[R] A Few MCLUST Questions

[Christian Hennig]

Hi Ken,

1) me starting with a partition converges toward the same result as
em starting with the parameters associated with the partition. So there is
no point in doing both and see which one is better. 

2) hc is an agglomerative hierarchical method. This means, it starts with
n clusters and reduces the number of clusters by 1 in every step. That is,
if you want to compute the solution for G=2 clusters, you *have to*
compute n, n-1, n-2,..., G+1 clusters first. By definition, it's not
possible to calculate 2, but not more clusters.

Christian

On Sun, 13 Jun 2004, KKThird at Yahoo.Com wrote:

> 
> Hello everyone. I have a few MCLUST questions and I was hoping someone could help me out. If you’re an MCLUST user, they will likely be pretty easy to answer. Thanks in advance for any help.
> 
> Ken 
> 
>  
> 
>    What are the pros/cons of starting a finite mixture model at the "m" step versus the "e" step (where "m" is the maximization step and "e" is the expectation step of the EM algorithm)? In particular, are there any reasons for using em(modelName=XXX) versus me(modelName=XXX). Other than MCLUST, I’ve not seen a finite mixture model "program" give such an option. Would it make sense to fit both models and take the one with the largest log likelihood?
> 
>  
> 
>    Rather than the hc() function performing cluster analysis for all of G possible clusters, can it be set to only perform a specified number (e.g., set so G=2 only). Although a minimum number of clusters can be specified, there doesn’t seem to be any way to limit the number of clusters. I want to do a simulation for a fixed number of components, and thus I would like to avoid the unnecessary computations. 
> 
>  
> 
>    Is there any difference between hc(modelName=VVV) and hcVVV or hc(modelName=EEE) and hcEEE, etc.? Likewise, are there any differences between mstep(modelName=VVV) and mstepVVV or mstep(modelName=EEE) and mstepEEE, etc. If not, why do the same functions have different names?
> 
> 
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Christian Hennig
Fachbereich Mathematik-SPST/ZMS, Universitaet Hamburg
hennig at math.uni-hamburg.de, http://www.math.uni-hamburg.de/home/hennig/
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