   nonlinearity;
          = 'S' : initialize the static nonlinearity only, X
                  already contains an initial approximation of the
                  linear part;
          = 'B' : initialize both linear and nonlinear parts;
          = 'N' : do not initialize anything, X already contains
                  an initial approximation.
          If INIT = 'S' or 'B', the error functions for the
          nonlinear part, and their Jacobian matrices, are evaluated
          by SLICOT Library routine 