n <- 100; data <- rnorm(n,1,0.1);hist(data)
N <- data[1:(n-1)]; r <- (data[2:n]-N)/N
plot(N,r,type="p")
lm(r~N,as.data.frame(cbind(N,r)))

# Make figure
size <- 5 #inch
pdf("regression.pdf",width=size,height=0.5*size)
par(mar=c(2.6,2.6,0.2,0.2),mgp=c(1.5,0.5,0)) 
plot(N,r,type="p",xlab="N(t)",ylab="[N(t+1)-N(t)]/N(t)")
dev.off()