Integration direction: +1 or -1.
t : float
    Current time.
y : ndarray
    Current state.
t_old : float
    Previous time. None if no steps were made yet.
step_size : float
    Size of the last successful step. None if no steps were made yet.
nfev : int
    Number evaluations of the system's right-hand side.
njev : int
    Number of evaluations of the Jacobian. Is always 0 for this solver
    as it does not use the Jacobian.
nlu : int
    Number of LU decompositions. Is always 0 for this solver.

References
----------
.. [1] E. Hairer, S. P. Norsett G. Wanner, "Solving Ordinary Differential
       Equations I: Nonstiff Problems", Sec. II.
.. [2] `Page with original Fortran code of DOP853
        <http://www.unige.ch/~hairer/software.html>`_.
é