R help - May 2007 - How to use filter function for this?

Hello,

I have been trying to compute the following:

for(t in 3:n){

		h[t]<-(omegac/(1-betac))+alphac*Y[t-1]

		b[t]<-Y[t-1]
		bb[t]<-0

		for(j in 2:(t-1)){
				h[t]<-h[t]+alphac*((betac)^(j-1))*Y[t-j]
				b[t]<-b[t]+((betac)^(j-1))*Y[t-j]
				bb[t]<-bb[t]+((betac)^(j-2))*Y[t-j]*(j-1)
				}
               }


but it takes a long time. I have heard that "filter" function can be
used
instead but dont know how to apply it. Did anyone use it and have any idea 
how to apply for this function?.
Thanks

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