Legacy operator arithmetic deprecation #6287
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doc/releases/changelog-dev.md
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| * Legacy operator arithmetic has been deprecated. This includes `qml.ops.Hamiltonian`, `qml.operation.enable_new_opmath`, | ||
| `qml.operation.disable_new_opmath`, and `qml.operation.convert_to_legacy_H`. | ||
| [(#6287)](https://github.com/PennyLaneAI/pennylane/pull/6287) | ||
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I am not suggesting doing that in this PR, but are we going to remove the Tensor class without deprecating it first? If so, then I guess it can cause quite a few issues
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I believe the logic behind not deprecating Tensor is that it is a private class. We've always exposed qml.Hamiltonian in a very public way, but Tensor has always been hidden inside the operation module, and the recommended way to create a Tensor has been using the @ operator. That being said, I see your point, and I'd feel wrong merging this PR before getting more input from product about it. cc @DSGuala
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After more discussions, Tensor has been deprecated.
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Should we also replace |
tests/devices/default_qubit/test_default_qubit_preprocessing.py
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| @pytest.mark.usefixtures("legacy_opmath_only") | ||
| @pytest.mark.usefixtures("use_legacy_and_new_opmath") |
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Actually the use_legacy_and_new_opmath fixture can be removed because everything is going to be tested with both legacy and new opmath unless marked new_opmath_only or legacy_opmath_only. The use_new_opmath fixture can also be removed because it doesn't really do anything.
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I still see merit in keeping the use_legacy_and_new_opmath fixture for things that we want to keep testing in regular CI with legacy op math. I agree we can remove the use_new_opmath fixture and should replace tests that use it with new_opmath_only where appropriate, or not use any fixture. That way, their behaviour in regular CI won't change, but we won't run unnecessary tests in legacy op math CI.
| :func:`~pennylane.operation.convert_to_opmath` and :func:`~pennylane.operation.convert_to_H` to convert legacy operators | ||
| into those using the new operator arithmetic. |
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Should we really suggest this? Since I guess these are also deprecated, so we just want them to enable new_opmath and stop explicitly making Tensors and Hamiltonians.
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I did not deprecate these functions because they're the only way users can easily convert legacy ops into new ops without having to do something like
new_op = qml.Hamiltonian(old_op.coeffs, old_op.ops)| Args: | ||
| op (Operator): The operator instance to convert. | ||
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| Returns: | ||
| Operator: The operator as a :class:`~pennylane.Hamiltonian` instance | ||
| """ | ||
| with disable_new_opmath_cm(): |
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we don't want a deprecation warning in this one?
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Because a deprecation warning will be raised when a legacy Hamiltonian is created.
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Looks like running some tests only when legacy op math is active has caused some humps with codecov. Not sure if it should be addressed or not. |
Context:
Legacy op math is being deprecated.
Description of the Change:
qml.ops.Hamiltonianis deprecated.qml.operation.Tensoris deprecated.qml.operation.disable_new_opmathandqml.operation.enable_new_opmath(as well as the context managers) are deprecated.qml.operation.convert_to_legacy_His deprecated.PauliWord.hamiltonianandPauliSentence.hamiltonianis deprecated.qml.pauli.simplifyis deprecated.Removed
use_legacy_opmathanduse_new_opmathfixtures. Instead, we use eitherlegacy_opmath_only,new_opmath_only, or no fixture, as appropriate for the tests.Added warning suppression for all the above deprecation warnings to
pytest.ini. Additionally, I also added the same warning suppressions toconftest.pyfor the case when--disable-opmath=True, since the warning filters inpytest.inionly suppress warnings that come from inside tests, not ones that come from outside the tests, such as when deprecated code is used for creating parameters for a test.Benefits:
Possible Drawbacks:
In some instances, there will be a LOT of deprecation warnings at the same time. The most impactful example of this if if using
qml.qchem.molecular_hamiltonian,qml.qchem.qubit_observable. These usingsimplifyandPauliSentence.hamiltonianwith legacy op math, so there will be up to 4 warnings at once when using these.Additionally,
qml.qchem.tapering.symmetry_generatorsandqml.qchem.tapering.cliffordusePauliSentence.hamiltonianwhen legacy op math is enabled, so there will be up to 3 warnings at once when using these.Related GitHub Issues:
I will run the test suite with
disable_new_opmathset toTrueonce before merging to confirm that legacy op math tests do not fail.[sc-71940] [sc-66727] [sc-66724]