微分熵

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Differential entropy (also referred to as continuous entropy) is a concept in information theory that began as an attempt by Shannon to extend the idea of (Shannon) entropy, a measure of average surprisal of a random variable, to continuous probability distributions. Unfortunately, Shannon did not derive this formula, and rather just assumed it was the correct continuous analogue of discrete entropy, but it is not. The actual continuous version of discrete entropy is the limiting density of discrete points (LDDP). Differential entropy (described here) is commonly encountered in the literature, but it is a limiting case of the LDDP, and one that loses its fundamental association with discrete entropy.

Differential entropy (also referred to as continuous entropy) is a concept in information theory that began as an attempt by Shannon to extend the idea of (Shannon) entropy, a measure of average surprisal of a random variable, to continuous probability distributions. Unfortunately, Shannon did not derive this formula, and rather just assumed it was the correct continuous analogue of discrete entropy, but it is not. The actual continuous version of discrete entropy is the limiting density of discrete points (LDDP). Differential entropy (described here) is commonly encountered in the literature, but it is a limiting case of the LDDP, and one that loses its fundamental association with discrete entropy.

微分熵(也称为连续熵)是信息论中的一个概念，最初由香农尝试将(香农)熵的概念扩展到连续的概率分布，香农熵是衡量一个随机变量的平均惊人程度的指标。不幸的是，香农没有推导出这个公式，而只是假设它是离散熵的正确连续模拟，但它不是。离散熵的实际连续形式是离散点的极限密度(LDDP)。在文献中经常会遇到微分熵，但它是 LDDP 的一个极限情况，并且它失去了与离散熵的基本联系。

Definition

定义

Let [math]\displaystyle{ X }[/math] be a random variable with a probability density function [math]\displaystyle{ f }[/math] whose support is a set [math]\displaystyle{ \mathcal X }[/math]. The differential entropy [math]\displaystyle{ h(X) }[/math] or [math]\displaystyle{ h(f) }[/math] is defined as

Let [math]\displaystyle{ X }[/math] be a random variable with a probability density function [math]\displaystyle{ f }[/math] whose support is a set [math]\displaystyle{ \mathcal X }[/math]. The differential entropy [math]\displaystyle{ h(X) }[/math] or [math]\displaystyle{ h(f) }[/math] is defined as

假设数学 x / math 是一个随机变量，它的数学 f / math 支持集合 math / mathcal x / math。这个数学 f / math 是一个概率密度函数。微分熵数学 h (x) / math 或 math h (f) / math 定义为

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|equation = [math]\displaystyle{ h(X) = -\int_\mathcal{X} f(x)\log f(x)\,dx }[/math]

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| 方程式数学 h (x)-整数{ x } f (x) log f (x) ，dx / math

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For probability distributions which don't have an explicit density function expression, but have an explicit quantile function expression, [math]\displaystyle{ Q(p) }[/math], then [math]\displaystyle{ h(Q) }[/math] can be defined in terms of the derivative of [math]\displaystyle{ Q(p) }[/math] i.e. the quantile density function [math]\displaystyle{ Q'(p) }[/math] as

For probability distributions which don't have an explicit density function expression, but have an explicit quantile function expression, [math]\displaystyle{ Q(p) }[/math], then [math]\displaystyle{ h(Q) }[/math] can be defined in terms of the derivative of [math]\displaystyle{ Q(p) }[/math] i.e. the quantile density function [math]\displaystyle{ Q'(p) }[/math] as

对于没有明确密度函数表达式但有明确分位函数表达式的概率分布，数学 q (p) / math，那么数学 h (q) / math 可以用数学 q (p) / math 的导数来定义。分位数密度函数 q’(p) / 数学作为

[math]\displaystyle{ h(Q) = \int_0^1 \log Q'(p)\,dp }[/math].

[math]\displaystyle{ h(Q) = \int_0^1 \log Q'(p)\,dp }[/math].

数学 h (q) int 0 ^ 1 log q’(p) ，dp / math。

As with its discrete analog, the units of differential entropy depend on the base of the logarithm, which is usually 2 (i.e., the units are bits). See logarithmic units for logarithms taken in different bases. Related concepts such as joint, conditional differential entropy, and relative entropy are defined in a similar fashion. Unlike the discrete analog, the differential entropy has an offset that depends on the units used to measure [math]\displaystyle{ X }[/math]. For example, the differential entropy of a quantity measured in millimeters will be 模板:Not a typo more than the same quantity measured in meters; a dimensionless quantity will have differential entropy of 模板:Not a typo more than the same quantity divided by 1000.

As with its discrete analog, the units of differential entropy depend on the base of the logarithm, which is usually 2 (i.e., the units are bits). See logarithmic units for logarithms taken in different bases. Related concepts such as joint, conditional differential entropy, and relative entropy are defined in a similar fashion. Unlike the discrete analog, the differential entropy has an offset that depends on the units used to measure [math]\displaystyle{ X }[/math]. For example, the differential entropy of a quantity measured in millimeters will be more than the same quantity measured in meters; a dimensionless quantity will have differential entropy of more than the same quantity divided by 1000.

和它的离散类似物一样，微分熵的单位依赖于对数的底，通常是2(也就是说，单位是位)。见对数单位的对数采取在不同的基地。相关的概念，如联合，条件微分熵，和相对熵，都是以类似的方式定义的。与离散模拟不同，微分熵的偏移量取决于用来测量数学 x / math 的单位。例如，以毫米为单位测量的量的微分熵将大于以米为单位测量的相同量; 无量纲量的微分熵将大于相同量除以1000。

One must take care in trying to apply properties of discrete entropy to differential entropy, since probability density functions can be greater than 1. For example, the uniform distribution [math]\displaystyle{ \mathcal{U}(0,1/2) }[/math] has negative differential entropy

One must take care in trying to apply properties of discrete entropy to differential entropy, since probability density functions can be greater than 1. For example, the uniform distribution [math]\displaystyle{ \mathcal{U}(0,1/2) }[/math] has negative differential entropy

因为概率密度函数可以大于1，所以在尝试将离散熵的性质应用于微分熵时必须小心谨慎。例如，均匀分布 math mathcal { u }(0,1 / 2) / math 具有负微分熵

[math]\displaystyle{ \int_0^\frac{1}{2} -2\log(2)\,dx=-\log(2)\, }[/math].

[math]\displaystyle{ \int_0^\frac{1}{2} -2\log(2)\,dx=-\log(2)\, }[/math].

数学0 ^ frac {1}-2 log (2) ，dx- log (2) ，/ math。

Thus, differential entropy does not share all properties of discrete entropy.

Thus, differential entropy does not share all properties of discrete entropy.

因此，微分熵并不具有离散熵的所有属性。

Note that the continuous mutual information [math]\displaystyle{ I(X;Y) }[/math] has the distinction of retaining its fundamental significance as a measure of discrete information since it is actually the limit of the discrete mutual information of partitions of [math]\displaystyle{ X }[/math] and [math]\displaystyle{ Y }[/math] as these partitions become finer and finer. Thus it is invariant under non-linear homeomorphisms (continuous and uniquely invertible maps), including linear transformations of [math]\displaystyle{ X }[/math] and [math]\displaystyle{ Y }[/math], and still represents the amount of discrete information that can be transmitted over a channel that admits a continuous space of values.

|arxiv = cond-mat/0305641 |bibcode = 2004PhRvE..69f6138K }}</ref> including linear transformations of [math]\displaystyle{ X }[/math] and [math]\displaystyle{ Y }[/math], and still represents the amount of discrete information that can be transmitted over a channel that admits a continuous space of values.

