Opened 5 years ago

Closed 5 years ago

#25159 closed defect (fixed)

Fix connected sum of knots

Reported by: mmarco Owned by:
Priority: major Milestone: sage-8.3
Component: algebraic topology Keywords: connected_sum, knot
Cc: slelievre Merged in:
Authors: Miguel Marco Reviewers: Samuel Lelièvre
Report Upstream: N/A Work issues:
Branch: d8cb5c1 (Commits, GitHub, GitLab) Commit: d8cb5c1fd9b25a4b9d5c089dddca1c9db4010245
Dependencies: Stopgaps:

Status badges

Description (last modified by slelievre)

As pointed in https://ask.sagemath.org/question/41985/connected-sum-of-knots/ the connected sum of knots is not correctly computed.

Before this ticket, the connected sum of the trefoil knot with itself is incorrect, and computing the connected sum with a third trefoil knot fails:

sage: c = Knot.connected_sum
sage: B = BraidGroup(2)
sage: t = Knot(B([1, 1, 1])); t
Knot represented by 3 crossings
sage: tt = c(t, t); tt
Knot represented by 7 crossings
sage: tt_t = c(tt, t); tt_t
Traceback (most recent call last)
...
ValueError: the input has more than 1 connected component
sage: t_tt = c(t, tt); t_tt
Traceback (most recent call last)
...
ValueError: generators not in the group

After this ticket, these problems are fixed:

sage: c = Knot.connected_sum
sage: B = BraidGroup(2)
sage: t = Knot(B([1, 1, 1])); t
Knot represented by 3 crossings
sage: tt = c(t, t); tt
Knot represented by 6 crossings
sage: t_tt = c(t, tt); t_tt
Knot represented by 9 crossings
sage: tt_t = c(tt, t); tt_t
Knot represented by 9 crossings
sage: t_tt = tt_t
True

Change History (10)

comment:1 Changed 5 years ago by mmarco

Branch: u/mmarco/connected_sum_of_knots_is_incorrect

comment:2 Changed 5 years ago by mmarco

Commit: d8cb5c1fd9b25a4b9d5c089dddca1c9db4010245
Status: newneeds_review

New commits:

d8cb5c1Compute the connected sum from the oriented gauss code

comment:3 Changed 5 years ago by slelievre

Keywords: connected_sum knot added
Status: needs_reviewpositive_review

This makes connected_sum correct (and a little faster it seems!).

comment:4 Changed 5 years ago by slelievre

Description: modified (diff)
Summary: Connected sum of knots is incorrectFix connected sum of knots

comment:5 Changed 5 years ago by slelievre

Description: modified (diff)

comment:6 Changed 5 years ago by chapoton

Reviewers: ​Samuel Lelièvre

comment:7 Changed 5 years ago by davidloeffler

Milestone: sage-8.2sage-8.3

comment:8 Changed 5 years ago by mmarco

Why hasn't this been merged?

comment:9 Changed 5 years ago by vbraun

Reviewers: ​Samuel LelièvreSamuel Lelièvre

There was an invisible unicode in the reviewer name

comment:10 Changed 5 years ago by vbraun

Branch: u/mmarco/connected_sum_of_knots_is_incorrectd8cb5c1fd9b25a4b9d5c089dddca1c9db4010245
Resolution: fixed
Status: positive_reviewclosed
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