rho

Look up Ρ or ρ in Wiktionary, the free dictionary.

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
History
Archaic local variants  ·  ·  ·  ·  ·
Ligatures (ϛ, ȣ, ϗ) · Diacritics
Numerals: (6) · (90) · (900)
In other languages
Bactrian  · Coptic  · Albanian
Scientific symbols
Book  · Category · Commons view talk edit

Rho (uppercase Ρ, lowercase ρ or ϱ; pronounced /ˈroʊ/) is the 17th letter of the Greek alphabet. In the system of Greek numerals, it has a value of 100. It is derived from Semitic resh "head". Its uppercase form is not to be confused with the Latin letter P, although both are typeset using the same glyph.

Uses

The Greek alphabet on a black figure vessel, with an R-shaped rho.

Greek

Rho is classed as a liquid consonant (together with lambda and sometimes the nasals mu and nu), which has important implications for morphology. In both Ancient and Modern Greek, it represents a trilled or tapped r.

In polytonic orthography a rho at the beginning of a word is written with a rough breathing (equivalent to h) — ῥ rh — and a double rho within a word is written with a smooth breathing over the first rho and a rough breathing over the second — ῤῥ rrh — apparently reflecting an aspirated or voiceless pronunciation in Ancient Greek, hence the various Greek-derived English words which start with rh or contain rrh.

The name of the letter is written in Greek as ῥῶ (polytonic) or ρω/ρο (monotonic).

Other alphabets

Letters that arose from rho include Roman R and Cyrillic Er (Р).

Maths and science

The characters Ρ, ρ and ϱ are also used outside its Greek alphabetical context in science and mathematics.

• In physics to represent:
  • Density (ρ)
  • Resistivity (ρ)
  • Charge density (ρ)
  • Rho meson (ρ⁺, ρ^-, ρ⁰)

• In mathematics to represent:
  • The radius in the spherical coordinate system
  • The correlation coefficient of a population parameter
  • The spectral radius of a matrix A denoted as ρ(A)
  • The plastic number
  • The sensitivity to interest rates of a pricing function

• In economics to represent the discount rate of future pence cash flows

• In molecular biology to represent the Rho protein responsible for termination of RNA synthesis. In such occasions, it is often represented as ϱ ("rho symbol" U+03F1), to avoid confusion with the Latin letter p

• In ecology to represent the population damping ratio where ρ = λ1 / |λ2|.

• In programming
  • For LaTeX, the symbols are P (Ρ), \rho (ρ), and \varrho ()
  • The lower-case rho ρ has a special meaning in the APL programming language

• In statistics to represent Spearman's rank correlation coefficient, commonly known as Spearman's rho

• In options theory to represent the rate of change of a portfolio with respect to interest rates

Chi Rho

The letter rho overlaid with chi forms the Chi Rho symbol, used to represent Jesus Christ.

Rhodes Scholars

Former Rhodes Scholars are entitled to use the Greek letter rho as a designation of their status. When used, the symbol should precede the name.^[1]

Unicode

See also

• Р, р - Er (Cyrillic)
• R, r - Latin
• P, p - Latin

References

1. ^ "Oxford University Calendar: Notes on Style". Oxford University Gazette. 2011-03-03. http://www.ox.ac.uk/media/global/wwwoxacuk/localsites/gazette/documents/universitycalendar/style--current_for_2011.pdf. Retrieved 2011-09-08.