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Fast and Flexible Difference Constraint Propagation for DPLL(T)
 IN PROC. SAT, VOLUME 4121 OF LNCS
, 2006
"... In the context of DPLL(T), theory propagation is the process of dynamically selecting consequences of a conjunction of constraints from a given set of candidate constraints. We present improvements to a fast theory propagation procedure for difference constraints of the form x − y ≤ c. These improve ..."
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In the context of DPLL(T), theory propagation is the process of dynamically selecting consequences of a conjunction of constraints from a given set of candidate constraints. We present improvements to a fast theory propagation procedure for difference constraints of the form x − y ≤ c. These improvements are demonstrated experimentally.
VerICS 2004: A model checker for real time and multiagent systems
 Humboldt University
, 2004
"... Abstract. VerICS is a model checking tool for verification of timed and multiagent systems. These systems can be represented by timed automata (TA), time Petri nets (TPNs), or given as Estelle and Intermediate Language specifications. VerICS offers three verification methods: Bounded Model Checking ..."
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Cited by 29 (4 self)
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Abstract. VerICS is a model checking tool for verification of timed and multiagent systems. These systems can be represented by timed automata (TA), time Petri nets (TPNs), or given as Estelle and Intermediate Language specifications. VerICS offers three verification methods: Bounded Model Checking (BMC), Unbounded Model Checking (UMC) and Splitting for properties to be specified in subsets of TCTL and CTLpK. The current version of VerICS uses also a new graphical user interface to design time Petri nets and timed automata. 1
Checking Reachability Properties for Timed Automata via SAT
 Fundamenta Informaticae
, 2002
"... The paper deals with the problem of checking reachability for timed automata. The main idea consists in combining the wellknow forward reachability algorithm and the Bounded Model Checking (BMC) method. In order to check reachability of a state satisfying some desired property, rst the transition r ..."
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Cited by 23 (10 self)
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The paper deals with the problem of checking reachability for timed automata. The main idea consists in combining the wellknow forward reachability algorithm and the Bounded Model Checking (BMC) method. In order to check reachability of a state satisfying some desired property, rst the transition relation of a timed automaton is unfolded iteratively to the depth k 2 N and encoded as a propositional formula. Next, the desired property is translated to a propositional formula and the satis ability of the conjunction of the two above de ned formulas is checked. The unfolding of the transition relation can be terminated when either a state satisfying the property has been found or all the states of the timed automaton have been searched. The eciency of the method is strongly supported by the experimental results.
Some progress in satisfiability checking for difference logic
 In FORMATS/FTRTFT
, 2004
"... Abstract. In this paper we report a new SAT solver for difference logic, a propositional logic enriched with timing constraints. The main novelty of our solver is a tighter integration of the incremental analysis of numerical conflicts with the process of Boolean conflict analysis. This and other im ..."
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Cited by 16 (2 self)
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Abstract. In this paper we report a new SAT solver for difference logic, a propositional logic enriched with timing constraints. The main novelty of our solver is a tighter integration of the incremental analysis of numerical conflicts with the process of Boolean conflict analysis. This and other improvements lead to significant performance gains for some classes of problems. 1
Verification of a Cruise Control System Using CounterexampleGuided Search
, 2003
"... Formal verification has been identified by the research community as a useful step in logic controller design since it reveals algorithmically whether the controller in conjunction with the controlled plant satisfies given design specifications. If it is necessary, however, to model the continuous/h ..."
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Cited by 12 (2 self)
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Formal verification has been identified by the research community as a useful step in logic controller design since it reveals algorithmically whether the controller in conjunction with the controlled plant satisfies given design specifications. If it is necessary, however, to model the continuous/hybrid behavior of the plant, the verification is a computationally expensive task, thus limiting its applicability to rather small systems. This paper shows for the example of a cruise control system that the recently proposed approach of counterexampleguided verification can reduce the computational costs considerably. The method generates a sequence of abstractions, for which those behaviors (the counterexamples) are identified that potentially violate the specifications. The paper presents a tailormade sequence of validation methods that aim at checking the existence of these behaviors for the hybrid model of the controlled plant with as small computational costs as possible. As is shown for the cruise control system, the iteration consisting of counterexample generation, validation, and model refinement checks the specification while computing only a relatively small portion of the continuous reachable set. Since determining reachable sets is the most costly step in existing approaches, the overall e#ort is found to be much smaller in many cases.
Unbounded, Fully Symbolic Model Checking of Timed Automata using Boolean Methods
 IN PROC. OF CAV’03. LNCS 2725
, 2003
"... We present a new approach to unbounded, fully symbolic model checking of timed automata that is based on an efficient translation of quantified separation logic to quantified Boolean logic. Our technique preserves the interpretation of clocks over the reals and can check any property in timed comput ..."
