Simple Point Process
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A simple point process is a special type of
point process In statistics and probability theory, a point process or point field is a collection of mathematical points randomly located on a mathematical space such as the real line or Euclidean space. Kallenberg, O. (1986). ''Random Measures'', 4th editio ...
in
probability theory Probability theory is the branch of mathematics concerned with probability. Although there are several different probability interpretations, probability theory treats the concept in a rigorous mathematical manner by expressing it through a set ...
. In simple point processes, every point is assigned the weight one.


Definition

Let S be a locally compact
second countable In topology, a second-countable space, also called a completely separable space, is a topological space whose topology has a countable base. More explicitly, a topological space T is second-countable if there exists some countable collection \mat ...
Hausdorff space In topology and related branches of mathematics, a Hausdorff space ( , ), separated space or T2 space is a topological space where, for any two distinct points, there exist neighbourhoods of each which are disjoint from each other. Of the m ...
and let \mathcal S be its Borel \sigma -algebra. A
point process In statistics and probability theory, a point process or point field is a collection of mathematical points randomly located on a mathematical space such as the real line or Euclidean space. Kallenberg, O. (1986). ''Random Measures'', 4th editio ...
\xi , interpreted as
random measure In probability theory, a random measure is a measure-valued random element. Random measures are for example used in the theory of random processes, where they form many important point processes such as Poisson point processes and Cox processes. ...
on (S, \mathcal S) , is called a simple point process if it can be written as : \xi =\sum_ \delta_ for an
index set In mathematics, an index set is a set whose members label (or index) members of another set. For instance, if the elements of a set may be ''indexed'' or ''labeled'' by means of the elements of a set , then is an index set. The indexing consists ...
I and
random element In probability theory, random element is a generalization of the concept of random variable to more complicated spaces than the simple real line. The concept was introduced by who commented that the “development of probability theory and expansi ...
s X_i which are almost everywhere pairwise distinct. Here \delta_x denotes the
Dirac measure In mathematics, a Dirac measure assigns a size to a set based solely on whether it contains a fixed element ''x'' or not. It is one way of formalizing the idea of the Dirac delta function, an important tool in physics and other technical fields. ...
on the point x .


Examples

Simple point processes include many important classes of point processes such as
Poisson process In probability, statistics and related fields, a Poisson point process is a type of random mathematical object that consists of points randomly located on a mathematical space with the essential feature that the points occur independently of one ...
es,
Cox process In probability theory, a Cox process, also known as a doubly stochastic Poisson process is a point process which is a generalization of a Poisson process where the intensity that varies across the underlying mathematical space (often space or time ...
es and
binomial process A binomial process is a special point process in probability theory. Definition Let P be a probability distribution and n be a fixed natural number. Let X_1, X_2, \dots, X_n be i.i.d. random variables with distribution P , so X_i \sim ...
es.


Uniqueness

If \mathcal I is a generating
ring Ring may refer to: * Ring (jewellery), a round band, usually made of metal, worn as ornamental jewelry * To make a sound with a bell, and the sound made by a bell :(hence) to initiate a telephone connection Arts, entertainment and media Film and ...
of \mathcal S then a simple point process \xi is uniquely determined by its values on the sets U \in \mathcal I . This means that two simple point processes \xi and \zeta have the same distributions iff : P(\xi(U)=0) = P(\zeta(U)=0) \text U \in \mathcal I


Literature

* *{{cite book , last1=Daley , first1=D.J. , last2= Vere-Jones , first2= D. , year=2003 , title=An Introduction to the Theory of Point Processes: Volume I: Elementary Theory and Methods,, location= New York , publisher=Springer , isbn=0-387-95541-0 Point processes