[Ifeffit] DAthena crashes when reconstructing data from PCA -- Update

[Bruce Ravel]

On 07/29/2013 01:35 PM, John Hayes wrote:
> I have noticed that when I changed the order of the data groups the
> calculated eigenvalues change when the first group on the list changes.
> The changes are very small and not significant, but based on my (very
> limited) knowledge of PCA, it would seem that the order of the data
> would not matter.

John,

I agree that order should not matter in terms of the useful output of
a PCA.  However, it seems plausible that the order of input vectors
could result in small numerical differences in the eigenvectors.  It
even seems plausible that input vectors in a different order could
result in eigenvectors that are rotated by some non-negligible angle.
In truth, I have neither thought about this nor investigated it before.
I'll put it on my to do list, but I suspect that the bottom line is
one of the two things I suggested.

BTW, the specific problem you reported will certainly be fixed in the
next release.  I got that working this morning.

B


-- 
  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
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