code: import langchain
  from dotenv import load_dotenv
  from langchain.chains import RetrievalQA
  from langchain.chat_models import ChatOpenAI
  from langchain.embeddings.openai import OpenAIEmbeddings
  from langchain.retrievers import BM25Retriever, EnsembleRetriever
  from langchain.vectorstores import FAISS
  
  langchain.verbose = True
  
  load_dotenv()
  
  # ChatGPTで生成した架空の人名とプロフィール
  texts = [
      """Name: Zephyrina Bluemoon
  Profile: Zephyrina Bluemoon is an astrophysicist who was awarded the Nobel Prize in Physics in 2040. His research on dark matter and multidimensional universes has led to the development of a new cosmological theory.
  """,
      """Name: Quill Solstice
  Profile: Quill Solstice is an internationally renowned environmental activist, working on climate change and biodiversity conservation. His initiatives have received widespread support, especially among the youth around the world.
  """,
      """Name: Seraphim Vortex
  Profile: Seraphim Vortex is a globally acclaimed pianist, whose performances are often described as "the voice of nature". Through her classical music, she conveys a message of environmental preservation to the world.
  """,
      """Name: Eclipse Stardust
  Profile: Eclipse Stardust is an AI developer known for her research in autonomous drones. Her drone technology has been used in disaster rescue and environmental surveys, saving many lives.
  """,
      """Name: Celestia Rainbow
  Profile: Celestia Rainbow is a world-famous novelist, and her works have been translated into more than 30 languages. Her novels, characterized by a deep understanding of humanity and delicate portrayals of the human heart, have received international acclaim.
  """,
  ]
  
  # 用意したデータをFAISSで検索する準備
  embeddings = OpenAIEmbeddings()
  db = FAISS.from_texts(texts, embeddings)
  faiss_retriever = db.as_retriever(search_kwargs={"k": 1})
  
  # 用意したデータをBM25で検索する準備
  bm25_retriever = BM25Retriever.from_texts(texts, k=1)
  
  # 2つのRetrieverを組み合わせる
  ensemble_retriever = EnsembleRetriever(
      retrievers=[bm25_retriever, faiss_retriever], weights=[0.5, 0.5]
  )
  
  # 「関連する文書を検索 => LLMに回答を生成させる」を実行する「RetrievalQA」を準備
  chat = ChatOpenAI(model_name="gpt-3.5-turbo", temperature=0)
  qa_chain = RetrievalQA.from_chain_type(
      llm=chat, chain_type="stuff", retriever=ensemble_retriever
  )
  
  query = "Zephyrina Bluemoonさんについて教えてください。"
  result = qa_chain.run(query)
  print(result)
  
apis: langchain.chat_models.ChatOpenAI langchain.vectorstores.FAISS.from_texts langchain.retrievers.BM25Retriever.from_texts langchain.retrievers.EnsembleRetriever langchain.embeddings.openai.OpenAIEmbeddings langchain.chains.RetrievalQA.from_chain_type
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