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.canonical_label() errors on bipartite graphs when partition= is not specified #38832

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maxale opened this issue Oct 20, 2024 · 1 comment · Fixed by #38842
Closed
2 tasks done

.canonical_label() errors on bipartite graphs when partition= is not specified #38832

maxale opened this issue Oct 20, 2024 · 1 comment · Fixed by #38842
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c: graph theory t: bug

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@maxale
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maxale commented Oct 20, 2024 •
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Steps To Reproduce

sage: G = BipartiteGraph( matrix([[1,1],[1,1]]) )
sage: G.canonical_label()
[...]
TypeError: itertools.chain() argument after * must be an iterable, not NoneType

Expected Behavior

Should work.

Actual Behavior

TypeError

Additional Information

Specifying partition= eliminates the issue:

sage: G.canonical_label(partition=G.bipartition())
Bipartite graph on 4 vertices

Perhaps, G.bipartition() should be the default value for partition= in the case of bipartite graphs.

Environment

  • OS: Ubuntu 24.04.1 LTS
  • Sage Version: 10.5.beta6

Checklist

  • I have searched the existing issues for a bug report that matches the one I want to file, without success.
  • I have read the documentation and troubleshoot guide
@maxale maxale added the t: bug label Oct 20, 2024
@maxale maxale changed the title .canonical_label() is broken for bipartite graphs .canonical_label() errors on bipartite graphs when partition= is not specified Oct 20, 2024
dcoudert added a commit to dcoudert/sage that referenced this issue Oct 23, 2024
@dcoudert
fix issue sagemath#38832
326c577
@dcoudert dcoudert mentioned this issue Oct 23, 2024
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@dcoudert
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good catch. I pushed a possible fix in #38842.

vbraun pushed a commit to vbraun/sage that referenced this issue Oct 26, 2024
sagemathgh-38842: fix issue sagemath#38832 about canonical_label in…
6f45442 
… bipartite graphs

    
Fixes sagemath#38832.

We fix call to `canonical_label` on `BipartiteGraph` when parameter
`partition` is `None`.
```py
sage: G = BipartiteGraph(matrix([[1, 1], [1, 1]]))
sage: C = G.canonical_label()
sage: C.left, C.right
({0, 1}, {2, 3})
```


### 📝 Checklist

<!-- Put an `x` in all the boxes that apply. -->

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [x] I have created tests covering the changes.
- [x] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

<!-- List all open PRs that this PR logically depends on. For example,
-->
<!-- - sagemath#12345: short description why this is a dependency -->
<!-- - sagemath#34567: ... -->
    
URL: sagemath#38842
Reported by: David Coudert
Reviewer(s): Kwankyu Lee
@vbraun vbraun closed this as completed in f2780d8 Nov 3, 2024
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fix issue #38832 about canonical_label in bipartite graphs dcoudert/sage
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@maxale @dcoudert