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Reply To: | Classification, clustering, and phylogeny estimation |
Date: | Thu, 24 Oct 2002 21:12:02 -0400 |
Content-Type: | text/plain |
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I agree. I don't yet see the point of why this should be done.
> -----Original Message-----
> From: Classification, clustering, and phylogeny estimation
> [mailto:[log in to unmask]]On Behalf Of Murray Jorgensen
> Sent: Thursday, October 24, 2002 8:21 PM
> To: [log in to unmask]
> Subject: Re: classification comparison/R=R1=R2=R3
>
>
> At 15:36 24/10/02 +0200, Christian Hennig wrote:
>
> >2) On clustering with R1=R2=R3=R. k-means clustering implicitly assumes
> > clusters to have unit matrix correlation. So transforming the data to
> > unit covariance and then applying 3-means will give clusters with
> > approximately R1=R2=R3=R.
>
> R1=R2=R3, maybe but =R???
>
> Surely it is most unlikely that the overall correlation structure
> would mirror
> the within-cluster structure? It is also hard to think why that might be
> desirable. If it were then an obvious way to achieve it would be
> to randomly
> allocate the data points to the three clusters.
>
> Murray Jorgensen
>
>
> May be even better with a Gausiian mixture
> > model where covariance matrices of the clusters are restricted to cI,
> > where I is unit matrix and c may depend on the cluster. This again has
> > to be applied to data which is sphered, i.e. transformed to unit
> > covariance first. I hope this "covariance model" can be found
> in mclust,
> > mentioned previously in this discussion.
> >
> >Christian Hennig
> >
> >
> >
> >--
> >***********************************************************************
> >Christian Hennig
> >Seminar fuer Statistik, ETH-Zentrum (LEO), CH-8092 Zuerich (current)
> >and Fachbereich Mathematik-SPST/ZMS, Universitaet Hamburg
> >[log in to unmask], http://stat.ethz.ch/~hennig/
> >[log in to unmask], http://www.math.uni-hamburg.de/home/hennig/
> >#######################################################################
> >ich empfehle www.boag.de
> >
> Dr Murray Jorgensen http://www.stats.waikato.ac.nz/Staff/maj.html
> Department of Statistics, University of Waikato, Hamilton, New Zealand
> Email: [log in to unmask] Fax +64-7 838 4155
> Phone +64-7 838 4773 wk +64 7 849 6486 home Mobile 021 395 862
>
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