 the polynomial
        should pass through
    yi : array_like, shape (..., npoints, ...), optional
        N-D array of y coordinates of the points the polynomial should pass through.
        If None, the y values will be supplied later via the `set_y` method.
        The length of `yi` along the interpolation axis must be equal to the length
        of `xi`. Use the ``axis`` parameter to select correct axis.
    axis : int, optional
        Axis in the yi array corresponding to the x-coordinate values. Defaults
        to ``axis=0``.

    Notes
    -----
    This class uses a "barycentric interpolation" method that treats
    the problem as a special case of rational function interpolation.
    This algorithm is quite stable, numerically, but even in a world of
    exact computation, unless the x coordinates are chosen very
    carefully - Chebyshev zeros (e.g., cos(i*pi/n)) are a good choice -
    polynomial interpolation itself is a very ill-conditioned process
    due to the Runge phenomenon.

    Based on Berrut and Trefethen 2004, "Barycentric Lagrange Interpolation".

    Nr