## Re: [jgrapht-users] BlockCutpointGraph - getBlock

 Re: [jgrapht-users] BlockCutpointGraph - getBlock From: H.N. de Ridder - 2013-11-30 08:02:32 ```On Fri, Nov 29, 2013 at 04:06:48PM +0100, Carl Witt wrote: Hello Carl, > I have a question concerning the public UndirectedGraph > ,E > >; > *getBlock*(V > ; vertex) > method. > The documentation says > > Returns the vertex if vertex is a cutpoint, and otherwise returns > the block (biconnected component) containing the vertex. > > But the example given in the introductory section of the > BlockCutpointGraph class clarifies that the a vertex can be part of more > than one block > > Is the documentation of the getBlock method being imprecise (should it > read "returns a block containing the vertex") or is the underlying > definition of a block not the one from Mathworld? I don't know how it could happen, but cutpoint is one of the very few concepts in graph theory that have only one meaning. A cutpoint is indeed in more than one block (x is a cutpoint iff x is in more than one block), but non-cutpoints are in precisely one block. So getBlock(x) returns x if x is a cutpoint and the unique block that contains x, otherwise. Hope this clears things up, Ernst -- Information System on Graph Classes and their Inclusions (ISGCI) http://www.graphclasses.org ```

 [jgrapht-users] BlockCutpointGraph - getBlock From: Carl Witt - 2013-11-29 15:41:31 Attachments: Message as HTML ```Hello JGraphT Users, I have a question concerning the public UndirectedGraph ,E >; *getBlock*(V ; vertex) method. The documentation says Returns the vertex if vertex is a cutpoint, and otherwise returns the block (biconnected component) containing the vertex. But the example given in the introductory section of the BlockCutpointGraph class clarifies that the a vertex can be part of more than one block http://mathworld.wolfram.com/Block.html Is the documentation of the getBlock method being imprecise (should it read "returns a block containing the vertex") or is the underlying definition of a block not the one from Mathworld? Best regards, Carl Witt ```
 Re: [jgrapht-users] BlockCutpointGraph - getBlock From: H.N. de Ridder - 2013-11-30 08:02:32 ```On Fri, Nov 29, 2013 at 04:06:48PM +0100, Carl Witt wrote: Hello Carl, > I have a question concerning the public UndirectedGraph > ,E > >; > *getBlock*(V > ; vertex) > method. > The documentation says > > Returns the vertex if vertex is a cutpoint, and otherwise returns > the block (biconnected component) containing the vertex. > > But the example given in the introductory section of the > BlockCutpointGraph class clarifies that the a vertex can be part of more > than one block > > Is the documentation of the getBlock method being imprecise (should it > read "returns a block containing the vertex") or is the underlying > definition of a block not the one from Mathworld? I don't know how it could happen, but cutpoint is one of the very few concepts in graph theory that have only one meaning. A cutpoint is indeed in more than one block (x is a cutpoint iff x is in more than one block), but non-cutpoints are in precisely one block. So getBlock(x) returns x if x is a cutpoint and the unique block that contains x, otherwise. Hope this clears things up, Ernst -- Information System on Graph Classes and their Inclusions (ISGCI) http://www.graphclasses.org ```