# [R] Adding LaTeX cross-references into Sweave plots

From: Peter Dunn <dunn_at_usq.edu.au>
Date: Wed, 27 Feb 2008 11:06:19 +1000

I'm using Sweave and LaTeX, and love how they interact.

But here's a different interaction I'm not sure how to achieve; I hope someone can help. I use a simple example, of course, to demonstrate.

Suppose in my LaTeX document I have this:

	Here is a linear equation:
$$y = -1 + 3 x \label{EQ:example}$$



This appears in the final product with an Equation number, say (1).

Now suppose I wish to produce a graphic in R:

	<<fig=TRUE>>=
plot( c(-1,1), c(-1,1), type="n",
main="Graph of Eq (1)")
abline(-1, 3)

@



All easy.

But... how to I ensure the correct LaTeX label appears in the plot? You see, if I run LaTeX again, and my equation is no longer labelled (1) and changes to (say) label (3), I have to manually fix the Sweave code to read

	<<fig=TRUE>>=
plot( c(-1,1), c(-1,1), type="n",
main="Graph of Eq (3)")
abline(-1, 3)

@



Any ideas of how that can be automated? I guess something like this (though this obviously will fail):

	<<fig=TRUE>>=
plot( c(-1,1), c(-1,1), type="n",
main="Graph of Eq (\label{EQ:equation})")
abline(-1, 3)

@



Thanks as always.

P.

--
Dr Peter Dunn  |  dunn <at> usq.edu.au
Faculty of Sciences, USQ; http://www.sci.usq.edu.au/staff/dunn
Aust. Centre for Sustainable Catchments: www.usq.edu.au/acsc

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