ins the jth derivative.
            Shape of d[j] is determined by replacing the interpolation
            axis in the original array with the shape of x.

        Examples
        --------
        >>> from scipy.interpolate import KroghInterpolator
        >>> KroghInterpolator([0,0,0],[1,2,3]).derivatives(0)
        array([1.0,2.0,3.0])
        >>> KroghInterpolator([0,0,0],[1,2,3]).derivatives([0,0])
        array([[1.0,1.0],
               [2.0,2.0],
               [3.0,3.0]])

        r