Re: CostOfPath
- To: mathgroup at smc.vnet.net
- Subject: [mg62491] Re: [mg62481] CostOfPath
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Sat, 26 Nov 2005 02:46:40 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
On 25 Nov 2005, at 16:25, Bart De Vylder wrote:
>
>
> Can anybody explain the following?
>
> << DiscreteMath`Combinatorica`;
> gr = FromOrderedPairs[{{2, 1}}];
> CostOfPath[gr, {2, 1}]
>
> Out[]= ° (infinity)
>
> I would expect 1 as answer.
>
CostOfPath seems to give correct answers only for undirected graphs.
Thus
gr = FromOrderedPairs[{{2, 1}},Type->Undirected];
CostOfPath[gr, {2, 1}]
1
It will give the same answer in the case of a "bi-directed" graph, e.g.
hr = FromOrderedPairs[{{2, 1},{1,2}}];
CostOfPath[hr, {2, 1}]
1
It seems that edges with only one direction are counted as
"impassable", and hence the answer Infinity.
I don't have my copy of Pemmaraju and Skiena book within reach (it is
currently on a different continent and my reach is not that long ;-))
so I can't guarantee that my explanation is completely correct, but I
think it is not far off.
Andrzej Kozlowski