R/EXP_Lmom.R

In NVE/fitdistrib: A list a functions to fit data to probability distributions

#' Fitting exponential distribution with L-moments
#' @param dat 
#' @param threshold 
#' 
#' @importFrom nsRFA par.exp  
#' @importFrom nsRFA Lmoments
#' 
#' @return param Estimated parameters (2) and standard error returned as a list($estimate, $se).
#' 
#' @export
#'
#' @examples estimate = exp_Lmom(test_data, threshold)
#' threshold was added as to the function because the function sometimes set the location parameter higher than threshold causing NA values in parameter estimation

exp_Lmom <- function(dat, threshold = NA){

  param <- list(estimate = c(NA, NA), se = c(NA, NA))
  if(length(dat) >= 1){
    if(is.na(threshold)){
      dat.mom <- Lmoments(dat)
      param$estimate <- invisible(as.numeric(par.exp(dat.mom[1], dat.mom[2])))
      invisible(param)
    } else{
      dat2 <- dat-threshold
      dat.Lmom <- Lmoments(dat2)
      param$estimate[1] <- threshold
      param$estimate[2] <- 2*dat.Lmom[2]
      invisible(param)
    }
  }
  else {
    print(paste("Warning:this station has les than ",1,"years of data, use another method", collapse = "", sep = ""))
  }
}