R/dbernppACmovement_exp.R

In nimbleSCR: Spatial Capture-Recapture (SCR) Methods Using 'nimble'

#' Bernoulli point process for activity center movement (exponential kernel)
#' 
#' Density and random generation functions of the Bernoulli point process for activity center movement between occasions based on a bivariate exponential distribution. 
#'
#' The \code{dbernppACmovement_exp} distribution is a NIMBLE custom distribution which can be used to model and simulate
#' movement of activity centers between consecutive occasions in open population models.
#' The distribution assumes that the new individual activity center location (\emph{x})
#' follows an isotropic exponential normal centered on the previous activity center (\emph{s}) with rate (\emph{lambda}).
#' 
#' @name dbernppACmovement_exp
#' 
#' @param x Vector of x- and y-coordinates of a single spatial point (typically AC location at time t+1) scaled to the habitat (see (\code{\link{scaleCoordsToHabitatGrid}}). 
#' @param n Integer specifying the number of realisations to generate.  Only n = 1 is supported.
#' @param lowerCoords,upperCoords Matrices of lower and upper x- and y-coordinates of all habitat windows. One row for each window.
#' Each window should be of size 1x1 (after rescaling if necessary). 
#' @param s Vector of x- and y-coordinates of the isotropic multivariate exponential distribution mean (AC location at time t).
#' @param rate Rate parameter of the isotropic multivariate exponential distribution.
#' @param lambda Rate parameter of the isotropic bivariate exponential distribution. Soon deprecated, use argument "rate" instead.
#' @param baseIntensities Vector of baseline habitat intensities for all habitat windows.
#' @param habitatGrid Matrix of habitat window indices. Cell values should correspond to the order of habitat windows in  \code{lowerCoords} and \code{upperCoords}. 
#'  When the habitat grid only consists of a single row or column of windows, an additional row or column of dummy indices has to be added because the \code{nimble} model code requires a matrix.     
#' @param numGridRows,numGridCols Numbers of rows and columns of the habitat grid. 
#' @param numWindows Number of habitat windows. This value (positive integer) can be used to truncate \code{lowerCoords} and \code{upperCoords} so that extra rows beyond \code{numWindows} are ignored.  
#' @param log Logical argument, specifying whether to return the log-probability of the distribution.
#' 
#' @return 
#' \code{dbernppACmovement_exp} gives the (log) probability density of the observation vector \code{x}. 
#' \code{rbernppACmovement_exp} gives coordinates of a randomly generated spatial point.  
#' 
#' @author Wei Zhang and Cyril Milleret
#' 
#' @import nimble
#' @references
#' 
#' W. Zhang, J. D. Chipperfield, J. B. Illian, P. Dupont, C. Milleret, P. de Valpine and R. Bischof. 2020. 
#' A hierarchical point process model for spatial capture-recapture data. bioRxiv. DOI 10.1101/2020.10.06.325035 
#'  
#' 
#' @examples 
#' # Use the distribution in R
#' lowerCoords <- matrix(c(0, 0, 1, 0, 0, 1, 1, 1), nrow = 4, byrow = TRUE)
#' upperCoords <- matrix(c(1, 1, 2, 1, 1, 2, 2, 2), nrow = 4, byrow = TRUE)  
#' s <- c(1, 1) # Currrent activity center location
#' rate <- 0.1
#' baseIntensities <- c(1:4)
#' habitatGrid <- matrix(c(1:4), nrow = 2, byrow = TRUE)
#' numRows <- nrow(habitatGrid)
#' numCols <- ncol(habitatGrid)
#' numWindows <- 4
#' # The log probability density of moving from (1,1) to (1.2, 0.8) 
#' dbernppACmovement_exp(x = c(1.2, 0.8),
#' lowerCoords = lowerCoords,
#' upperCoords = upperCoords,
#' s = s,
#' rate = rate,
#' baseIntensities = baseIntensities, 
#' habitatGrid = habitatGrid,
#' numGridRows = numRows,
#' numGridCols = numCols,
#' numWindows = numWindows,
#' log = TRUE)

