statsmodels.sandbox.distributions.extras.pdf_mvsk¶
- statsmodels.sandbox.distributions.extras.pdf_mvsk(mvsk)[source]¶
Return the Gaussian expanded pdf function given the list of 1st, 2nd moment and skew and Fisher (excess) kurtosis.
- Parameters:
- mvsk
list
of
mu
,mc2
,skew
,kurt
distribution is matched to these four moments
- mvsk
- Returns:
- pdffunc
function
function that evaluates the pdf(x), where x is the non-standardized random variable.
- pdffunc
Notes
Changed so it works only if four arguments are given. Uses explicit formula, not loop.
This implements a Gram-Charlier expansion of the normal distribution where the first 2 moments coincide with those of the normal distribution but skew and kurtosis can deviate from it.
In the Gram-Charlier distribution it is possible that the density becomes negative. This is the case when the deviation from the normal distribution is too large.
References
https://en.wikipedia.org/wiki/Edgeworth_series Johnson N.L., S. Kotz, N. Balakrishnan: Continuous Univariate Distributions, Volume 1, 2nd ed., p.30