{"action":"created","issue":{"url":"https://api.github.com/repos/rmjarvis/TreeCorr/issues/72","repository_url":"https://api.github.com/repos/rmjarvis/TreeCorr","labels_url":"https://api.github.com/repos/rmjarvis/TreeCorr/issues/72/labels{/name}","comments_url":"https://api.github.com/repos/rmjarvis/TreeCorr/issues/72/comments","events_url":"https://api.github.com/repos/rmjarvis/TreeCorr/issues/72/events","html_url":"https://github.com/rmjarvis/TreeCorr/issues/72","id":377443074,"node_id":"MDU6SXNzdWUzNzc0NDMwNzQ=","number":72,"title":"varxi missing factor of 2 for xi+/-","user":{"login":"NiallMac","id":7635269,"node_id":"MDQ6VXNlcjc2MzUyNjk=","avatar_url":"https://avatars3.githubusercontent.com/u/7635269?v=4","gravatar_id":"","url":"https://api.github.com/users/NiallMac","html_url":"https://github.com/NiallMac","followers_url":"https://api.github.com/users/NiallMac/followers","following_url":"https://api.github.com/users/NiallMac/following{/other_user}","gists_url":"https://api.github.com/users/NiallMac/gists{/gist_id}","starred_url":"https://api.github.com/users/NiallMac/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/NiallMac/subscriptions","organizations_url":"https://api.github.com/users/NiallMac/orgs","repos_url":"https://api.github.com/users/NiallMac/repos","events_url":"https://api.github.com/users/NiallMac/events{/privacy}","received_events_url":"https://api.github.com/users/NiallMac/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":0,"created_at":"2018-11-05T15:12:57Z","updated_at":"2018-11-05T15:15:56Z","closed_at":null,"author_association":"NONE","body":"I mentioned this to @rmjarvis a while back but I think I never actually started an issue. I believe the way treecorr calculates varxi for xi+/- is missing a factor of 2. I think this is most clear by considering xi+/- = C_tt +/- C_xx where C_tt is the correlation function of the tangential shear components and C_xx is the correlation function of the cross components. The expression in this line https://github.com/rmjarvis/TreeCorr/blob/releases/3.3/treecorr/ggcorrelation.py#L252 would be appropriate for C_tt or C_xx, so the variance of xi_+/- should be twice that. In case useful, I've attached some notes with a derivation of the shape noise variance for xi+/-. \r\n[shape_noise_xipm.pdf](https://github.com/rmjarvis/TreeCorr/files/2548959/shape_noise_xipm.pdf)\r\n"},"comment":{"url":"https://api.github.com/repos/rmjarvis/TreeCorr/issues/comments/435911416","html_url":"https://github.com/rmjarvis/TreeCorr/issues/72#issuecomment-435911416","issue_url":"https://api.github.com/repos/rmjarvis/TreeCorr/issues/72","id":435911416,"node_id":"MDEyOklzc3VlQ29tbWVudDQzNTkxMTQxNg==","user":{"login":"rmjarvis","id":623887,"node_id":"MDQ6VXNlcjYyMzg4Nw==","avatar_url":"https://avatars3.githubusercontent.com/u/623887?v=4","gravatar_id":"","url":"https://api.github.com/users/rmjarvis","html_url":"https://github.com/rmjarvis","followers_url":"https://api.github.com/users/rmjarvis/followers","following_url":"https://api.github.com/users/rmjarvis/following{/other_user}","gists_url":"https://api.github.com/users/rmjarvis/gists{/gist_id}","starred_url":"https://api.github.com/users/rmjarvis/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/rmjarvis/subscriptions","organizations_url":"https://api.github.com/users/rmjarvis/orgs","repos_url":"https://api.github.com/users/rmjarvis/repos","events_url":"https://api.github.com/users/rmjarvis/events{/privacy}","received_events_url":"https://api.github.com/users/rmjarvis/received_events","type":"User","site_admin":false},"created_at":"2018-11-05T15:15:56Z","updated_at":"2018-11-05T15:15:56Z","author_association":"OWNER","body":"Thanks Niall.  I agree.  This will help me remember to fix this before the next release."}}
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