solr 6.3 版本的打分公式

计算公式：

\[score(q,d) = coord(q,d) \cdot queryNorm(q) \cdot \sum_{t\;in\;q} {(\;tf(t\;in\;d) \cdot idf(t)^2 \cdot t.getBoost() \cdot norm(t,d)\;)}\]
  1. coord(q,d)： coordination factor

    how many of the query terms are found in the specified document 关键词命中率

  2. queryNorm(q)： query normalization

    serves as a normalization factor to attempt to make cores between queries comparable

    \[queryNorm(q) = queryNorm(sumOfSquaredWeights) = \frac{1}{\sqrt{sumOfSquaredWeights}}\]

    $sumOfSquaredWeights = q.getBoost()^2 \cdot (idf(t) \cdot t.getBoost())^2$

sumOfSquaredWeights 等于每个 term 相加。默认 boost = 1，则为每个 term 的 idf(t) 的平方相加

  1. tf(t in d): term frequency

    it is a measure of how often a particular term appears in a matching document

    $tf(t\;in\;d) = frequency^{1/2}$

  2. idf(t)： inverse document frequency

    rarer terms give higher contribution to the total score

    $idf(t) = 1 + \log \left(\frac{docCount\;+\;1}{docFreq\;+\;1} \right)$

    • $\log$ 是以 e 为底数的对数；对应 JAVA 中的 $\log$ 方法
  3. norm(t,d)： normalization factor

    combine the matching document’s boost, the matching field’s boost, and a length-normalization factor that penalizes longer documents

    $norm(t,d) = d.getBoost() \cdot lengthNorm(f) \cdot f.getBoost()$

    $lengthNorm = 1 \; / \; Math.sqrt(numTerms) $

  4. t.getBoost： 即每个词的权重，没给则默认为 1