Pi (letter)

The uppercase letter Π is used as a symbol for:

• 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.

In science and engineering:

• The product operator in mathematics, indicated with capital pi notation ∏ (in analogy to the use of the capital Sigma ∑ as summation symbol).
• The osmotic pressure in chemistry.
• The viscous stress tensor in continuum mechanics and fluid dynamics.

The lowercase letter π is used as a symbol for:

• The mathematical real 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.
• Homotopy groups in algebraic topology.
• Dimensionless parameters constructed using the Buckingham π theorem of dimensional analysis.
• The hadron called the pion (pi meson).
• Economic 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.
• Policy in reinforcement learning.
• Polyamory[1]

An early form of pi was , appearing almost like a gamma with a hook.

Variant pi or "pomega" (${\displaystyle \varpi \,\!}$ or ϖ) is a glyph variant of lowercase pi sometimes used in technical contexts. It resembles a lowercase omega with a macron, though historically it is simply a cursive form of pi, with its legs bent inward to meet. It was also used in the minuscule script. It is a symbol for:

• Angular frequency of a wave in fluid dynamics (angular frequency is usually represented by ${\displaystyle \omega }$ but this may be confused with vorticity in a fluid dynamics context).
• Longitude of pericenter in celestial mechanics.[2]
• Comoving distance in cosmology.[3]
• Single-scattering albedo in radiative transfer.
• Mean fitness of a population in biology.
• Fundamental weights of a representation (probably to better distinguish from elements ${\displaystyle w}$ of the Weyl group, than the usual notation ${\displaystyle \omega }$).

The various forms of pi are present in Unicode as:

• U+03A0 Π GREEK CAPITAL LETTER PI (HTML Π · Π)
• U+03C0 π GREEK SMALL LETTER PI (HTML π · π)
• U+03D6 ϖ GREEK PI SYMBOL (HTML ϖ · ϖ, ϖ)
• U+220F ∏ N-ARY PRODUCT (HTML ∏ · ∏, ∏)
• U+1D28 ᴨ GREEK LETTER SMALL CAPITAL PI (HTML ᴨ)
• U+1D70B 𝜋 MATHEMATICAL ITALIC SMALL PI (HTML 𝜋)
• U+1D6D1 𝛑 MATHEMATICAL BOLD SMALL PI (HTML 𝛑).[4]

Look up Π or π in Wiktionary, the free dictionary.

• П, п – Pe (Cyrillic)
• P, p – Pe (Latin)
• Greek letters used in mathematics, science, and engineering#Ππ (pi)