Re: subgraph error (errata)
- To: mathgroup at smc.vnet.net
- Subject: [mg125916] Re: subgraph error (errata)
- From: David Bailey <dave at removedbailey.co.uk>
- Date: Sat, 7 Apr 2012 05:54:35 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <jlh0l6$t5s$1@smc.vnet.net>
On 04/04/2012 09:27, dan jack wrote:
> I write an errata for the previous message:
>
> I obtain the error in this case:
>
> gg = Graph[{11 -> 2, 11 -> 3, 4 -> 11, 5-> 11, 11 -> 11}]
> Subgraph[gg, 1 ->_ ]
>
> Join::headsd: Expression {11,2} at position 1 is expected to have head
> List for all subexpressions through level 11.
> DeleteDuplicates::list: List expected at position 1 in
> DeleteDuplicates[Join[{11,2},{11,3},11]].
>
> but not in this case:
> gg = Graph[{1 -> 2, 1 -> 3, 4 -> 1, 5-> 1, 1-> 1}]
>
> so it seems that the only difference is the vertex number: 1 works but
> 11 do not works ...very strange.
>
> Obviously the arrows are the correct Directed Edges (ESC de ESC)...
>
> any help or solidarity comment is appreciated :-)
>
I think when you specify a subgraph using a pattern, you have to specify
edges using the DirectedEdge construct. This actually prints rather like
-> but there is a little blob at the left end (confusing eh?)
Thus the correct syntax is:
gr = Graph[{1 -> 2, 1 -> 3, 4 -> 1, 5 -> 1, 1 -> 1}]
Subgraph[gr, DirectedEdge[1, _]]
David Bailey
http://www.dbaileyconsultancy.co.uk