[R] Sweave, mle and curve

[Göran Broström]

I am trying to write a lesson on maximum likelihood with Sweave. I get
a surprising result with the following code, lec4.Snw:

\documentclass[a4paper,12pt]{article}
\usepackage[latin1]{inputenc}

\title{Maximum likelihood}

\author{GÃ¶ran BrostrÃ¶m}

\begin{document}

\maketitle

<<fig=TRUE>>=
## Simulate Y:
n <- 25
Y <- sum(rpois(n, lambda = 1))
Y
 ## Define minusloglik:
minusloglik <- function(theta) n * theta - Y  * log(theta)
curve(minusloglik, 0.2, 2, xlab = "theta")

library(stats4)
cat("Y is now ", Y, "\n")
fit <- mle(minusloglik, start = list(theta = Y/n))
summary(fit)
@

\end{document}

In R, I get:

> Sweave("lec4.Snw")
Writing to file lec4.tex
Processing code chunks ...
 1 : echo term verbatim eps pdf
Y is now  27
Y is now  24

You can now run LaTeX on 'lec4.tex'
>

and the latex document will have two different mle's,  one in the
figure, and another one from 'mle'.  One uses Y = 27 and the other Y =
24!

I can save the situation by moving "Y <- ..." to a separaye "code chunk".
Does 'fig=TRUE' imply that the code chunk is run twice?

--
GÃ¶ran BrostrÃ¶m