Improve efficiency of CouplingMap.make_symmetric (backport #9571) #9618
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* Improve efficiency of CouplingMap.make_symmetric Right now the CouplingMap.make_symmetric has a quadratic overhead. It was iterating over a list of each edgess' endpoints in the graph and for each edge it was iterating over the same list again to check whether the reverse edge is present or not. The overhead for this for large coupling maps can be quite large, for example with a 10497 qubit heavy hex coupling map the time it took to run this method as part of SabreLayout's initialization was 10x slower than actually running the pass (a equally sized Bernstein-Vazirani circuit). Instead of doing an O(n) contains check inside the loop this commit updates it to use a set which will be an O(1) lookup. This should address the performance issue with this method. In the future we should leverage the native rustworkx method to do this, which is being added in: Qiskit/rustworkx#814 * Further reduce the overhead by avoiding CouplingMap.add_edge() The CouplingMap add_edge() method has similar overhead to check whether nodes need to be added. However, in the case of make_symmetric we don't need this checking because both endpoints are already in the graph. This commit further improves the performance of the method by just adding the reverse edge directly to the graph via the rustworkx api instead. (cherry picked from commit 5afbb0b)
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jakelishman
approved these changes
Feb 17, 2023
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This is an automatic backport of pull request #9571 done by Mergify.
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