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Hidden variables in dissipative systems

The relevance of hidden variables in dissipative systems is examined. A definition of a dissipative dynamical system is introduced in which the storage function does not need to be observable from the variables that enter into the supply rate. It is shown that a controllable system is dissipative if and only if it has an observable storage function, but that there are uncontrollable dissipative systems that do not have an observable storage function. Finally, we argue that unobservable storage functions are indispensable: they occur in physical systems, for example in electrical circuits and in Maxwell's equations.