Questions tagged [even-and-odd-functions]
Even functions have reflective symmetry across the $y$-axis; odd functions have rotational symmetry about the origin.
298 questions
0 votes
1 answer
61 views
Computing Fourier transform for a real odd signal
Given a real and odd signal $x(t)$, such that $\vert X(\omega)\vert = e^{-\vert \omega\vert}$ is the magnitude of Fourier transform. Question: Find the Fourier Transform $X(w)$. My attempt: We know, $...
0 votes
0 answers
168 views
The S.E-One Method for a particular class of functions
Into this textbook Book of Integrals: Exploring Species of Integrals and Their Techniques of Miguel Santiago, I have read The S.E-One Method. Supposing to evaluate a definite integral over symmetric ...
2 votes
0 answers
79 views
Every odd function has a corresponding involution
Consider functions $f$ which are involutions, i.e. \begin{align} f(f(x))=x\quad \implies \quad f'(x)f'(f(x))=1. \end{align} Under the (Legendre-like) contact transformation \begin{align} f(x)=F'(X),\ ...
3 votes
2 answers
210 views
There exists at least one even function that is increasing
The following is an algebra exercise for public university applicants, where an increasing (or decreasing) function is understood in the strict sense: Determine if the following statements are True ...
1 vote
0 answers
69 views
Why can a rational function even in some argument be represented as a function of the square of that argument?
I am tackling some minor Analysis topic, which has nonetheless to do with rational functions and how they are integrated. My textbook says the following: If a rational function $R(u, v)$ is unaltered ...
-2 votes
1 answer
163 views
Odd functions like $\lfloor x \rfloor + 1/2$
Recently, it has come to my attention that $f(x)=\lfloor x \rfloor +\frac{1}{2}$ is an odd function. Verification: For $x\notin\Bbb{Z},$ using $\lfloor x \rfloor + \lfloor -x \rfloor=-1$ we get that $$...
0 votes
0 answers
39 views
Interpretation of boundary conditions
I am trying to interpret and visualize the effect that certain boundary conditions have on the future evolution of a wave. Assume $f(t,x)$ is solution to some wave equation in a box $x \in [-1,1]$ ...
2 votes
2 answers
177 views
How can the statements "$f(x) =x^3 - \frac4x$ is an odd function" and "if $f$ is an odd function, then $f(0)=0$" both be true?
In A Transition to Advanced Mathematics 8e pg. 52, there are two example proofs back to back that seem to contradict each other. One example proves "The function $f$ given by $f(x) = x^3 - \...
4 votes
3 answers
194 views
Find the minimum of $\sin (α-β-γ) \sin (α+β-γ) \sin (α-β+γ) \sin (α+β+γ)$
$α,β,γ\in\Bbb R,$ $$f(α,β,γ):=\sin (α-β-γ) \sin (α+β-γ) \sin (α-β+γ) \sin (α+β+γ)$$ Clearly, the maximum is $f(\frac{π}{2},\frac{π}{2},\frac{π}{2})=1$. I guessed the minimum is $-1$, but$$f(α,β,γ)=f(-...
1 vote
0 answers
58 views
How to prove that solutions of semilinear differential equations is even function?
My question comes from the book Stable Solutions of Elliptic Partial Differential Equations Louis Dupaigne, pages 30-32. Summary: Which uniqueness theorem to use for this differential equation ? I am ...
0 votes
1 answer
39 views
In what sense is this column-sum=1, row-sum=2 matrix even, since the imaginary part of its Fourier vanishes?
Consider the following matrix $$M := \begin{pmatrix} 1 & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 \\ 0 & 0 & 1 & 1 & 0 & 0 & 0 & 0 & 0 &...
2 votes
1 answer
131 views
Puzzled by asymmetry of cosine integral
I used Mathematica to calculate the antiderivative of $\cos (\pi x)/x$. I obtained the cosine integral $$ \int \frac {\cos (\pi x)}{x} dx = Ci(x) $$ where $$ \begin{aligned} Ci(x) &:= - \int_x^\...
2 votes
1 answer
134 views
Translation of odd and even functions
Let $\varphi: \mathbb{R} \to \mathbb{R}$ be a periodic function of period $L>0$, that is, \begin{equation}\label{periodicitycondition} \varphi(x+L)=\varphi(x),\; \forall\; x \in \mathbb{R}. \tag{1} ...
0 votes
1 answer
62 views
Even/Odd with reference to the interval (domain)
As the definition goes, a function $f(x)$ is even if $f(-x)=f(x)$ and it is odd if $f(-x)=-f(x)$, in which the domain is not paid enough attention to. For example, $f(x)=x^2$ is even for any symmetric ...
7 votes
0 answers
119 views
Anything interesting known about this generalization of even and odd functions?
Let $n \in \mathbb N$. Let's say a complex function $f: U \rightarrow \mathbb C$ is "of type $k \pmod n$" if for one (and hence every) primitive $n$-th root of unity $\omega$, $$f(\omega z) =...