[Xapian-tickets] [Xapian] #756: Implement dice coefficient weight metric

[Xapian]

#756: Implement dice coefficient weight metric
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 Reporter:  gp1308  |             Owner:  gp1308
     Type:  task    |            Status:  new
 Priority:  normal  |         Milestone:
Component:  Other   |           Version:
 Severity:  normal  |        Resolution:
 Keywords:          |        Blocked By:
 Blocking:          |  Operating System:  All
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Comment (by olly):

 I'm not sure about your d1_score - I get:

  * |Q₁ ∩ d₁| = 2
  * |Q₁| = 2
  * |d₁| = 5

 So ''dicecoefficient''(Q₁, d₁) = (2 * 2) / (2 + 5) = 4/7 (not 0.5)

 > Hence denominator need to be computed only once for a selected document

 Theoretically, but actually you'll really need to compute it once per
 matching term for a selected document as the weight contributions come
 from separate Weight objects.  You could invent some elaborate system for
 them to share the value rather than recompute it, but that's just going to
 end up being more costly than recomputing it - FP multiplication on modern
 hardware is fast.

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Ticket URL: <https://trac.xapian.org/ticket/756#comment:1>
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