Distinguish the primary difference in application between 'pre-filtering' and 'post-filtering' in optimizing vector search queries for a RAG system.

In optimizing vector search queries for a Retrieval-Augmented Generation (RAG) system, 'pre-filtering' and 'post-filtering' represent two distinct strategies for applying metadata constraints, primarily differing in their application timing relative to the vector similarity computation. Vector search involves finding data points (documents, chunks of text) whose numerical representations, called vectors, are semantically similar to a query vector. Optimizing this process means improving its speed, accuracy, and relevance for a RAG system, which uses retrieved information to ground a large language model's responses. Pre-filtering is the application of filters *beforethe vector similarity search is performed. This means that only data points that satisfy the specified metadata criteria are included in the pool of candidates for the similarity calculation. For example, if a user queries a RAG system for information about 'new drug regulations' but explicitly states they only want documents 'published in 2023 by the FDA', the 'published in 2023'....