Questions tagged [gauge-integral]
For questions about Henstock-Kurzweil integral or gauge integral.
45 questions
4 votes
1 answer
117 views
Gauge integral on infinite-dimensional Banach space and differentiability
Call $f:I\to F$ gauge integrable where $I = [a, b]$ is a compact interval and $F$ is a Banach space, if the usual definition holds like if $F = \mathbb{R}$, just replace absolute value by norm. How ...
4 votes
0 answers
55 views
Integration by substitution, monotone version for Henstock-Kurzweil integrals
Let $\mathcal{HK}(I)$ denote the Henstock-Kurzweil integrable functions on $I$. By mimicking the case for Lebesgue integral I've proven the following: Theorem $1$. Let $F$ be an indefinite integral of ...
2 votes
1 answer
70 views
Is the set of singularities of a gauge integral always a null set?
Let $\mathcal{R}^*(I)$ be the set of gauge integrable (generalized Riemann integrable) functions $f:I\to \mathbb{R}$ where $I = [a, b]$. Say that a point $c\in [a, b]$ is a singular for $f\in \mathcal{...
1 vote
1 answer
137 views
Bartle's Modern theory of integration, theorem 9.1
Bartle's book, Modern theory of integration, focuses on Henstock-Kurzweil integrals, where $\mathcal{R}^*(I)$ denotes the set of Henstock-Kurzweil integrable functions on $I = [a, b]$. Also, $\mathcal{...
5 votes
1 answer
260 views
Are all Henstock-Kurzweil integrable functions expressible as the sum of a Lebesgue and an improper Riemann integrable function?
This question is based on this post, where in the comments, Toby Bartels conjectures that every Henstock-Kurzweil (gauge) integrable function $f\in\mathcal{HK}$ can be expressed as $f= g + h$ for a ...
2 votes
0 answers
68 views
On the set of points where a Henstock-Kurzweil integrable function fails to be Lebesgue integrable
One example of a function that is Henstock-Kurzweil integrable but not Lebesgue integrable is $f(x) = \frac{1}{x} \cos\left(\frac{1}{x^2}\right)$ on $[0, 1]$. However, $f$ only fails to be locally-...
8 votes
1 answer
531 views
What makes Cousin's theorem remarkable?
I've stumbled upon a mention of Cousin's theorem in the context of Henstock–Kurzweil integral and got confused. I do not understand why this fact is called a theorem and what makes it any remarkable, ...
1 vote
0 answers
83 views
Some questions concerning the construction of the line integral in $\mathbb{C}$
I am comparing two ways of defining the integral along a path of a function of complex domain and value. One is the one given in Conway's Functions of one Complex Variable and the other is given in ...
5 votes
1 answer
252 views
If $f(x)$ is Henstock-Kurzweil integrable on $[a,b]$, then is $f(x)\mathrm{e}^{\mathrm{i}x}$ also Henstock-Kurzweil integrable on $[a,b]$?
I was wondering about how Fourier series behaves in the setting of Henstock-Kurzweil integration. For example, the non-Lebesgue-integrable function $f(x) = \dfrac{1}{x}\mathrm{e}^{\mathrm{i}/x}$ can ...
3 votes
1 answer
346 views
Is there a constructive presentation of the Henstock-Kurzweil integral?
Treating the Riemann integral in a constructive setting is easy and straightforward. Treating the closely related but much more powerful Henstock-Kurzweil integral constructively is almost easy, ...
6 votes
0 answers
70 views
Can the LCT and MCT for Lebesgue integrable functions be viewed as a lattice completeness result?
The set of Lebesgue integrable functions form a lattice under pointwise min and max (also more generally for R, Henstock-Kurzweil integrable functions with an upper or lower bound form a lattice as ...
11 votes
3 answers
720 views
Is every "almost everywhere derivative" Henstock–Kurzweil integrable?
It is well known that the Henstock–Kurzweil integral fixes a lot of issues with trying to integrate derivatives. The second fundamental theorem of calculus for this integral states: Given that $f : [...
1 vote
0 answers
95 views
Does the law of large numbers hold with the Henstock–Kurzweil integral?
If I am understanding, the law of large numbers correctly, one implication is this: Let $\lambda$ be the Lebesgue measure on $[0,1]$. Let $f_1,f_2,\dots,$ be functions, $[0,1] \rightarrow \mathbb{R}$, ...
1 vote
1 answer
77 views
Prove that if $|f|$ is gauge integrable then so is $f$.
I have tried to prove this using the Cauchy criterion for HK-integration but I have been unsuccessful thus far. I have various fancy theorems at my disposal such the MCT and the DCT but I can not ...
2 votes
0 answers
45 views
Henstock integrable
I doubt if this interval is true and satisfy this $$ x_{i-1}^{2} < \xi_{i}^{2} - \dfrac{1}{3}(x_{i}^{2} + x_{i}x_{i-1} + x_{i-1}^{2}) < x_{i}^{2} < 2\delta^{2}.$$ here is example $$\int_{a}...