best index for included `x_new` in the interpolation set.

Parameters
----------
x_new : `numpy.ndarray`, shape (n,), optional
    New point to be included in the interpolation set.

Returns
-------
int
    Index of the interpolation point to remove.
float
    Distance between `x_best` and the removed point.

Raises
------
`numpy.linalg.LinAlgError`
    If the computation of a determinant fails.
Nr­