update generators' documentation + small fix

R/generators.R

@@ -54,7 +54,9 @@ at <- function(...) {
 
 #' @rdname generators
 #' @param start_time the time at which to launch the initial arrival.
-#' @param dist a function modelling the interarrival times.
+#' @param dist a function modelling the interarrival times. It is supposed to be
+#' an infinite source of values \code{>= 0} (e.g., \code{rexp} and the like). If
+#' the function provided returns any negative value, the behaviour is undefined.
 #' @param arrive if set to \code{TRUE} (default) the first arrival will be
 #' generated at \code{start_time} and will follow \code{dist} from then on.
 #' If set to \code{FALSE}, will initiate \code{dist} at \code{start_time}
@@ -78,13 +80,16 @@ from <- function(start_time, dist, arrive=TRUE) {
  if (!started) {
  started <<- TRUE
  if (arrive) {
- return(start_time)
+ dt <- start_time
  } else {
- return(start_time + dist())
+ dt <- dist()
+ if (dt[1] >= 0)
+ dt[1] <- dt[1] + start_time
  }
  } else {
- return(dist())
+ dt <- dist()
  }
+ dt
  }
 }
 
@@ -138,7 +143,8 @@ from_to <- function(start_time, stop_time, dist, arrive=TRUE, every=NULL) {
  dt <- start_time - init
  } else {
  dt <- dist()
- dt[1] <- dt[1] + start_time - init
+ if (dt[1] >= 0)
+ dt[1] <- dt[1] + start_time - init
  }
  } else {
  dt <- dist()