69 research outputs found
The categorical limit of a sequence of dynamical systems
Modeling a sequence of design steps, or a sequence of parameter settings,
yields a sequence of dynamical systems. In many cases, such a sequence is
intended to approximate a certain limit case. However, formally defining that
limit turns out to be subject to ambiguity. Depending on the interpretation of
the sequence, i.e. depending on how the behaviors of the systems in the
sequence are related, it may vary what the limit should be. Topologies, and in
particular metrics, define limits uniquely, if they exist. Thus they select one
interpretation implicitly and leave no room for other interpretations. In this
paper, we define limits using category theory, and use the mentioned relations
between system behaviors explicitly. This resolves the problem of ambiguity in
a more controlled way. We introduce a category of prefix orders on executions
and partial history preserving maps between them to describe both discrete and
continuous branching time dynamics. We prove that in this category all
projective limits exist, and illustrate how ambiguity in the definition of
limits is resolved using an example. Moreover, we show how various problems
with known topological approaches are now resolved, and how the construction of
projective limits enables us to approximate continuous time dynamics as a
sequence of discrete time systems.Comment: In Proceedings EXPRESS/SOS 2013, arXiv:1307.690
Prefix orders as a general model of dynamics
In this report we formalize and study the notion of prex order on the executions of general dynamical systems and use basic category theory to show that appropriate structure preserving maps between such orders lead to the well-known notions of bisimulation, renement, product, and union of behavior, without relying on a notion of 'next state'. Thus these notions are generalized to apply to arbitrary dynamical systems, including continuous and hybrid systems
Formally Verified Simulations of State-Rich Processes using Interaction Trees in Isabelle/HOL
Simulation and formal verification are important complementary techniques necessary in high assurance model-based systems development. In order to support coherent results, it is necessary to provide unifying semantics and automation for both activities. In this paper we apply Interaction Trees in Isabelle/HOL to produce a verification and simulation framework for state-rich process languages. We develop the core theory and verification techniques for Interaction Trees, use them to give a semantics to the CSP and Circus languages, and formally link our new semantics with the failures-divergences semantic model. We also show how the Isabelle code generator can be used to generate verified executable simulations for reactive and concurrent programs
Quantitative reactive modeling and verification
Formal verification aims to improve the quality of software by detecting errors before they do harm. At the basis of formal verification is the logical notion of correctness, which purports to capture whether or not a program behaves as desired. We suggest that the boolean partition of software into correct and incorrect programs falls short of the practical need to assess the behavior of software in a more nuanced fashion against multiple criteria. We therefore propose to introduce quantitative fitness measures for programs, specifically for measuring the function, performance, and robustness of reactive programs such as concurrent processes. This article describes the goals of the ERC Advanced Investigator Project QUAREM. The project aims to build and evaluate a theory of quantitative fitness measures for reactive models. Such a theory must strive to obtain quantitative generalizations of the paradigms that have been success stories in qualitative reactive modeling, such as compositionality, property-preserving abstraction and abstraction refinement, model checking, and synthesis. The theory will be evaluated not only in the context of software and hardware engineering, but also in the context of systems biology. In particular, we will use the quantitative reactive models and fitness measures developed in this project for testing hypotheses about the mechanisms behind data from biological experiments
Doctor of Philosophy
dissertationOver the last decade, cyber-physical systems (CPSs) have seen significant applications in many safety-critical areas, such as autonomous automotive systems, automatic pilot avionics, wireless sensor networks, etc. A Cps uses networked embedded computers to monitor and control physical processes. The motivating example for this dissertation is the use of fault- tolerant routing protocol for a Network-on-Chip (NoC) architecture that connects electronic control units (Ecus) to regulate sensors and actuators in a vehicle. With a network allowing Ecus to communicate with each other, it is possible for them to share processing power to improve performance. In addition, networked Ecus enable flexible mapping to physical processes (e.g., sensors, actuators), which increases resilience to Ecu failures by reassigning physical processes to spare Ecus. For the on-chip routing protocol, the ability to tolerate network faults is important for hardware reconfiguration to maintain the normal operation of a system. Adding a fault-tolerance feature in a routing protocol, however, increases its design complexity, making it prone to many functional problems. Formal verification techniques are therefore needed to verify its correctness. This dissertation proposes a link-fault-tolerant, multiflit wormhole routing algorithm, and its formal modeling and verification using two different methodologies. An improvement upon the previously published fault-tolerant routing algorithm, a link-fault routing algorithm is proposed to relax the unrealistic node-fault assumptions of these algorithms, while avoiding deadlock conservatively by appropriately dropping network packets. This routing algorithm, together with its routing architecture, is then modeled in a process-algebra language LNT, and compositional verification techniques are used to verify its key functional properties. As a comparison, it is modeled using channel-level VHDL which is compiled to labeled Petri-nets (LPNs). Algorithms for a partial order reduction method on LPNs are given. An optimal result is obtained from heuristics that trace back on LPNs to find causally related enabled predecessor transitions. Key observations are made from the comparison between these two verification methodologies
Computer Aided Verification
This open access two-volume set LNCS 11561 and 11562 constitutes the refereed proceedings of the 31st International Conference on Computer Aided Verification, CAV 2019, held in New York City, USA, in July 2019. The 52 full papers presented together with 13 tool papers and 2 case studies, were carefully reviewed and selected from 258 submissions. The papers were organized in the following topical sections: Part I: automata and timed systems; security and hyperproperties; synthesis; model checking; cyber-physical systems and machine learning; probabilistic systems, runtime techniques; dynamical, hybrid, and reactive systems; Part II: logics, decision procedures; and solvers; numerical programs; verification; distributed systems and networks; verification and invariants; and concurrency
Generalized labelled Markov processes, coalgebraically
Coalgebras of measurable spaces are of interest in probability theory as a formalization of Labelled Markov Processes (LMPs). We discuss some general facts related to the notions of bisimulation and cocongruence on these systems, providing a faithful characterization of bisimulation on LMPs on generic measurable
spaces. This has been used to prove that bisimilarity on single LMPs is an equivalence, without assuming the state space to be analytic. As the second main contribution, we introduce the first specification rule format to define well-behaved composition operators for LMPs. This allows one to define process description languages on LMPs which are always guaranteed to have a fully-abstract semantics
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