Qiskit / qiskit / 32865258232

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Commit Message

Fix spurious clone on `SparsePauliOp.to_matrix(sparse=False)` (#16828) (#16831)

* Fix spurious clone on `SparsePauliOp.to_matrix(sparse=False)`

We always own the array; there was never a need to clone out to Python
space.  The actual performance improvement varies a lot depending on the
workload, the parallelism in the algorithm, and performance of the
memory allocator.  The clone was always done single-threaded previously,
so speedups in excess of 2x are quite reasonable.

* Reframe as bugfix

This isn't a longstanding issue; it was introduced accidentally in the
v2.5 cycle[^1].

[^1]: 230a09281b: Add `PauliProductRotation.matrix` (#15975)

(cherry picked from commit da7fd7f38)

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

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