contract("ij->jij", [[0, 0], [0, 0]])
# ValueError: einstein sum subscripts string includes output subscript 'j' multiple times
currently relies on the backend to throw an error if an output subscript is specified multiple times. However
contract_path("ij->jij", [[0, 0], [0, 0]])
would still return an einsum path despite the wrong einsum equation. This might lead to subtle errors if a user ends up relying on this behaviour by accident. E.g. when using the jax backend no error is thrown but only an internal assertion fails.
This PR raises the error already in parse_einsum_input which ensures that contract_path matches the behaviour of np.einsum and all backends that might rely on opt_einsum for error handling will do so as well.
This PR also extends the unittests to test error handling for both contract_path and contract which is independent of the backend.
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commented
1 year ago
Description
currently relies on the backend to throw an error if an output subscript is specified multiple times. However
would still return an einsum path despite the wrong einsum equation. This might lead to subtle errors if a user ends up relying on this behaviour by accident. E.g. when using the jax backend no error is thrown but only an internal assertion fails.
This PR raises the error already in
parse_einsum_inputwhich ensures thatcontract_pathmatches the behaviour ofnp.einsumand all backends that might rely onopt_einsumfor error handling will do so as well.This PR also extends the unittests to test error handling for both
contract_pathandcontractwhich is independent of the backend.For reference I made a similar PR to https://github.com/numpy/numpy/pull/25230 to fix the same issue for
np.einsum_path.Status