0305641 | bibcode 2004PhRvE. . 69 f6138K } / ref，包括 math x / math 和 math y / math 的线性转换，并且仍然表示可以通过允许连续空间的值的通道传输的离散信息量。

For the direct analogue of discrete entropy extended to the continuous space, see limiting density of discrete points.

For the direct analogue of discrete entropy extended to the continuous space, see limiting density of discrete points.

将离散熵的直接模拟推广到连续空间，请参阅离散点的极限密度。

Properties of differential entropy

微分熵的特性

• For probability densities [math]\displaystyle{ f }[/math] and [math]\displaystyle{ g }[/math], the Kullback–Leibler divergence [math]\displaystyle{ D_{KL}(f || g) }[/math] is greater than or equal to 0 with equality only if [math]\displaystyle{ f=g }[/math] almost everywhere. Similarly, for two random variables [math]\displaystyle{ X }[/math] and [math]\displaystyle{ Y }[/math], [math]\displaystyle{ I(X;Y) \ge 0 }[/math] and [math]\displaystyle{ h(X|Y) \le h(X) }[/math] with equality if and only if [math]\displaystyle{ X }[/math] and [math]\displaystyle{ Y }[/math] are independent.

• The chain rule for differential entropy holds as in the discrete case

[math]\displaystyle{ h(X_1, \ldots, X_n) = \sum_{i=1}^{n} h(X_i|X_1, \ldots, X_{i-1}) \leq \sum_{i=1}^{n} h(X_i) }[/math].

[math]\displaystyle{ h(X_1, \ldots, X_n) = \sum_{i=1}^{n} h(X_i|X_1, \ldots, X_{i-1}) \leq \sum_{i=1}^{n} h(X_i) }[/math].

数学 h (x1， ldots，xn) sum { i1} ^ { n } h (xi | x1， ldots，x { i-1}) leq sum { i1} ^ { n } h (xi) / math。

• Differential entropy is translation invariant, i.e. for a constant [math]\displaystyle{ c }[/math].

[math]\displaystyle{ h(X+c) = h(X) }[/math]

[math]\displaystyle{ h(X+c) = h(X) }[/math]

数学 h (x + c) h (x) / math

• Differential entropy is in general not invariant under arbitrary invertible maps.

In particular, for a constant [math]\displaystyle{ a }[/math]

In particular, for a constant [math]\displaystyle{ a }[/math]

特别是对于一个常数的数学 a / 数学

[math]\displaystyle{ h(aX) = h(X)+ \log |a| }[/math]

[math]\displaystyle{ h(aX) = h(X)+ \log |a| }[/math]

数学 h (aX) h (x) + log | a | / math

For a vector valued random variable [math]\displaystyle{ \mathbf{X} }[/math] and an invertible (square) matrix [math]\displaystyle{ \mathbf{A} }[/math]

For a vector valued random variable [math]\displaystyle{ \mathbf{X} }[/math] and an invertible (square) matrix [math]\displaystyle{ \mathbf{A} }[/math]

对于向量值随机变量 math mathbf { x } / math 和可逆矩阵 math mathbf { a } / math

[math]\displaystyle{ h(\mathbf{A}\mathbf{X})=h(\mathbf{X})+\log \left( |\det \mathbf{A}| \right) }[/math]

[math]\displaystyle{ h(\mathbf{A}\mathbf{X})=h(\mathbf{X})+\log \left( |\det \mathbf{A}| \right) }[/math]

Math h ( mathbf { a } mathbf { x }) h ( mathbf { x }) + log 左(| det mathbf { a } | 右) / math

• In general, for a transformation from a random vector to another random vector with same dimension [math]\displaystyle{ \mathbf{Y}=m \left(\mathbf{X}\right) }[/math], the corresponding entropies are related via

[math]\displaystyle{ h(\mathbf{Y}) \leq h(\mathbf{X}) + \int f(x) \log \left\vert \frac{\partial m}{\partial x} \right\vert dx }[/math]

[math]\displaystyle{ h(\mathbf{Y}) \leq h(\mathbf{X}) + \int f(x) \log \left\vert \frac{\partial m}{\partial x} \right\vert dx }[/math]

数学 h ( mathbf { y }) leq h ( mathbf { x }) + int f (x) log f f f f f f f f f f f f f f f f f f f f f f f f f f f f f f f f f f

where [math]\displaystyle{ \left\vert \frac{\partial m}{\partial x} \right\vert }[/math] is the Jacobian of the transformation [math]\displaystyle{ m }[/math]. The above inequality becomes an equality if the transform is a bijection. Furthermore, when [math]\displaystyle{ m }[/math] is a rigid rotation, translation, or combination thereof, the Jacobian determinant is always 1, and [math]\displaystyle{ h(Y)=h(X) }[/math].

where [math]\displaystyle{ \left\vert \frac{\partial m}{\partial x} \right\vert }[/math] is the Jacobian of the transformation [math]\displaystyle{ m }[/math]. The above inequality becomes an equality if the transform is a bijection. Furthermore, when [math]\displaystyle{ m }[/math] is a rigid rotation, translation, or combination thereof, the Jacobian determinant is always 1, and [math]\displaystyle{ h(Y)=h(X) }[/math].

其中，数学的部分 m 是变换数学 m / math 的雅可比矩阵。如果变换是一个双射，则上述不等式成为等式。此外，当数学 m / math 为刚性旋转、平移或其组合时，Jacobian 行列式总是为1，math h (y) h (x) / math。

• If a random vector [math]\displaystyle{ X \in \mathbb{R}^n }[/math] has mean zero and covariance matrix [math]\displaystyle{ K }[/math], [math]\displaystyle{ h(\mathbf{X}) \leq \frac{1}{2} \log(\det{2 \pi e K}) = \frac{1}{2} \log[(2\pi e)^n \det{K}] }[/math] with equality if and only if [math]\displaystyle{ X }[/math] is jointly gaussian (see below).

However, differential entropy does not have other desirable properties:

However, differential entropy does not have other desirable properties:

然而，微分熵并没有其他令人满意的特性:

• It is not invariant under change of variables, and is therefore most useful with dimensionless variables.

• It can be negative.

A modification of differential entropy that addresses these drawbacks is the relative information entropy, also known as the Kullback–Leibler divergence, which includes an invariant measure factor (see limiting density of discrete points).

A modification of differential entropy that addresses these drawbacks is the relative information entropy, also known as the Kullback–Leibler divergence, which includes an invariant measure factor (see limiting density of discrete points).

针对这些缺点，微分熵的一个改进是相对熵，也被称为 Kullback-Leibler 分歧，其中包括一个不变测度因子(见离散点的极限密度)。

Maximization in the normal distribution

正态分布下的最大化

Theorem

定理

With a normal distribution, differential entropy is maximized for a given variance. A Gaussian random variable has the largest entropy amongst all random variables of equal variance, or, alternatively, the maximum entropy distribution under constraints of mean and variance is the Gaussian.

With a normal distribution, differential entropy is maximized for a given variance. A Gaussian random variable has the largest entropy amongst all random variables of equal variance, or, alternatively, the maximum entropy distribution under constraints of mean and variance is the Gaussian.

