R-users
E-mail: r-help@r-project.org

>Please don't ask the same question multiple times!

   I am really sorry about it. I thought that my first mail did not
work.

>And no, backfitting and QR are unrelated concepts. You need to read up
>on the theory,

   To derive an additive model, we have two methods: (1) backfitting,
(2) solving multiple linear equation using QR decomposition.

>If i read the code correctly, lm.wfit is called iteratively in gam.fit,
>via the line
>       fit <- eval(bf.call)
>The iteration is necessary to the backfitting algorithm.

   This iteration seems to be for "iteratively reweighted least squares" not
for backfitting. And lm.wfit may solve multiple linear equation using
QR decomposition; but I am not sure.
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