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 |
|---|---|---|---|---|---|
226,520 | [
"https://softwareengineering.stackexchange.com/questions/226520",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/20304/"
] | I'm currently working on a php frontend. Specifically, the authentication process.
I'll spare everyone the exact details of the decision tree, but it includes a lot of checks and about half of them branch to a call to <code>do_logon()</code> which generates the login page and then calls <code>exit</code> to stop proce... | No, you should not <code>exit</code> or <code>die</code>. You can either have the <code>do_logon</code> end the script internally (bad practice) or allow the script to finish on it's own.
If you place this code in a function, then you can just return from the function. Allowing all the calls to propagate until the scr... | The general answer to your question is that you should Die() and not exit.
You are describing a place in your code that should never be reached and (regardless of what anyone thinks of this particular example) these situations do arise. The proper thing to do is to implement a Die() function (if you don't already hav... | https://softwareengineering.stackexchange.com |
96,447 | [
"https://security.stackexchange.com/questions/96447",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/83082/"
] | I have been thinking about ransomware and as I see it the password seems like it should be a problem for the attacker. I can see it going down one of two ways.
Either the password is included in the program and set prior to the attack in which case the password can be retrieved by the victim.
Or the password is se... | The attacker can use a form of public key cryptography. For each victim, the attacker creates a public/private key pair. The victim's files are encrypted using the public key, but need the private key to decrypt them again.
The private key is only disclosed to the victim once the ransom is paid.
| The ransomware creates a random password, sends it to the attacker, ciphers your files and forgets it. By the time you notice your files are encrypted, the password is no longer in your computer (it may be recoverable if you happen to spot the virus while it is still encrypting your files, as it will be in memory).
I ... | https://security.stackexchange.com |
146,179 | [
"https://chemistry.stackexchange.com/questions/146179",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/101509/"
] | Suppose we have the following reaction:
<span class="math-container">$$\ce{2A <=> B + C}\tag{1}$$</span>
which can be thought the sum of the following reactions:
<span class="math-container">$$\ce{A <=> B}\tag{2}$$</span>
<span class="math-container">$$\ce{A <=> C}\tag{3}$$</span>
with equilibrium con... | The equation
<span class="math-container">$$\ce{2A <=> B + C}$$</span>
implies a fixed stoichiometry between B and C. If the two separate reactions (2) and (3) were happening, the correct net equation would be
<span class="math-container">$$\ce{(x + y) A <=> x B + y C}$$</span>
Here is an example that would... | You have stated that the reaction:
<blockquote>
<span class="math-container">$$\ce{2A <=> B + C}\tag{1}$$</span>
[...] can be thought the sum of the following reactions:
<span class="math-container">$$\ce{A <=> B}\tag{2}$$</span>
<span class="math-container">$$\ce{A <=> C}\tag{3}$$</span>
</blockquote... | https://chemistry.stackexchange.com |
420,502 | [
"https://stats.stackexchange.com/questions/420502",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/234488/"
] | What is it mean by the statement
"X and Y explained a greater proportion of variance in Z than X alone "
More generally, what is it meant when the model "explains more variation" in the dependent variable -- certainly this is not equivalent to "this explains the variable" more?
Thank you for the insight into this b... | In a couple of words (the shorter the better!) when you add a variable to a model, if the added variable adds some explanatory power, then the addition increases the model fit (i.e. the capacity of the model as a whole of predicting the dependent variable in the sample where the model is estimated). However, bear in mi... | We have to be thinking about a model to answer your question so let's assume a linear model. For convenience, we'll use sums of squared deviations instead of variances; to translate for variances, divide through the sums of squares by <span class="math-container">$N - 1$</span>.
Let <span class="math-container">$Z = (... | https://stats.stackexchange.com |
5,101 | [
"https://computergraphics.stackexchange.com/questions/5101",
"https://computergraphics.stackexchange.com",
"https://computergraphics.stackexchange.com/users/6622/"
] | I understand that ambient light is light that occurs a result of light from a given source refecting off an infinite number of points in a scene, thereby illuminating all objects in the scene uniformly and explains why areas not directly illuminated by a light source in a scene aren't pitch black.
So I guess ambient l... | The formula you are seeking (and implying with the examples of a match and a lamp) is really a Radiosity formula - at which point we have to stop using the term "ambient light", as with Radiosity, everything (light source and surfaces of all scene objects including) is just energy, only converted to the monitor's RGB v... | Using an 'ambient light' term in your lighting calculations is an approximation of the indirect light reflected around the scene. Usually it's up to the artist to choose an appropriate value. There isn't really a formula, because the indirect light is dependent on many factors:
<ul>
<li>Light intensity</li>
<li>Light ... | https://computergraphics.stackexchange.com |
306,436 | [
"https://softwareengineering.stackexchange.com/questions/306436",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/65797/"
] | Simply put I'm new to the company, should I rather write advanced techniques with things like <code>template</code>s, <code>std</code> techniques..etc to make a first good impression and have my colleagues trust/be impressed at my work or should I be more concerned in writing more solid/based standard code for each cur... | <strong>Absolutely not.</strong>
If you joined my team and spent your whole time using more advanced techniques than were necessary for the task at hand, I would certainly be less than impressed. You'd be making it more difficult to read, understand and maintain the code … not only for your teammates, but also ... | <em>As a disclaimer, I'm interpreting "advanced" here as not like a basic class template for a data structure or a function template for a generic algorithm which inputs iterators. This hardly seems like showboating territory unless it's among a team of people who don't know how to use C++. I'm assuming things like, sa... | https://softwareengineering.stackexchange.com |
86,444 | [
"https://softwareengineering.stackexchange.com/questions/86444",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/28736/"
] | This is just a question to think about.
When you write technical documentation and programming comments, do you ever find yourself writing run-on sentences in order to be more precise?
Is packing more technical information into one sentence better than creating many little sentences each with a little bit of technica... | Not if I can help it :)
Think about it this way - what is the purpose of technical documents?
Right - to communicate something technical - and possibly quite involved/complex.
