Opened 11 months ago

Last modified 2 months ago

#33211 new defect

HOMFLY polynomial hangs on certain links

Reported by: Pavel Galashin Owned by:
Priority: major Milestone: sage-9.8
Component: algebraic topology Keywords: homfly
Cc: Miguel Marco, Samuel Lelièvre Merged in:
Authors: Reviewers:
Report Upstream: N/A Work issues:
Branch: Commit:
Dependencies: Stopgaps:

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Description (last modified by Samuel Lelièvre)

In the two below examples, the only difference is that -5 and -3 are switched. The first HOMFLY polynomial is computed very fast, while for the second one Sage just dies and I have to restart it. I tried lots of bigger and more complicated links and HOMFLY always works fine for them, but for some reason the second braid below is problematic.

sage: Br = BraidGroup(7)
sage: L1 = Link(Br([3, 4, 5, 6, 2, 3, 1, 2, 4, 5, 3, 4, -5, -4, -5, -3, -2, -4]))  # works super fast
sage: print(L1.homfly_polynomial())
sage: L2 = Link(Br([3, 4, 5, 6, 2, 3, 1, 2, 4, 5, 3, 4, -5, -4, -3, -5, -2, -4]))  # hangs forever
sage: print(L2.homfly_polynomial())
1 - M^-2 + L^-2 - 2*L^-2*M^-2 - L^-4*M^-2
ERROR: 'killed'

Communication with the Sage server is failing.

Change History (6)

comment:1 Changed 11 months ago by Samuel Lelièvre

Cc: Miguel Marco Samuel Lelièvre added
Component: PLEASE CHANGEalgebraic topology
Description: modified (diff)
Keywords: homfly added
Type: PLEASE CHANGEdefect

comment:2 Changed 10 months ago by Miguel Marco

I can't reproduce the error.

What version of Sage and OS are you using?

comment:3 Changed 10 months ago by Pavel Galashin

I tried it in CoCalc? (Sage ver. 9.4, Ubuntu 20.04) and in my local Docker container (Sage ver. 9.2, Mac OS Big Sur), and see this error in both cases. I also now tried https://sagecell.sagemath.org/ where both links worked fine for some reason.

comment:4 Changed 10 months ago by Samuel Lelièvre

Since SnapPy is installed on SageCell, perhaps it helps computing HOMFLY there?

comment:5 Changed 7 months ago by Matthias Köppe

Milestone: sage-9.6sage-9.7

comment:6 Changed 2 months ago by Matthias Köppe

Milestone: sage-9.7sage-9.8
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