to be a forum for researchers willing to tackle those issues, in order to exchange ideas, theoretical frameworks, design of algorithms and methods, implementation issues, experimental results and further boost this growing area through cross-fertilization.
Hybrid systems are systems consisting of discrete changes and continuous changes over time. Probl... more Hybrid systems are systems consisting of discrete changes and continuous changes over time. Problems in various fields such as physics can be modeled as hybrid systems. In a simulation of a hybrid system, it is difficult to obtain rigorous solution of the model because of computation errors in the handling of continuous states. Our proposed method integrates interval-based techniques for initial value problems for ordinary differential equations and consistency techniques for nonlinear problems. The method obtains complete interval enclosures of hybrid trajectories efficiently with a given accuracy. We implemented the method and evaluated its effectiveness. Using the method, we can simulate hybrid systems reliably with guaranteeing its accuracy. 1. は じ め に
Cyber Physical Systems. Design, Modeling, and Evaluation, 2017
Hybrid systems are dynamical systems that include both continuous and discrete changes. Some hybr... more Hybrid systems are dynamical systems that include both continuous and discrete changes. Some hybrid systems involve a large or infinite number of discrete changes within an infinitesimal-width region of phase space. Systems with sliding mode are typical examples of such hybrid systems. It is difficult to analyze such hybrid systems through ordinary numerical simulation, since the time required for simulation increases in proportion to the number of discrete changes. In this paper, we propose a method to symbolically analyze such models involving numerous discrete changes by detecting loops and checking loop invariants of the model's behavior. The method handles parameterized hybrid systems and checks inclusion of parameterized states focusing on the values of a switching function that dominate the dynamics of sliding mode. We implemented the main part of the method in our symbolic hybrid system simulator HyLaGI, and conducted analysis of example models.
Transactions of the Society of Instrument and Control Engineers, 1979
Remotely sensed multispectral images are analyzed by the methods of maximum likelihood, Euclidean... more Remotely sensed multispectral images are analyzed by the methods of maximum likelihood, Euclidean minimum distance and correlation etc. But a new fast analyzing method is searched because the processing speed of the
IEICE Transactions on Information and Systems, 2019
Nowadays the computing technology is going through a major paradigm shift. Local processing platf... more Nowadays the computing technology is going through a major paradigm shift. Local processing platforms are being replaced by physically out of reach yet more powerful and scalable environments such as the cloud computing platforms. Previously, we introduced the OJIT system as a novel approach for obfuscating remotely executed programs, making them difficult for adversaries to reverse-engineer. The system exploited the JIT compilation technology to randomly and dynamically transform the code, making it constantly changing, thereby complicating the execution state. This work aims to propose the new design iOJIT, as an enhanced approach that patches the old systems shortcomings, and potentially provides more effective obfuscation. Here, we present an analytic study of the obfuscation techniques on the generated code and the cost of applying such transformations in terms of execution time and performance overhead. Based upon this profiling study, we implemented a new algorithm to choose which obfuscation techniques would be better chosen for "efficient" obfuscation according to our metrics, i.e., less prone to security attacks. Another goal was to study the system performance with different applications. Therefore, we applied our system on a cloud platform running different standard benchmarks from SPEC suite.
Upon the retirement of two area editors, Toyoaki Nishida and Akihiko Konagaya, we are happy to in... more Upon the retirement of two area editors, Toyoaki Nishida and Akihiko Konagaya, we are happy to introduce three new area editors, Ryutaro Ichise, Ferdinand Peper, and Satoshi Murata. Ichise succeeds Nishida and continues to handle the major field ''Cognitive Computing'' though the topics of the field slightly change due to the expertise of Ichise. Peper and Murata succeed Konagaya, who has been handling the major field ''Biocomputing.'' Since the field of Peper and that of Murata overlap, papers mainly dealing with theoretical models will be handled by Peper while papers touching upon physical or chemical implementation will be handled by Murata. The description of the new major fields follows this short introduction.
Electronic Notes in Theoretical Computer Science, 2015
A modeling language for hybrid systems HydLa and its implementation HyLaGI are described. HydLa i... more A modeling language for hybrid systems HydLa and its implementation HyLaGI are described. HydLa is a constraint-based language that can handle uncertainties of models smoothly. HyLaGI calculates trajectories by symbolic formula manipulation to exclude errors resulting from floating-point arithmetic. HyLaGI features a nondeterministic simulation algorithm so it can calculate all possible qualitative different trajectories of models with uncertainties.
ratories. Current research interests include design and implementation of programming languages, ... more ratories. Current research interests include design and implementation of programming languages, logic programming, concurrency and parallelism, and knowledge information processing.
