Wednesday, May 2, 2012

3732.txt

cc: t.osborn@uea.ac.uk, anders.moberg@natgeo.su.se, hegerl@duke.edu, weber@knmi.nl, myles.allen@physics.ox.ac.uk, k.briffa@uea.ac.uk, jan.esperatXYZxyz.ch
date: Wed, 01 Nov 2006 15:25:56 +0100 (MET)
from: Eduardo Zorita <Eduardo.ZoritaatXYZxyzs.de>
subject: CPD submission
to: m.n.juckesatXYZxyzac.uk




dear co-authors,


On the question of data and code -sharing, I am not sure whether Climate of the Past is the adequate forum, but I have
in principle nothing against it. I see however the risk that the possible discussion drifts from
the manuscript itself towards those general questions.

Concerning the more particulat question of the errors in the code my MM05-ee, again I would tend to be very
cautious. I have tried to look a little bit into the R routines that may be used to calculate the
principal components, prcomb and princomb. There are several methods to do it, and apparently even those R-routines do not produce the same results with the same data. I am not an expert in the R languange and I feel completely unsure to as
what those routines do internally, e.g. whether the data are indeed centered or not in any internal steps.
However, I recall that when this issue was raised by MM, Mann itself recognized that the calculation by MM was
correct, i.e. the leading PC was dependent on the centering period, but that when choosing the correct truncation
(i.e. keeping more PCs than just the leading one) the final results were insensitive to this step.
Wegman also went through the code and apparently he found it to be ok. Of course, it is possible that both were wrong.
This, together with the fact that is quite easy to overlook aspects of the code written by others, guards
me against making any definitive assertions on a code written in a language that I do not command, the results of which I do not have the chance to test with my own software. Of course, you are free to do as you think is correct, but please not under my undorsement.




eduardo



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