These functions are used internally by PerformanceAnalytics to calculate centered moments for a multivariate distribution as well as the standardized moments of a portfolio distribution. They are exposed here for users who wish to use them directly, and we'll get more documentation written when we can.
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~~ Additional Details will be added to documentation as soon as we have time to write them. ~~
Ipower
Computes the constant $$\int_{-\infty}^{h} z^q \phi'(z)dz$$ needed for the estimation of mES and Component mES where where $\phi'(z)$ is the derivative of the standard gaussian density function and $h$ is typicall modified VaR if you are computing mES or Gaussian VaR if you are computing Gaussian Expected Shortfall.
Martellini, Lionel, and Volker Ziemann. 2007. Improved Forecasts of Higher-Order Comoments and Implications for Portfolio Selection. EDHEC Risk and Asset Management Research Centre working paper.
Ranaldo, Angelo, and Laurent Favre Sr. 2005. How to Price Hedge Funds: From Two- to Four-Moment CAPM. SSRN eLibrary.
Scott, Robert C., and Philip A. Horvath. 1980. On the Direction of Preference for Moments of Higher Order than the Variance. Journal of Finance 35(4):915-919.
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