HOME

TheInfoList



OR:

Rho (uppercase Ρ, lowercase ρ or ; el, ρο or el, ρω, label=none) 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 uses the same
glyph A glyph () is any kind of purposeful mark. In typography, a glyph is "the specific shape, design, or representation of a character". It is a particular graphical representation, in a particular typeface, of an element of written language. A g ...
, Ρ, as the distinct Latin letter P; the two letters have different Unicode encodings.


Uses


Greek

Rho is classed as a liquid consonant (together with Lambda and sometimes the nasals Mu and Nu), which has important implications for
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...
. In both
Ancient Ancient history is a time period from the beginning of writing and recorded human history to as far as late antiquity. The span of recorded history is roughly 5,000 years, beginning with the Sumerian cuneiform script. Ancient history cove ...
and Modern Greek, it represents a
alveolar trill The voiced alveolar trill is a type of consonantal sound used in some spoken languages. The symbol in the International Phonetic Alphabet that represents dental, alveolar, and postalveolar trills is , and the equivalent X-SAMPA symbol is r. I ...
,
alveolar tap Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...
, or
alveolar approximant The voiced alveolar approximant is a type of consonantal sound used in some spoken languages. The symbol in the International Phonetic Alphabet that represents the alveolar and postalveolar approximants is , a lowercase letter ''r'' rotated 1 ...
. In polytonic orthography, a rho at the beginning of a word is written with a
rough breathing In the polytonic orthography of Ancient Greek, the rough breathing ( grc, δασὺ πνεῦμα, dasỳ pneûma or ''daseîa''; la, spīritus asper) character is a diacritical mark used to indicate the presence of an sound before a vowel, ...
, equivalent to ''h'' ( ''rh''), and a
double A double is a look-alike or doppelgänger; one person or being that resembles another. Double, The Double or Dubble may also refer to: Film and television * Double (filmmaking), someone who substitutes for the credited actor of a character * ...
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 In linguistics, voicelessness is the property of sounds being pronounced without the larynx vibrating. Phonologically, it is a type of phonation, which contrasts with other states of the larynx, but some object that the word phonation implies v ...
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/ ρο (monotonic).


Other alphabets

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


Mathematics and science

The characters ρ and are also conventionally used outside the Greek alphabetical context in science and mathematics. *In the physical sciences to represent: **Densities: mass density,
air density The density of air or atmospheric density, denoted '' ρ'', is the mass per unit volume of Earth's atmosphere. Air density, like air pressure, decreases with increasing altitude. It also changes with variation in atmospheric pressure, temperature a ...
or
charge density In electromagnetism, charge density is the amount of electric charge per unit length, surface area, or volume. Volume charge density (symbolized by the Greek letter ρ) is the quantity of charge per unit volume, measured in the SI system in co ...
(''ρ'') **
Resistivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
(''ρ'') **
Rho meson Rho (uppercase Ρ, lowercase ρ or ; el, ρο or el, ρω, label=none) 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 uses the sa ...
+, 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 A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infini ...
, spherical, and toroidal coordinate systems, and toroidal and poloidal coordinates of the Earth's magnetic field. **The
correlation coefficient A correlation coefficient is a numerical measure of some type of correlation, meaning a statistical relationship between two variables. The variables may be two columns of a given data set of observations, often called a sample, or two component ...
of a population parameter **The spectral radius of a matrix A denoted as \rho(A) **The
plastic number In mathematics, the plastic number (also known as the plastic constant, the plastic ratio, the minimal Pisot number, the platin number, Carl Ludwig Siegel, Siegel's number or, in French, ) is a mathematical constant which is the unique real so ...
**The
prime constant The prime constant is the real number \rho whose nth binary digit is 1 if n is prime and 0 if n is composite or 1. In other words, \rho is the number whose binary expansion corresponds to the indicator function of the set of prime numbers. Tha ...
**The sensitivity to interest rates of a pricing function **The expected return of a given policy (\pi) in reinforcement learning, denoted \rho^\pi *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 , 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 APL (named after the book ''A Programming Language'') is a programming language developed in the 1960s by Kenneth E. Iverson. Its central datatype is the multidimensional array. It uses a large range of special graphic symbols to represent mo ...
, 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 Option or Options may refer to: Computing *Option key, a key on Apple computer keyboards *Option type, a polymorphic data type in programming languages *Command-line option, an optional parameter to a command *OPTIONS, an HTTP request method ...
theory to represent the rate of change of a portfolio with respect to interest rates


Chi Rho

The letter rho overlaid with
chi Chi or CHI may refer to: Greek *Chi (letter), the Greek letter (uppercase Χ, lowercase χ); Chinese * ''Chi'' (length) (尺), a traditional unit of length, about ⅓ meter * Chi (mythology) (螭), a dragon *Chi (surname) (池, pinyin: ''chí' ...
forms the ''
Chi Rho The Chi Rho (☧, English pronunciation ; also known as ''chrismon'') is one of the earliest forms of Christogram, formed by superimposing the first two (capital) letters—chi and rho (ΧΡ)—of the Greek word ( Christos) in such a way tha ...
'' symbol, used to represent Jesus Christ.


Rho with stroke (ϼ)

The rho with a stroke through its tail is used for abbreviations involving rho, most notably in γϼ for γράμμα as a unit of measurement.


Character encodings


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


Greek rho symbols


Coptic ro


Functional symbol


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.


See also

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


References

{{Wiktionary, Ρ, ρ Greek letters