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 |
|---|---|---|---|---|---|
83,558 | [
"https://dba.stackexchange.com/questions/83558",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/6108/"
] | I have a table that contains columns of Country, City, Location, Description. Due to the size of the description field it's not possible to bind the four fields into a composite key to prevent duplication. I have been trying to prevent duplication by way of a trigger but no matter what I try it rolls back every insert,... | Not too sure why still, but this problem disappeared after some of the troubleshooting steps I took to hunt down the culprit. Maybe it was the open files limit that caused the errors while opening the MyISAM tables, perhaps because of the high activity of other services running on the slave2 server, like Rackspace's cl... | I am not sure what was causing the issue for the original poster, but in my case it was a case sensitivity issue. A Master server in my replication topology was using PascalCase for its table names when specifying them in queries, where the actual table name files on disk were lowercase. For example, see my error messa... | https://dba.stackexchange.com |
378,259 | [
"https://softwareengineering.stackexchange.com/questions/378259",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/256726/"
] | To avoid magic numbers, we often hear that we should give a literal a meaningful name. Such as:
<pre><code>//THIS CODE COMES FROM THE CLEAN CODE BOOK
for (int j = 0; j < 34; j++) {
s += (t[j] * 4) / 5;
}
-------------------- Change to --------------------
int realDaysPerIdealDay = 4;
const int WORK_DAYS_PER_W... | No. In that example, 1 is perfectly meaningful.
However, what if persons.size() is zero? Seems strange that <code>persons.getMoney()</code> works for 0 and 2 but not for 1.
| Why does a piece of code contain that particular literal value?
<ul>
<li>Does this value have a special meaning in the <em>problem domain</em>?</li>
<li>Or is this value just an <em>implementation detail</em>, where that value is a direct consequence of the surrounding code?</li>
</ul>
If the literal value has a mean... | https://softwareengineering.stackexchange.com |
175,873 | [
"https://electronics.stackexchange.com/questions/175873",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/16051/"
] | I am working on a layout that will look similar (not final) to the illustration below. There are three high gauge wires (red) 3x230VAC passing directly below the PCB (isolation touching the PCB) that will carry up to 63A (worst case).
I have to get some signals across that section to switch several relays from my cont... | CPLDs are generally only used for replacing a relatively small amount of discrete logic. Namely, things like a bunch of address decoders and bus interface circuitry. CPLDs contain very little memory; genrally the number of flip-flops is of the same order of magnitude as I/O pins (i.e. a 32 macrocell CPLD has ~30 pins... | Differences:
<ol>
<li>Capacity - CPLD usually has less capacity of logic. The largest CPLD may be at a similar level of the smallest FPGA in the mainstream market.</li>
<li>Storage of the image - CPLD can boot by itself while most of the FPGA need to fetch the configuration bitstream from non-volatile storage because ... | https://electronics.stackexchange.com |
137,872 | [
"https://electronics.stackexchange.com/questions/137872",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/35919/"
] | I have say, 4 170 MHz signals coming in on 4 BNC cables. I would like to add these signals together. Is there a name for a piece of hardware that does this? Are there any special considerations I should make, is there a reason why I can't just use something like a BNC T-converter to add two lines into one?
Any help... | You could use RF transformers - each primary connects to each input and the secondaries are all wired in series to produce A+B+C+D as an overall output. What do you next depends on you - you could terminate the combined secondary with 200 ohms and use this into whatever it needs to feed or, you could use a fifth transf... | It's called a power combiner. There are several different types, and the idea is to make sure that all of the connections are properly matched so that you don't get any issues with reflections under normal operation. For example, if you use a BNC tee, then both sources will see a 25 ohm load and a very significant po... | https://electronics.stackexchange.com |
382,603 | [
"https://softwareengineering.stackexchange.com/questions/382603",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/196326/"
] | i’m working on a project where i’m using SQLite and where i have a few relation tables looking similar to this one:
<pre><code>CREATE TABLE tag_entry_relation
(
id INTEGER PRIMARY KEY,
tag_id INTEGER REFERENCES tag(id),
entry_id INTEGER REFERENCES entry(id)
);
</code></pre>
<strong>I know that the two “referencing” c... | I know two reasons for using an <code>id</code> column in that situation:
<ul>
<li>if you have a strict convention to give every table in your database a single primary key named <code>id</code></li>
<li>if you cannot exclude the possibility <code>tag_entry_relation</code> might becoming referenced by another table in... | It would be better to use composite primary key as it will be combined together so that the combination is unique. It will allow you to set multiple unique columns as a constraint.
| https://softwareengineering.stackexchange.com |
130,809 | [
"https://stats.stackexchange.com/questions/130809",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/64679/"
] | <strong>I have 50,000 images such as these two:</strong>
<img src="https://i.imgur.com/uSYyiGT.png" alt="data example">
<img src="https://i.imgur.com/k9xnODc.png" alt="data example2">
They depict graphs of data. I wanted to extract features from these images so I used autoencoder code provided by Theano (deeplearnin... | Debugging neural networks usually involves tweaking hyperparameters, visualizing the learned filters, and plotting important metrics. Could you share what hyperparameters you've been using?
<ul>
<li>What's your batch size?</li>
<li>What's your learning rate?</li>
<li>What <em>type</em> of autoencoder are you're using?... | I don't have enough rep to comment, so I will put this into in answer. I don't know exact reason, however:
<ol>
<li>The pattern in bottom left region looks similar to your second example, and pattern in right bottom corner seems very like to your first example, when inspected closely. The question is, how much variety... | https://stats.stackexchange.com |
454,912 | [
"https://math.stackexchange.com/questions/454912",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/88155/"
] | How to solve $$2\sin(x) / (1+2\cos(x)) = \sqrt{3}/2$$ where $0< x <180$.
(Final answer may be in inverse form)
| let $\sin{x} = a $
and as $ \cos^2{x} = 1 -\sin^2{x} $
$$ 2*a / (1 + 2 \sqrt {1-a^2}) = \frac{\sqrt{3}}{2} $$
solving we get
$$ a = \frac{\sqrt{3}}{7} \pm 5*\frac{\sqrt{3}}{14} $$
$$x = \sin^{-1}(a) $$
for $$ a = \frac{\sqrt{3}}{7} + 5*\frac{\sqrt{3}}{14} $$ you get x = $\sin^{-1}(\sqrt3/2) = \pi /3 $
And ... | There are a few ways to go about this problem, one way taking $c=\cos$ and $s=\sin$,
$\frac{2s}{1+2c}=\frac {\sqrt{3}} 2$ so $2s=\frac{\sqrt{3}}2+c\times\sqrt{3}$ which is $2s-\sqrt{3}\times c=\frac{\sqrt3}2$, the trick with the LHS is to consider the harmonic form, if you haven't come across this before search it, th... | https://math.stackexchange.com |
322,494 | [
"https://softwareengineering.stackexchange.com/questions/322494",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/218080/"
] | If I remember my compilers course correctly, the typical compiler has the following simplified outline:
<ul>
<li>A lexical analyzer scans (or calls some scanning function on) the source code <strong>character-by-character</strong> </li>
<li>The string of input characters is checked against the dictionary of lexemes fo... | Large software projects are usually composed of many compilation units that can be compiled relatively independently, and so compilation is often parallelized at a very rough granularity by invoking the compiler several times in parallel. This happens at the level of OS processes and is coordinated by the build system ... | Compilation is an "embarrassingly parallel" problem.
Nobody cares about the time for compiling one file. People care about the time of compiling 1000 files. And for 1000 files, each core of the processor can happily compile one file at a time, keeping all cores totally busy.
Tip: "make" uses multipl... | https://softwareengineering.stackexchange.com |
60,322 | [
"https://softwareengineering.stackexchange.com/questions/60322",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/18957/"
] | I'm in the job market and I have a set of priorities for my next job including salary, line of business, etc. One thing that is nowhere on my list of requirements however, is the development process methodology. I feel my job is to create software and I view the process structure as something I can adapt to whether it'... | It is important to me only as far as not getting in the way of the common sense that we hope most professionals would have.
When we talk about version control, there is the argument that <code>any version control beats not having anything at all</code>, this isn't the case with development methods. Methods mean rules,... | As a developer, I care that the development process is sane. A number of different development methodologies can provide a sane development process. Conversely a broken company can provide an insane process no matter what they call it.
Therefore I don't particularly care what their official "development methodology"... | https://softwareengineering.stackexchange.com |
32,533 | [
"https://softwareengineering.stackexchange.com/questions/32533",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/8163/"
] | In college, I was never interested in theory. I never read it. No matter how much I tried, I was unable to read stuff and not know what was actually happening practically. Like for example, in my course on automata theory, my professor told me everything possibly related to the mathematical aspect of it, but not even o... | Believe it or not, one of the things that turned out to be of critical importance to me in later life was Compiler Construction. Not the modern namby-pamby version using Lex and Yacc, thats for dummies.
REAL compiler construction where you write your own symbol scanner and parser from the ground up.
This is somethin... | <ol>
<li>Data Structures/Algorithms especially Graphs. The amount of real world situations in which I've managed to use graph-related algorithms has been a surprise to me. Focus on knowing the characteristics of when a data structure or algorithm is appropriate. Being able to see a problem and know to use dynamic pro... | https://softwareengineering.stackexchange.com |
319,955 | [
"https://stats.stackexchange.com/questions/319955",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/189353/"
] | I'm trying to think of a good way to explain latent Dirichlet allocation (LDA) to an audience that knows a decent amount about clustering, but nothing about text analysis.
Is it fair to draw a comparison between LDA and fuzzy c-means clustering (not sure if that terminology is official but that's how I've learned it). ... | We can write out a $k$ dimensional Multivariate Gaussian as
$${\bf X}=(X_1,\cdots,X_k)\sim\textsf{MVN}(\mu,\Sigma),$$ where $\mu=(\mu_1,\cdots,\mu_k)$ is the mean vector, and $\Sigma$ is the positive definite $k\times k$ covariance matrix.
We can write out a $k$ component mixture of (1 dimensional) Gaussians as
$$X\... | I do not intend to be rigorous here. I just want to give you the intuition.
You can go deeper on this subject by reading textbooks or googling it.
If you have a random variable <span class="math-container">$X$</span>, you say that it follows a
normal distribution with mean <span class="math-container">$\mu$</span> an... | https://stats.stackexchange.com |
84,133 | [
"https://stats.stackexchange.com/questions/84133",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/29137/"
] | Let's suppose I have a time series data that I would like to regress $y$ on $x$ and $Time$. See below for the dataset.
<pre><code>y x time
12 100 1
14 101 2
16 102 3
18 103 4
20 201 1
22 202 2
24 203 3
26 204 4
</code></pre>
<strong>Approach 1:</strong>
One approach is to do a multiple linear regression... | <ol>
<li>Modeling time continuously introduces the assumption that there is a linear influence of time upon the outcome, conditional upon $x$. However, adjusting for time as a fixed and random effect makes this interpretation a bit untenable.</li>
<li>Yes it does matter, it matters in absolutely all scenarios. You can ... | What makes you think that time has any effect on the dependent variable?
I'd suggest plotting the dependent variable against time to gauge what sort of model might be useful.
Both approaches - a linear (or non-linear) time trend <em>and</em> seasonal dummy variables might be necessary. (Normally dummy variables are ... | https://stats.stackexchange.com |
253,665 | [
"https://electronics.stackexchange.com/questions/253665",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/121482/"
] | I have a simple MOSFET PWM circuit switching a 12v/8A load at a rate of 500Hz. This is being powered by a 120w switch mode power supply.
The power supply is buzzing loudly and generally unhappy with this arrangement. From my reading it appears that I need to smooth the load ripple created by the PWM circuit, by strapp... | Without knowing much about the power supply how your power source was designed, just assume the worst case. Which is that it doesn't have significant output capacitance to absorb the ripple. Then calculate how much capacitance you need to achieve a certain amount of voltage ripple. Any capacitance your power source ... | You probably need multiple capacitors and probably some inductors as well.
