{"action":"created","issue":{"url":"https://api.github.com/repos/dealii/dealii/issues/3580","repository_url":"https://api.github.com/repos/dealii/dealii","labels_url":"https://api.github.com/repos/dealii/dealii/issues/3580/labels{/name}","comments_url":"https://api.github.com/repos/dealii/dealii/issues/3580/comments","events_url":"https://api.github.com/repos/dealii/dealii/issues/3580/events","html_url":"https://github.com/dealii/dealii/issues/3580","id":189170524,"number":3580,"title":"possibly wrong documentation in constraints on DoFs module","user":{"login":"davydden","id":8023934,"avatar_url":"https://avatars.githubusercontent.com/u/8023934?v=3","gravatar_id":"","url":"https://api.github.com/users/davydden","html_url":"https://github.com/davydden","followers_url":"https://api.github.com/users/davydden/followers","following_url":"https://api.github.com/users/davydden/following{/other_user}","gists_url":"https://api.github.com/users/davydden/gists{/gist_id}","starred_url":"https://api.github.com/users/davydden/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/davydden/subscriptions","organizations_url":"https://api.github.com/users/davydden/orgs","repos_url":"https://api.github.com/users/davydden/repos","events_url":"https://api.github.com/users/davydden/events{/privacy}","received_events_url":"https://api.github.com/users/davydden/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":2,"created_at":"2016-11-14T17:14:45Z","updated_at":"2016-11-14T19:12:16Z","closed_at":null,"body":"there is a section `Applying constraints indirectly with a LinearOperator` with\r\n\r\n> (C^T*A*C+Idc)x̃ =C^T(b−Ak) \r\n\r\nand\r\n\r\n> The matrix C describes the homogeneous part of the linear constraints stored in a ConstraintMatrix\r\n\r\nThe latter looks the notation used in ConstraintMatrix class, which stores only constraints, i.e. `[I-C]x = 0` where `C` is not square. \r\n\r\nJudging from \r\n\r\n>  x←Cx+k. \r\n\r\ni would say the intention was to write instead of `C` something like\r\n```\r\n[I, C]^T\r\n```\r\nwhere first bloc corresponds to the subspace of unconstrained DoFs; and the same for `k`\r\n```\r\n[0, k]^T\r\n```\r\n\r\nSince it's related to Linear operators, probably @tamiko or @luca-heltai know what is meant exactly."},"comment":{"url":"https://api.github.com/repos/dealii/dealii/issues/comments/260431200","html_url":"https://github.com/dealii/dealii/issues/3580#issuecomment-260431200","issue_url":"https://api.github.com/repos/dealii/dealii/issues/3580","id":260431200,"user":{"login":"davydden","id":8023934,"avatar_url":"https://avatars.githubusercontent.com/u/8023934?v=3","gravatar_id":"","url":"https://api.github.com/users/davydden","html_url":"https://github.com/davydden","followers_url":"https://api.github.com/users/davydden/followers","following_url":"https://api.github.com/users/davydden/following{/other_user}","gists_url":"https://api.github.com/users/davydden/gists{/gist_id}","starred_url":"https://api.github.com/users/davydden/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/davydden/subscriptions","organizations_url":"https://api.github.com/users/davydden/orgs","repos_url":"https://api.github.com/users/davydden/repos","events_url":"https://api.github.com/users/davydden/events{/privacy}","received_events_url":"https://api.github.com/users/davydden/received_events","type":"User","site_admin":false},"created_at":"2016-11-14T19:12:16Z","updated_at":"2016-11-14T19:12:16Z","body":"maybe one should follow the block notation in Shephard 1984 and introduce the following blocks:\r\n- `x_u` -- dofs which are not involved in constraints\r\n- `x_m` -- `master` dofs, which determine values of constrained dofs\r\n- `x_c` -- constrained dofs\r\n\r\nThen, hanging nodes constraints are\r\n`[0 C -I] [x_u x_m x_c]^T \\equiv C x_m - x_c = 0` "}}
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