R/draw_cumulative_intensity_orderstats.R

In nhppp: Simulating Nonhomogeneous Poisson Point Processes

#' Simulate from a non homogeneous Poisson Point Process (NHPPP) from
#'    (t_min, t_max) (order statistics method)
#'
#' @description  Sample NHPPP times using the order statistics method,
#' optionally using an `rstream` generator object.
#' @param Lambda (function, double vector) a continuous increasing R to R map
#'               which is the integrated rate of the NHPPP
#' @param Lambda_inv (function, double vector) the inverse of `Lambda()`
#' @param t_min (double) the lower bound of the time interval
#' @param t_max (double) the upper bound of the time interval
#' @param atmost1 boolean, draw at most 1 event time
#'
#' @return a vector of event times (t_); if no events realize,
#'         a vector of length 0
#' @keywords internal
draw_cumulative_intensity_orderstats <- function(Lambda,
                                                 Lambda_inv,
                                                 t_min,
                                                 t_max,
                                                 atmost1 = FALSE) {
  L_min <- Lambda(t_min)
  L_max <- Lambda(t_max)
  n <- stats::rpois(n = 1, lambda = L_max - L_min)
  tmp_u <- ppp_exactly_n(n = n, t_min = L_min, t_max = L_max)
  if (atmost1 == TRUE) {
    tmp_u <- tmp_u[1]
  }
  return(Lambda_inv(tmp_u))
}