r - Problems using the kf-function in the KFAS package -

i trying estimate local level state space model on data nile default r library.

install.packages("kfas") library("kfas")   #example of local level model #using nile observations data(nile)  yt<-t(data.matrix(nile)) s2_eps<-15099 s2_eta<-1469.1  f.out<-kf(yt = yt,  zt = 1,  tt=1,  rt=1,  ht= s2_eps,  qt=s2_eta,  a1 =             0,  p1=1e7) 

when evaluate function, error saying function kf not exist. however, kf-function should part of kfas package.

hope able help.

thanks