Kronecker delta

In mathematics, the Kronecker delta or Kronecker's delta, named after Leopold Kronecker (1823-1891), is a function of two variables, usually integers, which is 1 if they are equal, and 0 otherwise. So, for example, , but . It is written as the symbol δij, and treated as a notational shorthand rather than as a function.
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Noun
1. a function of two variables i and j that equals 1 when i=j and equals 0 otherwise
(hypernym) function, mathematical function