- #1
jostpuur
- 2,116
- 19
Here's a claim: Assume that a function [itex]f:[a,b]\to\mathbb{R}[/itex] is differentiable at all points in its domain. Then the inequality
[tex]
|f(b) - f(a)| \leq \int\limits_{[a,b]}|f'(x)|dm(x)
[/tex]
holds. The integral is the Lebesgue integral.
Looks simple, but I don't know if this is true. There exists functions, which are differentiable everywhere, but not monotonous on any interval. The result is related to Baire category theorem. Therefore we cannot assume that there would be intervals where the derivative has a non-changing sign, and I don't know where to start the proving.
[tex]
|f(b) - f(a)| \leq \int\limits_{[a,b]}|f'(x)|dm(x)
[/tex]
holds. The integral is the Lebesgue integral.
Looks simple, but I don't know if this is true. There exists functions, which are differentiable everywhere, but not monotonous on any interval. The result is related to Baire category theorem. Therefore we cannot assume that there would be intervals where the derivative has a non-changing sign, and I don't know where to start the proving.