DeepLearning4J - ParagraphVectors: Why is similarity negative?
I'm using the ParagraphVector tool in DeepLearning4j framework. What I'm doing is training a model on a set of text documents and then calculating the similarity between those documents.
Now, as the reference page (http://deeplearning4j.org/word2vec) says, the metric used by the tool to calculate similarity is cosine similarity, which should be included between 0 and 1. However, for some pair of documents, I get negative scores.
Can anybody tell why is that?
Thank you in advance.
By definition cosine similarity can be within [-1, 1]. https://en.wikipedia.org/wiki/Cosine_similarity
So technically it's still possible to get negative values for w2v/d2v.
However, usually you won't see -1 or even something close to that.