Equation 4 · Part 1 · From BM25 to Agentic Retrieval: A History of Retrieval-Augmented Generation
Symbol d_k
What this part means
is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.
Its job in the formula
is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.
Full expression→Symbol d_k→Article meaning
The passage around this formula
…sparse or dense, still does: score a term by how often it occurs locally and how rare it is globally. They define the inverse document frequency of a term k , for a collection of n documents in which k appears in of them, as
Learn the underlying idea
A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.
Open the illustrated subscripts: which member of a family? guide →
See this notation across published equations →
Sources cited in the surrounding passage
These citations provide research context; check each source for the exact claim it supports.