I've found it easiest to calculate this as a low pass filter. You can treat the PWM circuit as a signal source, and you want to design a filter that passes DC, but blocks the noise from reaching the power supply.
So step 1 is to measure the no... | https://electronics.stackexchange.com |
54,401 | [
"https://mathoverflow.net/questions/54401",
"https://mathoverflow.net",
"https://mathoverflow.net/users/10714/"
] | Let $M$ be a complete hyperbolic manifold of dimension $n$, let $\varepsilon=\varepsilon_n$ be the Margulis constant. Let $M_{[\varepsilon,\infty)}$ be the thick part of $M$ with respect to $\varepsilon$. Suppose that $\pi_1(M)$ is infinite. Is it true that $\pi_1(M_{[\varepsilon,\infty)})$ is also infinite. Or, in cas... | Yes, because $\pi_1$ of the boundary of a component of the $\epsilon$-thin part always
surjects to the fundamental group of that thin part, except in one special 2-dimensional
case: if there is a short orientation-reversing curve on a surface, then its component of
the thin part is a Moebius band, and the boundary gene... | By Margulis lemma, components of the $\varepsilon$-thin part are cusps or $\varepsilon$-tubes, so the interior of the $\varepsilon$-part is $M$ with cusps chopped off, and a finite (possibly empty) collection of embedded closed geodesics deleted. Thus the thick part is connected, and by general position the inclusion o... | https://mathoverflow.net |
563,866 | [
"https://stats.stackexchange.com/questions/563866",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/118998/"
] | Suppose we have a probability distribution <span class="math-container">$f(x)$</span> with a finite support <span class="math-container">$[a,b]$</span>. If we take the probability convolution of <span class="math-container">$\lambda f $</span> with <span class="math-container">$(1-\lambda)f,0 <\lambda<1$</span> r... | <span class="math-container">$Y_0=\lambda X + (1-\lambda) X'$</span> so
<span class="math-container">$\text{var}(Y_0) = (\lambda^2 + (1-\lambda)^2)\text{var}(X)$</span>
define <span class="math-container">$v = (\lambda^2 + (1-\lambda)^2)$</span>
note <span class="math-container">$0.5< v < 1$</span> for <span clas... | This is just an example that your statement seems to be wrong, at least in some scenarios.
Suppose there are two same but independent distributions:
<span class="math-container">$Y_0$</span>: 50% we get 1, 50% we get 0.
<span class="math-container">$Y_0'$</span>: 50% we get 1, 50% we get 0.
Let <span class="math-contai... | https://stats.stackexchange.com |
536,054 | [
"https://math.stackexchange.com/questions/536054",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/63360/"
] | Although this is a Discrete Structures problem, I am having trouble solving the pre-calculus portion of this problem.
The exercise gives us a $f(x)$ and a $g(x)$, and to figure out the asymptotic complexity. In this example, $f(x) = \log_{2}n^{3/2} $ and $g(x) = \log_{10}n $.
So I have a function: $ \log_{2}(n^{3/2})... | Apply basic logarithm rules:
$$\log_2(n^{3/2})=\frac 32\cdot\log_2(n)$$
and:
$$\log_{10}(n)=\frac{\log_2(n)}{\log_2(10)}$$
This gives us:
$$\frac{\log_2(n^{3/2})}{\log_{10}(n)}=\frac 32\cdot\log_2(10)$$
| Pull out the exponent 3/2 and retake the limit on the fraction. It becomes indeterminate but that can be dealt with through L'Hospital's Rule. If I am not mistaken, that fraction then becomes (ln10)/(ln2) when n→infinity
| https://math.stackexchange.com |
391,340 | [
"https://softwareengineering.stackexchange.com/questions/391340",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/334993/"
] | Is there any guideline on writing message which are shown to the user of an app using toast?
For example, if an error occurred, should the app display
<blockquote>
Failed writing to the file
</blockquote>
or
<blockquote>
Failed writing to the file.
</blockquote>
Should sentences use full stop? I don't see ful... | I recognize a general industry-wide problem. As long as I have been in interactive software development I have encountered cringing language. I can always tell it is bad, I can always make it better (and I usually do), but I have no cookbook to do this. It would be great to have a standard rule set that everyone (espec... | Captions, titles, menu items and such should not end in a full-stop.
So if <code>Failed writing to the file</code> is a dialog title, that is okay.
For content, a message a full stop is often missing, if the text contains just one sentence. This is not correct. In one case even I fail (colon style):
<pre><code>Faile... | https://softwareengineering.stackexchange.com |
484,828 | [
"https://electronics.stackexchange.com/questions/484828",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/-1/"
] | I have to develop a system composed of 2 PCBs :
<ul>
<li>The 1st PCB is supplied by a 3.7 V LiPo battery. A 3.3V DC-DC converter converts the battery voltage to 3.3 V to all components on this PCB (microcontroller, LED, etc.). </li>
<li>The 2nd PCB includes sensors. It receives the supply from the 1st PCB. It is about... | The voltage at the second PCB can be calculated through
<span class="math-container">$$ V_{2nd,PCB} = V_{3V3} - 2 \cdot I_{2nd,PCB} \cdot \frac{l_{cable}\cdot \rho}{A_{cable}} $$</span>
Where <span class="math-container">$$ \rho \approx 1.7 \cdot 10^{-8} \Omega m$$</span>
If your second PCB's lower supply voltag... | <h2>Raid the mains electrical parts bin</h2>
Get yourself plain old commodity line cord (or if a permanent non-moving installation, twin-and-earth) of common size like 1.0mm2, 1.5mm2, 2.5mm2 or 4.0mm2.
They make enough of that wire to circle the earth every day, and so it's dirt cheap thanks to economies of scale. ... | https://electronics.stackexchange.com |
389,955 | [
"https://physics.stackexchange.com/questions/389955",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/186821/"
] | I have been extremely confused about exactly how to think about voltage (and power) when it comes to circuit analysis. In physics, voltage is just described as the energy required to move a unit charge a specific distance across an electric field, but that seems to be in free space and my physics teacher didn't really ... | I admire your determination to understand, and your line of questioning. I'll try and address one or two of your points.
First of all potential difference in free space in an electric field. I prefer to define pd between two points, P and Q, as the work done <em>by the electric field</em> on a charge, per unit charge,... | Actually, electric potential does not push charges at all. The force on an electron is due to the <em>gradient</em> of the electric potential: the amount that the potential changes per unit distance. In a uniform electric field, the potential changes uniformly along the direction of the electric field vector. For ex... | https://physics.stackexchange.com |
4,137 | [
"https://electronics.stackexchange.com/questions/4137",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/1084/"
] | How do I lower the clock frequency of a PIC18F2550 and recalculate the peripheral dividers?
I'm trying to make it run cooler. Currently, it runs at 12MIPs/48mhz (USB-CDC-ACM).
| If you're currently running at 48 MHz, you're using an external crystal. You can decrease the frequency by changing bits 2:0 in the PLLDIV register, but we'd need to know the external crystal frequency and what peripherals you want to adjust. Is it just the USB subsystem you need to use?
<strong>In response to your co... | Depending on your application, you may want to try putting the PIC to sleep and using an interrupt with an RC circuit to wake it up periodically.
| https://electronics.stackexchange.com |
4,407,077 | [
"https://math.stackexchange.com/questions/4407077",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/691776/"
] | I am a graduate student of Mathematics.In the book Measure,Integration and Real Analysis by Sheldon Axler there is a question that asks the reader to show that there exists no measure space <span class="math-container">$(X,\mathcal S,\mu)$</span> such that <span class="math-container">$\{\mu(E):E\in \mathcal S\}=[0,1)$... | Use your idea along with the property of "continuity from below" that all measures have. You can show that an event has measure one in this way.
| If there would be a measure space with this property, then for a sequence of sets <span class="math-container">$(E_n)$</span> with <span class="math-container">$E_n\nearrow X$</span> in <span class="math-container">$\mathcal{S}$</span>, we have that <span class="math-container">$\mu(E_n)\leq\mu(E_{n+1})$</span>. Hence ... | https://math.stackexchange.com |
926,516 | [
"https://math.stackexchange.com/questions/926516",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/151864/"
] | I need to prove that $[x+y] \leq [x] +[y]+1$
I started by supposing that $[x]=m$ and $[y]=n$, where $m,n \in \Bbb {Z}$. So then that would mean that $m \leq x < m+1$ and $n \leq y < n+1$
But I don't know where to go from there. I tried added the inequalities but that gave me $m+n \leq x+y < (m+1)+(n+1)$
H... | Let $\{x\}=x-[x],\{y\}=y-[y]\iff x=[x]+\{x\},y=[y]+\{y\}$.
Noting that for $a\in\mathbb Z$
$$[a+b]=a+[b]$$
and that $0\le \{x\}\lt 1,0\le \{y\}\lt 1\Rightarrow 0\le \{x\}+\{y\}\lt 2\Rightarrow [\{x\}+\{y\}]\le 1$, we have
$$\begin{align}[x+y]&=[[x]+\{x\}+[y]+\{y\}]\\&=[x]+[y]+[\{x\}+\{y\}]\\&\le [x]+[y]+1... | Note that $x = [x] + \epsilon_x$ and $y = [y] + \epsilon_y$, where $0\leq \epsilon_x <1$ and $0\leq \epsilon_y <1$. Then $0\leq \epsilon_x + \epsilon_y<2$, so $[\epsilon_x + \epsilon_y] \leq 1$ and
$$[x+y] = [[x] + [y] + \epsilon_x + \epsilon_y]$$
$$=[x] + [y] + [\epsilon_x + \epsilon_y]$$
$$\leq [x] + [y] + ... | https://math.stackexchange.com |
12,294 | [
"https://cstheory.stackexchange.com/questions/12294",
"https://cstheory.stackexchange.com",
"https://cstheory.stackexchange.com/users/10368/"
] | I've been reading about mechanism design and the field seems a little abstract, in that I cannot ascertain whether a certain approach towards solving games falls under mechanism design.
Let me clarify with the help of a specific example of an evolutionary game.
I have a population within which agents are either muta... | Mechanism design is basically just algorithm design, where you don't control the inputs: instead, you assume that the inputs are controlled by different agents, who each have their own set of feasible actions, and their own utility function over outcomes, and are acting to maximize their own utility (and not yours, as ... | Great answer. I just want to add that the problem you posed seems to require a solution like Nash equilibrium or a Evolutionary stable strategy. That does not typically come under mechanism design. Its more basic game theory where everything (the game) is well defined and you find the equilibrium outcome. Mechanism de... | https://cstheory.stackexchange.com |
234,790 | [
"https://security.stackexchange.com/questions/234790",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/238213/"
] | Suppose I create an encrypted container using VeraCrypt and want to upload it to Google Drive/One Drive for storage. The container is encrypted with AES-256.
I know that no one can extract any meaning from that random data.
But I am a <em>very paranoid</em> person!
I know that the random data doesn't make any sense, bu... | Here is what you asked: "I want to hand the encrypted data to this party to store and process, but I don't want them to <em>see</em> the encrypted data."
That's not possible or realistic.
If you don't want them to have <strong>access</strong> to the data, then don't give them access. Don't give it to them.
Yo... | <blockquote>
Is there any way of preventing the adversaries from accessing the (encrypted) data at all, even after releasing the data?
</blockquote>
For almost every single case, there's no way. The "after releasing the data" statement means your data (or a copy of it) left your hands and went to someone else... | https://security.stackexchange.com |
193,834 | [
"https://softwareengineering.stackexchange.com/questions/193834",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/81480/"
] | Suppose I have a form in my web application where users can upload a profile picture.
I've got few requirements about file size, dimensions etc, but when the user uploads the image, how should I name them on my system? I suppose it would need to be consistent and also unique.
Maybe a GUID?
<pre><code>a5c627bedc3c44b... | You should try to meet two goals: Uniqueness, and usefulness.
Using a GUID guarantees uniqueness, but one day the files may become detached from their original source, and then you will be in trouble.
