qid int64 1 4.65M | metadata listlengths 3 3 | prompt stringlengths 31 25.8k | chosen stringlengths 17 28.2k | rejected stringlengths 19 40.5k | domain stringclasses 28
values |
|---|---|---|---|---|---|
509,392 | [
"https://physics.stackexchange.com/questions/509392",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/237411/"
] | When sufficiently high frequency light hits a metal surface it emits electrons. Now what will happen if the light is coming through two slits and forming an interference pattern similar to the double-slit experiment on the metal surface? Will the metal surface emit electrons or not?
| It will emit electrons according to where photons in the interference pattern hit.
| Bright spots in the pattern are where almost all photons hit, dark spots in the pattern are where almost no photons hit. The emission will occur in the bright areas.
In double slit interference the classical explanations implied photons were hitting in the dark areas but cancelling each other out (which is a violat... | https://physics.stackexchange.com |
3,371,733 | [
"https://math.stackexchange.com/questions/3371733",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/529090/"
] | Let <span class="math-container">$0 \leq f_n$</span> be a non-decreasing sequence on measurable functions converging to <span class="math-container">$f$</span>. Does <span class="math-container">$|f_n|_{L^\infty} $</span> converges to <span class="math-container">$|f|_{L^\infty}$</span>?
Motivation for the question:
I... | YES.
First of all, since <span class="math-container">$f_n$</span> is non-negative and non-decreasing, so is <span class="math-container">$|f_n|$</span>.
Hence
<span class="math-container">$$
|f_1|_\infty\le |f_2|_\infty\le \cdots\le |f_n|_\infty \le \sup_{n\in\mathbb N}|f_n|_\infty=\lim_{n\to\infty}|f_n|_\infty
$$</s... | The answer is YES. Clearly, <span class="math-container">$f_n$</span> increasing to <span class="math-container">$f$</span> implies <span class="math-container">$\|f_n\|_{\infty} \leq \|f\|_{\infty}$</span>. To prove the other way note that <span class="math-container">$|f(x)| \leq \sup |f_n(x)| \leq \sup \|f_n\|_{\in... | https://math.stackexchange.com |
277,940 | [
"https://softwareengineering.stackexchange.com/questions/277940",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/173164/"
] | What should be at the top of inheritance tree of Decorator design pattern?
I mean the base for both components and decorators
<ul>
<li><strong>non-abstract class</strong>: has data fields, implements methods </li>
<li><strong>abstract class</strong>: has data fields, has only abstract (pure virtual) methods </li>
<li>... | <blockquote>
What should be at the top of inheritance tree of Decorator design pattern?
</blockquote>
How to discriminate:
<ul>
<li>non-abstract class - Only if it makes sense in your code to instantiate it in client code (also see: liskov substitution)</li>
<li>abstract class <em>or</em> interface - most common ca... | It depends entirely on what you want. These variations exist for your convenience, not because one way is a better way than another.
Personally I'm partial to the non-abstract class, because it requires the fewest number of classes, which in my opinion is always a plus. However, you may find yourself in the situat... | https://softwareengineering.stackexchange.com |
29,220 | [
"https://security.stackexchange.com/questions/29220",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/19775/"
] | I want to know what the main differences are between HTTP GET and POST flood attacks and mitigation strategies for both.
I searched a lot but I really can't find some good articles nor examples about these attacks.
| When an HTTP client (say, a Web browser) talks to an HTTP server (a Web server), it sends requests which can be of several types, the two main being <code>GET</code> and <code>POST</code>. A <code>GET</code> request is what is used for "normal links", including images; such requests are meant to retrieve a static piece... | Really the only difference between these two is going to be the HTTP method used (GET vs POST). In terms of ease of attack there are more scenarios where a GET based attack would be practical (e.g. embedding an in-line image on a popular site which links to the target site could cause a DoS) but apart from that if you... | https://security.stackexchange.com |
388,866 | [
"https://physics.stackexchange.com/questions/388866",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/186216/"
] | The temperature last night in my suburb and in Montreal was 4 Celsius at 9 P.M. . The snow and rain of the day had melted and the roads were damp but not icy. This morning at 5 A.M, the temperature was 2 celsius. There was no moment during the night when the temperature dropped below zero. There was a south-west wind o... | You're doing a direct sum instead of a tensor product of the two vectors; as such, your input state is wrong.
A direct sum operates by concatenating the two vectors:
<span class="math-container">$$
\psi \oplus \phi
=
\begin{pmatrix}\psi_1\\\psi_2\end{pmatrix}
\oplus
\begin{pmatrix}\phi_1\\\phi_2\end{pmatrix}
=
\begin{... | For the CNOT gate matrix as you've written it, the basis for the state space is $\{|00\rangle,|01\rangle,|10\rangle,|11\rangle\}$. As such, the input state you started with was actually $|00\rangle + |11\rangle$, and you ended, as you should, with $|00\rangle+|10\rangle$. If you wanted to start with the state $|01\rang... | https://physics.stackexchange.com |
7,374 | [
"https://biology.stackexchange.com/questions/7374",
"https://biology.stackexchange.com",
"https://biology.stackexchange.com/users/3161/"
] | We are looking for an enzyme that appears in C. elegans but isn't common for: human, Drosophila or mouse.
We need it for a little research project, thanks for your help!
| Not really an answer I know, but too long for the comments...
This is still too broad a question. a well sealed, sterile plastic usually has a use by date, but can probably be used more than a year after you receive it. But these cases are not usually the issue.
Its sterile medium and chemicals, each of which nee... | If you work in a lab, there must be a SOP(Standard Operating Procedure) and you can (You should...) follow that. Each lab will have different standard so providing a single definitive answer here may not be beneficial.
| https://biology.stackexchange.com |
124,602 | [
"https://mathoverflow.net/questions/124602",
"https://mathoverflow.net",
"https://mathoverflow.net/users/32223/"
] | Given $\sigma$ a shift map, $m$ - a Markov measure, $C_a$, $C_b$ - cylinder sets.
Suppose $P \in C_b$. The problem is to show the following
\begin{equation}
m(C_a \cap \sigma^{-1}(P)) = \frac{m(C_a \cap \sigma^{-1}(C_b))}{m(C_b)} m(P).
\end{equation}
This seems to be obvious, but I don't see how to prove this in a simp... | There is a more conceptual explanation. This is a direct corollary of the Markov property formulated in "invariant form": <strong>the past and and the future are conditionally independent with respect to the present.</strong>
Your identity can be rewritten as
$$
\frac{m(C_a \cap \sigma^{-1}(P))}{m(P)} = \frac{m(C_a \... | I've got the following hint: to approximate $P$ with cylinder sets of increasing length (i.e. it seems, that HW was right). I'm not sure that this is the easiest way, but at least it will work.
Thanks to everyone for the help!
| https://mathoverflow.net |
254,496 | [
"https://softwareengineering.stackexchange.com/questions/254496",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/146937/"
] | this is a conceptual question, but if i initialize a variable in c# as public will it be able to be used in the class as I want a variable "<code>player1</code>" and a variable "<code>player2</code>" where either could be one of the two (or more)
<ol>
<li>Player</li>
<li>Computer </li>
</ol>
Here is what i would like... | It's a fundamental matter of scope.
Variables declared within a function are bound to the lifespan and accessibility of that function.<sup>*</sup>
C# doesn't allow you to declare variables that will persist as part of the class from within a function.
<sup>*</sup><sub>Lambda expression can sometimes invalidate that ... | To answer your question about declaring their type; the variables' types have to be known at compile-time, even before it knows which constructor it will use.
When declaring those variables, to be able to call the methods you'd like (Jump(), Move(), Die()) on both of them, you need to declare them as being the most-sp... | https://softwareengineering.stackexchange.com |
45,754 | [
"https://dsp.stackexchange.com/questions/45754",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/32654/"
] | suppose $y(n)=ax(n-1)+bx(n-2)+\dots$ ($y$ is the output and $x$ the input). What happens if I want to solve $x(n)$ from $y(n)$?
Z transform: $$Y(z)=G(z)X(z)\tag{1}$$
then $$X(z)=\frac{1}{G(z)}Y(z)\tag{2}$$
What are the properties of $1/G(z)$ ? If $(1)$ is causal what is the status of the inverse $(2)$? The r... | As you've pointed out, inversion leads to poles at locations of the zeros of the original transfer function and vice versa. Assuming that $G(z)$ is causal and stable (i.e., it has all its poles inside the unit circle), we have to distinguish $3$ cases:
<ol>
<li>$G(z)$ has at least some zeros outside the unit circle. T... | If G(z) is causal and minimum phase than 1/G(z) is causal and minimum phase as well.
Non-minimum phase systems have a non-causal inverse. Simple example: a 2-tap delay has in inverse that is "-2" taps of delay, i.e. it is non-causal.
In addition you need $|G(z)|> 0$, otherwise you have division by zero problems. ... | https://dsp.stackexchange.com |
42,192 | [
"https://dsp.stackexchange.com/questions/42192",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/29560/"
] | Are least square filters, or filters that minimize error energy, the same as least mean square adaptive filters?
| <strong>TL;DR:</strong> No, they are not necessarily the same.
<hr>
<strong>Gory Details</strong>
Least squares is just an optimization technique. It is used in a variety of ways.
For filter <strong>design</strong> it is used to select that realizable filter $H_r(e^{j\omega})$ that most closely matches, in the leas... | In complement to Peter, yes or no, depending on what you want to be adaptive to. Let us assume the world is made of signals AND systems. <strong>Signals pass</strong> (by temporary existence), <strong>while systems remain</strong> (by essence). I acknowledge that one may swap these philosophical terms, on instance.
In... | https://dsp.stackexchange.com |
248,935 | [
"https://stats.stackexchange.com/questions/248935",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/80366/"
] | I am building a Cox model containing around 8 variables. Two of the variables that are different measures of the same thing. Consequently, they are correlated with each other. When included in separate models, both show a strong association with survival.
I have read conflicting opinion regarding inclusion of correlat... | There is no rule against including correlated predictors in a Cox or a standard multiple regression. In practice it is almost inevitable, particularly in clinical work where there can be multiple standard measures of the severity of disease.
Determining which of 2 "measures of the same thing" is better, however, is di... | The usage of correlated predictors in a model is called colinearity, and is not something that you want. You need to use a dimensionality reduction approach.
The simplest way to avoid multicolinearity is to perform a principal component analysis (PCA) from the two correlated variables. If the correlation is high, as ... | https://stats.stackexchange.com |
321,484 | [
"https://softwareengineering.stackexchange.com/questions/321484",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/232344/"
] | I need some help in answering questions
This is <strong>Sprint 1</strong> and I have a 2 week sprint with the first week completed and the current burndown chart looks like:
<strong>Day 1</strong> with <strong>50</strong> Story points
<strong>Day 2</strong> with <strong>57</strong> Story points
<strong>Day 3</st... | Velocity is a historical measure, not a prediction. Your velocity is an average of the past few sprints. If this sprint is your very first sprint then you have no expected velocity. <em>Velocity is a measure of what you have done in the past, not what you plan to do in the future</em>.
It appears you've elected to do... | You question is very hard to answer. If your stories are all equal in size, all relatively small and can all be implemented and tested independently, than one could assume that your team will be able to continue at its current pace and will possibly finish the remaining 25 point in the remaining days.
And if the team ... | https://softwareengineering.stackexchange.com |
315,117 | [
"https://softwareengineering.stackexchange.com/questions/315117",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/223697/"
] | <h1>Question</h1>
Is there a rough consensus if the bitmask 0x01 is properly said to have the "zeroth" bit set, or the "first" bit set?
If there isn't rough consensus that there's a <em>generally</em> right answer, is there at least rough consensus that there is a <em>contextually</em> right answer (e.g. that how the... | <blockquote>
Is there a rough consensus if the bitmask 0x01 is properly said to
have the "zeroth" bit set, or the "first" bit set?
