Using L^ATEX

TEX formats

Before talking about L^ATEX one should understand TEX internals a little more. The basic TEX program contains only a few primitive commands and is written at too low a level to be generally useful. However, you can preload a set of macros--more complex commands built out of TEX primitives. One way to load these is to have them in a separate file, say macros.tex and then to write \input macros.tex as the first line of your document. This can be very slow if you have a lot of macros because TEX has to parse all of them and load them into memory. To get around this you can dump a memory image of your macros as a format file. TEX can then load this in each time very quickly--it just writes the file straight to memory. The default format is Plain TEX written by Donald Knuth during the development of TEX .

Plain TEX has enough commands to be able to use TEX --that is what our first document used--but it is not very user-friendly. There are many other formats available, the most popular of which is L^ATEX (now called L^ATEX2_e ) written by Leslie Lamport. It is on this that I shall concentrate.

TEX will automatically load a format on startup, depending on how you call the program. Typically, tex will run the default format, latex will run L^ATEX2_e and there may be other commands to load other formats. An alternate way of doing this is to specify the format when you run TEX :

tex &format \input file.tex

but you have to be careful to protect the `&' and the ` $\backslash$' from whatever shell you happen to be running. For example the following two commands are equivalent under unix:

rob@random:~/$ latex myfile.tex
rob@random:~/$ tex \&latex \\input myfile.tex

Summary

• TEX on its own is like having a C compiler with no libraries
• TEX's libraries are called packages or formats
• TEX can preload a single format when it is run, either by calling TEX with a different name, or by specifying the format on the command line.
• Formats are memory images of preloaded packages--they are fast to load
• You can use the command \input package to load extra packages
• The default format is Plain TEX
• L^ATEX (L^ATEX2_e) is the most popular format; it is analogous to running C++ instead of C.

The philosophy of L^ATEX

There are two main ideas behind L^ATEX . The first is to provide user-friendly wrappers around standard Plain TEX commands. For example the commands used in TEX and L^ATEX to typeset the matrix below are shown in Figure 7.

$$\left[ \begin{array}{cccc} a & b & c & d \\ b & a & c+d & c-d \\ 0 & 0 & a+b & a-b \\ 0 & 0 & ab & cd \end{array} \right]$$

As you can see, they are not very different.

Figure 7: Commands for the matrix above

But suppose you want to format the matrix a little differently, e.g. align everything on the right hand side. Figure 8 shows the new matrix and its L^ATEX commands, while Figure 9 shows the corresponding TEX .

Figure 8: Matrix and corresponding L^ATEX code

Figure: TEX code

The point is that in L^ATEX you can usually change the appearance of an environment by changing some parameter, while in TEX one must add extra commands.

The main idea is to free you from formatting concerns. TEX knows how to typset text correctly, but L^ATEX knows how to format a whole document. L^ATEX understands the form that a paper, article, report or book should take, provides you with commands to fill in things like chapter titles and section names, and then lets you concentrate on the content. This is the opposite of a WYSIWYG word-processor where you must be constantly aware of what your document looks like.

Your first L^ATEX document

The L^ATEX paradigm is that a document is broken into logical sectional units--chapter, section, subsection, etc. Within any unit you may produce extra formatting by using a special environment. The default environment is a paragraph, but anything else may be used with a pair:

\begin{environment} ... \end{environment}

For example the list

• Chapter
  
• Section
  
• Subsection
  

may be created with the commands:

\begin{itemize}
\item Chapter
\item Section
\item Subsection
\end{itemize}

The first line in your file must be

\documentclass[options]{class}

Next comes the preamble--global formatting commands which will affect the whole document--and then the text is contained between the pair:

\begin{document} ... \end{document}

If we create a file perfect2.tex containing the text below and then use the command latex perfect2.tex to run L^ATEX , then it will produce the output shown on the following page.

\documentclass[12pt]{article}

\begin{document}

\title{Unsolved Problems}
\author{Robert P. Judd}
\maketitle

\section{Odd Perfect Numbers}

A number is said to be \textbf{perfect} if it is the
sum of its divsors.  For example, $6$ is perfect
because $1+2+3=6$, and $1$, $2$ and $3$ are the only
numbers that divide evenly into $6$ (apart from $6$
itself).

It has been shown that all even perfect numbers have
the form \[2^{p-1}(2^p-1)\] where $p$ and $q$ are
both prime.

The existence of \textit{odd} perfect numbers is an
open question.

\end{document}