My typical solution is to embed crucial information into the filename, such as the userID (if it belongs to a user) o... | You don't want to stress applications (such as Explorer) and make it crash when you open the directory. Whilst it is unlikely you are going to stress the actual file system, you need to take this into account if you're going to be storing thousands of files.
If you're expecting to store thousands of files my suggestio... | https://softwareengineering.stackexchange.com |
9,631 | [
"https://dsp.stackexchange.com/questions/9631",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/4110/"
] | I have a signal which looks something like:
<img src="https://i.stack.imgur.com/5vwMD.png" alt="enter image description here">
The 12 main round peaks is what I'd like to keep. However, the peak detection algorithm I apply is picking up the in-between noisy peaks. Any strategies I could use to get rid of this noise?
... | Maybe you could tell us more about the peak picking algorithm you are using!
Some ideas:
<ul>
<li>Use median filtering to remove noise (rather than a linear filter).</li>
<li>If you have prior knowledge of the shape of the peaks you want to detect, use a correlator (matched filter) for this shape.</li>
<li>Discrimina... | A few more comments in support of pichenettes' answer:
<ul>
<li>the desired peaks seem to be equidistant. If you know this to be the case then you could use this knowledge in your peak detector.</li>
<li>otherwise I also believe that median filtering should help a lot.</li>
<li>don't try to solve everything by a super... | https://dsp.stackexchange.com |
457,146 | [
"https://physics.stackexchange.com/questions/457146",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/221116/"
] | My source of confusion comes from reading the following except from my general chemistry textbook,
"The energy of interaction between a pair of ions can be calculated using Coulomb's law"
<span class="math-container">$$V = \frac{k Q_1 Q_2}{r}$$</span>
Now, as I learned coulumbs law in general physics, the quantity ... | The force (vector) is given by the gradient of the potential energy:
<span class="math-container">$$
\vec F = -\vec\nabla V.
$$</span>
Even without calculating the gradient explicitly, dimensional analysis (that is, consistency of the units) implies
<span class="math-container">$$
|\vec F|\propto \frac{V}{r}
$$</span>
... | The voltage is the work done per unit charge so
<span class="math-container">$$
V=\frac{1}{q}\int \vec F \cdot d\vec r
$$</span>
so if <span class="math-container">$F\sim ~1/r^2$</span> then <span class="math-container">$V\sim \int \frac{dr}{r^2}\sim 1/r$</span>.
Note that, in the cylindrical geometry - say an infini... | https://physics.stackexchange.com |
5,085 | [
"https://security.stackexchange.com/questions/5085",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/793/"
] | If an attacker obtains a private key that was created with no passphrase, he obviously gains access to everything protected with that key. How secure are private keys set up <em>with</em> a passphrase? If an attacker steals a passphrase-protected key, how hard it is to compromise the key? In other words, is a private k... | With OpenSSL, OpenSSH and GPG/PGP the wrapping algorithm will be strong enough that you don't need to worry about it (and if you do need to worry about it then you have bigger problems, and this is the least of your worries).
Like any password or passphrase, it depends on the strength of the passphrase. A 40 character... | Once an encrypted block of data is in the hands of an attacker, it is never secure <em>forever</em> - it's a question of how long and what means are available to crack it.
Here's things to consider:
<ul>
<li><strong>strength of wrapping algorithm</strong> - I'm willing to believe bahamat about OpenSSL, OpenSSH and GP... | https://security.stackexchange.com |
47,979 | [
"https://softwareengineering.stackexchange.com/questions/47979",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/17332/"
] | Five years ago, I lost my ability to concentrate long-term, and therefore ability to code with professional efficiency.
I know why it happened, I understood how it happened, and on top of being able to re-create my calm and thus relaxed focus, I overcame the original (rooted in childhood) reason why my mind tilted on... | The best approach is to find a way to describe your situation in a <strong>learned-from-my-mistakes, learned-what-not-to-do</strong> way.
<ul>
<li><strong>Don't rationalize.</strong> No employer is going to be happy to hire an employee who spent five years on the dole if they completely rationalize it away. You may f... | <h2>Be honest</h2>
It will always pay on the long run.
<strong>You will fail to get many interviews, and many interviews will fail.</strong>
But <strong>it's a necessary recovery process</strong> to find the first employer that will actually understand what happened. That employer will be in position to give you be... | https://softwareengineering.stackexchange.com |
16,176 | [
"https://dsp.stackexchange.com/questions/16176",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/5648/"
] | I have a discrete signal <span class="math-container">$x[n]$</span> of length say <span class="math-container">$1024$</span>, such that :
<span class="math-container">$$-1 \leq x[n] \leq 1, \qquad \forall n$$</span>
and let <span class="math-container">$y[k]$</span> be its DFT.
<strong>Is there an upper bound for <span... | You can obtain a bound on the magnitude of the DFT of $x[n]$ ($|x[n]|\le 1$) as follows:
$$\big|X[k]\big|=\left|\sum_{n=0}^{N-1}x[n]e^{-jkn2\pi/N}\right|\le\sum_{n=0}^{N-1}|x[n]|\le N\max_n|x[n]|=N\tag{1}$$
Note that for signals $x[n]=e^{j2\pi nl/N}$, $l\in\mathbb{Z}$, the bound is tight. However, for most other sign... | The upper bound would be a coherent summation of all samples of $ x \left [ x \right ] $.
Specifically:
$$\begin{aligned}
X \left[ k \right ] & = \sum_{n = 0}^{N - 1} x \left[ n \right] \exp^{-j 2 \pi \frac{nk}{N}} \\
& \leq \left| \sum_{n = 0}^{N - 1} x \left[ n \right] \exp^{-j 2 \pi \frac{nk}{N}} \right| \... | https://dsp.stackexchange.com |
181,473 | [
"https://security.stackexchange.com/questions/181473",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/173333/"
] | I am creating a website which solely uses REST api for all the features and functionality, from signup and login to fetching data and populating the webpage using Mustache as template engine for objects.
Authentication is token based in which token dynamically added to header using JS functions to prevent CSRF attac... | <blockquote>
what if someone tries to trick users to paste some JS code in console
</blockquote>
What if someone tricks users into installing malware on their computer?<br>
What if someone dials a fake tech support number after encountering an issue with your website, and the scammers do something evil to the user's... | There is no way to distinguis an API call made from the "real" app from one made from the console. The server only sees the HTTP request, and it looks exactly the same. There really isn't anything you can do here.
Self XSS is not a vulnerability in your site, and hence you can not fix it. It is a vulnerability in the ... | https://security.stackexchange.com |
15,272 | [
"https://engineering.stackexchange.com/questions/15272",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/9226/"
] | I am trying to transform any arbitrary vector $\bf{v_{1}}$ in a Cartesian frame $\mathscr{F_{1}}$ into a different Cartesian frame $\mathscr{F_{2}}$. Both $\mathscr{F_{1}}$ and $\mathscr{F_{2}}$ have the same origin. I have consulted <em>Aircraft Flight Dynamics and Control</em> by Wayne Durham, and understand that boo... | Suppose Frame 1 is a world coordinate frame and Frame 2 local robot frame.
The thing that's a little confusing here is that when you transform from Frame 1 to Frame 2, you are saying that you want to... transform frame 1 to frame 2. You want to take all of frame 1's points, and put them in frame 2. You want measure w... | You have actually not done anything wrong. Its just that Matrix algebra, much to the chagrin of some, does not actually define how you need to pack your data into the matrix. Your choice.
So the question is do you consider that vectors inside your matrix to be columns or rows. This is called column major or row major.... | https://engineering.stackexchange.com |
17,380 | [
"https://physics.stackexchange.com/questions/17380",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/5265/"
] | At lower altitude an aeroplane usually has more lift. However an aeroplane flying at low altitudes (with gear/flaps up) at low velocity burns the same amount of fuel it would flying much faster at a higher altitude. Why?
| The lift basically depends on the the velocity of the plane and the the density of the air around it. That means, in higher altitude, a plane needs a higher velocity to maintain its height, BUT: The velocity is not just for staying up, but obviously is a desired feature of an airplane, thus, they would not speed down e... | Airplanes have a pitot tube, that has an air hole facing forward and one facing sideways. The difference of pressure between these two is what drives the airspeed indicator.
At a higher altitude, the air is thinner, so to get the necessary lift the airplane has to travel faster through it.
However, since the air is th... | https://physics.stackexchange.com |
107,308 | [
"https://security.stackexchange.com/questions/107308",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/34469/"
] | So, let's say a company has what could be referred to as an "access key". Each user has their own username and password, and there is an additional company-wide access key that people must input <em>with</em> their username and password to access back end resources. When an employee leaves, the old password is remove... | <h2>Works Against Robots</h2>
<h3>Secondary credentials are useful against non-targeted scripting attacks.</h3>
It completely depends on what is being protected from who and from what. In my personal experience as a Linux web systems administrator this kind of secondary credential scheme works well to protect known w... | You would be infinitely better off using certificates or two-factor authentication devices than a company-wide password.
The company password method suffers from the issue of key distribution (how do you get it out only to employees, and timely enough), people forgetting or otherwise losing t it, and wide distribution... | https://security.stackexchange.com |
354,332 | [
"https://softwareengineering.stackexchange.com/questions/354332",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/256929/"
] | It's a C#, ASP.NET MVC Project and here is the problem:
User can enter their email address in the reset password text field and click on the Reset Password button. Each time the user clicks on the Reset Password button a new email will be sent to that email address.
I am trying to limit the user reset password email ... | The second approach works well. I used something similar in a recent project. When someone requests a password reset, it generates the verification code (used for the verification link) and puts it into a table along with the email address and a timestamp. If a password reset is requested again, it checks that table... | Your assertion about cookies is correct. Cookies are in the hands of the enemy. They are not tamper-proof, so you can not use lack of a cookie as a proof that the user did not visit the site before.
Instead of creating a new database table, you could just add a field <code>last_password_reset_mail_send_timestamp</code... | https://softwareengineering.stackexchange.com |
322,170 | [
"https://softwareengineering.stackexchange.com/questions/322170",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/185519/"
] | I've been working on a project for a couple years now, and I'm starting to gather a decent user base. I've created a project page with some basic documentation, but it's really not much more than a FAQ at this point. I know that I need to improve it so that it's more informative for both new and power users, and that's... | Simple: Release a beta version! Then when documentation is done, do final release of the new version.
If you have users willing to try out the new stuff, then by all means take advantage of that. You will get bug reports, you probably get community questions about the difficult points so you know where to concentrate ... | If I got you right, you are doing this project on your <strong>free time</strong> and for <strong>no money</strong>. If this is the case, then please, do what makes you feel better (users wait, document on your time). You should not feel the pressure from your "users". Many people wrote about this on the Internet (Larg... | https://softwareengineering.stackexchange.com |
50,782 | [
"https://engineering.stackexchange.com/questions/50782",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/37762/"
] | I learned at at young age from a physics kit that one can blow up a large bag with your mouth by blowing into it from a distance and letting the air pick more air with it. Later in life when Dyson launched its fan, I understood the principle well. If I remember correctly Prusa also does something similar to help more a... | What about a blind pem nut? It might be hairy trying to make the a blind slot for the PEM nut, but even if you make a through-slot for it, it's a the blind PEM nut and if fitted well enough seals everything off anyways. You will need an arbor press and appropriate broach however, and likely a backing block for when you... | Usually holes are tapped to a depth of 1.5 times the diameter, and more for softer metals.
As aluminium is soft, then the thread will be engaging just one turn which won’t take much load at all.
A possibility is to weld a nut to the face side to give more purchase for the bolt and still leave the blind hole for the sea... | https://engineering.stackexchange.com |
266,205 | [
"https://physics.stackexchange.com/questions/266205",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/112190/"
] | How are the intensity of a <strong>sound wave</strong> and the Doppler shift of frequency related togheter?
That is, if the source or the observer are in relative motion, how does the intensity change?
