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Equation 13 · Part 5 · Ten Failure Modes That Define Production RAG

subtraction

keff=k−d,k_{\text{eff}} = k - d,
subtraction

What this part means

Subtract the following term or group from the preceding one. A leading minus marks a negative quantity.

Its job in the formula

Subtract the following term or group from the preceding one. A leading minus marks a negative quantity.

The passage around this formula

Real corpora are full of near-duplicates: a press release syndicated across a dozen outlets, a policy document copied into three different wikis, boilerplate repeated at the top of every ticket in a queue. A ranking function that scores by similarity to the query has no reason to penalise duplication, so a query that matches one instance of a widely republished passage tends to match all of them, and a naive top- k selection can fill a majority of its slots with restatements of a single fact rather than covering the breadth of what is actually in the corpus. If d of the k retrieved slots are occupied by near-duplicates of an already-retrieved passage, the effective evidence budget is not k…

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Learn the underlying idea

Addition combines quantities; subtraction measures the signed difference between them. Parentheses show what is combined before the rest of the expression is evaluated.

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Sources cited in the surrounding passage

These citations provide research context; check each source for the exact claim it supports.