R/gs5.R

In konkam/BNPdensity: Ferguson-Klass Type Algorithm for Posterior Normalized Random Measures

#' Conditional posterior distribution of sigma
#'
#' This function simulates from the conditional posterior distribution of
#' sigma.
#'
#' For internal use.
#'
#' @keywords internal
#' @examples
#'
#' ## The function is currently defined as
#' function(sigma, x, y, distr = 1, asigma = 1, bsigma = 2, delta = 4) {
#'   sigmaStar <- rgamma(1, shape = delta, rate = delta / sigma)
#'   sigmaT <- sigma
#'   qgammas <- sigmaT / sigmaStar
#'   Qgammas <- sigmaStar / sigmaT
#'   Term2 <- qgammas^(2 * delta - 1) * exp(-delta * (qgammas -
#'     Qgammas))
#'   Kgamma <- Qgammas^(asigma - 1) * exp(-bsigma * (sigmaStar -
#'     sigmaT))
#'   Prod <- 1
#'   for (i in seq(length(x))) {
#'     Prod <- Prod * (dk(x[i], distr = distr, mu = y[i], sigma = sigmaStar) / dk(x[i],
#'       distr = distr, mu = y[i], sigma = sigmaT
#'     ))
#'   }
#'   q3 <- min(1, Kgamma * Prod * Term2)
#'   sigma <- ifelse(runif(1) <= q3, sigmaStar, sigmaT)
#'   return(sigma)
#' }
gs5 <-
  function(sigma, x, y, distr, asigma, bsigma, delta) {
    sigmaStar <- rgamma(1, shape = delta, rate = delta / sigma)
    sigmaT <- sigma
    qgammas <- sigmaT / sigmaStar
    Qgammas <- sigmaStar / sigmaT
    Term2 <- qgammas^(2 * delta - 1) * exp(-delta * (qgammas -
      Qgammas))
    Kgamma <- Qgammas^(asigma - 1) * exp(-bsigma * (sigmaStar -
      sigmaT))
    Prod <- 1
    for (i in seq(length(x))) {
      Prod <- Prod * (dk(x[i], distr = distr, mu = y[i], sigma = sigmaStar) / dk(x[i],
        distr = distr, mu = y[i], sigma = sigmaT
      ))
    }
    q3 <- min(1, Kgamma * Prod * Term2)
    sigma <- ifelse(runif(1) <= q3, sigmaStar, sigmaT)
    return(sigma)
  }