Rodrigo Castro

A Formal Framework for Stochastic Discrete Event System Specification Modeling and Simulation

We introduce an extension of the classic Discrete Event System Specification (DEVS) formalism that includes stochastic features. Based on the use of the probability spaces theory we define the stochastic DEVS (STDEVS) specification, which provides a formal framework for modeling and simulation of general non-deterministic discrete event systems. The main theoretical properties of the STDEVS framework are treated, including a new definition of legitimacy of models in the stochastic context and a proof of STDEVS closure under coupling. We also illustrate the new stochastic modeling capabilities introduced by STDEVS and their relation with those found in classic DEVS. Practical simulation examples are given involving performance analysis of computer systems and hybrid modeling of networked control systems, applications where the modeling of stochastic components is vital.

Graphical modeling and simulation of discrete-event systems with CD++Builder

We introduce CD++Builder, an open-source environment that aims at providing easy-to-use graphical modeling tools to simplify the construction of models and the execution of simulations of complex Discrete Event System Specification (DEVS) models. The architecture and implementation of CD++Builder focuses on providing simple definition and reuse of components, offering easy extensibility to support new features. CD++Builder includes graphical editors for DEVS-coupled models, DEVS-Graphs and C++ atomic models; it provides code templates that are synchronized with their graphical versions, and it greatly simplifies the software installation and update procedures. We show how this environment can be used to build and simulate DEVS models, and we compare the process with previous versions and other simulation tools, showing that CD++Builder can improve model development by creating DEVS models in a completely assisted manner, including advanced graphical interfaces.

Discrete Event Modeling and Simulation-Driven Engineering for the ATLAS Data Acquisition Network

The authors present an iterative and incremental development methodology for simulation models in network engineering projects. Driven by the DEVS (Discrete Event Systems Specification) formal framework for modeling and simulation, they aim to assist network design, test, analysis, and optimization processes. A practical application of the methodology is presented for a case study in the data acquisition system of the ATLAS particle physics experiment at CERNs Large Hadron Collider at CERN. By adopting the DEVS M&S formal framework in combination with software engineering best practices, the authors develop network simulation models along with enhanced modeling capabilities and boosted simulation performance for tools in a robust yet flexible way.

Advanced IDE for modeling and simulation of discrete event systems

Creating models and analyzing simulation results can be a difficult and time-consuming task, especially for non-experienced users. Although several DEVS simulators have been developed, the software that aids in the modeling and simulation cycle still requires advanced development skills, and they are implemented using non-standard interfaces, which makes them difficult to extend. The architecture and design of CD++Builder we present here can simplify the construction and simulation of DEVS models, facilitate model reuse and promote good modeling practices by allowing enhanced graphical editing and integration of tools into a single environment. The Eclipse-based environment includes new graphical editors for DEVS coupled models, DEVS-Graphs and C++ atomic models (including code templates that are synchronized with the graphical versions). Integration with Eclipse allows extensibility while simplifying software development, installation and updates.

An integrative approach for hybrid modeling, simulation and control of data networks based on the DEVS formalism

In this chapter we present recently developed theoretical and practical tools for the modeling and simulation (M&S) of hybrid systems with a focus on data networks. An integrative methodology based on the Discrete EVent Systems specification (DEVS) permits the M&S of complex systems by choosing the most convenient representation paradigm for each subsystem, allowing discrete time, discrete event and continuous models to coexist. In particular, we focus on designing and studying Quality of Service (QoS) controllers for data networks at diverse granularity levels, enabling the adoption of control theory, and aiming at the final implementation of algorithms in real-time hardware.

Quantization-based integration methods for delay-differential equations

This paper introduces a new class of numerical delay differential equation solvers based on state quantization instead of time slicing. The numerical properties of these algorithms, i.e., stability and convergence, are discussed, and a number of benchmark problems are being simulated and compared with the state-of-the-art solutions to these problems as they have been previously reported in the open literature.

Architecture for integrated modeling, simulation and visualization of environmental systems using GIS and cell-devs

Online Geographic Information Systems (GIS) and their associated data visualization technologies are playing an increasingly important role in providing updated information for environmental models. The analysis of simulation results are often benefited from their georeferenced animated visualization. We present an architectural web-based integration of the DCD++ distributed modeling and simulation frame-work as the centerpiece of a GIS-based scientific workflow to study environmental phenomena. We demonstrate an end-to-end application of the proposed architecture by means of a wildfire spreading model, backed by online updates of different parameters affecting the environmental system under study. Google Earth and GRASS are the two GIS systems selected to highlight the flexibility of the integrated system.

A DEVS—based End-to-end Methodology for Hybrid Control of Embedded Networking Systems

Abstract We present a formal Modeling and Simulation (M&S) methodology for hybrid control of networking systems. The method is used for analysis, design and implementation of Quality of Service (QoS) control systems in Network Processor (NP)-based applications. We apply continuous Control Systems Theory to enforce Admission Control strategies into discrete–event network traffic. This represents a hybrid system modeling problem, that has to be treated formally to guarantee the applicability of the continuous control theoretical results into discrete– event systems. We show that using DEVS (Discrete Event System Specification), in combination with Quantized State Systems (QSS) numerical methods for the approximation of continuous systems, offers numerous advantages: these frameworks provide the means to accurately analyze and design hybrid models for Admission Control and they can be seamlessly integrated into a unified formal framework. It also enables the transition between the DEVS–based simulation and the deployment of the obtained hybrid models into the target networking platform.

Activity of order n in continuous systems

In this work we generalize the concept of activity of continuous time signals. We define the activity of order n of a signal and show that it allows us to estimate the number of sections of polynomials up to order n which are needed to represent that signal with a certain accuracy. Then we apply this concept to obtain a lower bound for the number of steps performed by quantization-based integration algorithms in the simulation of ordinary differential equations. We perform an exhaustive analysis over two examples, computing the activity of order n and comparing it with the number of steps performed by different integration methods. This analysis corroborates the theoretical predictions and also allows us to measure the suitability of the different algorithms depending on how close to the theoretical lower bound they perform.

GQLink: an implementation of Quantized State Systems (QSS) methods in Geant4

Simulations in high energy physics (HEP) often require the numerical solution of ordinary differential equations (ODE) to determine the trajectories of charged particles in a magnetic field when particles move throughout detector volumes. Each crossing of a volume interrupts the underlying numerical method that solves the equations of motion, triggering iterative algorithms to estimate the intersection point within a given accuracy. The computational cost of this procedure can grow significantly depending on the application at hand. Quantized State System (QSS) is a recent family of discrete-event driven numerical methods exhibiting attractive features for this type of problems, such as native dense output (sequences of polynomial segments updated only by accuracy-driven events) and lightweight detection and handling of volume crossings. In this work we present GQLink, a proof-ofconcept integration of QSS with the Geant4 simulation toolkit which stands as an interface for co-simulation that orchestrates robustly and transparently the interaction between the QSS simulation engine and aspects such as geometry definition and physics processes controlled by Geant4. We validate the accuracy and study the performance of the method in simple geometries (subject to intense volume crossing activity) and then in a realistic HEP application using a full CMS detector configuration.