Skip over identity operations in "default.qubit"
#2356
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@@ Coverage Diff @@
## master #2356 +/- ##
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Coverage 99.42% 99.42%
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Files 242 242
Lines 18341 18343 +2
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+ Hits 18235 18237 +2
Misses 106 106
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Hi @albi3ro, great catch! It would be great to cover this functionality with tests too. For example, one could check that no internal methods (e.g., _apply_unitary_einsum) are being called for applying identities.
| @@ -242,6 +242,8 @@ def _apply_operation(self, state, operation): | |||
| Returns: | |||
| array[complex]: output state | |||
| """ | |||
| if operation.base_name == "Identity": | |||
| return state | |||
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Are there any other "no-ops" to include here? e.g., things like a barrier
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Barrier and WireCut don't define a matrix, so we don't have to worry about matrix operations with them. They get expanded away to nothing prior to execution. Identity, on the other hand, is an explicitly supported gate, so it won't get expanded away.
| spy_unitary = mocker.spy(dev, "_apply_unitary") | ||
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| res = dev._apply_operation(starting_state, op) | ||
| assert res is starting_state |
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is makes sure that the state isn't just approximately the same values, but was literally unaffected by the method.
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@antalszava test is added. |
| * `"default.qubit"` now skips over identity operators instead performing matrix multiplication | ||
| with the identity. |
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| * `"default.qubit"` now skips over identity operators instead performing matrix multiplication | |
| with the identity. | |
| * `default.qubit` now skips over identity operators instead of performing matrix multiplication | |
| with the identity. |
| @@ -2341,6 +2341,24 @@ def compute_matrix(*params, **hyperparams): | |||
| assert np.allclose(res_mat, op.get_matrix()) | |||
| assert np.allclose(res_wires, wires) | |||
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| def test_identity_skipped(self, mocker): | |||
| """Test identity operation does not perform additional computations.""" | |||
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| """Test identity operation does not perform additional computations.""" | |
| """Test that applying the identity operation does not perform any additional computations.""" |
Currently,
"default.qubit"handles identity operations by performingeinsumwith the identity.This PR makes it so that identity operations are merely passed over.