Hyphenation algorithm

A hyphenation algorithm is a set of rules (especially one codified for implementation in a computer program) that decides at which points a word can be broken over two lines with a hyphen. For example, a hyphenation algorithm might decide that impeachment can be broken as impeach-ment or im-peachment, but not, say, as impe-achment.

One of the reasons for the complexity of the rules of word-breaking is that different "dialects" of English tend to differ on the rule: American English tends to work on sound, while British English tends to look to the origins of the word and then to sound. There are also a large number of exceptions, which further complicates matters.

Some rules of thumb can be found in the reference "On Hyphenation – Anarchy of Pedantry". Among algorithmic approaches to hyphenation, the one implemented in the TeX typesetting system is widely used. It is thoroughly documented in the first two volumes of Computers and Typesetting and in Frank Liang's dissertation. The aim of Liang's work was to get the algorithm as accurate as he practically could and keep any exception dictionary small. In TeX's original hyphenation patterns for US English, the exception list contains fourteen words.

Ports of the TeX hyphenation algorithm are available as libraries for several programming languages, including Haskell, JavaScript, Perl, PostScript, Python, Ruby, and TeX can be made to show hyphens in the log via the command \showhyphens.

In LaTeX hyphenation correction can be added by user using:

The \hyphenation command declares allowed hyphenation points, where words is a list of words, separated by spaces, in which each hyphenation point is indicated by a - character. For example

declares that in the current job "fortran" should not be hyphenated, and that if "ergonomic" must be hyphenated, it will be at one of the indicated points.

However, there are several limits. For example, the stock \hyphenation command only accepts ASCII letters (by default), so it cannot be used to correct hyphenation for words with non-ASCII characters (e.g. ä, é, ç) which are very common in almost all languages except English. Simple workarounds exist, however.

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