R help - Dec 2000 - calculation of inertial difference with huygens theorem in ward clustering ?

Hello to the R people,

within ward clustering the distance calculated to decide the clustering
of 2 subsets (h1 and h2) is the variation of inertia :
d(h1,h2)=I(h1Uh2)-I(h1)-I(h2);
i've been said that a way to calculate faster this d(h1,h2) is using the
huygens theorem decomposing the inertia into "the inertia to the
centroid + the distance to an axe" (that's my version ...). My problem
is that i don't really see how to simplify the d(h1,h2) expression using
the theorem and then go faster?

Thanks in advance,

cordialement,

--
Nicolas Baurin

Doctorant
Laboratoire de Chimiom?trie - Mod?lisation Mol?culaire
Institut de Chimie Organique et Analytique, UMR 6005
http://www.univ-orleans.fr/SCIENCES/ICOA/
Universit? d'Orl?ans, BP 6759
45067 ORLEANS Cedex 2, France
Tel: (33+) 2 38 49 45 77


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