{"action":"created","issue":{"url":"https://api.github.com/repos/gap-packages/Semigroups/issues/230","repository_url":"https://api.github.com/repos/gap-packages/Semigroups","labels_url":"https://api.github.com/repos/gap-packages/Semigroups/issues/230/labels{/name}","comments_url":"https://api.github.com/repos/gap-packages/Semigroups/issues/230/comments","events_url":"https://api.github.com/repos/gap-packages/Semigroups/issues/230/events","html_url":"https://github.com/gap-packages/Semigroups/issues/230","id":190062671,"number":230,"title":"Incorrect results in MaximalSubsemigroups","user":{"login":"wilfwilson","id":8956868,"avatar_url":"https://avatars.githubusercontent.com/u/8956868?v=3","gravatar_id":"","url":"https://api.github.com/users/wilfwilson","html_url":"https://github.com/wilfwilson","followers_url":"https://api.github.com/users/wilfwilson/followers","following_url":"https://api.github.com/users/wilfwilson/following{/other_user}","gists_url":"https://api.github.com/users/wilfwilson/gists{/gist_id}","starred_url":"https://api.github.com/users/wilfwilson/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/wilfwilson/subscriptions","organizations_url":"https://api.github.com/users/wilfwilson/orgs","repos_url":"https://api.github.com/users/wilfwilson/repos","events_url":"https://api.github.com/users/wilfwilson/events{/privacy}","received_events_url":"https://api.github.com/users/wilfwilson/received_events","type":"User","site_admin":false},"labels":[{"id":358206049,"url":"https://api.github.com/repos/gap-packages/Semigroups/labels/bug","name":"bug","color":"ee0701","default":true},{"id":358289821,"url":"https://api.github.com/repos/gap-packages/Semigroups/labels/major","name":"major","color":"ededed","default":false},{"id":396733464,"url":"https://api.github.com/repos/gap-packages/Semigroups/labels/unstable-3.0","name":"unstable-3.0","color":"f9d0c4","default":false}],"state":"open","locked":false,"assignee":{"login":"wilfwilson","id":8956868,"avatar_url":"https://avatars.githubusercontent.com/u/8956868?v=3","gravatar_id":"","url":"https://api.github.com/users/wilfwilson","html_url":"https://github.com/wilfwilson","followers_url":"https://api.github.com/users/wilfwilson/followers","following_url":"https://api.github.com/users/wilfwilson/following{/other_user}","gists_url":"https://api.github.com/users/wilfwilson/gists{/gist_id}","starred_url":"https://api.github.com/users/wilfwilson/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/wilfwilson/subscriptions","organizations_url":"https://api.github.com/users/wilfwilson/orgs","repos_url":"https://api.github.com/users/wilfwilson/repos","events_url":"https://api.github.com/users/wilfwilson/events{/privacy}","received_events_url":"https://api.github.com/users/wilfwilson/received_events","type":"User","site_admin":false},"assignees":[{"login":"wilfwilson","id":8956868,"avatar_url":"https://avatars.githubusercontent.com/u/8956868?v=3","gravatar_id":"","url":"https://api.github.com/users/wilfwilson","html_url":"https://github.com/wilfwilson","followers_url":"https://api.github.com/users/wilfwilson/followers","following_url":"https://api.github.com/users/wilfwilson/following{/other_user}","gists_url":"https://api.github.com/users/wilfwilson/gists{/gist_id}","starred_url":"https://api.github.com/users/wilfwilson/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/wilfwilson/subscriptions","organizations_url":"https://api.github.com/users/wilfwilson/orgs","repos_url":"https://api.github.com/users/wilfwilson/repos","events_url":"https://api.github.com/users/wilfwilson/events{/privacy}","received_events_url":"https://api.github.com/users/wilfwilson/received_events","type":"User","site_admin":false}],"milestone":null,"comments":3,"created_at":"2016-11-17T14:30:57Z","updated_at":"2016-11-17T16:46:10Z","closed_at":null,"body":"Whilst investigating the maximal subsemigroups of the inverse monoid PORI_n, I have discovered a problem with my code.