What is the R way of computing cumulative growth rates given a series of 
discrete values indexed .

For instance, given a matrix of 20 observations for each of 5 series (zz), 
what is the most straight forward technique in R for computing cumulative 
growth (zzcum) ?
It seems for the solution I'm after might be imbedding the following cum 
growth rate calc as a function into a function call to apply, mapply, ...? 



zz = rnorm(100)
dim(zz) = c(20,5)
zz
zzcum=matrix(nrow=20,ncol=5)
zzcum
zzcum[1,]=100*(1+zz[1,]/100)
zzcum
for(i in 2:20){zzcum[i,] = zzcum[i-1,]*(1+zz[i,]/100)}
zzcum





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