Now imagine you are listening to someone explain something to you that you are struggling to follow - they don't stop, they don't pause, info... | Unfortunately good writing skills appear to be rare among many technical people including programmers. The bonus is that with a little investment in improving your writing skills will make you stand out.
| https://softwareengineering.stackexchange.com |
112,162 | [
"https://stats.stackexchange.com/questions/112162",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/46128/"
] | Basic statistics courses often suggest using a normal distribution to estimate the mean of a population parameter when the sample size <em>n</em> is large (typically over 30 or 50). Student's T-distribution is used for smaller sample sizes to account for the uncertainty in the standard deviation of the sample. When sam... | Just to clarify on relation to the title, we aren't using the t-distribution to <em>estimate</em> the mean (in the sense of a point estimate at least), but to construct an interval for it.
<blockquote>
But why use an estimate when you can get your confidence interval exactly?
</blockquote>
It's a good question (as long... | It's a historical anachronism. There are many of them in statistics.
If you didn't have a computer, it was hard to use the t-distribution, and much easier to use a normal distribution. Once the sample size gets large, they two distributions become similar (how large is 'large' is another question).
| https://stats.stackexchange.com |
15,248 | [
"https://chemistry.stackexchange.com/questions/15248",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/6875/"
] | I think ionic compounds dissolve in just about any compound including nonpolar. My reasoning is this:
Neutral electric charge attracts both positive and negative (This I know from doing things with static electricity and putting it on a neutral surface).
Ionic compounds like strong acids and bases disassociate into i... | First, I think you have some misconceptions about electrical charge. There isn't neutral charge, it's either positive or negative, if it doesn't have either, it has no charge. Why are you seeing static charge interaction with neutral surfaces? It might be polarization, where a charged particle warps the electron cloud ... | <blockquote>
I think ionic compounds dissolve in just about any compound including nonpolar. My reasoning is this:
</blockquote>
Ionic compounds don't always dissolve in just about any compound. Consider sodium chloride. This <em>isn't</em> soluble in acetone.
<blockquote>
Neutral electric charge attracts both p... | https://chemistry.stackexchange.com |
253,029 | [
"https://physics.stackexchange.com/questions/253029",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/10236/"
] | Statistical mechanics allows us to consider an ensemble of systems, each of which consisting of only a single particle. Once we write the partition function for the system of one particle, we can easily derive all the thermodynamic quantities. One can accept that the internal energy computed from the partition function... | A canonical ensemble is a collection of weakly interacting systems, in thermal equilibrium with each other. The individual systems can be a single particle/molecule if the energy of interaction between the particles is negligible in comparison with their own (kinetic) energy. The energy of ensemble is then just the sum... | Pressure is defined as the rate of increase in internal energy to rate of decrease in volume, i.e.
$$P=-\frac{\partial U}{\partial V}$$
Assume a particle in a box, for example the classic infinite quantum potential well of width $L$. The quantized energy is
$$E_n=\frac{n^2h^2}{8mL^2}$$
In a 3D box this becomes
$$E_{... | https://physics.stackexchange.com |
137,122 | [
"https://electronics.stackexchange.com/questions/137122",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/10191/"
] | I am using a Microchip Bluetooth Pictail and a Sparkfun 3.3V USB-to-UART and a Arduino Uno (just for power-5V,gnd and 1 active high signal connected to 3.3V).
When I power the PicTail it outputs "CMD" to Realterm, but won't accept input (like a "H\n" for help). I see the Tx pin light up on the Sparkfun. The weird thin... | In the User Guide of the PicTail they say to jump JP1 to be in UART mode. I checked the schematic again and JP1 only works with the PIC motherboard is plugged in. JP1 is for holding the PicTail onboard PIC in reset. I hooked JP1 pin 2 to ground and it began working. The onboard PIC must have been holding onto the UART ... | This smacks of a grounds-not-tied-together issue. It looks like the USB-to-UART device has only 2 lines going to the Pictail board. I would presume those are just the UART Tx and Rx lines, and not ground.
If the grounds of all three boards are not tied together, digital signals between the boards will be interpreted i... | https://electronics.stackexchange.com |
374,194 | [
"https://physics.stackexchange.com/questions/374194",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/150854/"
] | At very low pressure gases become conducting in nature, as evident in cathode rat experiment. But upon still decreasing the pressure the electric discharge stops. Why does this happen?
| In order to have a discharge, you need to ionise matter (gas) so that the motion of the ionized matter (electrons and cations) carries the discharge current. Usually, the accelerated electrons collide with neutral atoms/molecules to produce even more ionised matter. If the gas density becomes too low between cathode ... | Because there is no free electron or ion created in the system. ... It is because when the gas is at very low pressure positive charged ions are not available to eject out the electron from the cathode hence the discharge current stops.No, vacuum cannot conduct electricity.
| https://physics.stackexchange.com |
429,026 | [
"https://physics.stackexchange.com/questions/429026",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/190849/"
] | Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces. This principle is derived from pascal's law.
What I find unintuitive about the principle is that for objects with ... | <blockquote>
for objects with a higher density than water, shouldn't the pressure exerted against it by water also be larger?
</blockquote>
No. Pressure is a function of state. For water at a given temperature and a given density, there is a pressure which can be found by the equation of state for water. Whether the... | <blockquote>
My reasoning is that since the weight of the object is >larger, the contact force exerted by the water below it >should also be greater.
</blockquote>
You are right - that's why the object is sinking, by pushing the water under it to the sides, where the pressure is lower.
Pascal's law, which states th... | https://physics.stackexchange.com |
140,293 | [
"https://chemistry.stackexchange.com/questions/140293",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/98911/"
] | After combining two solutions, a direction in a 1970s British chemistry book says to wash the new solution with a mixture of baking soda, table salt, and water. Then it says to dry it with anhydrous magnesium sulfate.
What does washing and drying mean? Do the chemicals get physically mixed together? Doesn't that contam... | This is standard for purifying substances.
