Xi (letter)

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## Greek

## Cyrillic

## Mathematics and science

### Uppercase

#### Pure mathematics

#### Physics

#### Other uses

### Lowercase

#### Pure mathematics

#### Physics and astronomy

#### Other uses

## Character encodings

## Other uses

## References

This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.

Xi Letter

Greek alphabet |
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History |

Use in other languages |

Related topics |

**Xi** (uppercase **?** or **?**, lowercase **?**; Greek: ) is the 14th letter of the Greek alphabet. It is pronounced [ksi] in Modern Greek, and generally or in English.^{[1]} In the system of Greek numerals, it has a value of 60. Xi was derived from the Phoenician letter samekh .

Xi is distinct from the letter chi, which gave its form to the Latin letter X.

Both in classical Ancient Greek and in Modern Greek, the letter ? represents the consonant cluster /ks/. In some archaic local variants of the Greek alphabet, this letter was missing. Instead, especially in the dialects of most of the Greek mainland and Euboea, the cluster /ks/ was represented by ? (which in classical Greek is chi, used for /k?/).

Because this variant of the Greek alphabet was used in Magna Graecia (the Greek colonies in Sicilly and the southern part of the Italian peninsula), the Latin alphabet borrowed ? rather than ? as the Latin letter that represented the /ks/ cluster that was also present in Latin.

The Xi was adopted into the early Cyrillic alphabet, as the letter ksi (?, ?).

The uppercase letter ? is used as symbol in various contexts.

- Harish-Chandra's ? function in harmonic analysis and representation theory
- The Riemann Xi function in analytic number theory and complex analysis

- The "cascade particles" in particle physics
- The partition function under the grand canonical ensemble in statistical mechanics

- Indicating "no change of state" in Z notation in computing
- Monetary units of the cryptocurrency Ether, equal to 10
^{18}Wei

The lowercase letter ? is used as a symbol for:

- Random variables
- A parameter in a generalized Pareto distribution
- The symmetric function equation of the Riemann zeta function in mathematics, also known as the Riemann Xi function
- A universal set in set theory
- A number used in the remainder term of Taylor's theorem that falls between the limits
*a*and*b* - A number used in error approximations for formulas that are applications of Taylor's theorem, such as Newton-Cotes formulas

- In fluid dynamics, the Iribarren parameter.
- The initial mass function in astronomy.
- The correlation function in astronomy.
- Spatial frequency;
^{[2]}also sometimes temporal frequency. - A small displacement in MHD plasma stability theory
- The x-coordinate of computational space as used in computational fluid dynamics
- Potential difference in physics (in volts)
- The radial integral in the spin-orbit matrix operator in atomic physics.
- The Killing vector in general relativity.
- Average logarithmic energy decrement per collision (neutron calculations in nuclear physics)
- Pippard's cohesion length in superconductors
- The diameter of a crystal nucleus in nucleation theory
- Microturbulence velocity in a stellar atmosphere
- The dimensionless longitudinal momentum loss of a beam particle after a two-body interaction in accelerator physics.
- Dimensionless distance variable used in the Lane-Emden equation

- Propositional variables in some philosophical works, first found in Wittgenstein's Tractatus
- Extent of reaction, a concept in physical chemistry
^{[3]}used often in chemical engineering kinetics and thermochemistry - Unknown stereochemistry or stereocentre configuration in a planar ring system in organic chemistry,
^{[4]}as well as uppercase Xi for unknown*R*/*S*/*E*/*Z*configuration in general^{[5]} - Damping Ratio C/Ccr(vibrational analysis)
- One of the two different polypeptide chains of the human embryonic hemoglobin types Hb-Portland (?
_{2}?_{2}) and Hb-Gower I (?_{2}?_{2}) - A parameter denoted as warped time used to derive the equations for homogeneous azeotropic distillation
- State Price Density in mathematical finance
- The information vector in the Information Filter, GraphSLAM, and a number of other algorithms used for robot localization and robotic mapping.
- Used in Support Vector machines in cases where the data is not linearly separable.

