Typesetting a document

With input_mode = "document", grid.latex() sets the body of a LaTeX document: paragraphs, headings, displayed equations, lists and tables. Use it for a methods section, an appendix or a long caption, with no LaTeX installation.

A document body

This is ordinary LaTeX, as it would appear between \begin{document} and \end{document}:

body <- r"(\section{Methods}
We fit a straight line to $n$ observations $(x_i, y_i)$ by least
squares, which chooses the intercept and slope that minimise the sum
of squared residuals
\[ S(\beta_0, \beta_1) = \sum_{i=1}^{n} (y_i - \beta_0 - \beta_1 x_i)^2. \]
Setting both partial derivatives to zero gives the estimates
\begin{align}
  \hat\beta_1 &= \frac{\sum_i (x_i - \bar x)(y_i - \bar y)}{\sum_i (x_i - \bar x)^2}, \label{slope} \\
  \hat\beta_0 &= \bar y - \hat\beta_1 \bar x. \label{intercept}
\end{align}

The fitted values are $\hat y_i = \hat\beta_0 + \hat\beta_1 x_i$, and
the residuals $e_i = y_i - \hat y_i$ are what is left over. Together
\eqref{slope} and \eqref{intercept} make them sum to zero.

\subsection{Assumptions}
The errors are taken to be
\begin{itemize}
  \item independent of one another,
  \item of constant variance $\sigma^2$, and
  \item normally distributed --- which matters only for the tests.
\end{itemize}
)"

max_width is the text width in big points (1/72 inch):

grid.newpage()
grid.latex(body, input_mode = "document", max_width = 5.6 * 72,
           x = 0.03, y = 0.97, hjust = 0, vjust = 1,
           gp = gpar(fontsize = 11))

How the body is read

As in LaTeX:

Paragraphs. A blank line or \par starts a new, indented paragraph. \noindent suppresses the indent.
Headings. \section, \subsection and \subsubsection are numbered; starred forms are not.
Math. $...$ and $...$ are inline. \[...\], $$...$$, equation, align, gather and multline are centred on their own line. The last four are numbered at the right margin, a row each (multline: one), unless starred or marked \notag; \tag{x} sets a number, and \label with \ref or \eqref refer to it.
Lists and tables. itemize, enumerate, description and tabular hold text, with math between $...$ .
Theorems. \newtheorem declares them, with the shared and [section] counters and a starred, unnumbered form; proof ends with a box.
Text. -- and --- are dashes, quotes are curly, and ~ is a non-breaking space. \centering and center centre lines. \textsc sets small capitals, and \verb and verbatim set code as it is typed.

Problems produce one warning, listing each with its line and column.

A theorem and its proof

thm <- r"(\newtheorem{thm}{Theorem}
\begin{thm}[Gauss--Markov]\label{gm}
With uncorrelated errors of equal variance, least squares has the least
variance among the linear unbiased estimators.
\end{thm}
\begin{proof}
Write any other such estimator as least squares plus a correction, and
show that the correction can only add variance.
\end{proof}
Theorem~\ref{gm} is why \verb|lm(y ~ x)| is the default.)"
grid.newpage()
grid.latex(thm, input_mode = "document", max_width = 5.6 * 72,
           x = 0.03, y = 0.97, hjust = 0, vjust = 1,
           gp = gpar(fontsize = 11))

Justified text

justify = TRUE fills every line but the last, and line_break = "optimal" chooses the breaks for the whole paragraph:

para <- r"(Least squares has a closed form, which is why it was the
method of choice long before computers made iterative fitting cheap. It
is also optimal among unbiased linear estimators when the errors are
uncorrelated with equal variance: the Gauss--Markov theorem.)"
grid.newpage()
grid.latex(para, input_mode = "document", max_width = 5.6 * 72,
           justify = TRUE, line_break = "optimal",
           x = 0.03, y = 0.95, hjust = 0, vjust = 1,
           gp = gpar(fontsize = 11))

Saving a PDF

Use cairo_pdf() so the text can be selected. latex_dims() gives the height to size the page:

d <- latex_dims(body, input_mode = "document", max_width = 5.5 * 72,
                gp = gpar(fontsize = 11))
height <- as.numeric(d$height) / 72 + 1   # inches, with margins

cairo_pdf("methods.pdf", width = 6.5, height = height)
grid.latex(body, input_mode = "document", max_width = 5.5 * 72,
           x = unit(0.5, "in"), y = unit(1, "npc") - unit(0.5, "in"),
           hjust = 0, vjust = 1, gp = gpar(fontsize = 11))
dev.off()