For a sound wave $$I=\frac{1}{2} \rho \omega^2 A^2 c=2 \pi^2 \rho f^2 A^2c$$
($c$ is sound speed, $\rho$ is density ... | In this type of problem one has to take great care in defining intensities. In this case there are 4 different intensities: 1. $I_{ss}$, the intensity received by the static observer as perceived by himself, 2. $I_{ms}$, the intensity received by the moving observer as perceived by a static observer. 3 $I_sm$, the inte... | Intensity is energy per unit area; over short distances, the intensity can be considered constant. In a time period dt, the sound wave travels a distance c.dt, so the total energy passing through an area A will be equal to the sound energy present in a volume cAdt. (think of water flowing through a pipe, if it travels ... | https://physics.stackexchange.com |
39,843 | [
"https://softwareengineering.stackexchange.com/questions/39843",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/7768/"
] | I have a build computer where Visual Studio not installed, only MSbuild which can build VS2008 projcets without having any Visual Studio installed.
I wonder whether it is possible to use MSbuild with VC++ 6.0 project files, although I am thinking this could not be possible. In the past I have used it with a VS2008 so... | You can't compile C++6 without the C++6 compiler. However, once you install the command line support for the compiler/linker on the build server you will be able to access it from MSBuild or NAnt (worth a look). Also note that VS C++ 6 supported a build tool called <code>nmake</code> which shipped with VS. VS knew h... | You should be able to call Visual Studio to compile through the following:
<pre><code><Exec Command='"C:\program files\....\devenv.exe" /somearguments "path to your dsw file"'/>
</code></pre>
and replacing the placeholders in my above code.
| https://softwareengineering.stackexchange.com |
6,034 | [
"https://mechanics.stackexchange.com/questions/6034",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/3125/"
] | How do I bleed a clutch for a Ford Econovan 1989 model after putting in new master cylinder kit? as in where is the bleed nipple? It sure isn't the one on the steering column, it only works for brake.
| You said that the service station didn't mention having to top up the coolant, but I'd start by checking the coolant level yourself. The coolant overflow bottle should be prominent in the engine compartment, and the min/max levels should be well marked.
If the coolant level is good, perhaps you have a failing thermost... | A fan problem or radiator problem seem likely. Clean out any debris near the radiator, and check the fins for build up of leaves/bugs etc. It could be a clogged radiator - test for cold spots or drain it.
| https://mechanics.stackexchange.com |
173,327 | [
"https://electronics.stackexchange.com/questions/173327",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/77648/"
] | I live in a New York apt and I woke up last Saturday (5/30/15) because our power went out at about 7:30 am. A quick check with the bldg's doorman revealed that it was just our apt and not a total blackout as I first thought it was. Our maintenance guy came and checked our circuit breaker using a simple power tester. He... | It's a scam, as the others say. At least consider that he, or two working together, may have disconnected your power in order to attempt to obtain money from you.<br>
How you deal with this is up to you, but regardless, he's talking rubbish and is 'up to no good'. If he's doing this to you then he's probably preying o... | It might be a scam.. but being an engineer pl. ref. to the ammended electrical wiring regulation for new constructions wherein earthing has been made mandetory. If your building is old and if in the distribution ckt. a new eaarth leakage protection relay is installed the then in cirtain situation it might trip. Just a ... | https://electronics.stackexchange.com |
162,853 | [
"https://softwareengineering.stackexchange.com/questions/162853",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/34327/"
] | Asking a job seeker to show some code is a fairly common practice for a software company. However, would it be acceptable for the candidate to ask the interviewer to show him a small piece of code that he thinks is well written?
| I always ask to see some code, for several reasons:
<ul>
<li><strong>I want to know what I'm getting into.</strong> Of course no software firm is perfect, and I don't expect everyone to pump out marvels of elegance all the time (because neither do I), but if I ask for a company's very best code, and all they can show ... | <blockquote>
However, would it be acceptable for the candidate to ask the interviewer to show him a small piece of code that he thinks is well written?
</blockquote>
I suppose that falls into the whole 'interviews are bidirectional' mantra, but I wouldn't expect to get any. Intellectual Property concerns are the mos... | https://softwareengineering.stackexchange.com |
3,214,600 | [
"https://math.stackexchange.com/questions/3214600",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/495992/"
] | Following problem:
<blockquote>
Given the polynomial <span class="math-container">$f$</span> with integer coefficients. If <span class="math-container">$a, t\in\Bbb Z$</span> and <span class="math-container">$m\in\Bbb N$</span>, show that:
<span class="math-container">$$f(a+t\cdot m) \equiv f(a) \pmod m$$</span>
<... | Problem is in last second line <span class="math-container">$2^{ln2}$</span> is not equal to <span class="math-container">$3^{ln3}$</span>
| Taking the logarithm on both sides we get
<span class="math-container">$$\ln(2)\ln(2x)=\ln(3)\ln(3y)$$</span>
so
<span class="math-container">$$\ln(2)(\ln(2)+\ln(x))=\ln(3)(\ln(3)+\ln(y))$$</span>
Can you finish?
| https://math.stackexchange.com |
281,590 | [
"https://physics.stackexchange.com/questions/281590",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/41178/"
] | So in my relativity course, we recently learned about the covariant derivative. it is defined as:
\begin{equation}
\nabla_{\mu}V^{\nu} = \partial_{\mu}V^{\nu}+\Gamma^{\nu}_{\mu,\lambda}V^{\lambda}
\end{equation}
where $V^{\mu}$ is a vector, and $\Gamma^{\nu}_{\mu,\lambda}$ is the connection, or Christoffel symbol. S... | In your first equation you gave the expression for the components of the covariant derivative of a contravariant vector field $V^\nu$. Your second equation is a bit different there you have the covariant derivative of a basis vector along a basis vector: we are dealing with vectors there.
Vectors and components (of ve... | The notation $e_i$ is commonly used for frame fields (basis vector fields) as a more general notation than $\partial_\mu$. The connection forms, $\gamma^i{}_j$ (note that these indices are <em>not</em> tensorial) are defined relative to the frame fields such that
$$
\nabla_v e_i = \gamma^j{}_i(v)e_j = \gamma^j{}_{ik}v^... | https://physics.stackexchange.com |
134,374 | [
"https://physics.stackexchange.com/questions/134374",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/58687/"
] | I know gamma-ray photon can only give its momentum energy to the electrons of an atom.
My question is: Can a photon give some of its momentum to the atom (including its nucleus) to give it heat or speed?
If yes, can you tell me how much energy can it give?
| It is not very clear to me if you are asking about energy or momentum. You should also ask about a specific interaction process as there are many, this is required especially to answer your last, quantitative, question.
However, generally speaking, a $\gamma$ photon cannot give <em>some</em> of its energy to anything ... | Not merely <em>can</em> it transfer its momentum as well as its energy when it interacts, but it <em>must</em>.
If the target atom is in a fluid context (liquid, gas, plasma), then that energy and momentum must end up in the target or some other reaction products(s).
In a solid context the Mössbauer effect can be an ... | https://physics.stackexchange.com |
2,414 | [
"https://astronomy.stackexchange.com/questions/2414",
"https://astronomy.stackexchange.com",
"https://astronomy.stackexchange.com/users/1630/"
] | More exactly what would to happen to us/Earth in general if any of the gas giants is removed by magic from the solar system ?
How long would it take after such change before we notice it ?
How major and would life resist to it ?
<strong>EDIT</strong>
For instance if Saturn or Jupiter is removed, what would happen ?... | This question isn't really very clear or practical. You need to add quite a bit of information, eg which planet?
<ul>
<li>If Sedna vanished, it would be detectable by instruments, but we would not notice. </li>
<li>Jupiter or Mars might make a bigger difference. We could spot it straight away by the naked eye. </li>
... | Short answer: the solar system would be less stable in the short run due to the massive gravitational influence of Jupiter vanishing.
Long answer: The current layout of the solar system is actually remarkably well balanced; without outside interference, it'll stay stable for a good long while. Anything that changes th... | https://astronomy.stackexchange.com |
3,492 | [
"https://dsp.stackexchange.com/questions/3492",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/89/"
] | We can write the error function ($E(w)=1/2\sum_{n=1}^{N}\{y(x_n,w)-t_n\}^2$) as a linear model using its partial derivatives. Is it possible to do the same thing about the modified error function?
The modified error function is (page 10- pattern recognition by Bishop):
$$E(w)=1/2\sum_{n=1}^{N}\{y(x_n,w)-t_n\}^2+\dfra... | Yes, you can do that.
$$E(w)=1/2\sum_{n=1}^{N}\{y(x_n,w)-t_n\}^2+\dfrac \lambda2||w||^2$$
$$\begin{align} \frac{\partial E(w)}{\partial w} &= \frac{\partial \left( 1/2\sum_{n=1}^{N}\{y(x_n,w)-t_n\}^2+\dfrac \lambda2||w||^2 \right)}{\partial w} \\ &= \frac{\partial \left( 1/2(y({\bf x},{\bf w} )-{\bf t})^T(y({... | @Phonon's answer is absolutely correct, and very worthy of the upvote I gave it. But I had to read it a few times to fully understand it, and I think the reason I was confused is that ${\bf w}$ has a different dimension from ${\bf x}$ and ${\bf t}$. In the book, the dimension of the former is $M$, and of the others i... | https://dsp.stackexchange.com |
23,827 | [
"https://scicomp.stackexchange.com/questions/23827",
"https://scicomp.stackexchange.com",
"https://scicomp.stackexchange.com/users/20160/"
] | I want to know what are the differences between two data structures in MATLAB: Structure Arrays and Cell Array.
In what circumstances we can use each of them?
| If $A$ and $B$ are real symmetric, then $A=B+AB$ if and only if the product $AB$ is also real symmetric. In turn, $AB=BA$ holds if any only if $A$ and $B$ share a common eigendecomposition. This latter statement gives a recipe for computing $A$ given $B$.
<ol>
<li>Given $B$, compute its eigendecomposition $B=V\Lambda ... | Your equation is a <em>Sylvester</em> equation
$$
AB - A = -B,
$$
for which there are numerous solution algorithms.
I would definitely recommend the <em>Bartels-Stewart</em> algorithm that bases on real Schur decompositions. These can be computed for general square matrices in a stable fashion and avoiding complex ari... | https://scicomp.stackexchange.com |
117,011 | [
"https://mathoverflow.net/questions/117011",
"https://mathoverflow.net",
"https://mathoverflow.net/users/30146/"
] | If B is a Boolean ring is of uncountable cardinality c, does B have 2^c distinct maximal ideals ?
Can you please give me a reference where this question is answered (hopefully) positively ? Thanks
| This particular question is easy to answer. Many related questions about the relationships between various cardinals associated with Boolean algebra (or Boolean rings), such as: cardinality, number of ultrafilters, density, cellularity, distributivity etc, can be found in
<ul>
<li>Monk, J. Donald: <em>Cardinal invar... | This is false. We might as well count the number of ultrafilters, since an ultrafilter is the complement of a maximal ideal.
Let $X$ be a set of cardinality $c$. If $B$ is the set of subsets $S \subseteq X$ such that $S$ or its complement is finite, then $B$ is a Boolean algebra under the usual set-theoretic operatio... | https://mathoverflow.net |
14,344 | [
"https://electronics.stackexchange.com/questions/14344",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/2993/"
] | Someone asked me the other day how an FTDI USB to serial UART works, and I realized I didn't know. I looked at the datasheet for the FT232R and the block diagram didn't really help me. Can anyone explain or link me to a good explanation?
| The FTDI chips implement the USB protocol stack. The responsibility of this hardware is to tell your PC what it is (using some identification information) such that your computer can load the right driver for it, and also to manage the data transactions with the PC there-on after - look up USB endpoints for a better e... | There's a USB microcontroller inside which talks a proprietary protocol over USB (hence the need for drivers) and converts that into "normal" UART signals and back again.
| https://electronics.stackexchange.com |
68,217 | [
"https://mechanics.stackexchange.com/questions/68217",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/49796/"
] | After driving for a few minutes above 60 mph when you apply the brakes the pedal goes to the floor. Pedal returns when pumped. All other times the brakes work fine. Took to Ford dealer they said it was the ABS system and made repairs. Drove truck again on the highway it happened again. Took back to Ford and they could ... | There is more to it than just a "criss-cross" pattern. You should also work your way out from the middle in stages of bolt torque.
