R/gen_exponential_anticoef.R

In skpr: Design of Experiments Suite: Generate and Evaluate Optimal Designs

#'@title Generates Exponential Anticipated Coefficients
#'
#'@description Generates Exponential Anticipated Coefficients
#'Solves the exponential link function
#'mean = exp(beta0 + beta1 * x)
#'such that mean = mean_low when x = -1, and mean = mean_high when x = +1.
#'Equivalently, solves this set of equations for beta0 and beta1:
#'mean_low = exp(beta0 - beta1)
#'mean_high = exp(beta0 + beta1)
#'@param anticoef input anticipated coefficeints
#'@param mean_low The low value of the mean value (= 1/rate)
#'@param mean_high The high value of the mean value (= 1/rate)
#'@return Anticipated coefficients.
#'@keywords internal
gen_exponential_anticoef = function(anticoef, mean_low, mean_high) {
  if (mean_low <= 0 || mean_high <= 0) {
    stop("skpr: Exponential anticipated coefficients generation error: mean values must be positive.")
  }
  b0 = 1 / 2 * (log(mean_high) + log(mean_low))
  b  = 1 / 2 * (log(mean_high) - log(mean_low))
  newanticoef = anticoef * b
  newanticoef[1] = b0
  return(newanticoef)
}