The ability to handle evolving graph structures is important both for programming languages and m... more The ability to handle evolving graph structures is important both for programming languages and modeling languages. Of various languages that adopt graphs as primary data structures, a graph rewriting language LMNtal provides features of both (concurrent) programming languages and modeling languages, and its implementation unifies ordinary program execution and model checking functionalities. Unlike pointer manipulation in imperative languages, LMNtal allows us to manipulate graph structures in such a way that the well-formedness of graphs is guaranteed by the language itself. However, since the shapes of graphs can be complex and diverse compared to algebraic data structures such as lists and trees, it is a non-obvious important task to formulate types of graphs to verify individual programs. With this motivation, this paper discusses LMNtal ShapeType, a type checking framework that applies the basic idea of Structured Gamma to a concrete graph rewriting language. Types are defined by generative grammars written as LMNtal rules, and type checking of LMNtal programs can accordingly be done by exploiting the model checking features of LMNtal itself. We gave a full implementation of type checking exploiting the features of the LMNtal meta-interpreter and confirmed that it works for practical operations on various graph structures, including single-step and multi-step operations on non-algebraic data structures and data structures with numerical shape constraints. INDEX TERMS Dynamic data structures, graph grammars, graph rewriting, type checking.
Graphs are a generalized concept that encompasses more complex data structures than trees, such a... more Graphs are a generalized concept that encompasses more complex data structures than trees, such as difference lists, doubly-linked lists, skip lists, and leaf-linked trees. Normally, these structures are handled with destructive assignments to heaps, which is opposed to a purely functional programming style and makes verification difficult. We propose a new purely functional language, λ GT , that handles graphs as immutable, first-class data structures with a pattern matching mechanism based on Graph Transformation and developed a new type system, F GT , for the language. Our approach is in contrast with the analysis of pointer manipulation programs using separation logic, shape analysis, etc. in that (i) we do not consider destructive operations but pattern matchings over graphs provided by the new higher-level language that abstract pointers and heaps away and that (ii) we pursue what properties can be established automatically using a rather simple typing framework.
Hybrid systems are dynamical systems with continuous evolution of states and discrete evolution o... more Hybrid systems are dynamical systems with continuous evolution of states and discrete evolution of states and governing equations. We have worked on the design and implementation of HydLa, a constraint-based modeling language for hybrid systems, with a view to the proper handling of uncertainties and the integration of simulation and verification. HydLa's constraint hierarchies facilitate the description of constraints with adequate strength, but its semantical foundations are not obvious due to the interaction of various language constructs. This paper gives the declarative semantics of HydLa and discusses its properties and consequences by means of examples.
Hybrid cc is a constraint-based programming language aimed for simple modeling and rigorous simul... more Hybrid cc is a constraint-based programming language aimed for simple modeling and rigorous simulation of hybrid systems. The existing implementation of Hybrid cc uses intervals to handle partially specified models. Although the implementation solves nonlinear equations and ordinary differential equations (ODEs) based on interval arithmetic, discrete changes are not properly computed with intervals. We propose a method for enclosing every solution of a hybrid system with a set of boxes. Our method computes continuous state changes by solving ODEs with initial time and values expressed by intervals. Then the method detects and encloses every state that will cause a discrete change. We devise algorithms for pruning and splitting intervals to obtain tight enclosures. The experimental results show the efficiency of the algorithms. * 1 This kind of phenomenon that causes an infinite number of discrete changes in a finite length of time is known as Zeno behavior.
Proceedings of the Second International ICST Conference on Simulation Tools and Techniques, 2009
We propose a framework called HydLa for simple modeling and reliable simulation of hybrid systems... more We propose a framework called HydLa for simple modeling and reliable simulation of hybrid systems which involve discrete and continuous changes over time. HydLa employs interval constraints as a central principle to express uncertainties in modeling, error bounds in the computation of nonlinear continuous changes, and reachable state sets that play key roles in verification. In this research, we propose a modeling language with hierarchical interval constraints to facilitate well-defined modeling, and its implementation which uses machine-representable interval constraints to enclose computation errors with intervals or boxes. The implementation is based on the integration of a consistency technique for nonlinear interval constraints and a technique for solving ordinary differential equations. We also present a method for solving constraint hierarchies among interval constraints.