在正态分布下，对于给定的方差，微分熵最大化。在所有方差相等的随机变量中，高斯型随机变量的熵最大，或者，在均值和方差约束下的最大熵分布是高斯型随机变量。

Proof

证据

Let [math]\displaystyle{ g(x) }[/math] be a Gaussian PDF with mean μ and variance [math]\displaystyle{ \sigma^2 }[/math] and [math]\displaystyle{ f(x) }[/math] an arbitrary PDF with the same variance. Since differential entropy is translation invariant we can assume that [math]\displaystyle{ f(x) }[/math] has the same mean of [math]\displaystyle{ \mu }[/math] as [math]\displaystyle{ g(x) }[/math].

Let [math]\displaystyle{ g(x) }[/math] be a Gaussian PDF with mean μ and variance [math]\displaystyle{ \sigma^2 }[/math] and [math]\displaystyle{ f(x) }[/math] an arbitrary PDF with the same variance. Since differential entropy is translation invariant we can assume that [math]\displaystyle{ f(x) }[/math] has the same mean of [math]\displaystyle{ \mu }[/math] as [math]\displaystyle{ g(x) }[/math].

设数学 g (x) / math 是一个高斯 PDF，其中包含均值和方差数学 sigma ^ 2 / math 和数学 f (x) / math，其中任意一个 PDF 具有相同的方差。由于微分熵是平移不变的，我们可以假设 math f (x) / math 与 math g (x) / math 具有相同的 math mu / math 的平均值。

Consider the Kullback–Leibler divergence between the two distributions

Consider the Kullback–Leibler divergence between the two distributions

考虑两个分布之间的 Kullback-Leibler 散度

[math]\displaystyle{ 0 \leq D_{KL}(f || g) = \int_{-\infty}^\infty f(x) \log \left( \frac{f(x)}{g(x)} \right) dx = -h(f) - \int_{-\infty}^\infty f(x)\log(g(x)) dx. }[/math]

[math]\displaystyle{ 0 \leq D_{KL}(f || g) = \int_{-\infty}^\infty f(x) \log \left( \frac{f(x)}{g(x)} \right) dx = -h(f) - \int_{-\infty}^\infty f(x)\log(g(x)) dx. }[/math]

数学0 leq d { KL }(f | g) int { infty } ^ infty f (x) log left (frac { f (x)}右) dx-h (f)-int { infty ^ infty f (x) log (g (x)) dx / math

Now note that

Now note that

现在请注意

[math]\displaystyle{ \begin{align} \lt math\gt \begin{align} 数学 begin { align } \int_{-\infty}^\infty f(x)\log(g(x)) dx &= \int_{-\infty}^\infty f(x)\log\left( \frac{1}{\sqrt{2\pi\sigma^2}}e^{-\frac{(x-\mu)^2}{2\sigma^2}}\right) dx \\ \int_{-\infty}^\infty f(x)\log(g(x)) dx &= \int_{-\infty}^\infty f(x)\log\left( \frac{1}{\sqrt{2\pi\sigma^2}}e^{-\frac{(x-\mu)^2}{2\sigma^2}}\right) dx \\ 整数 f (x) log (g (x)) dx & 整数 f (x) log 左(frac {1}2 pi sigma ^ 2} e-frac {(x-mu) ^ 2}右) &= \int_{-\infty}^\infty f(x) \log\frac{1}{\sqrt{2\pi\sigma^2}} dx + \log(e)\int_{-\infty}^\infty f(x)\left( -\frac{(x-\mu)^2}{2\sigma^2}\right) dx \\ &= \int_{-\infty}^\infty f(x) \log\frac{1}{\sqrt{2\pi\sigma^2}} dx + \log(e)\int_{-\infty}^\infty f(x)\left( -\frac{(x-\mu)^2}{2\sigma^2}\right) dx \\ & int-infty ^ infty f (x) log frac {2 pi sigma ^ 2} dx + log (e) int-infty ^ infty f (x) left (- frac (x-mu) ^ 2 sigma ^ 2} dx &= -\tfrac{1}{2}\log(2\pi\sigma^2) - \log(e)\frac{\sigma^2}{2\sigma^2} \\ &= -\tfrac{1}{2}\log(2\pi\sigma^2) - \log(e)\frac{\sigma^2}{2\sigma^2} \\ & tfrac {1}{2} pi sigma ^ 2)- log (e) frac {2 sigma ^ 2} &= -\tfrac{1}{2}\left(\log(2\pi\sigma^2) + \log(e)\right) \\ &= -\tfrac{1}{2}\left(\log(2\pi\sigma^2) + \log(e)\right) \\ & tfrac {2} log (2 pi sigma ^ 2) + log (e) right) &= -\tfrac{1}{2}\log(2\pi e \sigma^2) \\ &= -\tfrac{1}{2}\log(2\pi e \sigma^2) \\ & tfrac {2} log (2 pi e sigma ^ 2) &= -h(g) &= -h(g) &-h (g) \end{align} }[/math]

\end{align}</math>

End { align } / math

because the result does not depend on [math]\displaystyle{ f(x) }[/math] other than through the variance. Combining the two results yields

because the result does not depend on [math]\displaystyle{ f(x) }[/math] other than through the variance. Combining the two results yields

因为除了方差之外，结果不依赖于数学 f (x) / math。结合这两个结果就会产生

[math]\displaystyle{ h(g) - h(f) \geq 0 \! }[/math]

[math]\displaystyle{ h(g) - h(f) \geq 0 \! }[/math]

数学 h (g)-h (f) geq 0! / math

with equality when [math]\displaystyle{ f(x)=g(x) }[/math] following from the properties of Kullback–Leibler divergence.

with equality when [math]\displaystyle{ f(x)=g(x) }[/math] following from the properties of Kullback–Leibler divergence.

当数学 f (x) g (x) / math 遵循 Kullback-Leibler 散度的性质时。

Alternative proof

替代证据

This result may also be demonstrated using the variational calculus. A Lagrangian function with two Lagrangian multipliers may be defined as:

This result may also be demonstrated using the variational calculus. A Lagrangian function with two Lagrangian multipliers may be defined as:

这个结果也可以用变分演算来证明。具有两个拉格朗日乘数的拉格朗日函数可定义为:

[math]\displaystyle{ L=\int_{-\infty}^\infty g(x)\ln(g(x))\,dx-\lambda_0\left(1-\int_{-\infty}^\infty g(x)\,dx\right)-\lambda\left(\sigma^2-\int_{-\infty}^\infty g(x)(x-\mu)^2\,dx\right) }[/math]

[math]\displaystyle{ L=\int_{-\infty}^\infty g(x)\ln(g(x))\,dx-\lambda_0\left(1-\int_{-\infty}^\infty g(x)\,dx\right)-\lambda\left(\sigma^2-\int_{-\infty}^\infty g(x)(x-\mu)^2\,dx\right) }[/math]

