{"action":"opened","issue":{"url":"https://api.github.com/repos/scikit-learn/scikit-learn/issues/4544","labels_url":"https://api.github.com/repos/scikit-learn/scikit-learn/issues/4544/labels{/name}","comments_url":"https://api.github.com/repos/scikit-learn/scikit-learn/issues/4544/comments","events_url":"https://api.github.com/repos/scikit-learn/scikit-learn/issues/4544/events","html_url":"https://github.com/scikit-learn/scikit-learn/issues/4544","id":67043185,"number":4544,"title":"Curious for IDF calculations","user":{"login":"l1th1um","id":2639303,"avatar_url":"https://avatars.githubusercontent.com/u/2639303?v=3","gravatar_id":"","url":"https://api.github.com/users/l1th1um","html_url":"https://github.com/l1th1um","followers_url":"https://api.github.com/users/l1th1um/followers","following_url":"https://api.github.com/users/l1th1um/following{/other_user}","gists_url":"https://api.github.com/users/l1th1um/gists{/gist_id}","starred_url":"https://api.github.com/users/l1th1um/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/l1th1um/subscriptions","organizations_url":"https://api.github.com/users/l1th1um/orgs","repos_url":"https://api.github.com/users/l1th1um/repos","events_url":"https://api.github.com/users/l1th1um/events{/privacy}","received_events_url":"https://api.github.com/users/l1th1um/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":0,"created_at":"2015-04-08T03:58:38Z","updated_at":"2015-04-08T03:58:38Z","closed_at":null,"body":"Hi,\r\n\r\nI'm curious for IDF calculations (sklearn/feature_extraction/text.py) line 978\r\n\r\nIn 0.9, the formula for calculating IDF is log(n_samples/ (df + 1)), then in 16.0 the formula become log((n_samples + 1) / (df + 1) + 1. \r\n\r\nAccording to the Cornell SMART system, the formula of IDF is log((n_samples + 1) / (df + 1). So, may I know the reason or reference paper for adding another +1 at the end of formula?\r\n\r\n\r\n*smooth_idf = True"}}