[R] "gam()" in "gam" package

From: Kunio takezawa <r.otasuke_at_gmail.com>
Date: Tue, 18 Dec 2007 16:07:20 +0900


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E-mail: r-help_at_r-project.org

   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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