\documentclass[a4paper]{article}

\begin{document}

<<echo=false,results=hide>>=
library(lattice)
library(xtable)
data(cats, package="MASS")
@ 

\section*{The Cats Data}

Consider the \texttt{cats} regression example from Venables \& Ripley
(1997). The data frame contains measurements of heart and body weight
of \Sexpr{nrow(cats)} cats (\Sexpr{sum(cats$Sex=="F")} female,
\Sexpr{sum(cats$Sex=="M")} male).

A linear regression model of heart weight by sex and gender can be
fitted in R using the command
<<>>=
lm1 = lm(Hwt~Bwt*Sex, data=cats)
lm1
@ 
Tests for significance of the coefficients are shown in
Table~\ref{tab:coef}, a scatter plot including the regression lines is
shown in Figure~\ref{fig:cats}.

\SweaveOpts{echo=false}

<<results=tex>>=
xtable(lm1, caption="Linear regression model for cats data.", label="tab:coef")
@ 

\begin{figure}
  \centering
<<fig=TRUE,width=12,height=6>>=
lset(col.whitebg())
print(xyplot(Hwt~Bwt|Sex, data=cats, type=c("p", "r")))
@  
  \caption{The cats data from package MASS.}
  \label{fig:cats}
\end{figure}
\begin{center}
\end{center}

\end{document}