To wash means to add your product solution to an aqueous solution (or just water, but frequently a saturated solution) to a separatory funnel. After shaking, you drain the lower layer (which is usually aqueous). This process removes water soluble impurities. This is frequently... | The solvent of this experiment should be non polar, and may be a hydrocarbon, or a chlorinated hydrocarbon. This organic phase may contain as impurities some acids and other polar substances soluble in water, that should be eliminated. This liquid is then mixed with an aqueous solution of soda <span class="math-contain... | https://chemistry.stackexchange.com |
527,508 | [
"https://math.stackexchange.com/questions/527508",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/99833/"
] | A polynomial with integer coefficients is an expression of the form:
$f(x) = a_n x^n + a_{n-1} x^{n-1} + \cdots + a_1 x + a_0$
where $a_n$, $a_{n-1}, \ldots, a_1, a_0$ are integers and $a_n$ is not equal to $0$.
a zero of the polynomial is a $c \in \mathbb{R}$ such that $f(c)=0$
A real number is said to be algebraic... | The rational number $5/7$ is a zero of the polynomial $7x+(-5)$. We have $n=1$, $a_1=7$, $a_0=-5$.
So try showing that works with <em>every</em> rational number.
| <strong>Hint:</strong> The polynomials you need will have very simple forms.
<strong>Bigger hint:</strong>
<blockquote class="spoiler">
In particular, they will all have exactly two terms.
</blockquote>
| https://math.stackexchange.com |
74,499 | [
"https://electronics.stackexchange.com/questions/74499",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/25259/"
] | I'm pulling 5V from USB for testing an IC. Should I put a capacitor in there to filter the power supply, or will it already be steady coming from the laptop?
I don't have access to an oscilloscope, so I can't check how noisy the USB voltage is.
| Yes, put a cap in.
You don't say what the IC is, but you should have at the very least a decoupling cap across the power rail near the power pins of the IC, e.g. a 100nF ceramic is a typical value (or 1uF, 2.2uF, etc are cheap/common nowadays)<br>
Depending on the IC and if there are other components present, you ma... | Putting a capacitor on the 5 Volt line is a good idea even if the source supply is well-filtered. This meets several purposes:
<ul>
<li>Providing a supply reservoir to the device under test: varying current draw at the device will result in supply voltage variation without such a reservoir capacitor. </li>
<li>Filteri... | https://electronics.stackexchange.com |
129,617 | [
"https://cs.stackexchange.com/questions/129617",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/123911/"
] | I have a large number of equivalences which look like:
<span class="math-container">$(a \leq 0.54 \wedge b \geq 0.12) \vee (c \gt 0.98)$</span> <span class="math-container">$\Leftrightarrow$</span> <span class="math-container">$(x \leq 0.25) \vee (x \gt 0.91 \wedge y \geq 0.01)$</span>
This is just an example. In gener... | Yes, you could solve this with a SMT solver that supports linear real arithmetic. However SMT supports more general inequalities where you can have linear sums of variables (e.g., <span class="math-container">$2a+3x \le 5.7$</span>) instead of simple comparisons between a single variable and a constant (e.g., <span cl... | In your case, the simplest solution may be to use SAT.
Your first clause includes <span class="math-container">$x \le 0.25$</span> and <span class="math-container">$x > 0.91$</span>. This means that there are five regions of interest for the variable <span class="math-container">$x$</span>, which we identify with bo... | https://cs.stackexchange.com |
48,750 | [
"https://softwareengineering.stackexchange.com/questions/48750",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/13371/"
] | <em>Back story:</em>
My best friend is a self-taught coder for a community art site, written in PHP. Some time ago he mentioned he wanted to make the source code of the site public, to which my response was total horror - surely it was going to be full of security holes waiting to be found, and it was going to lead to... | It's fine!
If you're planning to dump out your database that contains private information about anything, I urge you to think again. In terms of security, if it's obvious that you haven't sanitised your user input, well... I guess you'll learn that lesson one way or another. Apart from the obvious security loopholes (... | Your thinking on the security is exactly backward. You should really only trust the code to be secure if it <em>has</em> been published and examined by at least a few security experts. Putting your code on github (or whatever) is much more likely to help security than hurt it. In fairness, getting security right -- or ... | https://softwareengineering.stackexchange.com |
55,558 | [
"https://datascience.stackexchange.com/questions/55558",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/77192/"
] | I have 2 column in data frame, X and Y. And I have some string values stored in text, which I want to put in X, Y as shown in the example.
Example :
<pre><code>text=9 10 13 110 14 16
12 1 6 1 1 2
</code></pre>
<pre><code>X Y
9 12
10 1
13 6
110 1
14 1
16 2
</code></pre>
| If you are looking to hard-code it for only 2 columns, this can be achieved as follows:
<pre><code>import pandas as pd
df = pd.DataFrame()
text = '9 10 13 110 14 16 12 1 6 1 1 2'
text = text.split()
df['X'] = text[:int(len(text)/2)]
df['Y'] = text[int(len(text)/2):]
</code></pre>
| I will assume your text is in two strings like this:
<pre><code>In [1]: import pandas as pd
In [2]: text1 = "9 10 13 110 14 16"
In [3]: text2 = "12 1 6 1 1 2"
</code></pre>... | https://datascience.stackexchange.com |
7,602 | [
"https://mechanics.stackexchange.com/questions/7602",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/3960/"
] | I went and had my 06 Cobalt checked out because the dreeded check engine light came one and I got the P0420 threshold bank 1 code. My mechanic, who has been a good friend of mine for quite some time, told me I needed to replace my B1S1 sensor from what the diagnostics showed. He even showed me on the machine it was not... | Sounds like a problem with a module. There is a feature in most BMW's that rolls down all the windows when the unlock button is held but if you are sure you didn't do that then it could be a module. (Note: some BMWs relock if no doors are open after a specified time period).
Since you also had incorrect rear light w... | BMW bulb holders are well known to overheat and deteriorate from the heat. Remove the bulb holders, one at a time and check for discolouration. Replace them if so.
| https://mechanics.stackexchange.com |
426,661 | [
"https://math.stackexchange.com/questions/426661",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/63554/"
] | Can someone please explain these answers? I have reviewed the slides and read about properties of equality but I still don't understand how to apply it to these sets.
For each the following relations on the set of integers list all that apply
(Reflexive, Symmetric, Antisymmetric, Transitive, or none):
$R1 = \{(a, b... | Let's review what each property means. Your question deals with relations on the integers; so, let's say that we are working with a relation $R\subseteq\mathbb{Z}\times\mathbb{Z}$.
