{ localUrl: '../page/function_image.html', arbitalUrl: 'https://arbital.com/p/function_image', rawJsonUrl: '../raw/3lh.json', likeableId: '2491', likeableType: 'page', myLikeValue: '0', likeCount: '1', dislikeCount: '0', likeScore: '1', individualLikes: [ 'EricRogstad' ], pageId: 'function_image', edit: '7', editSummary: '', prevEdit: '6', currentEdit: '7', wasPublished: 'true', type: 'wiki', title: 'Image (of a function)', clickbait: '', textLength: '1180', alias: 'function_image', externalUrl: '', sortChildrenBy: 'likes', hasVote: 'false', voteType: '', votesAnonymous: 'false', editCreatorId: 'NateSoares', editCreatedAt: '2016-06-10 16:45:50', pageCreatorId: 'NateSoares', pageCreatedAt: '2016-05-13 23:17:23', seeDomainId: '0', editDomainId: 'AlexeiAndreev', submitToDomainId: '0', isAutosave: 'false', isSnapshot: 'false', isLiveEdit: 'true', isMinorEdit: 'false', indirectTeacher: 'false', todoCount: '0', isEditorComment: 'false', isApprovedComment: 'true', isResolved: 'false', snapshotText: '', anchorContext: '', anchorText: '', anchorOffset: '0', mergedInto: '', isDeleted: 'false', viewCount: '66', text: 'The image $\\operatorname{im}(f)$ of a [3jy function] $f : X \\to Y$ is the set of all possible outputs of $f$, which is a subset of $Y$. Using [3lj set builder notation], $\\operatorname{im}(f) = \\{f(x) \\mid x \\in X\\}.$\n\nVisualizing a function as a map that takes every point in an input set to one point in an output set, the image is the set of all places where $f$-arrows land (pictured as the yellow subset of $Y$ in the image below).\n\n![Domain, Codomain, and Image](http://i.imgur.com/ZZgVHaI.png)\n\nThe image of a function is not to be confused with the [3lg codomain], which is the _type_ of output that the function produces. For example, consider the [43x Ackermann function], which is a very fast-growing (and difficult to compute) function. When someone asks what sort of thing the Ackermann function produces, the natural answer is not "something from a sparse and hard-to-calculate set of numbers that I can't tell you off the top of my head"; the natural answer is "it outputs a number." In this case, the codomain is "number", while the image is the sparse and hard-to-calculate subset of numbers. 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