Abstract: In Reference (1) an abstract semigroup approach is used to prove the identifiability of the initial state of one vibrating string with viscous damping at end point. It has been proved that the system isa spectral one, and that the identifiability depends completely on the measurement of the observation time interval. In this paper, the characteristic method is used directly to solve this problem of identifiability, and the obvious solution to this problem is obtained.

Key words: A string vibrating equation, Initial condition, Problem of identifiability, Obvious solution