<h2>Symmetric:</h2>
$R$ is called <em>symmetric</em> if for all $(a,b)\in R$, we also have $(b, a)\in R$.
For instance, $R_1$ is symme... | That’s potentially $6\cdot 4=24$ properties to check, so let me just do a sample. I’ll start with $R_1$.
<ul>
<li><strong>Reflexive?</strong> In order for $R_1$ to be reflexive, it has to be true that if $n$ is any integer, then $\langle n,n\rangle\in R_1$. This means that $n\ne n$. Obviously that’s not true for every... | https://math.stackexchange.com |
94,770 | [
"https://security.stackexchange.com/questions/94770",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/81634/"
] | I don't particularly want to implement Captcha on my login form for a website. But I've got a block mechanism already in place.
What's the best way to protect from Brute Force attacks?
Here's what I was thinking:
<ol>
<li>Implement a lockout, so after 30 failed logins I block the customer account. 30 is an arbitrar... | As others have mentioned already, currently the recommended way of implementing lockout is to require a Captcha only after a few failed login attempts. This method is good from both a security and usability standpoint - the Captcha is very effective on stopping automated attacks, but only requiring it after a few faile... | How are you planning on implementing the lockout? Is is per username or network address. If you consider the first option bear in mind that the attacker can launch a denial of service attack for any number of valid users(he can simply brute force a number of (very likely) invalid passwords for each valid username and t... | https://security.stackexchange.com |
518,665 | [
"https://physics.stackexchange.com/questions/518665",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/236133/"
] | Let a point charge <span class="math-container">$+Q$</span> is placed in center of hollow spherical conductor of inner radius <span class="math-container">$a$</span> and outer surface <span class="math-container">$b$</span>. Then the charge on the inner surface of radius <span class="math-container">$a$</span> is <span... | tl;dr: thats not how conductors behave.
I am guessing that your doubt stems from the following notion: oppositely charged surfaces when connected with a conductor equilibrate.
So the induced charges, being connected by a conductor's bulk, should merge and vanish!
After all, initially, when there wasn't any charg... | The positive charge at the center would like its outgoing field to exist in the conductor, but any field in the conductor will cause charges to move until there is no field in the conductor. The charge distribution on the surfaces of the conductor is what is required to neutralize the field from the inner charge.
| https://physics.stackexchange.com |
59,497 | [
"https://biology.stackexchange.com/questions/59497",
"https://biology.stackexchange.com",
"https://biology.stackexchange.com/users/30284/"
] | For a lab course we have been assigned to "remove a stop codon, using mutagenesis, that is in the middle of a gene in order for the full gene to be expressed. This will then fluoresce."
To do this we are considering site directed mutagenesis, which can replace the stop codon, however is this a good method? Are there a... | For directly outputting a sorted bam file you can use the following:
<pre><code>bwa mem genome.fa reads.fastq | samtools sort -o output.bam -
</code></pre>
Optionally using multiple threads:
<pre><code>bwa mem -t 8 genome.fa reads.fastq | samtools sort -@8 -o output.bam -
</code></pre>
| Found the solution. You just need to pipe the output from <code>bwa mem</code> into <code>samtools view</code> like so
<pre><code>bwa mem ref.fa in.fq | samtools view -bS - > out.bam
</code></pre>
The <code>-</code> in samtools view tells it to read from <code>stdin</code>.
| https://biology.stackexchange.com |
199,050 | [
"https://mathoverflow.net/questions/199050",
"https://mathoverflow.net",
"https://mathoverflow.net/users/68805/"
] | Let $K$ be a local field, e.g. $\mathbb{Q}_p$ or $\mathbb{F}_p((t))$. Let $G$ be a connected reductive group over $K$. Is it true that $G$ is already defined over a global field? More precisely, does there exist a global field $F$, a place $v$ in $F$ with $F_v\simeq K$ and a connected reductive group $\tilde{G}$ over $... | Pick a global field $E$ and finite place $w$ with $E_w=K$. The fraction field $k$ over $E$ of the henselization of the "algebraic" local ring at $w$ is the direct limit of finite separable sub extensions $F/E$ for which the place $v$ on $F$ from the valuation on $k$ satisfies $F_v=K$. Thus, it suffices to "algebraize" ... | I can't answer your question completely, but this extended comment may be helpful.
Probably the answer will be "yes", judging at least from the old classification by Tits summarized in the proceedings of the 1965 AMS Summer Institute at Boulder (published by AMS in 1966 as vol. 9 in their series <em>Proc. of Symposia i... | https://mathoverflow.net |
139,109 | [
"https://mathoverflow.net/questions/139109",
"https://mathoverflow.net",
"https://mathoverflow.net/users/16503/"
] | We're interested in recursive predicates $P(n)$ with RE range $R$ and non-RE complement $R^\prime$. For various $n \in R^\prime$ we may be able to prove that $n \in R^\prime$. For instance, if $P$ is the halting problem, then we can build a non-halting algorithm, figure out its index $n$, and we then know that $n \in... | This clearly depends on what you mean by "provably."
Under one reasonable interpretation, the answer is very much "yes." The set $S_T$ of theorems of a (consistent, recursively axiomatizable, extending $PA$) theory $T$ is r.e., but $T$ cannot prove that the complement of $S_T$ is nonempty (Goedel's Theorem), much less... | Noah has given an excellent answer. Here is another way to look at such an answer.
<strong>Theorem.</strong> For EVERY computably enumerable set $R$ and for every computably axiomatizable consistent theory $T$, there is a Turing machine that enumerates $R$, such that $T$ does not prove any assertion of the form $n\i... | https://mathoverflow.net |
2,086,628 | [
"https://math.stackexchange.com/questions/2086628",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/-1/"
] | I have found two different definitions and I wonder if they are equivalent:
Choose $(M_i)_{i\in I}$ a family of submodules of an $R$-Module $M$.
