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Generalized Normal Distribution

doc/source/tutorial/stats/continuous_gennorm.rst

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.. _continuous-gennorm:

Generalized Normal Distribution

This distribution is also known as the exponential power distribution. It has a single shape parameter :math:\beta>0. It reduces to a number of common distributions. The support is :math:x \in (-\infty, \infty).

Functions

.. math:: :nowrap:

\begin{eqnarray*} f\left(x; \beta\right) & = &\frac{\beta}{2\Gamma(1/\beta)} e^{-\left|x\right|^{\beta}} \end{eqnarray*}

.. math:: :nowrap:

\begin{eqnarray*} F\left(x; \beta\right) & = & \frac{1}{2} + \operatorname{sgn}\left(x\right) \frac{\gamma\left(1/\beta, \left|x\right|^{\beta}\right)}{2\Gamma\left(1/\beta\right)} \end{eqnarray*}
 

where :math:\gamma\left(s, x\right) = \int_0^x t^{s-1} e^{-t} dt is the lower incomplete gamma function.

.. math:: :nowrap:

\begin{eqnarray*} h\left[X; \beta\right] = \frac{1}{\beta} - \log\left(\frac{\beta}{2\Gamma\left(1/\beta\right)}\right)\end{eqnarray*}

Moments

.. math:: :nowrap:

\begin{eqnarray*}
\mu & = & 0 \\
m_{n} & = & 0 \\
m_{d} & = & 0 \\
\mu_2 &  = & \frac{\Gamma\left(3/\beta\right)}{\Gamma\left(1/\beta\right)} \\
\gamma_1 & = & 0 \\
\gamma_2 & = & \frac{\Gamma\left(5/\beta\right) \Gamma\left(1/\beta\right)}{\Gamma\left(3/\beta\right)^2} - 3 \\
\end{eqnarray*}

Special Cases

  • Laplace distribution (:math:\beta = 1)
  • Normal distribution with with scale :math:\frac{1}{\sqrt{2}} (:math:\beta = 2)
  • Uniform distribution over the interval :math:[-1, 1] (:math:\beta \rightarrow \infty)

Sources

Implementation: scipy.stats.gennorm