NSA-DEVS: Combining Mealy Behaviour and Causality

The RPDEVS ("Revised PDEVS") formalism has been introduced to allow for a simple description of Mealy-type components that behave consistently. This made it necessary to change the way the simulator handles event chains. Using a simple example model we show that the proposed algorithm has serious problems with the resulting sequence of concurrent events. Therefore we introduce NSA-DEVS, a variant formalism that is inspired by ideas from non-standard analysis (NSA). It uses infinitesimal time delays to make a natural ordering of concurrent events easy, without the need to fix lots of additional parameters. As proof of concept we describe the example model in NSA-DEVS and implement it in a suitably twisted RPDEVS simulator.