BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Jim Cruickshank (NUI Galway) DTSTART:20200430T140000Z DTEND:20200430T150000Z DTSTAMP:20260423T035608Z UID:VSAMRT/3 DESCRIPTION:Title: S urface graphs\, gain sparsity and some applications in discrete geometry\nby Jim Cruickshank (NUI Galway) as part of Virtual seminar on algebrai c matroids and rigidity theory\n\n\nAbstract\nA collection of line segment s in the plane forms a 2-contact system if the segments have pairwise disj oint interiors and no pair of segments have an endpoint in common. Thomass en has shown that a graph is the intersection graph of such a 2-contact sy stem if and only if it is a subgraph of a planar Laman graph. Also Haas\, Orden\, Rote\, Francisco\, Servatius\, Servatius\, Souvain\, Streinu and W hiteley have shown that a graph admits a plane embedding as a pointed pseu dotriangulation if and only if is a planar Laman graph. I will discuss rec ent work on symmetric versions of these results. In this context the graph s that arise are naturally embedded in the orbifold associated to the acti on of the symmetry group\, and the appropriate sparsity conditions are gai n sparsity conditions. Our main tools are new topological inductive constr uctions for the appropriate classes of surface graphs. All of the work pre sented here is joint with Bernd Schulze.\n LOCATION:https://researchseminars.org/talk/VSAMRT/3/ END:VEVENT END:VCALENDAR