{"action":"closed","issue":{"url":"https://api.github.com/repos/tensorflow/tensorflow/issues/4431","repository_url":"https://api.github.com/repos/tensorflow/tensorflow","labels_url":"https://api.github.com/repos/tensorflow/tensorflow/issues/4431/labels{/name}","comments_url":"https://api.github.com/repos/tensorflow/tensorflow/issues/4431/comments","events_url":"https://api.github.com/repos/tensorflow/tensorflow/issues/4431/events","html_url":"https://github.com/tensorflow/tensorflow/issues/4431","id":177625592,"number":4431,"title":"Forward mode ad, directional derivatives","user":{"login":"vladfi1","id":691536,"avatar_url":"https://avatars.githubusercontent.com/u/691536?v=3","gravatar_id":"","url":"https://api.github.com/users/vladfi1","html_url":"https://github.com/vladfi1","followers_url":"https://api.github.com/users/vladfi1/followers","following_url":"https://api.github.com/users/vladfi1/following{/other_user}","gists_url":"https://api.github.com/users/vladfi1/gists{/gist_id}","starred_url":"https://api.github.com/users/vladfi1/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/vladfi1/subscriptions","organizations_url":"https://api.github.com/users/vladfi1/orgs","repos_url":"https://api.github.com/users/vladfi1/repos","events_url":"https://api.github.com/users/vladfi1/events{/privacy}","received_events_url":"https://api.github.com/users/vladfi1/received_events","type":"User","site_admin":false},"labels":[],"state":"closed","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":2,"created_at":"2016-09-18T02:59:41Z","updated_at":"2016-11-18T00:12:16Z","closed_at":"2016-11-18T00:12:16Z","body":"Say I have `outputs = f(inputs)` and `g` of the same shape as `inputs`. I'd like to compute the directional derivative of `outputs` with respect to `inputs` in the direction `g` - in other words, the derivative of `f(inputs + alpha * g)` with respect to `alpha` at the point `alpha=0`.\n\nThis is a straightforward application of forward-mode automatic differentiation, which should be pretty easy to implement (much easier than the already-implemented reverse-mode ad). Are there any plans to add this feature?\n"}}
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