Kronecker delta
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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.

The original article can be found at: http://en.wikipedia.org/wiki/Kronecker_delta.
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