Gereon Kremer

Bio: Gereon Kremer is an academic researcher from RWTH Aachen University. The author has contributed to research in topics: Satisfiability modulo theories & Satisfiability. The author has an hindex of 6, co-authored 21 publications receiving 137 citations. Previous affiliations of Gereon Kremer include Stanford University & University of Bath.

cvc5: A Versatile and Industrial-Strength SMT Solver

Abstract: Abstract cvc5 is the latest SMT solver in the cooperating validity checker series and builds on the successful code base of CVC4. This paper serves as a comprehensive system description of cvc5 ’s architectural design and highlights the major features and components introduced since CVC4 1.8. We evaluate cvc5 ’s performance on all benchmarks in SMT-LIB and provide a comparison against CVC4 and Z3.

SMT-RAT: An Open Source C++ Toolbox for Strategic and Parallel SMT Solving

Abstract: During the last decade, popular SMT solvers have been extended step-by-step with a wide range of decision procedures for different theories. Some SMT solvers also support the user-defined tuning and combination of such procedures, typically via command-line options. However, configuring solvers this way is a tedious task with restricted options.

Deciding the Consistency of Non-Linear Real Arithmetic Constraints with a Conflict Driven Search Using Cylindrical Algebraic Coverings

Abstract: We present a new algorithm for determining the satisfiability of conjunctions of non-linear polynomial constraints over the reals, which can be used as a theory solver for satisfiability modulo theory (SMT) solving for non-linear real arithmetic. The algorithm is a variant of Cylindrical Algebraic Decomposition (CAD) adapted for satisfiability, where solution candidates (sample points) are constructed incrementally, either until a satisfying sample is found or sufficient samples have been sampled to conclude unsatisfiability. The choice of samples is guided by the input constraints and previous conflicts. The key idea behind our new approach is to start with a partial sample; demonstrate that it cannot be extended to a full sample; and from the reasons for that rule out a larger space around the partial sample, which build up incrementally into a cylindrical algebraic covering of the space. There are similarities with the incremental variant of CAD, the NLSAT method of Jovanovic and de Moura, and the NuCAD algorithm of Brown; but we present worked examples and experimental results on a preliminary implementation to demonstrate the differences to these, and the benefits of the new approach.

Zephyrus2: On the Fly Deployment Optimization Using SMT and CP Technologies

Abstract: Modern cloud applications consist of software components deployed on multiple virtual machines. Deploying such applications is error prone and requires detailed system expertise. The deployment optimization problem is about how to configure and deploy applications correctly while at the same time minimizing resource cost on the cloud. This problem is addressed by tools such as Zephyrus, which take a declarative specification of the components and their configuration requirements as input and propose an optimal deployment. This paper presents Zephyrus2, a new tool which addresses deployment optimization by exploiting modern SMT and CP technologies to handle larger and more complex deployment scenarios. Compared to Zephyrus, Zephyrus2 can solve problems involving hundreds of components to be deployed on hundreds of virtual machines in a matter of seconds instead of minutes. This significant speed-up, combined with an improved specification format, enables Zephyrus2 to interactively support on the fly decision making.

Linear And Nonlinear Programming

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Scheduling Real-Time Communication in IEEE 802.1Qbv Time Sensitive Networks

Abstract: The enhancements being developed by the Time-Sensitive Networking Task Group as part of IEEE 802.1 emerge as the future of real-time communication over Ethernet networks for automotive and industrial application domains. In particular IEEE 802.1Qbv is key to enabling timeliness guarantees via so-called time-aware shapers. In this paper, we address the computation of fully deterministic schedules for 802.1Qbv-compliant multi-hop switched networks. We identify and analyze key functional parameters affecting the deterministic behaviour of real-time communication under 802.1Qbv and, based on a generalized configuration of these parameters, derive the required constraints for computing offline schedules guaranteeing low and bounded jitter and deterministic end-to-end latency for critical communication flows. Furthermore, we discuss several optimization directions and concrete configurations exposing trade-offs against the required computation time. We also show the performance of our approach via synthetic network workloads on top of different network configurations.

A Survey of Symbolic Execution Techniques

Abstract: Many security and software testing applications require checking whether certain properties of a program hold for any possible usage scenario. For instance, a tool for identifying software vulnerabilities may need to rule out the existence of any backdoor to bypass a program’s authentication. One approach would be to test the program using different, possibly random inputs. As the backdoor may only be hit for very specific program workloads, automated exploration of the space of possible inputs is of the essence. Symbolic execution provides an elegant solution to the problem, by systematically exploring many possible execution paths at the same time without necessarily requiring concrete inputs. Rather than taking on fully specified input values, the technique abstractly represents them as symbols, resorting to constraint solvers to construct actual instances that would cause property violations. Symbolic execution has been incubated in dozens of tools developed over the past four decades, leading to major practical breakthroughs in a number of prominent software reliability applications. The goal of this survey is to provide an overview of the main ideas, challenges, and solutions developed in the area, distilling them for a broad audience.

The Probabilistic Model Checking Landscape

Abstract: Randomization is a key element in sequential and distributed computing. Reasoning about randomized algorithms is highly non-trivial. In the 1980s, this initiated first proof methods, logics, and model-checking algorithms. The field of probabilistic verification has developed considerably since then. This paper surveys the algorithmic verification of probabilistic models, in particular probabilistic model checking. We provide an informal account of the main models, the underlying algorithms, applications from reliability and dependability analysis---and beyond---and describe recent developments towards automated parameter synthesis.