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 δij, and treated as a notational shorthand rather than a function.
It is named after mathematician Leopold Kronecker
It is used in many areas of mathematics. For example, in linear algebra, the identity matrix can be written as:
See also Levi-Civita symbol