</blockquote>
Your question wouldn't have passed an honest pollsters(oxymoron?) sniff test because it was leading. Of course if you had your question might not have been around long. ... | I would say that 0x01 has "bit 0" set, since it has the bit that corresponds to 2<sup>0</sup> set. I have a hard time motivating a counting schedule for bits that doesn't preserve that "bit N" is the bit that corresponds to the value 2<sup>N</sup>.
| https://softwareengineering.stackexchange.com |
2,105,070 | [
"https://math.stackexchange.com/questions/2105070",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/127207/"
] | I have proven that $a^5|b^3$ implies that $a\mid b$ using prime factorization and showing that every prime factor of $a$ will divide every prime factor of $b$. I have to prove or disprove that the hypothesis also implies that $a^2|b$, however, I am not sure whether I should try to prove or disprove this. I think if I k... | No: if $a=8$ and $b=32$, then $a^5=2^{15}=32^3$, but $a^2=64$ does not divide $b$.
| use $a=2^3$ and $b=2^5$ and you have a counterexample.
| https://math.stackexchange.com |
3,604 | [
"https://bioinformatics.stackexchange.com/questions/3604",
"https://bioinformatics.stackexchange.com",
"https://bioinformatics.stackexchange.com/users/1075/"
] | I have a Mac Book Pro and I am about to start a sequencing run on the MinION. MinKNOW is going to be running for 2 days.
Can I use my computer during sequencing? Can I browse the web and use Excel, etc? I am not speaking about running a parallelised genome assembly on all my cores using my entire RAM but more mundane ... | Yes, that should be fine, especially if basecalling is disabled. Locking a screen should be fine as well.
I prefer to do basecalling after a run anyway, because there's a chance that it could chew up too much processor time and result in lots of skipped reads.
| Since biological samples and reagents cost time and money, I wouldn't push it too much. Checking your email would be fine, but I wouldn't be browsing the web (besides gmail/calendar) in case a plug-in (e.g. flash), bad javascript, etc. causes any trouble.
I'd disable any auto-updates too.
Locking the screen would ... | https://bioinformatics.stackexchange.com |
303,449 | [
"https://electronics.stackexchange.com/questions/303449",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/33899/"
] | !Hobby project!
I have a power supply form a printer (actually I have 3 :) ). The PSU is 24V, 1.25A.
I want to connect some COB LEDs to this PSU without additional electronics. The idea is that the LEDs requires no driver if they are under-volted (am I right?).
I have found some cheap 10W rated 32-34V. I use 3 of the... | Oh for pete's sake:
<ol>
<li>You can't "under volt" an led. Too little voltage and it won't turn on at all.</li>
<li>If you try to put leds in parallel, then you must provide each parallel line with its own current limiting.</li>
<li>You must use current limiting to drive your leds. An led operating at just over its... | You can use a boost step up constant current driver. Something like a $5 Mean Well LDD module would do the trick. You would need one for each CoB.
Or you could use 18V CoBs. There is not many CoBs available between 18 and 24 volts.<br>
<h2>UPDATE</h2>
You can use a supply with a voltage higher than 24v. You hav... | https://electronics.stackexchange.com |
3,337,748 | [
"https://math.stackexchange.com/questions/3337748",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/587828/"
] | To show that,
<span class="math-container">$$
(7 + 50^{1/2})^{1/3} + (7 - 50^{1/2})^{1/3} = 2
$$</span>
I am aware of the way where we can "guess" and come up with the following:
<pre><code>7 + 50^(1/2) = (1 + 2^(1/2))^3
7 - 50^(1/2) = (1 - 2^(1/2))^3
</code></pre>
Hence simplifying the expression. But can we do it ... | Hint:
Let <span class="math-container">$a,b=(7\pm\sqrt{50})^{1/3}$</span>
<span class="math-container">$ab=-1$</span>
<span class="math-container">$a^3+b^3=14$</span>
Use <span class="math-container">$(a+b)^3=a^3+b^3+3ab(a+b)=14+3(-1)(a+b)$</span>
So, <span class="math-container">$a+b$</span> is a real root of <sp... | Let <span class="math-container">$M = (7 + 50^{1/2})^{1/3} + (7 - 50^{1/2})^{1/3}$</span>.
Then <span class="math-container">$M^3 = [(7 + 50^{1/2})^{1/3} + (7 - 50^{1/2})^{1/3}]^3=$</span>
<span class="math-container">$(7+ 50^{\frac 12}) + 3(7 + 50^{1/2})^{2/3}(7 - 50^{1/2})^{1/3} + 3(7 + 50^{1/2})^{1/3}(7 - 50^{1/2}... | https://math.stackexchange.com |
511,452 | [
"https://electronics.stackexchange.com/questions/511452",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/225156/"
] | When making any prototype PCB it is always a great idea to have features within it that can be used to aid in debug of the design.
A few examples are:
<ol>
<li>Use the largest FPGA available that has migration path to the one we expect to use in the final product. This means we can have a lot of logic to implement debu... | Your prototype should have these features too 8in no order):
<ul>
<li>embedded USB to JTAG module<br />
like SMT3 from Digilent</li>
<li>2 port or 4 port USB-UART (I also like FTDI like you mentioned)<br />
note: a modern FPGA or FPGA+SoC needs one UARTs per operating system and FPGA part
<ul>
<li>1 => Linux</li>
<l... | I would actually advise against using the largest FPGA available simply due to the extraordinary device cost and implementation challenge of the largest FPGAs.
Don't forget adding some LEDs for debug output indicators.
You might also want to add jumpers to various places (like disconnecting power from certain sections)... | https://electronics.stackexchange.com |
1,311,773 | [
"https://math.stackexchange.com/questions/1311773",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/230412/"
] | Let $f: S \rightarrow T$ and $g: T \rightarrow U$. The function $h: S \rightarrow U$ given by $h(s)=g(f(s))$ is the composite function of $g$ and $f$, denoted by $h=g \circ f$. Prove that, if $g \circ f$ is an injection, then $f$ is an injection. <b>Hint</b>: prove by contraposition.
I tried using $g \circ f(x)=g \ci... | If $f$ is not injective, then there exist $x, y \in S$, with $x \neq y$, such that $f(x) = f(y)$. Hence, $(g \circ f)(x) = g(f(x)) = g(f(y)) = (g \circ f)(y)$, so $g \circ f$ is not injective, contrary to hypothesis.
| Suppose that $x\neq y$.
Then $g(f(x))=g\circ f(x)\neq g\circ f(y)=g(f(y))$ since $g\circ f$ is injective.
This implies $f(x)\neq f(y)$.
| https://math.stackexchange.com |
42,566 | [
"https://math.stackexchange.com/questions/42566",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/11351/"
] | I have encountered this step in my textbook and I do not understand it, could someone please list the intermediate steps?
$$ \frac{n^2(n+1)^2}{4} + (n+1)^3 = \frac{(n+1)^2}{4}(n^2+4n+4). $$
Thanks,
| Take out the common factor $(n+1)^{2}$ and simplify. So you get $$ (n+1)^{2} \cdot \biggl[ \frac{n^{2}}{4} + (n+1)\Bigr] = (n+1)^{2} \cdot \biggl[ \frac{n^{2}+4n + 4}{4}\biggr]$$
| One way to see it is to factor out the $(n+1)^2/4$. Then
$$
\begin{align*}
\frac{n^2(n+1)^2}{4} + (n+1)^3 &=\frac{(n+1)^2}{4}\bigl(n^2+4(n+1)\bigr) \\
&= \frac{(n+1)^2}{4}(n^2+4n+4)
\end{align*}
$$
Since you factor out a $1/4$, you have to keep a $4$ in the numerator in the second term.
| https://math.stackexchange.com |
91,457 | [
"https://mathoverflow.net/questions/91457",
"https://mathoverflow.net",
"https://mathoverflow.net/users/22209/"
] | Let $p,q$ be arbitrary primes.
Let $N = p * q$.
Let $I$ be the $N * N$ identity matrix.
Let $R$ be the $N * N$ matrix defined as follows:
$R[x_0 * p + y_0, x_1 * p + y_1]=1$ if and only if $x_0+1 \equiv x_1 (\mod q)$ and $y_0 + 1 \equiv y_1 (\mod p)$.
Let $A = \begin{pmatrix} \frac12I & \frac12R \\\\ \frac12R... | With reference to the tensor product formulation that I gave in my comment, we notice that $S$ is unitarily equivalent to
$$ diag(\alpha, \alpha^2, \dots, \alpha^q) $$
where $\alpha = exp(2\pi i/q)$, and likewise $T$ is unitarily equivalent to
$$ diag(\beta, \dots, \beta^p) $$
where $\beta = exp(2\pi i/p)$.
Therefore, ... | You matrix is non-negative. Thus $1$ is its Perron eigenvalue. You only have to verify that its is irreducible and not cyclic. Then apply Perron-Frobenius theorem (section 8.3 of my book <strong>Matrices</strong> (Springer-Verlad GTM 216, 2nd edition), together with Section 8.4.
| https://mathoverflow.net |
126,217 | [
"https://electronics.stackexchange.com/questions/126217",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/51844/"
] | I'm fairly new to LT spice and am trying to simulate an AC line filter, but it keeps giving me the error K1: coupling to shorted out (ignored) inductor L1. What am I doing wrong?
Here's the circuit:
<img src="https://i.stack.imgur.com/2YDEz.jpg" alt="Schematic">
| You could try a small resistor in series with each of L1 and L2 - I use microcap and similar things happen with coupled inductors. Maybe also try a 0.001 ohm resistor in series with V1 too. I don't see anything in particular that would cause a voltage discrepancy but sometimes you have to help the math engines work thi... | You have to define LINK FACTOR AS K1 L1 L2 1
| https://electronics.stackexchange.com |
86,387 | [
"https://physics.stackexchange.com/questions/86387",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/-1/"
] | I have the following homework problem:
<blockquote>
<em>A line of charge $\lambda$ is located on the z-axis. Determine the
electric flux for a rectangular surface with corners at coordinates:
$(0, R, 0)$, $(w, R, 0)$, $(0,R, L)$, and $(w, R, L)$.</em>
</blockquote>
This is what I have come up with so far:
Th... | Here is the solution in my opinion:
One thing you forgot is that flux involves the force perpendicular to the area. F.dA remember? So the solution integral would be $\frac{\lambda}{L2\pi\epsilon_0} \int\frac{1}{\sqrt{x^2 + R^2}}\sin\theta\ \mathrm{d}x\mathrm{d}z$. If you look at the figure attached
<img src="https://i... | flux is not a vector. hence you have to calculate E.dA . write the electric field with direction and then take its dot product with area vector and then do the double integral.
| https://physics.stackexchange.com |
600,620 | [
"https://electronics.stackexchange.com/questions/600620",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/11022/"
] | I have an old Sony TRV-14 with a built-in night shot mode for shooting videos in the dark. It is my understanding it works by using sensing infrared radiation which is also how thermal imaging cameras work. Unlike thermal imaging cameras, the images produces by my camera are in gray scale instead of color.
Is it possib... | Thermal radiation is still an electromagnetic radiation and the wavelength range of thermal radiation covers the IR area.
Your camera's sensor might be able to pick up IR signals just like an I² NV (Infrared-Illuminated Night Vision) so you would expect to detect (or distinguish) heat radiation. However, due to the lim... | No, the wavelengths of IR that your camera senses are much different than those emitted by warm objects.
| https://electronics.stackexchange.com |
1,761,673 | [
"https://math.stackexchange.com/questions/1761673",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/324815/"
] | I have to show that
$F_{n+k} = F_{k}F_{n+1} + F_{k-1}F_{n}$, where $F_{n}$ is nth Fibonacci element.
I was trying with mathematical induction applied to n and saying k is constant.
<ol>
<li>step for $n=1$
$F_{k+1} = F_{k}F_{2} + F_{k-1}F_{1}$ which is true, because $F_1=F_2=1$</li>
<li>step let say our theorem is t... | We wish to prove that the Fibonacci numbers $F_n$ satisfy $F_{n+k}=F_kF_{n+1}+F_{k-1}F_n$. We use induction on $n$. The result is true for $n=1$ because $F_1=F_2=1$ and $F_{k+1}=F_k+F_{k-1}$. Suppose it is true for $m<n$.
