Timeline for Proving non-convexity of a set of lattice points
Current License: CC BY-SA 3.0
9 events
| when toggle format | what | by | license | comment | |
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| Aug 3, 2013 at 16:43 | history | edited | Dima Pasechnik | CC BY-SA 3.0 |
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| Aug 3, 2013 at 16:34 | comment | added | Dima Pasechnik | e.g. here is a toy example using Sage: l=LatticePolytope([[2,0],[0,2],[1,1]],compute_vertices=True); l; l.npoints() it will output A lattice polytope: 1-dimensional, 2 vertices. 3 | |
| Aug 3, 2013 at 16:20 | comment | added | Dima Pasechnik | one can use Sage to compute the convex hull. It can even be done online, without installing Sage on a local machine, using e.g. cloud.sagemath.org | |
| Aug 3, 2013 at 14:28 | vote | accept | simpleperson | ||
| Aug 3, 2013 at 14:27 | vote | accept | simpleperson | ||
| Aug 3, 2013 at 14:28 | |||||
| Aug 3, 2013 at 13:53 | comment | added | simpleperson | @Joseph O'Rourke -- I looked a little at CGAL's manual which gave an idea. I want to take any two points x and y of S and show that any lattice point on the line xy is in S. This is a horrid, worse than |S| choose 2 algorithm but might be a quick enough (albeit dirty) way to just check (non)convexity. Is there any problem with that? | |
| Aug 3, 2013 at 13:03 | comment | added | Joseph O'Rourke | Two primary options for computing hulls in higher dimensions are Qhull and CGAL. Both require considerable study before you can use them. | |
| Aug 3, 2013 at 12:48 | comment | added | simpleperson | Hi (and thanks) -- I was afraid of that answer. Actually, how does one go about actually obtaining a description of the convex hull of S? | |
| Aug 3, 2013 at 11:58 | history | answered | Dima Pasechnik | CC BY-SA 3.0 |