Rho (/ˈroʊ/; uppercase Ρ, lowercase ρ or ϱ) is the 17th letter of theGreek alphabet. In the system of Greek numerals, it has a value of 100. It is derived from Phoenician letter res . Its uppercase form is not to be confused with the Latin letter P, although both are typeset using the sameglyph.
Contents
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1 Uses
1.1 Greek
1.2 Other alphabets
1.3 Mathematics and science
1.4 Chi Rho
1.5 Rhodes Scholars
2 Character encodings
3 See also
4 References
Uses[edit]

The Greek alphabet on a black figurevessel, with an R-shaped rho.
Greek[edit]
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 arough 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 voicelesspronunciation 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[edit]
Letters that arose from rho include Roman R and Cyrillic Er (Р).
Mathematics and science[edit]
The characters Ρ, ρ and ϱ are also used outside its Greek alphabetical context in science and mathematics.
In the physical sciences to represent:
Densities: mass 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:
The radius in the cylindrical or spherical coordinate systems
The correlation coefficient of a population parameter
The spectral radius of a matrix denoted as
The plastic number
The sensitivity to interest rates of a pricing function
The expected return of a given policy () in reinforcement learning, denoted
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 theology, it is used to sometimes denote the crucifixion of Jesus.[citation needed]
In computer programming
For LaTeX, the symbols are \rho (), and \varrho () (note: \Rho is not defined by default)
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[edit]
The letter rho overlaid with chi forms the Chi Rho symbol, used to represent Jesus Christ.
Rhodes Scholars[edit]
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]
Character encodings[edit]
Greek Rho[2]
Character
Ρ ρ Ῥ ῥ ῤ
Unicode name greek capital letter rho greek small letter rho greek capital letter rho with dasia