This paper addresses the problems related to data types used for time representation in DEVS, a formalism for the specification and simulation of discrete-event systems. When evaluating a DEVS simulation model into an actual computer simulation program, a data type is required to hold the virtual time of the simulation and the time elapsed in the model of the simulated system. We review the commonly data types used, and discuss the problems that each of them induce. In the case of floating point we show how, under certain conditions, the simulation can break causality relations, treat simultaneous events as non simultaneous or treat non simultaneous events as simultaneous. In the case of integers using fixed unit we list a number of problems arising when composing models operating at different timescales. In the case of structures that combine several fields, we show that, at the cost of a lower performance, most of the previous problems can be avoided, although not totally. Finally, we describe an alternative representation data type we developed to cope with the data type problems.
International audienceCellular automata were designed by John von Neumann in the 1940s, as a mathematical abstraction for modeling self-replicating algorithms. Since then, cellular automata have been widely studied theoretically and evolved into multiple variants. In the 1970s, Bernard P. Zeigler proposed a formalism rooted on systems theory principles, named DEVS (discrete-event systems specifications), which paved the way for component-based modeling and simulation and related methodologies. The purpose of this article is to survey how cellular automata and its variant, called cell-DEVS, may be used to implement computer simulations that can be used as digital serious games. The authors illustrate that implementation through some of the practical applications of such cellular automata. They show various serious game applications using real case studies: first, a simple bouncing ball and pinball game, a particle collision model, another on gossip propagation, and an application on human behavior at a metro station. Then, they show an application to social simulation using a voters game, a theoretical application (a model called Daisy World, which is derived from Gaia theory), and applications to physical phenomena such as a sandpile formation model or, finally, a three-dimensional model of a "virtual clay" that changes its shape when it is subject to pressure effects
To better support multiscale modeling and simulation, we present a multiscale time representation consisting of data types, data structures, and algorithms that collectively support the recording of past events and scheduling of future events in a discrete event simulation. Our approach addresses the drawbacks of conventional time representations: limited range in the case of 32-or 64-bit fixed-point time values; problematic rounding errors in the case of floating-point numbers; and the lack of a universally acceptable precision level in the case of brute force approaches. The proposed representation provides both extensive range and fine resolution in the timing of events, yet it stores and manipulates the majority of event times as standard 64-bit numbers. When adopted for simulation purposes, the representation allows a domain expert to choose a precision level for his/her model. This time precision is honored by the simulator even when the model is integrated with other models of vastly different time scales. Making use of C++11 programming language features and the Discrete Event System Specification formalism, we implemented a simulator to test the time representation and inform a discussion on its implications for collaborative multiscale modeling efforts.
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