Kronecker’s delta is defined as
0, if i ≠ j
δij =
1, if i = j
For example, δ12 = 0, whereas δ33 = 1.
Kronecker’s delta is a function between two variables, which are integers. The function is 1 if the two variables are the same or equal, and the function is zero if the two variables are not the same or unequal. This function is named after Leopold Kronecker, a German mathematician who discovered it. He once said: ‘The integers came from God and all else was man-made’.
