  The possibility has been suggested that high-frequency quasi-periodic
oscillations observed in low-mass X-ray binaries are resonantly excited disk
oscillations in deformed (warped or eccentric) relativistic disks (Kato 2004).
In this paper we examine this wave excitation process from a viewpoint somewhat
different from that of previous studies. We study how amplitudes of a set of
normal mode oscillations change secularly with time by their mutual couplings
through disk deformation. As a first step, we consider the case where the
number of oscillation modes contributing to the resonance coupling is two. The
results show that two prograde oscillations interacting through disk
deformation can grow if their wave energies have opposite signs.