数学 lint (x) ^ infty g (x) ln (g (x)) ，dx-lambda 0左(1-int (x) ^ infty g (x) ，dx-right)-lambda 左(2-int (infty) infty g (x)(x-mu) ^ 2，dx-right) / math

where g(x) is some function with mean μ. When the entropy of g(x) is at a maximum and the constraint equations, which consist of the normalization condition [math]\displaystyle{ \left(1=\int_{-\infty}^\infty g(x)\,dx\right) }[/math] and the requirement of fixed variance [math]\displaystyle{ \left(\sigma^2=\int_{-\infty}^\infty g(x)(x-\mu)^2\,dx\right) }[/math], are both satisfied, then a small variation δg(x) about g(x) will produce a variation δL about L which is equal to zero:

where g(x) is some function with mean μ. When the entropy of g(x) is at a maximum and the constraint equations, which consist of the normalization condition [math]\displaystyle{ \left(1=\int_{-\infty}^\infty g(x)\,dx\right) }[/math] and the requirement of fixed variance [math]\displaystyle{ \left(\sigma^2=\int_{-\infty}^\infty g(x)(x-\mu)^2\,dx\right) }[/math], are both satisfied, then a small variation δg(x) about g(x) will produce a variation δL about L which is equal to zero:

其中 g (x)是具有平均值的函数。当 g (x)的熵处于最大值时，满足归一化条件下的数学左(1int-infty) ^ infty g (x) ，dx 右) / math 和固定方差数学左(sigma ^ 2 infty) ^ 2(x-mu) ^ 2，dx 右) / math 要求，那么关于 g (x)的一个小变化 g (x)将产生关于 l 的一个变化 l，它等于零:

[math]\displaystyle{ 0=\delta L=\int_{-\infty}^\infty \delta g(x)\left (\ln(g(x))+1+\lambda_0+\lambda(x-\mu)^2\right )\,dx }[/math]

[math]\displaystyle{ 0=\delta L=\int_{-\infty}^\infty \delta g(x)\left (\ln(g(x))+1+\lambda_0+\lambda(x-\mu)^2\right )\,dx }[/math]

数学0 delta l int {- infty } ^ infty delta g (x) left ( ln (g (x))) + 1 + lambda 0 + lambda (x- mu) ^ 2 right) ，dx / math

Since this must hold for any small δg(x), the term in brackets must be zero, and solving for g(x) yields:

Since this must hold for any small δg(x), the term in brackets must be zero, and solving for g(x) yields:

因为这对任何小 g (x)都成立，括号中的项必须为零，求 g (x)的结果是:

[math]\displaystyle{ g(x)=e^{-\lambda_0-1-\lambda(x-\mu)^2} }[/math]

[math]\displaystyle{ g(x)=e^{-\lambda_0-1-\lambda(x-\mu)^2} }[/math]

数学 g (x) e ^ {- lambda 0-1- lambda (x- mu) ^ 2} / math

Using the constraint equations to solve for λ₀ and λ yields the normal distribution:

Using the constraint equations to solve for λ₀ and λ yields the normal distribution:

利用约束方程求解子0 / 子，得到正态分布:

[math]\displaystyle{ g(x)=\frac{1}{\sqrt{2\pi\sigma^2}}e^{-\frac{(x-\mu)^2}{2\sigma^2}} }[/math]

[math]\displaystyle{ g(x)=\frac{1}{\sqrt{2\pi\sigma^2}}e^{-\frac{(x-\mu)^2}{2\sigma^2}} }[/math]

数学 g (x) frac {1}{2 pi sigma ^ 2} e ^ {- frac {(x-mu) ^ 2}{2 sigma ^ 2}}} / math

Example: Exponential distribution

例如: 指数分布

Let [math]\displaystyle{ X }[/math] be an exponentially distributed random variable with parameter [math]\displaystyle{ \lambda }[/math], that is, with probability density function

Let [math]\displaystyle{ X }[/math] be an exponentially distributed random variable with parameter [math]\displaystyle{ \lambda }[/math], that is, with probability density function

设 math x / math 是一个具有参数 math lambda / math 的指数分布随机变量，也就是说，具有概率密度函数

[math]\displaystyle{ f(x) = \lambda e^{-\lambda x} \mbox{ for } x \geq 0. }[/math]

[math]\displaystyle{ f(x) = \lambda e^{-\lambda x} \mbox{ for } x \geq 0. }[/math]

数学 f (x) lambda e ^ { lambda x } mbox { for } x geq 0. / math

Its differential entropy is then

Its differential entropy is then

它的微分熵就在那时

[math]\displaystyle{ h_e(X)\, }[/math]	[math]\displaystyle{ h_e(X)\, }[/math]	math h e (x) ，/ math	[math]\displaystyle{ =-\int_0^\infty \lambda e^{-\lambda x} \log (\lambda e^{-\lambda x})\,dx }[/math]	[math]\displaystyle{ =-\int_0^\infty \lambda e^{-\lambda x} \log (\lambda e^{-\lambda x})\,dx }[/math]	math- nint 0 ^ infty lambda e ^ {- lambda x } log ( lambda ^-lambda x }) ，dx / math
			[math]\displaystyle{ = -\left(\int_0^\infty (\log \lambda)\lambda e^{-\lambda x}\,dx + \int_0^\infty (-\lambda x) \lambda e^{-\lambda x}\,dx\right) }[/math]	[math]\displaystyle{ = -\left(\int_0^\infty (\log \lambda)\lambda e^{-\lambda x}\,dx + \int_0^\infty (-\lambda x) \lambda e^{-\lambda x}\,dx\right) }[/math]	math- left ( int 0 ^ infty ( log lambda) lambda e ^ { lambda } ，dx + int 0 ^ infty (- lambda x) lambda ^ { lambda x } ，dx right) / math
			[math]\displaystyle{ = -\log \lambda \int_0^\infty f(x)\,dx + \lambda E[X] }[/math]	[math]\displaystyle{ = -\log \lambda \int_0^\infty f(x)\,dx + \lambda E[X] }[/math]	math- log lambda int 0 ^ infty f (x) ，dx + lambda e [ x ] / math
			[math]\displaystyle{ = -\log\lambda + 1\,. }[/math]	[math]\displaystyle{ = -\log\lambda + 1\,. }[/math]	math- log lambda + 1. / math

Here, [math]\displaystyle{ h_e(X) }[/math] was used rather than [math]\displaystyle{ h(X) }[/math] to make it explicit that the logarithm was taken to base e, to simplify the calculation.

Here, [math]\displaystyle{ h_e(X) }[/math] was used rather than [math]\displaystyle{ h(X) }[/math] to make it explicit that the logarithm was taken to base e, to simplify the calculation.

在这里，使用了数学 h (x) / math 而不是数学 h (x) / math 来明确对数是以 e 为底的，以简化计算。

Relation to estimator error

与估计误差的关系

The differential entropy yields a lower bound on the expected squared error of an estimator. For any random variable [math]\displaystyle{ X }[/math] and estimator [math]\displaystyle{ \widehat{X} }[/math] the following holds:

The differential entropy yields a lower bound on the expected squared error of an estimator. For any random variable [math]\displaystyle{ X }[/math] and estimator [math]\displaystyle{ \widehat{X} }[/math] the following holds:

微分熵对估计量的预期平方误差产生了一个下限。对于任何随机变量的数学 x / math 和估计量 math widehat { x } / math，有以下几点:

[math]\displaystyle{ \operatorname{E}[(X - \widehat{X})^2] \ge \frac{1}{2\pi e}e^{2h(X)} }[/math]

[math]\displaystyle{ \operatorname{E}[(X - \widehat{X})^2] \ge \frac{1}{2\pi e}e^{2h(X)} }[/math]

数学运算器名称{ e }[(x- widehat { x }) ^ 2] ge frac {1}{2 pi e } e ^ {2h (x)} / math

with equality if and only if [math]\displaystyle{ X }[/math] is a Gaussian random variable and [math]\displaystyle{ \widehat{X} }[/math] is the mean of [math]\displaystyle{ X }[/math].

with equality if and only if [math]\displaystyle{ X }[/math] is a Gaussian random variable and [math]\displaystyle{ \widehat{X} }[/math] is the mean of [math]\displaystyle{ X }[/math].

