Aaah, good catch. There is an "optimization" in igraph_is_separator(): when the vertex sequence that you pass to the graph has more than n-1 unique vertices, it returns true because for some reason it considers a graph with a single vertex disconnected. However, this is inconsistent with what igraph_is_connected() says for graphs with a single vertex only. (And it is also inconsistent for graphs with no vertices at all). I'll fix it. T.
On Wed, Aug 31, 2016 at 4:31 PM, Szabolcs Horvát <[email protected]> wrote: > It would seem that a single node graph is not considered connected by this > function. However, igraph_is_connected does consider a single-node graph > connected (imo correctly), so this would be an inconsistency. > > On 31 August 2016 at 16:12, Szabolcs Horvát <[email protected]> wrote: >> >> Hello, >> >> What is the reasoning for the following behaviours of the is_separator() >> function? >> >> http://igraph.org/c/doc/igraph-Separators.html#igraph_is_separator >> >> This makes sense to me: >> >> graph: 1 - 2 - 3 >> vertex set: {2} >> result: true >> >> Removing 2 does disconnect the graph. >> >> graph: 1 - 2 - 3 >> vertex set: {3} >> result: false >> >> Removing 3 doesn't. >> >> graph: 1 - 2 - 3 - 4 >> vertex set: {1, 4} >> result: false >> >> Removing 1 and 4 doesn't. >> >> graph: 1 - 2 >> vertex set: {} >> result: false >> >> Removing nothing does not disconnect it. >> >> graph: 1, 2 (disconnected) >> vertex set: {} >> result: true >> >> Makes sense because the graph was already disconnected >> >> >> But I am puzzled by these: >> >> graph: 1 - 2 - 3 >> vertex set: {1,3} >> result: true >> >> graph: 1 - 2 >> vertex set: {1} >> result: true >> >> Removing these does not disconnect the graph, it merely leaves a 1-node >> graph behind. >> >> Why is the result then true? >> >> >> Szabolcs >> >> >> >> > > > _______________________________________________ > igraph-help mailing list > [email protected] > https://lists.nongnu.org/mailman/listinfo/igraph-help > _______________________________________________ igraph-help mailing list [email protected] https://lists.nongnu.org/mailman/listinfo/igraph-help
