R/logis.R

In CUB: A Class of Mixture Models for Ordinal Data

#' @title The logistic transform
#' @description Create a matrix YY binding array \code{Y} with a vector of ones, placed as the first column of YY. 
#' It applies the logistic transform componentwise to the standard matrix multiplication between YY and \code{param}.
#' @aliases logis
#' @usage logis(Y,param)
#' @export logis
#' @param Y A generic matrix or one dimensional array
#' @param param Vector of coefficients, whose length is NCOL(Y) + 1 (to consider also an intercept term)
#' @return Return a vector whose length is NROW(Y) and whose i-th component is the logistic function
#' at the scalar product between the i-th row of YY and the vector \code{param}.
#' @keywords utilities
#' @examples
#' n<-50 
#' Y<-sample(c(1,2,3),n,replace=TRUE) 
#' param<-c(0.2,0.7)
#' logis(Y,param)

logis <-
function(Y,param){
  Y<-as.matrix(Y)
  
  if (ncol(Y)==1){
    Y<-as.numeric(Y)
  }
  
  YY<-cbind(1,Y)          # add 1's first column to matrix Y
  val<-1/(1+exp(-YY%*%param))
  
  if (all(dim(val)==c(1,1))){
    return(as.numeric(val))
    
  } else{
    return(val)
  }
}