From f5faac8859e8adbfa52b9c6e6cfb7a2d33ca66af Mon Sep 17 00:00:00 2001
From: Jan-Luca Barthel <63152896+JL-B@users.noreply.github.com>
Date: Tue, 29 Aug 2023 19:29:51 +0200
Subject: [PATCH] addition of cosine distance function for faiss (#9939)

- Description: added the _cosine_relevance_score_fn to
_select_relevance_score_fn of faiss.py to enable the use of cosine
distance for similarity for this vector store and to comply with the
Error Message, that implies, that cosine should be a valid distance
strategy
- Issue: no relevant Issue found, but needed this function myself and
tested it in a private repo
  - Dependencies: none
---
 libs/langchain/langchain/vectorstores/faiss.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libs/langchain/langchain/vectorstores/faiss.py b/libs/langchain/langchain/vectorstores/faiss.py
index a8c835e5ca..ec95c67e0b 100644
--- a/libs/langchain/langchain/vectorstores/faiss.py
+++ b/libs/langchain/langchain/vectorstores/faiss.py
@@ -736,6 +736,8 @@ class FAISS(VectorStore):
         elif self.distance_strategy == DistanceStrategy.EUCLIDEAN_DISTANCE:
             # Default behavior is to use euclidean distance relevancy
             return self._euclidean_relevance_score_fn
+        elif self.distance_strategy == DistanceStrategy.COSINE:
+            return self._cosine_relevance_score_fn
         else:
             raise ValueError(
                 "Unknown distance strategy, must be cosine, max_inner_product,"