[R] Setting up 3D tensor product interactions in mgcv

Mark Payne markpayneatwork at gmail.com
Fri Aug 23 10:05:13 CEST 2013


Hi,

I am trying to fit a smoothing model where there are three dimensions
over which I can smooth (x,y,z). I expect interactions between some,
or all, of these terms, and so I have set up my model as

mdl <- gam(PA ~ s(x) + s(y) + s(z) + te(x,y) + te(x,z) + te(y,z) +
te(x,y,z),...)

I have recently read about the ti(), "tensor product interaction
smoother", which takes care of these interaction terms elegantly and
does the nesting properly. The help file says "This is much better
than attempting the same thing with ‘s’or ‘te’ terms representing the
interactions (although mgcv does not forbid it)." There is a 2D
example there also. But I don't understand how I should set this up
for my 3D example. Do I simply replace the te's above with ti? Or is
there more to it than that?

Does anyone have experience with this, and can explain how I should do
it properly?

Mark



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