Dynamic Systems

The Essence of Dynamical Systems

  • A dynamical system is a system in which a function describes the time dependence of a point in a geometrical space
  • Said another way, a dynamical system is a collection of random variables that is indexed by time
  • A stochastic dynamical system is a dynamic system subjected to the effects of noise

    • In other words, a dynamic system is considered to be stochastic if the system requires mapping its inputs to outputs using probabilities
  • A deterministic dynamical system is a dynamic system that isn't subjected to the effect of noise
  • We will be interested in stochastic dynamical systems in the majority of our research

Systems and States

  • In our case, a system refers to a collection of states indexed by time, which represents some broader notion

    • Some examples of this include the stock market, weather, etc.
  • A state refers to a distinct observation of some random variable

    • Some examples of this include if the stock market goes up, the weather being sunny, etc.

State Space versus Sample Space

  • State Spaces are used in Dynamics

    • State spaces imply that there is a time progression and that our system will assume different states as time progresses
    • For example, the state space of the largest number up to nthn^{th} roll is a number from the following state space: 1,2,3,4,5,6{1, 2, 3, 4, 5, 6}
  • Sample Spaces are used more often in Statistics

    • A sample space represents a set of distinct observations of some random variable
    • There is typically a probability distribution associated with each state
    • For example, the sample space of a single die roll is the following
    Ω=1,2,3,4,5,6\Omega = {1, 2, 3, 4, 5, 6}
  • In summary, we expect to be thinking about probabilities when we hear sample spaces, unlike state spaces, which do not carry the same connotation
  • State spaces are typically indexed by time, unlike sample spaces, which do not carry the same connotation

References

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Credible Intervals

Stochastic Processes