Pi (letter)

Uppercase pi

• 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 mathematical finance, it represents a portfolio.

• The product operator in mathematics, indicated with capital pi notation .
• The osmotic pressure in chemistry.
• The viscous stress tensor in continuum mechanics and fluid dynamics.

  Lowercase pi

• The mathematical real transcendental constant π ≈ 3.14159..., the ratio of a circle's circumference to its diameter in Euclidean geometry, exactly half of the circle constant. The letter "" is the first letter of the Greek words 'periphery' and '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.
• Often inflation rate in macroeconomics.
• Sometimes profit in microeconomics.
• 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.
• Sometimes an element of a permutation group.
• Policy in reinforcement learning.

• Polyamory.

  History

Variant pi

• Angular frequency of a wave in fluid dynamics.
• Longitude of pericenter in celestial mechanics.
• Comoving distance in cosmology.
• Single-scattering albedo in radiative transfer.
• Mean fitness of a population in biology.
• Fundamental weights of a representation.
• The lemniscate constant.

  Unicode