Equation 5 · Part 6 · From BM25 to Agentic Retrieval: A History of Retrieval-Augmented Generation
subtraction
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.
Full expression→subtraction→Article meaning
The passage around this formula
Before any of this involved learning, it involved geometry. Salton, Wong, and Yang proposed representing each document as a vector of weighted index terms and ranking documents by the similarity of their vectors to a query vector, arguing that a well-separated document space — one where unrelated documents sit far apart — should correspond to better retrieval performance than a densely packed one [ 1 ] . Their paper is worth reading in the original rather than through summary, because the term-weighting scheme it specifies is exactly the ancestor of what every later retriever, sparse or dense, still does: score a term by how often it occurs locally and how rare it is globally. They define…
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.
Open the illustrated addition and subtraction in an equation guide →
Sources cited in the surrounding passage
These citations provide research context; check each source for the exact claim it supports.