Random draw from inverse gamma and inverse chisquare

InverseGammaAndChiSquare.R

#' @title
#' rInvGamma
#' 
#' @description
#' Random draws from the inverse gamma distribution.
#' 
#' @param n See n in rgamma()
#' @param shape Alpha 
#' @param scale Beta 
#' 
#' @details
#' Samples an inverse gamma (taken from MCMCpack - cred to them)
#' 
#' @refereces
#' http://en.wikipedia.org/wiki/Inverse-gamma_distribution

rInvGamma <- function (n, shape, scale = 1) {
  return(1/rgamma(n = n, shape = shape, rate = scale))
}

#' @title
#' rInvChiSq
#' 
#' @description
#' Random draws from the inverse chisquare distribution.
#' 
#' @param n See n in rgamma()
#' @param nu See nu at the Wiki page.
#'
#' @references
#' http://en.wikipedia.org/wiki/Inverse-gamma_distribution
#' 
rInvChiSq <- function (n, nu) {
  return(rInvGamma(n, shape = nu / 2, scale = 1/2))
}

#' @title
#' rScaledInvChiSq
#' 
#' @description
#' Random draws from the scaled inverse chisquare distribution.
#' 
#' @param n See n in rgamma()
#' @param nu See nu at the Wiki page.
#' @param tau2 See tau2 at the Wiki page.
#' 
#' @references
#' http://en.wikipedia.org/wiki/Scaled-inverse-chi-squared_distribution
#'
rScaledInvChiSq <- function (n, nu, tau2) {
  return(rInvGamma(n, shape = nu / 2, scale = (nu * tau2) / 2))
}