<ol>
<li>The sum of the $M_i$ over all $i\in I$ is derect.</li>
<li>For every finite subset $F\subset I$ the sum of all $M_i$ with $i\in F$ is direct.</li>
</ol>
So, is th... | Let $f:(\Bbb Q, +)\to (\Bbb Q^+,\cdot)$ be an isomorphism. Let $a=f(1)$. Then $f(1/n)=a^{1/n}$ for every natural $n$. Then the $n$th root of $a$ is rational for every $n$. This implies $f(1)=1$. But then $f(2)=f(1+1)=1\cdot 1=1$ and $f$ is not injective.
| The equation $x+x=a$ has a solution for all $a$ for the additive group, but the equation (written multiplicatively) $x\cdot x=a'$ in $\mathbb{Q}^{+}$ does not. Hence the groups cannot be isomorphic.
| https://math.stackexchange.com |
948,554 | [
"https://math.stackexchange.com/questions/948554",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/179232/"
] | How can I proof using math induction that
$$\overline{z^n} =\overline{z}^n$$
where $z$ is a complex number, $n$ is a positive whole number.
| Start with the base case.
Suppose $n=1$. Because $z^1 = z$ for all $z \in \mathbb{C}$,
$$\overline{z^1} = \overline{z} = \overline{z}^1$$
and we're done.
Now, for our inductive step, suppose this is true for $n$. We want to show it is also true for $n+1$. But before we can do this, I claim that, for all $x,y \in \m... | Our base case is $n=1$. $(z^1)^* = z^* = (z^*)^1$ so our base case holds.
Suppose then that for $n$, $(z^n)^* = (z^*)^n$. We wish to show that $(z^{n+1})^* = (z^*)^{n+1}$. Note that
$$(z^{n+1})^* = (z^nz)^* = (z^n)^*z^*.$$
Can you take it from here?
| https://math.stackexchange.com |
139,670 | [
"https://mathoverflow.net/questions/139670",
"https://mathoverflow.net",
"https://mathoverflow.net/users/29992/"
] | Is it true that a general curve of genus 3 is a plane section of an appropriate Kummer surface in $\mathbb P^3$? By Kummer surface I mean image of a principally polarized Abelian surface w.r.t. the map defined by the complete linear system $|2\Theta|$, where $\Theta$ is a theta divisor of polarization.
This assertion ... | Let $C$ be a non hyperelliptic curve of genus 3, let $f\colon C'\to C$ be an e'tale double cover and let $A$ be the Prym variety of $f$. Then $A$ is a principally polarized surface and the Abel-Prym map embeds $C'$ in $A$ as an element of $|2\Theta|$. Multiplication by $-1$ on $A$ restricts on $C'$ to the involution i... | The paper by Alessandro Verra (Math. Ann. 276 (1987), no. 3, 433–448) gives a very precise description of all fibers of the Prym map $\mathcal{R}_3\to \mathcal{A}_2$ from which the answer to your question can be obtained.
Although your count of constants luckily works in this case, it does not work in general for no... | https://mathoverflow.net |
126,852 | [
"https://dba.stackexchange.com/questions/126852",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/21763/"
] | Could somebody tell what is wrong with obvious query below:
<pre><code>db2 => select next value for schema_name.sequence_name;
</code></pre>
As a result I'm getting:
<pre><code>SQL0104N An unexpected token "END-OF-STATEMENT" was found following
"schema_name.sequence_name". Expected tokens may include: "<t... | You need to select from something. Another option is:
<pre><code>db2 => values next value for schema_name.sequence_name;
</code></pre>
As you noted you can also use <code>SYSIBM.SYSDUMMY1</code> or create a virtual table:
<pre><code>db2 => select next value for schema_name.sequence_name from ( values 1 );
</c... | <code>db2 => select next value for schema_name.sequence_name from SYSIBM.SYSDUMMY1;</code>
did the trick
| https://dba.stackexchange.com |
165,384 | [
"https://mathoverflow.net/questions/165384",
"https://mathoverflow.net",
"https://mathoverflow.net/users/15482/"
] | Suppose we have an algebraic group $G$ defined over a field $k$. Suppose we consider the fraction field of $k[G]$. Is it possible to get a situation where this field is not a separable extension of $k$? An example would be very helpful.
| The answer depends on what you mean by "algebraic group". If you mean algebraic group in the sense of Borel/Humphreys/Springer, the field of fractions of $k[G]$ is always separably generated, more-or-less by definition. If you mean algebraic group scheme, which must be integral for the question to make sense, then it d... | Yes, this is possible. (Notice that your question implicitly requires $k[G]$ to be an integral domain, otherwise you cannot take its fraction field.)
Let $k$ be a non-perfect field of characteristic $p$, and let $a \in k \setminus k^p$. Consider the
algebraic group defined as a functor from $k$-algebras to groups via... | https://mathoverflow.net |
95,437 | [
"https://mathoverflow.net/questions/95437",
"https://mathoverflow.net",
"https://mathoverflow.net/users/23290/"
] | Consider the algorithm that goes over all proofs in peano arithmetic. Allegedly, for a given multivariate polynomial equation we should find a proof or disproof of existence of an integer solution. Therefore, given the negaative solution of Hilbert's 10th problem, there should be a polynomial for which we could neither... | Hi Daniel.
The point with Hilbert's 10th problem is that diophantine equations are complex enough to encode Turing machines and other complicated stuff that has some kind of no-can-do-theorem. In particular: To each Turing machine there is a polynomial $p\in\mathbb{Z}[X_1,\ldots,X_n]$ such that $p$ has a solution in $... | Yes, your description of the situation is essentially correct. The way it can happen is this.
On the one hand, if a given diophantine equation does have a solution in the integers, then it will be easy to prove in PA that this solution is indeed a solution, since the proof amounts to checking that that particular sol... | https://mathoverflow.net |
295,232 | [
"https://physics.stackexchange.com/questions/295232",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/57218/"
] | I am learning about inductors and capacitors and we derived the energy stored on a capacitor to be 50% of that delivered by the battery. We did this considering a circuit of a capacitor connected to a battery and resistor in series, to not encounter the problem of an infinite initial current if we assumed there was no ... | When you try to force current through a superconducting inductor, the change of current will generate a back emf that will limit how much current can flow. The value of this back e.m.f. is $-L\frac{dI}{dt}$, and the work done by the current is the product of the current and the back emf. If the back emf is exactly equa... | <blockquote>
however I can't think of the fundamental reason as to why it is
completely impossible to charge a capacitor with anything but 50% of
the battery energy whereas an inductor could theoretically store 100%.
