It has been a long time since i looked at gravity models but if I
they are formulated as log linear models with a particular weight
matrix. I would guess
that that could be written as a generalized linear mixed model, and fit
with lme, or lmer, though if a parameterized covariance matrix matrix is
needed, lmer will not work. The geoRglm package is also worth a look.
And doing a search on Rseek I found that the package nettheory fits
several gravity models, I think the command is CONSTRUCT. And look at
though I don't think gravity models per say are addressed in that
You may get more mileage sending your query to R-sig-geo.
hope this helps
> Message: 3
> Date: Mon, 5 May 2008 16:35:25 -0700
> From: "Melanie Murphy" <[hidden email]>
> Subject: [R-sig-eco] Gravity (spatial interaction) models in R
> To: <[hidden email]>
> Message-ID: <000701c8af08$b29ea640$3c19a8c0@dru>
> Content-Type: text/plain
> Hi All,
> I am constructing "gravity" (spatial interaction) models in R for
> ecological application. I have linearized the unconstrained model and
> solved using OLS. However, I would like to do some further, more
> in-depth, analyses.
> 1) Is there an R package actually designed for gravity models? I
> have done several searches on the CRAN site with no luck. My preference
> would be to use R for this manuscript versus commercially available
> 2) I would like to estimate my linearized unconstrained model using
> maximum likelihood. This may be a simple solution, but I have yet to
> figure out how to do this (my apologies if this is something I should
> have been able to figure out on my own).
> 3) For a production (origin) constrained model, I can linearize the
> equation as in the unconstrained model. The models are similar, accept
> I need to estimate a constant (k) for each origin, but with only one
> estimate of the remaining parameters. Any ideas on how to
> operationalize this? I have tried exploring options with multiple
> regression, but am not finding a solution with the appropriate
> mechanics. This would also be an ML estimate.
> 4) Any feedback/experience from people who have used gravity models
> in R and/or ecological application would be appreciated.
> 5) I have tried to keep this posting as brief as possible. Please
> let me know if you need further information to answer my questions.
> Thank you all in advance
> Melanie Murphy
> EPA-STAR Fellow
> School of Biological Sciences
> Washington State University
> e-mail: [hidden email] >
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> End of R-sig-ecology Digest, Vol 2, Issue 4