  In several frustrating systems incommensurate behaviors are often observed.
For the S=1 bilinear-biquadratic model, we show that the main oscillatory
behavior, which is proportional to the free edge spins, is eliminated in the
incommensurate subphase, considering the average of triplet and singlet energy
spectra under open boundary conditions. In the same way, the $\pi$-mode
oscillation is also removed in the commensurate subphase. Moreover, we find
that higher order corrections are exponentially decaying from an analysis of
small size data.
