Stop using faer-rs for uc_gate.rs #13956
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This commit stops using faer and ndarray for the uc_gate.rs module and switches to use nalgebra instead. The uc_gate.rs module works all in terms of 2x2 matrices and moving to nalgebra brings the advantage of having everything be fixed size stack allocated for the arrays used. While this code path isn't performance critical this should improve performance, despite the goal here being to remove a dependency on faer. The tradeoff here is that nalgebra doesn't seem to have a general eigensolver natively. There is functionality for this in the nalgebra-lapack crate, but as the name implies this depends on linking against lapack to work. The reason we originally started using faer is because it's pure rust and doesn't complicate our build system. In this specific case this is not a big deal because the matrices we need to compute the eigenvectors and eigenvalues for is a 2x2 so this commit includes a function to compute that directly. This lack of functionality is something to keep in mind for the future if we need this functionality more generally we will have to make a choice between faer and linking against lapack. Part of Qiskit#13665 Co-authored-by: Gadi Aleksandrowicz <[email protected]> Co-authored-by: Alexander Ivrii <[email protected]>
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Pull Request Test Coverage Report for Build 13662732606Details
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| .into_iter() | ||
| .map(|x| x.as_array().to_owned()) | ||
| .map(|x| { | ||
| let res: MatrixView2<Complex64> = x.try_as_matrix().unwrap(); |
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As discussed offline, we should change this to let res: MatrixView2<Complex64, Dyn, Dyn> = x.try_as_matrix().unwrap();, otherwise the conversion fails.
| @@ -286,7 +286,7 @@ def _dec_ucg_help(self): | |||
| This method finds the single qubit gate arising in the decomposition of UCGates given in | |||
| https://arxiv.org/pdf/quant-ph/0410066.pdf. | |||
| """ | |||
| single_qubit_gates = [gate.astype(complex) for gate in self.params] | |||
| single_qubit_gates = [np.asarray(gate, dtype=complex, order="f") for gate in self.params] | |||
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Or does this line make the rust code work without needing the Dyn trait?
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Summary
This commit stops using faer and ndarray for the uc_gate.rs module and switches to use nalgebra instead. The uc_gate.rs module works all in terms of 2x2 matrices and moving to nalgebra brings the advantage of having everything be fixed size stack allocated for the arrays used. While this code path isn't performance critical this should improve performance, despite the goal here being to remove a dependency on faer.
The tradeoff here is that nalgebra doesn't seem to have a general eigensolver natively. There is functionality for this in the nalgebra-lapack crate, but as the name implies this depends on linking against lapack to work. The reason we originally started using faer is because it's pure rust and doesn't complicate our build system. In this specific case this is not a big deal because the matrices we need to compute the eigenvectors and eigenvalues for is a 2x2 so this commit includes a function to compute that directly. This lack of functionality is something to keep in mind for the future if we need this functionality more generally we will have to make a choice between faer and linking against lapack.
Details and comments
Part of #13665
Co-authored-by: Gadi Aleksandrowicz [email protected]
Co-authored-by: Alexander Ivrii [email protected]