1,721,201 research outputs found
Opere matematiche della Pubblica Biblioteca di Ferrara (1753-1815)
No full textCatalogo della mostra di opere matematiche allestita in occasione del 250° anniversario della nascita di Gianfrancesco Malfatti, matematico di notevole interesse che è stato professore all'Università di Ferrara. La mostra mirava a ricostruire anche la biblioteca matematica dell'Università nel Settecento, particolarmente dopo la riforma del 1770, che regolamentava la biblioteca come un istituto universitario. Il volume comprende le schede bibliografiche e la riproduzione dei frontespizi di 173 opere (alcune in più volumi, o raccolte miscellanee, o collezioni di giornali); un saggio introduttivo pensato per delineare una possibile lettura della mostra con riferimento alla storia delle scienze fisico-matematiche; un indice alfabetico; un indice geografico; la bibliografia; alcune indicazioni di appartenenza delle opere. Il catalogo può essere utilizzato come strumento bibliografico per la storia delle scienze matematiche dato che tra le schede elencate si trovano descritte in dettaglio molte opere di primaria importanza per queste discipline. Esso sottolinea anche l'interesse delle raccolte librarie dell'Ariostea come documentazione di prim'ordine per la storia delle scienze. I curatori si sono divisi i compiti nel modo seguente: M. T. Borgato si è occupata della redazione dell'intero volume, L. Capra ha redatto le schede dei manoscritti e degli incunaboli e ha fornito consulenza bibliografica, A. Ficca ha predisposto la quasi totalità delle schede e collaborato alla compilazione degli indici, L. Pepe ha scritto il saggio iniziale ed è intervenuto nella scelta delle opere e nella schedatura dei giornali
Towards a Petri net Model for Graph Transformation Systems
Full text linkGraph transformation systems (GTS) have been successfully proposed as a general, theoretically sound model for concurrency. Petri nets (PN), on the other side, are a central and intuitive formalism for concurrent or distributed systems, well supported by a number of analysis techniques/tools. Some PN classes have been shown to be instances of GTS. In this paper, we change perspective presenting an operational semantics of GTS in terms of Symmetric Nets, a well-known class of Coloured Petri nets featuring a structured syntax that outlines model symmetries. Some practical exploitations of the proposed operational semantics are discussed. In particular, a recently developed structural calculus for SN is used to validate graph rewriting rules in a symbolic way
(Toward) Discrete-event simulation of reflective Petri nets
No full textThe design of dynamic, adaptable discrete-event systems calls for adequate modeling formalisms and tools in order to manage possible changes occurring during system's lifecycle. A common approach is to pollute the design with details not concerning the current system behavior, rather its evolution. That hampers analysis, reuse and maintenance in general. A Petri net-based reflective model (based on classical Petri nets) was recently proposed to support dynamic discrete-event system's design, and was applied to dynamic workflow's management. Behind there is the idea that keeping functional aspects separated from evolutionary ones, and applying evolution to the (current) system only when necessary, results in a clean formal model for dynamic systems. This model preserves the ability of verifying properties typical of classical Petri nets. As a first step toward the implementation (in the short time) of a discrete-event simulator, Reflective Petri nets are provided in this paper with a semantics defined in terms of labeled state-transitions
Addressing soundness and efficiency issues in dynamic processes : a reflective PN-based modeling approach
No full textThe design of dynamic workflows needs adequate modeling formalisms and tools to soundly handle changes during workflow operation. A common approach is to pollute workflow design with details that do not regard the current behavior, but rather evolution. That hampers analysis, reuse and maintenance in general. We propose and discuss the adoption of a recent Petri net-based reflective model as a support to dynamic workflow design. Keeping separated functional aspects from evolution, results in a dynamic workflow model merging flexibility and ability of formally verifying basic workflow properties. A structural characterization of sound dynamic workflows is adopted. An application to a well localized problem is presented: how to determine what tasks should be redone and which ones do not when transferring a workflow instance from an old to a new template
Extending the symmetry approach in (S)WN models
