R/gompertz.R

In ssdtools: Species Sensitivity Distributions

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#' Gompertz Distribution
#'
#' Density, distribution function, quantile function and random generation
#' for the Gompertz distribution.
#' The functions are wrappers on the equivalent VGAM functions that
#' return a zero length numeric vector if x, q or p are zero length.
#'
#' @param x,q	vector of quantiles.
#' @param p	vector of probabilities.
#' @param n	number of observations.
#' @param scale	scale parameter.
#' @param shape shape parameter.
#' @param log,log.p logical; if TRUE, probabilities p are given as log(p).
#' @param lower.tail	logical; if TRUE (default), probabilities are P[X <= x],otherwise, P[X > x].
#' @return
#' dgompertz gives the density, pgompertz gives the distribution function,
#' qgompertz gives the quantile function, and rgompertz generates random deviates.
#' @seealso \code{\link[VGAM]{dgompertz}}
#' @name gompertz
#' @examples
#' x <- rgompertz(1000,1,0.1)
#' hist(log(x),freq=FALSE,col='gray',border='white')
#' hist(x,freq=FALSE,col='gray',border='white')
#' curve(dgompertz(x,1,0.1),add=TRUE,col='red4',lwd=2)
NULL

#' @rdname gompertz
#' @export
dgompertz <- function(x, scale = 1, shape, log = FALSE){
  if(!length(x)) return(numeric(0))
  VGAM::dgompertz(x, scale = scale, shape = shape, log = log)
}

#' @rdname gompertz
#' @export
qgompertz <- function(q, scale = 1, shape, lower.tail = TRUE, log.p = FALSE){
  if(!length(q)) return(numeric(0))
  VGAM::qgompertz(q, scale = scale, shape = shape, lower.tail = lower.tail, log.p = log.p)
}

#' @rdname gompertz
#' @export
pgompertz <- function(p, scale = 1, shape, lower.tail = TRUE, log.p = FALSE){
  if(!length(p)) return(numeric(0))
  VGAM::pgompertz(p, scale = scale, shape = shape, lower.tail = lower.tail, log.p = log.p)
}

#' @rdname gompertz
#' @export
rgompertz <- function(n, scale = 1, shape){
  VGAM::rgompertz(n, scale = scale, shape = shape)
}