- Greek Xi / Coptic Ksi

Preview | Ξ | ξ | Ⲝ | ⲝ | ||||
---|---|---|---|---|---|---|---|---|

Unicode name |
GREEK CAPITAL LETTER XI | GREEK LOWERCASE LETTER XI | COPTIC CAPITAL LETTER KSI | COPTIC LOWERCASE LETTER KSI | ||||

Encodings | decimal | hex | decimal | hex | decimal | hex | decimal | hex |

Unicode | 926 | U+039E | 958 | U+03BE | 11420 | U+2C9C | 11421 | U+2C9D |

UTF-8 | 206 158 | CE 9E | 206 190 | CE BE | 226 178 156 | E2 B2 9C | 226 178 157 | E2 B2 9D |

Numeric character reference | Ξ |
Ξ |
ξ |
ξ |
Ⲝ |
Ⲝ |
ⲝ |
ⲝ |

Named character reference | Ξ | ξ | ||||||

DOS Greek | 141 | 8D | 165 | A5 | ||||

DOS Greek-2 | 189 | BD | 232 | E8 | ||||

Windows 1253 | 206 | CE | 238 | EE | ||||

TeX | \Xi | \xi |

^{[6]}

- Mathematical Xi

Preview | 𝚵 | 𝛏 | 𝛯 | 𝜉 | 𝜩 | 𝝃 | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|

Unicode name |
MATHEMATICAL BOLD CAPITAL XI |
MATHEMATICAL BOLD LOWERCASE XI |
MATHEMATICAL ITALIC CAPITAL XI |
MATHEMATICAL ITALIC LOWERCASE XI |
MATHEMATICAL BOLD ITALIC CAPITAL XI |
MATHEMATICAL BOLD ITALIC LOWERCASE XI | ||||||

Encodings | decimal | hex | decimal | hex | decimal | hex | decimal | hex | decimal | hex | decimal | hex |

Unicode | 120501 | U+1D6B5 | 120527 | U+1D6CF | 120559 | U+1D6EF | 120585 | U+1D709 | 120617 | U+1D729 | 120643 | U+1D743 |

UTF-8 | 240 157 154 181 | F0 9D 9A B5 | 240 157 155 143 | F0 9D 9B 8F | 240 157 155 175 | F0 9D 9B AF | 240 157 156 137 | F0 9D 9C 89 | 240 157 156 169 | F0 9D 9C A9 | 240 157 157 131 | F0 9D 9D 83 |

UTF-16 | 55349 57013 | D835 DEB5 | 55349 57039 | D835 DECF | 55349 57071 | D835 DEEF | 55349 57097 | D835 DF09 | 55349 57129 | D835 DF29 | 55349 57155 | D835 DF43 |

Numeric character reference | 𝚵 |
𝚵 |
𝛏 |
𝛏 |
𝛯 |
𝛯 |
𝜉 |
𝜉 |
𝜩 |
𝜩 |
𝝃 |
𝝃 |

Preview | 𝝣 | 𝝽 | 𝞝 | 𝞷 | ||||
---|---|---|---|---|---|---|---|---|

Unicode name |
MATHEMATICAL SANS-SERIF BOLD CAPITAL XI |
MATHEMATICAL SANS-SERIF BOLD LOWERCASE XI |
MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL XI |
MATHEMATICAL SANS-SERIF BOLD ITALIC LOWERCASE XI | ||||

Encodings | decimal | hex | decimal | hex | decimal | hex | decimal | hex |

Unicode | 120675 | U+1D763 | 120701 | U+1D77D | 120733 | U+1D79D | 120759 | U+1D7B7 |

UTF-8 | 240 157 157 163 | F0 9D 9D A3 | 240 157 157 189 | F0 9D 9D BD | 240 157 158 157 | F0 9D 9E 9D | 240 157 158 183 | F0 9D 9E B7 |

UTF-16 | 55349 57187 | D835 DF63 | 55349 57213 | D835 DF7D | 55349 57245 | D835 DF9D | 55349 57271 | D835 DFB7 |

Numeric character reference | 𝝣 |
𝝣 |
𝝽 |
𝝽 |
𝞝 |
𝞝 |
𝞷 |
𝞷 |

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.

*Media related to Xi (letter) at Wikimedia Commons*

Uppercase ? is used as an 'E' to stylise company names/logos like Razer (styled as **R?Z?R**), musician Banners (styled as **BANN?RS**), and in South Korean Boygroup ZE:A newest logo (styled as "Z?A") (Compare: Heavy Metal umlaut; Faux Cyrillic)

**^**"xi". New Oxford American Dictionary, 2nd Edition.**^**SPIE Optipedia article: "Spatial Frequency"**^**IUPAC Gold Book Entry: "Extent of Reaction" Archived June 29, 2012, at the Wayback Machine**^**John Buckingham; Caroline M. Cooper; Rupert Purchase (18 November 2015).*Natural Products Desk Reference*. CRC Press. pp. 53-. ISBN 978-1-4398-7362-5.**^***Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names*. 2014. pp. 1159-1160. ISBN 9780854041824. Retrieved 2017.**^**Unicode Code Charts: Greek and Coptic (Range: 0370-03FF)

This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.

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