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Xi

Xi (uppercase ?, lowercase ?) is the 14th letter of the Greek alphabet

Greek alphabet

The Greek alphabet is a set of twenty-four letters that has been used to write the Greek language since the late 9th century BC or early 8th century BCE....
. It is in Modern Greek

Modern Greek

Modern Greek refers the varieties of Greek spoken in the modern era. The beginning of the "modern" period of the language is often symbolically assigned to the fall of the Byzantine Empire in 1453, even though that date marks no clear linguistic boundary and many characteristic modern features of the language had been present centuries earli...
, and generally (UK) or (US) in English

English language

English is a West Germanic language that originated in Anglo-Saxon England and has lingua franca status in many parts of the world as a result of the military, economic, scientific, political and cultural influence of the British Empire in the 18th, 19th and early 20th centuries and that of the United States from the mid 20th century onwa...
. In the system of Greek numerals

Greek numerals

Greek numerals are a numeral system using letters of the Greek alphabet. They are also known by the names Milesian numerals, Alexandrian numerals, or alphabetic numerals....
, it has a value of 60. The Xi is not to be confused with the letter Chi

Chi (letter)

Chi is the 22nd letter of the Greek alphabet, pronounced as [kai] in English. Its value in Ancient Greek was an aspirated voiceless velar plosive ....
, which gave its form to the Latin letter X

X is the twenty-fourth letter in the modern Latin alphabet. Its name in English language is spelled ex , plural exes .History...
. In ancient times, the Western Greek alphabet used it to represent , while it was used to represent /ks/ in other alphabets. As the alphabet was standardized, Xi was decided to be used for /ks/ and Chi for .

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Encyclopedia

Xi (uppercase ?, lowercase ?) is the 14th letter of the Greek alphabet

Greek alphabet

The Greek alphabet is a set of twenty-four letters that has been used to write the Greek language since the late 9th century BC or early 8th century BCE....
. It is in Modern Greek

Modern Greek

English language

Greek numerals

Chi (letter)

Chi is the 22nd letter of the Greek alphabet, pronounced as [kai] in English. Its value in Ancient Greek was an aspirated voiceless velar plosive ....
, which gave its form to the Latin letter X

Early Cyrillic alphabet

The old Cyrillic alphabet was a writing system developed in the First Bulgarian Empire in the tenth century to write the Old Church Slavonic liturgical language....
, as the letter ksi ().

It should not be confused with = (equivalence sign, Unicode

Unicode

Unicode is a computing industry standard allowing computers to consistently represent and manipulate Character expressed in most of the world's writing systems....
hex 2261).

The lower-case letter ? is used as a symbol for:

random variable
Random variable

In mathematics, random variables are used in the study of Randomness and probability. They were developed to assist in the analysis of Game of chance, stochastic events, and the results of experiment by capturing only the mathematical properties necessary to answer probability questions....
s;
extent of reaction (a topic found most often in chemical engineering
Chemical engineering

Chemical engineering is the branch of engineering that deals with the application of physical science , with mathematics, to the process of converting raw materials or chemicals into more useful or valuable forms....
kinetics);
eigenvectors;
a parameter in a generalized Pareto distribution
Pareto distribution

The Pareto distribution, named after the Italian economist Vilfredo Pareto, is a power law probability distribution that coincides with social sciences, scientific, geophysical, actuarial science, and many other types of observable phenomena....
;
the symmetric function equation of the Riemann zeta function
Riemann zeta function

In mathematics, the Riemann zeta function, named after Germany mathematician Bernhard Riemann, is a prominent function of great significance in number theory because of its relation to the prime number theorem....
in mathematics
Mathematics

Mathematics is the study of quantity, structure, space, change, and related topics of pattern and form. Mathematicians seek out patterns whether found in numbers, space, natural science, computers, imaginary abstractions, or elsewhere....
, also known as the Riemann Xi function
Riemann Xi function

In mathematics, the Riemann Xi function is a variant of the Riemann zeta function, and is defined so as to have a particularly simple functional equation....
;
a universal set in the set theory
Set theory

Set theory is the branch of mathematics that studies Set , which are collections of objects. Although any type of object can be collected into a set, set theory is applied most often to objects that are relevant to mathematics....
;
a number used in the error term of Newton–Cotes formulas that falls between a and b;
one of the two different polypeptide chains of the human embryonic hemoglobin
Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and the tissues of some invertebrates....
types Hb-Portland (?₂?₂) and Hb-Gower I (?₂e₂);
the correlation function
Correlation function (astronomy)

astronomy describe the distribution of galaxy in the universe by means of a correlation function. By default, correlation function refers to the two-point autocorrelation function....
in astronomy
Astronomy

Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
;
frequency;
a small displacement in MHD plasma stability
Plasma stability

An important field of plasma physics is the stability of the Plasma . It usually only makes sense to analyze the stability of a plasma once it has been established that the plasma is in Mechanical equilibrium....
theory.

The upper-case letter ? is used as symbol for

The "cascade particles
Xi (particle)

In particle physics, is a name given to a range of baryons with one up or down quark and two heavier quarks. They are sometimes called the cascade particles because of their unstable state, they decay rapidly into lighter particles through a chain of decays....
" in particle physics;
indicating "no change of state" in Z notation
Z notation

The Z notation , named after Zermelo-Fr?nkel set theory ? J.R. Abrial answers the question "Why Z?" with "Because it is the ultimate language!" ? , is a Formal specification specification language used for describing and modeling computing systems....
.