[GAP Forum] labels in xgap

[Russ Woodroofe]

	Dear William,
	Here's a short sample, which relabels an inserted Sylow 2-subgroup of S_4 as P_2:

G:=SymmetricGroup(4);
Sym( [ 1 .. 4 ] )

L:=GraphicSubgroupLattice(G);
<graphic subgroup lattice "GraphicSubgroupLattice">

H:=SylowSubgroup(G,2);
Group([ (1,2), (3,4), (1,3)(2,4) ])

ret:=InsertVertex(L, H);
[ <vertex of graphic graph, label: "2", Serial:6>, true ]

Relabel(L, ret[1], "P_2");

	I think you should be able to work this around to your own situation.

	The subgroup lattice library seems to internally use Relabel to label the vertices, and I don't see it pulling information from the subgroup itself -- though I didn't look terribly carefully.  But the above sample should make relabeling things under program control not too inconvenient...

	Sincerely,

						--Russ Woodroofe

PS:  If you're using a Mac, let me recommend my native "Gap.app" front-end, which is a workalike for xgap.  Available at
http://cocoagap.sourceforge.net/


On Mar 22, 2011, at 4:52 PM, William DeMeo wrote:

> Dear Forum,
> 
> Is it possible to change the labels of vertices in a subgroup lattice
> drawn by XGAP using the command line (rather than using "Change
> Labels" in the "Poset" menu)?
> 
> Here's an example:
> 
> L:=GraphicSubgroupLattice(G1xG2);
> 
> InsertVertex(L, HxK);
> # insert here some command to change vertex label to "HxK"
> 
> InsertVertex(L, HxG2);
> # insert here some command to change vertex label to "HxG2"
> 
> InsertVertex(L, G1xK);
> # insert here some command to change vertex label to "G1xK"
> 
> intsubs:=IntermediateSubgroups(G1xG2, HxK);
> for j in [1..Size(intsubs.subgroups)] do
>   InsertVertex(L,intsubs.subgroups[j]);
> od;
> 
> After I execute the loop, it's hard to tell what's what unless I have
> already changed some labels with names like "HxK", "HxG2", etc. before
> the loop.  Using the menu to do this each time is a bit tedious.
> 
> (Also, it would be nice if I could use some stored list of short names
> -- maybe acquired from StructureDescription -- to insert labels inside
> the loop as well, but maybe that's asking too much... and perhaps such
> a labelling would be even harder to interpret than the default number
> labels; e.g. when the names are not unique.)
> 
> Thanks in advance for any tips!
> 
> -William
> 
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