Thanks Paul,

I understand that I can multiplied my data without problem but I'm still
wondering why I have to this operation. Maybe it's about the precision
floats in gstat like you said.

regards,
Sam

2010/7/19 Paul Hiemstra <p.hiemstra@geo.uu.nl>

> On 07/17/2010 06:19 PM, Samuel Turgeon wrote:
>
>> Hi,
>>
>> I'm a new user of gstat, so my question is maybe very simple.
>>
>> I'm trying to fit a variogram with the function fit.variogram and I get
>> this
>> error message:
>>
>> Warning: singular model in variogram fit
>> [1] "a possible solution MIGHT be to scale semivariances and/or distances"
>>
>> My data have values between 2.54e-10  et 2.56e-06. If I multiply my data
>> by
>> a constant in the semivariogram:
>>
>> vario=variogram(NASC*10000000~1,data,cutoff=1000)
>>
>> When I do this multiplication I'm able to fit a variogram.
>>
>> So my question is, Is it possible to this? Can I back transform (by a
>> division) my predited values when the ordinary kriging will be done?
>>
>>
>
> Hi Sam,
>
> It is possible, probably the covariance matrix has a lot of zeros because
> of rounding of your small values. Could this be linked to using single
> precision floats in gstat (edzer?)? I think there is no problem in
> 'backtransforming' your values, i.e. you only change the unit of the
> variable you are using (e.g. from milligram to microgram). Take care though
> that when predicting whilst using the fitted variogram model, your
> observations also need to be multiplied by this constant. My suggestion
> would be to multiply the data at the very beginning of the script, do all
> you analysis and at the very end do the division. You could also skip the
> division and present your results in the new unit.
>
> regards,
> Paul
>
>  Thanks!
>>
>> Sam
>>
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>>
>>
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>
>
> --
> Drs. Paul Hiemstra
> Department of Physical Geography
> Faculty of Geosciences
> University of Utrecht
> Heidelberglaan 2
> P.O. Box 80.115
> 3508 TC Utrecht
> Phone:  +3130 253 5773
> http://intamap.geo.uu.nl/~paul <http://intamap.geo.uu.nl/%7Epaul>
> http://nl.linkedin.com/pub/paul-hiemstra/20/30b/770
>
>

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