If you imagine tightening a cylinder head down starting at the two very ends. You have a gasket between the head and the block that doesn't really want to be crushed. When you tighten t... | In general things should be tightened in stages with some sort of crossed pattern depending on the number of fasteners in the circle.
Not doing so creates a bias that could result in false torque readings on the final fasteners. In other cases it can warp or damage the item being fastened, or perhaps prevent proper s... | https://mechanics.stackexchange.com |
322,249 | [
"https://softwareengineering.stackexchange.com/questions/322249",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/12893/"
] | Correct me if I'm wrong, but if I have an operating system that makes a context switch, then that context switch is in practice a switch from one thread to another, where one thread was running one task and then switches to another task and the reason the threads needs a stack is to save the variables of the task to be... | The stack has nothing to do with multi-threading. The stack saves information about a subroutine. When I say sub-routine, I am not speaking about any particular language, but the process of making a call to another area of the program space, and returning from that area when finished. When making the call, the currentl... | You're mostly on the right track. The stack's purpose in general is to hang onto data you'll need later. Most of the time, that's done when calling subroutines, at the very least to save the return address, but also to save any state that may be destroyed otherwise and as a mechanism to store local variables and to p... | https://softwareengineering.stackexchange.com |
207,034 | [
"https://softwareengineering.stackexchange.com/questions/207034",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/98559/"
] | I'm wondering how to write BDD test cases for a real system. All examples I can find are trivial and do not answer the question.
Sample use case/story basically goes like that:
<ol>
<li>User is on the main application page</li>
<li>He clicks retrieve to fetch some order to work on</li>
<li>He fills 4 textboxes and hi... | You should be describing it using terminology that makes sense to the business, not to a HTTP client. For example,
<pre><code>Scenario: Mark Order as Pending
Given we have an Order Y // creates order
When the user edits Order Y // click/load edit page
And marks it for review // toggles tickbox... | So, If I understand you correctly, you're asking how we could formulate our gherkin scenarios in such a way that we are only covering one thing whilst the problem is that the outcome depends in fact on several things.
I think an example of this would be something like - a table booking system with the rules: cannot bo... | https://softwareengineering.stackexchange.com |
716,303 | [
"https://math.stackexchange.com/questions/716303",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/123207/"
] | I came across this problem in my book:
$$\sum_{n=1}^\infty \frac{\ln(n)}{e^n \sqrt{n}}$$
I don't really know the approach to solving this off the bat, can this be solved by the comparison test while using the limit comparison test? Or will this require the ratio test?
If it is the comparison test, I jsut want to kno... | Converges by comparison test: $$\sum_{n=1}^\infty \frac{\ln(n)}{e^n \sqrt{n}}\leq 2\sum_{n=1}^\infty \frac{1}{e^n }=2\sum_{n=1}^\infty (\frac{1}{e })^n$$ (convergent geometric series with $r=\frac{1}{e}<1$) since $\ln(n)\leq 2\sqrt{n}$ for all $n\geq 1$.
| In each case, I think that your easiest solution may well be the <em>ratio test</em>.
The ratio test works a lot like comparison to a geometric series, but it isn't quite as sensitive to the "non-geometric" terms of a series.
By inspection: when you use the ratio test on the two series, you should get $\frac{1}{e}$ f... | https://math.stackexchange.com |
301,180 | [
"https://physics.stackexchange.com/questions/301180",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/140269/"
] | Suppose we have two tanks connected by a tube with a tap in the middle. One tank is filled with water to a height of $h$ and the other is empty. The tap is then opened and the water 'levels itself'. I had problems with understanding how such a system brings about a loss of $\frac{mgh}{4}$ in the water's potential energ... | If you had an ideal fluid (with zero viscosity), then the difference in potential energy would appear as kinetic energy of the fluid (mostly the one in the originally empty tank). In other words, you would have some sort of fluid motion in that tank (probably some large-scale vortices, and possibly others, depending on... | The potential energy will go down because the water level in the final state is lower than in the initial state (aka some water has fallen). This provides the energy released. This energy will go into friction, thermal or turbulant losses, or could be used to drive a turbine.
If there isn't enough energy to ovecome th... | https://physics.stackexchange.com |
10,174 | [
"https://quantumcomputing.stackexchange.com/questions/10174",
"https://quantumcomputing.stackexchange.com",
"https://quantumcomputing.stackexchange.com/users/10356/"
] | I have a state <code>psi</code> as an ndarray of shape (<code>2 ** 3</code>,) s.t.
<code>psi[0]= amplitude of 000</code>
<code>psi[1] = amplitude of 001.</code>
So my qubit ordering is reversed w.r.t. qiskit's. To initialize the circuit correctly and apply the IQFT on the first 2 qubits from the left I tried the fo... | Let's say I know that
<span class="math-container">$$
U_1|\Psi_1\rangle\otimes U_2|\Psi_2\rangle=e^{i\theta}|\Psi_1\rangle\otimes|\Psi_2\rangle.
$$</span>
Now, let's imagine that <span class="math-container">$U_1|\Psi_1\rangle=|\phi_1\rangle$</span> and <span class="math-container">$U_2|\Psi_2\rangle=|\phi_2\rangle$</s... | Let <span class="math-container">$H_1,H_2$</span> be two Hilbert spaces and for unit vectors <span class="math-container">$u_1,v_1 \in H_1$</span> and <span class="math-container">$u_2,v_2 \in H_2$</span> we have
<span class="math-container">$$
u_1 \otimes u_2 = v_1 \otimes v_2 \in H_1 \otimes H_2.
$$</span>
Then it m... | https://quantumcomputing.stackexchange.com |
55,857 | [
"https://dba.stackexchange.com/questions/55857",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/32260/"
] | Quick question guys!
Will there be any issues if I use the default instance (MSSQLSERVER) for both test and production environments? They are on separate physical servers. I'm using MS SQL Server 2012 which will run on clustered Windows Server 2012?
Thanks in advance and Happy New Year.
| That will be no problem to have multiple default instances in your environment. The only real restriction here is you can only have <strong>one default instance per machine</strong>.
You will have different network names for the different failover cluster instances. In short, if I'm understanding your question correc... | That should be fine. As long as they are on different servers ("Prod" and "Dev"), you would just address them across the network by their server name.
| https://dba.stackexchange.com |
1,146,711 | [
"https://math.stackexchange.com/questions/1146711",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/177104/"
] | The question is Prove: If $G$ is a group, a is in $G$ and the operation of $a*b=b$ (not multiplication, the $*$ stands for the operation) for some $b$ in $G$, then $a$ is the identity element of $G$. I don't understand why just because an element acted as the identity element one time it would be have to the identity e... | We are told to use the following definition of the Cantor set $C$: A point $x\in[0,1]$ is in $C$ if it has a ternary expansion $x=\sum_{k=1}^\infty{d_k\over 3^k}$ with all $d_k\in\{0,2\}$.
Let $x$ be an accumulation point of $C$. We have to prove that $x\in C$. Assume to the contrary. Then $x$ has a ternary expansion ... | Suppose (in ternary) $x=0.1=0.0222...,$ a point of the cantor set. This point $x$ is approached by the sequence $x_1,x_2,...=0.022,0.0222,0.02222,...$ and even though each term of the approaching sequence is all 0's or 2's, it is not <em>immediate</em> that the approached number $x$ must be all 0's or 2's.
This kind o... | https://math.stackexchange.com |
91,956 | [
"https://physics.stackexchange.com/questions/91956",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/8205/"
] | For a project i need to separate items based on their mass in real time. I like to explore measuring weight of an object (round metal ball) by taking photographs (several) during free fall and calculate mass from the pictures. Even if I cannot find the real mass I like to get a good estimate of the mass delta among man... | This approach will not work. Let's assume we are doing the experiment in vacuum for now. As you are saying, the basic logic is that you can measure velocity and acceleration from images with good accuracy. The problem is that <strong>any</strong> metal ball, irrespectively of their mass or weight will have exactly the ... | You could use cylindrical hollow capacitor and electrical bridge circuit and measure changes to the capacitance when the metal balls passing through it. As the ball pass through the capacitor, its capacitance will change due to the change in the dielectric properties inside the capacitor. The changes to the capacitanc... | https://physics.stackexchange.com |
59,097 | [
"https://electronics.stackexchange.com/questions/59097",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/15953/"
] | I'm new to VHDL and I'm having a problem with my code that I can't seem to fix. We're supposed to do this using either selected signal assignment or table lookup. Mine is kind of a combination of the two since we are supposed to use don't cares for inputs that will not happen.
The code is basically supposed to give th... | <pre><code>with input select
led <= table(to_integer(unsigned(d & tmp)))
when "0000" | "0001" | "0010" | "0011" |
"0100" | "0101" | "0110" | "0111" |
"1000" | "1001" | "1010" | "1011" |
"1100" | "1101" | "1110" | "1111"
and ob = '1',
...
</code></pre>
Th... | You have all possible combinations of <code>input</code> in the <code>when</code>, so you can remove that code.
What stays is 'if ob='1' or '0'`
<pre><code>led <= table(to_integer(unsigned(d & tmp))) when ob = '1' else table(to_integer(unsigned(not d & tmp)));
</code></pre>
Note there is no ob = '0' anymor... | https://electronics.stackexchange.com |
8,208 | [
"https://cstheory.stackexchange.com/questions/8208",
"https://cstheory.stackexchange.com",
"https://cstheory.stackexchange.com/users/6346/"
] | A language $L$ is in the class $DP$ iff there are two languages $L1 \in NP$ and $L2 \in coNP$ such that $L = L1 \cap L2$
A canonical $DP$-complete problem is SAT-UNSAT : given two 3-CNF expressions, $F$ and $G$, is it true that $F$ is satisfiable and $G$ is not?
The Critical SAT problem is also known to be $DP$-compl... | [I made it into a proper answer b/c somebody gave it -1]
If <em>any</em> clause is allowed to be added, then the language is empty -- clearly to any satisfiable formula $F$ you can add a 3-clause $c$ made up of variables that do not appear in $F$: $F \cup \{ c \}$ will be satisfiable.
If the added clauses must use va... | May I propose an answer to my own question thanks to your comments : the variant of Critical SAT is in P.
Let us call "Problem 1" the variant of Critical SAT : Given a 3-CNF expression $F$, is it true that $F$ is satisfiable but adding any clause out of $F$ makes it unsatisfiable?
And "Problem 2" : Given a 3-CNF ex... | https://cstheory.stackexchange.com |
185,678 | [
"https://mathoverflow.net/questions/185678",
"https://mathoverflow.net",
"https://mathoverflow.net/users/51596/"
] | Let n points in the plane be given whose coordinates we don't know.
Assume, however, that for any triple of the points we know the angle.
Question: Can we decide whether the n points are realizable in the plane, i.e. can we determine whether there is an assignment of coordinates to the points such that the angular con... | I assume that the angles are nonzero and we know which angle corresponds to each triplet.
If there are zero angles (collinear points) or the lists of angles and points are unrelated, the problem is harder.
With these assumptions there is a method.
First, take any three points.
They can be realized in the plane if and ... | To answer Joonas's comment in the last paragraph: yes, it is possible to check the realizability without constructing the whole realization. It is sufficient to test whether every 5-tuple of points
is realizable. (For simplicity, I am also assuming general position, that is, no three points on a line.)
To see this, n... | https://mathoverflow.net |
531,725 | [
"https://math.stackexchange.com/questions/531725",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/66883/"
] | I was playing around with the integral $\int x^ndx$ and noticed that it is always $\frac{x^{n-1}}{n-1}+c$ <em>except</em> for the singular case $n=-1$. So I could pick $n$ arbitrarily close to $-1$, and the formula works, but as soon as I hit $-1$, it breaks (so to speak)!