当且仅当数学 x / math 是高斯型随机变量，数学广义数学是数学 x / math 的平均值。

Differential entropies for various distributions

各种分布的微分熵

In the table below [math]\displaystyle{ \Gamma(x) = \int_0^{\infty} e^{-t} t^{x-1} dt }[/math] is the gamma function, [math]\displaystyle{ \psi(x) = \frac{d}{dx} \ln\Gamma(x)=\frac{\Gamma'(x)}{\Gamma(x)} }[/math] is the digamma function, [math]\displaystyle{ B(p,q) = \frac{\Gamma(p)\Gamma(q)}{\Gamma(p+q)} }[/math] is the beta function, and γ_E is Euler's constant.

In the table below [math]\displaystyle{ \Gamma(x) = \int_0^{\infty} e^{-t} t^{x-1} dt }[/math] is the gamma function, [math]\displaystyle{ \psi(x) = \frac{d}{dx} \ln\Gamma(x)=\frac{\Gamma'(x)}{\Gamma(x)} }[/math] is the digamma function, [math]\displaystyle{ B(p,q) = \frac{\Gamma(p)\Gamma(q)}{\Gamma(p+q)} }[/math] is the beta function, and γ_E is Euler's constant.

在下表中，Gamma (x) int 0 ^ { infty } e ^ {-t } t ^ { x-1} dt / math 是 Gamma 函数, 数学(x) frac { d } ln Gamma (x) frac { γ’(x)} / math 是双伽玛函数, 数学 b (p，q) frac { Gamma (p) Gamma (q)}{ Gamma (p + q)}} / math 是 beta 函数，子 e / sub 是欧拉常数。

{ | class“ wikitable”样式“ background: white”

