[Rd] bug (PR#13570)

[Prof Brian Ripley]

I've found the discrepancy, so the patched code from current dloess is 
now available in R-patched and R-devel.

On Fri, 6 Mar 2009, Prof Brian Ripley wrote:

> On Thu, 5 Mar 2009, Benjamin Tyner wrote:
>
>> Hi
>> 
>> Nice to hear from you Ryan. I also do not have the capability to debug on 
>> windows; however, there is a chance that the behavior you are seeing is 
>> caused by the following bug noted in my thesis (available on ProQuest; 
>> email me if you don't have access):
>> 
>> "When lambda = 0 there are no local slopes to aid the blending algorithm, 
>> yet the
>> interpolator would still assume they were available, and thus use arbitrary 
>> values
>> from memory. This had implications for both fit and tr[L] computation. In 
>> the
>> updated code these are set equal to zero which seems the best automatic 
>> rule when
>> lambda = 0." [lambda refers to degree]
>> 
>> I submitted a bug fix to Eric Grosse, the maintainer of the netlib 
>> routines; the fixed lines of fortran are identified in the comments at 
>> (just search for my email address):
>> 
>> http://www.netlib.org/a/loess
>> 
>> These fixes would be relatively simple to incorporate into R's version of 
>> loessf.f
>
> The fixes from dloess even more simply, since R's code is based on dloess. 
> Thank you for the suggestion.
>
> Given how tricky this is to reproduce, I went back to my example under 
> valgrind.  If I use the latest dloess code, it crashes, but by selectively 
> importing some of the differences I can get it to work.
>
> So it looks as if we are on the road to a solution, but something in the 
> current version (not necessarily in these changes) is incompatible with the 
> current R code and I need to dig further (not for a few days).
>
>> Alternatively, a quick check would be for someone to compile the source 
>> package at https://centauri.stat.purdue.edu:98/loess/loess_0.4-1.tar.gz and 
>> test it on windows. Though this package incorporates this and a few other 
>> fixes, please be aware that it the routines are converted to C and thus 
>> there is a slight performance hit compared to the fortran.
>> 
>> Hope this helps,
>> Ben
>
> [...]
>
> -- 
> Brian D. Ripley,                  ripley at 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 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>

-- 
Brian D. Ripley,                  ripley at 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 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595