Psi (letter)
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| Greek alphabet | |
|---|---|
| Α α Alpha | Β β Beta |
| Γ γ Gamma | Δ δ Delta |
| Ε ε Epsilon | Ζ ζ Zeta |
| Η η Eta | Θ θ Theta |
| Ι ι Iota | Κ κ Kappa |
| Λ λ Lambda | Μ μ Mu |
| Ν ν Nu | Ξ ξ Xi |
| Ο ο Omicron | Π π Pi |
| Ρ ρ Rho | Σ σ Sigma |
| Τ τ Tau | Υ υ Upsilon |
| Φ φ Phi | Χ χ Chi |
| Ψ ψ Psi | Ω ω Omega |
| obsolete letters | |
| [[Digamma|Template:Polytonic Digamma]] | [[San (letter)|Template:Polytonic San]] |
| [[Qoppa|Template:Polytonic Qoppa]] | [[Sampi|Template:Polytonic Sampi]] |
Psi (Ψ ψ) is the 23rd letter of the Greek alphabet and has a numeric value of 700. It is also used as a symbol/icon for psychology.
It is perhaps most famous in science for representing a wavefunction in quantum mechanics, particularly with the Schrödinger equation.
Psi is also used as the symbol for the polygamma function, defined by
- <math> \psi_n(x) = \frac{d^{(n)}}{dx^{(n)}}\frac{\Gamma '(x)}{\Gamma (x)}\,\!<math>
where <math>\Gamma (x)<math> is the gamma function Template:Math-stub da:Psi (bogstav) de:Psi el:Ψι es:Psi (letra) fr:Ψ ja:Ψ nl:Psi (letter) pl:Psi pt:Ψ sv:Psi zh:Ψ