Table of differential entropies

Table of differential entropies

+ 微分熵表
Distribution Name	Probability density function (pdf)	Entropy in nats	Support	Distribution Name	Probability density function (pdf)	Entropy in nats	Support	支持
Uniform	[math]\displaystyle{ f(x) = \frac{1}{b-a} }[/math]	[math]\displaystyle{ \ln(b - a) \, }[/math]	[math]\displaystyle{ [a,b]\, }[/math]	Uniform	[math]\displaystyle{ f(x) = \frac{1}{b-a} }[/math]	[math]\displaystyle{ \ln(b - a) \, }[/math]	[math]\displaystyle{ [a,b]\, }[/math]	math f (x) frac {1}{ b-a } / math | math ln (b-a) ，/ math | math [ a，b ] ，/ math
Normal	[math]\displaystyle{ f(x) = \frac{1}{\sqrt{2\pi\sigma^2}} \exp\left(-\frac{(x-\mu)^2}{2\sigma^2}\right) }[/math]	[math]\displaystyle{ \ln\left(\sigma\sqrt{2\,\pi\,e}\right) }[/math]	[math]\displaystyle{ (-\infty,\infty)\, }[/math]	Normal	[math]\displaystyle{ f(x) = \frac{1}{\sqrt{2\pi\sigma^2}} \exp\left(-\frac{(x-\mu)^2}{2\sigma^2}\right) }[/math]	[math]\displaystyle{ \ln\left(\sigma\sqrt{2\,\pi\,e}\right) }[/math]	[math]\displaystyle{ (-\infty,\infty)\, }[/math]	数学 f (x) frac {1} | | | | 数学 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | (- frac {(x-mu) ^ 2}右) ，/ / 数学，数学
Exponential	[math]\displaystyle{ f(x) = \lambda \exp\left(-\lambda x\right) }[/math]	[math]\displaystyle{ 1 - \ln \lambda \, }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	Exponential	[math]\displaystyle{ f(x) = \lambda \exp\left(-\lambda x\right) }[/math]	[math]\displaystyle{ 1 - \ln \lambda \, }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	| math f (x) lambda exp left (- lambda x right) / math | math 1- ln lambda ，/ math | math [0， infty) ，/ math
Rayleigh	[math]\displaystyle{ f(x) = \frac{x}{\sigma^2} \exp\left(-\frac{x^2}{2\sigma^2}\right) }[/math]	[math]\displaystyle{ 1 + \ln \frac{\sigma}{\sqrt{2}} + \frac{\gamma_E}{2} }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	Rayleigh	[math]\displaystyle{ f(x) = \frac{x}{\sigma^2} \exp\left(-\frac{x^2}{2\sigma^2}\right) }[/math]	[math]\displaystyle{ 1 + \ln \frac{\sigma}{\sqrt{2}} + \frac{\gamma_E}{2} }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	math f (x) frac { x } sigma ^ 2} exp 左(- frac { x ^ 2}右) / math | math 1 + ln frac { sigma } + frac {2} | math | math [0，infty) ，/ math
Beta	[math]\displaystyle{ f(x) = \frac{x^{\alpha-1}(1-x)^{\beta-1}}{B(\alpha,\beta)} }[/math] for [math]\displaystyle{ 0 \leq x \leq 1 }[/math]	[math]\displaystyle{ \ln B(\alpha,\beta) - (\alpha-1)[\psi(\alpha) - \psi(\alpha +\beta)]\, }[/math] [math]\displaystyle{ - (\beta-1)[\psi(\beta) - \psi(\alpha + \beta)] \, }[/math]	[math]\displaystyle{ [0,1]\, }[/math]	Beta	[math]\displaystyle{ f(x) = \frac{x^{\alpha-1}(1-x)^{\beta-1}}{B(\alpha,\beta)} }[/math] for [math]\displaystyle{ 0 \leq x \leq 1 }[/math]	[math]\displaystyle{ \ln B(\alpha,\beta) - (\alpha-1)[\psi(\alpha) - \psi(\alpha +\beta)]\, }[/math] [math]\displaystyle{ - (\beta-1)[\psi(\beta) - \psi(\alpha + \beta)] \, }[/math]	[math]\displaystyle{ [0,1]\, }[/math]	math f (x) frac { x ^ alpha-1}(1-x) ^ beta-1}{ b ( alpha， beta)} / math 0 leq x leq 1 / math | | math ln b ( alpha， beta)-( alpha-1)[ alpha ( alpha)- psi ( alpha + beta)] ，/ math br / math-( beta-1)[ psi ( alpha + beta)] ，/ math 数学[0,1]数学
Cauchy	[math]\displaystyle{ f(x) = \frac{\gamma}{\pi} \frac{1}{\gamma^2 + x^2} }[/math]	[math]\displaystyle{ \ln(4\pi\gamma) \, }[/math]	[math]\displaystyle{ (-\infty,\infty)\, }[/math]	Cauchy	[math]\displaystyle{ f(x) = \frac{\gamma}{\pi} \frac{1}{\gamma^2 + x^2} }[/math]	[math]\displaystyle{ \ln(4\pi\gamma) \, }[/math]	[math]\displaystyle{ (-\infty,\infty)\, }[/math]	| math f (x) frac {1} gamma ^ 2 + x ^ 2} / math | math | ln (4 pi gamma) ，/ math | math (- infty，infty) ，/ math
Chi	[math]\displaystyle{ f(x) = \frac{2}{2^{k/2} \Gamma(k/2)} x^{k-1} \exp\left(-\frac{x^2}{2}\right) }[/math]	[math]\displaystyle{ \ln{\frac{\Gamma(k/2)}{\sqrt{2}}} - \frac{k-1}{2} \psi\left(\frac{k}{2}\right) + \frac{k}{2} }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	Chi	[math]\displaystyle{ f(x) = \frac{2}{2^{k/2} \Gamma(k/2)} x^{k-1} \exp\left(-\frac{x^2}{2}\right) }[/math]	[math]\displaystyle{ \ln{\frac{\Gamma(k/2)}{\sqrt{2}}} - \frac{k-1}{2} \psi\left(\frac{k}{2}\right) + \frac{k}{2} }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	| math f (x) frac {2}{2 ^ { k / 2} Gamma (k / 2)}{ x ^ { k-1} exp left (- frac ^ 2}{右) / math | math ln Gamma (k / 2)}}-frac {2}-frac {2}-1}左(frac {2}右) + c {2} | inf| math [0，math)) ，/ math
Chi-squared	[math]\displaystyle{ f(x) = \frac{1}{2^{k/2} \Gamma(k/2)} x^{\frac{k}{2}\!-\!1} \exp\left(-\frac{x}{2}\right) }[/math]	[math]\displaystyle{ \ln 2\Gamma\left(\frac{k}{2}\right) - \left(1 - \frac{k}{2}\right)\psi\left(\frac{k}{2}\right) + \frac{k}{2} }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	Chi-squared	[math]\displaystyle{ f(x) = \frac{1}{2^{k/2} \Gamma(k/2)} x^{\frac{k}{2}\!-\!1} \exp\left(-\frac{x}{2}\right) }[/math]	[math]\displaystyle{ \ln 2\Gamma\left(\frac{k}{2}\right) - \left(1 - \frac{k}{2}\right)\psi\left(\frac{k}{2}\right) + \frac{k}{2} }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	math f (x) frac {1} | Gamma (k / 2)} x ^ frac {2} !-1} exp 左(- frac {2}右) / math | math | ln 2 | Gamma 左(frac {2}右)-左(1-frac {2}左) psi (k {2}右) + frac {2} | math [0，infty) ，/
Erlang	[math]\displaystyle{ f(x) = \frac{\lambda^k}{(k-1)!} x^{k-1} \exp(-\lambda x) }[/math]	[math]\displaystyle{ (1-k)\psi(k) + \ln \frac{\Gamma(k)}{\lambda} + k }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	Erlang	[math]\displaystyle{ f(x) = \frac{\lambda^k}{(k-1)!} x^{k-1} \exp(-\lambda x) }[/math]	[math]\displaystyle{ (1-k)\psi(k) + \ln \frac{\Gamma(k)}{\lambda} + k }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	| math f (x) frac { lambda ^ k }{(k-1) ! }X ^ { k-1} exp (- lambda x) / math | math (1-k) psi (k) + ln frac { Gamma (k)} + k / math | math [0，infty) ，/ math
F	[math]\displaystyle{ f(x) = \frac{n_1^{\frac{n_1}{2}} n_2^{\frac{n_2}{2}}}{B(\frac{n_1}{2},\frac{n_2}{2})} \frac{x^{\frac{n_1}{2} - 1}}{(n_2 + n_1 x)^{\frac{n_1 + n2}{2}}} }[/math]	[math]\displaystyle{ \ln \frac{n_1}{n_2} B\left(\frac{n_1}{2},\frac{n_2}{2}\right) + \left(1 - \frac{n_1}{2}\right) \psi\left(\frac{n_1}{2}\right) - }[/math] [math]\displaystyle{ \left(1 + \frac{n_2}{2}\right)\psi\left(\frac{n_2}{2}\right) + \frac{n_1 + n_2}{2} \psi\left(\frac{n_1\!+\!n_2}{2}\right) }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	F	[math]\displaystyle{ f(x) = \frac{n_1^{\frac{n_1}{2}} n_2^{\frac{n_2}{2}}}{B(\frac{n_1}{2},\frac{n_2}{2})} \frac{x^{\frac{n_1}{2} - 1}}{(n_2 + n_1 x)^{\frac{n_1 + n2}{2}}} }[/math]	[math]\displaystyle{ \ln \frac{n_1}{n_2} B\left(\frac{n_1}{2},\frac{n_2}{2}\right) + \left(1 - \frac{n_1}{2}\right) \psi\left(\frac{n_1}{2}\right) - }[/math] [math]\displaystyle{ \left(1 + \frac{n_2}{2}\right)\psi\left(\frac{n_2}{2}\right) + \frac{n_1 + n_2}{2} \psi\left(\frac{n_1\!+\!n_2}{2}\right) }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	math f (x) frac { n 1 ^ { n 1}{ n 2}{ n 2}}{ b ( frac { n 1}{2} ， frac { n 2}{2}}}}}}}}{ frac { x ^ { n 1}{ n 1}-1}{(n 2 + n 1) ^ { frac { n 1 + n 2}}{2}}}}{数学 | | | 数学 ln frac { n 1}{ n 2} b 左( frac { n 1}{2} , (1-frac { n 1}右) psi left ( frac { n 1}右)-/ math br / math left (1 + frac { n 2}右) psi left ( frac { n 2}右) + frac { n 1 + 2}{2} {2} psi left ( frac { n 1！ +\！ 数学 | math [0，infty ] ，math
