Opened 8 months ago

Closed 8 months ago

# bug in 'tedder' modular decomposition

Reported by: Owned by: dimpase major sage-duplicate/invalid/wontfix graph theory dcoudert Dima Pasechnik N/A

in #26496 a simple implementation of modular decomposition was added, but no explicit example showing that 'tedder' is buggy. (PS - but see #25872) An example is now posted on sage-devel:

```sage:     d = {
....:         1  :  [2, 3, 4],
....:         2  :  [1, 3, 4],
....:         3  :  [1, 2, 4],
....:         4  :  [1, 2, 3, 5],
....:         5  :  [10, 4, 6, 7, 8, 9],
....:         6  :  [5, 7],
....:         7  :  [5, 6, 8, 9],
....:         8  :  [5, 7, 9],
....:         9  :  [10, 5, 7, 8],
....:         10  :  [5, 9]
....:     }
....:     g = Graph(d)
sage: g.modular_decomposition(algorithm='tedder') # --- wrong ?!
(PRIME, [5, (SERIES, [9, (PARALLEL, [10, 7, 8, 6])]), 4, (SERIES, [3, 2, 1])])
sage: g.modular_decomposition(algorithm='habib')
(PRIME, [5, 4, (SERIES, [1, 2, 3]), (PRIME, [9, 7, 6, 8, 10])])
```

### comment:1 Changed 8 months ago by dimpase

Description: modified (diff)

### comment:2 Changed 8 months ago by dcoudert

Since we remove algorithm `'tedder'` in #25872, we can move this ticket to `wontfix`.

### comment:3 Changed 8 months ago by dimpase

Milestone: sage-9.7 → sage-duplicate/invalid/wontfix new → needs_review

will be fixed in #25872

### comment:4 Changed 8 months ago by dimpase

Reviewers: → Dima Pasechnik needs_review → positive_review

### comment:5 Changed 8 months ago by chapoton

Resolution: → duplicate positive_review → closed
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