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Pointwise complexity of the derivative of a computable function
Archive For Mathematical Logic ( IF 0.3 ) Pub Date : 2021-04-16 , DOI: 10.1007/s00153-021-00769-4
Ethan McCarthy

We explore the relationship between analytic behavior of a computable real valued function and the computability-theoretic complexity of the individual values of its derivative (the function’s slopes) almost-everywhere. Given a computable function f, the values of its derivative \(f'(x)\), where they are defined, are uniformly computable from \(x'\), the Turing jump of the input. It is known that when f is \({\mathcal {C}}^2\), the values of \(f'(x)\) are actually computable from x. We construct a \({\mathcal {C}}^1\) function f so that, almost everywhere, \(f'(x)\ge _T x'\). Although the values \(f'(x)\) at each point x cannot uniformly compute the corresponding jumps \(x'\) of the inputs x almost everywhere for any \({\mathcal {C}}^1\) function f, we produce an example of a \({\mathcal {C}}^1\) function f such that \(f(x)\ge _T \emptyset '\) uniformly on subsets of arbitrarily large measure, effectively (using the notion of a Schnorr test). We also explore analogous questions for weaker smoothness conditions, such as for f differentiable everywhere, and f differentiable almost everywhere.



中文翻译:

可计算函数的导数的逐点复杂度

我们探讨了可计算的实值函数的分析行为与其几乎所有位置的导数(函数的斜率)的各个值的可计算性-理论复杂性之间的关系。给定一个可计算的函数f,可以根据输入的图灵跳转\(x'\)统一计算其导数\(f'(x)\)的值(在此处定义它们。众所周知,当f\({\ mathcal {C}} ^ 2 \)时\(f'(x)\)的值实际上可以从x计算得到。我们构造了一个\({\ mathcal {C}} ^ 1 \)函数f,以便几乎在任何地方,\(f'(x)\ ge _T x'\)。尽管每个点x的值\(f'(x'\)不能均匀地为任何\({\ mathcal {C}} ^ 1 \)函数来计算输入x的相应跳跃\(x'\)f,我们生成一个\({\ mathcal {C}} ^ 1 \)函数f的示例,使得\(f(x)\ ge _T \ emptyset'\)均匀地分布在任意大尺度子集上,有效地(使用Schnorr测试的概念)。我们还针对较弱的光滑度条件(例如针对f随处可微)和f 几乎无处不在。

更新日期:2021-04-18
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