Kronecker delta

In mathematics, the Kronecker delta is a function of two variables, which is 1 if they are equal, and 0 otherwise. It is written as the symbol δ_ij, and treated as a notational shorthand rather than a function.

It is named after mathematician Leopold Kronecker (1823-1891).

It is used in many areas of mathematics. For example, in linear algebra, the identity matrix can be written as:

(δ_ij)

See also Levi-Civita symbol.