Knot database including text names - MathOverflow most recent 30 from http://mathoverflow.net 2013-06-19T10:37:53Z http://mathoverflow.net/feeds/question/39916 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/39916/knot-database-including-text-names Knot database including text names qwerty1793 2010-09-24T23:47:00Z 2013-02-28T17:33:53Z <p>Knots such as the 3_1 knot and the 4_1 knot are often referred to as the trefoil and figure-eight knots respectively. There are more obscure names for some of the later ones in the knot tables, for example the 6_1 knot is also know as the stevedore knot. These names are not listed on the online knot database at <a href="http://www.indiana.edu/~knotinfo/" rel="nofollow">http://www.indiana.edu/~knotinfo/</a> are they listed anywhere else?</p> <blockquote> <p>Is there an (online) database of knots that includes their (text) names.</p> </blockquote> http://mathoverflow.net/questions/39916/knot-database-including-text-names/123244#123244 Answer by Neil Hoffman for Knot database including text names Neil Hoffman 2013-02-28T17:33:53Z 2013-02-28T17:33:53Z <p>As the comments suggest, the tables enumerated knots are much larger than any table of "named" knots. So it might be easier to start with the "named" knots and identify them in the table. The snappy software (http://www.math.uic.edu/t3m/SnapPy/index.html) allows you to do this quite easily for hyperbolic knots. Here is a general outline of how to do that. (snappy: "text" are instructions to give snappy comments have a bullet in front of them.)</p> <p>snappy: M = Manifold()</p> <ul> <li>If you have installed plink a window pops up where you can draw your knot</li> </ul> <p>snappy: M.solution_type()</p> <ul> <li>This should be 'all tetrahedra positively oriented' if you have something hyperbolic</li> </ul> <p>snappy: CK = CensusKnots()</p> <ul> <li>This loads the list of knots known to decompose into 8 or fewer tetrahedra </li> </ul> <p>snappy: CK.identify(M)</p> <ul> <li>This will return the name of the manifold in the census you are looking at.</li> </ul> <p>You can also get something similar to work if you want to look at the AlternatingKnotExteriors or NonalternatingKnotExteriors. Unfortunately, the identify function won't work on these list, but you can you can still get something to work.</p> <p>snappy: M = Manifold()</p> <p>snappy: M.solution_type()</p> <ul> <li>Again begin the same way and check that you have a hyperbolic knot that admits a diagram with fewer than 16 crossings.</li> </ul> <p>snappy: volM = M.volume()</p> <p>snappy: for k in AlternatingKnotExteriors():</p> <p>snappy: if k.volume() &lt; volM + .002 and k.volume() > volM - .002:</p> <p>snappy: print k</p> <p>snappy: print k.is_isometric_to(M)</p> <ul> <li>This will give you a good list of what your knot could be. You could also do the same thing for the NonalternatingKnotExteriors(). Finally, the .002 is there to account for any error that might arise computationally. In principle, you could probably choose a number much smaller.</li> </ul>