Then we have $F_{n+k}=F_{n+k-1}+F_{n+k-2}=(F_kF_n+F_{k-1}F_{n-1})+(F_kF_{n-1}+F_{k-1}F_{n-2})$... | Here's a slightly different approach, for kicks:
Claim: $$A_n = \begin{bmatrix}F_n & F_{n-1}\\F_{n-1} & F_{n-2}\end{bmatrix} = \begin{bmatrix}1 & 1\\1 & 0\end{bmatrix}^{n-1}$$
Which is easily proven with induction.
Then $$A_{n+1}A_{k}=\begin{bmatrix}1 & 1\\1 & 0\end{bmatrix}^{n}\begin{bmatrix}1... | https://math.stackexchange.com |
1,644,943 | [
"https://math.stackexchange.com/questions/1644943",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/39212/"
] | I am trying to solve the following exercise:
Let $f$ be integrable. Assume that $\int_A f d\mu = 0$ for every measurable set $A$. Prove that $f = 0$ a.e. [$\mu$].
I have the following proof but it seems to me too simple to be true. What is wrong with it?
For any $a>0$, define $W_a:=\{w|f(w)\geq a\}$. Now we have:... | Indeed, your proof shows that $\{f > 0\}$ has measure zero. Similarly, you show $\{f < 0\}$ has measure zero, and hence $f=0$ a.s. Yes it really is this easy.
| It remains to show that the set $\{w\mid f(w)\ne0\}$ has measure $0$. Consider the nonzero rational $a$'s to complete the proof.
| https://math.stackexchange.com |
117,994 | [
"https://electronics.stackexchange.com/questions/117994",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/18442/"
] | I'm working on a project with a few stepper motors. I want to breadboard them so I know the circuit works well before creating a physical PCB.
Each of the three motors is rated 2A, but I'll be prototyping with 1A (controled with driver chip) at 12V. How dangerous is this much current on a solderless breadboard? It's a... | Engineers with a conscience don't let others use breadboards.
Oh, I know, it starts out easy, like any other drug. You're uncertain of yourself and instead of doing calculations, or even back of the envelope calculations you say to yourself " I'll do the <em>easy</em> thing, I'll breadboard it- I don't have to think ... | I have been breadboarding for several years, and I keep the current through the traces below 500mA just to be safe. Anything more than that I run through separate wires.
I suppose one way to check a breadboard, if you have one that is no longer any good, would be to dig out one of the metal traces and run an increasin... | https://electronics.stackexchange.com |
93,256 | [
"https://security.stackexchange.com/questions/93256",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/80401/"
] | Someone in my neighborhood is using a WEP encrypted wifi router. I am not sure who they are yet, but if I find out, should I inform them of the security risks which that poses or are there any legal ramifications to doing so?
| To be honest, I find that most people don't / won't care.
Unless they are running a business or similar functionality over the network I wouldn't bother explaining the difference between WEP and WPA2 to them, especially since they might not be tech savvy and just get more confused or worried about it.
At least they... | I don't believe there are legal ramifications in advising someone about security, but you may want to approach it cautiously. You'll definitely want to explain in a way that fits the user's ability level as far as tech is concerned, and if they're using WEP they may not be very well versed. They may ask for your help i... | https://security.stackexchange.com |
24,470 | [
"https://electronics.stackexchange.com/questions/24470",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/6406/"
] | Even a $20 mobile phone with a speakerphone has no problems of feedback. While I understand that companies like Mediatek have use crazy volumes to bring down mobile chipset prices so low, but reading some articles I get the impression that the circuitry/electronics to suppress/remove feedback from such speaker-phone ar... | The audio processing algorithm you are interested in is called "Acoustic Echo Cancellation", or AEC. It is most commonly used in speakerphones to remove the output of the speaker from the mic signal. Most of this benefit is to the person on the other end of the phone call, since he won't be hearing echos of himself.
... | One approach which is very common in low-cost speakerphones is to adjust the gain downward (possibly to zero) on whichever 'direction' has the lower apparent signal at the input. Some phones will mute the microphone except when the audio level at the mic is higher than could be attributed to speaker feedback, in which... | https://electronics.stackexchange.com |
213,702 | [
"https://softwareengineering.stackexchange.com/questions/213702",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/104239/"
] | So I'm reading a book on Design Patterns (Design Patterns Explained 2nd Edition), and all throughout the book it says to "favor aggregation over inheritance".
I'm trying to wrap my head around trying to design something, and I feel so stupid.
So conceptually, I have <code>Recruiters</code>. I figured these recruiters... | I think you may be confusing objects in a programming language with tuples in a database. You don't have object inheritance in a database, unless it's an object-oriented database. While you can <em>simulate</em> inheritance in a table-oriented database, it's usually not thought of in that way. When it is, we designate... | Tables primarily describe relationships, not neccessarily objects. Your design contains the following relationships:
<pre><code>Recruiter n:m Region
Region 1:n SubRegion
SubRegion 1:n Recruitment
</code></pre>
… and each of these could be a table of its own. Instances of recruiters and regions etc. are referenced ... | https://softwareengineering.stackexchange.com |
364,370 | [
"https://softwareengineering.stackexchange.com/questions/364370",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/293892/"
] | I am learning Python and when I learned that we can build Custom classes for exception, I got into a confusion of Why ?
for example1 :
<pre><code>class MyException(Exception):
def __init__(self, error):
self.error = error
def __str__(self):
# DO THE WORK TO BE DONE FOR THE EXCEPTION
... | Why do you <em>throw</em> Exceptions?
Because something's happened that you can't deal with and you need to tell whoever called you that it did, in a well-defined, structured manner.
Why do you <em>catch</em> Exceptions?
Because you can can do something <em>useful</em> with/ about them.
How can you tell that you... | The biggest reason for implementing your own exception is that you can filter on it. If you have an <code>except</code> block which names your exception, then it won't catch anything except your custom exception (and anything subclassed from that).
| https://softwareengineering.stackexchange.com |
350,673 | [
"https://softwareengineering.stackexchange.com/questions/350673",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/65549/"
] | Say I have a Business class called person:
<pre><code>public class Student { }
</code></pre>
Say I want to create a factory method for this Student class - something like this:
<pre><code>public Student getStudent(string studentType)
{
if (StudentType=="P")
return new PostGraduate();
else
return new Under... | <blockquote>
1) Should the factory method be created in the Student class or in its own class?
</blockquote>
Definitely its own class. As you said, your Student class has a responsibility, and constructing instances of itself is not that responsibility.
That said, I don't normally write factories for business layer... | The very first line and code example outlines the real problem to be solved:
<blockquote>
Say I have a Business class called person:
<pre><code>public class Student { }
</code></pre>
</blockquote>
You have a business class called "person" but the class is named "Student." You want to know how to ret... | https://softwareengineering.stackexchange.com |
3,364,294 | [
"https://math.stackexchange.com/questions/3364294",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/579544/"
] | Let's say that <span class="math-container">$f: M \to\mathbb{R}^n$</span>, where <span class="math-container">$M \subset \mathbb{R}^m$</span>, is totally differentiable at point <span class="math-container">$a$</span> so that we have an open subeset <span class="math-container">$U$</span> with <span class="math-contain... | Part I. I'm going to give a meta-answer here: most definitions in elementary mathematics (let's say "up to junior year in college") are pretty well established and tested. There are some bad books/papers out there, but if four different linear algebra books define "vector space" the same way, you can bet that there's a... | Take for example the subset <span class="math-container">$V = \mathbb{R}_{\geq 0} \subset \mathbb{R}$</span> with the usual addition and define the scalar multiplication via <span class="math-container">$k \cdot x = \vert k \vert x$</span>. Then 1) and 6) hold, but 5) does for example not hold as we do not have negativ... | https://math.stackexchange.com |
114,924 | [
"https://softwareengineering.stackexchange.com/questions/114924",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/1468/"
] | If you add new configuration options to a program, it can often have tons of ripple effects in terms of getting the options to where they need to be acted upon. There are three basic ways to deal with this that I'm aware of:
<ol>
<li>Pass all configuration settings to the parts of your program that need them explicit... | The <em>best</em> solution would be to make several configuration interfaces and implement them as you wish. This both limits accessibility and keeps things localized. However, it's far too much effort to be worth it over simply chucking all the config in a single class and moving on to a problem with a lot more gravit... | I prefer your option 1 because the decoupling enables easier testing, and the configuration settings the object depends on are made explicit. If an object requires a configuration setting, then explicitly provide it to the object by a constructor argument or setter method. Reduce the verbosity by using a dependency i... | https://softwareengineering.stackexchange.com |
630,619 | [
"https://math.stackexchange.com/questions/630619",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/76802/"
] | I was asked to prove the following:
let $\gamma$ be a well ordered set with the following property: for any $\alpha$ and $\beta$ well ordered sets, if $\alpha+\gamma=\beta+\gamma$ then $\alpha=\beta$. Show that $\gamma$ is a finite set.
This might be a very doable question to solve, but I don't understand it. What d... | Ordinals numbers <strong>are</strong> numbers. They have their addition and multiplication and even exponentiation.
The notation $\alpha+\gamma$ means that we take the ordinal $\alpha$ then we concatenate it with $\gamma$. Formally speaking, this is the only ordinal $\eta$ which is isomorphic to the lexicographic orde... | Given well-ordered sets $\alpha$ and $\gamma,$ the set $\alpha+\gamma$ is the disjoint union of $\alpha$ and $\gamma,$ ordered with all the elements of $\alpha$ first (in their given order), followed by all the elements of $\gamma$ (in their given order). This ordering is in fact a well-ordering of the disjoint union.
... | https://math.stackexchange.com |
44,797 | [
"https://mechanics.stackexchange.com/questions/44797",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/28940/"
] | I very much need your experience about CAN bus. My bike (Ducati) got a serious problem about CAN bus. The first time, my bike shows the "CAN line" error, dead totally on the street.
I found the CAN IC in the dashboard was faulty, so I replaced it, and the bike lived again. I started the crank, engine running about one... | What makes you think it was the CAN bus transceiver at fault, could it be a coincidence that the intermittent fault disappears after you replaced it?
I would do the following to determine the fault or to see what is causing the IC to fail:
Scope the CAN bus H&L lines - They should be a near perfect mirror image o... | DO you know how CM impulse current from spark induces V overvoltage in inductive cables? Then you ought to know why CM chokes are needed.
Is it resistance carbon wire to plug or pure copper? Why does this make a difference?
| https://mechanics.stackexchange.com |
10,782 | [
"https://dba.stackexchange.com/questions/10782",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/-1/"
] | It is said that if we create index on a column with more uniqueness than performance of
that index will be more. But I believe that whether it is unique or not it will occupy same no. of blocks than why due to uniqueness it will be faster.
| The more unique the key is, the more you filter the data.
For example if you had an index on a field with only 2 unique values such as gender, the index would only split the search space in half or the number of records / 2.
Choosing to index a field with a greater amount of unique records (cardinality) will divide t... | A unique index guarantees that the index key contains no duplicate values and therefore every row in the table is in some way unique. Specifying a unique index makes sense only when uniqueness is a characteristic of the data itself. For example, if you want to make sure that the values in the <code>NationalIDNumber</co... | https://dba.stackexchange.com |
11,235 | [
"https://dba.stackexchange.com/questions/11235",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/-1/"
] | Am running asp.net application.Am searching records.if i click the view button i got this error,
<blockquote>
an inconsistency was detected during an internal operation in
database(database name) on page(some page).please contact technical
support.reference number 6.
</blockquote>
I Googled and i got the result... | This inconsistency error can be resolved by running the following command:
<pre><code>dbcc checkdb(database name,repair_allow_data_loss)
</code></pre>
| Like Jeni said, you can run that command and it will do a repair, but CAN make it loose some data.
