The total wave function for this eigenmode is then the linear combination u ω ω ( x , t ) = e − − i ω ω t ( A e − − i k x + B e i k x ) = A e − − i ( k x + ω ω t ) + B e i ( k x − − ω ω t ) , where complex numbers A, B depend in general on any initial and boundary conditions of the problem.