number of line search steps (per iteration). Default is 20.

    Returns
    -------
    x : array_like
        Estimated position of the minimum.
    f : float
        Value of `func` at the minimum.
    d : dict
        Information dictionary.

        * d['warnflag'] is

          - 0 if converged,
          - 1 if too many function evaluations or too many iterations,
          - 2 if stopped for another reason, given in d['task']

        * d['grad'] is the gradient at the minimum (should be 0 ish)
        * d['funcalls'] is the number of function calls made.
        * d['nit'] is the number of iterations.

    See also
    --------
    minimize: Interface to minimization algorithms for multivariate
        functions. See the 'L-BFGS-B' `method` in particular. Note that the
        `ftol` option is made available via that interface, while `factr` is
        provided via this interface, where `factr` is the factor multiplying
        the default machine floating-point precision to arrive at `ftol`:
        ``ftol = factr * numpy.finfo(float).eps``.

    Notes
    -----
    License of L-BFGS-B (FORTRAN code):

    The version included here (in fortran code) is 3.0
    (released April 25, 2011). It was written by Ciyou Zhu, Richard Byrd,
    and Jorge Nocedal <nocedal@ece.nwu.edu>. It carries the following
    condition for use:

    This software is freely available, but we expect that all publications
    describing work using this software, or all commercial products using it,
    quote at least one of the references given below. This software is released
    under the BSD License.

    References
    ----------
    * R. H. Byrd, P. Lu and J. Nocedal. A Limited Memory Algorithm for Bound
      Constrained Optimization, (1995), SIAM Journal on Scientific and
      Statistical Computing, 16, 5, pp. 1190-1208.
    * C. Zhu, R. H. Byrd and J. Nocedal. L-BFGS-B: Algorithm 778: L-BFGS-B,
      FORTRAN routines for large scale bound constrained optimization (1997),
      ACM Transactions on Mathematical Software, 23, 4, pp. 550 - 560.
    * J.L. Morales and J. Nocedal. L-BFGS-B: Remark on Algorithm 778: L-BFGS-B,
      FORTRAN routines for large scale bound constrained optimization (2011),
      ACM Transactions on Mathematical Software, 38, 1.

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