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(gnus)Score Decays

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Score Decays
============

   You may find that your scores have a tendency to grow without
bounds, especially if you're using adaptive scoring.  If scores get too
big, they lose all meaning--they simply max out and it's difficult to
use them in any sensible way.

   Gnus provides a mechanism for decaying scores to help with this
problem.  When score files are loaded and `gnus-decay-scores' is
non-`nil', Gnus will run the score files through the decaying mechanism
thereby lowering the scores of all non-permanent score rules.  The
decay itself if performed by the `gnus-decay-score-function' function,
which is `gnus-decay-score' by default.  Here's the definition of that
function:

     (defun gnus-decay-score (score)
       "Decay SCORE.
     This is done according to `gnus-score-decay-constant'
     and `gnus-score-decay-scale'."
       (floor
        (- score
           (* (if (< score 0) 1 -1)
              (min (abs score)
                   (max gnus-score-decay-constant
                        (* (abs score)
                           gnus-score-decay-scale)))))))

   `gnus-score-decay-constant' is 3 by default and
`gnus-score-decay-scale' is 0.05.  This should cause the following:

  1. Scores between -3 and 3 will be set to 0 when this function is
     called.

  2. Scores with magnitudes between 3 and 60 will be shrunk by 3.

  3. Scores with magnitudes greater than 60 will be shrunk by 5% of the
     score.

   If you don't like this decay function, write your own.  It is called
with the score to be decayed as its only parameter, and it should return
the new score, which should be an integer.

   Gnus will try to decay scores once a day.  If you haven't run Gnus
for four days, Gnus will decay the scores four times, for instance.