Pi (letter)
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Look up Π or π in Wiktionary, the free dictionary. |
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| 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 | |||
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Digamma |  |
Qoppa |
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San |  |
Sampi |
| Other characters | |||
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Stigma |  |
Sho |
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Heta | ||
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| Greek diacritics | |||
Pi (uppercase Π, lower case π) is the sixteenth letter of the Greek alphabet, representing [p]. In the system of Greek numerals it has a value of 80. Letters that arose from pi include Cyrillic Pe (П, п).
In Modern Greek, the name of the letter is pronounced [ˈpi]; in modern English, it is pronounced /ˈpaɪ/, in particular when referring to the mathematical constant (see below).
The upper-case letter Π is used as a symbol for:
- The product operator in mathematics, indicated with capital pi notation ∏ (in analogy to the use of the capital Sigma Σ as summation symbol).
- In textual criticism, Codex Petropolitanus, a 9th century, uncial codex of the Gospels, now located in St. Petersburg, Russia.
- In legal shorthand, it represents a plaintiff.
The lower-case letter π is used as a symbol for:
- The mathematical transcendental (and thus irrational) constant π ≈ 3.14159..., the ratio of a circle's circumference to its diameter in Euclidean geometry. The letter "π" is the first letter of the Greek words "περιφέρεια" 'periphery' and "περίμετρος" 'perimeter', i.e. the circumference.
- The prime-counting function in mathematics.
- Dimensionless parameters constructed using the Buckingham π theorem of dimensional analysis.
- The osmotic pressure in chemistry. π=MRT
- The elementary particle called the pi meson or pion.
- Profit in microeconomics.
- Inflation rate in macroeconomics.
- A type of chemical bond in which the P-orbitals overlap, called a pi bond.
- The natural projection on the tangent bundle on a manifold.
- The unary operation of projection in relational algebra.
Variant pi or "pomega" (
or ϖ) is a glyph variant of lower case pi sometimes used in technical contexts as though it were a lower-case omega with a macron, though historically it is simply a cursive form of pi, with its legs bent inward to meet. It is used as a symbol for:
- The angular frequency of a wave in fluid dynamics (angular frequency is usually represented by ω but this may be confused with vorticity in a fluid dynamics context).
- The longitude of pericenter in celestial mechanics.[1]
- Comoving distance in cosmology.[2]
In HTML, the capital letter Π can be produced using the codes Π or Π, and the lower-case by using π or π within the source code.
