On Wed, 27 Sep 2000, Paul Schwarz wrote:
>
> S-News readers,
>
> I'm interested in learning about the algorithms used to compute
> empirical or sample semivariograms. I have S+SpatialStats, for example,
> so I have the means for calculating empirical semivariograms. I also
> understand the basic formula
>
> gamma(h) = 0.5*N(h)*sum(Zi - Zj)^2
>
> used for estimating the semivariogram where h = i - j is the Euclidean
> distance or "lag" and N(h) is the number of data pairs. So my interest
> is in learning about how to do these calculations in S-PLUS so that I
> can experiment with other approaches for estimating these kinds of
> statistics. I am assuming that there are some relatively efficient ways
> to do these calculations using vectors and matrices. If anyone has
> written code to do this in S-PLUS that they wouldn't mind sharing, I
> would be grateful.
Only relatively efficient. Early versions of my spatial library had
pure S versions, but the C versions are several times faster and use much
less memory. Assuming that you are happy handling C code, you can start
with those programs (part of the VR suite).
--
Brian D. Ripley, ripley@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272860 (secr)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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