No full textThe most useful qualitative/quantitative analysis tech niques for Discrete-Event Dynamic Systems are still state space based. It is well known that similar techniques suf fer from the possible state space combinatorial explosion. An approach to face the problem is the exploitation of be havioral symmetries of systems for building quotient (i.e. reduced) state-transition graphs. Behavioral symmetries can be naturally described using a high-level Petri Net formalism, Well-Formed Coloured Nets (WN). WNs ex ploit symmetries for the automatic generation of a quotient graph, the Symbolic Reachability Graph (SRG). The SRG provides a compact representation of the ordinary state transition graph of the modeled system. Performance anal ysis is possible with the SWN formalism (a stochastic ex tension of WNs), which allows to automatically build a lumped Continuous Time Markov Chain from the SRG. The SRG technique reveals very effective when applied to systems with a high degree of symmetry, but it looses most of its efficacy when considering partially symmetrical sys tems, namely systems mixing a (prevalent) symmetric be havior with some asymmetry. The intuitive explanation is that in WNs (a)symmetries are specified at syntax level as part of the model color (i.e. data) structure, on which the SRG definition relies. A first attempt of adding flexibility to the static symmetry approach (typical of the SRG), based on the very intuitive idea of taking into account asymmetries only when they ac tually take place, has lead to the so-called Extended Sym bolic Reachability Graph (ESRG). The ESRG gives a rep resentation of the system behavior significantly more com pact than the SRG in case of “nearly symmetrical” systems (a restricted class of partially symmetrical systems). The main ESRG limit lies in its reduced capability of capturing more general kinds of symmetries. In the paper the (E)SRG technique is surveyed and is ex tended to caught local symmetries, extremely frequent in real systems. A new high-level reachability graph is intro duced, which reveals more compact than the corresponding (E)SRG for SWN models exhibiting a diffuse asymmetric behavior. The extension retains the basic (E)SRG proper ties
Algebraic techniques & symmetries : an efficient simulation approach for well-formed Petri nets
No full textPerformance-based characterization of fault tolerant embedded electric applications by means of stochastic hlpn models
No full textIn embedded automation systems, functional, performance and fault-tolerant (FT) requirements are strongly related. The use of formal models since the early design phases of such systems is by now considered not only as a promising opportunity, but as a real need. From this point of view a challenging issue is the possibility of integrating/combining the different modeling approaches that are usually adopted in the specification and val idation/evaluation phases. In this paper we present a selection of outcomes of a modeling activity started some years ago, that aims at experiencing a class of High-Level Stochastic Petri Nets (SWNs) as unifying specification/analysis framework in the field of embedded FT electric applications. We here focus on the speci fication and the performance-based characterization of the the stable memory mechanism, the blueprint of a FT architecture still employed in several plants of the Italian electric power distribution network. In particular we show that quantitative results can be also used to infer interesting functional properties of the mechanism
ANALYSIS/SIMULATION OF COMPLEX SWN MODELS: A STRUCTURAL APPROACH
No full textPetri nets structural techniques may be used not only to study interesting system properties, but also to manage state space explosion and discrete-event simulation complexity. In order to avoid net unfolding, a symbolic calculus for high level PN structural analysis is needed, directly working on net annotations. Colored Petri Nets structural analysis relies upon a common subset of functional operators. A language to denote structural relations in WN (a CPN flavor retaining expressive power) was recently introduced and proved to be closed under these operators. The paper shows an application of structural techniques for efficient performanceoriented analysis of a complex StochasticWNmodel representing a P2P configuration management tool. Structural techniques are used in combination with symmetries specified through the SWN formalism
State-space reduction in colored PN with linearly constrained domains
No full textColored Petri Nets (CPN) State-space reduction is nor mally based upon behavioral equivalences or symmetries. Well-Formed Nets (WN) are a CPN flavor retaining expres sive power and allowing the direct construction of a Sym bolic Reachability Graph (SRG), that captures symmetries suitably encoded in the WN syntax. Statically specified symmetries, however, are not effective in many real cases. In this paper a new quotient graph for WN-like models is introduced, that relies upon a simple mapping of color domains into numerical domains, and makes use of linear constraints to perform a sort of symbolic execution. It is compared to a recently presented approach exploiting lo cal symmetries. The model of an asymmetric distributed algorithm is used as running example
A symbolic reachability graph and associated Markov process for a class of dynamic Petri nets
No full textThe design of evolving discrete-event systems needs for adequate modeling techniques. A Petri net-based reflective layout has been recently proposed to support dynamic discreteevent system's design. Keeping functional aspects separated from evolutionary ones, deploying changes to the (current) system configuration when necessary, results in a clean formal model preserving the ability of verifying properties typical of Petri nets. Reflective Petri nets are provided with a pseudo-symbolic statetransition graph, and an associated lumped Markov process
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