Random variables and probability spaces¶
This introduces a class of random variables, with the focus on discrete random variables (i.e. on a discrete probability space). This avoids the problem of defining a measure space and measurable functions.
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class
sage.probability.random_variable.
DiscreteProbabilitySpace
(X, P, codomain=None, check=False)¶ Bases:
sage.probability.random_variable.ProbabilitySpace_generic
,sage.probability.random_variable.DiscreteRandomVariable
The discrete probability space
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entropy
()¶ The entropy of the probability space.
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set
()¶ The set of values of the probability space taking possibly nonzero probability (a subset of the domain).
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class
sage.probability.random_variable.
DiscreteRandomVariable
(X, f, codomain=None, check=False)¶ Bases:
sage.probability.random_variable.RandomVariable_generic
A random variable on a discrete probability space.
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correlation
(other)¶ The correlation of the probability space X = self with Y = other.
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covariance
(other)¶ The covariance of the discrete random variable X = self with Y = other.
Let \(S\) be the probability space of \(X\) = self, with probability function \(p\), and \(E(X)\) be the expectation of \(X\). Then the variance of \(X\) is:
\[\text{cov}(X,Y) = E((X-E(X)\cdot (Y-E(Y)) = \sum_{x \in S} p(x) (X(x) - E(X))(Y(x) - E(Y))\]
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expectation
()¶ The expectation of the discrete random variable, namely \(\sum_{x \in S} p(x) X[x]\), where \(X\) = self and \(S\) is the probability space of \(X\).
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function
()¶ The function defining the random variable.
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standard_deviation
()¶ The standard deviation of the discrete random variable.
Let \(S\) be the probability space of \(X\) = self, with probability function \(p\), and \(E(X)\) be the expectation of \(X\). Then the standard deviation of \(X\) is defined to be
\[\sigma(X) = \sqrt{ \sum_{x \in S} p(x) (X(x) - E(x))^2}\]
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translation_correlation
(other, map)¶ The correlation of the probability space X = self with image of Y = other under map.
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translation_covariance
(other, map)¶ The covariance of the probability space X = self with image of Y = other under the given map of the probability space.
Let \(S\) be the probability space of \(X\) = self, with probability function \(p\), and \(E(X)\) be the expectation of \(X\). Then the variance of \(X\) is:
\[\text{cov}(X,Y) = E((X-E(X)\cdot (Y-E(Y)) = \sum_{x \in S} p(x) (X(x) - E(X))(Y(x) - E(Y))\]
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translation_expectation
(map)¶ The expectation of the discrete random variable, namely \(\sum_{x \in S} p(x) X[e(x)]\), where \(X\) = self, \(S\) is the probability space of \(X\), and \(e\) = map.
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translation_standard_deviation
(map)¶ The standard deviation of the translated discrete random variable \(X \circ e\), where \(X\) = self and \(e\) = map.
Let \(S\) be the probability space of \(X\) = self, with probability function \(p\), and \(E(X)\) be the expectation of \(X\). Then the standard deviation of \(X\) is defined to be
\[\sigma(X) = \sqrt{ \sum_{x \in S} p(x) (X(x) - E(x))^2}\]
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translation_variance
(map)¶ The variance of the discrete random variable \(X \circ e\), where \(X\) = self, and \(e\) = map.
Let \(S\) be the probability space of \(X\) = self, with probability function \(p\), and \(E(X)\) be the expectation of \(X\). Then the variance of \(X\) is:
\[\mathrm{var}(X) = E((X-E(x))^2) = \sum_{x \in S} p(x) (X(x) - E(x))^2\]
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variance
()¶ The variance of the discrete random variable.
Let \(S\) be the probability space of \(X\) = self, with probability function \(p\), and \(E(X)\) be the expectation of \(X\). Then the variance of \(X\) is:
\[\mathrm{var}(X) = E((X-E(x))^2) = \sum_{x \in S} p(x) (X(x) - E(x))^2\]
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class
sage.probability.random_variable.
ProbabilitySpace_generic
(domain, RR)¶ Bases:
sage.probability.random_variable.RandomVariable_generic
A probability space.
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domain
()¶
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class
sage.probability.random_variable.
RandomVariable_generic
(X, RR)¶ Bases:
sage.structure.parent_base.ParentWithBase
A random variable.
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codomain
()¶
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domain
()¶
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field
()¶
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probability_space
()¶
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sage.probability.random_variable.
is_DiscreteProbabilitySpace
(S)¶
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sage.probability.random_variable.
is_DiscreteRandomVariable
(X)¶
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sage.probability.random_variable.
is_ProbabilitySpace
(S)¶
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sage.probability.random_variable.
is_RandomVariable
(X)¶