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Psi (letter): Wikis

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Psi uc lc.svg
Greek alphabet
Αα Alpha Νν Nu
Ββ Beta Ξξ Xi
Γγ Gamma Οο Omicron
Δδ Delta Ππ Pi
Εε Epsilon Ρρ Rho
Ζζ Zeta Σσς 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
Ϻϻ San Ϡϡ Sampi
Other characters
Ϛϛ Stigma Ϸϸ Sho
Ͱͱ Heta

Greek diacritics
For other uses, see Psi.

Psi (uppercase Ψ, lowercase ψ; pronounced in English as sigh) is the 23rd letter of the Greek alphabet and has a numeric value of 700. In both Classical and Modern Greek, the letter indicates the combination /ps/ (like in English "lapse"). The letter was adopted into the Old Italic alphabet, and its shape is continued into the Algiz rune of the Elder Futhark. Psi was also adopted into the early Cyrillic alphabet as Ѱ. In Greek loanwords in Latin and modern languages with Latin alphabets, Psi is usually transliterated as "ps". In English, due to phonotactic constraints, its pronunciation is usually simplified to /s/.

The letter psi is commonly used in physics for representing a wavefunction in quantum mechanics, particularly with the Schrödinger equation and bra-ket notation: \langle\phi|\psi\rangle. It is also used to represent the (generalized) positional states of a qubit in a quantum computer.

Psi is also used as the symbol for the polygamma function, defined by

 \psi_n(x) = \frac{d^{(n)}}{dx^{(n)}}\frac{\Gamma '(x)}{\Gamma (x)}\,\!

where Γ(x) is the gamma function.

The letters Ψ or ψ can also be a symbol for:

See also

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Simple English

Common letters
ΑaA ΜmEm
ΒbBe ΝnEn
GgGe ΟοO
ΔdDe ΠpPe
hHa ЖжZhe
ΕɛE RrAr
ΖzZe SsEs
ΗeEe ΤtTe
ΘөEth UuU
ΙiI FfEf
JjJe WwWa
ΚkKa ΧxXa
LlEl ОWоwWe
VvVe
Uncommon letters
Digamma Qoppa
San Sampi
Other letters
Stigma Sho

Greek alphabet

Psi (uppercase/lowercase Ψ ψ), is the letter of the Greek alphabet, used to represent the "ps" sound in Ancient and Modern Greek. In the system of Greek numerals, it has a value of 700. Letters that came from it include Cyrillic Ѱ.



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