Ch (digraph)
Ch is a digraph in the Latin script. It is treated as a letter of its own in Chamorro, Old Spanish, Czech, Slovak, Igbo, Uzbek, Quechua, Guarani, Welsh, Cornish, Breton and Belarusian Łacinka alphabets. In Vietnamese and Modern Spanish, it also used to be considered a letter for collation purposes but this is no longer common.
History
The digraph was first used in Latin since the 2nd century B.C. to transliterate the sound of the Greek letter chi in words borrowed from that language. In classical times, Greeks pronounced this as an aspirated voiceless velar plosive [kʰ]. In post-classical Greek (Koine and Modern) this sound developed into a fricative [x]. Since neither sound was found in native Latin words (with some exceptions like pulcher 'beautiful', where the original sound [k] was influenced by [l] or [r]), in Late Latin the pronunciation [k] occurred.
In Old French, a language that had no [kʰ] or [x] and represented [k] by c, k or qu, ch began to be used to represent the voiceless palatal plosive [c], which came from [k] in some positions and later became [tʃ] and then [ʃ]. Now the digraph ch is used for all the aforementioned sounds, as shown below. The Old French usage of ch was also a model of several other digraphs for palatals or postalveolars: lh (digraph), nh (digraph), sh (digraph).
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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