Rho - Alchetron, The Free Social Encyclopedia

Rho (/ˈroʊ/; uppercase Ρ, lowercase ρ or ϱ; Greek: ῥῶ) is the 17th letter of the Greek 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 types use the same glyph: P.

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 that 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).

Mathematics and science

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, 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.

Momentum (ρ)

In mathematics to represent:

The radius in the cylindrical and spherical coordinate systems

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

The expected return of a given policy ( π ) in reinforcement learning, denoted ρ π

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 computer programming

For LaTeX, the symbols are

ho

( ρ ), and varrho ( ϱ ) (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

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.

Mathematical Rho

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.

References

Rho Wikipedia

(Text) CC BY-SA

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