Hi,

I'm trying to convert a hamiltonian like this:

H = sum_ijkl A_ijkl q_i q_j q_k q_l

into a QUBO. I came across the dimod module called higherorder . To my understanding, it creates additional variables to convert a polynominal binary function to a quadratic binary function. I did a few tests "by hand" and it worked fine at least technically.

However, if I try a combination like this:

`H = {(0, 1, 0, 1): -4.61898,(0, 1, 1, 0): 4.61898,(0, 2, 0, 2): -5.18353,(0, 2, 2, 0): 5.18353,(1, 0, 0, 1): 4.61898,(1, 0, 1, 0): -4.61898,(1, 2, 2, 1): 4.97017,(2, 0, 0, 2): 5.18353,(2, 0, 2, 0): -5.18353,(2, 1, 1, 2): 4.97017,}`

and then

`bqm = dimod.make_quadratic(Q, strength, dimod.BINARY)`

I get the following error:

`Traceback (most recent call last):  File "./nbody.py", line 136, in <module>    bqm = dimod.make_quadratic(Q, strength, dimod.BINARY)  File "/Users/disipio/dwave/lib/python3.7/site-packages/dimod/higherorder/utils.py", line 136, in make_quadratic    return _reduce_degree(bqm, new_poly, vartype, strength)  File "/Users/disipio/dwave/lib/python3.7/site-packages/dimod/higherorder/utils.py", line 198, in _reduce_degree    return _reduce_degree(bqm, new_poly, vartype, scale)  File "/Users/disipio/dwave/lib/python3.7/site-packages/dimod/higherorder/utils.py", line 144, in _reduce_degree    bqm.add_interactions_from(poly)  File "/Users/disipio/dwave/lib/python3.7/site-packages/dimod/binary_quadratic_model.py", line 651, in add_interactions_from    for (u, v), bias in iteritems(quadratic):ValueError: not enough values to unpack (expected 2, got 1)`

I'm not sure what it means. Is it a problem with the indices, or is it just not possible to convert such hamiltonian to QUBO? The error message seems very cryptic to me.

Cheers,
Riccardo