We propose a translation method from a constraint-based language into real-time transition system... more We propose a translation method from a constraint-based language into real-time transition systems that are a traditional framework for formalizing HA. We discuss differences between the two modeling languages with respect to the translation method.
Constraint programming is an emergent technology that allows modeling and solving various problem... more Constraint programming is an emergent technology that allows modeling and solving various problems in many areas such as artificial intelligence, computer programming, computeraided design, computer graphics, and user interfaces. In this report, we recount the recent activities of research collaboration on constraint programming conducted by the authors and other researchers in France and Japan. First, we outline our joint research projects on constraint programming and then present the backgrounds, goals, and approaches of several research topics treated in the projects. Second, we describe the two Franco-Japanese Workshops on Constraint Programming (FJCP), which we held in Japan in October 2004 and in France in November 2005. We conclude with future prospects for collaboration between French and Japanese researchers in this area.
International Journal on Software Tools for Technology Transfer, 2011
This paper presents a bounded model checking (BMC) tool called hydlogic for hybrid systems. It tr... more This paper presents a bounded model checking (BMC) tool called hydlogic for hybrid systems. It translates a reachability problem of a nonlinear hybrid system into a predicate logic formula involving arithmetic constraints, and checks the satisfiability of the formula based on a satisfiability modulo theories (SMT) method. We tightly integrate (i) an incremental SAT solver to enumerate the possible sets of constraints and (ii) an interval-based solver for hybrid constraint systems (HCSs) to solve the constraints described in the formulas. The HCS solver verifies the occurrence of a discrete change by enclosing continuous states that may cause the discrete change by a set of boxes. We adopt the existence property of a unique solution in the boxes computed by the HCS solver as (i) a proof of the reachability of a model, and (ii) a guide in the over-approximation refinement procedure. Our hydlogic implementation successfully handled several examples including those with nonlinear constraints.
Hybrid systems are dynamical systems with continuous evolution of states and discrete evolution o... more Hybrid systems are dynamical systems with continuous evolution of states and discrete evolution of states and governing equations. We have been working on the design and implementation of HydLa, a constraint-based modeling language for hybrid systems, with a view to the proper handling of uncertainties and the integration of simulation and verification. HydLa's constraint hierarchies facilitate the description of constraints with adequate strength, but its semantical foundations are not obvious due to the interaction of various language constructs. This paper gives the declarative semantics of HydLa and discusses its properties and consequences by means of examples.
We developed a technique for modeling formal systems involving name binding in a modeling languag... more We developed a technique for modeling formal systems involving name binding in a modeling language based on hypergraph rewriting. A hypergraph consists of graph nodes, edges with two endpoints and edges with multiple endpoints. The idea is that hypergraphs allow us to represent terms containing bindings and that our notion of a graph type keeps bound variables distinct throughout rewriting steps. We previously encoded the untyped λ-calculus and the evaluation and type checking of System F<:, but the encoding of System F<: type inference requires a unification algorithm. We studied and successfully implemented a unification algorithm modulo α-equivalence for hypergraphs representing untyped λ-terms. The unification algorithm turned out to be similar to nominal unification despite the fact that our approach and nominal approach to name binding are very different. However, some basic properties of our framework are easier to establish compared to the ones in nominal unification. We believe this indicates that hypergraphs provide a nice framework for encoding formal systems involving binders and unification modulo α-equivalence.
