Re: [igraph] how to plot a very basic MST with igraph

[Steve Boudreault]

>
> 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.

This *is* what I want to do. I want to do a plot like this.

I have a list of objects in RA and DEC :

alpa (RA)   delta (DEC)
0.923   -12.345
0.912   -11.222
0.812   -11.763
0.902   -11.923
0.942   -12.001
...   ...

I would like to produce a plot with my list of objects. A plot like the
one presented in the link I have provided.

More generally, I would like to use MST as a tool to see if the
distribution is clustered (e.g. M11, obviously there is a cluster) or
homogeneously distributed (e.g. IC 2391, not obvious that there is a
cluster).

Ultimately, I would like to use the normalised correlation length of the
MST (say, "s") and the mean edge length of the MST (say, "m") to make a
distinction between overall radial density (m/s > 0.8, most-likely there
is a cluster, like for M11) and subclustering (m/s < 0.8, most-likely
there are *no* cluster, like for IC 2391).

I hope I better explained what I wanted.


>
> On Wed, Mar 5, 2014 at 9:42 AM, Steve Boudreault
> <address@hidden>wrote:
>> Greetings,
>> I am new to R, and probably this is a very simple problem with very few
things to do. (Sorry if this is the case.)
>> Here I go ...
>> I have a list of about 1000 objects in the file "list.csv". It looks like
>> this :
>> alpa   delta
>> 0.923   -12.345
>> 0.912   -11.222
>> 0.812   -11.763
>> 0.902   -11.923
>> 0.942   -12.001
>> ...   ...
>> Alpha is the X axis and delta is the Y axis.
>> I would like to produce a very simple minimum spanning tree plot, like the
>> ones I attached with this message.
>> The informations I got so far using igraph in R implied using an adjacent
>> matrix (e.g. "G <- graph.adjacency(as.matrix(D), weighted=TRUE)").
Maybe
>> I
>> miss something important ...
> I don't know where you collect your information from, but I would
suggest
> to use the documentation of igraph, e.g.
> http://igraph.org/r/doc/aaa-igraph-package.html
>> but I fail to understand why I should need a
>> n x n matrix to make an MST for my list of [X,Y] objects.
>> Can someone tell me how I can produce a simple minimum spanning tree plot?
> Minimum spanning trees are defined for graphs, at least in igraph. What
is
> your graph? A set of points is not a graph.
> Maybe you mean that you have a full graph, with your points on the plane as
> vertices, the weights of the edges are Euclidean distances between pairs or
> points, and you want the MST of this graph.
> But I'd prefer you tell us want you want to do, and then we don't need
to
> guess.
> Gabor
> Thank you very much for your help.
>> Best regards,
>>      Steve Boudreault
>> --
>> ============================================================
>> Steve Boudreault, Ph.D.
>> CNRS UMR 8111 / GÉPI
>> Bâtiment 11 - Hipparque     Email: address@hidden
>> 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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>> https://lists.nongnu.org/mailman/listinfo/igraph-help


-- 
============================================================
Steve Boudreault, Ph.D.
CNRS UMR 8111 / GÉPI
Bâtiment 11 - Hipparque     Email: address@hidden
Observatoire de Paris       Phone : +33 (0) 145077868
5 Place Jules Janssen       Fax: +33 (0) 145077878
92190 Meudon, France        Mobile : +33 (0) 604530082
============================================================