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.

<math>\delta_{ij} = \left\{\begin{matrix}

1 & \mbox{if } i=j \\ 0 & \mbox{if } i \ne j \end{matrix}\right.</math>

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.