title: Why does the notion of Paragraph Vector make sense?
body: <p>In paragraph vector modeling, they refer paragraph as a memory information, together with context words to predict the target word. I can't see why a paragraph will be useful information to predict the target word.
  Should the paragraph include the target word?
  <a href="https://i.stack.imgur.com/ZqwFo.png" rel="nofollow noreferrer">1</a></p>
  
  <p>Can anyone give me examples of how to do it? What's D here? Is the paragraph ID also a one hot paragraph vector?</p>
  
  <p>For example , I have  paragraph A, B, C and word a,b,c,d,e,f,g.
  Paragraph B is the sequence of abcdefg.
  The document is A+B +C
  If I want to train this document and I want to predict word d.
  What's the input paragraph here?
  I know the word input should be hot word vector of a,b,c,e,f,g,if the window size is 7.</p>