Gh (digraph)
Gh is a digraph found in many languages.
In Latin-based orthographies
English
In English, ⟨gh⟩ historically represented [x] (the voiceless velar fricative, as in the Scottish Gaelic word Loch), and still does in lough and certain other Hiberno-English words, especially proper nouns. In the dominant dialects of modern English, ⟨gh⟩ is almost always either silent or pronounced /f/ (see ough). It is thought that before disappearing, the sound became partially or completely voiced to [ɣx] or [ɣ], which would explain the new spelling - Old English used a simple ⟨h⟩ - and the diphthongization of any preceding vowel.
It is also occasionally pronounced [ə], such as in Edinburgh.
When gh occurs at the beginning of a word in English, it is pronounced /ɡ/ as in "ghost", "ghastly", "ghoul", "ghetto", "ghee" etc. In this context, it does not derive from a former /x/.
American Literary Braille has a dedicated cell pattern for the digraph ⟨gh⟩ (dots 126, ⠣).
Esperanto
In Esperanto orthography, ⟨gh⟩ can be used when printers lack type for ⟨ĝ⟩ which represents /dʒ/.
Digraph
Digraph may refer to:
Digraphs and trigraphs
In computer programming, digraphs and trigraphs are sequences of two and three characters, respectively, that appear in source code and, according to a programming language specification, should be treated as if they were single characters.
Various reasons exist for using digraphs and trigraphs: keyboards may not have keys to cover the entire character set of the language, input of special characters may be difficult, text editors may reserve some characters for special use and so on. Trigraphs might also be used for some EBCDIC code pages that lack characters such as { and }.
History
The basic character set of the C programming language is a subset of the ASCII character set that includes nine characters which lie outside the ISO 646 invariant character set. This can pose a problem for writing source code when the encoding (and possibly keyboard) being used does not support any of these nine characters. The ANSI C committee invented trigraphs as a way of entering source code using keyboards that support any version of the ISO 646 character set.
Directed graph
In mathematics, and more specifically in graph theory, a directed graph (or digraph) is a graph, or set of vertices connected by edges, where the edges have a direction associated with them. In formal terms, a directed graph is an ordered pair G = (V, A) (sometimes G = (V, E)) where
It differs from an ordinary or undirected graph, in that the latter is defined in terms of unordered pairs of vertices, which are usually called edges, arcs, or lines.
A directed graph is called a simple digraph if it has no multiple arrows (two or more edges that connect the same two vertices in the same direction) and no loops (edges that connect vertices to themselves). A directed graph is called a directed multigraph or multidigraph if it may have multiple arrows (and sometimes loops). In the latter case the arrow set forms a multiset, rather than a set, of ordered pairs of vertices.
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