R/simm.bb.r

In adehabitatLT: Analysis of Animal Movements

"simm.bb" <- function(date=1:100, begin = c(0,0),
                      end=begin, id="A1", burst=id, proj4string=CRS())
  {
      if (!inherits(date, "POSIXct")) {
          class(date) <- c("POSIXct", "POSIXt")
          attr(date, "tzone") <- ""
      }
      n <- length(date)
      dt <- c(diff(unclass(date)),NA)

      dx <- c(rnorm(n-1,0,sqrt(dt[-n])),NA)
      dy <- c(rnorm(n-1,0,sqrt(dt[-n])),NA)
      W <- cbind(dx,dy)

      xtmp <- begin
      x <- begin
      for (i in 2:(n-1)) {
          a <- diag(1/(unclass(date[n])-unclass(date[i-1])),2)
      dX <- as.numeric((a%*%(end - xtmp)*dt[i-1] + W[i-1,]))
          x <- rbind(x,xtmp+dX)
          xtmp <- xtmp+dX
      }
      x <- rbind(x,end)

      res <- as.ltraj(data.frame(x[,1],x[,2]),date, id, burst, typeII=TRUE,
                      proj4string=proj4string)
      return(res)

  }