[R] optimizing speed of calculation (recursive product)

[Wolfgang Raffelsberger]

Dear list,
I'm wondering how to optimize functions/processes like the one shown 
below (which simplifies something we're trying to do with very large 
datasets).
In many cases I've noticed that using apply, sapply etc can help 
speeding up processes, but in this case I don't see how I could do so.

a <- runif(10000000,0.5,1.6)
C <- 2
M <- 10000000
system.time( for (i in 1:(M-1)) {C <- C* c(a[i],a[i+1])} )


By the way, I'm using R-2.7.2 on Win XP and/or Fedora Linux.

Thank's in advance for any hints,
Wolfgang Raffelsberger

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Wolfgang Raffelsberger, PhD
Laboratoire de BioInformatique et Génomique Intégratives
CNRS UMR7104, IGBMC 
1 rue Laurent Fries,  67404 Illkirch  Strasbourg,  France