Variable structure refers to the ability of a system to dynamically change its structure according to different situations. It provides component-based modeling and simulation environments with powerful modeling capability and the flexibility to design and analyze complex systems. In this paper, we discuss variable structure, specifically the structure and interface change capability, in DEVS-based modeling and simulation environments. The operations of structure and interface changes are discussed and their respective operation boundaries are defined. Three examples are given to illustrate the role of variable structure and how it can be used to model and design adaptive complex systems. Principles for the implementation of variable structure are also presented and illustrated in the DEVSJAVA modeling and simulation environment.

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Dynamic reconfiguration refers to the ability of a system to dynamically change its structure and interface according to different situations. It provides component-based modeling and simulation environments with powerful modeling capability and the extra flexibility to design and analyze complex systems. In this paper, we discuss dynamic reconfiguration, specifically the variable structure and interface change capability, in DEVS modeling and simulation environments. The operations of structure and interface changes are discussed and their operation boundaries are defined. Three examples are given to illustrate the role of dynamic reconfiguration and how it can be used to model and design adaptive complex systems. Principles for the implementation of dynamic reconfiguration are also presented and illustrated in the DEVSJAVA modeling and simulation environment.

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dynamic lookahead, optimistic DEVS. The conservative Parallel DEVS protocol offers a novel approach that allows conservative simulation of DEVSbased PDES systems. The protocol is based on the classical Chandy-Misra-Bryant synchronization mechanism, and it extends the DEVS abstract simulator to provide means for lookahead computation and null-messages. We present a purely conservative simulator, called CCD++, designed for running large-scale DEVS and Cell-DEVS models in parallel and distributed fashion. A comparative performance analysis is presented, analyzing the performance of CCD++ compared to an optimistic DEVS simulator. Several DEVS-based environmental models with different characteristics are studied. The experiments indicate that the conservative simulator improves performance in terms of execution time, memory usage, operational cost, and system stability for very large models. 1.