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Gabrielek
  • Member for 2 years, 10 months
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6 votes
1 answer
217 views

Problem in the theory of finding the unique solution of $-u'' = \delta_0$ and $-u'' + cu= \delta_0$

5 votes
1 answer
72 views

Poiseuille flow: can I avoid the simplification that $u=u(y)$?

4 votes
1 answer
158 views

How to solve explicitly the Dirichlet problem (in dimension 2) with boundary data $f(e^{i\theta}) := ( \sin(\theta) - \cos(2\theta))^2$

3 votes
1 answer
101 views

Suppose $f,g$ are two absolutely continous functions in an interval $[a,b]$. Show $fg \in AC[a,b]$.

3 votes
1 answer
43 views

A different music "shuffle" feature

2 votes
1 answer
138 views

Show that $H(x) := |x|^{-1} u(x/|x|^2) $ is harmonic if $u$ is harmonic

2 votes
2 answers
120 views

How to derive Bernoulli's theorem for an elastic fluid from Lamb's equation

2 votes
0 answers
26 views

Example of function that is in $C^\infty([0,\infty))\cap L^1((0,\infty))$ but not in $W^{1,1}(0,\infty)$

2 votes
1 answer
77 views

Question on integration: $\int_{k}^{k+1}\int_{k}^{k+1}\frac{1}{x^2+y^2}dxdy$

2 votes
1 answer
101 views

Artin's lemma and some morphisms.

2 votes
1 answer
106 views

Show that the sequence $\frac{0}{1}, \frac{0}{2}, \frac{1}{2}, \frac{0}{3}, \frac{1}{3}, \frac{2}{3}, \dots \frac{k-1}{k}$ is equidistributed mod 1

1 vote
1 answer
47 views

Question about the convolution $\mathbb{1}_{[0,1]} * \mathbb{1}_{[0,1]}$

1 vote
1 answer
40 views

Show that an operator is continuous

1 vote
2 answers
117 views

Show that there exist $f_1 \in L^{p_1}$ and $f_2 \in L^{p_2}$ such that $f = f_1 +f_2$.

1 vote
1 answer
283 views

Doubt about Jacobson Basic Algebra I

1 vote
1 answer
79 views

Evaluate $\lim_{n \rightarrow \infty} \int_0^{+\infty} \frac{e^{-n^2x}}{\sqrt{|x-n^2|}} dx$

1 vote
1 answer
48 views

Lebesgue integrability $e^{-\frac{y}{x}}\frac{sen(x)}{y}$

1 vote
1 answer
66 views

Some questions about $\sum_{n=1}^{\infty} (2z)^{-n^2}$

1 vote
1 answer
44 views

Rouché's theorem about the equation $\log(z + 3) + z = 0$ in $D_{1/4}(0)$

1 vote
0 answers
46 views

Some question on $F(z) := \sum_{n=1}^{\infty} \frac{1}{n} \text{log} \Big(1+\frac{z}{n} \Big)$

1 vote
4 answers
81 views

Show $ ( \sin(\theta) - \cos(2\theta))^2 = 1+ \sin(\theta) - \sin(3 \theta) - \frac{1}{2}\cos(2 \theta) + \frac{1}{2}\cos(4 \theta) $

1 vote
0 answers
54 views

Proof of the conservation law for the mass

1 vote
0 answers
34 views

Is the Fourier series independent from the basis used in its calculation?

1 vote
1 answer
99 views

Problem using Bessel's inequality to prove that an orthonormal system is complete in Vitali-Dalzell theorem.

1 vote
2 answers
111 views

Find all functions $f:\mathbb{R} \to \mathbb{R}$ such that $f(x^2 + y + f(y)) = 2y + (f(x))^2$ [duplicate]

1 vote
1 answer
67 views

How to solve $\frac{\partial V}{\partial t} + x + \frac{\partial V}{\partial x}- \frac{1}{2} \frac{1}{\left(\frac{\partial V}{\partial x}\right)} = 0$

1 vote
0 answers
33 views

Compute the Discrete Fourier Transform (DFT) of the 4-point signal $f = [3, 2, 5, 1]$.

1 vote
1 answer
71 views

Take $f$ in $L^1(\mathbb{R})$, define $g(x) := f (ax + b)$. Compute the Fourier transform of $g$ in terms of that of $f$.

1 vote
0 answers
23 views

Help in the choice of the best coefficients to study the convergence of the finite element method for PDE

1 vote
1 answer
38 views

How to discretize the trilinear form $m(w;,u,v) := \int_\Omega w^{2p} u \ v$ to get a matrix for FEM methods