Qiskit / qiskit / 26525262478

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github

Committed by web-flow

Commit Message

Fix panic on `1.0` error in `VF2Layout` (#16285) (#16287)

* Fix panic on `1.0` error in `VF2Layout`

`VF2Layout` and `VF2PostLayout` internally use an `f64` to represent
their score, and they're supposed to be allowed to treat this as fully
ordered by validating that `nan` never enters as an error rate.  This
overlooked that `0 * inf` is `nan`, which was a reachable scoring path
if an error rate was reported as `1.0` (since we actually score using
$\sum -\ln(1 - e)$ and normalise this with $e = 1$ to $\infty$) on a
single-qubit node but didn't use any 1q operations on it.

* Fix degeneracy in test

(cherry picked from commit 0b2cdf2b6)

Co-authored-by: Jake Lishman <jake.lishman@ibm.com>

Coverage Stats

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

12 existing lines in 2 files now uncovered.

104337 of 118862 relevant lines covered (87.78%)

1009722.64 hits per line