1\chapter{Gretl and \TeX} 2\label{chap:gretltex} 3 4 5\section{Introduction} 6\label{tex-intro} 7 8\TeX\ --- initially developed by Donald Knuth of Stanford University 9and since enhanced by hundreds of contributors around the world --- is 10the gold standard of scientific typesetting. Gretl provides 11various hooks that enable you to preview and print econometric results 12using the \TeX\ engine, and to save output in a form suitable for 13further processing with \TeX. 14 15This chapter explains the finer points of gretl's \TeX-related 16functionality. The next section describes the relevant menu items; 17section~\ref{tex-tune} discusses ways of fine-tuning \TeX\ output; and 18section~\ref{tex-install} gives some pointers on installing (and 19learning) \TeX\ if you do not already have it on your computer. (Just 20to be clear: \TeX\ is not included with the gretl distribution; 21it is a separate package, including several programs and a large 22number of supporting files.) 23 24Before proceeding, however, it may be useful to set out briefly the 25stages of production of a final document using \TeX. For the most 26part you don't have to worry about these details, since, in regard to 27previewing at any rate, gretl handles them for you. But having 28some grasp of what is going on behind the scences will enable you to 29understand your options better. 30 31The first step is the creation of a plain text ``source'' file, 32containing the text or mathematics to be typset, interspersed with 33mark-up that defines how it should be formatted. The second step is 34to run the source through a processing engine that does the actual 35formatting. Typically this a program called \app{pdflatex} that 36generates PDF output.\footnote{Experts will be aware of something 37 called ``plain \TeX'', which is processed using the program 38 \app{tex}. The great majority of \TeX\ users, however, use the 39 \LaTeX\ macros, initially developed by Leslie Lamport. gretl does 40 not support plain \TeX.} (In times gone by it was a program called 41\app{latex} that generated so-called DVI (device-independent) output.) 42 43So gretl calls \app{pdflatex} to process the source file. On MS 44Windows and Mac OS X, gretl expects the operating system to find the 45default viewer for PDF output. On GNU/Linux you can specify your 46preferred PDF viewer via the menu item ``Tools, Preferences, 47General,'' under the ``Programs'' tab. 48 49\section{\TeX-related menu items} 50\label{tex-menus} 51 52\subsection{The model window} 53 54The fullest \TeX\ support in gretl is found in the GUI model 55window. This has a menu item titled ``LaTeX'' with sub-items 56``View'', ``Copy'', ``Save'' and ``Equation options'' (see 57Figure~\ref{fig:latex-menu}). 58 59\begin{figure}[htbp] 60 \caption{\LaTeX\ menu in model window} 61 \label{fig:latex-menu} 62 \begin{center} 63 \includegraphics[scale=0.75]{figures/latex_menu} 64 \end{center} 65\end{figure} 66 67The first three sub-items have branches titled ``Tabular'' and 68``Equation''. By ``Tabular'' we mean that the model is represented in 69the form of a table; this is the fullest and most explicit 70presentation of the results. See Table~\ref{tab:mod1} for an example; 71this was pasted into the manual after using the ``Copy, Tabular'' item 72in gretl (a few lines were edited out for brevity). 73 74\begin{table}[htbp] 75\caption{Example of \LaTeX\ tabular output} 76\label{tab:mod1} 77\begin{center} 78 79Model 1: OLS estimates using the 51 observations 1--51\\ 80Dependent variable: ENROLL\\ 81 82\vspace{1em} 83 84\begin{tabular*}{.8\textwidth}{@{\extracolsep{\fill}} 85l% col 1: varname 86 D{.}{.}{-1}% col 2: coeff 87 D{.}{.}{-1}% col 3: sderr 88 D{.