</blockquote>
Essentially, to charge a capacitor with <em>finite</em> current from a voltage sou... | https://physics.stackexchange.com |
8,814 | [
"https://quantumcomputing.stackexchange.com/questions/8814",
"https://quantumcomputing.stackexchange.com",
"https://quantumcomputing.stackexchange.com/users/8321/"
] | In Nielsen and Chuang Quantum Computation and Quantum Information book section 2.2.6, a POVM of three elements are used to measure a single qubit in order to know for sure whether the state is <span class="math-container">$|0\rangle$</span> or <span class="math-container">$|+\rangle$</span> if the first two measurement... | Three outcomes amounts to more than one bit if the outcomes are all deterministic, and give you information about the original qubit.
But suppose I have a coin (that is either heads or tails). I roll a dice, and if it comes 1 through 5, I tell you "H" or "T", depending on what the coin is. If it comes up 6, I tell yo... | Thanks Peter for the clarification about information vs. outcomes. I accept his answer to acknowledge that, and want to add the possible construction of such measurement.
In the same book section 2.2.8, a general method is described. In this case, one can add two qubits prepared as <span class="math-container">$|00\r... | https://quantumcomputing.stackexchange.com |
299,013 | [
"https://physics.stackexchange.com/questions/299013",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/131639/"
] | If we have an object attached to a spring, and the net force on that object is $-kx,$ how do we prove that its motion (if you move the object to $x\ne 0$) is sinusoidal? I know that you must integrate from $ma=-kx,$ but I don't see how (because you must integrate with respect to time).
| Here is a rigorous derivation of the sinusoidal solution to your mass-spring system. I'm writing this from memory so if someone could take a second look at it that would be great.
The simple harmonic oscillator model for an ideal spring-mass system is one of the most straightforward examples of a differential equation... | $ma=-kx$ is a differential equation that is best solved by inspection. That means, knowing that $a=\ddot x$, you think through your calc 2 and try to remember a function whose second derivative is the original function with a negative sign. "That's it!", you exclaim. "Sin and cos fit that description exactly!"
| https://physics.stackexchange.com |
544,547 | [
"https://physics.stackexchange.com/questions/544547",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/207730/"
] | The gravitational potential energy of a mass <span class="math-container">$x$</span> meters away from the center of the Earth is calculated from the formula <span class="math-container">$$G\frac {Mm}{x}$$</span> where <span class="math-container">$M$</span> is the mass of the Earth and <span class="math-container">$m$<... | Statistically, the fluctuations from the mean scales as <span class="math-container">$1/\sqrt{N}$</span>. So as long as the experiment is within this variance, you can be certain that nothing exotic is occurring.
| It matters not because a mole is <span class="math-container">$6.02214076×10^{23}$</span>, being the number of particles in a small number of grams of the substance. In any normal amount of the substance <span class="math-container">$N$</span> is far larger than needed for the validity of statistical analysis.
| https://physics.stackexchange.com |
20,386 | [
"https://security.stackexchange.com/questions/20386",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/485/"
] | Had this question at Owasp Scotland this evening, and didn't get useful answers.
Is there too much specialisation in security now which means that enterprise architects can't know enough to delivery security as part of their day job?
| My first observation is that security is everybody's responsibility. No one person is going to be able to police an entire organization's codebase. Security design and enterprise design are inherently different in purpose and goal, but the two should interact closely for best result. An enterprise architect's goal i... | To post a contrary view to AJ's excellent answer:
At a large corporation, architecture may end up being the responsibility of multiple teams in different departments, countries, regions etc. in order to be performant for each region, whereas enterprise security is likely to be managed from a global perspective to redu... | https://security.stackexchange.com |
212,684 | [
"https://dba.stackexchange.com/questions/212684",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/156668/"
] | I am working on multiple projects but the back-end will remain the same. I have a different server for auth, data, etc. and one database to store all the details.
If one projects are creating any data then only that project can access that data and others project shouldn't access that.
For example, if users saving so... | The best way to evaluate performance is by measuring it- you are the only person that can evaluate that on the real application, or, much better, on a staging environment with a copy of the traffic or an emulation of such.
Hardware, other code running, throughput, how slow are those new queries, amount of data you hav... | It does not matter.
A valid login is a tiny percentage of the total work a user does with the system, correct? So, if that 'tiny' percentage grows, it is still a 'small' impact.
Meanwhile, who cares what happens with the hacker.
As for the overhead, it will be minor.
| https://dba.stackexchange.com |
412,855 | [
"https://physics.stackexchange.com/questions/412855",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/195466/"
] | My class went over magnetism and electricity, and my professor repeatedly mentioned how the field moves from north to south, and he would say "they" and "it." I wasn't sure if he meant that the field itself was moving, or particles within the field were moving.
If my professor was referring to the field, then what doe... | It seems that the way he was describing it is confusing you. First off, let's just clarify the assumption that we are dealing with the magnetic field from a fixed source (ie a magnet). Then:
<ul>
<li>As you correctly stated, the magnetic field is stationary and is just a visual representation of how the magnetic field... | Your confusion is probably brought about by history and the use of the English language.
Magnetic field lines (lines of force) are used as a visual aid and were very important in the development of what we now call <em>Electromagnetism</em>.<br>
These lines have a number of properties one of which is that they start... | https://physics.stackexchange.com |
206,401 | [
"https://mathoverflow.net/questions/206401",
"https://mathoverflow.net",
"https://mathoverflow.net/users/70593/"
] | A couple of months ago, i saw a construction, that somehow looks like the construction of the tautological section of the pullback of a vector bundle to its total space, i am trying to piece it together, hope that somebody can help me:
Let $X$ be a projective scheme, say a surface over $\mathbb{C}$, let $S=Spec(R)$ be... | What you have is the fiber diagram.
$$
\begin{array}[c]{ccc}
X\times T & {\stackrel{\beta}{\rightarrow}} & X\times S \\
{\scriptstyle \delta} \downarrow & & \downarrow\scriptstyle{\pi}\\
T & {\stackrel{\alpha}{\rightarrow}} & S
\end{array}
$$
Now, there is a natural morphism
$\alpha^* V = ... | Anton has already answered, but here's a (very) slightly different explanation: for any locally free sheaf $E$ of finite rank on a scheme $X$, the 'geometric' vector bundle $V=\underline{\mathrm{Spec}}_{X}(\mathrm{Sym}(E^\vee))$ has the following functorial description: for a scheme $f\colon T\to X$ over $X$, the set $... | https://mathoverflow.net |
3,537,924 | [
"https://math.stackexchange.com/questions/3537924",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/746617/"
] | What is <span class="math-container">$A\cap(A\cup B)'$</span>?
