Return the angles between given atoms.

        Calculates the angle in degrees between the atoms with
        indices ``i, b, a``.
        The indices can be given in three ways:

        * As simple list ``[i, b, a]``
        * As list of lists: ``[[i1, b1, a1], [i2, b2, a2]...]``
        * As :class:`pd.DataFrame` where ``i`` is taken from the index and
          ``b`` and ``a`` from the respective columns ``'b'`` and ``'a'``.

        Args:
            indices (list):

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

def get_angle_degrees(self, indices):
        """Return the angles between given atoms.

        Calculates the angle in degrees between the atoms with
        indices ``i, b, a``.
        The indices can be given in three ways:

        * As simple list ``[i, b, a]``
        * As list of lists: ``[[i1, b1, a1], [i2, b2, a2]...]``
        * As :class:`pd.DataFrame` where ``i`` is taken from the index and
          ``b`` and ``a`` from the respective columns ``'b'`` and ``'a'``.

        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
            a_pos = self.loc[indices.loc[:, 'a'], 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
            a_pos = self.loc[indices[:, 2], coords].values

        BI, BA = i_pos - b_pos, a_pos - b_pos
        bi, ba = [v / np.linalg.norm(v, axis=1)[:, None] for v in (BI, BA)]
        dot_product = np.sum(bi * ba, axis=1)
        dot_product[dot_product > 1] = 1
        dot_product[dot_product < -1] = -1
        angles = np.degrees(np.arccos(dot_product))
        return angles