  Determining the border between ergodic and localized behavior is of central
interest in the case of interacting many-body systems. A convenient description
of kicked many-body systems is achieved by the dual operator that evolves the
system in contrast to the time-evolution operator not in time but in particle
direction. We identify in this paper the largest eigenvalue of a function based
on the dual operator as a convenient tool to identify if the system shows
ergodic or many-body localized features. We show how to determine this
eigenvalue by analytical as well as by numerical methods.
