utt − ∆u + qu =0 u?t=0 = ut?t=0 =0 in Ω× (0,T) in Ω
in ∂Ω × [0,T] , where Ω ⊂ Rn is a bounded domain, q ∈ L∞(Ω) is a real-valued function, ν is the outward normal to ∂Ω, u = uf (x, t) is a solu-tion. The input/ou?tput correspondence is realized by a response
