A data type for discretized time representation in DEVS

International audienceThis 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 com- puter 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 cer- tain 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 devel- oped to cope with the data type problems

Improved Cell-DEVS model definition in CD

Abstract. We describe two improvements made to CD++, a tool for modeling and simulation of cellular models based on the Cell-DEVS formalism. The modifications described in this work remove some limitations existing in the previous implementation. These modifications allow the cells to use multiple state variables and multiple ports for inter-cell communication. The cellular model specification language has been extended to cover these cases, making CD++ a more powerful tool