Fix sparse heuristic not applied to diagonal blocks in stochastic_block_model#8557
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dean985 wants to merge 1 commit intonetworkx:mainfrom
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Fix sparse heuristic not applied to diagonal blocks in stochastic_block_model#8557dean985 wants to merge 1 commit intonetworkx:mainfrom
dean985 wants to merge 1 commit intonetworkx:mainfrom
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…ck_model The diagonal block (i==j) case consumed the edges iterator before the sparse/dense branching logic, so the sparse heuristic was never used for diagonal blocks. Remove the premature edge addition so diagonal blocks flow into the same sparse/dense logic as off-diagonal blocks.
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rossbar
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Mar 9, 2026
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Presumably the change in results is a result of the random state changing due to the removal of special handling of the i==j case. I think this is fine, though it's worth noting that this change will have an impact even outside of the sparse codepath as a result. Again this is probably fine, but just pointing it out so folks more familiar with the stochastic block model can take a look and double check!
rossbar
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Mar 9, 2026
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Also - it'd be nice to have a test that illustrates the original issue in the sparse branch (presumably that the sparsity algorithm wasn't being applied to the diagonal blocks) and illustrates the fix.
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fixes #8536
Summary
i==j) case instochastic_block_modelconsumed theedgesiterator before the sparse/dense branching logic, so the sparse heuristic was never used for diagonal blocks.Test plan
test_community.pypass (22/22)test_stochastic_block_modelexpected edge count to match the corrected sparse heuristic behavior