Setup of the options for the spline interpolation

        Args:
            spline_options (dict): Options for cubic spline. For example,
                {"saddle_point": "zero_slope"} forces the slope at the saddle to
                be zero.

def setup_spline(self, spline_options=None):
        """
        Setup of the options for the spline interpolation

        Args:
            spline_options (dict): Options for cubic spline. For example,
                {"saddle_point": "zero_slope"} forces the slope at the saddle to
                be zero.
        """
        self.spline_options = spline_options
        relative_energies = self.energies - self.energies[0]
        if scipy_old_piecewisepolynomial:
            if self.spline_options:
                raise RuntimeError('Option for saddle point not available with'
                                   'old scipy implementation')
            self.spline = PiecewisePolynomial(
                self.r, np.array([relative_energies, -self.forces]).T,
                orders=3)
        else:
            # New scipy implementation for scipy > 0.18.0
            if self.spline_options.get('saddle_point', '') == 'zero_slope':
                imax = np.argmax(relative_energies)
                self.spline = CubicSpline(x=self.r[:imax + 1],
                                          y=relative_energies[:imax + 1],
                                          bc_type=((1, 0.0), (1, 0.0)))
                cspline2 = CubicSpline(x=self.r[imax:], y=relative_energies[imax:],
                                       bc_type=((1, 0.0), (1, 0.0)))
                self.spline.extend(c=cspline2.c, x=cspline2.x[1:])
            else:
                self.spline = CubicSpline(x=self.r, y=relative_energies,
                                          bc_type=((1, 0.0), (1, 0.0)))