  The Manley--Rowe constants of motion (MRC) are conservation laws written out
for a dynamical system describing the time evolution of the amplitudes in
resonant triad. In this paper we extend the concept of MRC to resonance
clusters of any form yielding generalized Manley--Rowe constants (gMRC) and
give a constructive method how to compute them. We also give details of a
\emph{Mathematica} implementation of this method. While MRC provide
integrability of the underlying dynamical system, gMRC generally do not but may
be used for qualitative and numerical study of dynamical systems describing
generic resonance clusters.