I would first start with:
<blockquote>
DBCC CHECKDB('DB Name',REPAIR_REBUILD)
</blockquote>
If that fails use the command provided by jeni:
<blockquote>
dbcc checkdb(database name.repair_allow_data_loss)
</blockqu... | https://dba.stackexchange.com |
119,118 | [
"https://mathoverflow.net/questions/119118",
"https://mathoverflow.net",
"https://mathoverflow.net/users/14454/"
] | Suppose that $N$ is a totally geodesic submanifold of a complete Riemannian manifold $(M,g)$. Is it the case that a geodesic segment that minimizes length in the submanifold $N$ also minimizes length in the ambient manifold $M$?
| Let $M$ be the flat cylinder $\mathbb{R} \times S^1 \subset \mathbb{R} \times \mathbb{C}$ and $N = \{(t,e^{it}) | t \in \mathbb{R}\}$, which is a geodesic (hence a complete totally geodesic submanifold of $M$) minimizing between any two points of $N$ (among the geodesics of $N$). But the minimizing geodesic in $M$ betw... | As for an example where $N$ is complete: Slice a 2-sphere just above and below a great circle. Keep the piece containing the great circle. Glue flat disks along the resulting boundaries and smooth the surface near the boundaries.
| https://mathoverflow.net |
52,729 | [
"https://softwareengineering.stackexchange.com/questions/52729",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/18667/"
] | I currently work in a professional capacity as a software engineer working with the Android OS. We work at integrating our platform as a native daemon among other facets of the project. I primarily work in Java developing the SDK and Android applications, but get to help with the platform in C/C++.
Anywho, I have a g... | I write Linux device drivers for my company, and I got into this position by knowing the most about Linux development in my department and they promoted/hired me into a new role. It was very much a junior level style entry, so they do exist and don't lose hope!
My immediate advice for you is to see if you can narrow d... | I am a software developer with 15+ years experience working at Motorola and a few other hi tech companies. I have a BSCE degree. So I'm not an amateur.
This question... how to break in... is a common one not only for Linux but for virtually any area of specialization. Software engineering has become just like medi... | https://softwareengineering.stackexchange.com |
299,446 | [
"https://math.stackexchange.com/questions/299446",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/61706/"
] | This is homework. Firstly, the question that I am trying to answer is
"What is the area bound by the $y$ and $x$-axis for $y=2\sin(2x)$?"
However, I cannot seem to find the right method to solve this problem. I think I need to find the integral of $y=2\sin(2x)$ and $y=0$ for when $x \gt 0$, but I am at at loss of h... | As the question is written, I would refer you to amWhy's answer.
On the other hand, perhaps it would be better to deal with the following similar question:
<blockquote>
What is the area bounded by the curve $y = 2\sin(2x)$ and the $x$ axis from $x = x_0$ to $x_1$?
</blockquote>
In this case, the question has a def... | Note that $y = 0$ when $x = 0$ (because $y = 2\sin(2\cdot 0) = 0$). But $y = 0$ also when $x = k\cdot \pi/2$ for any integer $k$.
So you're the bounds you need to be concerned about are those x for which $x \geq 0$ and $y = 2 \sin 2x \geq 0$: $$x \in [0,\pi/2] \cup [\pi, 3\pi/2] \cup [2\pi, 5\pi/2] \cup\,\cdots \left[... | https://math.stackexchange.com |
334,022 | [
"https://electronics.stackexchange.com/questions/334022",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/165573/"
] | I've a 12 volt 1 Amp rated adapter and would like to hook up 2 12 volt 0.18 Amps Dc motor in parallel circuit to power them up, would the over rated amps effect my dc motors and if so how can i reduce Amps without reducing its volts ?
| Let's use another example: I have a 100 W motor that I'm going to plug into the Irish national grid which has a capacity of 5 GW at peak capacity. Do you think it will burn out my motor?
Answer: No. The motor will draw the current it requires. This current is limited by the resistance of the motor.
Back to your quest... | 2 * 0.18 is less than 1 amp so it will be fine. The extra capacity from the adaptor will not be a problem.
| https://electronics.stackexchange.com |
4,833 | [
"https://dsp.stackexchange.com/questions/4833",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/1837/"
] | I'm computing 1 sec. hanning windows from a signal that has a variable frequency between 1-4Hz. My first impression is that data loss caused by the distortion due to the window function is greater than the correction that it is expected to give while taking FFT of that window. Am I right?
Is it a bad approach to apply... | A 1s Hann window will have (in the frequency domain) a main lobe width of 4Hz. This will severely mask your signal components.
Even a rectangular window will be ~2Hz main lobe.
You should use a greater windowing time depending on the accuracy you need for frequency detection.
| A von Hann window does not "correct" the results of an FFT.
It (1) reduces interference from other portions of the spectrum in the window's stop-band at the cost of (2) reduced resolution (due a fatter main lobe in the frequency domain) and less total information.
You have to trade-off the 2 effects for your part... | https://dsp.stackexchange.com |
230,687 | [
"https://physics.stackexchange.com/questions/230687",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/98940/"
] | I'm pretty confused. So I've been told that the equation of state for <span class="math-container">$n$</span> moles of some type of gas is <span class="math-container">$P(V-b) = nRT$</span>. That's not quite like an ideal gas. But then the relations <span class="math-container">$C_p - C_v = R$</span>, and <span class="... | The gas you are describing is not precisely an ideal gas, but is pretty close. In an ideal gas, the molecules are dots, they don't have volume ; moreover, threr are no interactions except for the elastic collisions that allows the gas to thermalize.
The gas you describe is is a gas with no interactions, but with molec... | The heat capacities of this gas behave the same as for an ideal gas. The PVT behavior is not. So, what is the problem? Note that, for this gas, even though $C_v$, $C_p$, and U are functions only of temperature, like an ideal gas, H is a function not only of temperature but also of pressure p: $dH=C_pdT+bdP$.
| https://physics.stackexchange.com |
34,713 | [
"https://electronics.stackexchange.com/questions/34713",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/9927/"
] | In computer science, recursion chews up a valuable and limited resource – the stack – and can lead to an unrecoverable type of runtime error: the dreaded StackOverflow. Tail Recursion however is a form of recursion that doesn’t use any stack space, and thus is a way to use recursion safely.
freeRam() is the function t... | In both cases, your <code>setup()</code> function is looking for a memory leak, but there is no memory leak. A recursive function will only increase stack usage as the recursion takes place. Eventually, the stack unwinds until the final <code>return</code> statement executes, leaving the stack as it was when the functi... | Once the function exits back to main, the stack is returned. The function doesn't continue to use the stack once it's finished, so measuring the memory after the function is done won't tell you anything. You need to measure the memory when the recursion is at its deepest point.
For instance, you can create a variabl... | https://electronics.stackexchange.com |
9,873 | [
"https://softwareengineering.stackexchange.com/questions/9873",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/92/"
] | Some companies, like Blizzard, make software that continues to work well in future versions of Windows and with newer versions of their other software dependencies. Other companies (mostly ones that are not hardcore software companies) sometimes write software that breaks with a release of a new OS or other software de... | Did Blizzard write software that works well with future versions of Windows (Starcraft still plays on 7 for example)...
or did Microsoft write "future versions" of software that is backwards looking?
Something like WoW isn't exactly "forward looking" since it's still in active development. Other software, like Starc... | Several reasons:
<ol>
<li>They write to standards that continue to be supported in future OS's</li>
<li>OS companies (e.g. MS) actually put in a good deal of code to support older software</li>
<li>Large popular software houses tend to have formal or informal relationships with the OS companies, so they get to see stu... | https://softwareengineering.stackexchange.com |
453,494 | [
"https://electronics.stackexchange.com/questions/453494",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/229051/"
] | The other day in class, our professor told us that care should be taken while closing a capacitive circuit and while opening an inductive circuit.
Why is this so?
I partly understand the inductive part. Since inductor only allows current to change gradually through it, if the current flow is suddenly stopped, then t... | In theory when an empty capacitor is connected to a ideal voltage source, infinite current flows until capacitor is charged to the supplied voltage. Basically same thing when disconnecting a powered inductor, in theory the voltage goes to infinity. Many devices like computer power supplies, LED lamps and phone chargers... | <blockquote>
edit /correction. ...
</blockquote>
A step voltage cause a step current max <strong>Ic (t)=Vcc/ESR</strong>.<br>
(@ t=0) when contact is made from discharged cap to an ideal voltage source then ....
Current decays at a slope by ~60% of initial surge <strong>max Ic</strong> at t=0 when t = ESR*C =<... | https://electronics.stackexchange.com |
2,044,893 | [
"https://math.stackexchange.com/questions/2044893",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/396212/"
] | I'm new to this forum but I've done my best to check that my question hasn't been answered before, but I may have missed something, feel free to correct me if that's the case.
Anyway, I'm trying to figure out how to solve this problem:
"Determine the equation on the parameter form for the line that represents the int... | For ii) just note that $ Tx\in Im(T)=Ker(T) $ implies that $ T(T(x))=0$, i.e., $ T^2 (x)=0$, then $ T^2=O $.
For iii) we have $Im(T)\subseteq Ker(T)$ because $T^2=O$, so we can view $Im(T)$ as a subspace of $Ker(T)$. Now, since $T\neq O$, then there is some $Tx\neq 0$ such that $Tx\in Ker(T)$, so $dim(Ker(T)), dim(Im(... | Second one : $T^2 x=T(Tx)$. If $Tx$ is in image of $T$, $T^2 x=0$ by ker$T$=Image$T$($Tx$ is in kernel). Even if $x$ is in kernel, $T^2 x=0$. Done.
Third one : Since $T$ is not equivalent to zero matrix, Image of $T$ is not trivial, so that the dimension of Image $\geq$ 1. And also, from $T^2=0$, Kernel of $T$ is not ... | https://math.stackexchange.com |
575,314 | [
"https://physics.stackexchange.com/questions/575314",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/190315/"
] | If technology allowed it one day, would it be possible to physically photograph how quarks are arranged inside a nucleus?<br />
What would you see?
For example, would it be possible to distinguish a neutron from a proton by taking an image inside the nucleus? Or would it look like a mixture of quarks?
| You need extraordinarily high-energy fundamental particles to see that small directly. Typically when we hit a proton or neutron with that much energy, it fragments and new particles are created, shooting off in various directions. Direct images are out of the question. The best we can do is calculate backwards from th... | In my opinion, no. At least in the sense of ordinary human notion of seeing. When speaking about objects, smaller than the wavelength of visible light the ordinary notion to see becomes obscured. The structure of objects smaller, that the distances of order <span class="math-container">$\simeq 500 $</span> nm, is deter... | https://physics.stackexchange.com |
164,333 | [
"https://stats.stackexchange.com/questions/164333",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/83903/"
] | I have been looking at some tutorials and articles and couldn't get a scenario where two variables are in different scales and used in modeling.
So, firstly lets assume I have one metric of numeric type, other in percentages, and other in decimals.
<ol>
<li>If I want to use those variables in a regression model for
... | For a linear regression you do not have to standardise. You just have to take care with the interpretation of the estimated coefficients. Assume e.g. that you have two independent variables, $x_1$ in meter and $x_2$ in kilometer and you estimate the regression model $y = \beta_1 x_1 + \beta_2 x_2 + \beta_3 + \epsilon$... | for the standardizing part of your question, if you want to standardize a vector x in R, use the function
<pre><code> scale(x)
</code></pre>
it is equivalent to
<pre><code> (x-mean(x))/sd(x)
</code></pre>
| https://stats.stackexchange.com |
252,911 | [
"https://physics.stackexchange.com/questions/252911",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/115292/"
] | How is the work done by the internal forces acting in a rigid body zero?
Actually I read in a book an example for the same.
Let me present that example here.
Consider a rigid body having two particles $A$ and $B$. Suppose, the particles move in such a way that the line $AB$ translates parallel to itself. The displac... | I disagree with both other answers.
<ul>
<li>It's not enough that the sum of forces is zero </li>
<li>This is not a vocabulary problem</li>
</ul>
The work-energy theorem applies also to systems of interacting bodies, where the total work of all forces (internal and external) equals the variation of the sum of the kin... | Your confusion <em>might</em> be coming from not clearly understanding that you need to define a <em>system</em>, and then all of your quantities are referenced to the system you have defined.
If your system is <em>A and B</em>, then the force that A applies to B is by definition an internal force, and no work is do... | https://physics.stackexchange.com |
125,971 | [
"https://softwareengineering.stackexchange.com/questions/125971",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/6001/"
] | I never used SQL Server Reporting Services (SSRS) before but used little Crystal Reports. My present project has extensive use of Crystal Reports for Visual Studio 2005. This choice brought some nasty issues of Crystal Reports in front. The very first report failed to print or export because of a bug. After wasting a w... | Its hard to say for certain, because currently there is no business intelligence component to Visual Studio 2010, and there seems to be no plans to add one, so all reports for SSRS must be developed in Visual Studio 2008. However crystal reports can be made in Visual Studio 2010. SSRS does seem to be better than cryst... | Here's what I'm seeing based on viewing classified and my own job search process earlier this year.
