One very general example is a form of the electric field equation and then efficiently reduced into a single uni-directional wave equation by means of a simple slow - evolution approximation .
The electric field equation was factorized into a pair of explicitly directional wave equations .
One very general example is a form of the electric field equation , which was factorized into a pair of explicitly directional wave equations , and then efficiently reduced into a single uni-directional wave equation by means of a simple slow - evolution approximation .