Qiskit / qiskit / 12677480117

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Commit Message

Fix phase of `pauli_list.insert(..., qubit=True)` for length-1 `pauli_list` (#13624)

* switch order of if-clauses

`len(value) == 1` is the simplest case, and is also the case where the problematic clause `len(value) == size` fails.

This commit switches the order, so we check for `len(value) == 1` first.

This ensures that when the `len(value) == size` clause runs, we know that `size != 1`, avoiding the bug in #13623.

* add test

* Simplify `value.phase` broadcasting

Here, `phase` should be a 1D array. `np.vstack()` docs say explicitly output will be at least 2D, so we should not use that to create `phase`.

The intent of using `np.vstack()` was essentially to broadcast `phase` to properly add to `self.phase`. But, this happens automatically and correctly if we just add as-is. So this commit simplifies the code accordingly.

* Verify that `phase` is 1D in `from_symplectic()`

Verifying the input arg `phase`, since otherwise `from_symplectic()` will silently create PauliLists with malformed `phase` attributes (i.e. not 1D).

Zero-dimensional is OK (e.g. `phase` defaults to `0`) since that can broadcast per the shape of the `z` and `x` arrays.

* remove vestigial line

* lint

* release note

* Update releasenotes/notes/fix-paulilist-length1-phase-688d0e3a64ec9a9f.yaml

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

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

Run Details

6 of 7 new or added lines in 1 file covered. (85.71%)

6 existing lines in 3 files now uncovered.

79443 of 89321 relevant lines covered (88.94%)

367336.76 hits per line