Kronecker’s delta – A function between two integers

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’.