\r\n\r\nThere are maximal subsemigroups of PORI_n which arise from the group of units (no problem there), and some which arise from the D-classes of elements of rank n-1 (these are the problem ones). The `MaximalSubsemigroups` code is missing some maximal subsemigroups of this type which intersect every H-class. Since it does not find them, it believes that the subsemigroup formed by removing this entire D-class is maximal, which is not the case.\r\n\r\nI currently do not know why this is occurring. I hope it's nothing disastrous.\r\n```\r\ngap> S := Monoid( [ PartialPerm( [ 1, 2, 3, 4, 5, 6 ], [ 2, 3, 4, 5, 6, 1 ] ),\r\n>  PartialPerm( [ 1, 2, 3, 4, 5 ], [ 1, 2, 3, 4, 6 ] ),\r\n>  PartialPerm( [ 1, 2, 3, 4, 6 ], [ 1, 2, 3, 4, 5 ] ),\r\n>  PartialPerm( [ 1, 2, 3, 4, 5, 6 ], [ 6, 5, 4, 3, 2, 1 ] ) ] );; # PORI_6\r\ngap> U := InverseMonoid( [ PartialPerm( [ 1, 2, 3, 4, 5, 6 ], [ 6, 1, 2, 3, 4, 5 ] ),\r\n>  PartialPerm( [ 1, 2, 3, 4, 5, 6 ], [ 3, 2, 1, 6, 5, 4 ] ),\r\n>  PartialPerm( [ 2, 3, 4, 5, 6 ], [ 2, 3, 4, 5, 6 ] ),\r\n>  PartialPerm( [ 2, 3, 5, 6 ], [ 6, 5, 4, 3 ] ),\r\n>  PartialPerm( [ 2, 3, 4, 6 ], [ 5, 4, 1, 6 ] ) ] );;\r\ngap> IsMaximalSubsemigroup(S, U);\r\ntrue\r\ngap> U in MaximalSubsemigroups(S);\r\nfalse\r\ngap> V := InverseMonoid( [ PartialPerm( [ 1, 2, 3, 4, 5, 6 ], [ 2, 3, 4, 5, 6, 1 ] ),\r\n>  PartialPerm( [ 1, 2, 3, 4, 5, 6 ], [ 6, 5, 4, 3, 2, 1 ] ),\r\n>  PartialPerm( [ 1, 2, 3, 4 ], [ 1, 4, 3, 2 ] ),\r\n>  PartialPerm( [ 1, 2, 3, 4 ], [ 3, 2, 6, 5 ] ),\r\n>  PartialPerm( [ 1, 2, 3, 4 ], [ 3, 5, 6, 1 ] ) ] );;\r\ngap> IsMaximalSubsemigroup(S, V);\r\nfalse\r\ngap> V in MaximalSubsemigroups(S);\r\ntrue\r\ngap> IsSubsemigroup(U, V);\r\ntrue\r\n```"},"comment":{"url":"https://api.github.com/repos/gap-packages/Semigroups/issues/comments/261300093","html_url":"https://github.com/gap-packages/Semigroups/issues/230#issuecomment-261300093","issue_url":"https://api.github.com/repos/gap-packages/Semigroups/issues/230","id":261300093,"user":{"login":"wilfwilson","id":8956868,"avatar_url":"https://avatars.githubusercontent.com/u/8956868?v=3","gravatar_id":"","url":"https://api.github.com/users/wilfwilson","html_url":"https://github.com/wilfwilson","followers_url":"https://api.github.com/users/wilfwilson/followers","following_url":"https://api.github.com/users/wilfwilson/following{/other_user}","gists_url":"https://api.github.com/users/wilfwilson/gists{/gist_id}","starred_url":"https://api.github.com/users/wilfwilson/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/wilfwilson/subscriptions","organizations_url":"https://api.github.com/users/wilfwilson/orgs","repos_url":"https://api.github.com/users/wilfwilson/repos","events_url":"https://api.github.com/users/wilfwilson/events{/privacy}","received_events_url":"https://api.github.com/users/wilfwilson/received_events","type":"User","site_admin":false},"created_at":"2016-11-17T16:46:09Z","updated_at":"2016-11-17T16:46:09Z","body":"I haven't looked deeply into the problem yet, but I'm pretty sure it's my fault. `PORI_16` has 9,617,257,185 elements so there's no chance that it would terminate in 2.8.1. So I can't verify the situation there. However `PORI_6` only has 5059 elements, and so I can confirm that 2.8.1 gives the **correct** result. \r\n\r\nThat's not too surprising, since almost none of the maximal subsemigroups code from 2.8.1 is present in unstable-3.0. The relevant case now involves calculating the maximal subsemigroups of a Rees 0-matrix semigroup which contain a particular set of elements. This is the most complicated part of the algorithm and the only part which we don't have written up formally, so I think it's most likely that I've just coded something wrongly here.\r\n\r\nI'll sort it out tomorrow."}}
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