Questions tagged [function-and-relation-composition]
For questions about the composition of functions and relations.
1,235 questions
7 votes
5 answers
564 views
Prove that the iterate $f^{n}$ is a constant function.
Let $A \subset \mathbb{R}$ be a finite set with $|A| = n$ and let $f : A \to A$ satisfy the strict contraction condition $|f(x) - f(y)| < |x - y|$ for all $x \neq y$ in $A$. Prove that $f$ is not ...
3 votes
1 answer
52 views
Powers and roots of 2-nd order tensors in Euclidean space
I'm currently studying tensor algebra and analysis in $\mathbb{R}^3$ because I need it for continuum mechanics purposes and I'm currently focusing on 2-nd order tensors. The vector space is Euclidean ...
0 votes
1 answer
111 views
Why, if we drop $f(D_f) \subseteq D_g$ for $f(a) \in D_g$, then chain rule can't hold?
I am having difficulties to formally prove that, in the derivative of composition of two functions $g$ and $f$, the requirement that $f(D_f) \subseteq D_g$ (where $D_f$ and $D_g$ are intervals and ...
6 votes
1 answer
277 views
Is the condition about composition needed to stay with the elementary functions?
We use the definition of elementary functions given in Spivak's calculus (with some changes so this is not exactly the same). An elementary function is one which can be obtained by a finite number of ...
10 votes
1 answer
364 views
The number of real roots of $f^n(x) = 0$ where $f(x) = 2x^2 + x - 1$
Let $f(x) = 2x^2 + x - 1$ and $$ f^n(x) = (\underbrace{f \circ \dotsb \circ f}_{n \text{ copies of } f})(x). $$ Given $n \ge 1$, what is the number of real roots to $f^n(x) = 0$? Note: This is an ...
6 votes
0 answers
225 views
The number of real solutions of $f^n(x)=0$ where $f(x)=2x^2+x-1$. [closed]
The problem is: Find the number of real solutions of $f^n(x)=0$ where $f(x)=2x^2+x-1$. ($f^1(x)=f(x)$, $f^n(x)=f(f^{n-1}(x))$.) I tried drawing graph and counting the zeros, and I got the conjecture ...
1 vote
1 answer
198 views
Is the composition of two continuous functions a continuous operation?
I have three topological space, $\Omega$, $R$, and $S$. Then consider function spaces $\bigotimes_{\omega \in \Omega} R$ (here $\bigotimes$ is a generalized Cartesian product; not my prefered $\LaTeX$ ...
7 votes
2 answers
454 views
Let $f(x) = x^3 - \frac{3}{2}x^2 + x + \frac{1}{4}$. Evaluate $\int_0^1 f^{2025}(x)\, dx. $
Found on AoPS $$ \text{Let } f(x) = x^3 - \frac{3}{2}x^2 + x + \frac{1}{4}. \text{ For every } n \in \mathbb{N} \text{ let } f^n \text{ denote } f \text{ composed } n\text{-times, i.e.,} $$ $$ f^{n}(...
0 votes
1 answer
72 views
How to identify incorrect value of $a$
For a suitably chosen real constant $a$, let function $f:\mathbb{R}-\{-a\}\to \mathbb{R}$ be defined by $$f(x)=\dfrac{a-x}{a+x}$$ Further suppose that for any real number $x\neq -a$ and $f(x)\neq -a$, ...
0 votes
0 answers
56 views
Harmonizing composition in Matrix Calculus
Matrix Calculus utilizes function composition of, at least phenomenologically, several different types. While I've encountered each before in different subjects, synthesizing them all into the same ...
0 votes
2 answers
163 views
Existence of a continuous function $h$ such that $g=h\circ f$ given $f$ and $g$
(1)Let $f,g :[0,1] \rightarrow \mathbb{R}$ be continuous functions such that for $a,b\in [0,1]$ , we have $f(a)=f(b) \implies g(a)=g(b)$ Show that there exist a continuous map $h:f([0,1]) \rightarrow \...
4 votes
2 answers
450 views
Is there any way to compare growth of function compositions?
I was wondering if say for increasing functions $f(x),g(x)$ with $f(x)$ asymptotically growing faster, $f(g(x))$ grows faster than $g(f(x))$. As is, I know you cannot say as you can find examples ...
4 votes
1 answer
112 views
If $f, g_n, g = \lim_n g_n \in C^1(M, M)$, where $M$ is a compact manifold, does $\lim_n f \circ g_n = f \circ g$ in the $C^1$ topology?
Edit: $f, g_n, g$ are diffeomorphisms. There are several instances of this question for the uniform topology, but I'm concerned at least with the case in which $f$ and $g$ are bi-Lipschitz ...
0 votes
0 answers
57 views
Which Composite Limit Theorem to Trust?
I was reviewing Khan Academy's composite limit theorem and tried to cross reference it to other sources to understand it better. I understand it less now. I found out that there is at least two ...
1 vote
1 answer
87 views
Linear transformations and their composition: why is this an isomorphism? [SOLVED]
I'm having troubles in understanding a rapidly solved exercise, which is actually a sort of chain of consequences. It says: be $A; B$ two matrices $n\times n$ over a field $K$ and be $F_A, F_B$ their ...