}{.}{-1}% col 4: t-stat 89 D{.}{.}{4}}% col 5: p-value (or slope) 90Variable & 91 \multicolumn{1}{c}{Coefficient} & 92 \multicolumn{1}{c}{Std.\ Error} & 93 \multicolumn{1}{c}{$t$-statistic} & 94 \multicolumn{1}{c}{p-value} \\[1ex] 95const & 96 0.241105 & 97 0.0660225 & 98 3.6519 & 99 0.0007 \\ 100CATHOL & 101 0.223530 & 102 0.0459701 & 103 4.8625 & 104 0.0000 \\ 105PUPIL & 106 -0.00338200 & 107 0.00271962 & 108 -1.2436 & 109 0.2198 \\ 110WHITE & 111 -0.152643 & 112 0.0407064 & 113 -3.7499 & 114 0.0005 \\ 115\end{tabular*} 116 117\vspace{1em} 118 119\begin{tabular}{lD{.}{.}{-1}} 120Mean of dependent variable & 0.0955686 \\ 121 S.D. of dependent variable & 0.0522150 \\ 122Sum of squared residuals & 0.0709594 \\ 123Standard error of residuals ($\hat{\sigma}$) & 0.0388558 \\ 124Unadjusted $R^2$ & 0.479466 \\ 125Adjusted $\bar{R}^2$ & 0.446241 \\ 126$F(3, 47)$ & 14.4306 \\ 127\end{tabular} 128\end{center} 129\end{table} 130 131The ``Equation'' option is fairly self-explanatory---the results are 132written across the page in equation format, as below: 133 134%%% the following needs the amsmath LaTeX package 135 136\begin{gather} 137\widehat{\rm ENROLL} = 138\underset{(0.066022)}{0.241105} 139+\underset{(0.04597)}{0.223530}\,\mbox{CATHOL} 140-\underset{(0.0027196)}{0.00338200}\,\mbox{PUPIL} 141-\underset{(0.040706)}{0.152643}\,\mbox{WHITE} 142 \notag \\ 143T = 51 \quad \bar{R}^2 = 0.4462 \quad F(3,47) = 14.431 \quad \hat{\sigma} = 0.038856\notag \\ 144\centerline{(standard errors in parentheses)} \notag 145\end{gather} 146 147The distinction between the ``Copy'' and ``Save'' options (for both 148tabular and equation) is twofold. First, ``Copy'' puts the \TeX\ 149source on the clipboard while with ``Save'' you are prompted for the 150name of a file into which the source should be saved. Second, with 151``Copy'' the material is copied as a ``fragment'' while with ``Save'' 152it is written as a complete file. The point is that a well-formed 153\TeX\ source file must have a header that defines the 154\texttt{documentclass} (article, report, book or whatever) and tags 155that say \verb|\begin{document}| and \verb|\end{document}|. This 156material is included when you do ``Save'' but not when you do 157``Copy'', since in the latter case the expectation is that you will 158paste the data into an existing \TeX\ source file that already has the 159relevant apparatus in place. 160 161The items under ``Equation options'' should be self-explanatory: when 162printing the model in equation form, do you want standard errors or 163$t$-ratios displayed in parentheses under the parameter estimates? 164The default is to show standard errors; if you want $t$-ratios, select 165that item. 166 167\subsection{Other windows} 168 169Several other sorts of output windows also have \TeX\ preview, copy 170and save enabled. In the case of windows having a graphical toolbar, 171look for the \TeX\ button. Figure~\ref{fig:tex-icon} shows this icon 172(second from the right on the toolbar) along with the dialog that 173appears when you press the button. 174 175\begin{figure}[htbp] 176 \caption{\TeX\ icon and dialog} 177 \label{fig:tex-icon} 178 \begin{center} 179 \includegraphics[scale=0.75]{figures/texdialog} 180 \end{center} 181\end{figure} 182 183One aspect of gretl's \TeX\ support that is likely to be 184particularly useful for publication purposes is the ability to produce 185a typeset version of the ``model table'' (see 186section~\ref{model-table}). An example of this is shown in 187Table~\ref{tab:modeltab}. 