\epsilon
( ) denotes the lunate form, while \varepsilon
( ) denotes the reversed-3 form.
There is also a 'Latin epsilon', or "open e", which looks similar to the Greek lowercase epsilon. It is encoded in Unicode as and and is used as an International Phonetic Alphabet, IPA phonetic symbol. The lunate or uncial epsilon provided inspiration for the euro sign, .
The lunate epsilon, , is not to be confused with the set membership symbol ; nor should the Latin uppercase epsilon, , be confused with the Greek uppercase (sigma). The symbol , first used in set theory and logic by Giuseppe Peano and now used in mathematics in general for set membership ("belongs to") evolved from the letter epsilon, since the symbol was originally used as an abbreviation for the Latin word . In addition, mathematicians often read the symbol as "element of", as in "1 is an element of the natural numbers" for , for example. As late as 1960, ε itself was used for set membership, while its negation "does not belong to" (now ) was denoted by (epsilon prime). Only gradually did a fully separate, stylized symbol take the place of epsilon in this role. In a related context, Peano also introduced the use of a backwards epsilon, , for the phrase "such that", although the abbreviation ''s.t.'' is occasionally used in place of ϶ in informal cardinals.
History
Origin
The letter Ε was taken over from the Phoenician alphabet, Phoenician letter He (letter), He (Sound value
While the original pronunciation of the Phoenician letter ''He'' was , the earliest Greek sound value of Ε was determined by the vowel occurring in the Phoenician letter name, which made it a natural choice for being reinterpreted from a consonant symbol to a vowel symbol denoting an sound.Jeffery, ''Local scripts'', p.24. Besides its classical Greek sound value, the short phoneme, it could initially also be used for other -like sounds. For instance, in early Attic Greek, Attic before c. 500 BC, it was used also both for the long, open-mid vowel, open , and for the long close-mid vowel, close . In the former role, it was later replaced in the classic Greek alphabet by Eta (Η), which was taken over from eastern Ionic Greek, Ionic alphabets, while in the latter role it was replaced by the digraph (orthography), digraph spelling ΕΙ.Epichoric alphabets
Some dialects used yet other ways of distinguishing between various e-like sounds. In Ancient Corinth, Corinth, the normal function of Ε to denote and was taken by a glyph resembling a pointed B (Glyph variants
After the establishment of the canonical classical Ionian (Eucleidean)Uses
International Phonetic Alphabet
Despite its pronunciation as mid front unrounded vowel, mid, in the International Phonetic Alphabet, the Latin epsilon represents open-mid front unrounded vowel, as in the English word ''pet'' .Symbol
The uppercase Epsilon is not commonly used outside of the Greek language because of its similarity to the Latin alphabet, Latin letter E. However, it is commonly used in structural mechanics with Young's Modulus equations for calculating tensile, compressive and areal Deformation (mechanics), strain. The Greek lowercase epsilon , the lunate epsilon symbol , or the Latin epsilon, Latin lowercase epsilon (see above) is used in a variety of places: *In engineering mechanics, strain calculations ϵ = increase of length / original length. Usually this relates to extensometer testing of metallic materials. *In mathematics **(particularly calculus), an arbitrarily small positive quantity is commonly denoted ε; see (ε, δ)-definition of limit. ***In reference to this, the late mathematician Paul Erdős also used the term "epsilons" to refer to children (Paul Hoffman (science writer), Hoffman 1998, p. 4). **David Hilbert, Hilbert introduced epsilon terms as an extension to first order logic; see epsilon calculus. ** it is used to represent the Levi-Civita symbol. ** it is used to represent dual numbers: ''a'' + ''bε'', with ''ε''2 = 0 and ''ε'' ≠ 0. ** it is sometimes used to denote the Heaviside step function. ** in set theory, the epsilon numbers (mathematics), epsilon numbers are ordinal numbers that satisfy the Fixed point (mathematics), fixed point ε = ωε. The first epsilon number, ε0, is the limit ordinal of the set . ** in numerical analysis and statistics it is used as the error term ** in group theory it is used as the idempotent group when e is in use as a variable name *In computer science, it often represents the empty string, though different writers use a variety of other symbols for the empty string as well; usually the lower-case Greek letter lambda (λ). *In computer science, the machine epsilon indicates the upper bound on the relative error due to rounding in floating point arithmetic. *In physics, **it indicates the permittivity of a medium; with the subscript 0 (ε0) it is the permittivity of free space. **it can also indicate the Strain (materials science), strain of a material (a ratio of extensions). *In automata theory, it shows a transition that involves no shifting of an input symbol. *In astronomy, **it stands for the fifth-brightest star in a constellation (see Bayer designation). **Epsilon is the name for the most distant and most visible ring of Uranus. **In planetary science, ε denotes the axial tilt. *In chemistry, it represents the molar extinction coefficient of a chromophore. *In economics, ε refers to elasticity (economics), elasticity. *In statistics, **it is used to refer to Errors and residuals in statistics, error terms. ** it also can to refer to the degree of Mauchly's sphericity test, sphericity in Repeated measures design, repeated measures ANOVAs. *In agronomy, it is used to represent the "photosynthetic efficiency" of a particular plant or crop.Unicode
* Greek Epsilon * Coptic Eie * Latin Open E * Mathematical Epsilon These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style.Initial
References
Further reading
*Paul Hoffman (science writer), Hoffman, Paul; ''The Man Who Loved Only Numbers''. Hyperion, 1998. {{ISBN, 0-7868-6362-5. Greek letters Vowel letters