[R] Almost a GAM?

[Prof Brian D Ripley]

On Tue, 29 Jan 2002, Michael Roberts wrote:

> I don't think I can solve my problem in this way because w1
> and w2 are continuous variables.
>
> A second problem is that my f(x,y) is not f(x, df), i.e., I'd
> like to have a sum of *two* dimensional smoothers interacted
> with other variables.
>
> After my first post I did find a discussion of this problem on the
> S archive, which suggested the same appraoch as Vito did.  S can
> fit 2-d smooths, but still can't handle the interaction terms.

I think you need to define carefully what you mean. I had no idea what

z ~ f(x,y):w1 + g(x,y):w2 + e

is about, and now you tell me w1 and w2 are continuous I have even less
idea.  What is the interaction you are talking about?  And how can the
model possibly be identifiable?

`:' is S model notation for an interaction, and at least one of the
components is a factor (otherwise special rules apply, generally
multiplication).  But smooth functions cannot be factors.

[...]

-- 
Brian D. Ripley,                  ripley at 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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