1,721,002 research outputs found
CEGAR Based Bounded Model Checking of Discrete Time Hybrid Systems
No full textMany hybrid systems can be conveniently modeled as Piecewise Affine Discrete Time Hybrid Systems PA-DTHS. As well known Bounded Model Checking (BMC) for such systems comes down to solve a Mixed Integer Linear Programming (MILP) feasibility problem.
We present a SAT based BMC algorithm for automatic verification of PA-DTHSs. Using Counterexample Guided Abstraction Refinement (CEGAR) our algorithm gradually transforms a PA-DTHS verification problem into larger and larger SAT problems.
Our experimental results show that our approach can handle PA-DTHSs that are more then 50 times larger than those that can be handled using a MILP solver
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Formal verification at system level
No full textSystem Level Analysis calls for a language comprehensible to experts with different background and yet precise enough to support meaningful analyses. SysML is emerging as an effective balance between such conflicting goals. In this paper we outline some the results obtained as for SysML based system level functional formal verification by an ESA/ESTEC study, with a collaboration among INTECS and La Sapienza University of Roma. The study focuses on SysML based system level functional requirements techniques
Linear Constraints as a Modeling Language for Discrete Time Hybrid Systems
No full textModel Based Design is particularly appealing in embedded software design where system level specifications are much easier to define than the control software behavior itself. Formal analysis of Embedded Systems requires modelling both continuous systems (typically, the plant) as well as discrete systems (the controller). This is typically done using Hybrid Systems. Mixed Integer Linear Programming (MILP) based abstraction techniques have been successfully applied to automatically synthesize correct-by-construction control software for Discrete Time Linear Hybrid System, where plant dynamics is modeled as a linear predicate over state, input, and next state variables. MILP solvers requires constraints represented as conjunctive predicates. In this paper we show that, under the hypothesis that each variable ranges over a bounded interval, any linear predicate built upon conjunction and disjunction of linear constraints can be automatically transformed into an equisatisfiable conjunctive predicate. Moreover, since variable bounds play a key role in this transformation, we present an algorithm that taking as input a linear predicate, computes implicit variable bounds
SyLVaaS
No full textThe goal of System Level Formal Verification is to show system correctness notwithstanding uncontrollable events (disturbances), as for example faults, variation in system parameters, external inputs, etc. This may be achieved with an exhaustive Hardware In the Loop Simulation based approach, by considering all relevant scenarios in the System Under Verification (SUV) operational environment.
SyLVaaS is a Web-based tool enabling Verification as a Service (VaaS). SyLVaaS implements an assume-guarantee approach to the verification problem outlined above. SyLVaaS takes as input a high-level model defining the SUV operational environment and computes, using parallel algorithms deployed in a cluster infrastructure, a set of highly optimised simulation campaigns, which can be executed in an embarrassingly parallel fashion on a set of Simulink instances, using a platform independent Simulink driver downloadable from the SyLVaaS
Web site. As the actual simulation is carried out at the user premises (e.g., in a private cluster), SyLVaaS allows full Intellectual Property protection on the SUV model and the user verification flow.
The simulation campaigns computed by SyLVaaS randomise the verification order of operational scenarios and this enables, at anytime during the parallel simulation activity, the estimation of the completion time and the computation of an upper bound to the Omission Probability, i.e., the probability that there is a yet-to-be-simulated operational scenario which violates the property under verification. This information supports graceful degradation in the verification activity
Control Software Visualization
No full textMany software as well digital hardware automatic
synthesis methods define the set of
implementations meeting the given system
specifications with a boolean relation K
(controller). Such relation, given a system state
s and an action u, returns 1 iff taking action u
in state s leads in the system goal or at least
one step closer to it. In order to determine at
hand if K is a "good" controller, e.g., if it
covers a wide enough portion of the system state
space, or to provide an high level view of the
actions enabled by K, it is useful to picture K in
a 2D or 3D diagram. In this paper, starting from a
canonical representation for K, we propose an
algorithm to automatically generate such a
picture, relying on available graphing tools
Linear Constraints and Guarded Predicates as a Modeling Language for Discrete Time Hybrid Systems
No full textModel based design is particularly appealing in
software based control systems (e.g., embedded
software) design, since in such a case system
level specifications are much easier to define
than the control software behavior itself. In
turn, model based design of embedded systems
requires modeling both continuous subsystems
(typically, the plant) as well as discrete
subsystems (the controller). This is typically
done using hybrid systems. Mixed Integer Linear
Programming (MILP) based abstraction techniques
have been successfully applied to automatically
synthesize correct-by-construction control
software for discrete time linear hybrid systems,
where plant dynamics is modeled as a linear
predicate over state, input, and next state
variables. Unfortunately, MILP solvers require
such linear predicates to be conjunctions of
linear constraints, which is not a natural way of
modeling hybrid systems. In this paper we show
that, under the hypothesis that each variable
ranges over a bounded interval, any linear
predicate built upon conjunction and disjunction
of linear constraints can be automatically
translated into an equivalent conjunctive
predicate. Since variable bounds play a key role
in this translation, our algorithm includes a
procedure to compute all implicit variable bounds
of the given linear predicate. Furthermore, we
show that a particular form of linear predicates,
namely guarded predicates, are a natural and
powerful language to succinctly model discrete
time linear hybrid systems dynamics. Finally, we
experimentally show the feasibility of our
approach on an important and challenging case
study taken from the literature, namely the
multi-input Buck DC-DC Converter. As an example,
the guarded predicate that models (with 57
constraints) a 6-inputs Buck DC-DC Converter is
translated in a conjunctive predicate (with 102
linear constraints) in about 40 minutes
QKS
No full textQKS is an available at http://mclab.di.uniroma1.it. It is a software tool for the automatic synthesis of quantized feedback control software from the plant model and formal closed loop specifications
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