R/zeta.R

In iTOS: Methods and Examples from Introduction to the Theory of Observational Studies

zeta <-
  function(bigN,n,m,g){
    #The zeta function in expression (8) of Rosenbaum and Krieger (1995), JASA, 85, 493-498.
    low<-max(0,(m+n)-bigN)
    if ((m<0)|(n<0)) o<-0
    else {
      high<-min(n,m)
      a<-low:high
      term<-choose(m,a)*choose(bigN-m,n-a)*(g^a)
      o<-sum(term)
    }
    o
  }