Most companies with a long established .NET and/or VB6 code are sticking with Crystal for now. Unfortunately, they have too much invested in this or that weird report for various accounting managers, sales managers and... | https://softwareengineering.stackexchange.com |
73,845 | [
"https://stats.stackexchange.com/questions/73845",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/31672/"
] | I need a numerical example to illustrate cases where $Cov(X_1, X_2) = 0$. Can you think of examples involving functions or matrices?
| As a very simple example (maybe too simple?), consider $X,Y\in\{0,1\}$ with joint distribution defined by the table
<pre><code> Y \ X 0 1
0 1/4 1/4 1/2
1 1/4 1/4 1/2
1/2 1/2 1
</code></pre>
This table also displays the marginal distributions of $X$ and $Y$. First, check that $X$ and... | Obviously whenever $X_1,X_2$ are independent but I guess that's not the point.
My go-to for dependent rvs is $U$ uniform on $[0,1]$ and take $X_1 = \sin(2\pi U), X_2=\cos(2\pi U)$. This basically says that if you pick a point uniformly on the unit circle then the coordinate functions are uncorrelated. This fact boils ... | https://stats.stackexchange.com |
31,022 | [
"https://physics.stackexchange.com/questions/31022",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/7896/"
] | For a two-level quantum system with energy eigenstates $|\phi_1\rangle$ and $|\phi_2\rangle$ at finite temperature, we can write a general state as $$|\Phi\rangle=c_1|\phi_1\rangle+c_2|\phi_2\rangle.$$
In quantum mechanics, we know that the expectation of an operator $\hat{O}$ is given by $$\langle\Phi|\hat{O}|\Phi\ra... | Your formula for the expectation value in statistical mechanics is wrong.
A pure quantum mechanical state in this system is a sum $$|\Phi\rangle = c_1 |\lambda_1\rangle + c_2|\lambda_2\rangle$$ of two basis vectors, with complex coefficients. Note that I'm using your notation $\Phi$ for a general state, and switchin... | Nothing is actually wrong.
The quantum answer includes $c_2^*c_1$ term which depends on the phase difference between $c_1$ and $c_2$. But the phase difference is something that would vary randomly with even the tiniest coupling between states 1 and 2. And thermodynamics requires such a coupling to exist to be applie... | https://physics.stackexchange.com |
61,273 | [
"https://security.stackexchange.com/questions/61273",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/35158/"
] | I started using a password manager last year and updated nearly all of my internet accounts to super-strong, unique passwords, and that isn't a problem, cause I only access them from web browsers or my phone, which has said password manager installed.
But device level access is a different story. Having super-strong, ... | A good password is a trade-off between several parameters:
<ul>
<li>Value of that which is protected (this should condition the effort invested by potential attackers).</li>
<li>Cost of brute force (this depends a lot on the target, e.g. some will allow offline attacks on a hash value, while others limit attackers to ... | Access controls need to be proportionate to the risks involved. Best practice does not apply.
Passwords to product forum sites need not be as complex as passwords to banking accounts, for obvious reasons: compromise has limited risk on the product forum site.
The question you need to ask of yourself is, what level of... | https://security.stackexchange.com |
2,797,360 | [
"https://math.stackexchange.com/questions/2797360",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/460810/"
] | There are 4 basic combinatoric formulas when picking $k$ elements among $n$
We have repetition is allowed or not allowed, and order matters or does not matter.
When order matters and repetition is not allowed we call it a permutation.
When order does not matter and repetition is not allowed we call it a combination.... | We have the following cases for the number of subsets of size $k$ chosen from a set of $n$ distinct elements:
<ul>
<li>replacement and ordered, "permutation with repetition" $$n^k$$</li>
<li>no replacement and ordered, "k-permutations of n" $$\frac{n!}{(n-k)!}$$</li>
<li>no replacement and unordered, "combinations" $... | When order matters and repetition is allowed, you get all the functions from $\{1,2, \cdots, k\}$ to your set $S$ of $n$ elements. Every function corresponds to a unique choice, and every choice allows you to construct a function by setting $f(r)$ to be the $r^{th}$ element chosen. The formula for these is simpler, ... | https://math.stackexchange.com |
162,250 | [
"https://dba.stackexchange.com/questions/162250",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/50749/"
] | I have to update a <code>bigint[]</code> column named <code>permissao_ver</code>.<br>
Example value: <code>'{1,2,3,4,5,11,44,56,75,11}'</code>.
Pseudo code:
<pre><code>UPDATE callcenter.pausa
SET permissao_ver = '{"(SELECT cod_grupo FROM crm.usuariosgrupos
WHERE habilitar = 1)"}'::bigint[]
... | Use <code>array</code>:
<pre><code>UPDATE callcenter.pausa
SET permissao_ver = array(SELECT cod_grupo
FROM crm.usuariosgrupos
WHERE habilitar = 1)
WHERE habilitado = 1
AND permissao_ver is null
</code></pre>
| Yet another option
<pre><code>UPDATE callcenter.pausa
SET permissao_ver = (SELECT array_agg(cod_grupo)
FROM crm.usuariosgrupos
WHERE habilitar = 1)
WHERE habilitado = 1
AND permissao_ver is null
</code></pre>
| https://dba.stackexchange.com |
136,466 | [
"https://softwareengineering.stackexchange.com/questions/136466",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/48314/"
] | Please have a look at following snippet:
<pre><code>public class Foo {
int digit;
String name;
Foo (int d, String n) {
this(d);
// cannot do following.
//compile-time error: Constructor call must be first statement in a Constructor
//this(n);
}
Foo (int p) {
digit = p;
}
Foo (String q) {
na... | Constructors are not just "methods that are called when object is created", they are conceptually different.
Constructor's purpose is to constrain what states objects can be in initially. A freshly created object is zeroed on all fields (null/0/false) and that may be an invalid state in your program. For example, a Cu... | The reason is that the Java Language Specification says so. It could probably have been written to allow what you describe, but not for free: enforcing the order makes things simpler. Think about inheritance and calls to <code>super()</code>. If it wouldn't be the first statement in a constructor, then the subclass cou... | https://softwareengineering.stackexchange.com |
91,284 | [
"https://electronics.stackexchange.com/questions/91284",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/16307/"
] | <img src="https://i.stack.imgur.com/KBpTX.png" alt="enter image description here">
In the figure(V2 is a DC motor by the way) an isolated way of switching recommended. But what if we use a transistor such as in the figure. Why many say that the motor current would harm the micro controller and we need an opto transist... | Those that don't understand the science resort to religion. The rule of <i>always opto-isolate a motor driver</i> is a religious belief that seems to have a small cult following, but that doesn't make it good engineering.
If the motor power supply and the micro power supply both have the same ground, then there is li... | There is probably a mistake in your schematics. You used a PNP transistor would it rather be a NPN?
By the way, a bipolar transistor doesn't provide a galvanic insulation. If your transistor got burnt it could be that the base voltage become higher that the max allowed on a arduino pin.
Using a optocoupler, event if... | https://electronics.stackexchange.com |
419,969 | [
"https://softwareengineering.stackexchange.com/questions/419969",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/373596/"
] | I don't want to spam you with a ton of code, but please have a quick look at this boiler-plate method:
In this scenario let's say I have a <code>ProcessingText.py</code> file (class) that I finished its unit testing, including the methods <code>setTextToClean(text)</code> and <code>getCleanedText()</code>.
And I have a... | Your handle text function is just calling another function in processing text object so it is not worth testing in unit and integration.
You instead test processing text functions (set text to clean in your code) in unit test, and the entrypoint of the ui class.
| <strong>Unit test</strong> is helpful to verify your code path in individual component works as you expect, and it is faster to locating the potential bugs in smaller piece. Here there may be two parts that worth (unit) testing:
<ul>
<li>The logic inside <code>setTextToClean</code>, in which you <code>assert</code> som... | https://softwareengineering.stackexchange.com |
149,179 | [
"https://electronics.stackexchange.com/questions/149179",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/52754/"
] | I am looking at buying a chip holder for a chip that comes in the form of DIP28S according to different datasheets on it. However when I searched for DIP28S chip holders I could only find SOP28 chip holders, and the measurements of them would allow the DIP28S chip to fit in those chip holders. So my assumption would be... | Your first circuit is fine. You could even use 100k resistors instead of 10k to save power. Note that your first op amp will need to <em>output</em> 0-10V, which means you won't be able to run it off of a 0-10V supply. If you don't have a rail-to-rail op amp, I'd recommend at least a +13/-3 V supply.
As Matt said, you... | Depends on your requirements. Do you need to sample at a very high frequency? If so, you will definitely need to add some buffers. The first circuit you have would work, presuming the op amps can achieve the required output swing. The first amp will need to be powered off of at least 0 to 10 volts, and the second a... | https://electronics.stackexchange.com |
212,137 | [
"https://electronics.stackexchange.com/questions/212137",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/88465/"
] | I want to put a firewall hardware product between a RTU and PLC to block some Modbus function codes (e.g. write coil, read coil). (This firewall product is able to do deep packet inspection on Modbus protocol.)
This firewall hardware has two ethernet (RJ45) ports, IN and OUT. But the Modbus uses serial buses (should b... | Modbus is a serial communications protocol, a link layer standard. In your situation, it is being transported over RS-485, a physical layer standard. So, you might say that you have "Modbus over RS-485".
Ethernet/RS-485 converters take "Ethernet over copper", and turn it into "Ethernet over RS-485". RS-485 is the phys... | It isn't clear what do you mean with firewall device. Ethernet/Rs485 converters are product specific and usualy require a virtual com port driver on PC to be able to work, therefore you can get PC->ethernet->serial device.<br>
You will need embedded Modbus RTU to Modbus TCP/IP converters and somehow pair them together,... | https://electronics.stackexchange.com |
14,585 | [
"https://stats.stackexchange.com/questions/14585",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/5921/"
] | I'm currently working on my thesis, more specifically I'm analyzing some data collected from researchers about the project's they're working on.
In the end, I have performed a multiple linear regression to verify which determinants (budget, team size,...) significantly influence the external impact of a research proje... | The fact that your outcome variable is subjective suggests that it will be measured with quite imperfect reliability. The lower the reliability, the more dampened correlations with other variables will tend to be, so one has to lower one's standards.
I'll take a stab at giving you a more concrete reaction. Knowing... | There are no absolutes. Different problems have different difficulties. The only thing that would make one reject a certain $R^2$ is another approach getting a much bigger $R^2$ from the same dataset, using a pre-specified or overfitting-corrected model.
| https://stats.stackexchange.com |
21,567 | [
"https://dba.stackexchange.com/questions/21567",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/7511/"
] | This question regards the proper use of NULL and utilizing CHECK constraints for business logic vs stored procedures.
I have the following tables setup.
<img src="https://i.stack.imgur.com/1UrGK.jpg" alt="Entity Relationship Diagram">
I normalized the tables to avoid using NULLs. The problem is that some of these ta... | Querying a column that can contain nulls is more complex than querying a column that cannot. So also is querying multiple tables more complex than querying one table. I wouldn't let the avoidance of null drive the normalization.
For example, you mentioned that all devices will eventually be disposed and get a disp... | I would go for the check constraints, you cannot be positive that records will never get manually entered or adjusted. Data integrity trumps avoiding nulls every single time.
| https://dba.stackexchange.com |
177,804 | [
"https://electronics.stackexchange.com/questions/177804",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/7910/"
] | I'm pretty new/noob with electronics. I'm trying to reproduce a sound (I'm using Proteus as simulator) in a circuit.
I wasted hours of looking for but I can only found solutions with Arduino or synthetic sounds, I need to reproduce a "wav" sound or any other format, recorded previously.
Which is the simplest method/... | You can't just connect them in parallel.
