B.1 Font

B.1.1 Roman

The roman alphabet is used in mathematics for anything that isn’t a variable – constants (e.g. e, i), subscripted labels (e.g. $m_\mathrm{ball}$), units (e.g. km), and operators (e.g. d in calculus, cos, ln).

B.1.2 Italic

Italic font is used for variables, including functions and physical constants (e.g. $c$, the speed of light).

Note that italic is not just a slanted form of roman; the shapes of many letters are different, e.g. compare a with $a$.

B.1.3 Bold

A lowercase bold letter, e.g. $\boldsymbol{v}$, usually indicates a vector (see Section 11.6: Vectors). Uppercase, e.g. $\boldsymbol{A}$, usually indicates a matrix (see Section 12.2: Matrices). Sometimes bold roman is used, e.g. $\mathbf{a}$, although this is incorrect for variables.

B.1.4 Blackboard Bold

\[\mathbb{ABCDEFGHIJKLMNOPQRSTUVWXYZ}\] Blackboard bold often indicates a set of numbers, e.g. $\mathbb{R}$ is the set of real numbers (see Section 8.1: Sets).

B.1.5 Calligraphic

\[\mathcal{ABCDEFGHIJKLMNOPQRSTUVWXYZ}\] Calligraphic fonts are occasionally used in mathematics, e.g. $\mathcal{L}$ can indicate a laplace transform, and $\mathcal{N}$ a normal distribution.

B.1.6 Fraktur

Fraktur (or other blackletter fonts) is also sometimes used, e.g. $\mathfrak{R}$ indicates the real part of a complex number (see Section 16.2: Real and Imaginary).