**T _{E}X** (usually written

**TeX**in plain text) is a typesetting system written by Donald Knuth, which is popular in academia, especially in the mathematics, physics and computer science communities. It has largely displaced Unix troff, the other favored formatter, in many Unix installations.

TeX is generally considered to be the best way to typeset complex mathematical formulas, but, especially in the form of LaTeX and other template packages, is now also being used for many other typesetting tasks. It can be used to compose mathematical expressions on Wikipedia pages; see Wikipedia:TeX markup.

Table of contents |

2 The typesetting system 3 License 4 Quality 5 The name 6 Derived works 7 Compatible tools 8 TeX and Wikipedia 9 TeX examples |

## History

Knuth began TeX because he had become annoyed at the declining quality of the typesetting in volumes I-III of his monumental*The Art of Computer Programming*. In a manifestation of the typical hackish urge to solve the problem at hand once and for all, he began to design his own typesetting language. He thought he would finish it on his sabbatical in 1978; he was wrong by only about 8 years. The language was finally frozen around 1985.

Guy Steele happened to be at Stanford during the summer of 1978, when Knuth was developing his first version of TeX. When he returned to MIT that fall, he rewrote TeX's I/O to run under ITS.

The first version of TeX was written in the SAIL programming language to run on a PDP-10 under Stanford's WAITS operating system. For later versions of TeX, Knuth invented the concept of literate programming, a way of producing compilable source code and high quality cross-linked documentation (typeset in TeX of course) from the same original file. The language used is called WEB and produces programs in Pascal.

TeX has an idiosyncratic version numbering system. Since version 3, updates have been indicated by adding an extra digit at the end of the decimal, so that the version number asymptotically approaches pi. The current version is 3.14159. This is a reflection of the fact that TeX is now very stable, and only minor updates are anticipated.

## The typesetting system

TeX commands start with a backslash. TeX is a macro based language: every command expands into a list of other commands or text (possibly with side effects), and the other commands are then expanded in turn until everything is fully expanded. Users can define their own macros. Loops and if-then-else constructs are available, making TeX a Turing-complete language.The TeX system has precise knowledge of the sizes of all characters and symbols, and using this information, it computes the optimal arrangement of letters per line and lines per page. It then produces a DVI file (for "device independent") containing the final locations of all characters. This dvi file can be printed directly given an appropriate printer driver, or it can be converted to other formats.

The ultimate reference works for TeX are the first two volumes of Knuth's Computers and Typesetting, *The TeXbook* and *TeX: The Program* (which includes the complete documented source code for TeX).

## License

The license allows free distribution and modification but demands that any changed version not be called T_{E}X, TeX, or anything confusingly similar, providing rights similar to those of a trademark.

## Quality

Though well-written, TeX is so large (and so full of cutting edge technique) that it is said to have unearthed at least one bug in every Pascal system it has been compiled with. TeX runs on almost all operating systems.Knuth offers monetary awards to people who find and report a bug in it. The award per bug started at one cent and doubled every year until it was frozen at its current value of $327.68. This has not made Knuth poor, however, as there have been very few bugs and in any case a cheque proving that the owner found a bug in TeX is usually framed instead of cashed.

## The name

The name TeX is intended to be pronounced "tekh", where "kh" represents the sound at the end of Scottish "loch" (but not English "loch"; in SAMPA: /tex/). The X is meant to be the Greek letter χ. TeX is the abbreviation of τεχνε, Greek for "art" and "craft," which is also the source word of "technical".The name is properly typeset with the "E" below the baseline; systems that do not support subscript layout use the approximation "TeX". Fans like to proliferate names from the word "TeX" - such as TeXnician (user of TeX software), TeXhacker (TeX programmer), TeXmaster (competent TeX programmer), TeXhax, and TeXnique.

## Derived works

Several document processing systems are based on TeX, notably:- LaTeX (Lamport TeX), which incorporates document styles for books, letters, slides, etc., and adds support for referencing and automatic numbering of sections and equations,
- AMS-TeX, produced by the American Mathematical Society, this has a lot of more user-friendly commands, which can be altered by journals to fit with the house style. Most of the features of AMS-Tex can be used in LaTeX by using the AMS "packages". This is then referred to as AMS-LaTeX. The main AMS-TeX manual is entitled
*The Joy of TeX*. - jadeTeX which uses TeX as a backend for printing from James' DSSSL Engine,
- Texinfo, the GNU documentation processing system.

## Compatible tools

The TeXmacs text editor is a WYSIWYG scientific text editor that is intended to be compatible with TeX. It uses Knuth's fonts, and can generate TeX output. LyX is a similar tool.## TeX and Wikipedia

As of 2003, Wikipedia implements TeX markup, using`<math>...</math>`tags enclosing blocks of TeX. This capability is implemented via Texvc which is basically a script that pipes the markup through TeX, then dvips to produce a PostScript file which Ghostscript renders into a PNG image. Due to the nature of the web environment, this is done in an efficient (cached) and security-conscious way -- allowing third parties to pass unsanitised text through the standard TeX engine is a bad idea if you value your files.

The example fragments of TeX below are rendered using Texvc, and simple ones such as $\backslash \backslash frac\{a\}\{b\}$ can be used to generate , although it is recommended that one writes the HTML-rendered a/b instead.

## TeX examples

A simple plain TeX example - Create a text file*myfile.tex*with the following content:

hello \\byeThen open a command line interpreter and type

tex myfile.texTeX then creates a file

*myfile.dvi*Use a viewer to look at the file. MikTeX for example contains a viewer called

`yap`:

yap myfile.dviThe viewer shows

*hello*on a page.

*\\bye*is a TeX command which marks the end of the file and is not shown in the final output.

The dvi file can either be printed directly from the viewer or converted to a more common format such as PostScript using the `dvips` program.

To see TeX further in action, look at its formatting of mathematical formulas. For example, to write the well-known quadratic formula, try entering

The quadratic formula is ${-b\\pm\\sqrt{b^2-4ac} \\over {2a}}$ \\byeUse TeX as above, and you should get something that looks like

- The quadratic formula is

*math mode*is done by starting with a $, then entering a formula in TeX semantics and closing again with another $. Display math, or math presented centered on a new line is done by using $$. For example, the above with the quadratic formula in display math:

The quadratic formula is $${-b\\pm\\sqrt{b^2-4ac} \\over {2a}}$$ \\byerenders as

- The quadratic formula is

*See also:*

*References:*

- The T
_{E}X users group: http://www.tug.org/ - Comprehensive T
_{E}X Archive Network: http://www.ctan.org/ . Repository of the T_{E}X source and hundreds of add-ons and style files. - The LaTeX project: http://www.latex-project.org/ .
- Donald E. Knuth,
*The T*(Computers and Typesetting Volume A), Reading, Massachusetts: Addison-Wesley, 1984. ISBN 0201134489._{E}Xbook - Norman Walsh,
*Making TeX Work*, http://makingtexwork.sourceforge.net/mtw/index.html Free online book - Omega (16 bit version of TeX; use
*lambda*, not*omega*on the command line!)

*This article (or an earlier version of it) contains material from FOLDOC's article on TeX, used with permission.*