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Pi (; Greek: (:pi), uppercase Π, lowercase π) is the sixteenth letter of the Greek alphabet, representing . In the system of Greek numerals it has a value of 80. It was derived from the Phoenician letter pe . Letters that arose from pi include Cyrillic Pe (П, п), Coptic pi ((unicode:Ⲡ, ⲡ)), and Gothic pairthra ((unicode:𐍀)). == Symbol == 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 osmotic pressure in chemistry. Π=MRT The lower-case letter π is used as a symbol for: * The mathematical real transcendental (and thus irrational) constant π ≈ 3.1415926535897932384626433832795028841971…, 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 pi meson or pion. * 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. * In reinforcement learning π denotes policy. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pi (letter)」の詳細全文を読む スポンサード リンク
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