In the last decade, with the development of multi-core workstations, the availability of GPGPU-en... more In the last decade, with the development of multi-core workstations, the availability of GPGPU-enhanced systems and the access to Grid platforms and supercomputers worldwide, Parallel Programming reached mainstream programming and appeared as a key issue in order to use in an efficient manner the computing power at hand. Search methods and combinatorial optimization techniques are not isolated from this phenomenon, as bigger computing power means the ability to attack more complex combinatorial problems. In the last years some experiments have been done to extend to parallel execution search methods such as Constraint Programming or SAT solving (Boolean satisfiability), and combinatorial optimization methods such as Local Search, Meta-heuristics and Brand & Bound. However these works have mostly been done for shared memory multi-core systems (i.e. with a few cores) or for small PC clusters (a few machines). The next challenge is to devise efficient techniques and algorithms for massively parallel computers with tens or hundreds of thousands of cores in the form of heterogeneous hybrid systems based on both multi-core processors and GPUs. We would like to provide a cross-community forum for researchers working on search methods (Constraint Solving, Artificial Intelligence, Logic Programming, SAT solving, etc.), combinatorial optimization methods (metaheuristics, local search, tabu search, evolutionary algorithms, ant colony optimization, particle swarm optimization, memetic algorithms, and other types of algorithms) and High Performance Computing (Grids, large PC clusters, massively parallel computers, GPGPUs) in order to tackle the challenge of efficient implementations on all kinds of parallel hardware: multi-core, GPU-based or heterogeneous massively parallel systems. This meeting is designed to be a forum for researchers willing to tackle those issues, in order to exchange ideas, theoretical frameworks, design of algorithms and methods, implementation issues, experimental results and further boost this growing area through cross-fertilization.
Hybrid systems are systems consisting of discrete changes and continuous changes over time. Probl... more Hybrid systems are systems consisting of discrete changes and continuous changes over time. Problems in various fields such as physics can be modeled as hybrid systems. In a simulation of a hybrid system, it is difficult to obtain rigorous solution of the model because of computation errors in the handling of continuous states. Our proposed method integrates interval-based techniques for initial value problems for ordinary differential equations and consistency techniques for nonlinear problems. The method obtains complete interval enclosures of hybrid trajectories efficiently with a given accuracy. We implemented the method and evaluated its effectiveness. Using the method, we can simulate hybrid systems reliably with guaranteeing its accuracy. 1. は じ め に
Cyber Physical Systems. Design, Modeling, and Evaluation, 2017
Hybrid systems are dynamical systems that include both continuous and discrete changes. Some hybr... more Hybrid systems are dynamical systems that include both continuous and discrete changes. Some hybrid systems involve a large or infinite number of discrete changes within an infinitesimal-width region of phase space. Systems with sliding mode are typical examples of such hybrid systems. It is difficult to analyze such hybrid systems through ordinary numerical simulation, since the time required for simulation increases in proportion to the number of discrete changes. In this paper, we propose a method to symbolically analyze such models involving numerous discrete changes by detecting loops and checking loop invariants of the model's behavior. The method handles parameterized hybrid systems and checks inclusion of parameterized states focusing on the values of a switching function that dominate the dynamics of sliding mode. We implemented the main part of the method in our symbolic hybrid system simulator HyLaGI, and conducted analysis of example models.
Transactions of the Society of Instrument and Control Engineers, 1979
Remotely sensed multispectral images are analyzed by the methods of maximum likelihood, Euclidean... more Remotely sensed multispectral images are analyzed by the methods of maximum likelihood, Euclidean minimum distance and correlation etc. But a new fast analyzing method is searched because the processing speed of the
IEICE Transactions on Information and Systems, 2019
Nowadays the computing technology is going through a major paradigm shift. Local processing platf... more Nowadays the computing technology is going through a major paradigm shift. Local processing platforms are being replaced by physically out of reach yet more powerful and scalable environments such as the cloud computing platforms. Previously, we introduced the OJIT system as a novel approach for obfuscating remotely executed programs, making them difficult for adversaries to reverse-engineer. The system exploited the JIT compilation technology to randomly and dynamically transform the code, making it constantly changing, thereby complicating the execution state. This work aims to propose the new design iOJIT, as an enhanced approach that patches the old systems shortcomings, and potentially provides more effective obfuscation. Here, we present an analytic study of the obfuscation techniques on the generated code and the cost of applying such transformations in terms of execution time and performance overhead. Based upon this profiling study, we implemented a new algorithm to choose which obfuscation techniques would be better chosen for "efficient" obfuscation according to our metrics, i.e., less prone to security attacks. Another goal was to study the system performance with different applications. Therefore, we applied our system on a cloud platform running different standard benchmarks from SPEC suite.
Upon the retirement of two area editors, Toyoaki Nishida and Akihiko Konagaya, we are happy to in... more Upon the retirement of two area editors, Toyoaki Nishida and Akihiko Konagaya, we are happy to introduce three new area editors, Ryutaro Ichise, Ferdinand Peper, and Satoshi Murata. Ichise succeeds Nishida and continues to handle the major field ''Cognitive Computing'' though the topics of the field slightly change due to the expertise of Ichise. Peper and Murata succeed Konagaya, who has been handling the major field ''Biocomputing.'' Since the field of Peper and that of Murata overlap, papers mainly dealing with theoretical models will be handled by Peper while papers touching upon physical or chemical implementation will be handled by Murata. The description of the new major fields follows this short introduction.
