Xi

From Wikipedia, the free encyclopedia

Greek alphabet
Αα Alpha	Νν Nu
Ββ Beta	Ξξ Xi
Γγ Gamma	Οο Omicron
Δδ Delta	Ππ Pi
Εε Epsilon	Ρρ Rho
Ζζ Zeta	Σσ Sigma
Ηη Eta	Ττ Tau
Θθ Theta	Υυ Upsilon
Ιι Iota	Φφ Phi
Κκ Kappa	Χχ Chi
Λλ Lambda	Ψψ Psi
Μμ Mu	Ωω Omega
Obsolete letters
Ϝϝ Digamma	Ϙϙ Qoppa
Ϛϛ Stigma	Ϡϡ Sampi
Ϻϻ San	Ϸϸ Sho
Greek diacritics

Xi (uppercase Ξ, lowercase ξ) is the 14th letter of the Greek alphabet. It is pronounced [zaɪ] by US English speakers, but [ksi] is the correct Greek pronunciation. The 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 damping factor in an RLC circuit;
• a universal set in the set theory.

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).