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The absolute value function is continuous (i.e. it has no gaps). It is differentiable everywhere except at the point x = 0, where it makes a sharp turn as it crosses the y-axis. A cusp on the graph of a continuous function. At zero, the function is continuous but not differentiable. If f is differentiable at a point x 0, then f must also be ...
The Weierstrass function has historically served the role of a pathological function, being the first published example (1872) specifically concocted to challenge the notion that every continuous function is differentiable except on a set of isolated points. [1]
It is called the delta function because it is a continuous analogue of the Kronecker delta function, which is usually defined on a discrete domain and takes values 0 and 1. The mathematical rigor of the delta function was disputed until Laurent Schwartz developed the theory of distributions, where it is defined as a linear form acting on functions.
the function f is n − 1 times continuously differentiable on the closed interval [a, b] and the n th derivative exists on the open interval (a, b), and; there are n intervals given by a 1 < b 1 ≤ a 2 < b 2 ≤ ⋯ ≤ a n < b n in [a, b] such that f (a k) = f (b k) for every k from 1 to n. Then there is a number c in (a, b) such that the n ...
The 1971 Ph.D. Thesis by Dimitri P. Bertsekas (Proposition A.22) [3] proves a more general result, which does not require that (,) is differentiable. Instead it assumes that (,) is an extended real-valued closed proper convex function for each in the compact set , that ( ()), the interior of the effective domain of , is nonempty, and that is continuous on the set ( ()).
An everywhere differentiable function g : R → R is Lipschitz continuous (with K = sup |g′(x)|) if and only if it has a bounded first derivative; one direction follows from the mean value theorem. In particular, any continuously differentiable function is locally Lipschitz, as continuous functions are locally bounded so its gradient is ...
In particular, the derivative of the function (/) is a Darboux function even though it is not continuous at one point. An example of a Darboux function that is nowhere continuous is the Conway base 13 function. Darboux functions are a quite general class of functions. It turns out that any real-valued function ƒ on the real line can be ...
A more general form was proven independently by Meyer [3] and Wang; [4] the formula extends Itô's lemma for twice differentiable functions to a more general class of functions. If F : R → R {\displaystyle F:\mathbb {R} \rightarrow \mathbb {R} } is absolutely continuous with derivative F ′ , {\displaystyle F',} which is of bounded variation ...