Electronic Notes in Theoretical Computer Science, 2015
A modeling language for hybrid systems HydLa and its implementation HyLaGI are described. HydLa i... more A modeling language for hybrid systems HydLa and its implementation HyLaGI are described. HydLa is a constraint-based language that can handle uncertainties of models smoothly. HyLaGI calculates trajectories by symbolic formula manipulation to exclude errors resulting from floating-point arithmetic. HyLaGI features a nondeterministic simulation algorithm so it can calculate all possible qualitative different trajectories of models with uncertainties.
ratories. Current research interests include design and implementation of programming languages, ... more ratories. Current research interests include design and implementation of programming languages, logic programming, concurrency and parallelism, and knowledge information processing.
The ability to handle evolving graph structures is important both for programming languages and m... more The ability to handle evolving graph structures is important both for programming languages and modeling languages. Of various languages that adopt graphs as primary data structures, a graph rewriting language LMNtal provides features of both (concurrent) programming languages and modeling languages, and its implementation unifies ordinary program execution and model checking functionalities. Unlike pointer manipulation in imperative languages, LMNtal allows us to manipulate graph structures in such a way that the well-formedness of graphs is guaranteed by the language itself. However, since the shapes of graphs can be complex and diverse compared to algebraic data structures such as lists and trees, it is a non-obvious important task to formulate types of graphs to verify individual programs. With this motivation, this paper discusses LMNtal ShapeType, a type checking framework that applies the basic idea of Structured Gamma to a concrete graph rewriting language. Types are defined by generative grammars written as LMNtal rules, and type checking of LMNtal programs can accordingly be done by exploiting the model checking features of LMNtal itself. We gave a full implementation of type checking exploiting the features of the LMNtal meta-interpreter and confirmed that it works for practical operations on various graph structures, including single-step and multi-step operations on non-algebraic data structures and data structures with numerical shape constraints. INDEX TERMS Dynamic data structures, graph grammars, graph rewriting, type checking.
Graphs are a generalized concept that encompasses more complex data structures than trees, such a... more Graphs are a generalized concept that encompasses more complex data structures than trees, such as difference lists, doubly-linked lists, skip lists, and leaf-linked trees. Normally, these structures are handled with destructive assignments to heaps, which is opposed to a purely functional programming style and makes verification difficult. We propose a new purely functional language, λ GT , that handles graphs as immutable, first-class data structures with a pattern matching mechanism based on Graph Transformation and developed a new type system, F GT , for the language. Our approach is in contrast with the analysis of pointer manipulation programs using separation logic, shape analysis, etc. in that (i) we do not consider destructive operations but pattern matchings over graphs provided by the new higher-level language that abstract pointers and heaps away and that (ii) we pursue what properties can be established automatically using a rather simple typing framework.
Hybrid systems are dynamical systems with continuous evolution of states and discrete evolution o... more Hybrid systems are dynamical systems with continuous evolution of states and discrete evolution of states and governing equations. We have worked on the design and implementation of HydLa, a constraint-based modeling language for hybrid systems, with a view to the proper handling of uncertainties and the integration of simulation and verification. HydLa's constraint hierarchies facilitate the description of constraints with adequate strength, but its semantical foundations are not obvious due to the interaction of various language constructs. This paper gives the declarative semantics of HydLa and discusses its properties and consequences by means of examples.
Hybrid cc is a constraint-based programming language aimed for simple modeling and rigorous simul... more Hybrid cc is a constraint-based programming language aimed for simple modeling and rigorous simulation of hybrid systems. The existing implementation of Hybrid cc uses intervals to handle partially specified models. Although the implementation solves nonlinear equations and ordinary differential equations (ODEs) based on interval arithmetic, discrete changes are not properly computed with intervals. We propose a method for enclosing every solution of a hybrid system with a set of boxes. Our method computes continuous state changes by solving ODEs with initial time and values expressed by intervals. Then the method detects and encloses every state that will cause a discrete change. We devise algorithms for pruning and splitting intervals to obtain tight enclosures. The experimental results show the efficiency of the algorithms. * 1 This kind of phenomenon that causes an infinite number of discrete changes in a finite length of time is known as Zeno behavior.
