Time Discretization
In ordinary differential equations, one focuses on different ways of represent d?i(t)/dt in some difference form such as Euler’s form d?i(t)/dt = (?i(t + ?t) - ?i(t)) / ?t
Or more accurate Runge-Kutta and other formulae
The same time discretization methods are applicable to (time derivatives in) partial differential equations involving time and are used to approximate ??i(x,t) / ?t