If you're fluent with this stuff, you can drive each one directly from 230 V, but with PWM so that the average power doesn't exceed 600 W. There are various ways to do this, including triacs, but there are issues beyond what we can reasonably get into here. You have to consid... | The crude but secure and working solution:
Get a 230V primary / 110V secondary isolating transformer used for US equipment in europe with about 2kVA and use that for your oven. Since you're working on 110V, now, you can easily connect them in parallel. They are not that cheap though.
Any other solution involves compli... | https://electronics.stackexchange.com |
17,900 | [
"https://physics.stackexchange.com/questions/17900",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/2320/"
] | Say I put a bunch of powerful square magnets on a nearly frictionless table in a disordered fashion. The second law of thermodynamics states that the system shall spontaneously get more disordered, yet the magnets will attract each other and form a chain (typically), thereby increasing the order of the system-and, seem... | The magnets will indeed attract each other. This attraction will put them in motion, and they will head towards each other, converting electromagnetic energy into kinetic energy. Then they will collide, and loose their kinetic energies in the collision, finally coming to rest in a more ordered, low-energy state.
In te... | It's actually a nice example of why the 2nd law is useful: if you go around trying to account in microscopic detail the balance of things like energy and entropy, then you can easily go wrong. I used to have a student who would do this all the time; I don't know if he ever learnt the lesson...
In this specific case, y... | https://physics.stackexchange.com |
4,413,299 | [
"https://math.stackexchange.com/questions/4413299",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/833894/"
] | I'm trying to proof the ratio test for convergence of sum of a sequence:
<span class="math-container">$l :=\lim_\limits{n\rightarrow \infty}\left| \frac{a_{n+1}}{a_n} \right| <1 \Rightarrow s_n := \sum_\limits{k=0}^n a_k$</span> converges absolutely
Currently I'm stuck proving it, and online I've seen other proofs, ... | The question was why
<span class="math-container">$\forall\epsilon>0 \quad \exists n_0>0: \left|\left|\frac{a_{n+1}}{a_n} \right| - l\right| < \epsilon \quad \forall n\geq n_0$</span>
would imply the following:
<span class="math-container">$\forall\epsilon>0 \quad \exists n_0>0:\left|\frac{a_{n+1}}{a_n} ... | You are assuming that<span class="math-container">$$\lim_{n\to\infty}\left|\frac{a_{n+1}}{a_n}\right|=l<1.$$</span>Take <span class="math-container">$\varepsilon>0$</span> such that <span class="math-container">$l+\varepsilon<1$</span>. Since <span class="math-container">$\varepsilon>0$</span>,<span class="... | https://math.stackexchange.com |
254,655 | [
"https://dba.stackexchange.com/questions/254655",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/196293/"
] | On aws RDS I have an mysql <code>8.0.16</code> instance running.
My problem is now, that the <code>INFORMATION_SCHEMA.ST_SPATIAL_REFERENCE_SYSTEMS</code> table is empty.
This is a problem for me because I would like to create the following table:
<pre class="lang-sql prettyprint-override"><code>CREATE TABLE my_table
... | The new MySQL v8.0.16 image on RDS (as of writing this) is missing spatial references other than <code>SRID 0</code>.
As a workaround, you can create a new instance with v8.0.15 and then perform the minor upgrade (requires reboot).
<pre><code>select count(*) from INFORMATION_SCHEMA.ST_SPATIAL_REFERENCE_SYSTEMS
</cod... | I ran into this issue as well with MySQL 8.0.16 on RDS. On a MySQL instance running on your own server, you could add the missing reference systems yourself, but this requires SUPER access, which isn't available with RDS.
I ended up contacting AWS support via the AWS console, and they were able to add the missing SRID... | https://dba.stackexchange.com |
3,923,260 | [
"https://math.stackexchange.com/questions/3923260",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/749428/"
] | <blockquote>
<span class="math-container">$a_1=1.$</span> <span class="math-container">$a_{n+1}=1+\frac{1}{1+a_{n}}$</span>
</blockquote>
<strong>Prove that the sequence is convergent.</strong>
I'm trying to prove the convergence of this sequence but having trouble. At first I thought this might be a monotone sequence ... | Usually when we write <span class="math-container">$\sqrt{x}$</span> where <span class="math-container">$x$</span> is a real number, we usually mean the principal root. This means the positive square root. While <span class="math-container">$(-4)^2=16$</span>, we don't say that <span class="math-container">$\sqrt{16}=-... | <em>In the reals</em>, if <span class="math-container">$a>0$</span> then <span class="math-container">$\sqrt x=-a$</span> has no solution since the square root in this context is usually understood to return a non-negative number.
<em>In the complexes</em>, <span class="math-container">$\sqrt x=-a$</span> has two so... | https://math.stackexchange.com |
602,248 | [
"https://physics.stackexchange.com/questions/602248",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/258720/"
] | I find it written many places that "you can find the work along a short segment of the path by taking the dot product of the force and the tangent vector."
I can solve these problems, but I have a question about the intuition. Why do I use the unit tangent vector? Is it because the distance being traveled is ... | The work over a short segment of path is the dot product between force <span class="math-container">$\vec F$</span> and small displacement <span class="math-container">$\delta r$</span>.
<span class="math-container">$$\delta W=\vec F \cdot \delta\vec r$$</span>
Now, the work over the entire path (i.e. not very small di... | I <em>think</em> the intuition you're looking for is that the contribution of the force to the work is its component in the direction of the path. So if you have force defined as a vector field <span class="math-container">$ \mathbf F$</span> and a smooth curve <span class="math-container">$ s $</span> you calculate th... | https://physics.stackexchange.com |
82,955 | [
"https://dba.stackexchange.com/questions/82955",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/29663/"
] | Can any one please explain what is happening with our DB dumps?
We are executing dump as below
<pre><code>mysqldump -v --single-transaction --quick --lock-tables=false --skip-triggers -uXXX -pXXX $EXCLUDETABLES dbname -h xxx.xxx.xxx > $FLNM
</code></pre>
$EXCLUDETABLES contains multiple --ignore-table statements
... | Something like the following should be good enough to get you started. It should be quite lightweight as well.
<pre><code>DECLARE @Name NVARCHAR( MAX ),
@SQL NVARCHAR( MAX );
DECLARE @t_BindingErrors TABLE
(
ViewName NVARCHAR( MAX ),
ErrorMessage NVARCHAR( MAX )
);
DECLARE c C... | You can generate <code>SELECT</code> statements for all the views in a database and just run the results:
<code>SELECT 'SELECT * FROM dbo.' + name from sys.sysobjects WHERE type = 'V'</code>
Which should return
<pre><code>SELECT * FROM dbo.xxxx
SELECT * FROM dbo.yyyy
etc...
</code></pre>
For all the views in the c... | https://dba.stackexchange.com |
81,484 | [
"https://physics.stackexchange.com/questions/81484",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/31401/"
] | If you have, say, a proton it has gluon field fluctuations around it. Those flux tubes between the quarks suppresses the gluon field fluctuations and create a true vacuum between them(correct me if I'm wrong), but how does that bind the quarks together?
I've read that it costs energy to clear the vacuum out, but I sti... | The flux tube contains a certain energy per unit distance. Therefore, pulling quarks further apart costs energy; pulling them infinitely far apart costs infinitely much energy (because the flux tube must then be infinitely long).
BTW, you talk about the "true" vacuum in your question. Do you mean the true physical va... | The existense of the quarks suppresses the gluon fluctuations creating the flux-tubes. But yeah, it requires energy to separate the quarks with the flux tubes, that's why when they are sufficiently separated the energy is used to create the quark-anti quark pair called meson.
And you probably mentioned The "true" vacuu... | https://physics.stackexchange.com |
84,145 | [
"https://stats.stackexchange.com/questions/84145",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/38348/"
] | I have a few questions with regards to a solution to the problem below:
<img src="https://i.stack.imgur.com/aTeir.png" alt="Question and Answer:">
<ol>
<li>How is it possible to have $max_{1\leq{i}\leq{n}}x_i-1<\theta<min_{1\leq{i}\leq{n}}x_i$?
How can a value of $\theta$ be both greater than a larger value and... | <ol>
<li>The value of θ is <em>not</em> greater than a larger value and less than a smaller value. Note that you subtract 1 from the maximum value, and the difference between the maximum and minimum can never be greater than 1.</li>
<li>Your example is not consistent with the probability distribution. The probability d... | <ol>
<li>You might be missing the $-1$ after the max: $\theta$ lies above the maximum value of the $x_i$s $-1$ and the minimum value of the $x_i$s. Another way is two write $\max x_i \leq \theta + 1 \leq \min x_i +1$.</li>
<li>The likelihood function of $\theta$ given $n$ independent observations $x_1, \dots, x_n$ is g... | https://stats.stackexchange.com |
61,573 | [
"https://mathoverflow.net/questions/61573",
"https://mathoverflow.net",
"https://mathoverflow.net/users/9509/"
] | Is the category of finite flat group schemes equipped with "tensor products" and Hom-objects, encoding bilinear maps? I'm aware that the Cartier dual is $Hom(\mathbb{G}, \mathbb{G}_m)$, and want to know if this is part of a systematic collection of objects. For example, is there a "free ring scheme on $\mathbb{G}$"?
... | In analytic geometry, you can see to the Douady's example in Fischer book (p.151) where $X:=\lbrace{(x,s,t)\in {\Bbb C}^{3}: x^{3}+sx +t=0; 27t^{2}+4s^{3}=0}\rbrace$, $S:=\lbrace{(s,t): 27t^{2}+4s^{3}=0\rbrace}$ and $f:X\rightarrow S$ is a finite, surjective and flat map (induced by the canonical projection). Then, it ... | An extremely partial answer: If $S$ is Dedekind, then the answer is yes (for quite general $X$). Indeed, for a reduced Noetherian scheme all embedded points are generic points of components, so if $X_{red} \to S$ is non-flat then $X_{red}$ would have a component lying over some closed point of $S$, hence so would the ... | https://mathoverflow.net |
175,072 | [
"https://dba.stackexchange.com/questions/175072",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/125898/"
] | I'm struggling to come up with an answer to this problem and so hope to find some help here.
I have the following time series data table with missing entries:
<pre><code>CREATE TABLE foo
AS
SELECT timestamp::timestamp, deviceid, eventcount
FROM ( VALUES
( '2017-01-01 00:00:00', 'AAAAA', 1000 ),
( '2017-01-... | This should work for you.
<pre><code>SELECT t.timestamp, t.deviceid, coalesce(eventcount, 0)
FROM foo
RIGHT OUTER JOIN (
SELECT timestamp, deviceid
FROM ( SELECT DISTINCT deviceid FROM foo ) AS d
CROSS JOIN ( SELECT min(timestamp), max(timestamp) FROM foo ) AS ts
CROSS JOIN LATERAL generate_series(ts.min, ts.m... | <code>Left join</code> is OK but you are missing one field.
You need to include <code>DeviceID</code> in your generated series and then <code>left join</code> on the two fields.<br>
<code>DeviceID</code> is hardcoded but can be pulled from a table.<br>
Start and stop series parameters also hardcoded.
