R-users
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I have a quenstion on "gam()" in "gam" package.
The help of gam() says:
'gam' uses the _backfitting
algorithm_ to combine different smoothing or fitting methods.
On the other hand, lm.wfit(), which is a routine of gam.fit() contains:
z <- .Fortran("dqrls", qr = x * wts, n = n, p = p, y = y *
wts, ny = ny, tol = as.double(tol), coefficients = mat.or.vec(p,
ny), residuals = y, effects = mat.or.vec(n, ny), rank = integer(1),
pivot = 1:p, qraux = double(p), work = double(2 * p),
PACKAGE = "base")
It may indicate that QR decomposition is used to derive an additive model
instead of backfitting.
I am wondering if my guess is correct, or this "the _backfitting
algorithm"
has another meaning.
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