The imaginary unit is one of the four units of the domain of complex numbers. (The others are 1, –1 and ). In electrical engineering applications, the symbol is generally used instead of , which is then generally used as an iterator. The imaginary unit is
I in Wolfram Mathematica's InputForm and a blackboard bold lowercase I in StandardForm.
- Paul J. Nahin, An Imaginary Tale: The Story of . Princeton, New Jersey: Princeton University Press (1988): 125