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OrderedSetPartitions() fails for the empty set #35654

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2 tasks done
maxale opened this issue May 19, 2023 · 0 comments · Fixed by #35700
Closed
2 tasks done

OrderedSetPartitions() fails for the empty set #35654

maxale opened this issue May 19, 2023 · 0 comments · Fixed by #35700
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t: bug
Milestone
sage-10.1

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@maxale
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maxale commented May 19, 2023 •
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Is there an existing issue for this?

  • I have searched the existing issues for a bug report that matches the one I want to file, without success.

Did you read the documentation and troubleshoot guide?

  • I have read the documentation and troubleshoot guide

Environment

- **OS**: Ubuntu 22.04
- **Sage Version**: 9.8.rc0

Steps To Reproduce

OrderedSetPartitions() well supports parts of zero size.
For example, OrderedSetPartitions({1,2},[1,1,0,0]).list() gives:

[[{1}, {2}, {}, {}], [{2}, {1}, {}, {}]]

However, it does not work when the input set is empty.

Expected Behavior

For example, calling OrderedSetPartitions(set(),[0,0,0]).list() should produce the partition of the empty set into empty (sub)sets:

[[{}, {}, {}]]

Actual Behavior

However, at the moment it results in the error:

IndexError: list index out of range

Additional Information

No response
@maxale maxale added the t: bug label May 19, 2023
@videlec videlec mentioned this issue May 31, 2023
Merged
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vbraun pushed a commit that referenced this issue Jun 3, 2023
gh-35700: Fix corner case of ordered set partitions iteration
bc6d3bd 
    
### 📚 Description

The function `multiset_permutation_next_lex` was wrong on empty input
and is fixed in this PR.

Fixes #35654

### 📝 Checklist

- [x] The title is concise, informative, and self-explanatory.
- [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.
- [ ] I have updated the documentation accordingly.
    
URL: #35700
Reported by: Vincent Delecroix
Reviewer(s): Frédéric Chapoton
@mkoeppe mkoeppe added this to the sage-10.1 milestone Jun 3, 2023
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Fix corner case of ordered set partitions iteration videlec/sage
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@maxale @mkoeppe