Martin Fränzle

Carl von Ossietzky University of Oldenburg, Computing Science, Faculty Member

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M. Fränzle’s research interests are in modelling, verification, and synthesis of reactive, real-time, and hybrid dynamics in embedded and cyber-physical systems. He has worked on the semantics of high-level modelling and specification languages and on decision problems and their application to verifying and synthesizing real-time and hybrid discrete-continuous systems including settings subject to stochastic disturbances.

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Papers by Martin Fränzle

Optimal Explanation Generation using Attention Distribution Model

AHFE international, 2023

With highly automated and Autonomous Vehicles (AVs) being one of the most prominent emerging tech... more With highly automated and Autonomous Vehicles (AVs) being one of the most prominent emerging technologies in the automotive industry, efforts to achieve SAE Level 3+ vehicles have skyrocketed in recent years. As new technologies emerge on a daily basis, these systems are becoming increasingly complex. To help people understand - and also accept - these new technologies, there is a need for explanation. There are three essential dimensions to designing explanations, namely content, frequency, and timing. Our goal is to develop an algorithm that optimises explanation in AVs. Most of the existing research focuses on the content of an explanation, whereas the fine-granularity of the frequency and timing of an explanation is relatively unexplored. Previous studies concerning "when to explain" have tended to make broad distinctions between explaining before, during or after an action is performed. For AVs, studies have shown that passengers prefer to receive an explanation before an autonomous action takes place. However, it seems likely that the acclimatisation that occurs through prolonged exposure to and use of a particular AV will reduce the need for explanation. As comprehension of explanations is workload-intensive, it is necessary to optimise both the frequency, i.e. skipping explanations when they are not helpful to reduce workload, and the precise point in time when an explanation is given, i.e. giving an explanation when it provides the maximum workload reduction. Extra mental workload for passengers can be caused by both giving and omitting an explanation. Every explanation that is presented requires cognitive processing in order to be understood, even if its content is considered to be redundant or if it will not be remembered by the addressee. On the other hand, skipping the explanation can cause the passenger to actively scan the environment for potential cues themselves, if necessary. Such an attention strategy would also impose a significant cognitive load on the passenger. In our work, to predict the mental workload of the passenger, we use the state-of-the-art attention model called SEEV (Salience, Effort, Expectancy, and Value). The SEEV model is dynamically used for forecasting the likelihood of the direction of attention. Our work aims to generate an optimally timed strategy for presenting an explanation. Using the SEEV model we build a probabilistic reactive game, i.e., 1.5-player game or Markov Decision Process, and we use reactive synthesis to generate an optimal reactive strategy for presenting an explanation that minimises workload.

Robustness in Cyber-Physical Systems (Dagstuhl Seminar 16362)

Dagstuhl Reports, 2016

Electronically controlled systems have become pervasive in modern society and are increasingly be... more Electronically controlled systems have become pervasive in modern society and are increasingly being used to control safety-critical applications, such as medical devices and transportation systems. At the same time, these systems are increasing in complexity at an alarming rate, making it difficult to produce system designs with guaranteed robust performance. Cyber-physical systems (CPS) is a new multi-disciplinary field aimed at providing a rigorous framework for designing and analyzing these systems, and recent developments in CPS-related fields provide techniques to increase robustness in the design and analysis of complex systems. This seminar brought together researchers from both academia and industry working in hybrid control systems, mechatronics, formal methods, and real-time embedded systems. Participants identified and discussed newly available techniques related to robust design and analysis that could be applied to open issues in the area of CPS and identified open issues and research questions that require collaboration between the communities. This report documents the program and the outcomes of Dagstuhl Seminar 16362 "Robustness in Cyber-Physical Systems".

A sampling-based approach for handling delays in continuous and hybrid systems

IT, Sep 23, 2021

Delays in feedback dynamics of coupled dynamical systems arise regularly, especially in embedded ... more Delays in feedback dynamics of coupled dynamical systems arise regularly, especially in embedded control where the physical plant and the controller continuously interact through digital networks. Systems featuring delays are however notoriously difficult to analyze. Consequently, formal analysis often addresses simplified, delay-free substitute models, risking negligence of the adverse impact of delay on control performance. In this ongoing work, we demonstrate that for continuous systems such as delay differential equations, a major part of the delay-induced complexity can be reduced effectively when adding natural constraints to the model of the delayed feedback channel, namely that it transports a band-limited signal and implements a non-punctual, distributed delay. The reduction is based on a sampling approach which is applicable when the above conditions on the feedback are satisfied. We further discuss the possibilities of lifting this method to mixed discrete-continuous dynamics of delayed hybrid systems and the open issues thereof.