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We present a new approach to unbounded, fully symbolic model checking of timed automata that is based on an efficient translation of quantified separation logic to quantified Boolean logic. Our technique preserves the interpretation of clocks over the reals and can check any property in timed computation tree logic. The core operations of eliminating quantifiers over real variables and deciding the validity of separation logic formulas are respectively translated to eliminating quantifiers on Boolean variables and checking Boolean satisfiability (SAT). We can
WELL (AND BETTER) QUASIORDERED TRANSITION SYSTEMS
"... Abstract. In this paper, we give a step by step introduction to the theory of well quasiordered transition systems. The framework combines two concepts, namely (i) transition systems which are monotonic wrt. a wellquasi ordering; and (ii) a scheme for symbolic backward reachability analysis. We de ..."
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Cited by 10 (4 self)
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Abstract. In this paper, we give a step by step introduction to the theory of well quasiordered transition systems. The framework combines two concepts, namely (i) transition systems which are monotonic wrt. a wellquasi ordering; and (ii) a scheme for symbolic backward reachability analysis. We describe several models with infinitestate spaces, which can be analyzed within the framework, e.g., Petri nets, lossy channel systems, timed automata, timed Petri nets, and multiset rewriting systems. We will also present better quasiordered transition systems which allow the design of efficient symbolic representations of infinite sets of states. §1. Introduction. 1.1. Background. Current capabilities in computer technology allow enormously complicated implementations of such systems, making the task of producing errorfree products more and more difficult. Consequently, it is of great practical and economical importance to develop methods which make the design
Optimizing bounded model checking for linear hybrid systems
 LNCS
, 2005
"... In this document we describe our experimental results for the application of bounded model checking with optimization and explanation learning to linear hybrid systems. Furthermore, we describe termination conditions and their optimizations. Section 1 contains short descriptions of the examples in o ..."
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Cited by 8 (4 self)
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In this document we describe our experimental results for the application of bounded model checking with optimization and explanation learning to linear hybrid systems. Furthermore, we describe termination conditions and their optimizations. Section 1 contains short descriptions of the examples in our test suite. We report on our experimental results in Section 2. The termination conditions are described in
SDSAT: Tight Integration of Small Domain Encoding and Lazy Approaches in a Separation Logic Solver
 In Proc. TACAS’06, volume 3920 of LNCS
, 2006
"... Existing difference logic (DL) solvers can be broadly classified as eager or lazy, each with its own merits and demerits. We propose a novel difference logic solver SDSAT that combines the strengths of both these approaches and provides a robust performance over a wide set of benchmarks. The solver ..."
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Cited by 6 (2 self)
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Existing difference logic (DL) solvers can be broadly classified as eager or lazy, each with its own merits and demerits. We propose a novel difference logic solver SDSAT that combines the strengths of both these approaches and provides a robust performance over a wide set of benchmarks. The solver SDSAT works in two phases: allocation and solve. In the allocation phase, it allocates nonuniform adequate ranges for variables appearing in difference predicates. This phase is similar to previous small domain encoding approaches, but uses a novel algorithm NuSMOD with 12 orders of magnitude improvement in performance and smaller ranges for variables. Furthermore, the difference logic formula is not transformed into an equisatisfiable Boolean formula in a single step, but rather done lazily in the following phase. In the solve phase, SDSAT uses a lazy refinement approach to search for a satisfying model within the allocated ranges. Thus, any partially DLtheory consistent model can be discarded if it cannot be satisfied within the allocated ranges. Note the crucial difference: in eager approaches, such a partially consistent model is not allowed in the first place, while in lazy approaches such a model is never discarded. Moreover, we dynamically refine the allocated ranges and search for a feasible solution within the updated ranges. This combined approach benefits from both the smaller search space (as in eager approaches) and also from the theoryspecific graphbased algorithms (characteristic of lazy approaches). Experimental results show that our method is robust and always better than or comparable to stateofthe art solvers using similar eager or lazy techniques.
Satisfiability checking with difference constraints
 in IMPRS Computer Science, Saarbruceken
, 2005
"... This thesis studies the problem of determining the satisfiability of a Boolean combination of binary difference constraints of the form x − y ≤ c where x and y are numeric variables and c is a constant. In particular, we present an incremental and modelbased interpreter for the theory of difference ..."
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Cited by 5 (2 self)
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This thesis studies the problem of determining the satisfiability of a Boolean combination of binary difference constraints of the form x − y ≤ c where x and y are numeric variables and c is a constant. In particular, we present an incremental and modelbased interpreter for the theory of difference constraints in the context of a generic Boolean satisfiability checking procedure capable of incorporating interpreters for arbitrary theories. We show how to use the model based approach to efficiently make inferences with the option of complete inference.