Return the distances between given atoms.

        Calculates the distance between the atoms with
        indices ``i`` and ``b``.
        The indices can be given in three ways:

        * As simple list ``[i, b]``
        * As list of lists: ``[[i1, b1], [i2, b2]...]``
        * As :class:`pd.DataFrame` where ``i`` is taken from the index and
          ``b`` from the respective column ``'b'``.

        Args:
            indices (list):

        Returns:
            :class:`numpy.ndarray`: Vector of angles in degrees.

def get_bond_lengths(self, indices):
        """Return the distances between given atoms.

        Calculates the distance between the atoms with
        indices ``i`` and ``b``.
        The indices can be given in three ways:

        * As simple list ``[i, b]``
        * As list of lists: ``[[i1, b1], [i2, b2]...]``
        * As :class:`pd.DataFrame` where ``i`` is taken from the index and
          ``b`` from the respective column ``'b'``.

        Args:
            indices (list):

        Returns:
            :class:`numpy.ndarray`: Vector of angles in degrees.
        """
        coords = ['x', 'y', 'z']
        if isinstance(indices, pd.DataFrame):
            i_pos = self.loc[indices.index, coords].values
            b_pos = self.loc[indices.loc[:, 'b'], coords].values
        else:
            indices = np.array(indices)
            if len(indices.shape) == 1:
                indices = indices[None, :]
            i_pos = self.loc[indices[:, 0], coords].values
            b_pos = self.loc[indices[:, 1], coords].values
        return np.linalg.norm(i_pos - b_pos, axis=1)