  A new non-perturbative method of solution of the nonlinear Heisenberg
equations in the finite-dimensional subspace is illustrated. The method, being
a counterpart of the traditional Schrodinger picture method, is based on a
finite operator expansion into the elementary processes. It provides us with
the insight into the nonlinear quantal interaction from the different point of
view. Thus one can investigate the nonlinear system in both pictures of quantum
mechanics.
