def yield_pair_hessians(self, index1, index2):
strength = self.strengths[index1, index2]<EOL>distance = self.distances[index1, index2]<EOL>yield <NUM_LIT:12>*<NUM_LIT>*strength*distance**(-<NUM_LIT>), np.zeros((<NUM_LIT:3>, <NUM_LIT:3>))<EOL>
Yields pairs ((s''(r_ij), grad_i (x) grad_i v(bar{r}_ij))