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counting process (Definition)

A stochastic process $ \lbrace X(t)\mid t\in \mathbb{R}^{+}\cup\lbrace 0 \rbrace \rbrace$ is called a counting process if, for each outcome $ \omega$ in the sample space $ \Omega$,

  1. $ X(t)\in \mathbb{Z}^{+}\cup\lbrace 0 \rbrace$ for all $ t$,
  2. $ X(t)(\omega)$ is piecewise constant,
  3. $ X(t)(\omega)$ is non-decreasing,
  4. $ X(t)(\omega)$ is right continuous (continuous from the right), and
  5. for any $ t$, there is an $ s\in\mathbb{R}$ such that $ t<s$ and $ X(t)(\omega)+1=X(s)(\omega)$.

Remark. For any $ t$, the random variable $ X(t)$ is usually called the number of occurrences of some event by time $ t$. Then, for $ s<t$, $ X(t)-X(s)$ is the number of occurrences in the half-open interval $ (s,t]$.



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Cross-references: half-open interval, event, occurrences, number, random variable, continuous from the right, continuous, right, piecewise, outcome, stochastic process
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This is version 2 of counting process, born on 2005-02-09, modified 2005-02-15.
Object id is 6730, canonical name is CountingProcess.
Accessed 3087 times total.

Classification:
AMS MSC60G51 (Probability theory and stochastic processes :: Stochastic processes :: Processes with independent increments)

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