Qiskit / qiskit / 24511728189

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Commit Message

Switch TwoQubitWeylDecomposition to use nalgebra internally (#15960)

* Switch TwoQubitWeylDecomposition to use nalgebra internally

This is the next step towards using nalgebra as the matrix container
type in the two qubit decomposers. This commit updates the
weyl_decomposition module to leverage nalgebra to contain all the 1 and
2 qubit unitary matrices used during the decomposition.

This has the same advantages outlined in the previous patches in this
series, mainly that the nalgebra types used are fixed size and stack
allocated which provides advantages for these small matrices.

This commit also undoes some of the temporary work in the previous
commit that was adding a dual nalgebra path for some utility functions
in the two qubit basis decomposer. Now that both the weyl decomposition
and the two qubit basis decomposer are based on storage types in
nalgebra a lot of these aren't needed anymore and can be removed.

* Use nalgebra determinant instead of faer's

* Cleanup internal helper functions

This commit cleans up the internal helper functions added for working
with nalgebra and converting between the other libraries used. These
functions were not intended to be used outside of the specific cases
as in this PR as they make assumptions about matrix shape and/or layout.
This adjusts the visibility of the functions and adds docstrings around
the assumptions they make in case someone tries to use them outside of
in this PR.

* Reuse identity in decompose_two_qubit_product_gate()

Coverage Stats

230 of 256 new or added lines in 5 files covered. (89.84%)

22 existing lines in 7 files now uncovered.

104575 of 119524 relevant lines covered (87.49%)

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