msmarco-MiniLM-L12-cos-v5

这是一个模型：它将句子和段落映射到一个768维的稠密向量空间，并且专门设计用于语义搜索。它是在来自 MS MARCO Passages dataset 的50万个（查询，答案）对上进行训练的。如果想了解语义搜索的介绍，请查看： SBERT.net - Semantic Search

用法（Sentence-Transformers）

安装了 sentence-transformers 后，使用这个模型变得很容易：

pip install -U sentence-transformers

然后可以像这样使用该模型：

from sentence_transformers import SentenceTransformer, util

query = "How many people live in London?"
docs = ["Around 9 Million people live in London", "London is known for its financial district"]

#Load the model
model = SentenceTransformer('sentence-transformers/msmarco-MiniLM-L12-cos-v5')

#Encode query and documents
query_emb = model.encode(query)
doc_emb = model.encode(docs)

#Compute dot score between query and all document embeddings
scores = util.dot_score(query_emb, doc_emb)[0].cpu().tolist()

#Combine docs & scores
doc_score_pairs = list(zip(docs, scores))

#Sort by decreasing score
doc_score_pairs = sorted(doc_score_pairs, key=lambda x: x[1], reverse=True)

#Output passages & scores
for doc, score in doc_score_pairs:
    print(score, doc)

用法（HuggingFace Transformers）

没有安装 sentence-transformers ，您可以像这样使用该模型：首先，将输入传递给变换器模型，然后必须在上下文化的单词嵌入之上应用正确的汇聚操作。

from transformers import AutoTokenizer, AutoModel
import torch
import torch.nn.functional as F

#Mean Pooling - Take average of all tokens
def mean_pooling(model_output, attention_mask):
    token_embeddings = model_output.last_hidden_state #First element of model_output contains all token embeddings
    input_mask_expanded = attention_mask.unsqueeze(-1).expand(token_embeddings.size()).float()
    return torch.sum(token_embeddings * input_mask_expanded, 1) / torch.clamp(input_mask_expanded.sum(1), min=1e-9)


#Encode text
def encode(texts):
    # Tokenize sentences
    encoded_input = tokenizer(texts, padding=True, truncation=True, return_tensors='pt')

    # Compute token embeddings
    with torch.no_grad():
        model_output = model(**encoded_input, return_dict=True)

    # Perform pooling
    embeddings = mean_pooling(model_output, encoded_input['attention_mask'])

    # Normalize embeddings
    embeddings = F.normalize(embeddings, p=2, dim=1)
    
    return embeddings


# Sentences we want sentence embeddings for
query = "How many people live in London?"
docs = ["Around 9 Million people live in London", "London is known for its financial district"]

# Load model from HuggingFace Hub
tokenizer = AutoTokenizer.from_pretrained("sentence-transformers/msmarco-MiniLM-L12-cos-v5")
model = AutoModel.from_pretrained("sentence-transformers/msmarco-MiniLM-L12-cos-v5")

#Encode query and docs
query_emb = encode(query)
doc_emb = encode(docs)

#Compute dot score between query and all document embeddings
scores = torch.mm(query_emb, doc_emb.transpose(0, 1))[0].cpu().tolist()

#Combine docs & scores
doc_score_pairs = list(zip(docs, scores))

#Sort by decreasing score
doc_score_pairs = sorted(doc_score_pairs, key=lambda x: x[1], reverse=True)

#Output passages & scores
for doc, score in doc_score_pairs:
    print(score, doc)

技术细节

以下是关于如何使用此模型的一些技术细节：

注意：使用sentence-transformers加载时，该模型会产生长度为1的归一化嵌入。在这种情况下，点积和余弦相似度是等价的。由于点积更快，所以它更受推荐。欧氏距离与点积成正比，也可以使用。

引用和作者

该模型由 sentence-transformers 进行训练。

如果您发现该模型有帮助，请随意引用我们的出版物 Sentence-BERT: Sentence Embeddings using Siamese BERT-Networks ：

@inproceedings{reimers-2019-sentence-bert,
    title = "Sentence-BERT: Sentence Embeddings using Siamese BERT-Networks",
    author = "Reimers, Nils and Gurevych, Iryna",
    booktitle = "Proceedings of the 2019 Conference on Empirical Methods in Natural Language Processing",
    month = "11",
    year = "2019",
    publisher = "Association for Computational Linguistics",
    url = "http://arxiv.org/abs/1908.10084",
}