188 189\begin{table}[htbp] 190\caption{Example of model table output} 191\label{tab:modeltab} 192\begin{center} 193OLS estimates\\ 194Dependent variable: ENROLL \\ 195\vspace{1em} 196 197\begin{tabular}{lccc} 198 & Model 1 & Model 2 & Model 3 \\ [6pt] 199const & $\,\,$0.2907$^{**}$ & $\,\,$0.2411$^{**}$ & 0.08557 \\ 200& \footnotesize{(0.07853)} & \footnotesize{(0.06602)} & \footnotesize{(0.05794)} \\ [4pt] 201CATHOL & $\,\,$0.2216$^{**}$ & $\,\,$0.2235$^{**}$ & $\,\,$0.2065$^{**}$ \\ 202& \footnotesize{(0.04584)} & \footnotesize{(0.04597)} & \footnotesize{(0.05160)} \\ [4pt] 203PUPIL & $-$0.003035 & $-$0.003382 & $-$0.001697 \\ 204& \footnotesize{(0.002727)} & \footnotesize{(0.002720)} & \footnotesize{(0.003025)} \\ [4pt] 205WHITE & $\,\,$$-$0.1482$^{**}$ & $\,\,$$-$0.1526$^{**}$ & \\ 206& \footnotesize{(0.04074)} & \footnotesize{(0.04071)} & \\ [4pt] 207ADMEXP & $-$0.1551 & & \\ 208& \footnotesize{(0.1342)} & & \\ [4pt] 209$n$ & 51 & 51 & 51 \\ 210$\bar R^2$ & 0.4502 & 0.4462 & 0.2956 \\ 211$\ell$ & 96.09 & 95.36 & 88.69 \\ 212\end{tabular} 213 214\vspace{1em} 215Standard errors in parentheses\\ 216{}* indicates significance at the 10 percent level\\ 217{}** indicates significance at the 5 percent level\\ 218\end{center} 219\end{table} 220 221 222\section{Fine-tuning typeset output} 223\label{tex-tune} 224 225There are three aspects to this: adjusting the appearance of the 226output produced by gretl in \LaTeX\ preview mode; adjusting the 227formatting of gretl's tabular output for models when using the 228\texttt{tabprint} command; and incorporating gretl's output into 229your own \TeX\ files. 230 231 232\subsection{Previewing in the GUI} 233 234As regards \emph{preview mode}, you can control the appearance of 235gretl's output using a file named \verb+gretlpre.tex+, which 236should be placed in your gretl user directory (see the \GCR). 237If such a file is found, its contents will be used as the ``preamble'' 238to the \TeX\ source. The default value of the preamble is as follows: 239 240\begin{code} 241\documentclass[11pt]{article} 242\usepackage[utf8]{inputenc} 243\usepackage{amsmath} 244\usepackage{dcolumn,longtable} 245\begin{document} 246\thispagestyle{empty} 247\end{code} 248 249Note that the \verb+amsmath+ and \verb+dcolumn+ packages are required. 250(For some sorts of output the \verb+longtable+ package is also 251needed.) Beyond that you can, for instance, change the type size or 252the font by altering the \texttt{documentclass} declaration or 253including an alternative font package. 254 255In addition, if you wish to typeset gretl output in more than 256one language, you can set up per-language preamble files. A 257``localized'' preamble file is identified by a name of the form 258\verb|gretlpre_xx.tex|, where \texttt{xx} is replaced by the first two 259letters of the current setting of the \texttt{LANG} environment 260variable. For example, if you are running the program in Polish, 261using \verb|LANG=pl_PL|, then gretl will do the following when 262writing the preamble for a \TeX\ source file. 263 264\begin{enumerate} 265\item Look for a file named \verb|gretlpre_pl.tex| in the gretl 266 user directory. If this is not found, then 267\item look for a file named \verb|gretlpre.tex| in the gretl 268 user directory. If this is not found, then 269\item use the default preamble. 270\end{enumerate} 271 272Conversely, suppose you usually run gretl in a language other 273than English, and have a suitable \verb|gretlpre.tex| file in place 274for your native language. If on some occasions you want to produce 275\TeX\ output in English, then you could create an additional 276file \verb|gretlpre_en.tex|: this file will be used for the preamble 277when gretl is run with a language setting of, say, 278\verb|en_US|. 