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

$\delta _{ij}=\left\{{\begin{array}{lll}0&{\rm {for}}~i\neq j\\1&{\rm {for}}~i=j\end{array}}\right.$