On the Expressive Power of Schedulers in Distributed Probabilistic Systems

AbstractIn this paper, we consider several subclasses of distributed schedulers and we investigate the ability of these subclasses to attain worst-case probabilities.Based on previous work, we consider the class of distributed schedulers, and we prove that randomization adds no extra power to distributed schedulers when trying to attain the supremum probability of any measurable set, thus showing that the subclass of deterministic schedulers suffices to attain the worst-case probability. Traditional schedulers are a particular case of distributed schedulers. So, since our result holds for any measurable set, our proof generalizes the well-known result that randomization adds no extra power to schedulers when trying to maximize the probability of an ω-regular language. However, non-Markovian schedulers are needed to attain supremum probabilities in distributed systems.We develop another class of schedulers (the strongly distributed schedulers) that restricts the nondeterminism concerning the order in which components execute. We compare this class against previous approaches in the same direction, showing that our definition is an important contribution. For this class, we show that randomized and non-Markovian schedulers are needed to attain worst-case probabilities.We also discuss the subclass of finite-memory schedulers, showing the intractability of the model checking problem for these schedulers

systems

Verification of partial-information probabilisti

Sobre la verificación automática de autómatas probabilistas distribuidos con información parcial /

Tesis (Doctor en Ciencias de la Computación)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía y Física, 2010.En esta tesis desarrollamos algoritmos y técnicas de análisis basadas en model checking para analizar la corrección de sistemas distribuidos con características aleatorias y no deterministas. Una contribución importante es la demostración de que no existe un algoritmo que resuelva el problema de verificación de forma totalmente automática. A pesar de este resultado, presentamos algoritmos que, si bien no pueden determinar la corrección para todos los sistemas y propiedades, sirven para detectar que ciertos sistemas son correctos o incorrectos. Uno de los impedimentos más frecuentes a la hora de verificar PDMs es el problema de la explosión de estado. Este problema, bien conocido y atacado en model checking, se agrava en el ámbito de model checking cuantitativo. Existen trabajos previos que, con el fin de atacar este problema, presentan adaptaciones de las técnicas de reducción orden parcial para model checking cualitativo al caso cuantitativo. Presentamos una nueva adaptación de la técnica de reducción de orden parcial. Nuestra adaptación aprovecha el hecho de que las componentes de un sistema concurrente tienen acceso limitado a la información sobre el estado global del sistema. Concluímos con casos de estudio que muestran las mejoras de nuestros algoritmos y nuestra técnica de orden parcial.Sergio Giro ; dirigido por Pedro R. D'Argenio

Efficient computation of exact solutions for quantitative model checking

Quantitative model checkers for Markov Decision Processes typically use finite-precision arithmetic. If all the coefficients in the process are rational numbers, then the model checking results are rational, and so they can be computed exactly. However, exact techniques are generally too expensive or limited in scalability. In this paper we propose a method for obtaining exact results starting from an approximated solution in finite-precision arithmetic. The input of the method is a description of a scheduler, which can be obtained by a model checker using finite precision. Given a scheduler, we show how to obtain a corresponding basis in a linear-programming problem, in such a way that the basis is optimal whenever the scheduler attains the worst-case probability. This correspondence is already known for discounted MDPs, we show how to apply it in the undiscounted case provided that some preprocessing is done. Using the correspondence, the linear-programming problem can be solved in exact arithmetic starting from the basis obtained. As a consequence, the method finds the worst-case probability even if the scheduler provided by the model checker was not optimal. In our experiments, the calculation of exact solutions from a candidate scheduler is significantly faster than the calculation using the simplex method under exact arithmetic starting from a default basis.Comment: In Proceedings QAPL 2012, arXiv:1207.055

Sustainable magnesium phosphate micromortars formulated with PAVAL® alumina by-product as micro-aggregate

Magnesium phosphate cement (MPC) is an attractive alternative to Portland cement (PC) since it can also be obtained using by-products and wastes as raw materials. This research uses low-grade MgO (LG-MgO) as a magnesium source to obtain MPC, reducing CO2 emissions related to MPC production. The obtained binder can be referred to as 'sustainable MPC' (sust-MPC). Moreover, this investigation incorporates a by-product obtained in the aluminium recycling process, named PAVAL® (PV). The addition of PV (5, 17.5, and 35 wt.%) and water to solid (W/S) ratio (0.23, 0.25, 0.28, and 0.31) were studied in terms of mechanical and fresh properties, leaching behaviour, and microstructure to evaluate the degree of PV inclusion in the K-struvite matrix. The addition of PV into sust-MPC improves the mechanical behaviour of the micromortars, indicating a good inclusion of PV. The mechanical and fresh behaviour of the formulations, and BSEM-EDS analysis revealed the potential chemical interaction between Al and K-struvite matrix. The addition of 17.5 wt.% of PV with a W/S of 0.25 showed the best mechanical performance (∼40 MPa of compressive strength at 28 days of curing). The amount of PV should be lower than 17.5 wt.% to classify it as non-hazardous material at the end-of-life

Testing Reactive Probabilistic Processes

We define a testing equivalence in the spirit of De Nicola and Hennessy for reactive probabilistic processes, i.e. for processes where the internal nondeterminism is due to random behaviour. We characterize the testing equivalence in terms of ready-traces. From the characterization it follows that the equivalence is insensitive to the exact moment in time in which an internal probabilistic choice occurs, which is inherent from the original testing equivalence of De Nicola and Hennessy. We also show decidability of the testing equivalence for finite systems for which the complete model may not be known

VizieR Online Data Catalog: HD 284149 SPHERE/IFS spectrum (Bonavita+, 2017)

HD 284149 was observed with SPHERE in IRDIFS mode on 2015-10-25 and with IRDIFS_EXT mode on 2015-11-27 as part of the SHINE (SpHere INfrared survey for Exoplanet) GTO campaign. (1 data file)

Modelling Workflows using Petri Nets with Multiple Instances

Abstract. In this paper we present a graphical language for workflow specification and some examples of its use. This graphical language is expected to be the basis for more complete formalisms, and focuses in the fact that there are some processes for which multiple instances are executed, and that these instances may interact (e. g., by sharing resources). Each instance may represent a different actor or a different instance of a task performed by an actor (in addition, the different actors and tasks may share some resource). For this reason, we believe that the notion of multiple instances is essential to the specification of workflows and distributed systems.

Distributed probabilistic input/output automata: Expressiveness, (un)decidability and algorithms

Probabilistic model checking computes the probability values of a given property quantifying over all possible schedulers. It turns out that maximum and minimum probabilities calculated in such a way are over-estimations on models of distributed systems in which components are loosely coupled and share little information with each other (and hence arbitrary schedulers may result too powerful). Therefore, we introduced definitions that characterise which are the schedulers that properly capture the idea of distributed behaviour in probabilistic and nondeterministic systems modelled as a set of interacting components. In this paper, we provide an overview of the work we have done in the last years which includes: (1) the definitions of distributed and strongly distributed schedulers, providing motivation and intuition; (2) expressiveness results, comparing them to restricted versions such as deterministic variants or finite-memory variants; (3) undecidability results—in particular the model checking problem is not decidable in general when restricting to distributed schedulers; (4) a counterexample-guided refinement technique that, using standard probabilistic model checking, allows to increase precision in the actual bounds in the distributed setting; and (5) a revision of the partial order reduction technique for probabilistic model checking. We conclude the paper with an extensive review of related work dealing with similar approaches to ours.Fil: Giro, Sergio Sebastian. Technische Universität München; AlemaniaFil: D'argenio, Pedro Ruben. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ferrer Fioriti, Luis Maria. Saarland University; Alemani