This page lists the notation we use across the Bempp website, and may be a useful reference.
Domains, surfaces, etc.
Symbol(s) 
Meaning 

A domain 

An interior domain 

An exterior domain 

The boundary of a domain 

The outward point normal to the surface 
Points, vectors, etc.
Symbol(s) 
Meaning 
Bold lowercase: , , … 
A point in 3D space 
, and 
The three components of a point 
Operators and matrices
Symbol(s) 
Meaning 
Curly capitals: , , … 
Potential operators 
Sansserif capitals: , , … 
Boundary operators 
Serif capitals with subscripts: , , … 
Matrices arising from discretisation of an operator 
Serif capitals: , , … 
Other matrices 
, 
Interior and exterior Calderón projectors 

Multitrace operator 
, 
Identity operators 
, , 
Single layer operators/matrices 
, , 
Double layer operators/matrices 
, 
Adjoint double layer operators/matrices 
, 
Hypersingular operators/matrices 
, , 
Electric field operators/matrices 
, , 
Magnetic field operators/matrices 
Functions and spaces
Symbol(s) 
Meaning 

The domain of an operator 

The range of an operator 

The dual to the range of an operator 
Lowercase Greek letters: , , … Lowercase Roman letters: , , … 
Scalar valued functions 
Capital Greek letters: , , … Bold capital Roman letters: , , … 
Vector valued functions 
Functions with subscripts: , , , … 
Basis functions of a discrete space 