Gamma	[math]\displaystyle{ f(x) = \frac{x^{k - 1} \exp(-\frac{x}{\theta})}{\theta^k \Gamma(k)} }[/math]	[math]\displaystyle{ \ln(\theta \Gamma(k)) + (1 - k)\psi(k) + k \, }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	Gamma	[math]\displaystyle{ f(x) = \frac{x^{k - 1} \exp(-\frac{x}{\theta})}{\theta^k \Gamma(k)} }[/math]	[math]\displaystyle{ \ln(\theta \Gamma(k)) + (1 - k)\psi(k) + k \, }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	math f (x) frac { x ^ { k-1} exp (- frac { x } theta ^ k Gamma (k)} / math | math ln (theta Gamma (k)) + (1-k) psi (k) + k，/ math | math [0，infty) ，/ math
Laplace	[math]\displaystyle{ f(x) = \frac{1}{2b} \exp\left(-\frac{|x - \mu|}{b}\right) }[/math]	[math]\displaystyle{ 1 + \ln(2b) \, }[/math]	[math]\displaystyle{ (-\infty,\infty)\, }[/math]	Laplace	[math]\displaystyle{ f(x) = \frac{1}{2b} \exp\left(-\frac{|x - \mu|}{b}\right) }[/math]	[math]\displaystyle{ 1 + \ln(2b) \, }[/math]	[math]\displaystyle{ (-\infty,\infty)\, }[/math]	| math f (x) frac {1} exp 左(- frac { | x- mu | }{ b 右) / math | math 1 + ln (2b) ，/ math | math | math (- infty infty) ，/ math
Logistic	[math]\displaystyle{ f(x) = \frac{e^{-x}}{(1 + e^{-x})^2} }[/math]	[math]\displaystyle{ 2 \, }[/math]	[math]\displaystyle{ (-\infty,\infty)\, }[/math]	Logistic	[math]\displaystyle{ f(x) = \frac{e^{-x}}{(1 + e^{-x})^2} }[/math]	[math]\displaystyle{ 2 \, }[/math]	[math]\displaystyle{ (-\infty,\infty)\, }[/math]	| math f (x) frac { e ^ {-x }) ^ 2} / math | math 2，/ math | math (- infty， infty) ，/ math
Lognormal	[math]\displaystyle{ f(x) = \frac{1}{\sigma x \sqrt{2\pi}} \exp\left(-\frac{(\ln x - \mu)^2}{2\sigma^2}\right) }[/math]	[math]\displaystyle{ \mu + \frac{1}{2} \ln(2\pi e \sigma^2) }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	Lognormal	[math]\displaystyle{ f(x) = \frac{1}{\sigma x \sqrt{2\pi}} \exp\left(-\frac{(\ln x - \mu)^2}{2\sigma^2}\right) }[/math]	[math]\displaystyle{ \mu + \frac{1}{2} \ln(2\pi e \sigma^2) }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	math f (x) frac {1} | sigma x } sqrt left (- frac {(x-mu) ^ 2}{2 sigma ^ 2}右) / math | math mu + frac {1} ln (2 pi e ^ 2) / math | math | math | math [0，infty) ，/ math
Maxwell–Boltzmann	[math]\displaystyle{ f(x) = \frac{1}{a^3}\sqrt{\frac{2}{\pi}}\,x^{2}\exp\left(-\frac{x^2}{2a^2}\right) }[/math]	[math]\displaystyle{ \ln(a\sqrt{2\pi})+\gamma_E-\frac{1}{2} }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	Maxwell–Boltzmann	[math]\displaystyle{ f(x) = \frac{1}{a^3}\sqrt{\frac{2}{\pi}}\,x^{2}\exp\left(-\frac{x^2}{2a^2}\right) }[/math]	[math]\displaystyle{ \ln(a\sqrt{2\pi})+\gamma_E-\frac{1}{2} }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	| math f (x) frac {1} a ^ 3} frac {2} ，x ^ 2} exp 左(- frac ^ 2 ^ 2) / math | math ln (a ^ 2 pi) + gamma-frac | math | 0，infty) ，/ math
Generalized normal	[math]\displaystyle{ f(x) = \frac{2 \beta^{\frac{\alpha}{2}}}{\Gamma(\frac{\alpha}{2})} x^{\alpha - 1} \exp(-\beta x^2) }[/math]	[math]\displaystyle{ \ln{\frac{\Gamma(\alpha/2)}{2\beta^{\frac{1}{2}}}} - \frac{\alpha - 1}{2} \psi\left(\frac{\alpha}{2}\right) + \frac{\alpha}{2} }[/math]	[math]\displaystyle{ (-\infty,\infty)\, }[/math]	Generalized normal	[math]\displaystyle{ f(x) = \frac{2 \beta^{\frac{\alpha}{2}}}{\Gamma(\frac{\alpha}{2})} x^{\alpha - 1} \exp(-\beta x^2) }[/math]	[math]\displaystyle{ \ln{\frac{\Gamma(\alpha/2)}{2\beta^{\frac{1}{2}}}} - \frac{\alpha - 1}{2} \psi\left(\frac{\alpha}{2}\right) + \frac{\alpha}{2} }[/math]	[math]\displaystyle{ (-\infty,\infty)\, }[/math]	math f (x) frac {2 beta ^ { frac { alpha }{2}{ frac {2}}}{ x ^ { alpha-1} exp (- beta x ^ 2) / math | 数学 ln frac { Gamma ( alpha / 2)}{2 beta ^ { frac {1}}- frac {2} alpha-1}{2} psi 左( frac {2}右) + frac {2} {2} / 数学 数学-数学，数学
Pareto	[math]\displaystyle{ f(x) = \frac{\alpha x_m^\alpha}{x^{\alpha+1}} }[/math]	[math]\displaystyle{ \ln \frac{x_m}{\alpha} + 1 + \frac{1}{\alpha} }[/math]	[math]\displaystyle{ [x_m,\infty)\, }[/math]	Pareto	[math]\displaystyle{ f(x) = \frac{\alpha x_m^\alpha}{x^{\alpha+1}} }[/math]	[math]\displaystyle{ \ln \frac{x_m}{\alpha} + 1 + \frac{1}{\alpha} }[/math]	[math]\displaystyle{ [x_m,\infty)\, }[/math]	math f (x) frac { alpha ^ alpha + 1} / math | math | ln frac { x m } + 1 + frac {1} / math | math [ x m，infty ] ，/ math
Student's t	[math]\displaystyle{ f(x) = \frac{(1 + x^2/\nu)^{-\frac{\nu+1}{2}}}{\sqrt{\nu}B(\frac{1}{2},\frac{\nu}{2})} }[/math]	[math]\displaystyle{ \frac{\nu\!+\!1}{2}\left(\psi\left(\frac{\nu\!+\!1}{2}\right)\!-\!\psi\left(\frac{\nu}{2}\right)\right)\!+\!\ln \sqrt{\nu} B\left(\frac{1}{2},\frac{\nu}{2}\right) }[/math]	[math]\displaystyle{ (-\infty,\infty)\, }[/math]	Student's t	[math]\displaystyle{ f(x) = \frac{(1 + x^2/\nu)^{-\frac{\nu+1}{2}}}{\sqrt{\nu}B(\frac{1}{2},\frac{\nu}{2})} }[/math]	[math]\displaystyle{ \frac{\nu\!+\!1}{2}\left(\psi\left(\frac{\nu\!+\!1}{2}\right)\!-\!\psi\left(\frac{\nu}{2}\right)\right)\!+\!\ln \sqrt{\nu} B\left(\frac{1}{2},\frac{\nu}{2}\right) }[/math]	[math]\displaystyle{ (-\infty,\infty)\, }[/math] 句子太长，请短一点
Triangular	[math]\displaystyle{ f(x) = \begin{cases} | Triangular || \lt math\gt f(x) = \begin{cases} | 三角形 | | math f (x) begin { cases } \frac{2(x-a)}{(b-a)(c-a)} & \mathrm{for\ } a \le x \leq c, \\[4pt] \frac{2(x-a)}{(b-a)(c-a)} & \mathrm{for\ } a \le x \leq c, \\[4pt] [2(x-a)}{(b-a)(c-a)} & [4 pt ] \frac{2(b-x)}{(b-a)(b-c)} & \mathrm{for\ } c \lt x \le b, \\[4pt] \frac{2(b-x)}{(b-a)(b-c)} & \mathrm{for\ } c \lt x \le b, \\[4pt] 2(b-x)}{(b-a)(b-c)} & (4 pt) \end{cases} }[/math]	[math]\displaystyle{ \frac{1}{2} + \ln \frac{b-a}{2} }[/math]	[math]\displaystyle{ [0,1]\, }[/math] \end{cases}</math> || [math]\displaystyle{ \frac{1}{2} + \ln \frac{b-a}{2} }[/math]||[math]\displaystyle{ [0,1]\, }[/math] 数学 | | math frac {1} + ln frac { b-a }{2} / math | math [0,1] / math
Weibull	[math]\displaystyle{ f(x) = \frac{k}{\lambda^k} x^{k-1} \exp\left(-\frac{x^k}{\lambda^k}\right) }[/math]	[math]\displaystyle{ \frac{(k-1)\gamma_E}{k} + \ln \frac{\lambda}{k} + 1 }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	Weibull	[math]\displaystyle{ f(x) = \frac{k}{\lambda^k} x^{k-1} \exp\left(-\frac{x^k}{\lambda^k}\right) }[/math]	[math]\displaystyle{ \frac{(k-1)\gamma_E}{k} + \ln \frac{\lambda}{k} + 1 }[/math]	[math]\displaystyle{ [0,\infty)\, }[/math]	| math f (x) frac { k }{ λ ^ k-1} exp left (- frac { x ^ k }{ λ ^ k }右) / math | math frac {(k-1) e } + ln frac { k } + 1 / math | math | math [0，infty) ，/ math
Multivariate normal	[math]\displaystyle{ | Multivariate normal || \lt math\gt 多元正态分布 | 数学 f_X(\vec{x}) = }[/math] [math]\displaystyle{ \frac{\exp \left( -\frac{1}{2} ( \vec{x} - \vec{\mu})^\top \Sigma^{-1}\cdot(\vec{x} - \vec{\mu}) \right)} {(2\pi)^{N/2} \left|\Sigma\right|^{1/2}} }[/math]	[math]\displaystyle{ \frac{1}{2}\ln\{(2\pi e)^{N} \det(\Sigma)\} }[/math]	[math]\displaystyle{ \mathbb{R}^N }[/math] f_X(\vec{x}) =</math> [math]\displaystyle{ \frac{\exp \left( -\frac{1}{2} ( \vec{x} - \vec{\mu})^\top \Sigma^{-1}\cdot(\vec{x} - \vec{\mu}) \right)} {(2\pi)^{N/2} \left|\Sigma\right|^{1/2}} }[/math] || [math]\displaystyle{ \frac{1}{2}\ln\{(2\pi e)^{N} \det(\Sigma)\} }[/math]||[math]\displaystyle{ \mathbb{R}^N }[/math] F x (x) / math br / math frac { exp left (- frac {1}(- frac {1}-vec { mu }) ^ top Sigma ^ (- 1)-dot (- 1)-vec mu)右) ^ {(2 pi) ^ { n / 2}左 | Sigma | right | | | | math | | c {1 / 2}(2 pi) | | | | | | | | | det {1 | ln (2 pi) | n (Sigma) / math | bb | n | n | n | n | n | ^

