Inpolytonic orthography, a rho at the beginning of a word is almost always written ⟨ῥ⟩ (rh) with arough breathing mark, indicating that it isvoiceless. Very rarely, it is written ⟨ῤ⟩ (r) with asmooth breathing mark, indicating that it isvoiced, instead. Rho is not written with breathing marks at any other place in a word, where it is always voiced, with the exception of double rho, which was traditionally written ⟨ῤῥ⟩ (rrh), with a smooth breathing mark over the first rho, and a rough breathing mark over the second, representing ageminated voiceless consonant. However, this practice fell out of use over the 19th century in favour of ⟨ρρ⟩, since double rho cannot take any other combination of breathing marks. Various Greek-derived English words containingrh andrrh derive from words containing ⟨ῤ⟩ and ⟨ρρ⟩.
The name of the letter is written in Greek asῥῶ (polytonic) or ρω/ρο (monotonic).
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.
Inmolecular biology to represent theRho protein responsible for termination of RNA synthesis. In such occasions, it is often represented asU+03F1ϱGREEK RHO SYMBOL, to avoid confusion with the Latin letterp
The letter rho overlaid withchi forms theChi Rho symbol, used to representJesus Christ. It was first used by EmperorConstantine the Great. An example of this can be seen on his standard known as theLabarum.
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:
U+1D6B8𝚸MATHEMATICAL BOLD CAPITAL RHO
U+1D6D2𝛒MATHEMATICAL BOLD SMALL RHO
U+1D6E0𝛠MATHEMATICAL BOLD RHO SYMBOL
U+1D6F2𝛲MATHEMATICAL ITALIC CAPITAL RHO
U+1D70C𝜌MATHEMATICAL ITALIC SMALL RHO
U+1D71A𝜚MATHEMATICAL ITALIC RHO SYMBOL
U+1D72C𝜬MATHEMATICAL BOLD ITALIC CAPITAL RHO
U+1D746𝝆MATHEMATICAL BOLD ITALIC SMALL RHO
U+1D754𝝔MATHEMATICAL BOLD ITALIC RHO SYMBOL
U+1D766𝝦MATHEMATICAL SANS-SERIF BOLD CAPITAL RHO
U+1D780𝞀MATHEMATICAL SANS-SERIF BOLD SMALL RHO
U+1D78E𝞎MATHEMATICAL SANS-SERIF BOLD RHO SYMBOL
U+1D7A0𝞠MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL RHO
U+1D7BA𝞺MATHEMATICAL SANS-SERIF BOLD ITALIC SMALL RHO
U+1D7C8𝟈MATHEMATICAL SANS-SERIF BOLD ITALIC RHO SYMBOL
^Natrella, Mary Gibbons (August 1, 1963).Experimental Statistics. National Bureau of Standards. pp. 5–40.What is the Degree of Relationship of the Two Variables X and Y as Measured by ρ, the Correlation Coefficient?{{cite book}}: CS1 maint: date and year (link)
^Weisstein, Eric W."Spectral Radius".mathworld.wolfram.com. Retrieved2025-01-22.
^Weisstein, Eric W."Plastic Constant".mathworld.wolfram.com. Retrieved2025-01-31.The plastic constant ρ, sometimes also called le nombre radiant, the minimal Pisot number, plastic number, plastic ratio,...
^Weisstein, Eric W."Prime Constant".mathworld.wolfram.com. Retrieved2025-01-31.
^Weisstein, Eric W."Spearman Rank Correlation Coefficient".mathworld.wolfram.com. Retrieved2025-01-22.The Spearman rank correlation coefficient, also known as Spearman's rho,
^"What Is Rho? Definition, How It's Used, Calculation, and Example".Investopedia. Retrieved2025-01-22.Rho is the rate at which the price of a derivative changes relative to a change in the risk-free rate of interest. Rho measures the sensitivity of an option or options portfolio to a change in interest rate.
^Paul of Aegina explains conventional usage in the last chapter of Book VII on weights and measures and uses it throughout his work.
