[R] About help on 'mahalanobis'

2005-12-13 Thread Henrik Bengtsson 
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

__
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html

Re: [R] About help on 'mahalanobis'

2005-12-14 Thread Martin Maechler 
> "HenrikB" == Henrik Bengtsson <[EMAIL PROTECTED]>
> on Wed, 14 Dec 2005 17:05:32 +1100 writes:

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

HenrikB> "Description:

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

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

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

Indeed, thank you!
Committed {even to R-beta}.

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

__
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html