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 > ============================================================ > > >
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