loess documentation
Hi all, I 've got a question about the usage of loess in the modreg package. The documentation (loess.html) states that the smoothing window is either set by span or enp.target. If span is used, the details section of the docs state... <SNIP> DETAILS Fitting is done locally. That is, for the fit at point x, the fit is made using points in a neighbourhood of x, weighted by their distance from x (with differences in `parametric' variables being ignored when computing the distance). The size of the neighbourhood is controlled by α (set by span or enp.target). For α < 1, the neighbourhood includes proportion α of the points, and these have tricubic weighting (proportional to (1 - (dist/maxdist)^3)^3. For α > 1, all points are used, with the `maximum distance' assumed to be α times the actual maximum distance. </SNIP> I understand the situation when alpha is less than one, presuming it uses the same convention set forth in any number of Clevelend and Devlin articles, ie, nearest neighbor smoothing. However, I'm interested in looking at fixed bandwidth smoothing and I'm wondering if the second option, (alpha>1) is some variation of this theme. I don't understand the "alpha times actual maxdistance" statement. If my estimation point is 10 meters from the farthest data point in physical space and I set my alpha = 2, then according to the statement above the smoothing window would be 20m???? Obviously this can't be right. Where have I gone wrong? Thanks in advance for your comments. Derrick
Derrick Snowden NOAA / AOML / PhOD 4301 Rickenbacker Cswy. Miami, FL 33149 Derrick.Snowden at noaa.gov -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._