fix edge coloring bug in plot_coupling_map

[kevinsung]

Summary

Fixes #12354 .

Details and comments

The conversion to an undirected graph changes the edge ordering, causing it not to match the color ordering. This change uses a dictionary to recover the correct ordering.

[qiskit-bot]

One or more of the the following people are requested to review this:

• @enavarro51
• @Qiskit/terra-core

[coveralls]

Pull Request Test Coverage Report for Build 9021050859

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This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 0 of 2 (0.0%) changed or added relevant lines in 1 file are covered.
• 10 unchanged lines in 5 files lost coverage.
• Overall coverage increased (+0.01%) to 89.649%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit/visualization/gate_map.py	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/expr.rs	1	94.03%
qiskit/visualization/gate_map.py	1	6.98%
crates/qasm2/src/lex.rs	2	93.13%
qiskit/transpiler/passes/synthesis/unitary_synthesis.py	3	88.02%
qiskit/quantum_info/states/stabilizerstate.py	3	93.49%

Totals
Change from base Build 8999743027:	0.01%
Covered Lines:	62211
Relevant Lines:	69394

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💛 - Coveralls

[mtreinish]

This looks good to me. It relies on the internal implementation detail about how the to_undirected method works in rustworkx (internally iterates over the edges in id order). But while undocumented it is unlikely to ever change so it's fine. The only thing is could you add a release note to document this fix?

[kevinsung]

This looks good to me. It relies on the internal implementation detail about how the to_undirected method works in rustworkx (internally iterates over the edges in id order). But while undocumented it is unlikely to ever change so it's fine. The only thing is could you add a release note to document this fix?

Sorry, I don't understand. I think the iteration order doesn't matter because line_color_map is a dictionary.

[mtreinish]

Sorry that was mistake I misread the edge_list() method as edge_indices() somehow and thought you were just doing a mapping of explicit index to the index in a list. Which would work (and actually would be slightly faster) but would depend on the internal behavior. What you have here is more robust and a better approach.