Equation 18 · Part 1 · From BM25 to Agentic Retrieval: A History of Retrieval-Augmented Generation
Symbol z
What this part means
z 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
z 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 z→Article meaning
The passage around this formula
By the time Lewis and colleagues published in 2020, learned dense retrieval and large pretrained generators both already existed as separate lines of work. The paper’s specific technical contribution was neither — it was making the whole pipeline trainable end to end through a single differentiable objective, treating the retrieved passage as a latent variable to be marginalized over rather than a fixed input handed to a frozen reader [ 8 ] . Writing x for the input, y for the output, z for a retrieved passage, and and for the retriever’s and generator’s parameters respectively, the RAG-Sequence variant approximates
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Sources cited in the surrounding passage
These citations provide research context; check each source for the exact claim it supports.