R/tcplObjCnst.R

In USEPA/CompTox-ToxCast-tcpl: ToxCast Data Analysis Pipeline

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# tcplObjCnst: Generate a constant model objective function to optimize
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#' @rdname Models
#' 
#' @section Constant Model (cnst): 
#' \code{tcplObjCnst} calculates the likelyhood for a constant model at 0. The 
#' only parameter passed to \code{tcplObjCnst} by \code{p} is the scale term 
#' \eqn{\sigma}. The constant model value \eqn{\mu_{i}}{\mu[i]} for the  
#' \eqn{i^{th}}{ith} observation is given by:
#' \deqn{\mu_{i} = 0}{\mu[i] = 0}
#' 
#' @importFrom stats dt
#' @export

tcplObjCnst <- function(p, resp) {
  
  ### This function takes creates an objective function to be optimized using
  ### the starting constant model parameter, and response. 
  ###
  ### Arguments: 
  ###   p:     a numeric vector of length 1 containg the starting values for 
  ###          the constant model, in order: log error term
  ###   lresp: a numeric vector containing the response values to produce the 
  ###          objective function
  ### 
  ### Value:
  ###   An objective function for the constant model and the given resp data
  
  mu <- 0
  sum(dt((resp - mu)/exp(p[1]), df = 4, log = TRUE) - p[1])
  
}

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