see my comment on trac #9136 for a complete example. On Nov 24, 11:17 pm, Dima Pasechnik <dimp...@gmail.com> wrote: > Are you reinventing the wheel? :-) > > One should be able to import into Sage any graph that GAP can make > using its package Grape. Grape is essentially doing what you seem to > be doing: takes a permutation group and constructs a graph invariant > under it. > E.g. > gap> LoadPackage("grape"); > gap> G:=NullGraph(DihedralGroup(IsPermGroup,20),10); > rec( isGraph := true, order := 10, > group := Group([ (1,2,3,4,5,6,7,8,9,10), (2,10)(3,9)(4,8)(5,7) ]), > schreierVector := [ -1, 1, 1, 1, 1, 1, 2, 2, 2, 2 ], adjacencies := > [ [ ] ], > representatives := [ 1 ], isSimple := true ) > gap> AddEdgeOrbit(G,[1,2]); > gap> G; > rec( isGraph := true, order := 10, > group := Group([ (1,2,3,4,5,6,7,8,9,10), (2,10)(3,9)(4,8)(5,7) ]), > schreierVector := [ -1, 1, 1, 1, 1, 1, 2, 2, 2, 2 ], > adjacencies := [ [ 2, 10 ] ], representatives := [ 1 ], isSimple := > true ) > gap> AddEdgeOrbit(G,[1,3]); > gap> G; > rec( isGraph := true, order := 10, > group := Group([ (1,2,3,4,5,6,7,8,9,10), (2,10)(3,9)(4,8)(5,7) ]), > schreierVector := [ -1, 1, 1, 1, 1, 1, 2, 2, 2, 2 ], > adjacencies := [ [ 2, 3, 9, 10 ] ], representatives := [ 1 ], > isSimple := true ) > > we thus constructed a vertex-transitive degree 4 graph on 10 vertices, > with the dihedral group of order 20 as an automorphism group. > > Unfortunately Sage does not handle graphs that are specified by edge > orbits, last time I checked. > > Dima > > On Nov 24, 6:28 pm, Nathann Cohen <nathann.co...@gmail.com> wrote: > > > > > Hello everybody !!! > > > Working on Minh's patches for new graph generators, I had to create > > Dihedral groups, which took me more than.... half a second. Which mean > > it can be improved :-D > > > More seriously, the way I found to create them was to use the > > DihedralGroup() method, which one does not have to import first. It is > > nice, but it also means that I still do not know how to list all the > > group Sage knows how to build.. Well, for graphs and words we already > > have something nice : > > > We create a graph/word with the Graph/Word constructor, which appears > > in the namespace. If we omit the upper case, we have a graphs/words > > object, whose methods are the different constructors of graphs/words. > > So graphs.<tab>/words.<tab> gives you the list of all constructors, > > which is the best way to find one quickly. What about doing the same > > with groups, or finding a common way to organise this ? :-) > > > Nathann > > > P.S. (if anybody has any smart idea about how to deal with classes > > having *far too many* different methods, I am also very interested. > > Something will have to be decided soon for the Graph class anyway... > > :-/ )
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