I am not sure how to solve these using Venn diagrams. I tried de Morgan, but I am not sure, please clarify.
| We spend a lot of time in real analysis telling students that a set being not open does not mean it is necessarily closed, and a set being not closed does not mean it is necessarily open. But we can have metric spaces which are door spaces, that is every set is either open or closed (but possibly both). Consider for ex... | <ul>
<li>You may have sets which are both closed and open but which are neither <span class="math-container">$\emptyset$</span> nor the whole space.</li>
<li>You may have Cauchy sequences which do not converge.</li>
<li>You may have uncountable sets such that the distance between any two distinct points is greater than... | https://math.stackexchange.com |
21,831 | [
"https://softwareengineering.stackexchange.com/questions/21831",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/8474/"
] | I believe it is. Why?
<ol>
<li>I've encountered many Software Engineers who believe they are somehow superior to QA engineers. I think it may help quench this belief if they do the job of a QA engineer for some time, and realize that it is a unique and valuable skill-set of its own.</li>
<li>The better a Software En... | <blockquote>
1. I've encountered many Software Engineers who believe they are somehow superior to QA engineers. I think it may help quench this belief if they do the job of a QA engineer for some time, and realize that it is a unique and valuable skill-set of its own.
</blockquote>
A good software engineering has a ... | Making programmers accountable for their code and requiring them to fix their own bugs can take care of this. That and a loss of bonus and/or job.
Not that this experience wouldn't help, but how far can you go with this line of thinking? Technical Support, Sales, Beta User, scrub the toilets (that would be a humbling... | https://softwareengineering.stackexchange.com |
154,598 | [
"https://stats.stackexchange.com/questions/154598",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/78404/"
] | I have a set of lines (y = numbers between 1 and 100, x= discrete) that I am trying to cluster to group similarly-shaped profiles. I have found that the profiles seem to cluster the cleanest when only passing a smaller subset of the total x values to the k means function. Is this a valid approach? Can anyone point m... | There are a couple of basic strategies to use with data like this. You can treat each point as a measurement on a different dimension, or you can fit models to each row / set of observations, and cluster the parameters of those models.
Here is an example with your data:
<pre class="lang-r prettyprint-override"... | Clustering will give good results when using significant data. What I mean is, if you have two random columns, you might not want to include them in your clustering algorithm because it would bring useless noise.
Clustering is actually all about feature selection (for a fixed clustering algorithm, e.g. K-means, EM...... | https://stats.stackexchange.com |
3,315,376 | [
"https://math.stackexchange.com/questions/3315376",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/87430/"
] | <blockquote>
If <span class="math-container">$$7^{\log_7(x^2-4x+5)}=x-1$$</span> then <span class="math-container">$x$</span> may have values...
</blockquote>
My attempt: <span class="math-container">$$x^2-4x+5=x-1$$</span>
So, <span class="math-container">$$x^2-5x+6=0$$</span>
So, <span class="math-container">$... | The tag says "complex numbers". In complex numbers you do not have any restriction that <span class="math-container">$x^2 - 4x +5$</span> must be positive. It could be negative or even non-real. But it can't be <span class="math-container">$0$</span>.
so your only restriction is that <span class="math-container">$x... | Note that <span class="math-container">$$x^2-4x+5 = (x-2)^2 +1 >0 $$</span> for all x, so there is no problem with logarithm and we have<br>
<span class="math-container">$$7^{log_7(x^2-4x+5)}=x^2-4x+5$$</span>
Therefore <span class="math-container">$$ 7^{log_7(x^2-4x+5)}=x-1 \iff x^2-5x+6=0$$</span>
Thus the solu... | https://math.stackexchange.com |
423,765 | [
"https://softwareengineering.stackexchange.com/questions/423765",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/353791/"
] | I know an empty method without any good reason is a code smell, but it can be required for constructors.
What would be a good way to write an empty constructor among the following?
<pre><code>class A
{
private int a;
public A(int v)
{
a = v;
}
}
class B : A
{
// 1
public B(int v) : b... | This is how I do it:
<pre><code> public B(int v)
: base(v)
{
// Empty
}
</code></pre>
Motivation is that I want to be explicit on the fact that I intend this to be an empty code block. When I come back to this code some time in the future, I'd know that it is not that I forgot to write the co... | If the class won't be used by third parties and you don't need an overloaded constructor, don't write an empty constructor.
But...
Imagine you already shipped the product, and third parties use your class. A few months later there's a new requirement that makes you add a constructor with an argument.
Now, by doing so, ... | https://softwareengineering.stackexchange.com |
250,045 | [
"https://stats.stackexchange.com/questions/250045",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/141406/"
] | I'm looking at the bivariate relationships among a set of time-series data that have the same units. I have computed the covariance matrix and am working on interpreting it. My hunch is that it would make sense to take the square root of the off-diagonals, yielding a result in the same units as the data, just like conv... | Covariance matrices are positive semi-definite or positive definite (bundle both terms under "positive")
A matrix $V$ is positive if and only if there exists a positive matrix $C$ such that
$$V = CC$$
If $V$ is positive definite, so will be $C$. $C$ is unique.
