Kronecker delta

The Kronecker delta (Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \delta_{ij}} ) is as the discrete version of the Dirac delta distribution defined by

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \delta_{ij} = \left\{ \begin{array}{lll} 0 & {\rm for} ~i \neq j \\ 1 & {\rm for} ~i = j \end{array} \right. }