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#' Simulate trophic discrimination factors
#'
#' This function returns trophic discrimination factors (TDF), given a
#' number of observations, a mean and/or a standard deviation for deltaN and/or
#' deltaC.
#'
#' @param nN number of observations for deltaN.
#' @param meanN mean for deltaN.
#' @param sdN standard deviation for deltaN.
#' @param nC number of observations for deltaC.
#' @param meanC mean for deltaC.
#' @param sdC standard deviation for deltaC.
#' @param seed numerical value to indicate reproducible results.
#'
#' @return a named list with TDF values for nitrogen and/or carbon
#' @export
#'
#' @examples
#' # 25 values of TDF for nitrogen, mean 3, sd, 1
#' simulateTDF(nN = 25, meanN = 3, sdN = 1)
#'
#' # 18 values of TDF for carbon, mean 0.6, sd, 0.7
#' simulateTDF(nC = 18, meanC = 0.6, sdC = 0.7)
#'
#'
simulateTDF <- function (nN = 56,
meanN = NULL,
sdN = 0.98,
nC = 107,
meanC = NULL,
sdC = 1.3,
seed = 3) {
meanSD <- function(x, mean, sd) {
x <- stats::rnorm(x, mean, sd)
X <- x
MEAN <- mean
SD <- sd
Z <- (((X - mean(X, na.rm = TRUE))/sd(X, na.rm = TRUE))) * SD
MEAN + Z
}
set.seed(seed = seed)
deltaN <- NULL
deltaC <- NULL
if (!is.null(meanN)) deltaN <- meanSD(nN, meanN, sdN)
if (!is.null(meanC)) deltaC <- meanSD(nC, meanC, sdC)
if (!is.null(deltaN) & !is.null(deltaC))
return (list("deltaC" = deltaC, "deltaN" = deltaN))
else {
if (!is.null(deltaN))
return(deltaN)
else if (!is.null(deltaC))
return(deltaC)
}
return(list("deltaN" = meanSD(nN, 3.4, sdN), "deltaC" = meanSD(nC, 0.39,
sdN)))
}
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