Lukas Lewark
FoamHo, an sl3-homology calculator

sl3-homology of the (6,5)-torus knot:

q \ t012345678910111213141516171819
-78 (6,5)-torus knot
1
-761
-74
1
1
-722
1
1
1
1
-7012
1
2
1
-68121
1
3
2
-662
1
3
4
1
1
1
-6412
1
4
2
3
1
1
-6212
2
5
1
1
1
1
1
1
-6011
1
5
1
1
1
3
2
-58
1
43
2
3
1
1
-562
1
4
1
1
1
2
3
-541311
2
31
-5221
1
3
1
1
-5011
1
23 red: 2-torsion, green: 3-torsion, yellow: 5-torsion
-4811
1
21
-46
1
21
-4411
-4211
-401
-381

Computed in six minutes on an AMD Opteron, 2.2 GHz, using 80 MB of RAM.
Diagram drawn with the KnotTheory` package for Mathematica.

For details, see my paper sl3-foam homology calculations: arxiv.org/abs/1212.2553.

Download

foamho-1.1.tar.gz containing the source code and installation instructions in the README file. To compile, you will need at least the MPIR library, which is used for rational and integral arbitrary precision arithmetic. Optionally, the PARI library is used to obtain Smith normal forms (not necessary if you only want to compute rational homology), and the procps library to display memory consumption (on Linux only).

foamho.exe, a Windows executable compiled using MinGW running on Windows XP. No additional libraries necessary, but it is not guaranteed to work on your system.

foamho, a Linux executable. No additional libraries are necessary, but it is not guaranteed to work on your system.

Old version (1.0): foamho-1.0.tar.gz, foamho.exe, foamho.

Some results

Let us list all knots with up to twelve crossings for which the sl3- and sl2-concordance invariants differ (click on the knot to see its diagram on the Knot Atlas or on KnotInfo). In our normalization, both invariants have a value of 2 for the right-handed trefoil knot.

Knot1012511n82 12n195 12n235 12n238 12n340 12n346 12n571 12n673 12n723 12n821
s222-2-4-202-2-22-2
s311-1-3-111-1-11-1
Last update: 13 November 2026.