Strategies Resilient to Delay: Games under Delayed Control vs. Delay Games (full version)

arXiv (Cornell University), May 31, 2023

We compare games under delayed control and delay games, two types of infinite games modelling asy... more We compare games under delayed control and delay games, two types of infinite games modelling asynchronicity in reactive synthesis. In games under delayed control both players suffer from partial informedness due to symmetrically delayed communication, while in delay games, the protagonist has to grant lookahead to the alter player. Our first main result, the interreducibility of the existence of sure winning strategies for the protagonist, allows to transfer known complexity results and bounds on the delay from delay games to games under delayed control, for which no such results had been known. We furthermore analyse existence of randomized strategies that win almost surely, where this correspondence between the two types of games breaks down. In this setting, some games surely won by the alter player in delay games can now be won almost surely by the protagonist in the corresponding game under delayed control, showing that it indeed makes a difference whether the protagonist has to grant lookahead or both players suffer from partial informedness. These results get even more pronounced when we finally address the quantitative goal of winning with a probability in [0, 1]. We show that for any rational threshold θ ∈ [0, 1] there is a game that can be won by the protagonist with exactly probability θ under delayed control, while being surely won by alter in the delay game setting. All these findings refine our original result that games under delayed control are not determined.

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The Quest for an Adequate Semantic Basis of Dense-Time Metric Temporal Logic

Arithmetic Satisfiability-Modulo-Theory Solving Applied to Nonstandard Analysis Problems of Cyber-Physical Systems

Springer eBooks, Feb 24, 2012

Modelling Turning Intention in Unsignalized Intersections with Bayesian Networks

Springer eBooks, 2021

Formal Modeling and Analysis of Timed Systems

Lecture Notes in Computer Science, 2016

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Neue autoMobilität II. Kooperativer Straßenverkehr und intelligente Verkehrssteuerung für die Mobilität der Zukunft

Generalized Craig Interpolation

Logical Methods in Computer Science, 2012

NMPC-based Trajectory Tracking and Collison Avoidance of Underactuated Vessels with Elliptical Ship Domain**This research is supported by the State of Lower Saxony as part of the project Critical Systems Engineering for Socio-Technical Systems (CSE)

IFAC-PapersOnLine, 2016

This paper presents a Nonlinear Model Predictive Control (NMPC) for position and velocity trackin... more This paper presents a Nonlinear Model Predictive Control (NMPC) for position and velocity tracking of underactuated surface vessels of elliptical ship domains with a collision avoidance scheme. A constrained nonlinear optimization problem is formulated to minimize vessel states' deviation from a time varying reference generated by a virtual vessel over a finite horizon. Linear constraints is imposed on input force and moment to be within the physical limits. Collision avoidance is represented as separation of each pair of the elliptic disks, representing the ship domain of our vessel and each encountered one, and is formulated as nonlinear time-varying constraint over the prediction horizon. A real-time C-code is generated using the ACADO toolkit and qpOASES solver with multiple shooting technique for discretization and Gauss-Newton iteration algorithm. This algorithm is computationally efficient, thus enabling real-time implementation of the proposed technique. MATLAB simulations are used to assess the validity of the proposed technique.

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Estimation of Counterfactual Interventions under Uncertainties

arXiv (Cornell University), Sep 14, 2023

Counterfactual analysis is intuitively performed by humans on a daily basis eg. "What should I ha... more Counterfactual analysis is intuitively performed by humans on a daily basis eg. "What should I have done differently to get the loan approved?". Such counterfactual questions also steer the formulation of scientific hypotheses. More formally it provides insights about potential improvements of a system by inferring the effects of hypothetical interventions into a past observation of the system's behaviour which plays a prominent role in a variety of industrial applications. Due to the hypothetical nature of such analysis, counterfactual distributions are inherently ambiguous. This ambiguity is particularly challenging in continuous settings in which a continuum of explanations exist for the same observation. In this paper, we address this problem by following a hierarchical Bayesian approach which explicitly models such uncertainty. In particular, we derive counterfactual distributions for a Bayesian Warped Gaussian Process thereby allowing for non-Gaussian distributions and non-additive noise. We illustrate the properties our approach on a synthetic and on a semi-synthetic example and show its performance when used within an algorithmic recourse downstream task.

