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Fix approximation_degree default in generate_preset_pass_maanger #11695

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merged 2 commits into from
Feb 1, 2024
Merged

Fix approximation_degree default in generate_preset_pass_maanger #11695

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d246b56
Fix `approximation_degree` default in `generate_preset_pass_maanger`
jakelishman Jan 31, 2024
4aa866d
Correct release note
jakelishman Jan 31, 2024
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2 changes: 1 addition & 1 deletion qiskit/transpiler/preset_passmanagers/__init__.py
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Expand Up @@ -84,7 +84,7 @@ def generate_preset_pass_manager(
routing_method=None,
translation_method=None,
scheduling_method=None,
approximation_degree=None,
approximation_degree=1.0,
seed_transpiler=None,
unitary_synthesis_method="default",
unitary_synthesis_plugin_config=None,
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12 changes: 12 additions & 0 deletions releasenotes/notes/preset-pass-manager-approximation-degree-503198b1974adf79.yaml
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@@ -0,0 +1,12 @@
---
upgrade:
- |
The implicit use of ``approximation_degree!=1.0`` by default in the
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FWIW, I think was only the case if a backend or target with error properties are set. The default of approximation_degree=None was a short hand of approximate up to the error rate reported in the target. So if there was no error rate it wouldn't approximate the decomposition.

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tbh I just copied the first sentence of the note from #8595. Happy to change it to whatever you like

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It's fine this was more just me musing out loud. It's why I didn't leave a concrete suggestion.

:func:`~.generate_preset_pass_manager` function has been
disabled. The previous default could cause undue and unexpected approximations, especially in
workloads involving Trotterization or similar runs of operations that are close, but decidedly
not equal, to the identity.

This change brings the inner pass-manager generation defaults in line with :func:`.transpile`,
which was always the intention. See `#8595 <https://github.com/Qiskit/qiskit/pull/8595>`__ for
more detail.
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