Xi

From Wikipedia, the free encyclopedia

Greek alphabet
Α α Alpha	Ν ν Nu
Β β Beta	Ξ ξ Xi
Γ γ Gamma	Ο ο Omicron
Δ δ Delta	Π π ϖ Pi
Ε ε Epsilon	Ρ ρ Rho
Ζ ζ Zeta	Σ σ ς Sigma
Η η Eta	Τ τ Tau
Θ θ Theta	Υ υ Upsilon
Ι ι Iota	Φ φ Phi
Κ κ Kappa	Χ χ Chi
Λ λ Lambda	Ψ ψ Psi
Μ μ Mu	Ω ω Omega
Obsolete letters
Ϝ ϝ Digamma	Ϻ ϻ San
Ϙ ϙ Qoppa	Ϡ ϡ Sampi
Ϛ ϛ Stigma	Ϸ ϸ Sho
diacritics

Xi (uppercase Ξ, lowercase ξ) is the 14th letter of the Greek alphabet. It is pronounced zai by English speakers, but ksi by ancient and modern Greeks. The modern Greek pronunciation has also become fairly common among mathematicians, even speaking in English. In the system of Greek numerals, it has a value of 60. Its Latin equivalent is X.

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

• Random variables
• Extent of reaction (a topic found most often in chemical engineering kinetics)
• Eigenvectors
• 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

The upper-case letter Ξ is used as symbol for:

• The 'cascade particles' in particle physics.
• indicating "no change of state" in Z notation.

Xi was also adopted into the early Cyrillic alphabet, as the letter ksi (Ѯ, ѯ).