> > So, what constitutes a system is arbitrary? In the mind of the beholder? > > > > I remember when we used to argue about this at The Complex. > > > > I always wanted to argue that a system is in some sense “self-bounding”. > It consists of a group of entities that are interacting more intimately > with one another than they are with entities outside the system. > > > In the context of complex systems research, a *system* is an abstraction of a set of connected components and its boundary. The system's boundary can be defined as open, closed or isolated to flows of quantities of energy, mass, information, symbols etc. Defining information is a different thread ;-)
A *model* is the mathematical/computational formalization of the system. *Is what constitutes a system arbitrary?* George Box famously said "all models are wrong, but some are useful <https://en.wikipedia.org/wiki/All_models_are_wrong>". Given that models are formalizations of systems and if arbitrary means: "based on random choice or personal whim, rather than any reason or system.", I would say researchers use reason and systemic thought to develop "useful" system descriptions. So, system descriptions are not arbitrary. They are designed to be useful for the question being asked. No system description nor model can answer all questions - they are specifically designed for a problem at hand. Relatedly, a *simulation,* in the way we use it, is a single instance of a model run based on initializing a model's parameters computing next states to observe its behavior/dynamics. The *phase space* is the behavior of the model over all possible input states.
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