[R] vectorizing an iterative process.

[Geoffrey Zhu]

Hi Everyone,
 
I am stuck with a simple problem. Suppose I have a vector x, and I want
to calculate y[i]=3Dx[i+1]-x[i], it is very easy. I just need to write
y<-x[2:length(x)]-x[1:length(x)-1]. 
 
Now if I know y, and want to know the vector x defined by
x[i]=3Dx[i-1]+y[i-1] for all i, how can I do this without a loop? 
 
Thanks,
Geoffrey

PS. Sorry if you see a duplicate message. The previous one was in a
weird format that most people would not be able to read.

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