[R] how to vectorize a for loop

[stephen sefick]

#Is there a way to vectorize the for loop
#maybe a fancy indexing trick?
#thanks

d=0.5
L=20
x=seq(20, by=1, length.out=20)
reflecting <- function(pre, d, L){
	r=L-1
	x=rep(0, L)
	for(j in 2:r){
	x[j]=((1-(2*d))*pre[j])+(d*pre[(j+1)])+(d*pre[(j-1)])
	}
	x[1]=((1-d)*pre[1])+(d*pre[2])
	x[L]=((1-d)*pre[L])+(d*pre[(L-1)])
	y=x
}

f = reflecting(x, d, L)
-- 
Stephen Sefick
Research Scientist
Southeastern Natural Sciences Academy

Let's not spend our time and resources thinking about things that are
so little or so large that all they really do for us is puff us up and
make us feel like gods.  We are mammals, and have not exhausted the
annoying little problems of being mammals.

								-K. Mullis