{"action":"created","issue":{"url":"https://api.github.com/repos/goma/goma/issues/94","repository_url":"https://api.github.com/repos/goma/goma","labels_url":"https://api.github.com/repos/goma/goma/issues/94/labels{/name}","comments_url":"https://api.github.com/repos/goma/goma/issues/94/comments","events_url":"https://api.github.com/repos/goma/goma/issues/94/events","html_url":"https://github.com/goma/goma/issues/94","id":135842525,"number":94,"title":"Minimum Resolved Timestep","user":{"login":"acochrane","id":6686614,"avatar_url":"https://avatars.githubusercontent.com/u/6686614?v=3","gravatar_id":"","url":"https://api.github.com/users/acochrane","html_url":"https://github.com/acochrane","followers_url":"https://api.github.com/users/acochrane/followers","following_url":"https://api.github.com/users/acochrane/following{/other_user}","gists_url":"https://api.github.com/users/acochrane/gists{/gist_id}","starred_url":"https://api.github.com/users/acochrane/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/acochrane/subscriptions","organizations_url":"https://api.github.com/users/acochrane/orgs","repos_url":"https://api.github.com/users/acochrane/repos","events_url":"https://api.github.com/users/acochrane/events{/privacy}","received_events_url":"https://api.github.com/users/acochrane/received_events","type":"User","site_admin":false},"labels":[{"url":"https://api.github.com/repos/goma/goma/labels/bug","name":"bug","color":"fc2929"}],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":5,"created_at":"2016-02-23T19:42:24Z","updated_at":"2016-02-23T21:58:32Z","closed_at":null,"body":"I'm not sure that I'm using this input deck card correctly.\r\nThe Goma manual states,\r\n\"Its role is to set a lower bound for the time step with respect to the Time step error\r\ntolerance. When a converged time step is obtained by GOMA, the difference between\r\nthe predicted solution and final solution for that time step is compared to the Time step\r\nerror tolerance. If the difference exceeds this tolerance the step fails and the time step\r\nis cut (usually by a factor of 2), UNLESS the time step falls below the Minimum\r\nResolved Time Step size. In this case the step is accepted, even if this error tolerance is\r\nnot achieved. This provides a mechanism for the modeler to control what phenomena is\r\nresolved and what phenomena is ignored.\"\r\n\r\nThe behavior I observe,\r\nI set the Minimum Resolved Timestep to be some value, x. Even when a time step fails to converge through Newton iteration, the time step still does not get cut below x. The simulation retries the same calculation for the same x that failed Newton convergence previously. Resulting in retrying the same timestep over and over, until, I assume, it runs out of timesteps.\r\n\r\nIs this the expected behavior or can we fix it? I think the card should allow further timesteps with the same dt only if Newton convergence succeeds, and cuts the timestep if the Newton convergence fails, no matter what."},"comment":{"url":"https://api.github.com/repos/goma/goma/issues/comments/187933171","html_url":"https://github.com/goma/goma/issues/94#issuecomment-187933171","issue_url":"https://api.github.com/repos/goma/goma/issues/94","id":187933171,"user":{"login":"acochrane","id":6686614,"avatar_url":"https://avatars.githubusercontent.com/u/6686614?v=3","gravatar_id":"","url":"https://api.github.com/users/acochrane","html_url":"https://github.com/acochrane","followers_url":"https://api.github.com/users/acochrane/followers","following_url":"https://api.github.com/users/acochrane/following{/other_user}","gists_url":"https://api.github.com/users/acochrane/gists{/gist_id}","starred_url":"https://api.github.com/users/acochrane/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/acochrane/subscriptions","organizations_url":"https://api.github.com/users/acochrane/orgs","repos_url":"https://api.github.com/users/acochrane/repos","events_url":"https://api.github.com/users/acochrane/events{/privacy}","received_events_url":"https://api.github.com/users/acochrane/received_events","type":"User","site_admin":false},"created_at":"2016-02-23T21:58:32Z","updated_at":"2016-02-23T21:58:32Z","body":"Now that I've tested what happens when cutting the time step ONLY IF Newton convergence succeeds, I think the best solution is to have Goma give up if the Newton convergence failure causes the dt to fall below the _Minimum Resolved Time Step_.\r\n\r\nDoes that contradict any expected behavior?\r\n\r\nAs it stands, if the Newton convergence succeeds on a time step significantly smaller than _Minimum Resolved Time Step_, then dt gets immediately reset to _Minimum Resolved Time Step_. Then convergence fails, and several failing time steps cut the time step down so that another small time step can succeed, causing dt to get reset to _Minimum Resolved Time Step_ again."}}