Here's my work thus far:
$$\int x^{-(n+1)/n}... | The key to this is to be careful with the integral, and in particular, the limits of integration. Note that $$\int^t_1 x^n=\frac{t^{n+1}-1}{n+1}, n\neq 1$$ So now we want to compute $$\lim_{n\to -1}\frac{t^{n+1}-1}{n+1}.$$ By making a change of variables, $n\mapsto n-1$, we get $$\lim_{n\to 0}\frac{t^{n}-1}{n}$$ which ... | After re-writing, you get
$$
-nx^{-1/n}+n=n(1-e^{-1/n\ln x}).
$$
Now you can use Taylor expansions, for instance, to get
$$
n(1-e^{-1/n\ln x})=n(1-(1-\frac1n\,\ln x+O(n^{-2}))=\ln x +O(n^{-1}).
$$
Then
$$
\lim_{n\to\infty}n-nx^{-1/n}=\ln x.
$$
| https://math.stackexchange.com |
109,079 | [
"https://electronics.stackexchange.com/questions/109079",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/7624/"
] | I'm learning about RFID and am trying to figure out what the data rates are for the different types of RFID technologies.
I've learned that there are three different frequencies tags and readers operate on:
<pre><code>LF - 125-134 kHz
HF - 13.56 MHz
UHF - 850-960 MHz
</code></pre>
There are also a number of differe... | By reading the standards documents for each one.
I know that in LF at least, the data rate is normally a simple divider from the carrier frequency. A 128 kHz carrier might be divided by a factor of 32 or 16 to create a data rate 4 or 8 kbps, for example.
| Nate said:
<blockquote>
By reading the standards documents for each one.
I know that in LF at least, the data rate is normally a simple divider
from the carrier frequency. A 128 kHz carrier might be divided by a
factor of 32 or 16 to create a data rate 4 or 8 kbps, for example.
</blockquote>
Yes, and yes!
... | https://electronics.stackexchange.com |
80,151 | [
"https://electronics.stackexchange.com/questions/80151",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/4028/"
] | I have a problem that I need to measure an RPM of a rotating axle with a single element (circuit) attached to it - i.e. I can't use a hall effect sensor, because I can't use a separate magnet - I can only use what's mounter on the axle. The axle will rotate only on one axis - but that could be X, Y or Z. So the solutio... | Gyroscopes are designed for this - measurement of angular velocity on a rotating body without needing a separate stationary component. I recommend a MEMS gyroscope. Several are available with analog or digital outputs (SPI or I²C). They are usually specified in degrees per second -- 150 RPM is 900°/second, which is h... | I'd go with an optical interrupter, either with a mechanical interruption or reflection based. Either will easily give you a pulse per revolution (or more!) which should give you a pretty good estimate of rpm if the speed is fast enough. Bonus: no mechanical connection to shaft. If you need better accuracy at low s... | https://electronics.stackexchange.com |
3,227 | [
"https://quant.stackexchange.com/questions/3227",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/2257/"
] | Is there a technique to choose the time-frame for a cointegration test (eg Augmented Dickey-Fueller's)?
| I have never read about any formal procedure for this. And, I don't remember this issue is even treated in C.Alexander's book Market Risk Analysis, Practical Financial Econometrics that dedicate a whole part to the cointegration of financial time series. One may well find tests for cointegration succeeding (failing) fo... | Why not use the entire data. But before you do clean the data by checking for structural breaks (t / F statistic of a dummy variable). If there exist a functional break, then you know you have to perform the co-integration tests separately for each time frames.
If you use a preferable time then the question is what cr... | https://quant.stackexchange.com |
75,894 | [
"https://dba.stackexchange.com/questions/75894",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/46964/"
] | Per the PGSQL 9.3 docs:
<blockquote>
Because this is not always needed, and there are many choices available on how to index, declaration of a foreign key constraint does not automatically create an index on the referencing columns.
</blockquote>
Yet after I create such a constraint, when I run <code>\d <table&g... | I discovered that pgAdmin III does this by default. When you create a new foreign key constraint using the GUI, there is a checkbox "Auto FK Index" on the Definition tab. I hadn't noticed this until just now so it explains why the index was being created.
| <blockquote>
What could explain why this gets created?
</blockquote>
<em>You</em> created the index. Or the <em>client software</em> you are working with did it for you. Postgres certainly didn't.
<blockquote>
Do I still need to create another index on my product column to improve performance of queries on it?
</... | https://dba.stackexchange.com |
198,026 | [
"https://physics.stackexchange.com/questions/198026",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/48904/"
] | Air molecules scatter sunlight and makes the sky blue. Many books say that the air molecules are oscillated by E field and so they become sources of EM waves. Is it because the air molecules have charges? I wonder, if air molecules or molecules of other medium (e.g. water) are completely neutral (i.e. no excess charges... | A model for the interaction of light with atoms and molecules treats the charge distribution as an electric dipole, because the particles consist af separate positively and negatively charged particles that can be polarised to have a non-zero electric dipole moment. Neutral particles where no (internal) charge separati... | Electromagnetic waves are produced whenever charged particles are accelerated, and these waves can subsequently interact with any charged particles, they dont interact with neutral particles.Though I do remember reading somewhere that neutral particles can lead to acoustic waves but I dont remember the concept or condi... | https://physics.stackexchange.com |
529,697 | [
"https://physics.stackexchange.com/questions/529697",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/253164/"
] | Wave is a disturbance in a medium, due to this disturbance the particles in the medium oscillate. Due to this oscillation we say that the wave is sinusoidal because the motion of the particle is periodic. So we REPRESENT the motion in sine wave.
Periodic motion can be represented by sine graphs. So if instead of repre... | I prefer to think like this. Inertial observer (<span class="math-container">$X$</span>) is at rest in his/hers reference frame. The world-line of <span class="math-container">$X$</span> is the <em>longest</em> possible route between any two events. This follows since, in its frame, <span class="math-container">$X$</sp... | For a single particle, it does not matter what prefactor you use, the equations of motion and everything else stays the same. The factors only start to matter when you couple different systems to each other. For example, consider a charged particle in an electromagnetic field described by a vector potential <span class... | https://physics.stackexchange.com |
3,381,532 | [
"https://math.stackexchange.com/questions/3381532",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/-1/"
] | Evaluate the surface Integral of <span class="math-container">$H(x,y,z) = yz$</span> over the part of the sphere <span class="math-container">$x^2+ y^2+ z^2 =4$</span> that lies above the cone <span class="math-container">$z = \sqrt{x^2 + y^2}$</span>
My question is How can I setup the integral to calculate the surfac... | Given the symmetry, it is convenient to set up the integral in spherical coordinates. Use <span class="math-container">$r=2$</span>, <span class="math-container">$y=r\sin\phi\sin\theta$</span>, <span class="math-container">$z=r\cos\theta$</span> and the surface element <span class="math-container">$ds = r^2\sin\theta d... | Okay so it has been a while for me but I will give it a try.
We want to evaluate a surface integral using coordinate transformation:
So let's start with the transformation:
<span class="math-container">$$\phi(u,v)= r\cdot\begin{bmatrix} cos(u)cos(v) \\sin(u)cos(v) \\ sin(v) \end{bmatrix}$$</span>
We can calculate o... | https://math.stackexchange.com |
342,739 | [
"https://stats.stackexchange.com/questions/342739",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/116205/"
] | Assume we have a categorical variable (one-hot encoded) with three or more categories. <code>{race1, race2, ..., race-n}</code>
To avoid the dummy variable trap, assume we omitted <code>race1</code>. Knowing the coefficients of <code>race2,3,...n</code> would help us compare each to <code>race1</code>.
What I'm trying... | Assume your outcome variable Y is continuous and the model includes only the race factor, so that:
<pre><code>Y = beta0 + beta1* race2 + beta2*race3 + ... +
beta-n-1*race-n + error
</code></pre>
Then:
<pre><code>beta0 = mean value of Y when race is equal to
race1
beta0 + beta1 = mean value of Y when race is ... | There are several ways to do this, but they all entail constructing linear combinations of the coefficients, such as their difference. This is doable since the original regression gives you the covariances between coefficients in addition to their standard errors, so that you can use the formula for linear combinations... | https://stats.stackexchange.com |
243,069 | [
"https://softwareengineering.stackexchange.com/questions/243069",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/71548/"
] | I am using a proper binary tree to simulate a tournament bracket. It's preferred any competitors in the bracket that are teammates don't meet each other until the later rounds. What is an efficient method in which I can ensure that teammates in the bracket have as much distance as possible from each other? Are there ... | Just sort the players by team and number them starting from 0, so e.g.
<pre><code>0(000) T1a (team 1 player a)
1(001) T1b
2(010) T1c
3(011) T2a
4(100) T2b
5(101) T3a
6(110) T3b
7(111) T3c
</code></pre>
Then reverse the bits in each number to fill out your bracket sheet
<pre><code>0(000) T1a\______
1(001) T... | I hope this has a proof built into itself.
The main idea is to delay the meeting of 2 teammates as much as possible.
So a greedy algorithm would work.
The most we can delay is in the final, then semi-final1, semi-final2, quarter-final1, etc... Save this ordered list of match-up in list L1.
Sort the list of players w... | https://softwareengineering.stackexchange.com |
312,957 | [
"https://electronics.stackexchange.com/questions/312957",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/122430/"
] | I'm trying to read the temperature of a Si7050 using a TI CC3220SF. I'm not sure if clock stretching is handled correctly from the TI's driver as well as the NACK option (alternative to clock streching, according to the datasheet).
Is there a way to read that temperature avoiding those specific features? I mean, for m... | I wasn't able to get the clock stretching to work. I've ended up in this way:
<pre><code>_i16 WriteRegister(_u8 address)
{
I2C_Transaction i2cTransaction;
_u8 writeBuf[1];
writeBuf[0] = address;
i2cTransaction.slaveAddress = SI7051_ADDRESS;
i2cTransaction.writeBuf = writeBuf;
i2cTransaction.w... | The driver does not handle clock stretching because it is already handled by the hardware.
Ensure that the I²C Master Clock Low Timeout Count is set high enough (see section 7.2.1.6 of the Technical Reference Manual).
| https://electronics.stackexchange.com |
448,194 | [
"https://electronics.stackexchange.com/questions/448194",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/223269/"
] | I am using a VS1053 (on a SparkFun Music Maker shield) to provide audio for my project. I am taking a line out signal and inputting it into an op amp for signal processing, ultimately being input to an Arduino.
The op amp(s) are using Vcc and ground from the Arduino as their power supply. The module with the VS1053 a... | Voltage is not part of the equation, and that is because the voltage does not matter.
I confirm that the default voltage references are 1/3 and 2/3 of the VCC.
The RC time is also constant. In electronics we can use RC time simply because it does not depend on voltage when using a constant voltage accros the R+C comp... | You're correct to think that the capacitor charges faster and cancels out the different reference voltages. Remember that ohm's law is <span class="math-container">\$I = \frac{V}{R}\$</span>, so higher voltage with the same resistance means higher current charging that capacitor.
| https://electronics.stackexchange.com |
155,943 | [
"https://softwareengineering.stackexchange.com/questions/155943",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/38223/"
] | I was in a heated discussion the other day, about whether or not it's practical to have a perfect validation score on any HTML document. By practical I mean:
<ul>
<li>Does not take a ridiculous amount of time compared to it's almost-perfect counterpart.</li>
<li>Can be made to <strong>look good on <em>older browsers</... | Unless you're going to validate as HTML 3.2 or something (and lose all the perks that come with HTML 4 or 5), your HTML is going to break in <em>very old</em> browsers anyway. You're not really helping them just by having valid HTML 5. You'd have to wrap your CSS and JS in comments, provide fallback mechanisms for br... | Since you didn't specify what kind of test are you talking about, i'm discussing this in general terms.
