\documentclass[11pt]{article}
\begin{document}
\section{Introduction}
Let's first simulate some data.
<<computetime,echo=true>>=
x <- rnorm(100); y <- x + rnorm(100, sd = 0.5)
@
Here is a scatterplot of the data.
<<scatterplot,fig=true,width=8,height=4>>=
par(mar = c(5, 4, 1, 1), las = 1)
plot(x, y, main = "My Data")
@
\end{document}