On Wed, 28 Mar 2001 08:57:36 +0200, "Nicolas V." <[EMAIL PROTECTED]>
wrote:
> Hi,
>
> What are "rotations" in PCA ?
> What is the difference between "rotated" and "unrotated" PCA ?
> Does it exist in others analysis ?
= just on 'existence' =
Rotations certain exist in other analyses, and for other purposes.
Anytime you have a coordinate system, you have potential for drawing
in different axes, and then describing locations in terms of the new
system.
On a map in 2D, you can describe positions as directions, N-E-S-W.
But if a river cuts along the diagonal, it could be more sensible to
describe cities as "up-river" from the ocean by some amount,
and by how far they are from the main tributary. - simplification like
that, is the idea behind rotation.
Common Factors are usually selected from the full-rank set, and
rotated: so the description will be simpler.
The full-rank set of PCs is often used as a matter of convenience
(vectors are not correlated); and there's no help from rotation if
there's no separate description being used.
The set of "significant" Factors in canonical correlation might be
subjected to rotation, because they are rather like Common Factors;
but that is seldom done (in what I read).
--
Rich Ulrich, [EMAIL PROTECTED]
http://www.pitt.edu/~wpilib/index.html
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