NULL
#' @rdname dbernppACmovement_exp
#' @export  
dbernppACmovement_exp <- nimbleFunction(
  run = function(
    x               = double(1),
    lowerCoords     = double(2),
    upperCoords     = double(2),
    s               = double(1),
    lambda          = double(0, default = -999),
    rate            = double(0),
    baseIntensities = double(1),
    habitatGrid     = double(2),
    numGridRows     = integer(0),
    numGridCols     = integer(0),
    numWindows      = integer(0),
    log             = integer(0, default = 0)
  ) {
    ## Check if the point x falls within the habitat
    if(min(x) < 0 | x[2] >= numGridRows | x[1] >= numGridCols) {
      if(log) return(-Inf) 
      else return(0.0)
    }
    ## Index of the window where x falls
    windowInd <- habitatGrid[trunc(x[2])+1, trunc(x[1])+1]
    ## windowInd == 0 means this window is not defined as habitat
    if(windowInd == 0) {
      if(log) return(-Inf)
      else return(0.0)
    }
    
    ## Check if the exponential rate is given as "rate" or "lambda"
    if(lambda == -999){
      lambda <- rate
    }
    ## Integrate the intensity function over all habitat windows
    windowIntensities <- integrateIntensity_exp(lowerCoords = lowerCoords[1:numWindows,,drop = FALSE], 
                                                upperCoords = upperCoords[1:numWindows,,drop = FALSE], 
                                                s = s,
                                                baseIntensities = baseIntensities[1:numWindows], 
                                                lambda = lambda,
                                                numWindows = numWindows)
    sumIntensity <- sum(windowIntensities)
    ## Log intensity at x
    logPointIntensity <-  log(baseIntensities[windowInd]) - lambda * sum(abs(x - s)) 
    
    ## Log probability density under the Bernoulli point process
    logProb <- logPointIntensity - log(sumIntensity)
    
    if(log) return(logProb)
    else return(exp(logProb))
    returnType(double(0))
  }
)

NULL
#' @rdname dbernppACmovement_exp
#' @export
rbernppACmovement_exp <- nimbleFunction(
  run = function(
    n               = integer(0),
    lowerCoords     = double(2),
    upperCoords     = double(2),
    s               = double(1),
    lambda          = double(0, default = -999),
    rate            = double(0),
    baseIntensities = double(1),
    habitatGrid     = double(2),
    numGridRows     = integer(0),
    numGridCols     = integer(0),
    numWindows      = integer(0)
  ) {
    ## Ensure that only one sample is requested
    if(n <= 0) {
      stop("The number of requested samples must be above zero")
    } else if(n > 1) {
      print("rbernppACmovement only allows n = 1; using n = 1")
    }
    ## Check if the exponential rate is given as "rate" or "lambda"
    if(lambda == -999){
      lambda <- rate
    }
    ## Integrate the intensity function over all habitat windows
    windowIntensities <- integrateIntensity_exp(lowerCoords = lowerCoords[1:numWindows,,drop = FALSE],
                                                upperCoords = upperCoords[1:numWindows,,drop = FALSE],
                                                s = s,
                                                baseIntensities = baseIntensities[1:numWindows],
                                                lambda = lambda,
                                                numWindows = numWindows)
    ## Call the statified rejection sampler
    outCoordinates <- stratRejectionSampler_exp(numPoints = 1,
                                                lowerCoords = lowerCoords[1:numWindows,,drop = FALSE],
                                                upperCoords = upperCoords[1:numWindows,,drop = FALSE],
                                                s = s,
                                                windowIntensities = windowIntensities[1:numWindows],
                                                lambda = lambda)
    return(outCoordinates[1,])
    returnType(double(1))
  }
)