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The little Bernshtein theorem: A function that is absolutely monotonic on a closed interval [,] can be extended to an analytic function on the interval defined by | | <. A function that is absolutely monotonic on [ 0 , ∞ ) {\displaystyle [0,\infty )} can be extended to a function that is not only analytic on the real line but is even the ...
As explained in Riesz & Sz.-Nagy (1990), every non-decreasing non-negative function F can be decomposed uniquely as a sum of a jump function f and a continuous monotone function g: the jump function f is constructed by using the jump data of the original monotone function F and it is easy to check that g = F − f is continuous and monotone. [10]
for every ε > 0, and whether the corresponding series of the f(n) still diverges. Once such a sequence is found, a similar question can be asked with f(n) taking the role of 1/n, and so on. In this way it is possible to investigate the borderline between divergence and convergence of infinite series.
Stated precisely, suppose that f is a real-valued function defined on some open interval containing the point x and suppose further that f is continuous at x. If there exists a positive number r > 0 such that f is weakly increasing on (x − r, x] and weakly decreasing on [x, x + r), then f has a local maximum at x.
Hence, an antitone function f satisfies the property (), for all x and y in its domain. A constant function is both monotone and antitone; conversely, if f is both monotone and antitone, and if the domain of f is a lattice, then f must be constant. Monotone functions are central in order theory.
Let > be given. For each , let =, and let be the set of those such that () <.Each is continuous, and so each is open (because each is the preimage of the open set (,) under , a continuous function).
Every countable subset of the real numbers - such as the rational numbers - has measure zero, so the above discussion shows that Thomae's function is Riemann integrable on any interval. The function's integral is equal to 0 {\displaystyle 0} over any set because the function is equal to zero almost everywhere .
A differentiable function f is (strictly) concave on an interval if and only if its derivative function f ′ is (strictly) monotonically decreasing on that interval, that is, a concave function has a non-increasing (decreasing) slope. [3] [4] Points where concavity changes (between concave and convex) are inflection points. [5]