Many of this so called "validation test" are just a syntax check with a DOM of reference, this means that an high score is for a well formatted source, a lower score is for documents that does not respect the DOM gu... | https://softwareengineering.stackexchange.com |
352,126 | [
"https://mathoverflow.net/questions/352126",
"https://mathoverflow.net",
"https://mathoverflow.net/users/150264/"
] | Let's consider a bounded (maybe compact) set <span class="math-container">$\Lambda \subset \mathbb{R}^{d}$</span> with particles interacting on it. Suppose, for each <span class="math-container">$N \in \mathbb{N}$</span>, <span class="math-container">$U_{N}: (\mathbb{R}^{d})^{N} \to \mathbb{R}\cup \{+\infty\}$</span> i... | Looking at your formula (1), it appears that <span class="math-container">$\mu$</span> must be a measure defined on a <span class="math-container">$\sigma$</span>-algebra <span class="math-container">$\mathscr F$</span> over the finite set <span class="math-container">$\Lambda$</span>. The natural <span class="math-con... | The configuration space is the disjoint union of <span class="math-container">$\Lambda^N$</span> for each nonnegative integer <span class="math-container">$N$</span>. You can
take the Borel <span class="math-container">$\sigma$</span>-algebra on each of these (or Lebesgue if you prefer, but you're unlikely to encounte... | https://mathoverflow.net |
3,546 | [
"https://scicomp.stackexchange.com/questions/3546",
"https://scicomp.stackexchange.com",
"https://scicomp.stackexchange.com/users/414/"
] | I have a time series representing the result of a complex calculation (physical simulation). Due to round-off errors and approximation errors, there will be some "noise" on the data series. In some cases, the physical simulation represents a "steady state" situation meaning that, in theory, the time series should be a ... | I'd follow your suggestion of fitting a line $ax+b$ to your data. You don't even have to smooth it first -- fitting a line already takes care of it.
There are, however, two questions: first, how do you fit the line? This is a question of the statistics of your noise. If noise is Gaussian then you'd use least squares. ... | You should try a Kalman filter, if possible for your problem. It's used in accelerometers, which also tend to drift.
| https://scicomp.stackexchange.com |
157,315 | [
"https://electronics.stackexchange.com/questions/157315",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/56112/"
] | I am currently able to read byte by byte from USART with this code
<pre><code>ISR(USART_RX_vect)
{
cli();
while(!(UCSR0A&(1<<RXC0))){};
// clear the USART interrupt
received = UDR0;
if(pinState == 0)
{
OCR2A = received;
pinState = 1;
}
else if(pinState == 1)... | You did not mention which microcontroller you are using, but it probably doesn't matter. USART peripherals generally operate exactly as you have discovered: one byte at a time. This, however, is not a limitation.
Based on the code snippet you posted in your question, you're trying to execute some functionality with ev... | The conventional method for dealing with multi-byte receives in an interrupt routine is to setup a circular queue. As each byte is received it is placed into the next available slot in the queue. This would replace your single byte save code that you have now.
The output side of the circular queue is polled for availa... | https://electronics.stackexchange.com |
27,799 | [
"https://biology.stackexchange.com/questions/27799",
"https://biology.stackexchange.com",
"https://biology.stackexchange.com/users/11855/"
] | Why draw blood from veins rather than arteries? Is it more convenient or safer?
| Veins have several advantages over arteries. From a purely practical standpoint, veins are easier to access due to their superficial location compared to the arteries which are located deeper under the skin. They have thinner walls (much less smooth muscle surrounding them) than arteries, and have less innervation, so ... | Right of the bat, veins are superficial so it is much easier to hit a vein than an artery. Arterial sticks are very difficult if you are not practiced at them while veins are much much easier. Also arterial sticks have a very specific purpose usually for example arterial blood gas. Also veins are low pressure compared ... | https://biology.stackexchange.com |
11,183 | [
"https://bioinformatics.stackexchange.com/questions/11183",
"https://bioinformatics.stackexchange.com",
"https://bioinformatics.stackexchange.com/users/4595/"
] | I have a data frame like with more samples like
<pre><code>> head(a[1:2,1:4])
ID ids pre.or.post.treatment
1 OCCAMS/AH/120 LP6005409-DNA_F01 pre
2 OCCAMS/AH/126 LP2000325-DNA_A01 pre
TRG
1 non-responder
2 non-responder
> dim(a)
[1] 160 ... | Assuming your column ID in both dataframes <code>a</code> and <code>b</code> shared same IDs, and as your dataframe are not particularly heavy, you can have the use of the function <code>left_join</code> from <code>dplyr</code> package as this:
<pre class="lang-r prettyprint-override"><code>library(dplyr)
DF <- lef... | @dc37's dplyr solution is quite elegant, but you can also use base R's merge:
<pre><code>merge(x = df_a, y = df_b, by = "ID", all.x = TRUE, all.y = TRUE)
</code></pre>
You can tweak various parameters, such as use <code>by.x</code> and <code>by.y</code> instead of just <code>by</code>, change <code>all.x</code> and <... | https://bioinformatics.stackexchange.com |
612,432 | [
"https://physics.stackexchange.com/questions/612432",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/276706/"
] | When deriving Gauss’s law in differential form (GLDF), <span class="math-container">$$\nabla \cdot \mathbf E = \frac{\rho}{\epsilon_0},$$</span> from Gauss’s law in integral form (GLIF) we get a tidier formula, which is however less general (to my understanding). In fact, while we can freely apply GLIF to point charges... | You can always think of line- and surface-densities as a collection of point charges. If you already have no problem in using Dirac deltas, then we can easily just extend them to more complex geometries. Weird deltas might be harder to handle, but in principle it is possible.
For example you could write, for a series o... | You can have <span class="math-container">$\rho$</span> represent any charge distribution you like, e.g. for a charged spherical shell of radius <span class="math-container">$r_0$</span> <span class="math-container">$$\rho(r) = q \delta(r-r_0)$$</span>
| https://physics.stackexchange.com |
11,965 | [
"https://electronics.stackexchange.com/questions/11965",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/3240/"
] | I have in my possession two stepper motors that are clearly marked as 50 ohm, 22V motors. They have six leads each, which I believe makes them unipolar stepper motors.
It is my understanding (and experience) that unipolar stepper motors can be driven as bipolar stepper motors by ignoring the center lead, and that is w... | I would suggest driving the motor with 72% of rated current, or about 310mA. That should yield the same power dissipation as would be expected from unipolar drive at 440mA. When the motor isn't moving, the voltage would have to be about 31 volts. I wouldn't expect insulation problems at 31 volts, or even 50, but I d... | If you are driving motor in non-standard mode, the only reliable way is to increase drive current while monitoring coil temperatures. When it reaches some 60-80C in continious operation - that's your power limit.
In any case, going much higher than 22V might cause insulation breakdown, so I would not go higher than 1.... | https://electronics.stackexchange.com |
165,078 | [
"https://electronics.stackexchange.com/questions/165078",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/20250/"
] | In Design of Analog CMOS integrated circuits by Razavi I found the following differential pair design. It uses a MOS as load and it acts as a current source.
<img src="https://i.imgur.com/JmvGNrc.png" alt="current osurce load">
My question is how should you bias the current source loads? My initial guess would be tha... | Your initial guess is right: you size M3 and M4 so that with zero differential input the current through the two branches is the same, i.e. Iss/2.
For small differential inputs this condition is always nearly true, i.e. the current through M1 and M2 drains is nearly Iss/2 if you neglect a very tiny difference. Luckily... | Question 1) Simply bias them so that their currents are equal. The "current mirror" configuration does exactly that - then you need no knowledge of what Iss actually is.
Question 2) You are correct : there is a conflict between the two requirements (M1 on, M2 off) and equal current in M3,M4. This conflict is what give... | https://electronics.stackexchange.com |
316,750 | [
"https://physics.stackexchange.com/questions/316750",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/33870/"
] | My 1D harmonic oscillator of mass $m$ is in a potential $V(x) = \frac{m\omega^2x^2}{2}$. Here's its state: $\left|\psi\right> = Ne^{\lambda a^\dagger}\left|0\right>$, where
$\lambda$ is given, $\lambda \in \mathcal{C}$, and $a^\dagger$ is a ladder operator, $a^\dagger = \sqrt{\frac{m\omega}{2\hbar}}\left(\hat{x}... | The exponential of the creation operator has a lot of physical meaning, the state is very important.
There are several classes of wisdom about it, including
<ul>
<li>how it's calculated</li>
<li>what algebraic properties the exponential or its action on a state obeys</li>
<li>what is the physical importance or interp... | I did a quick calculation and (using the earlier mentioned relations) I found the following (beware, I may have been sloppy)
$|\psi\rangle=N\sum_n\frac{\sqrt{(n+1)}\lambda^n}{\sqrt{n!}}|n+1\rangle$. Inserting the eigenfunctions of the Hamiltonian
$$
\psi_n(x) = N_n \cdot e^{
- \frac{m\omega x^2}{2 \hbar}} \cdot H_n\l... | https://physics.stackexchange.com |
427,083 | [
"https://physics.stackexchange.com/questions/427083",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/205865/"
] | I am struggling with the following problem:
<blockquote>
A platform has a rope attached to it which extends vertically upward, over a pulley, and then back down. You stand on the platform. The combined mass of you and the platform is $m$.<br>
Consider the scenario where you grab the other end of the rope and hoist... | Remember that the rope goes both ways over the pulley. So, to move the platform (and yourself) upwards by a height $h$, the rope on both sides of the pulley decreases by a length $h$, so you need to pull a length $2h$ of rope. That is the flaw in your reasoning, which is your assumption that $d = h$. In reality, you <e... | The rope shortens by the amount $h$ on both sides, so the work done will be $W=F\cdot d=\frac{mg}{2}\cdot 2h$.
You can also consider that you have done work to gain $mgh$ potential energy, that extra energy has to come from somewhere - it comes from the work done.
| https://physics.stackexchange.com |
369,267 | [
"https://softwareengineering.stackexchange.com/questions/369267",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/48364/"
] | I've been reading Robert Martin's Clean Code book where it suggests we should separate a programs startup/construction process from its run time logic.
In Java (the language the book uses) this involves moving all aspects of construction to <code>main</code> and designing the rest of the system assuming all objects ha... | In the superclass, there is (very likely) a default value for the <code>fileSize</code> parameter. We can take advantage of that fact here.
First, we need to get an idea of what that default value might be. We could see something like:
<pre><code>public class Handler {
public static final long DEFAULT_FILE_SIZE =... | You put the duplicate code in a new private method, just like you would in any other refactoring of duplicate code.
<pre><code>private SourceCache sourceCache;
private ServiceCache serviceCache;
private MethodCache methodCache;
private ModelCache modelCache;
private QueryFactory queryFactory;
public MetaDataPersisten... | https://softwareengineering.stackexchange.com |
715,657 | [
"https://physics.stackexchange.com/questions/715657",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/339198/"
] | According law of conservation of charge "the total electric charge in the universe is constant and charge can neither be created nor be destroyed" so how did the existing charge came. I f it can not be created how it is was created in the first place
| When Einstein derived his equations the Newtonian limit (and it may be taken also in the present of sources) was an important check for the theory. It is also useful to understand the limits of the Newtonian theory, and sometimes helps to work out the intuition about the relativistic case.
However to solve Einstein equ... | If, in some limit, GR didn't reduce down to <span class="math-container">$\kappa \nabla ^{2}\phi = \rho$</span> for some constant kappa, (where <span class="math-container">$\phi$</span> is a gravitational potential such that <span class="math-container">${\vec g} = {\vec \nabla}\phi$</span>), then it wouldn't be a ver... | https://physics.stackexchange.com |
200,357 | [
"https://dba.stackexchange.com/questions/200357",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/146837/"
] | I am trying to make a stock management software according to my client's requirement, where I bought products by weight or qty depending on product type. Which has following database structure.
<pre><code>User { id, name, address, role (Customer, Vendor, Labor etc)}
Product {id, name, type}
</code></pre>
Types of produ... | You could approach it as double-entry book keeping. Each user has an "account" for each product, to which you credit and debit transfers. You act as the "bank" in the middle of the network. Each account's balance is the stock, either on-hand for sale or out for work.
The tables would be something like:
<pre><code>Par... | <blockquote>
(number of pcs are not same every time due to scrap generated during
this process is not fixed so I cannot calculate the number of pcs by
formula as of now we can expect the approximate pcs which may vary +/-
10 to 100).
