[R] About help on 'mahalanobis'

From: Henrik Bengtsson <hb_at_maths.lth.se>
Date: Wed 14 Dec 2005 - 17:05:32 EST


Hi,

help on 'mahalanobis' (in the stats package in Rv2.2.0) now says:

"Description:

      Returns the Mahalanobis distance of all rows in 'x' and the vector
      mu='center' with respect to Sigma='cov'. This is (for vector 'x')
      defined as

                  D^2 = (x - mu)' Sigma^{-1} (x - mu)"

It does return D^2 as written. However, would the text be more clear if it says "Returns the _squared_ Mahalanobis distance D^2..." instead? If so, then text in the example code, e.g. "##- Here, D^2 = usual Euclidean distances" and the title of the first plot will also have to be updated.

Compare this with what dist() in the same package returns. When asking for the Equlidean distance (matrix) between rows in a matrix, we get D not D^2, e.g. dist(c(1,3)) == 2.

Cheers

Henrik



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