> > Anyway, igraph is not optimal for this, then. igraph does MSTs, not EMSTs. >
Ok. To put you in the context, some of the works done in my field using MST were done using and IDL routine. For some reasons related to the job I have to do, I wanted to use R, and this is why I have tried igraph in the first place. I have to admit that, before your emails, I didn't knew that what I needed was an EMST. Perhaps I should have pointed out that I was new to R and to the used of minimum spanning tree. > > So you expected us to guess that you wanted an EMST, without you telling > us? :) > Well *sorry* ... I *thought* I have explained clearly what I wanted. I think we can close this topic : I will try to get help somewhere else, or to use another tool. Thank you anyway. > > On Wed, Mar 5, 2014 at 1:50 PM, Steve Boudreault > <[email protected]>wrote: >> > Maybe you want this: >> > http://en.wikipedia.org/wiki/Euclidean_minimum_spanning_tree >> > Do you? >> Yes, this is correct. > Anyway, igraph is not optimal for this, then. igraph does MSTs, not EMSTs. > As I wrote in my very first email, you can create a full graph, set edge weights to Euclidean distances, and then you can use > minimum.spanning.tree() in igraph. But this is very suboptimal. It might work if you have a couple of hundred points, maybe a couple of thousands. > Btw. this naive algorithm is the first one discussed at the wikipedia page: > http://en.wikipedia.org/wiki/Euclidean_minimum_spanning_tree#Algorithms_for_computing_EMSTs_in_two_dimensions >> In the link you gave me, I see the following sentence : << [...] an EMST >> (Euclidean minimum spanning tree) connects a set of dots using lines such >> that the total length of all the lines is minimised and any dot can be reached from any other by following the lines. >> >> Isn't that the rule? i.e. that my objects in the RA vs DEC place are connected such that the total length of all the lines is minimised? > So you expected us to guess that you wanted an EMST, without you telling us? :) > I can add that all my objects have the same weight. > I have no idea what you mean. You don't need to assign weights to your objects. Please read that wikipedia page. > G. >> > On Wed, Mar 5, 2014 at 11:17 AM, Steve Boudreault >> > <[email protected] >> >> wrote: >> >> > But I'd prefer you tell us want you want to do, and then we don't >> need >> >> > to >> >> > guess. >> >> Please look at the following image : >> >> http://inspirehep.net/record/833443/files/mst.png >> >> These are "minimum spanning tree" (right?) of stars distributed in X >> (i.e. >> >> right ascension, RA) and Y (i.e. declination, DEC). You have this for >> three open clusters : IC2391, M34, M11. >> > Again. The minimum spanning trees in igraph are defined for graphs >> (=networks), not for points: >> > http://en.wikipedia.org/wiki/Minimum_spanning_tree >> > Maybe you want this: >> > http://en.wikipedia.org/wiki/Euclidean_minimum_spanning_tree >> > Do you? >> > This *is* what I want to do. I want to do a plot like this. >> > This is not an explanation, I am sorry. What is the rule to connect >> the >> dots? Maybe this is evident for people in your field, but not to me. G. >> > [...] >> -- >> ============================================================ >> Steve Boudreault, Ph.D. >> CNRS UMR 8111 / GÉPI >> Bâtiment 11 - Hipparque Email: [email protected] >> Observatoire de Paris Phone : +33 (0) 145077868 >> 5 Place Jules Janssen Fax: +33 (0) 145077878 >> 92190 Meudon, France Mobile : +33 (0) 604530082 >> ============================================================ -- ============================================================ Steve Boudreault, Ph.D. CNRS UMR 8111 / GÉPI Bâtiment 11 - Hipparque Email: [email protected] Observatoire de Paris Phone : +33 (0) 145077868 5 Place Jules Janssen Fax: +33 (0) 145077878 92190 Meudon, France Mobile : +33 (0) 604530082 ============================================================ _______________________________________________ igraph-help mailing list [email protected] https://lists.nongnu.org/mailman/listinfo/igraph-help