279 280 281\subsection{Command-line options} 282 283After estimating a model via a script---or interactively via the gretl 284console or using the command-line program \app{gretlcli}---you can use 285the commands \texttt{tabprint} or \texttt{eqnprint} to print the model 286to file in tabular format or equation format respectively. These 287options are explained in the \GCR{}. 288 289If you wish alter the appearance of gretl's tabular output for 290models in the context of the \texttt{tabprint} command, you can 291specify a custom row format using the \option{format} flag. The 292format string must be enclosed in double quotes and must be tied to 293the flag with an equals sign. The pattern for the format string is as 294follows. There are four fields, representing the coefficient, 295standard error, $t$-ratio and p-value respectively. These fields 296should be separated by vertical bars; they may contain a 297\texttt{printf}-type specification for the formatting of the numeric 298value in question, or may be left blank to suppress the printing of 299that column (subject to the constraint that you can't leave all the 300columns blank). Here are a few examples: 301 302\begin{code} 303--format="%.4f|%.4f|%.4f|%.4f" 304--format="%.4f|%.4f|%.3f|" 305--format="%.5f|%.4f||%.4f" 306--format="%.8g|%.8g||%.4f" 307\end{code} 308 309The first of these specifications prints the values in all columns 310using 4 decimal places. The second suppresses the p-value and prints 311the $t$-ratio to 3 places. The third omits the $t$-ratio. The last 312one again omits the $t$, and prints both coefficient and standard 313error to 8 significant figures. 314 315Once you set a custom format in this way, it is remembered and used 316for the duration of the gretl session. To revert to the default 317formatting you can use the special variant \verb|--format=default|. 318 319 320\subsection{Further editing} 321 322Once you have pasted gretl's \TeX\ output into your own 323document, or saved it to file and opened it in an editor, you can of 324course modify the material in any wish you wish. In some cases, 325machine-generated \TeX\ is hard to understand, but gretl's 326output is intended to be human-readable and -editable. In addition, 327it does not use any non-standard style packages. Besides the standard 328\LaTeX\ document classes, the only files needed are, as noted above, 329the \verb+amsmath+, \verb+dcolumn+ and \verb+longtable+ packages. 330These should be included in any reasonably full \TeX\ implementation. 331 332 333\section{Installing and learning \TeX} 334\label{tex-install} 335 336This is not the place for a detailed exposition of these matters, but 337here are a few pointers. 338 339So far as we know, every GNU/Linux distribution has a package or set 340of packages for \TeX, and in fact these are likely to be installed by 341default. Check the documentation for your distribution. For MS 342Windows, several packaged versions of \TeX\ are available: one of the 343most popular is MiK\TeX\, at \url{http://www.miktex.org/}. For Mac OS 344X a nice implementation is i\TeX{}Mac, at 345\url{http://itexmac.sourceforge.net/}. An essential starting point for 346online \TeX\ resources is the Comprehensive 347\TeX\ Archive Network (CTAN) at \url{http://www.ctan.org/}. 348 349As for learning \TeX, many useful resources are available both online 350and in print. Among online guides, Tony Roberts' ``\LaTeX: from quick 351and dirty to style and finesse'' is very helpful, at 352 353\url{http://www.sci.usq.edu.au/staff/robertsa/LaTeX/latexintro.html} 354 355An excellent source for advanced material is \emph{The \LaTeX\ 356 Companion} \citep{goossens04}. 357 358 359%%% Local Variables: 360%%% mode: latex 361%%% TeX-master: "gretl-guide" 362%%% End: 363