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.esper@wsl.ch date: Wed, 1 Nov 2006 15:40:45 +0000 from: Martin Juckes subject: Re: CPD submission to: Eduardo Zorita I've attached the document I intend to put on the MITRIE web site. Following Eduardo's comments, I've only put myself as author, but I'm happy to include anyone else who would like to endorse it. It is important to emphasise that figure 2 of MM2005 (Energy and Environment) which shows a line with clearly non-zero mean and claims it is a principal component of centred data cannot be correct: principal components of centred data have zero mean. It is slightly embarassing to have missed this rather obvious point until now, but it is nevertheless true. Studying their code, and getting it to run so that I am not dependent on assuming that routines are platform independent, allows the source of this error to be determined. I've also attached the MM2005 paper, so you can check that their figure is properly reproduced. cheers, Martin On Wednesday 01 November 2006 14:25, Eduardo Zorita wrote: > > 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 > > > > > Attachment Converted: "c:\eudora\attach\comment_ee_figure2.pdf" Attachment Converted: "c:\eudora\attach\mcintyre_mckitrick2005_ee.pdf"