r :math:`x, p \in ( - \infty; \infty)`,
:math:`|b| < a` if :math:`p \ge 0`,
:math:`|b| \le a` if :math:`p < 0`.
:math:`K_{p}(.)` denotes the modified Bessel function of the second
kind and order :math:`p` (`scipy.special.kv`)

`genhyperbolic` takes ``p`` as a tail parameter,
``a`` as a shape parameter,
``b`` as a skewness parameter.

%(after_notes)s

The original parameterization of the Generalized Hyperbolic Distribution
is found in [1]_ as follows

.. math::

    f(x, \lambda, \alpha, \beta, \delta, \mu) =
       \frac{(\gamma/\delta)^\lambda}{\sqrt{2\pi}K_\lambda(\delta \gamma)}
       e^{\beta (x - \mu)} \times \frac{K_{\lambda - 1/2}
       (\alpha \sqrt{\delta^2 + (x - \mu)^2})}
       {(\sqrt{\delta^2 + (x - \mu)^2} / \alpha)^{1/2 - \lambda}}

for :math:`x \in ( - \infty; \infty)`,
:math:`\gamma := \sqrt{\alpha^2 - \beta^2}`,
:math:`\lambda, \mu \in ( - \infty; \infty)`,
:math:`\delta \ge 0, |\beta| < \alpha` if :math:`\lambda \ge 0`,
:math:`\delta > 0, |\beta| \le \alpha` if :math:`\lambda < 0`.

The location-scale-based parameterization implemented in
SciPy is based on [2]_, where :math:`a = \alpha\delta`,
:math:`b = \beta\delta`, :math:`p = \lambda`,
:math:`scale=\delta` and :math:`loc=\mu`

Moments are implemented based on [3]_ and [4]_.

For the distributions that are a special case such as Student's t,
it is not recommended to rely on the implementation of genhyperbolic.
To avoid potential numerical problems and for performance reasons,
the methods of the specific distributions should be used.

References
----------
.. [1] O. Barndorff-Nielsen, "Hyperbolic Distributions and Distributions
   on Hyperbolae", Scandinavian Journal of Statistics, Vol. 5(3),
   pp. 151-157, 1978. https://www.jstor.org/stable/4615705

.. [2] Eberlein E., Prause K. (2002) The Generalized Hyperbolic Model:
    Financial Derivatives and Risk Measures. In: Geman H., Madan D.,
    Pliska S.R., Vorst T. (eds) Mathematical Finance - Bachelier
    Congress 2000. Springer Finance. Springer, Berlin, Heidelberg.
    :doi:`10.1007/978-3-662-12429-1_12`

.. [3] Scott, David J, Würtz, Diethelm, Dong, Christine and Tran,
   Thanh Tam, (2009), Moments of the generalized hyperbolic
   distribution, MPRA Paper, University Library of Munich, Germany,
   https://EconPapers.repec.org/RePEc:pra:mprapa:19081.

.. [4] E. Eberlein and E. A. von Hammerstein. Generalized hyperbolic
   and inverse Gaussian distributions: Limiting cases and approximation
   of processes. FDM Preprint 80, April 2003. University of Freiburg.
   https://freidok.uni-freiburg.de/fedora/objects/freidok:7974/datastreams/FILE1/content

%(example)s

c