{"action":"closed","issue":{"url":"https://api.github.com/repos/SheffieldML/GPy/issues/498","repository_url":"https://api.github.com/repos/SheffieldML/GPy","labels_url":"https://api.github.com/repos/SheffieldML/GPy/issues/498/labels{/name}","comments_url":"https://api.github.com/repos/SheffieldML/GPy/issues/498/comments","events_url":"https://api.github.com/repos/SheffieldML/GPy/issues/498/events","html_url":"https://github.com/SheffieldML/GPy/issues/498","id":221265554,"number":498,"title":"inconsistent input_dim when adding/multiplying kernels","user":{"login":"pgmoren","id":3373762,"avatar_url":"https://avatars0.githubusercontent.com/u/3373762?v=4","gravatar_id":"","url":"https://api.github.com/users/pgmoren","html_url":"https://github.com/pgmoren","followers_url":"https://api.github.com/users/pgmoren/followers","following_url":"https://api.github.com/users/pgmoren/following{/other_user}","gists_url":"https://api.github.com/users/pgmoren/gists{/gist_id}","starred_url":"https://api.github.com/users/pgmoren/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/pgmoren/subscriptions","organizations_url":"https://api.github.com/users/pgmoren/orgs","repos_url":"https://api.github.com/users/pgmoren/repos","events_url":"https://api.github.com/users/pgmoren/events{/privacy}","received_events_url":"https://api.github.com/users/pgmoren/received_events","type":"User","site_admin":false},"labels":[],"state":"closed","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":5,"created_at":"2017-04-12T13:38:54Z","updated_at":"2018-02-12T22:30:21Z","closed_at":"2018-02-12T22:30:21Z","author_association":"NONE","body":"The definition of input_dim seems to be non-consistent. In a base kernel, input_dim seems to represent the dimensionality of the inputs and does not change when we change active_dims. \r\n\r\nHowever, when we add/multiply two kernels with same input dimensionality, the variable input_dim seems to be recomputed, i.e. as the cardinality of the union set of the active_dims of the original kernels.\r\n\r\nShould not be the input_dim of the output kernel equal to that of the inputs? \r\n\r\nIn my opinion, in the example below, \"print k3.input_dim\" should output 2 instead of 1.\r\n```\r\nk1 = GPy.kern.RBF(2)\r\nk1.active_dims = [1]\r\nprint k1.input_dim\r\n\r\nk2 = GPy.kern.RBF(2)\r\nk2.active_dims = [1]\r\nprint k2.input_dim\r\n\r\nk3 = k1 + k2\r\nprint k3.active_dims\r\nprint k3.input_dim\r\n```\r\n"}}
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