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diff --git a/R/WP_known.R b/R/WP_known.R
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+#' WP method background function WP_known
+#'
+#' This is a background/internal function called by \code{WP}.  It computes the maximum likelihood estimator of R0 assuming that the serial distribution is known and finite discrete.
+#'
+#' @param NT vector of case counts
+#' @param p discretized version of the serial distribution
+#' @return The function returns \code{Rhat}, the maximum likelihood estimator of R0.
+#' @export
+# 
+
+WP_known		<-	function(NT, p){
+	
+	k		<-	length(p)
+	TT		<-	length(NT)-1
+	mu_t	<-	rep(0, TT)
+	for(i in 1:TT){
+		Nt		<-	NT[i:max(1,i-k+1)]
+#		print(Nt)
+#		print(p[1:min(k,i)])
+		mu_t[i]	<-	sum(p[1:min(k,i)]*Nt)	
+	}
+	Rhat	<-	sum(NT[-1])/sum(mu_t)
+	return(list(Rhat=Rhat))
+		
+}
+
+