From Prof Brian Ripley <ripley@stats.ox.ac.uk>  Mon Sep 27 12:25:05 1999
From: Prof Brian Ripley <ripley@stats.ox.ac.uk> (Prof Brian Ripley)
Date: Mon, 27 Sep 1999 12:25:05 +0100 (BST)
Subject: chol() dimnames
Message-ID: <199909271125.MAA07858@toucan.stats.ox.ac.uk>


> Date: Mon, 27 Sep 1999 11:18:52 +0100 (BST)
> From: Jonathan Rougier <J.C.Rougier@durham.ac.uk>
> To: r-devel@stat.math.ethz.ch
> Subject: chol() dimnames
> 
> Hi Everyone,
> 
> Just a minor point, but could chol() be changed to include the dimnames of
> the original matrix?  This will ensure that x and t(R) %*% R have the same
> dimnames, where R <- chol(x).  So we just need to insert
> 
>     if (!is.null(dx <- dimnames(x))) 
>         dimnames(z$v) <- dx
> 
> ahead of the return.  Cheers, Jonathan.

This is a picky comment, but maybe we should try to get this spot on.

(i) Suppose that the row and column names of x are different? Which should
one use?

(ii) I don't think that R has any obvious row names: effectively this is
a linear transformation to a different and unamed basis for the space.

I believe all one actually knows is that the colnames of R should be the
colnames of x, if the row and column names of x match. However, the 
prototype does preserve the names.  Should we just preserve the colnames?


-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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chol() dimnames
Prof Brian Ripley