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• Yesterday, 17:22
I believe that it should be: \begin{align*}\frac{\partial}{\partial{t}}f(x+c(t-\tau ),\tau)&=f_x(x+c(t-\tau ),\tau)\cdot...
11 replies | 152 view(s)
• Yesterday, 14:06
I think this is correct yes. (Nod) And we can simplify it bit more since $f(y,\tau)$ does not depend on $t$. Therefore $\pd{}t f(y,\tau)=0$....
11 replies | 152 view(s)
• Yesterday, 06:39
I am reading T. S. Blyth's book: Module Theory: An Approach to Linear Algebra ... I am focused on Chapter 2: Submodules; intersections and sums...
0 replies | 32 view(s)
• Yesterday, 03:00
In Chapter 1 of his book: "Modules and Rings", John Dauns (on page 7) considers a subset T of an R-module M and defines the R-submodule generated by...
0 replies | 35 view(s)
• Yesterday, 00:27
Hi steenis ... despite your help (thank you) ... I have not been able to make much progress on the converse ... see below ... Converse: ...
14 replies | 240 view(s)
• May 24th, 2018, 16:06
Ah okay. My mistake. (Blush) So we have: \begin{tikzpicture} \coordinate (A) at (-1,0); \coordinate (B) at (1,0); \coordinate (C) at...
6 replies | 86 view(s)
• May 24th, 2018, 16:00
MarkFL replied to a thread Word problem on vectors in Geometry
Hello, and welcome to MHB, Gummg! (Wave) I would write the plane's velocity vector as: \vec{v}=485\left\langle...
3 replies | 78 view(s)
• May 24th, 2018, 15:38
Brainstorming some more, I believe we are approximating $y(x)$ with its Fourier form, which is: $$y(x) \approx \sum_{j=1}^{n-1} a_j \sin(jx)$$ It...
2 replies | 70 view(s)
• May 24th, 2018, 15:16
Because: \begin{tikzpicture} \coordinate (A) at (-1,0); \coordinate (B) at (1,0); \coordinate (C) at (0,{sqrt(3)}); \coordinate (D) at...
6 replies | 86 view(s)
• May 24th, 2018, 14:18
Hi ion88, welcome to MHB! (Wave) No worries. I believe you've already correctly filled in the table, which is what MarkFL uploaded for you. ...
4 replies | 97 view(s)
• May 24th, 2018, 14:06
Can it be that it should be side length $2b$ and height $a$? (Wondering) I don't think $AFA_1$ is equilateral. And $A_1$ is not in the...
6 replies | 86 view(s)
• May 24th, 2018, 10:27
Hey mathmari!! (Wave) It seems to me that the matrix indeed comes from the finite differences method. It identifies the problem that we want to...
2 replies | 70 view(s)
• May 23rd, 2018, 17:20
I assume a theory $T$ is called effectively axiomatized if its set of axioms is decidable. (The following argument does not change if the set of...
2 replies | 61 view(s)
• May 23rd, 2018, 14:46
I think it should be $f(y,t)$ and $f_t(y,t)$, shouldn't it? Otherwise I believe it's all correct. (Happy)
11 replies | 152 view(s)
• May 23rd, 2018, 10:55
If $\phi(x)\ne 0$ then we must have that $x\le \beta$ yes? And $\beta \le |\beta| \le \max(|\alpha|,|\beta|)$ isn't it? So if $\phi(x)\ne 0$ then...
19 replies | 298 view(s)
• May 23rd, 2018, 10:39
Suppose $\phi(x)=0$ for $x\in \mathbb R \setminus$. Then that means that we have that $\phi(x)=0$ for $x >\max(|\alpha|,|\beta|)$ don't we? And...
19 replies | 298 view(s)
• May 23rd, 2018, 10:16
Hey mathmari!! (Wave) How about defining $g(x,t,\tau) = \int_{c(t-\tau)-x}^{x+c(t-\tau)}f(y,\tau)dy$, and then differentiating one integral at a...
11 replies | 152 view(s)
• May 23rd, 2018, 10:05
How about picking $L= \max(|\alpha|, |\beta|, |\gamma|, |\delta|)$? Then $\phi=\psi=0$ on $\mathbb R\setminus$ isn't it? (Wondering) Btw, we...
19 replies | 298 view(s)
• May 23rd, 2018, 07:55
Now consider \phi \ : \ M^{(\Delta)} = \bigoplus_\Delta M_\alpha \to N Let ( x_\alpha ) \in \bigoplus_\Delta M_\alpha ... Then by...
14 replies | 240 view(s)
• May 23rd, 2018, 07:01
Thanks ... OK now ... Peter
14 replies | 240 view(s)
• May 23rd, 2018, 06:47
Thanks again steenis ... ... But ... just a clarification ... $f \neq 0$, so there is a $y \in N$ with $f(x) \neq 0$. ... ... " Did you...
14 replies | 240 view(s)
• May 23rd, 2018, 06:27
Can't we take the union of those 2 bounded sets? That is, pick $L$ such that it's bigger than any $x$-value for which either $\phi(|x|)$ or...
19 replies | 298 view(s)
• May 23rd, 2018, 06:15
14 replies | 240 view(s)
• May 23rd, 2018, 04:39
I found that there's usually a pattern to these exercises. The first series are usually questions about the words, symbols, and definitions that...
14 replies | 326 view(s)
• May 23rd, 2018, 04:27
I just realized that there is yet another notation. What if we write $f=f(\cdot)$? That is correct (i.e. equivalent) without ambiguity isn't it?...
14 replies | 326 view(s)
• May 23rd, 2018, 02:54
All correct. (Happy)
19 replies | 298 view(s)
• May 23rd, 2018, 01:07
Thanks for the advice ...!!! We are trying to show that M \text{ generates } N \Longrightarrow for each non-zero R-linear mapping f \ : \ N...
14 replies | 240 view(s)
• May 22nd, 2018, 18:28
Suppose $x-cT<-L$ and $x+cT>L$, don't we have that $\int_{x-cT}^{x+cT}\psi(\tau)d\tau$ and therefore $u(x,T)$ might be non-zero? (Worried) ...
19 replies | 298 view(s)
• May 22nd, 2018, 18:08
Indeed. (Nod) Now let's try to use that in your solution as Krylov suggested: u(x,t)=\frac{1}{2} \left+\frac{1}{2c} \int_{x-ct}^{x+ct}...
19 replies | 298 view(s)
• May 22nd, 2018, 15:02
Similarly it is trivial or it is obvious are often used when it is not trivial or obvious. I believe it is again out of laziness or actual lack of...
14 replies | 326 view(s)
• May 22nd, 2018, 14:03
Here's the image you tried to hotlilnk:
4 replies | 97 view(s)
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### 24 Visitor Messages

1. Thanks Fantini
2. Haha. \widehat's cool. Also check out \widetilde. But these sometimes get ugly.
3. Yep. Corrected now.
4. Thanks for the thanks. For what it's worth, I have already let Jameson know that an option to turn off or disable the social media buttons would be a good idea in my opinion.
5. Hey, good catch...that is in fact what I meant to type, but my darn keyboard seems to have a mind of its own at times. Thanks for letting me know so I could fix it.
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