[R-sig-Geo] nugget in variogram

[Edzer Pebesma]

> vgm(1, "Exp", 300)
  model psill range
1   Exp     1   300

and

> vgm(1, "Exp", 300, 0)
  model psill range
1   Nug     0     0
2   Exp     1   300

are definitions of exactly the same variogram, with zero nugget --
passing either to krige() will yield identical results. If they are
passed to fit.variogram, in the first case no nugget will be fitted, but
in the second case a (zero or positive) nugget will be fitted.

Hth,

On 12/14/2010 06:09 PM, Piero Campalani wrote:
> Of course, I forgot actually to say I'm using the gstat package, and its
> variogram and vgm functions.
> 
> Piero
> 
> On 14 December 2010 14:42, kapo coulibaly <kmcoulib at gmail.com> wrote:
> 
>> Which packages and which commands are you using? A little bit of background
>> on how you did it would help.
>>
>>
>> On Tue, Dec 14, 2010 at 4:42 AM, piero campa <piero.campa at gmail.com>wrote:
>>
>>>
>>> Hi,
>>> I am trying to fit my first variograms.
>>> I'm however noticing some weird behaviour I cannot explain.
>>> I'm a 100% newbie.
>>>
>>> - without setting a nugget element (so that it should be implicitly 0,
>>> isn't
>>> it? In fact the resulting variogram has 0 nugget), the psill and range of
>>> the fitted variogram don't change on different psill inputs.
>>> - If I explicitly set a nugget to 0, then actually the nugget is no more
>>> 0,
>>> but higher.
>>> - I tried also setting the fit.sills booleans to TRUE or FALSE to see what
>>> would change, but the output does not really care about it.
>>>
>>> Does someone have any hint about this?
>>>
>>> Thank you.
>>> Regards,
>>> Piero
>>> --
>>> View this message in context:
>>> http://r-sig-geo.2731867.n2.nabble.com/nugget-in-variogram-tp5587929p5833937.html
>>> Sent from the R-sig-geo mailing list archive at Nabble.com.
>>>
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>>
>>
> 
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-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics      e.pebesma at wwu.de