How does gensim calculate doc2vec paragraph vectors

Question

i am going thorugh this paper http://cs.stanford.edu/~quocle/paragraph_vector.pdf

and it states that

\" Theparagraph vector and word vectors are a

Answer 1

A simple (and sometimes useful) vector for a range of text is the sum or average of the text's words' vectors – but that's not what the 'Paragraph Vector' of the 'Paragraph Vectors' paper is.

Rather, the Paragraph Vector is another vector, trained similarly to the word vectors, which is also adjusted to help in word-prediction. These vectors are combined (or interleaved) with the word vectors to feed the prediction model. That is, the averaging (in DM mode) includes the PV alongside word-vectors - it doesn't compose the PV from word-vectors.

In the diagram, on is the target-word being predicted, in that diagram by a combination of closely-neighboring words and the full-example's PV, which may perhaps be informally thought of as a special pseudoword, ranging over the entire text example, participating in all the sliding 'windows' of real words.