Debugging/scoring question

[LOPEZ-CORTES Mariano-ext]

Hi all

I've a 20 document collection. In a debugging plan, we have:

"1000000051":"
20.794415 = max of:
  20.794415 = weight(nomUsageE:jean in 1) [SchemaSimilarity], result of:
    20.794415 = score(doc=1,freq=1.0 = termFreq=1.0
), product of:
      15.0 = boost
      1.3862944 = idf, computed as log(1 + (docCount - docFreq + 0.5) / 
(docFreq + 0.5)) from:
        1.0 = docFreq
        5.0 = docCount
      1.0 = tfNorm, computed as (freq * (k1 + 1)) / (freq + k1 * (1 - b + b * 
fieldLength / avgFieldLength)) from:
        1.0 = termFreq=1.0
        1.2 = parameter k1
        0.75 = parameter b
        1.0 = avgFieldLength
        1.0 = fieldLength

  "1000000053":"
21.11246 = max of:
  21.11246 = weight(prenomE:jean in 3) [SchemaSimilarity], result of:
    21.11246 = score(doc=3,freq=1.0 = termFreq=1.0
), product of:
      8.0 = boost
      2.6390574 = idf, computed as log(1 + (docCount - docFreq + 0.5) / 
(docFreq + 0.5)) from:
        1.0 = docFreq
        20.0 = docCount
      1.0 = tfNorm, computed as (freq * (k1 + 1)) / (freq + k1 * (1 - b + b * 
fieldLength / avgFieldLength)) from:
        1.0 = termFreq=1.0
        1.2 = parameter k1
        0.75 = parameter b
        1.0 = avgFieldLength
        1.0 = fieldLength

docCount = 5.0 for the document 1000000051. Why? docCount is the total number 
of documents, isn't it?

Thanks in advance!