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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 an alveolar trill {{IPA-el|r|IPA}}, alveolar tap {{IPA-el|ɾ|IPA}}, or alveolar approximant {{IPA-el|ɹ|IPA}}.In polytonic orthography, a rho at the beginning of a word is written with a rough breathing, equivalent to h ( 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 ( rrh). That apparently reflected an aspirated or voiceless pronunciation in Ancient Greek, which led to the various Greek-derived English words starting with rh or containing rrh.The name of the letter is written in Greek as (polytonic) or ρω/(wikt:ρο|ρο) (monotonic).

Other alphabets

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

Mathematics and science

The characters ρ and {{not a typo|ϱ}} are also conventionally used outside the Greek alphabetical context in science and mathematics.

• In the physical sciences to represent:
  • Densities: mass density, air density or charge density (ρ)
  • Resistivity (ρ)
  • Rho meson (ρ+, ρ−, ρ0)
  • General quantum states
  • Hammett Equation, ρ is used to represent the reaction constant, this is independent of the position and nature of the substituents of the benzene ring.
• In mathematics to represent:
  • A length coordinate in polar, cylindrical, spherical, and toroidal coordinate systems, and toroidal and poloidal coordinates of the Earth’s magnetic field.
  • The correlation coefficient of a population parameter
  • The spectral radius of a matrix A denoted as rho(A)
  • The plastic ratio
  • The prime constant
  • The sensitivity to interest rates of a pricing function
  • The expected return of a given policy (pi) in reinforcement learning, denoted rho^pi
  • The rename operation in relational algebra
• 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 {{unichar|03f1|Greek rho symbol}}, to avoid confusion with the Latin letter p
• In molecular biology to represent the Rho family of GTPases, important for cytoskeletal dynamic regulation.
• In ecology to represent the population damping ratio where ρ = λ1 / |λ2|.
• In computer programming
  • The lower-case rho “⍴” means reshape in the APL programming language, and by extension also queries shape
  • The lower-case rho “ρ” is used for the unary rename operation in relational algebra
• 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 (☧)

File:Simple Labarum2.svg|thumb|181x181px|The Chi Rho symbol representing Christ.]]The letter rho overlaid with chi forms the Chi Rho symbol, used to represent Jesus Christ. It was first used by Emperor Constantine the Great. A can be seen on his standard known as the Labarum.

Rho with stroke (ϼ)

The rho with a stroke through its tail is used for abbreviations involving rho, most notably in for as a unit of measurement.Paul of Aegina explains conventional usage in the last chapter of Book VII on weights and measures and uses it throughout his work.

Character encodings

Greek and Coptic (Range: 0370-03FF)“>

Greek rhoUnicode Code Charts: Greek and Coptic (Range: 0370-03FF)

{{charmap

name1=Greek Capital Letter Rho

name2=Greek Small Letter Rho

name3=Greek Capital Letter Rho with Dasia

name4=Greek Small Letter Rho with Dasia

name5=Greek Small Letter Rho with Psili

map2char1=90|map2char2=A8

map3char1=C7|map3char2=EB

map4char1=D1|map4char2=F1

TeX>ref1char2=rho}} Greek rho symbols {{charmap

name1=Greek Rho Symbol

name2=Greek Rho with Stroke Symbol

name3=Greek Letter Small Capital Rho

name4=Greek Subscript Small Letter Rho

name5=Chi Rho

TeX>ref1char1=varrho}} Coptic ro {{charmap

name1=Coptic Capital Letter Ro

name2=Coptic Small Letter Ro

name3=Coptic Symbol Chi Rho}} Functional symbol {{charmap

name1=APL Functional Symbol Rho}} Mathematical rho {{charmap

name1=Mathematical BoldCapital Rho

name2=Mathematical BoldSmall Rho

name3=Mathematical BoldRho Symbol

name4=Mathematical ItalicCapital Rho

name5=Mathematical ItalicSmall Rho}}{{charmap

name1=Mathematical ItalicRho Symbol

name2=Mathematical Bold ItalicCapital Rho

name3=Mathematical Bold ItalicSmall Rho

name4=Mathematical Bold ItalicRho Symbol

name5=Mathematical Sans-SerifBold Capital Rho}}{{charmap

name1=Mathematical Sans-SerifBold Small Rho

name2=Mathematical Sans-SerifBold Rho Symbol

name3=Mathematical Sans-SerifBold Italic Capital Rho

name4=Mathematical Sans-SerifBold Italic Small Rho

name5=Mathematical Sans-SerifBold Italic Rho Symbol}}These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style. See also Р, р - Er (Cyrillic) R, r - Latin P, p - Latin References {{Wiktionary|Ρ|ρ}}