Qiskit / qiskit / 31706586499

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Sum VF2Layout average errors in a deterministic order (#16732)

* Sum VF2Layout average errors in a deterministic order

`build_average_error_map` summed per-qubit gate errors while iterating the
`HashSet` returned by `Target::operation_names_for_qargs`, whose order is
randomized per call.  Floating-point addition is non-associative, so the averaged
error -- and therefore the `VF2Layout` score of two symmetric layouts -- varied
between runs.  On a target with control-flow support and a symmetric coupling map
this made the selected layout, and hence the 1q-gate count and depth of the output
circuit, non-deterministic.

Sort the operation names before summing so the result is reproducible.

Fixes #16490.

Signed-off-by: Sophia Wen <hfwen@us.ibm.com>
(cherry picked from commit 8ea89abaa)

* Update releasenotes/notes/fix-vf2layout-nondeterminism-error-sum-2b8d4e6f0a1c3d57.yaml

Co-authored-by: Julien Gacon <gaconju@gmail.com>

* Update releasenotes/notes/fix-vf2layout-nondeterminism-error-sum-2b8d4e6f0a1c3d57.yaml

---------

Signed-off-by: Sophia Wen <hfwen@us.ibm.com>
Co-authored-by: Julien Gacon <gaconju@gmail.com>

Coverage Stats

5 of 5 new or added lines in 1 file covered. (100.0%)

14 existing lines in 3 files now uncovered.

113693 of 129512 relevant lines covered (87.79%)

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