[GRASS-dev] Re: New module v.surf.trend but with external dependencies and ccmath problem

Jarek Jasiewicz jarekj at amu.edu.pl
Tue May 4 15:11:46 EDT 2010

Roger Bivand pisze:
> Hi Jarek,
> Are you rescaling the coordinates before powering them? I see that you are
> making some conversions in main.c, but they may not be enough. Try using the
> unit square 0,1 instead, for example (x_i - min(x))/(max(x) - min(x)) or
> something like this. Or see dscale() in the recommended R package
> spatial/src/krc.c around line 452, which uses -1, 1 for the same reason, for
> a code example.
> Roger
> -----
> Roger Bivand
> Economic Geography Section
> Department of Economics
> Norwegian School of Economics and Business Administration
> Helleveien 30
> N-5045 Bergen, Norway
Hi Roger!!
unfortunately not. The same problem. OK to polynom 2 for all three method.
Ok for polynominal 4 for gls and qr decomposition
Ok only for gls with polynom over the 5.

I think it is a problem of matrix decomposition and additional parameter 
called "balance" in gsl which is still out of my knowledge.

The funny is that solution I proposed is as very simple that probably it 
should not work, except that it work for gls library! The only problem 
is that it is external dependency (for Grass as far as I know not for R)

thanks for suggestion. I will try in that way also with krc


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