</blockquote>
Scrap generated is not fix becasue of product quality or dimens... | https://dba.stackexchange.com |
566,675 | [
"https://electronics.stackexchange.com/questions/566675",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/251929/"
] | Considering an N-type semiconductor, when we talk about carrier density, it means number of electrons per unit volume. But, when we define current density(J), it is measured as total current per unit area.
Why?
Why not volume?
| From first principles, to compute the current density at a point in space you:
<ol>
<li>select a small box around the point</li>
<li>add up <span class="math-container">\$\rho \vec{v}\$</span> for all of the particles in the box where <span class="math-container">\$\rho\$</span> is the electric charge of the particle a... | Current is a one-dimensional quantity, while charge is a zero-dimensional one. It doesn't really make sense to talk about current per volume, for the same reason it doesn't really make sense to talk about, say, how many strands per length a stranded wire has--the current (and the strands of wire) are the same all along... | https://electronics.stackexchange.com |
97,660 | [
"https://softwareengineering.stackexchange.com/questions/97660",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/14774/"
] | I am a Web application developer who also is responsible for project managing some projects, I sometimes have to manage remote developers, who work for me under a contract basis. I feel that sometimes it is really difficult to manage. I am facing some strange situations. For example:
<ul>
<li>Once a developer didn't r... | I don't know your precise situation, so it's very difficult to tell what's happening. Nevertheless, here a few elements which may or may not apply to you:
<strong>1. Communication</strong>
Do you communicate clearly your ideas? I mean, are you sure that those developers understand correctly what is the work to do?
<... | One practical thing I do is pay half up front, then I pay the other half upon completion to spec. If it doesn't meet spec, they don't get the other half. I don't do unlimited hourly pay as that is asking for trouble. I ask for an hourly estimate up front and pay according to that number. If you don't, then they have no... | https://softwareengineering.stackexchange.com |
384,978 | [
"https://physics.stackexchange.com/questions/384978",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/113208/"
] | Firstly, let me say that I understand that what basically happens in gauge theories is that we keep the unphysical degrees of freedom present but in check, instead of removing them at once, which besides being generally really hard to do would cause further headaches related to Lorentz invariance.
I was trying to foll... | I'm with you. I don't want to be unprofessional, but I find the whole "breaking causality" thing to be complete bogus. I see absolutely no way that the humble Klein Gordon field "breaks causality." In my opinion, just ignore it.
"Why" we consider gauge invariant theories is a good question... | I think Ryder's argument is misleading.
Because of causality charge conservation only needs to be ensured inside the light cone and seen from a particular point of spacetime there is no requirement of a truly global phase invariance. It is because charge needs to be conserved in <em>any</em> point of space time that ... | https://physics.stackexchange.com |
380,584 | [
"https://math.stackexchange.com/questions/380584",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/21813/"
] | The following is a lecture slide. A couple of questions:
1) Is "code extension" being used correctly here? From my googling, what is described doesn't seem to be a code extension.
2) Does $C$ really have length $2n$? For each word $\vec a$, surely there are more than two $\vec a + \vec b$ that can be appended?
3) Is... | <ol>
<li>In the coding theory class I took, I was told that an extended code is one where the dimension stays the same but the length increases. So, in that sense, $C$ is neither an extension of $A$ nor $B$. However, I don't have any references on that, other than my personal class notes.</li>
<li>Yes, $C$ has length $... | The construction in question is sometimes called the <em>Plotkin</em> construction. It is described in Chapter 2, Section 9, of MacWilliams and Sloane's <em>Theory of Error-Correcting Codes</em> (1978) under the name of the $|u|u+v|$ construction, and used in
several other places (chapters) in that tome. As a special ... | https://math.stackexchange.com |
61,498 | [
"https://physics.stackexchange.com/questions/61498",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/16015/"
] | The following identity is used in Peskin & Schroeder's book Eq.(19.43), page 660:
$$\int\frac{d^4k}{(2\pi)^4}\,\frac{1}{(k^2)^2}e^{ik\cdot\epsilon}=\frac{i}{(4\pi)^2}\log\frac{1}{\epsilon^2},\quad \epsilon\rightarrow 0$$
I can't figure out why it holds. Could someone provide a method to prove this? Many thanks in... | That's equivalent simply to $c\int dx/x$. Switch to the Euclidean spacetime, $k_0=ik_4$ where $(k_1,\dots k_4)$ is $k_E$; i.e. analytically continue in $k_0$ (Wick rotation). The integral is
$$\int \frac{i\cdot d^4 k_E}{(2\pi)^4} \frac{1}{(k_E^2)^2} \exp(ik\cdot \epsilon)$$
So it's proportional to the Fourier transform... | I will give another approach to this identity. First, we notice that
$$\int\frac{d^4k}{(2\pi)^4}\,\frac{1}{(k^2-m^2)^2}e^{ik\cdot\epsilon}=-i\frac{\partial}{\partial m^2}D_F(x)\big|_{x=\epsilon}$$
For space-like vector $\epsilon^2=-r^2<0$, we have
$$D_F(x)=\frac{m}{4\pi^2r}K_1(mr)$$
whose derivation refers to We... | https://physics.stackexchange.com |
177,262 | [
"https://dba.stackexchange.com/questions/177262",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/127510/"
] | I am using mssql and I would like to achieve this:
Have 1 database, 2 non-SA users. 1st user should be owner of database, 2nd one should have read permissions on some tables, read+write on others.
Tables for 2nd user are created by our application which uses 1st user.
Steps to what I do: <br/>
1) I execute script whi... | You've created the login for user1 and user2 to the master database not the database you want.
rearrange to:
<pre><code>CREATE LOGIN USER1
WITH PASSWORD = 'password';
GO
CREATE DATABASE my_database;
ALTER AUTHORIZATION ON DATABASE ::my_database TO USER1;
CREATE LOGIN USER2
WITH PASSWORD = 'password';
GO
USE my_data... | In my case, the issue was a typo.
I had written something like the following, and it took me about an hour to see the typo:
<pre class="lang-sql prettyprint-override"><code>CREATE USER [DOMAIN\DB_DatabaseName_Writers] FOR LOGIN [DOMAIN\DB_DatabaseName_Writers]
GO
CREATE USER [DOMAIN\DB_DatabaseName_Readers] FOR LOGIN [... | https://dba.stackexchange.com |
52,388 | [
"https://engineering.stackexchange.com/questions/52388",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/39178/"
] | To simplify the problem, I liken the problem to a ship approaching the shore and a device wants to collect the rope in such a way that the rope is neither stretched too much nor released to the extent that it falls into the water.
For this purpose, I thought that a motor with a ratchet should collect the rope at a high... | The "problem" is that you are solving a problem in the stationary regime, where dynamic effects are neglected.
You are thinking on the transient regime. And in any case, if you consider even the most basic damping for the set-up, it will very quickly converge to the stationary answer.
| Yes if you attach the bar to the ceiling and release it very suddenly, then what you assume will happen and the bar will start to vibrate.
You need to use stiffness tensor, mass tensor, and continuum mechanics. which is going to be a research project.
For a rough quick estimate, I would replace the bar with a trapezoid... | https://engineering.stackexchange.com |
6,845 | [
"https://mathoverflow.net/questions/6845",
"https://mathoverflow.net",
"https://mathoverflow.net/users/2082/"
] | A random walk matrix has largest eigenvalue 1 with multiplicty 1 - why?
Let $G$ be a non-directed, regular connected graph with degree $d$. Let $A$ be its random walk matrix, i.e. it's adjacency matrix, with each entry divided by $d$.
i) It is easy to observe that $A$ is symmetric, hence normal, that it has real eige... | Here is a simple proof.
Suppose $Ax = x$. Consider the entry of $x$ with the largest absolute value; lets use $x_k$ to denote this entry (e.g. if $x=[1,2,-4,3]^T$, then $k=3, x_k=-4$). Consider the $k$'th row of the equation $Ax=x$; it's telling you
that $x_k$ is a convex combination of the $x_i$'s of its neighbors $... | For large enough n, the matrix B = A + A<sup>2</sup> + ... + A<sup>n</sup> has positive entries since there's a path of length at most n connecting any two vertices. Thus by the Perron-Frobenius theorem B has a unique maximal eigenvalue and its multiplicity is 1.
Any eigenvector of A with eigenvalue λ is an ei... | https://mathoverflow.net |
391,250 | [
"https://physics.stackexchange.com/questions/391250",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/187502/"
] | I have a question about special relativity and Lorentz force which bugs me:
Consider an infinitely long, initially uncharged, wire (lying along the x-axis) resting in a inertial frame S. Now let's assume a current is flowing through the wire into the positive x-direction, this means that the electrons in the wire have... | Note that f(x) and g(x) are functions of x alone [not "x and t"].<BR>
f(x) is what the string looks like on a photo [taken at t=0]...<BR>
and you don't have access to other snapshots.<BR>
That is, "f" doesn't have information on how the string is moving.<BR>
<BR>
g(x) is what the velocity profile would look like at t=... | consider a wave on a rope, if you choose to define the height of a point on this wave at x, there will be two possible conditions for this wave. The two conditions are that the point may move either up or down, so you need to define the velocity in order to know the motion of the wave.
| https://physics.stackexchange.com |
195,645 | [
"https://mathoverflow.net/questions/195645",
"https://mathoverflow.net",
"https://mathoverflow.net/users/38290/"
] | I was wondering if there exists a Poisson Summation formula (like the one existing with primitive character) for imprimitive Dirichlet characters ?
For a primitive Dirichlet character $\chi$ we have:
$$ \sum\limits_{n=-\infty}^{\infty}\chi(n) f\bigg(\frac{n}{q}x\bigg) =\frac{K}{x} \sum\limits_{n=-\infty}^{\infty} \o... | The reason we can get that (twisted) Poisson summation formula in the first place is that in the primitive case you can interpolate the character to a smooth real function via Gauss sums.
In the imprimitive case this is not the case anymore, and you can't get a function nice enough to anything that resembles a Poisson... | Yes, of course.
Poisson summation formula has nothing to do with characters. If χ is any periodic function, all you need to do is to replace χ̅ by the discrete Fourier Transform of χ.
| https://mathoverflow.net |
383,785 | [
"https://stats.stackexchange.com/questions/383785",
"https://stats.stackexchange.com",
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] | <h2>X is Uniform <span class="math-container">$[-\theta,\theta], \theta>0$</span> what is the distribution of <span class="math-container">$Y=\frac{1}{x^{2}}$</span></h2>
So I've been working on some transformation questions; however, most of them have been one to one. I am a bit stuck on how to proceed with this q... | First, <span class="math-container">$G(0) = 0$</span>. For <span class="math-container">$y > 0$</span>, <span class="math-container">$P(x^{-2} \leq y) = P(x^2 \geq y^{-1}) = P(x \geq y^{-0.5}) + P(x \leq - y^{-0.5})$</span>.
You just missed one change from <span class="math-container">$\leq$</span> to <span class="... | Or just directly apply the change of variables formula, somewhat mechanically.
Pdf of <span class="math-container">$X$</span> is <span class="math-container">$$f_X(x)=\frac{1}{2\theta}\mathbf1_{|x|<\theta}\quad,\,\theta>0$$</span>
You are transforming <span class="math-container">$X\to Y$</span> such that <span... | https://stats.stackexchange.com |
43,448 | [
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] | A client's website was operating under a certain policy for membership sign ups for over a year. At the start of October 2012 the client implemented a new policy for sign ups that was supposed to encourage more registrations. This policy was applied site wide so there is no control group to compare against (except for ... | You are describing "intervention analysis" or "interrupted time series". It refers to estimating how much an intervention has changed a time series. (Intervention-analysis is even one of the tags here, so I am proposing an edit to add it to your question.)
Among other ways, it can be done using an autoregressive inte... | Yes, you can simply do a t-test, although you may very well have confounding variables that will affect how you want to go about this, and perhaps you may want to use an ANOVA with blocks.
One confounding variable that you may want to watch out for is effects over time. Does the site have more sign-ups in certain part... | https://stats.stackexchange.com |
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