Reaching escape velocity

June 22, 2010
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(This article was first published on Probability and statistics blog » r, and kindly contributed to R-bloggers)

Sample once from the Uniform(0,1) distribution. Call the resulting value x. Multiply this result by some constant c. Repeat the process, this time sampling from Uniform(0, x*c). What happens when the multiplier is 2? How big does the multiplier have to be to force divergence. Try it and see:

iters = 200
locations = rep(0,iters)
top = 1
multiplier = 2
for(i in 1:iters) {
	locations[i] = runif(1,0,top)
 
	top = locations[i] * multiplier
}
 
windows()
plot(locations[1:i],1:i,pch=20,col="blue",xlim=c(0,max(locations)),ylim=c(0,iters),xlab="Location",ylab="Iteration")
 
# Optional save as movie, not a good idea for more than a few hundred iterations. I warned you!
# library("animation")
# saveMovie(for (i in 1:iters) plot(locations[1:i],1:i,pch=20,col="blue",xlim=c(0,max(locations)),ylim=c(0,iters),xlab="Location",ylab="Iteration"),loop=1,interval=.1)

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