R/alpha.fun.R

In dfalster/smatr3: (Standardised) Major Axis Estimation and Testing Routines

#' Utility functions for robust fitting
#' 
#' @description Functions used by \code{\link{sma}} when 'robust = TRUE'.
#' 
#' 
#' @param r,k,q, Parameters.
#' @param data .....
#' @author Warton, D. I. \email{David.Warton@@unsw.edu.au}, S. Taskinen
#' @seealso \code{\link{sma}}
#' @keywords internal
alpha.fun<-function(r,k,q) 
{
  c<-qchisq(q,k)
  sig<-pchisq(c,k+2)+(c/k)*(1-q)

  c<-sqrt(c)
  eta<-NULL
  eta[r<=c]<-(r[r^2<=c^2])^2/(k*sig) 
  eta[r>c]<-c^2/( (k+2)*sig ) 
  eta <- mean(eta)

  alpha<-NULL
  alpha[r<=c]<-(r[r<=c])^2/(eta*sig)
  alpha[r>c]<-c^2/(eta*sig)
  alpha
}