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SPGWR - gw.adapt() command question
2 messages · Paul Bidanset, Roger Bivand
On Wed, 10 Jul 2013, Paul Bidanset wrote:
Hello all, I am doing some exploratory analysis with adaptive and fixed kernels in the SPGWR package. I am hoping to glean further insight from someone who has a better understanding of the gw.adapt(dp, fp, quant, longlat=FALSE) command. I understand 'quant' is proportion of data points to include in the weight. Is there a common trade off moving from 0 to 1? The bandwidth it assigns are consistently much larger and perform significantly worse than when employing a fixed bandwidth, which seems counter-intuitive to much of the literature I am reading. As the proportion I use increases, some of the bandwidths are reaching as high as 200 km, which I know cannot be correct as the geographical area is no more than 30 square kilometers.
If you do not provide a reproducible example, the only conclusion is that your usage of the function - which is used internally rather than by users - is incorrect. I can reproduce your artefact by using quant > 1, that is more than 100% of points included in the pointwise bandwidths: library(spgwr) data(columbus) col.bw <- gwr.sel(crime ~ income + housing, data=columbus, coords=cbind(columbus$x, columbus$y), adapt=TRUE) gw.adapt(cbind(columbus$x, columbus$y), cbind(columbus$x, columbus$y), quant=col.bw) gw.adapt(cbind(columbus$x, columbus$y), cbind(columbus$x, columbus$y), quant=0.1) gw.adapt(cbind(columbus$x, columbus$y), cbind(columbus$x, columbus$y), quant=0.9) gw.adapt(cbind(columbus$x, columbus$y), cbind(columbus$x, columbus$y), quant=0.99) gw.adapt(cbind(columbus$x, columbus$y), cbind(columbus$x, columbus$y), quant=15) Is this your scenario? Roger
Any insight is very much appreciated. I am very aware of the warnings and pitfalls of GWR ; I am simply looking to have a better understanding of the intuition behind this package and command specifically. Thanks very much for your time! Best, Paul Old Dominion University [[alternative HTML version deleted]]
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Roger Bivand Department of Economics, NHH Norwegian School of Economics, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: Roger.Bivand at nhh.no