Logics of Dynamical Systems

Abstract

We study the logic of dynamical systems, that is, logics and proof principles for properties of dynamical systems. Dynamical systems are mathematical models describing how the state of a system evolves over time. They are important for modeling and understanding many applications, including embedded systems and cyber-physical systems. In discrete dynamical systems, the state evolves in discrete steps, one step at a time, as described by a difference equation or discrete state transition relation. In continuous dynamical systems, the state evolves continuously along a function, typically described by a differential equation. Hybrid dynamical systems or hybrid systems combine both discrete and continuous dynamics. Distributed hybrid systems combine distributed systems with hybrid systems, i.e., they are multi-agent hybrid systems that interact through remote communication or physical interaction. Stochastic hybrid systems combine stochastic dynamics with hybrid systems.We survey dynamic logics for specifying and verifying properties for each of those classes of dynamical systems. A dynamic logic is a first-order modal logic with a pair of parametrized modal operators for each dynamical system to express necessary or possible properties of their transition behavior. Due to their full basis of first-order modal logic operators, dynamic logics can express a rich variety of system properties, including safety, controllability, reactivity, liveness, and quantified parametrized properties, even about relations between multiple dynamical systems. In this survey, we focus on some of the representatives of the family of differential dynamic logics, which share the ability to express properties of dynamical systems having continuous dynamics described by various forms of differential equations.We explain the dynamical system models, dynamic logics of dynamical systems, their semantics, their axiomatizations, and proof calculi for proving logical formulas about these dynamical systems. We study differential invariants, i.e., induction principles for differential equations. We survey theoretical results, including soundness and completeness and deductive power. Differential dynamic logics have been implemented in automatic and interactive theorem provers and have been used successfully to verify safety-critical applications in automotive, aviation, railway, robotics, and analogue electrical circuits.

Characterizing Algebraic Invariants by Differential Radical Invariants

“…Fundamentally, however, the study of the safety of hybrid systems can be shown to reduce constructively to the problem of generating invariants for their differential equations [18]. We focus on this core problem in this paper.…”

A Formally Verified Hybrid System for the Next-Generation Airborne Collision Avoidance System

“…We model our system using Differential Dynamic Logic dL [Pla08,Pla10,Pla12], a logic for reasoning about hybrid programs. dL allows discrete assignments, control structures, and execution of differential equations.…”

KeYmaera X: An Axiomatic Tactical Theorem Prover for Hybrid Systems

“…Hybrid dynamical systems [2,12] are mathematical models for analyzing the interaction between discrete and continuous dynamics.…”

“…Hybrid automata are not conducive to compositional reasoning; to establish a property about a hybrid automaton, it does not suffice to establish that property about each component of a decomposed system. Hybrid programs [10,11,12], in contrast, are a compositional programming language model of hybrid dynamics. They extend regular programs with differential equations.…”

“…Differential dynamic logic (dL) [10,11,12] is a first-order multimodal logic for specifying and proving properties of hybrid programs. Each hybrid program α is associated with modal operators [α] and α , which express state reachability properties of the parametrizing program.…”