Query to use i... | https://dba.stackexchange.com |
362,250 | [
"https://mathoverflow.net/questions/362250",
"https://mathoverflow.net",
"https://mathoverflow.net/users/36886/"
] | Let <span class="math-container">$\nu$</span> be a <em>finite</em> Borel measure on <span class="math-container">$\mathbb{R}^n$</span> and define the shift operator <span class="math-container">$T_a$</span> on <span class="math-container">$L^p_{\nu}(\mathbb{R}^n)$</span> by <span class="math-container">$f\to f(x+a)$</s... | Well, for large <span class="math-container">$a$</span> the norm goes to infinity. Find a ball <span class="math-container">$B$</span> such that <span class="math-container">$\nu(B) > \nu(\mathbb{R}^n) - \epsilon$</span> and consider the characteristic function of <span class="math-container">$B$</span> shifted by <... | You get a rather obvious bound for <span class="math-container">$\|T_a\|_{op}$</span> from
<span class="math-container">$$ \int|f(x+a)|^p h(x)dx =\int |f(y)^p|h(y-a)dy = \int |f(y)|^ph(y) \left|h(y-a)/h(y)\right|dy \le c\int|f(y)|^ph(y)dy$$</span> with <span class="math-container">$c=\|h(y-a)/h(y)\|_\infty$</span>.
| https://mathoverflow.net |
832,022 | [
"https://math.stackexchange.com/questions/832022",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/153303/"
] | Well, the point is to find all linear operators $\widehat{A}$ that satisfy the following conditions:
<ul>
<li>$\operatorname{ker}{\widehat{A}} = \operatorname{im}{\widehat{A}}$ and </li>
<li>$\widehat{A} : \mathbb{V}_2 \longrightarrow \mathbb{V}_2, \widehat{A} \ne \widehat{ \mathcal{O} }$
where $\widehat{ \mathcal{... | Take a basis $\{u,v\}$ for $\mathbb{V}_2$, and define your operator as
$$\hat{A}u=v$$
$$\hat{A}v=0$$
Now you need to prove two things:
<ol>
<li>Every choice of basis gives an operator that satisfies your conditions.</li>
<li>Every operator that satisfies your conditions may be represented in this manner as a basis.</... | $\newcommand{\V}{\mathbb{V}}$
$\newcommand{\F}{\mathbb{F}}$
<strong>Hint:</strong> Let $A$ be an operator satisfying these criteria. Since the dimension of the image is $1$, we may state that there exists a $u \in \V_2$ such that for all $x \in \V_2$, we have
$$
A x = \alpha u
$$
for some $\alpha \in \F$. Now, since ... | https://math.stackexchange.com |
20,511 | [
"https://chemistry.stackexchange.com/questions/20511",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/-1/"
] | If two alkali metal atoms join with an oxygen atom, an ionic bond forms. Since hydrogen has the same number of valence electrons as alkali metals, why can't water be ionic?
This is what I'm thinking:
<span class="math-container">$$\ce{(H+)2O^2-}$$</span>
| First of all, the difference between ionic and covalent bonds is not sharp. As electronegativity differences increase, you move away from covalent and towards ionic bonds. There are "in between" states like <em>polar covalent</em>, where one side of the bond is stronger but not fully ionic. And this I think is the main... | No compound is purely ionic. Water is about 33% ionic.
Linus Pauling discusses the ionic character of water in his famous "<em>The Nature of the Chemical Bond</em>" [1] at pages 100-101.
Pauling says as a first approximation water should be considered as having contributions from four resonance structures:
\begin{... | https://chemistry.stackexchange.com |
1,847,140 | [
"https://math.stackexchange.com/questions/1847140",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/-1/"
] | How to find ?$$\int \frac{x^2-1}{x^3\sqrt{2x^4-2x^2+1}} dx$$
I tried using the substitution $x^2=z$.But that did not help much.
| You can apply $u=x^2$ :
$$\int \frac{x^2-1}{x^3\sqrt{2x^4-2x^2+1}} dx=\frac{1}{2}\int \frac{x^2-1}{x^4\sqrt{2x^4-2x^2+1}} 2xdx=\frac{1}{2}\int \frac{u-1}{u^2\sqrt{2u^2-2u+1}} du$$
Now note that :
$$\int \frac{u-1}{u^2\sqrt{2u^2-2u+1}} du=\int \frac{u-1}{u^2\sqrt{2(u^2-u)+1}} du$$
we can substitute $v=\frac{1}{u}$ :
$$\... | By setting $x^2=z$ we are left with:
$$ \frac{1}{2}\int\frac{z-1}{z^2\sqrt{2z^2-2z+1}}\,dz=C+\frac{\sqrt{2z^2-2z+1}}{2z}.$$
| https://math.stackexchange.com |
416,574 | [
"https://mathoverflow.net/questions/416574",
"https://mathoverflow.net",
"https://mathoverflow.net/users/476491/"
] | I am looking for the best way to approximate <span class="math-container">$\exp(x)$</span> on a finite domain <span class="math-container">$[0,M]$</span> with a piecewise-linear function. My initial approach is to take <span class="math-container">$K$</span> evenly-spaced segments from <span class="math-container">$0$<... | For <span class="math-container">$b$</span> not much larger than <span class="math-container">$a$</span>, the maximum difference between <span class="math-container">$e^x$</span> and the line from <span class="math-container">$(a,e^a)$</span> to <span class="math-container">$(b,e^b)$</span>, for <span class="math-conta... | If you choose the <span class="math-container">$L^2$</span> norm, computing
<span class="math-container">$$\Phi(a,b)=\int_a^b \Big[\alpha+\beta\, x -e^x\Big]^2\,dx$$</span> and minimizing, we have
<span class="math-container">$$\beta(a,b) =\frac{6}{(b-a)^3}\Big[(b-a +2)\,e^a+(b-a-2)\,e^b\Big]$$</span>
<span class="math... | https://mathoverflow.net |
538,507 | [
"https://electronics.stackexchange.com/questions/538507",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/250135/"
] | I'm developing a system that needs to periodically wake up and perform a process. We're currently targeting for an hourly wake up (give or take, this spec is very loose).
The key here is the unit cost and I really hope to avoid a real time clock on board. We're even trying to avoid an external crystal, if possible.
I e... | The MCU of your choice has an internal oscillator called FIRC, and it is likely to be calibrated at factory and datasheet says it has a tolerance of +/- 2%, over the whole temperature range and whole supply voltage range.
Therefore, 2% of an hour is 72 seconds, or 1 minute and 12 seconds.
So without further tricks, the... | Some chips have an internal RC oscillator that is "calibrated" at the factory, and you won't likely do much better without herculean efforts such as individual characterization in a temperature chamber. And even so it may not be all that stable. The target there for the chip suppliers is things like reliable ... | https://electronics.stackexchange.com |
377,856 | [
"https://softwareengineering.stackexchange.com/questions/377856",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/85226/"
] | <blockquote>
Given a file containing at most ten million 7-digit integers with no
duplicates. What is an efficient way to print these numbers in
ascending order using just 1.5MB RAM and reading the data just once?
What if duplicates were permitted?
</blockquote>
I have come across above question at google but ... | I would say you could use a bit field. That is you use one bit for each number from 0 to 9,999,999. This is 1.25 MByte of RAM.
You read the file once and mark the corresponding bit when a number is read. Then in the second pass you walk over the bitfield and print the index to all entries that have the bit set. This ... | 10 million 7 digit numbers with no duplicates sorted are: 0, 1, 2, 3, ..., 9,999,999.
Hope that gives you a hint for fewer than 10 million, using 1.25 MB of memory and running in linear time.
| https://softwareengineering.stackexchange.com |
17,026 | [
"https://quantumcomputing.stackexchange.com/questions/17026",
"https://quantumcomputing.stackexchange.com",
"https://quantumcomputing.stackexchange.com/users/14994/"
] | Question 4.6: One reason why the
<span class="math-container">$R_\hat{n}(θ)$</span> operators are referred to as rotation operators is the following fact, which
you are to prove. Suppose a single qubit has a state represented by the Bloch
vector <span class="math-container">$λ$</span>. Then the effect of the rotation<s... | Imagine you have a state <span class="math-container">$|\psi\rangle$</span> with Bloch vector <span class="math-container">$\vec{m}$</span>. Now apply this rotation <span class="math-container">$R_n(\theta)$</span> to <span class="math-container">$|\psi\rangle$</span>. Can you show how the vector <span class="math-cont... | <blockquote>
I don't understand the idea of this question? I need some explanation of this question.
</blockquote>
You're supposed to show that the operation is the same in both representations. That applying a rotation matrix to the state vector gives the same result as converting the state to a bloch vector, rotating... | https://quantumcomputing.stackexchange.com |
17,478 | [
"https://electronics.stackexchange.com/questions/17478",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/2062/"
] | For quite some time I am thinking about making 'passive' usb 'amplifier' - but the main question is how it is possible to detect direction of the transfer by some clever way, so that I can disable one of amplifiers?
Classical approach of using USB-HUB chips to extend cable for another 5 meters is too boring.
| Signal strength is not the only reason for the USB cable length restriction. Two other reasons are reply timing and voltage drop on the power line.
It is possible to watch the bus and know who is sending, but this requires the kind of complexity only available in a IC for any reasonable size. However, that alone isn... | I'm not sure this is possible without intelligence. The signal looks the same any which way it comes from; you'll at least have to decode the communication to tell them apart.
Kellen mentions the advantage that retransmitting means that you start with a clean signal again, and that's true, but I'm more worried about... | https://electronics.stackexchange.com |
525,106 | [
"https://physics.stackexchange.com/questions/525106",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/206319/"
] | I was thinking of some very basics concept when a doubt came to my mind, therefore I will briefly explain the argument that led me to the doubt so that the question will be clear.
Newton law states: <span class="math-container">$\vec F= m \ddot{\vec x}$</span>
For what I know this isn't a definition of force but a r... | You are touching a quite delicate point at the foundation of Newtonian mechanics: the interplay between principles, definitions and basic objects the theory is built on.
Your doubts probably stem from the fact that different basic formulations of the basic principles have been proposed over more than three centuries, ... | A force is simply a quantification of the external physical influences on a body. All forces can be modelled by <span class="math-container">$F=ma$</span> including gravitation.
Gravitation is simply a specific case of <span class="math-container">$F=ma$</span> where <span class="math-container">$a$</span> in this cas... | https://physics.stackexchange.com |
355,074 | [
"https://softwareengineering.stackexchange.com/questions/355074",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/267045/"
] | Is overriding a pure virtual function with default arguments good or bad?
<pre><code>class Base {
public:
virtual int func(int i, int j = 10) = 0;
};
class Derived : public Base {
public:
int func(int i, int j = 20) override;
};
</code></pre>
| I would not venture to do this. At best, as <em>@Bart van Ingen Schenau</em> said, it <em>will</em> cause you nasty surprises. Furthermore, I would not even recommend using default parameters in virtual functions in the first place. If you want to have something like that, I suggest doing something like this:
<pre><co... | EDIT
It <strong>IS</strong> a <strong>terrible</strong> idea! Although you will call the overridden method, it will get the base class defaults
c# code
<pre><code>public class Base
{
public virtual int Func(int i = 10)
{
Console.WriteLine("base");
return i;
}
}
public class Derived : Bas... | https://softwareengineering.stackexchange.com |
71,368 | [
"https://softwareengineering.stackexchange.com/questions/71368",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/12142/"
] | One of the five people who interviewed me asked a question that resulted in an hour-long discussion: <strong>"Explain how you would develop a frequency-sorted list of the ten thousand most-used words in the English language."</strong>
My initial response was to assail the assumptions underlying the problem. Language i... | <blockquote>
My initial response was to assail the
assumptions underlying the problem.
... that resulted in an hour-long discussion
</blockquote>
Assuming that you were not interviewing for a position as a developer within the domain of linguistic processing (or where specification errors have life threatenin... | This question is a good interview question because it invites discussion on several levels. At one level, it is a programming question, to see if you know how to efficiently scan a corpus of English text to count the occurrance of words. A person with a good CS education and a couple years experience will probably tack... | https://softwareengineering.stackexchange.com |
223,353 | [
"https://electronics.stackexchange.com/questions/223353",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/98056/"
] | Ring buffers are the go to choice by most veteran embedded programmers for asynchronous communications.
Assume that data arrives over UART from only a single source and only when a msg is asked for(Master->Slave,Slave->Master), since codes are sequential in nature, we can just implement an ordinary array(max size of da... | If you want to run the motor at a higher speed, the most serious mechanical problem is the rotor bursting, though you will also have higher windage losses, and there is also the potential for unbalance vibrations.
<strong>Windage load</strong>
These rise as the <strong>cube</strong> of the speed. As you say the moto... | We have a pump application where we run a 14v rated brushless motor at 24v without issues. The core issue is really total watts, within reason. A motor basically becomes a large dc dc converter anyway, for sure under pwm conditions.
You'll have to keep rpms within spec of course.
Some approximate values from this s... | https://electronics.stackexchange.com |
274,135 | [
"https://stats.stackexchange.com/questions/274135",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/157594/"
] | I am currently studying Statistical Inference class on Coursera. In one of the assignments, the following question comes up.
<pre><code>| Suppose you rolled the fair die twice.
What is the probability of rolling the same number two times in a row?
1: 2/6
2: 1/36
3: 0
4: 1/6
Selection: 2
| You're close...I can... | The probability of rolling a <em>specific</em> number twice in a row is indeed 1/36, because you have a 1/6 chance of getting that number on each of two rolls (1/6 x 1/6).
The probability of rolling <em>any</em> number twice in a row is 1/6, because there are six ways to roll a specific number twice in a row (6 x 1/36... | To make it perfectly clear, consider the sample space for rolling a die twice.
<strong>(1, 1)</strong> (1, 2) (1, 3) (1, 4) (1, 5) (1, 6)<br>
(2, 1) <strong>(2, 2)</strong> (2, 3) (2, 4) (2, 5) (2, 6)<br>
(3, 1) (3, 2) <strong>(3, 3)</strong> (3, 4) (3, 5) (3, 6)<br>
(4, 1) (4, 2) (4, 3) <strong>(4, 4)</strong> (4, 5)... | https://stats.stackexchange.com |
118 | [
"https://mechanics.stackexchange.com/questions/118",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/99/"
] | I have a '99 Maxima.
I am considering installing strut tower braces. In order to do so, would I need to get spring compression tools to hold the springs on the struts, or will the weight of the car be sufficient to hold it in place when I remove the bolts on the towers?
| The weight of the car will be sufficient to keep the spring from decompressing fully and pulling out the bottom of the strut frame in the car.
You must be careful not to jack the car up without the bolts secured tightly though, this could produce a dangerous situation. Also if you are ever working on the 'southern' ha... | Usually the bolts that strut braces attach to are the ones that attach the strut assembly to the car. The spring is held in place in the strut assembly by the nut in the middle, which I have never needed to remove to install any strut braces. See how the brace below has a hole in the middle for the top shock nut:
<img... | https://mechanics.stackexchange.com |
124,555 | [
"https://mathoverflow.net/questions/124555",
"https://mathoverflow.net",
"https://mathoverflow.net/users/32210/"
] | I am interested in the following problem : given a finite field $F$ and two unipotent elements $g_1,g_2\in\mathrm{SL}_2(F)$ which do not commute, what can we say about the subgroup they generate? More specifically, is there an additional condition under which it is known that they generate all of $\mathrm{SL}_2(F)$?
... | You should look up Dickson's Theorem. It deals pretty comprehensively with the two dimensional case when $F$ is finite, at least in odd characteristic. The proof may be found in Gorenstein's 1968 book "Finite Groups". I don't remember the statement precisely, but I think it's that $\langle \left( \begin{array}{clcr} 1 ... | A few complements to Geoff's answer and Agol's comment:
1) Dickson's theorem is worked out in detail (somewhat lengthy) in Gorenstein's
Chapter 2, page 44+, as Theorem 8.4. His section 8 is devoted to a study of this matrix group and its projective quotient. The treatment is elementary but not conceptual. In the ... | https://mathoverflow.net |
214,305 | [
"https://dba.stackexchange.com/questions/214305",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/110366/"
] | If I run the following query on my database I get the results pasted below:
<pre><code>SELECT t.id as ID,
j.text as Text,
l.location as Location,
FROM [text] t WITH (nolock)
INNER JOIN Text_Location tl WITH (nolock) on tl.textid = t.id
INNER JOIN Location l WITH (nolock) on tl.locationId = l.id
ID Text ... | The table <code>SpotArtSong</code> which you are trying to insert some records has at least these columns:
<ul>
<li>ID</li>
<li>Artist</li>
</ul>
You are just supplying a value for ID, but column <code>Artist</code> has a <code>NOT NULL</code> constraint. When you don't supply a value for a column (by omitting it fro... | <blockquote>
Column [ID] on [DB1].[dbo].[SpotArtSong] has some null values that I am trying to replace.
</blockquote>
Then why are you inserting <em>whole new rows</em>?
The <strong>insert</strong> statement inserts new rows.
You're telling the database to create <em>new rows</em> containing only the ID values ... | https://dba.stackexchange.com |
18,916 | [
"https://electronics.stackexchange.com/questions/18916",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/5599/"
] | I am working with a friend to develop a spinning disk with LED lights on it.
The issue we are having is wrapping our minds around the idea of electronics on a surface that is spinning.
How do we interface with the LED lights without cords getting tangled around the spinning rod?
Is there a way to provide power to el... | The lowest tech, probably easiest method - Use brushes, just like for a motor. On the rotating part, you'd have the equivalent of slip rings, although the orientation would be flat rather than axial. The power thus obtained on the rotating part might have a bit of high frequency noise in it from the sliding contacts, s... | You can use contacts (e.g. carbon brushes, or copper) to press lightly against traces on the spinning disk and transfer power. Probably the simplest way.
Or you could possibly use inductive coupling, e.g. something like a toroidal power coil on the base transfers power to a toroidal coil on the disk, although this wou... | https://electronics.stackexchange.com |
689,488 | [
"https://physics.stackexchange.com/questions/689488",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/325736/"
] | I am very confused when building the Lie algebra of the Lorentz Group. In every books, they expand <span class="math-container">$\Lambda^{\mu}_{\nu} = \delta^{\mu}_{\nu} + \omega^{\mu}_{\nu}$</span> at the origin and you end up with the condition that <span class="math-container">$\omega_{\mu\nu} = - \omega_{\nu\mu}$</... | Well, let us consider the fundamental representation of <span class="math-container">$SO(1,3)_+$</span> made of matrices <span class="math-container">$$\Lambda = [{\Lambda^a}_b]_{a,b=0,1,2,3}\:.$$</span>
The position of indices is of crucial relevance here. The Lorentz-group condition is
<span class="math-container">$$... | Thanks for your answer. I am not sure that's really where my confusion lies. I can try develop my analogy with the SU(2) group so that you can better understand my problem. In this case let's not <span class="math-container">$T^a$</span> the generators, expanding and applying the group constraint we get that matrices <... | https://physics.stackexchange.com |
183,645 | [
"https://physics.stackexchange.com/questions/183645",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/78636/"
] | I have an assignment, where I have an object moving in 1-D with a given mass and energy, and the potential V(x), and I'm supposed to calculate the period of the movement as a function of the energy
$$
V(x)=\begin{cases}\infty &x < -a \\
0 &-a < x < 0\\
\alpha ... | It seems, based on the comments above, that you have figured it out. Just for closure, I am writing the steps out.
If you had just a parabolic potential well, $V(x) = \alpha x^2$, you could get the period quite easily - for a given mass $m$, the frequency would be
$$\omega = \sqrt{\frac{2\alpha}{m}}\\
T = \frac{2\pi}... | You can calculate the action integral as a function of energy
$$
J(E) = \oint p_x dx = 2\sqrt {2m} \int_{x_0(E)}^{x_1(E)} \sqrt {E-V(x)}dx
$$
where $x_0$ and $x_1$ are the turning points. (In your case: $x_0 = -a$ and $x_1 = \sqrt{E/\alpha}$). The Period is then given by the derivative
$$
T(E) = dJ/dE
$$
| https://physics.stackexchange.com |
99,382 | [
"https://math.stackexchange.com/questions/99382",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/22430/"
] | $$f(x)=\sum_{n=-\infty}^\infty e^{nx} \longrightarrow
f(x) = \infty\text{ for all }x\text{ values}$$
$$\frac{y f''(x)}{1!}=\sum_{n=-\infty}^\infty \frac {y n^2 e^{nx}}{1!}$$
$$\frac{y^2 f^{(4)}(x)}{2!}=\sum_{n=-\infty}^\infty \frac {y^2 n^4 e^{nx}}{2!}$$
$$\frac{y^3 f^{(6)}(x)}{3!}=\sum_{n=-\infty}^\infty \... | $$f(x):=\sum_{n=0}^\infty x\;,$$
$$g(x,y):=f(y) - f(x)\;,$$
$$g(x,x)=f(x)-f(x)=0\;.$$
How could we get this result although we produced $g(x,x)$ from $f(x)$ that doesn't have any defined values for $x\ne0$? You don't need any fancy exponential series to get this effect; examples of this kind abound. It just goes to ... | If $f(x)$ is infinite for all real $x$, then does it make sense to take a derivative of this function?
| https://math.stackexchange.com |
274,116 | [
"https://softwareengineering.stackexchange.com/questions/274116",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/699/"
] | From Tanebaum's Computer Network:
<blockquote>
A five-layer network is illustrated in Fig. 1-13. The entities comprising the
corresponding layers on different machines are called <strong>peers</strong>. The peers may be software processes, hardware devices, or even human beings. In other words, it is
the peers t... | In figure 1-13, there are many peers.
<ul>
<li>Host 1, Layer 5 is a peer to Host 2, Layer 5. </li>
<li>Host 1, Layer 4 is a peer to Host 2, Layer 4.</li>
<li>Host 1, Layer 3 is a peer to Host 2, Layer 3. </li>
<li>Host 1, Layer 2 is a peer to Host 2, Layer 2. </li>
<li>Host 1, Layer 1 is a peer to Host 2, Layer 1.</li... | A peer is something or someone that is an equal member of a group, where there's some kind of relationship between the members of the group. For example, "a jury of your peers" means people with the same (legal) status as you.
For networking and distributed systems; a lot of it is either "client server" (HTTP, FTP, N... | https://softwareengineering.stackexchange.com |
53,791 | [
"https://security.stackexchange.com/questions/53791",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/2689/"
] | To prevent cross-site request forgery attacks, I'm considering the following scheme:
For each user, store a random key. If the user submits any "dangerous" information, include a security token and a creation date in the upload. If the creation date older than T (I'm currently leaning 5 minutes), the request is consid... | Once you connect to a VPN service, they can record what they wish. A potential way around this is to VPN the VPN, if the service allows it (most do not). An alternate method is to connect to Tor from within the VPN connection, if the service allows it.
Secure connections, like https, should be encrypted, so passwords ... | When you connect to a VPN, you are connecting to private network, but your network is only private from the greater network/Internet. Inside of the network, you have no additional protections - you are not private to the other members of the network.
You can still use HTTPS/TLS/SSL to encrypt your connection from your... | https://security.stackexchange.com |
1,174,560 | [
"https://math.stackexchange.com/questions/1174560",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/-1/"
] | Let $R$ be a relation on $\mathbb{R}$ such that $xRy$ iff $|x|< 2 $ $\textbf{and}$ $y = 3$ and $S$ be relation on $\mathbb{R}$ such that $xSy$ iff $|x|< 2 $ $\mathbf{or}$ $y = 3$. Im trying to find domain and range of both relations: I was able to work out the following:
$$ Dom( R) = \{ x \in \mathbb{R} : \exist... | Every pair $\langle x,y\rangle\in R$ is also in $S$, but $S$ contains many pairs that are not in $R$. For instance, $\langle 0,4\rangle\in S$ (because $|0|<2$) and $\langle 6,3\rangle\in S$ (because the second element is $3$); neither statement is true if you replace $S$ with $R$. In order for $\langle x,y\rangle$ t... | @BrianMScott above has already formulated a well thought answer. Since I already finished making these images, I'll post them anyways as it may help highlight the difference between the two sets.
<blockquote>
Relation $R$ ($|x|<2$ <strong>and</strong> $y=3$)
<img src="https://i.stack.imgur.com/8hxbv.png" alt="... | https://math.stackexchange.com |
115,622 | [
"https://dba.stackexchange.com/questions/115622",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/70392/"
] | I have a virtual machine running SQL Server 2012 in Azure and have also generated a script of my database to be run on the <code>SQLSERVER2012</code> VM on Azure, however I am getting an error
<blockquote>
"C:\Program Files\Microsoft SQL Server\MSSQL10_50.SQLEXPRESS\MSSQL\DATA\PXDEV.mdf" failed with the operating s... | Are you getting the error on the destination server?
Is the path present on the destination server?
You need to make sure that the paths defined in your CREATE DATABASE script exist on the destination server or you need to create them there.
| Run the restore with file list only eg.
<pre><code>restore FILELISTONLY from disk= 'D:\MSSQL\full.bak'
</code></pre>
to see where it is attempting to place the database files (observe the PhysicalName column). if that location (not the file the location) doesn't exist then you will need to move the file
This can be ... | https://dba.stackexchange.com |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.