Changelog
Upgrades
- The `qiskit-algorithms` code uses a common random number generator, which can be seeded for reproducibility. The algorithms code here, having originated in Qiskit and having been moved here, used random function from qiskit.utils which was seeded as follows:
python
from qiskit.utils import algorithm_globals
algorithm_globals.random_seed = 101
Now this will continue to work in `qiskit-algorithms`, until such time as the `algorithm_globals` are removed from Qiskit, however you are highly recommended to already change to import/seed the `algorithm_globals` that is now supplied by `qiskit-algorithms` thus:
python
from qiskit_algorithms.utils import algorithm_globals
algorithm_globals.random_seed = 101
As can be seen it’s simply a change to the import statement, so as to import the `qiskit-algorithms` instance rather than the one from qiskit.
This has been done to afford a transition and not break end-users code by supporting seeding the random generator as it was done before. How does it work - well, while the `qiskit.utils` version exists, the `qiskit-algorithms` version simply delegates its function to that instance. However the main codebase of `qiskit-algorithms` has already been altered to use the new instance and the delegation function, that accesses the random generator, will warn with a message to switch to seeding the `qiskit-algorithms` version if it detects a difference in the seed. A difference could exist if the random_seed was set direct to the `qiskit.utils` instance.
At such a time when the `qiskit.utils` `algorithm_globals` version no longer exists, rather than delegating the functionality to that, it will use identical logic which it already has, so no further user change will be required if you already transitioned to seeding the `qiskit_algorithms.utils` `algorithms_globals`.
- A couple of algorithms here, [PVQD](https://qiskit.org/ecosystem/algorithms/stubs/qiskit_algorithms.PVQD.html#qiskit_algorithms.PVQD), [AdaptVQE](https://qiskit.org/ecosystem/algorithms/stubs/qiskit_algorithms.AdaptVQE.html#qiskit_algorithms.AdaptVQE) and optimizer [SNOBFIT](https://qiskit.org/ecosystem/algorithms/stubs/qiskit_algorithms.optimizers.SNOBFIT.html#qiskit_algorithms.optimizers.SNOBFIT), directly raised a [QiskitError](https://qiskit.org/documentation/apidoc/exceptions.html#qiskit.exceptions.QiskitError). These have been changed to raise an [AlgorithmError](https://qiskit.org/ecosystem/algorithms/apidocs/qiskit_algorithms.AlgorithmError.html#qiskit_algorithms.AlgorithmError) instead. Algorithms have now been moved out of Qiskit and this better distinguishes the exception to the algorithms when raised. Now `AlgorithmError` was already raised elsewhere by the algorithms here so this makes things more consistent too. Note, that as `AlgorithmError` internally extends `QiskitError`, any code that might have caught that specifically will continue to work. However we do recommend you update your code accordingly for `AlgorithmError`.
The deprecated threshold input argument of [AdaptVQE](https://qiskit.org/ecosystem/algorithms/stubs/qiskit_algorithms.AdaptVQE.html#qiskit_algorithms.AdaptVQE) has been removed, and replaced by gradient_threshold`. This change was made to avoid confusion with the later introduced `eigenvalue_threshold` argument. The updated `AdaptVQE` use would look like this:
python
from qiskit_algorithms import VQE, AdaptVQE
adapt_vqe = AdaptVQE(
VQE(Estimator(), ansatz, optimizer),
gradient_threshold=1e-3,
eigenvalue_threshold=1e-3
)
Other Notes
- Removed the custom `__str__` method from [SamplingMinimumEigensolverResult](https://qiskit.org/ecosystem/algorithms/stubs/qiskit_algorithms.SamplingMinimumEigensolverResult.html#qiskit_algorithms.SamplingMinimumEigensolverResult) so that string conversion is based on the method of its parent `AlgorithmResult` which prints all the result fields in a dictionary like format. The overridden method had only printed a select couple of fields, unlike when normally printing a result all fields are shown, and the lack of fields expected to be shown caused confusion when printing results derived from that, such as returned by [SamplingVQE](https://qiskit.org/ecosystem/algorithms/stubs/qiskit_algorithms.SamplingVQE.html#qiskit_algorithms.SamplingVQE) and [QAOA](https://qiskit.org/ecosystem/algorithms/stubs/qiskit_algorithms.QAOA.html#qiskit_algorithms.QAOA).