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Verification of LSTM Neural Networks with Non-linear Activation Functions

Lecture Notes in Computer Science, 2023

Scenario-Oriented Contract Based Design for Safety of Autonomous Vehicles

Smart Innovation, Systems and Technologies, 2022

Multicore Performance analysis of a Multi-phase Electrical Motor Controller

HAL (Le Centre pour la Communication Scientifique Directe), Feb 5, 2014

Symbolic-Numeric Methods for Problem Solving in CPS (Dagstuhl Seminar 16491)

Dagstuhl Reports, 2016

Reflecting the fundamental role numeric and mixed symbolic-numeric arguments play in the analysis... more Reflecting the fundamental role numeric and mixed symbolic-numeric arguments play in the analysis, decision making, and control of cyber-physical processes, this seminar promoted cross-fertilization between the following research areas relevant to problem solving in cyber-physical domains: verification of numerical reactive systems such as embedded floating-point programs and hybrid systems, including novel means of error-propagation analysis; numerical and/or symbolic methods such as verified integrations, interval methods and arithmetic constraint solving; reactive and in-advance planning and optimization methods in complexly constrained spaces, robotics, astrodynamics and more. This combination of up to now only loosely coupled areas shed light on how advanced numerical methods can help improve the state of the art in rigorously interpreting and controlling cyber-physical phenomena. It naturally included the broad set of domain-specific solutions to the pertinent issues of perfor...

A prototype model checker for Duration Calculus

Improving the Detection of User Uncertainty in Automated Overtaking Maneuvers by Combining Contextual, Physiological and Individualized User Data

Highly automated driving will be a novel experience for many users and may cause uncertainty and ... more Highly automated driving will be a novel experience for many users and may cause uncertainty and discomfort for them [1]. An efficient real-time detection of user uncertainty during automated driving may trigger adaptation strategies, which could enhance the driving experience and subsequently the acceptance of highly automated driving [2]. In this study, we compared three different models to classify a user’s uncertainty regarding an automated vehicle’s capabilities and traffic safety during overtaking maneuvers based on experimental data from a driving-simulator study. By combining physiological, contextual and user-specific data, we trained three different deep neural networks to classify user uncertainty during overtaking maneuvers on different sets of input features. We evaluated the models based on metrics like the classification accuracy and F1 Scores. For a purely context-based model, we used features such as the Time-Headway and Time-To-Collision of cars on the opposing lan...

Functional verification of cyber-physical systems containing machine-learnt components

it - Information Technology, 2021

Functional architectures of cyber-physical systems increasingly comprise components that are gene... more Functional architectures of cyber-physical systems increasingly comprise components that are generated by training and machine learning rather than by more traditional engineering approaches, as necessary in safety-critical application domains, poses various unsolved challenges. Commonly used computational structures underlying machine learning, like deep neural networks, still lack scalable automatic verification support. Due to size, non-linearity, and non-convexity, neural network verification is a challenge to state-of-art Mixed Integer linear programming (MILP) solvers and satisfiability modulo theories (SMT) solvers [2], [3]. In this research, we focus on artificial neural network with activation functions beyond the Rectified Linear Unit (ReLU). We are thus leaving the area of piecewise linear function supported by the majority of SMT solvers and specialized solvers for Artificial Neural Networks (ANNs), the successful like Reluplex solver [1]. A major part of this research i...

Requirements for e-Navigation Architectures

International Journal of e-Navigation and Maritime Economy, 2016

Technology is changing the way of navigation. New technologies for communication and navigation c... more Technology is changing the way of navigation. New technologies for communication and navigation can be found on virtually every vessel. System architectures define structure and cooperation of components and subsystems. IMO, IALA, costal authorities, technology provider and many more actually propose new architectures for e-Navigation. This paper looks at other transportation domains and technical as normative requirements for e-Navigation architectures. With the aim of identifying possible synergies in the research, development, certification and standardization, this paper sets out to compare requirements and approaches of these two domains with respect to safety and security aspects. Since from an autonomy perspective, the automotive domain has started earlier and therefore has achieved a higher degree of technical progress, we will start with an overview of the developments in this domain. After that, the paper discusses the requirements on automation and assistance systems in the maritime domain and gives an overview of the developments into this direction within the maritime domain. This then allows us to compare developments in both domains and to derive recommendations for further developments in the maritime domain at the end of this paper.

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Martin Fränzle

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