: Mathématiques: Kronecker delta

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Kronecker delta

In mathematics, the Kronecker delta (named after Leopold Kronecker) is a function of two variables, usually just non-negative integers. The function is 1 if the variables are equal, and 0 otherwise: ${\\displaystyle \\delta _{ij}={\egin{cases}0&{\ ext{if }}i\ eq j,\\\\1&{\ ext{if }}i=j.\\end{cases}}}$ or with use of Iverson brackets: ${\\displaystyle \\delta _{ij}=[i=j]\\,}$ For example, ${\\displaystyle \\delta _{12}=0}$ because ${\\displaystyle 1\ eq 2}$ , whereas ${\\displaystyle \\delta _{33}=1}$ because ${\\displaystyle 3=3}$ .
(Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/wiki/Kronecker_delta)