  Density matrices and Discrete Wigner Functions are equally valid
representations of multiqubit quantum states. For density matrices, the partial
trace operation is used to obtain the quantum state of subsystems, but an
analogous prescription is not available for discrete Wigner Functions. Further,
the discrete Wigner function corresponding to a density matrix is not unique
but depends on the choice of the quantum net used for its reconstruction. In
the present work, we derive a reduction formula for discrete Wigner functions
of a general multiqubit state which works for arbitrary quantum nets. These
results would be useful for the analysis and classification of entangled states
and the study of decoherence purely in a discrete phase space setting and also
in applications to quantum computing
