aov
Jim Robison-Cox
jimrc@mathfs.math.montana.edu
Thu, 4 Jun 1998 17:38:27 -0600 (MDT)
R developers,
Last week I asked several questions which I think I can now answer
myself in large part.
>
> Q 1) Is aov supposed to avoid qr decomposition and matrix inversion?
> In S it is claimed to be faster than lm() for large datasets. Is
> that due to avoidance of qr()?
> (My main goal is to get the Error strata working.)
My use of matrix manipulation to avoid qr decompositon takes more
time than the complied solver build into lm.fit. It seems that the real
reason for doing aov differently would be if the determination of Error
strata and which factors to evaluate in any given error statum requires
a different approach from lm.fit. I'm not going to worry about speed of
lm.fit anymore, so that avoids most of the other questions I had posed.
Douglas Bates has suggested:
DB> I think that a general approach via maximum likelihood or REML to
DB> anova models with random effects in them will eventually be superior
DB> to approaches based on sum-of-squares decompositions.
Perhaps one could make an aov function which fit using lme and then
repackaged the output a bit. I intend to look into that possibility.
In pursuit of a sum-of-squares decomp, I have looked at the C code
in model.c, particularly the do_termsform definition. I see
these comments (line 821 in June 2 snapshot)
/* Step 2: Recode the model terms in binary form */
/* and at the same time, expand the model formula. */
/* FIXME: this includes specials in the model */
/* There perhaps needs to be a an extra pass */
/* through the model to delete any terms which */
/* contain specials. Actually, specials should */
/* only enter additively so this should also be */
/* checked and abort forced if not. */
/* FIXME: this is also the point where nesting */
/* needs to be taken care of. */
To continue on this approach, and follow up on these FIXMEs, I need to
understand some of the internal functions like CAR, CDR, and
combinations thereof. I found the definition of CAR in
src/include/Defn.h as:
#define CAR(e) ((e)->u.listsxp.carval)
But where is u.listsxp.carval defined? For that matter, where is the
Scheme/LISP interpreter?
Is there a roadmap? list of where the different pieces of R reside?
Jim Robison-Cox ____________
Department of Math Sciences | | phone: (406)994-5340
2-214 Wilson Hall \ BZN, MT | FAX: (406)994-1789
Montana State University | *_______|
Bozeman, MT 59717 \_| e-mail: jimrc@math.montana.edu
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