  A minimal model for reservoir computing is studied. We demonstrate that a
reservoir computer exists that emulates given coupled maps by constructing a
modularized network. We describe a possible mechanism for collapses of the
emulation in the reservoir computing by introducing a measure of finite scale
deviation. Such transitory behaviour is caused by either (i) an escape from a
finite-time stagnation near an unstable chaotic set, or (ii) a critical
transition driven by the effective parameter drift. Our approach reveals the
essential mechanism for reservoir computing and provides insights into the
design of reservoir computer for practical applications.
