Add LookaheadSwap condition to prevent hangs #4112
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so cases that previously hung now raise error, or they actually move forward? |
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The example in the issue now completes (its in the added test). |
faisaldebouni
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Aug 5, 2020
* Add LookaheadSwap logging, document step['swaps_added']. * Ensure candidate swap improves at least one metric. * Remove redundant edge counting for symmetric 2q gates. Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
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Summary
Resolves #2171 by adding a check that a candidate swap is able to either map at least one gate or improve the score of the resulting layout before it is considered. A follow up PR is needed to generalize this approach. (Ideally, this should be incorporated into
_score_step, and we should make sure this does not limit our ability to find a long-range improvement that requires first passing through short-term loss).Additionally, adds some debug level logging and removes duplicate edges for symmetric 2q gates from the list of available swaps.
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