“…To solve this problem effectively, we made use of the symplectic geometry based analytic gradient-holonomic algorithm [5,19], recently devised for studying integrability properties of nonlinear dynamical systems with hidden symmetries and partially motivated by the classical optimal control theory [3,17] approach. Being applied to the parametrically extended Kardar-Parisi-Zhang equation (2), this algorithm allowed us to solve the posed above problem and to to state that it belongs to the class of completely integrable dark type [5,6,4,12,15,16] Hamiltonian systems on functional manifolds with hidden symmetry. Namely, there was stated the following proposition.…”