{"action":"created","issue":{"url":"https://api.github.com/repos/johntfoster/bspline/issues/4","repository_url":"https://api.github.com/repos/johntfoster/bspline","labels_url":"https://api.github.com/repos/johntfoster/bspline/issues/4/labels{/name}","comments_url":"https://api.github.com/repos/johntfoster/bspline/issues/4/comments","events_url":"https://api.github.com/repos/johntfoster/bspline/issues/4/events","html_url":"https://github.com/johntfoster/bspline/issues/4","id":339359651,"node_id":"MDU6SXNzdWUzMzkzNTk2NTE=","number":4,"title":"Matrix bug?","user":{"login":"luksen99","id":36759141,"node_id":"MDQ6VXNlcjM2NzU5MTQx","avatar_url":"https://avatars0.githubusercontent.com/u/36759141?v=4","gravatar_id":"","url":"https://api.github.com/users/luksen99","html_url":"https://github.com/luksen99","followers_url":"https://api.github.com/users/luksen99/followers","following_url":"https://api.github.com/users/luksen99/following{/other_user}","gists_url":"https://api.github.com/users/luksen99/gists{/gist_id}","starred_url":"https://api.github.com/users/luksen99/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/luksen99/subscriptions","organizations_url":"https://api.github.com/users/luksen99/orgs","repos_url":"https://api.github.com/users/luksen99/repos","events_url":"https://api.github.com/users/luksen99/events{/privacy}","received_events_url":"https://api.github.com/users/luksen99/received_events","type":"User","site_admin":false},"labels":[{"id":216848826,"node_id":"MDU6TGFiZWwyMTY4NDg4MjY=","url":"https://api.github.com/repos/johntfoster/bspline/labels/bug","name":"bug","color":"fc2929","default":true}],"state":"open","locked":false,"assignee":{"login":"Technologicat","id":16972251,"node_id":"MDQ6VXNlcjE2OTcyMjUx","avatar_url":"https://avatars0.githubusercontent.com/u/16972251?v=4","gravatar_id":"","url":"https://api.github.com/users/Technologicat","html_url":"https://github.com/Technologicat","followers_url":"https://api.github.com/users/Technologicat/followers","following_url":"https://api.github.com/users/Technologicat/following{/other_user}","gists_url":"https://api.github.com/users/Technologicat/gists{/gist_id}","starred_url":"https://api.github.com/users/Technologicat/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/Technologicat/subscriptions","organizations_url":"https://api.github.com/users/Technologicat/orgs","repos_url":"https://api.github.com/users/Technologicat/repos","events_url":"https://api.github.com/users/Technologicat/events{/privacy}","received_events_url":"https://api.github.com/users/Technologicat/received_events","type":"User","site_admin":false},"assignees":[{"login":"Technologicat","id":16972251,"node_id":"MDQ6VXNlcjE2OTcyMjUx","avatar_url":"https://avatars0.githubusercontent.com/u/16972251?v=4","gravatar_id":"","url":"https://api.github.com/users/Technologicat","html_url":"https://github.com/Technologicat","followers_url":"https://api.github.com/users/Technologicat/followers","following_url":"https://api.github.com/users/Technologicat/following{/other_user}","gists_url":"https://api.github.com/users/Technologicat/gists{/gist_id}","starred_url":"https://api.github.com/users/Technologicat/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/Technologicat/subscriptions","organizations_url":"https://api.github.com/users/Technologicat/orgs","repos_url":"https://api.github.com/users/Technologicat/repos","events_url":"https://api.github.com/users/Technologicat/events{/privacy}","received_events_url":"https://api.github.com/users/Technologicat/received_events","type":"User","site_admin":false}],"milestone":null,"comments":0,"created_at":"2018-07-09T08:52:00Z","updated_at":"2018-07-18T22:04:42Z","closed_at":null,"author_association":"NONE","body":"Hi Johnt, \r\nwe are using your B-spline package in the framework of tackling parabolic differential equations. \r\nCreating a spline matrix A using ‘collmat’ we find that the last entry (A_nn) is, just like the entire last row 0. Is this a bug? We expected  the entire row to be 0, **except** for the A_nn element, which should be 1. (Just like the A_00 element is 1 and the rest of the A_0-row is 0). Right now we do some ‘artificial fixing’, i.e. setting A_nn to 1 manually.\r\nThe problem is also present in the 1st order derivative.\r\n"},"comment":{"url":"https://api.github.com/repos/johntfoster/bspline/issues/comments/406088975","html_url":"https://github.com/johntfoster/bspline/issues/4#issuecomment-406088975","issue_url":"https://api.github.com/repos/johntfoster/bspline/issues/4","id":406088975,"node_id":"MDEyOklzc3VlQ29tbWVudDQwNjA4ODk3NQ==","user":{"login":"Technologicat","id":16972251,"node_id":"MDQ6VXNlcjE2OTcyMjUx","avatar_url":"https://avatars0.githubusercontent.com/u/16972251?v=4","gravatar_id":"","url":"https://api.github.com/users/Technologicat","html_url":"https://github.com/Technologicat","followers_url":"https://api.github.com/users/Technologicat/followers","following_url":"https://api.github.com/users/Technologicat/following{/other_user}","gists_url":"https://api.github.com/users/Technologicat/gists{/gist_id}","starred_url":"https://api.github.com/users/Technologicat/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/Technologicat/subscriptions","organizations_url":"https://api.github.com/users/Technologicat/orgs","repos_url":"https://api.github.com/users/Technologicat/repos","events_url":"https://api.github.com/users/Technologicat/events{/privacy}","received_events_url":"https://api.github.com/users/Technologicat/received_events","type":"User","site_admin":false},"created_at":"2018-07-18T22:04:42Z","updated_at":"2018-07-18T22:04:42Z","author_association":"COLLABORATOR","body":"Hi,\r\nThe bspline package defines each piecewise polynomial to have support on the half-open interval [x_k, x_{k+1}). Hence, evaluating the last basis function at the final endpoint yields 0, making the whole B-spline zero there.\r\n\r\nAs a workaround, in my own codes I've scaled the whole interval (which is to be spanned by the B-spline) by a factor of 1 + ε, where ε is some suitably small positive number. Then evaluating the last basis function at the *original* endpoint yields a value that is sufficiently close to 1 for practical purposes - and hence evaluating the whole B-spline there then gives sensible results.\r\n\r\nI think it is theoretically possible to fix the issue, but doing so complicates the (currently very short and elegant) implementation of the Cox - de Boor algorithm. However, if you and John feel this is important to fix, it could be done."}}
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