Monday 24 December 2012
Many Roman letters, both capital and small, are used in mathematics, science and engineering to denote by
convention specific or abstracted constants, variables of a certain type, units,
multipliers, physical entities. Certain letters, when combined with special
formatting, take on special meaning.
Aa
- A represents:
- the first corner of a triangle
- the digit "10" in hexadecimal and other positional numeral systems with a radix of 11 or greater
- the unit ampere for electrical current
- area
- represents the algebraic numbers or affine space in Algebraic Geometry
- a represents:
- the first side of a triangle (opposite corner A)
- the acceleration in mechanics equations
- the x-intercept of a line
- the unit are for area (100 m²)
- the unit prefix atto (10−18)
- the first term in a sequence or series (eg. Sn = n(a+l)/2)
- B represents:
- the digit "11" in hexadecimal and other positional numeral systems with a radix of 12 or greater
- the second corner of a triangle
- a ball (also denoted by or )
- a basis of a vector space or of a filter (both also denoted by )
- B with various subscripts represents several variations of Brun's constant and Betti numbers
- b represents:
- the second side of a triangle (opposite corner B)
- the y-intercept of a line
- (usually with an index, sometimes with an arrow over it) a basis vector
Cc
- C represents:
- the third corner of a triangle
- the digit "12" in hexadecimal and other positional numeral systems with a radix of 13 or greater
- the unit coulomb of electrical charge
- C with indices denotes the number of combinations, a binomial coefficient
- represents the set of complex numbers
- A vertically elongated C with an integer subscript n sometimes denotes the n-th coefficient of a formal power series.
- c represents:
- the third side of a triangle (opposite corner C)
- the unit prefix centi (10−2)
- c represents:
- the speed of light in vacuum
- Small bold C denotes the cardinality of the set of real numbers (the "continuum"), or,
Dd
- D represents the digit "13" in hexadecimal and other positional numeral systems with a radix of 14 or greater
- d represents
- the differential operator
- the unit day of time (86 400 s)
- the difference in an arithmetic sequence (eg. Sn = n(2a+(n-1)d)/2)
Ee
- E represents:
- the digit "14" in hexadecimal and other positional numeral systems with a radix of 15 or greater
- an exponent in decimal numbers 1.2E3 is 1.2×10³ or 1200
- the set of edges in a graph or matroid
- the unit prefix exa (1018)
- Energy in physics
- e represents:
- Euler's number, a transcendental number equal to 2.71828182845… which is used as the base for natural logarithms
- a vector of unit length, especially in the direction of one of the coordinates axes
- the elementary charge in physics
Ff
- F represents
- the digit "15" in hexadecimal and other positional numeral systems with a radix of 16 or greater
- force in mechanics equations
- the probability distribution function in statistics
- the unit farad of electrical capacity
- f represents:
Gg
- G represents
- an arbitrary graph, as in: G(V,E)
- an arbitrary group
- the unit prefix giga (109)
- Newton's gravitational constant
- the Einstein tensor
- g represents:
- the generic designation of a second function
- the acceleration due to gravity on Earth
Hh
- H represents:
- a Hilbert space
- the unit henry of magnetic inductance
- the homology and cohomology functors
- h represents:
- a small increment in the argument of a function
- the unit hour for time (3600 s)
- the unit prefix hecto (10²)
- represents the quaternions (after William Rowan Hamilton, representing the rationals)
- represents the Hamiltonian in Hamiltonian mechanics
Ii
- I represents:
- the closed unit interval, which contains all real numbers from 0 to 1, inclusive
- the identity matrix
- i represents:
- the imaginary unit, a complex number that is the square root of −1
- a subscript to denote the ith term (that is, a general term or index) in a sequence or list
- the index to the elements of a vector, written as a subscript after the vector name
- the index to the rows of a matrix, written as the first subscript after the matrix name
- an index of summation using the sigma notation
- J represents the unit joule of energy
- j represents:
- the index to the columns of a matrix, written as the second subscript after the matrix name
- in electrical engineering, the square root of −1, instead of i
- in electrical engineering, the principal cube root of 1:
Kk
- K represents:
- k represents
- the unit prefix kilo- (10³)
- the Boltzmann constant
- an integer, e.g. a dummy variable in summations, or an index of a matrix.
- an unspecified (real) constant
Ll
- L represents:
- the unit litre of volume
- the space of all integrable real (or complex) functions
- the space of linear maps, as in L(E,F) or L(E) = End(E)
- the Likelihood function
- l represents:
- the length of a side of a rectangle or a rectangular prism (eg. V = lwh; A = lw)
- the last term of a sequence or series (eg. Sn = n(a+l)/2)
- (or sometimes just L) represents the Lagrangian
Mm
- M represents:
- a manifold
- a metric space
- a matroid
- the unit prefix mega (106)
- m represents:
Nn
- N represents
- the unit newton of force
- NA represents the Avogadro constant which is the number of entities in one mole (used mainly in the counting of molecules and atoms)
- represents the natural numbers
- n represents
Oo
- O represents the order of asymptotic behavior of a function; see Big O notation
- O represents — the origin of the coordinate system in Cartesian coordinates
Pp
- P represents:
- the pressure in physics equations
- the unit prefix peta (1015)
- represents
- p represents the unit prefix pico (10−12)
- represents the rational numbers
Rr
- R represents:
- the Ricci tensor
- represents the set of real numbers and various algebraic structures built upon the set of real numbers, such as
- r represents:
- the radius of a circle or sphere
- the ratio of a geometric series (eg. arn-1)
Ss
- S represents
- a sum
- the unit siemens of electric conductance
- the unit sphere (with superscript denoting dimension)
- the scattering matrix
- s represents:
- represents a system's action in physics
Tt
- T represents:
- the top element of a lattice
- a tree (a special kind of graph)
- temperature in physics equations
- the unit tesla of magnetic flux density
- the unit prefix tera (1012)
- the stress-energy tensor
- t represents:
- time in graphs, functions or equations
- a term in a sequence or series (eg. tn = tn-1+5)
Uu
- U represents:
- a U-set which is a set of uniqueness
- a unitary operator
- U(n) represents the unitary group of degree n
- ∪ represents the union operator
Vv
- V represents:
- v represents the velocity in mechanics equations
Ww
- W represents the unit watt of power
Xx
- x represents
- an unknown variable, most often (but not always) from the set of real numbers, while a complex unknown would rather be called z, and an integer by a letter like m from the middle of the alphabet.
- the coordinate on the first or horizontal axis in a cartesian coordinate system, the viewport in a graph or window in computer graphics
Yy
- Y represents:
- the unit prefix yotta (1024)
- y represents:
- the unit prefix yocto (10−24)
- y represents:
Zz
- Z represents:
- the unit prefix zetta (1021)
- a standarized normal random variable in Probability Theory and Statistics
- represents the integers
- z represents:
- the unit prefix zepto (10−21)
- the coordinate on the third or vertical axis in three dimensional space
- the view depth in computer graphics, see also "z-buffering"
- the argument of a complex function, or any other variable used to represent a complex value .