R/GHpoints.R

In qpcg/MEM: Multiple-Cycle Expectation-Maximization Calibration and Linking of IRT models

#' Gaussian-Hermite Points
#'
#' Gets the Gaussian-Hermite points for a paticular form and size.
#' @param form form
#' @param k The number of points
#' @keywords add one here
#' #@export
#' #@examples
#' GHpoints()


GHpoints <- function (form, k) {
  av <- all.vars(form)
  factors <- sum(av %in% c("z1", "z2"))
  cf <- paste(form[3])
  #form. <- paste(" ~ ", paste("z", 1:factors, collapse = " + ", sep = ""), " + ", cf)
  form. <- paste(" ~ ", cf)
  form. <- as.formula(form.)
  GH <- gauher(k)
  grid.t <- expand.grid(lapply(1:factors, function (k, u) u$x, u = GH))
  names(grid.t) <- paste("z", 1:factors, sep = "")
  out <- model.matrix(form., sqrt(2) * grid.t)
  colnams <- colnames(out)
  dimnames(out) <- attr(out, "assign") <- NULL
  grid.w <- as.matrix(expand.grid(lapply(1:factors, function (k, u) u$w, u = GH)))
  grid.w <- (2^(factors/2)) * apply(grid.w, 1, prod) * exp(rowSums(grid.t * grid.t))
  grid.w <- grid.w * exp(rowSums(dnorm(out[, seq(2, factors + 1), drop = FALSE], log = TRUE)))
  names(grid.w) <- NULL
  list(x = out, w = grid.w, colnams = colnams)
}