Ππ

PI

πεῖ · [p]

The 16th letter of the Greek alphabet.

MATHEMATICS

  • Constant π.
  • Product operator Π (uppercase Pi).

PROBABILITY

  • Appears in densities/normalizations (π).
  • In Bayes, π(θ) may denote a prior.

STATISTICS

  • May denote proportion/probability (π).
  • In logistic: π(x)=P(Y=1|x).

PRONUNCIATION

Ancient Greek
sound [p]
Modern Greek
πι [pi] · sound [p]

IN FORMULAS

  • f(x) = e^(−(x − μ)²/(2σ²)) / (σ√(2π))π in the normal density: it makes the area under the curve equal 1.See it explained at morrisonkuhlsen.com →
  • C = 2πrπ is the ratio of a circle's circumference to its diameter.
  • Π xᵢ = x₁ · x₂ · … · xₙThe uppercase Π is the product operator, as Σ is for sums.

HOW TO WRITE IT — click to copy

lowercase
variant
uppercase

Note: notations vary between books/fields; these are the most common usages.