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In mathematics, a half-exponential function is a function ''ƒ'' so that if ''ƒ'' is composed with itself the result is exponential: : Another definition is that ''ƒ'' is half-exponential if it is non-decreasing and ''ƒ''−1(''x''''C'') ≤ o(log ''x''). for every ''C'' > 0. It has been proven that every function ''ƒ'' composed of basic arithmetic operations, exponentials, and logarithms, then ''ƒ''(''ƒ''(''x'')) is either subexponential or superexponential: half-exponential functions are not expressible in terms of elementary functions. There are infinitely many functions whose self-composition is the same exponential function as each other. In particular, for every in the open interval and for every continuous strictly increasing function ''g'' from onto , there is an extension of this function to a continuous monotonic function on the real numbers such that . In particular, : Half-exponential functions are used in computational complexity theory for growth rates "intermediate" between polynomial and exponential.〔 ==See also== * Functional square root 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Half-exponential function」の詳細全文を読む スポンサード リンク
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