查看文章

There are four main objectives of this survey. First, the general theory of multilevel systems is outlined, and basic related issues are presented. Second, the literature on the research topics that utilize the fundamental concepts, structures, and methodologies of multilevel systems is classified and documented. Third, principal features, advantages, and limitations as pertinent to various practical applications are pointed out. Finally, extensions to other research areas as well as prospects for future investigations are delineated.