Linear Functions to the Extended Reals
Linear Functions to the Extended Reals
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扩展实数的线性函数
DOI:
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发表时间:
2021
期刊:
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通讯作者:
Bo Waggoner
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文献类型:
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作者:
Bo Waggoner
This note investigates functions from Rd to R∪{±∞} that satisfy axioms of linearity wherever allowed by extended-value arithmetic. They have a nontrivial structure defined inductively on d, and unlike finite linear functions, they require Ω(d2) parameters to uniquely identify. In particular they can capture vertical tangent planes to epigraphs: a function (never −∞) is convex if and only if it has an extended-valued subgradient at every point in its effective domain, if and only if it is the supremum of a family of “affine extended” functions. These results are applied to the well-known characterization of proper scoring rules, for the finite-dimensional case: it is carefully and rigorously extended here to a more constructive form. In particular it is investigated when proper scoring rules can be constructed from a given convex function.