Proceedings of the Second International ICST Conference on Simulation Tools and Techniques, 2009
We propose a framework called HydLa for simple modeling and reliable simulation of hybrid systems... more We propose a framework called HydLa for simple modeling and reliable simulation of hybrid systems which involve discrete and continuous changes over time. HydLa employs interval constraints as a central principle to express uncertainties in modeling, error bounds in the computation of nonlinear continuous changes, and reachable state sets that play key roles in verification. In this research, we propose a modeling language with hierarchical interval constraints to facilitate well-defined modeling, and its implementation which uses machine-representable interval constraints to enclose computation errors with intervals or boxes. The implementation is based on the integration of a consistency technique for nonlinear interval constraints and a technique for solving ordinary differential equations. We also present a method for solving constraint hierarchies among interval constraints.
We propose a translation method from a constraint-based language into real-time transition system... more We propose a translation method from a constraint-based language into real-time transition systems that are a traditional framework for formalizing HA. We discuss differences between the two modeling languages with respect to the translation method.
Constraint programming is an emergent technology that allows modeling and solving various problem... more Constraint programming is an emergent technology that allows modeling and solving various problems in many areas such as artificial intelligence, computer programming, computeraided design, computer graphics, and user interfaces. In this report, we recount the recent activities of research collaboration on constraint programming conducted by the authors and other researchers in France and Japan. First, we outline our joint research projects on constraint programming and then present the backgrounds, goals, and approaches of several research topics treated in the projects. Second, we describe the two Franco-Japanese Workshops on Constraint Programming (FJCP), which we held in Japan in October 2004 and in France in November 2005. We conclude with future prospects for collaboration between French and Japanese researchers in this area.
International Journal on Software Tools for Technology Transfer, 2011
This paper presents a bounded model checking (BMC) tool called hydlogic for hybrid systems. It tr... more This paper presents a bounded model checking (BMC) tool called hydlogic for hybrid systems. It translates a reachability problem of a nonlinear hybrid system into a predicate logic formula involving arithmetic constraints, and checks the satisfiability of the formula based on a satisfiability modulo theories (SMT) method. We tightly integrate (i) an incremental SAT solver to enumerate the possible sets of constraints and (ii) an interval-based solver for hybrid constraint systems (HCSs) to solve the constraints described in the formulas. The HCS solver verifies the occurrence of a discrete change by enclosing continuous states that may cause the discrete change by a set of boxes. We adopt the existence property of a unique solution in the boxes computed by the HCS solver as (i) a proof of the reachability of a model, and (ii) a guide in the over-approximation refinement procedure. Our hydlogic implementation successfully handled several examples including those with nonlinear constraints.
Hybrid systems are dynamical systems with continuous evolution of states and discrete evolution o... more Hybrid systems are dynamical systems with continuous evolution of states and discrete evolution of states and governing equations. We have been working on the design and implementation of HydLa, a constraint-based modeling language for hybrid systems, with a view to the proper handling of uncertainties and the integration of simulation and verification. HydLa's constraint hierarchies facilitate the description of constraints with adequate strength, but its semantical foundations are not obvious due to the interaction of various language constructs. This paper gives the declarative semantics of HydLa and discusses its properties and consequences by means of examples.
We developed a technique for modeling formal systems involving name binding in a modeling languag... more We developed a technique for modeling formal systems involving name binding in a modeling language based on hypergraph rewriting. A hypergraph consists of graph nodes, edges with two endpoints and edges with multiple endpoints. The idea is that hypergraphs allow us to represent terms containing bindings and that our notion of a graph type keeps bound variables distinct throughout rewriting steps. We previously encoded the untyped λ-calculus and the evaluation and type checking of System F<:, but the encoding of System F<: type inference requires a unification algorithm. We studied and successfully implemented a unification algorithm modulo α-equivalence for hypergraphs representing untyped λ-terms. The unification algorithm turned out to be similar to nominal unification despite the fact that our approach and nominal approach to name binding are very different. However, some basic properties of our framework are easier to establish compared to the ones in nominal unification. We believe this indicates that hypergraphs provide a nice framework for encoding formal systems involving binders and unification modulo α-equivalence.
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Papers by Kazunori Ueda