code: def ellipticity(self):
          '''
          Most meaningful for bond critical points,
          can be physically interpreted as e.g. degree
          of pi-bonding in organic molecules. Consult
          literature for more information.
          :return:
          '''
          eig = np.linalg.eig(self.field_hessian)
          eig.sort()
          return eig[0]/eig[1] - f ellipticity(self):
          '''
          Most meaningful for bond critical points,
          can be physically interpreted as e.g. degree
          of pi-bonding in organic molecules. Consult
          literature for more information.
          :return:
          '''
          eig = np.linalg.eig(self.field_hessian)
          eig.sort()
          return eig[0]/eig[1] - 1
docs: Most meaningful for bond critical points,
          can be physically interpreted as e.g. degree
          of pi-bonding in organic molecules. Consult
          literature for more information.
          :return: