1. The problem statement, all variables and given/known data In Gasiorowicz's textbook, he provided the schemetic expession of the wave function(95page) ; psi(x) = Sigma[C_n X U_n(x)] + Integral[dE C(E) X u_E(x)] ("X" means multiplication symbol) In this equation, I think that 1st term(sigma) is the case of the discrete spectrum and 2nd term(integral) is the case of the continuous spectrum. Textbooks explain many example of bound state(i.e. state having discrete spectrum), but most of them didn't explain about continuos spectrum. I am curious about it. Would you tell me about refences containing this problem, or tell me some examples of the continuos spectrum? 2. Relevant equations psi(x) = Sigma[C_n X U_n(x)] + Integral[dE C(E) X u_E(x)] 3. The attempt at a solution I tried to find examples of continuos spectrum in many textbooks, but I failed.