The representation, beloved of engineers and physicists, of a complex number in terms of a complex exponential x + i y = left bracketing bar z right bracketing bar e^(i ϕ), where i (called j by engineers) is the imaginary number and the complex modulus and complex argument (also called phase) are left bracketing bar z right bracketing bar | = | sqrt(x^2 + y^2) ϕ | = | tan^(-1)(y/x).