280 research outputs found
Dimensions of Neural-symbolic Integration - A Structured Survey
Research on integrated neural-symbolic systems has made significant progress
in the recent past. In particular the understanding of ways to deal with
symbolic knowledge within connectionist systems (also called artificial neural
networks) has reached a critical mass which enables the community to strive for
applicable implementations and use cases. Recent work has covered a great
variety of logics used in artificial intelligence and provides a multitude of
techniques for dealing with them within the context of artificial neural
networks. We present a comprehensive survey of the field of neural-symbolic
integration, including a new classification of system according to their
architectures and abilities.Comment: 28 page
Generalized Property-Directed Reachability for Hybrid Systems
Generalized property-directed reachability (GPDR) belongs to the family of
the model-checking techniques called IC3/PDR. It has been successfully applied
to software verification; for example, it is the core of Spacer, a
state-of-the-art Horn-clause solver bundled with Z3. However, it has yet to be
applied to hybrid systems, which involve a continuous evolution of values over
time. As the first step towards GPDR- based model checking for hybrid systems,
this paper formalizes HGPDR, an adaptation of GPDR to hybrid systems, and
proves its soundness. We also implemented a semi-automated proof-of-concept
verifier, which allows a user to provide hints to guide verification steps.Comment: To appear in VMCAI 202
Input Synthesis for Sampled Data Systems by Program Logic
Inspired by a concrete industry problem we consider the input synthesis
problem for hybrid systems: given a hybrid system that is subject to input from
outside (also called disturbance or noise), find an input sequence that steers
the system to the desired postcondition. In this paper we focus on sampled data
systems--systems in which a digital controller interrupts a physical plant in a
periodic manner, a class commonly known in control theory--and furthermore
assume that a controller is given in the form of an imperative program. We
develop a structural approach to input synthesis that features forward and
backward reasoning in program logic for the purpose of reducing a search space.
Although the examples we cover are limited both in size and in structure,
experiments with a prototype implementation suggest potential of our program
logic based approach.Comment: In Proceedings HAS 2014, arXiv:1501.0540
Workshop on Verification and Theorem Proving for Continuous Systems (NetCA Workshop 2005)
Oxford, UK, 26 August 200
Bridging scales in cancer progression: Mapping genotype to phenotype using neural networks
In this review we summarize our recent efforts in trying to understand the
role of heterogeneity in cancer progression by using neural networks to
characterise different aspects of the mapping from a cancer cells genotype and
environment to its phenotype. Our central premise is that cancer is an evolving
system subject to mutation and selection, and the primary conduit for these
processes to occur is the cancer cell whose behaviour is regulated on multiple
biological scales. The selection pressure is mainly driven by the
microenvironment that the tumour is growing in and this acts directly upon the
cell phenotype. In turn, the phenotype is driven by the intracellular pathways
that are regulated by the genotype. Integrating all of these processes is a
massive undertaking and requires bridging many biological scales (i.e.
genotype, pathway, phenotype and environment) that we will only scratch the
surface of in this review. We will focus on models that use neural networks as
a means of connecting these different biological scales, since they allow us to
easily create heterogeneity for selection to act upon and importantly this
heterogeneity can be implemented at different biological scales. More
specifically, we consider three different neural networks that bridge different
aspects of these scales and the dialogue with the micro-environment, (i) the
impact of the micro-environment on evolutionary dynamics, (ii) the mapping from
genotype to phenotype under drug-induced perturbations and (iii) pathway
activity in both normal and cancer cells under different micro-environmental
conditions
A temporal logic for micro- and macro-step-based real-time systems: Foundations and applications
Many systems include components interacting with each other that evolve at possibly very different speeds. To deal with this situation many formal models adopt the abstraction of “zero-time transitions”, which do not consume time. These, however, have several drawbacks in terms of naturalness and logic consistency, as a system is modeled to be in different states at the same time. We propose a novel approach that exploits concepts from non-standard analysis and pairs them with the traditional “next” operator of temporal logic to introduce a notion of micro- and macro-steps; our approach is enacted in an extension of the TRIO metric temporal logic, called X-TRIO. We study the expressiveness and decidability properties of the new logic. Decidability is achieved through translation of a meaningful subset of X-TRIO into Linear Temporal Logic, a traditional way to support automated verification. We illustrate the usefulness and the generality of our approach by applying it to provide a formal semantics of timed Petri nets, which allows for their automated verification. We also give an overview of a formal semantics of Stateflow/Simulink diagrams, defined in terms of X-TRIO, which has been applied to the automated verification of a robotic cell
Enclosing the behavior of a hybrid automaton up to and beyond a Zeno point
Even simple hybrid automata like the classic bouncing ball can exhibit Zeno behavior. The existence of this type of behavior has so far forced a large class of simulators to either ignore some events or risk looping indefinitely. This in turn forces modelers to either insert ad-hoc restrictions to circumvent Zeno behavior or to abandon hybrid automata. To address this problem, we take a fresh look at event detection and localization. A key insight that emerges from this investigation is that an enclosure for a given time interval can be valid independent of the occurrence of a given event. Such an event can then even occur an unbounded number of times. This insight makes it possible to handle some types of Zeno behavior. If the post-Zeno state is defined explicitly in the given model of the hybrid automaton, the computed enclosure covers the corresponding trajectory that starts from the Zeno point through a restarted evolution
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