{"action":"created","issue":{"url":"https://api.github.com/repos/odlgroup/odl/issues/571","repository_url":"https://api.github.com/repos/odlgroup/odl","labels_url":"https://api.github.com/repos/odlgroup/odl/issues/571/labels{/name}","comments_url":"https://api.github.com/repos/odlgroup/odl/issues/571/comments","events_url":"https://api.github.com/repos/odlgroup/odl/issues/571/events","html_url":"https://github.com/odlgroup/odl/issues/571","id":176342384,"node_id":"MDU6SXNzdWUxNzYzNDIzODQ=","number":571,"title":"Callback for primal-dual gap and others","user":{"login":"kohr-h","id":5030250,"node_id":"MDQ6VXNlcjUwMzAyNTA=","avatar_url":"https://avatars2.githubusercontent.com/u/5030250?v=4","gravatar_id":"","url":"https://api.github.com/users/kohr-h","html_url":"https://github.com/kohr-h","followers_url":"https://api.github.com/users/kohr-h/followers","following_url":"https://api.github.com/users/kohr-h/following{/other_user}","gists_url":"https://api.github.com/users/kohr-h/gists{/gist_id}","starred_url":"https://api.github.com/users/kohr-h/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/kohr-h/subscriptions","organizations_url":"https://api.github.com/users/kohr-h/orgs","repos_url":"https://api.github.com/users/kohr-h/repos","events_url":"https://api.github.com/users/kohr-h/events{/privacy}","received_events_url":"https://api.github.com/users/kohr-h/received_events","type":"User","site_admin":false},"labels":[{"id":288999701,"node_id":"MDU6TGFiZWwyODg5OTk3MDE=","url":"https://api.github.com/repos/odlgroup/odl/labels/new%20feature","name":"new feature","color":"fad8c7","default":false},{"id":289000326,"node_id":"MDU6TGFiZWwyODkwMDAzMjY=","url":"https://api.github.com/repos/odlgroup/odl/labels/odl%20solvers","name":"odl solvers","color":"5319e7","default":false}],"state":"closed","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":20,"created_at":"2016-09-12T10:26:23Z","updated_at":"2018-06-28T13:32:15Z","closed_at":"2018-06-28T13:32:15Z","author_association":"MEMBER","body":"Besides printing information on the primal iterates, which is what most current `Callback<xyz>` classes do, one often wants to observe the primal-dual gap during the iteration of a method operating in both primal and dual variables. Similarly, other information (norm etc.) about the dual variable would be valuable during iteration, too. With the current design, this is not possible.\n\nWhat is missing is a way to distinguish callbacks that act only on the primal variable (usable in primal-only or dual-only methods) from ones that act on both of them.\n\nOnce that is settled, it would be rather simple to implement the primal-dual gap callback by initializing it with a `Functional` (and its convex conjugate if not present in the class), and call it in an iterative method on `(primal, dual)`.\n"},"comment":{"url":"https://api.github.com/repos/odlgroup/odl/issues/comments/401035719","html_url":"https://github.com/odlgroup/odl/issues/571#issuecomment-401035719","issue_url":"https://api.github.com/repos/odlgroup/odl/issues/571","id":401035719,"node_id":"MDEyOklzc3VlQ29tbWVudDQwMTAzNTcxOQ==","user":{"login":"kohr-h","id":5030250,"node_id":"MDQ6VXNlcjUwMzAyNTA=","avatar_url":"https://avatars2.githubusercontent.com/u/5030250?v=4","gravatar_id":"","url":"https://api.github.com/users/kohr-h","html_url":"https://github.com/kohr-h","followers_url":"https://api.github.com/users/kohr-h/followers","following_url":"https://api.github.com/users/kohr-h/following{/other_user}","gists_url":"https://api.github.com/users/kohr-h/gists{/gist_id}","starred_url":"https://api.github.com/users/kohr-h/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/kohr-h/subscriptions","organizations_url":"https://api.github.com/users/kohr-h/orgs","repos_url":"https://api.github.com/users/kohr-h/repos","events_url":"https://api.github.com/users/kohr-h/events{/privacy}","received_events_url":"https://api.github.com/users/kohr-h/received_events","type":"User","site_admin":false},"created_at":"2018-06-28T13:32:15Z","updated_at":"2018-06-28T13:32:15Z","author_association":"MEMBER","body":"Agreed, that one will get rid of the issue without requiring hacks."}}
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