|}

Many of the differential entropies are from.

Many of the differential entropies are from.

许多熵的差异来自于。

Variants

变体

As described above, differential entropy does not share all properties of discrete entropy. For example, the differential entropy can be negative; also it is not invariant under continuous coordinate transformations. Edwin Thompson Jaynes showed in fact that the expression above is not the correct limit of the expression for a finite set of probabilities.

As described above, differential entropy does not share all properties of discrete entropy. For example, the differential entropy can be negative; also it is not invariant under continuous coordinate transformations. Edwin Thompson Jaynes showed in fact that the expression above is not the correct limit of the expression for a finite set of probabilities.

如上所述，微分熵并不具有离散熵的所有属性。例如，微分熵可以是负的，也不是连续坐标变换下的不变量。事实上，埃德温·汤普森·杰尼斯表明上面的表达式并不是一组有限概率表达式的正确极限。

A modification of differential entropy adds an invariant measure factor to correct this, (see limiting density of discrete points). If [math]\displaystyle{ m(x) }[/math] is further constrained to be a probability density, the resulting notion is called relative entropy in information theory:

A modification of differential entropy adds an invariant measure factor to correct this, (see limiting density of discrete points). If [math]\displaystyle{ m(x) }[/math] is further constrained to be a probability density, the resulting notion is called relative entropy in information theory:

一个修改的微分熵增加了一个不变测度因子来纠正这个错误。如果数学 m (x) / math 进一步被限定为概率密度，那么在信息论中，由此产生的概念被称为相对熵:

[math]\displaystyle{ D(p||m) = \int p(x)\log\frac{p(x)}{m(x)}\,dx. }[/math]

[math]\displaystyle{ D(p||m) = \int p(x)\log\frac{p(x)}{m(x)}\,dx. }[/math]

数学 d (p | | m) int p (x) log frac { p (x)}{ m (x)} ，dx. / math

The definition of differential entropy above can be obtained by partitioning the range of [math]\displaystyle{ X }[/math] into bins of length [math]\displaystyle{ h }[/math] with associated sample points [math]\displaystyle{ ih }[/math] within the bins, for [math]\displaystyle{ X }[/math] Riemann integrable. This gives a quantized version of [math]\displaystyle{ X }[/math], defined by [math]\displaystyle{ X_h = ih }[/math] if [math]\displaystyle{ ih \le X \le (i+1)h }[/math]. Then the entropy of [math]\displaystyle{ X_h = ih }[/math] is

The definition of differential entropy above can be obtained by partitioning the range of [math]\displaystyle{ X }[/math] into bins of length [math]\displaystyle{ h }[/math] with associated sample points [math]\displaystyle{ ih }[/math] within the bins, for [math]\displaystyle{ X }[/math] Riemann integrable. This gives a quantized version of [math]\displaystyle{ X }[/math], defined by [math]\displaystyle{ X_h = ih }[/math] if [math]\displaystyle{ ih \le X \le (i+1)h }[/math]. Then the entropy of [math]\displaystyle{ X_h = ih }[/math] is

上述微分熵的定义可以通过将数学 x / math 的范围划分到数学 h / math 的容器中，在容器中放入相关的样本点 math ih / math，用于数学 x / math Riemann 可积。这给出了数学 x / math 的量化版本，定义为 math x h ih / math if math ih le x le (i + 1) h / math。然后数学的熵 x h ih / math 是

[math]\displaystyle{ H_h=-\sum_i hf(ih)\log (f(ih)) - \sum hf(ih)\log(h). }[/math]

[math]\displaystyle{ H_h=-\sum_i hf(ih)\log (f(ih)) - \sum hf(ih)\log(h). }[/math]

数学 h- sum i hf (ih) log (f (ih))- sum hf (ih) log (h) . / math

The first term on the right approximates the differential entropy, while the second term is approximately [math]\displaystyle{ -\log(h) }[/math]. Note that this procedure suggests that the entropy in the discrete sense of a continuous random variable should be [math]\displaystyle{ \infty }[/math].

The first term on the right approximates the differential entropy, while the second term is approximately [math]\displaystyle{ -\log(h) }[/math]. Note that this procedure suggests that the entropy in the discrete sense of a continuous random variable should be [math]\displaystyle{ \infty }[/math].

右边的第一项近似于微分熵，而第二项近似于 math- log (h) / math。请注意，这个过程表明，连续随机变量的离散意义上的熵应该是数学 infty / math。

See also

参见

• Information entropy

• Self-information

• Entropy estimation

References

参考资料

External links

外部链接

• 模板:Springer

• 模板:Planetmath reference

Category:Entropy and information

类别: 熵和信息

Category:Information theory

范畴: 信息论

Category:Statistical randomness

分类: 统计的随机性

This page was moved from wikipedia:en:Differential entropy. Its edit history can be viewed at 微分熵/edithistory