R/model-sigmoid-stanvars.R

In maomlab/BayesPharma: Tools for Bayesian Analysis of Non-Linear Pharmacology Models

#' Stan Code for the Sigmoid Model.
#'
#' @note stanvar script of a sigmoid dose response equation. For log dose
#'   greater than negative infinity (dose greater than 0), the sigmoid dose
#'   response equation is used. `ac50` is the half maximal response, hill is the
#'   slope, top is the maximum response, and bottom is the minimum response. For
#'   log dose equal to negative infinity (dose equal to 0), if hill is positive,
#'   then the bottom value is returned. If hill is negative, then the top value
#'   is returned.
#'
#' @export
sigmoid_stanvar <- function() {
  brms::stanvar(
    scode = paste(
      "   real sigmoid(",
      "      real ac50,",
      "      real hill,",
      "      real top,",
      "      real bottom,",
      "      real log_dose) {",
      "        if( log_dose > negative_infinity() ) {",
      "          return (bottom + (top - bottom) /",
      "            (1 + 10 ^ ((ac50 - log_dose) * hill)));",
      "        } else { ",
      "           if( hill > 0) {",
      "             return bottom;",
      "           } else {",
      "             return top;",
      "           }",
      "        }",
      "   }", sep = "\n"),
    block = "functions")
}