$C$ is called "the square root of $V$", and it can be ... | I think it might be simpler than all that. In the case of normally distributed data, the <em>standard deviation</em> is the square root of the 2nd central moment of a distribution. The 2nd central moment is sometimes called the <em>variance</em>. Thus, for nomral variates, the variance is the square of the standard dev... | https://stats.stackexchange.com |
80,396 | [
"https://mechanics.stackexchange.com/questions/80396",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/60937/"
] | I have a Subaru Forester 2011. Yesterday I noticed passenger rear wheel is extremely hot and has a burnt smell, and sent the car to my mechanic. Today he told me he did not find anything wrong with the calipers and the pistons move well. The only thing he suspects is the brake fluid is dirty and need to be replaced. Ho... | You can always go get a 2nd opinion. In your case, though, if your caliper was stuck (or sticking) and caused the brakes to overheat as you suggested, it is completely within reason the excess heat/wear presented to the rotor has caused it to fail (or become out of its tolerance range). This would mean it needed to be ... | there are several issues to this problem.it can be driving style,sticking caliper pins,caliper not fully releasing,restricted brake hose and if your subaru has an electronic parking brake that is bad.also in some cases a brake pad can get jammed in crooked and wedge itself against the rotor.
| https://mechanics.stackexchange.com |
387,225 | [
"https://softwareengineering.stackexchange.com/questions/387225",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/325783/"
] | For the most part, I am able to distinguish between functional and non-functional requirements, but at times it is not clear for me.
For example, the following are non-functional but they seem functional to me:
<pre><code>The software must use SSL encryption for transmissions
</code></pre>
Or
<pre><code>The softwar... | Functional requirements describe the functionality that a system must offer to its users. All the other requirements are non-functional requirements.
With that in mind, you can ask yourself, if, for example, the requirement for storing configurations in an XML file is not satisfied (for example, the configurations are... | A common heuristic is if they end in <em>-ility</em>: Availability, flexibility, changeability, maintainability, adaptability etc.,
It’s a “non-functional” requirement (NFRs) - your system will still function without it but not as effectively.
Think scalability: Twitter still provides functionality if it’s running o... | https://softwareengineering.stackexchange.com |
52,077 | [
"https://chemistry.stackexchange.com/questions/52077",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/2558/"
] | What is a simple chemical test to tell the difference between a tertiary alcohol (e.g. 2-methylpropan-2-ol) and an ether (specifically diethylether/ethoxyethane)?
Neither of them can be oxidised by reagents such as potassium dichromate, Tollens reagent or fehlings reagent.
I came up with a test in which a less than s... | As mentioned in the comments, using Lucas' Reagent is the best option in this case because you're dealing with a tertiary alcohol vs an ether, but let's consider your proposal as well.
In principle, it should work because an ether will not react with ethanoic acid whereas an alcohol would. However, the formation of an... | Diethyl ether is minimally soluble in water (6 grams per 100), but t-butyl alcohol is completely miscible with water, according to Wikipedia.
Selecting between these two compounds can be made by mixing 5 mL of H2O with 5 mL of the unknown. A single phase means t-butanol; two phases means diethyl ether.
| https://chemistry.stackexchange.com |
3,212,102 | [
"https://math.stackexchange.com/questions/3212102",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/460595/"
] | <strong>The Problem:</strong>
An urn contains 3 red and 4 black balls and another contains 4 red and 5 black.
A random ball is chosen from the first urn and is inserted into the second urn.
After this a random ball is chosen from the second urn.
Consider the events:
<span class="math-container">$A$</span> : "first... | The issue that you raised is a legitimate one. The calculation leading to <span class="math-container">$\frac12$</span> in your question (and the calculations in both of the answers available as I write this) use the assumption that, when a ball is drawn from an urn, each of the balls in that urn is equally likely to b... | <blockquote>
(And <span class="math-container">$P$</span> is a function, we don't know what function just this function respect Kolmogorov axioms)
</blockquote>
We do know more. We know that our <span class="math-container">$\mathsf P$</span> is the probability measure for the events of <em>the described proc... | https://math.stackexchange.com |
53,819 | [
"https://physics.stackexchange.com/questions/53819",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/20913/"
] | <pre><code>^
|
|
|
| +
| +|
| + |
| + |
| + |
| + |
| + |
| + |
| + |
| + |
|+ |
+----------------------------->
o x1
</... | This solution is based on the following interpretation of the OP's question (see the comments beneath the question):
Give a function $a(x)$ such that $a(x)$ is the acceleration of a particle at $x$:
$$ \ddot{x} = a(x) $$
and the motion is subject to the following boundary conditions:
$$ \begin{array}{lcl}
x(0) &... | If you know the initial velocity and final velocity then you can calculate the acceleration from the $O$ to $X_1$.
$v^2 = u^2 + 2as$
$v = $ velocity at point $X_1$<br>
$u = $ velocity at point $O$<br>
$s = $ distance traveled (which is $X_1$ units)<br>
$a = $ acceleration of the point from $O$ to $X_1$
Here $a$ is n... | https://physics.stackexchange.com |
223,593 | [
"https://dba.stackexchange.com/questions/223593",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/165853/"
] | I'm loading data into a data warehouse. Customers/transactions are coming from the ERP and from Salesforce. Product codes do not match up between the systems.
Is there a standard pattern for solving this problem?
I'm trying to be careful to avoid a big opinion-based question/answer. I'm really just looking for the <s... | We can use <code>mysqldump --replace --where "..." db table</code>. It will output the <code>REPLACE</code> statement. It remains to edit this <code>REPLACE</code> to change the table name and then execute this SQL code.
| <pre><code>UPDATE table1, table2
SET table1.field1 = table2.field1,
table1.field2 = table2.field2,
-- .....
table1.fieldN = table2.fieldN
WHERE table1.id = table2.id
AND table1.id IN ('id1', 'id2', /* ... */ 'idN' )
</code></pre>
Or you can use
<pre><code>REPLACE table1
SELECT *
FROM table2
WHERE table... | https://dba.stackexchange.com |
27,820 | [
"https://dba.stackexchange.com/questions/27820",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/11006/"
] | Just curious, now Oracle 11g installs by default in folder C:\app\
Why? Before, Oracle was installed by default in folder C:\oracle... Why now is created "app" folder?
| <pre><code>SELECT id FROM pixels WHERE pixel_id='some_pixel_id' ORDER BY id LIMIT n, 1
</code></pre>
| This is only an improvement over @david's query, so you have the same result when there are less than <code>1000</code> rows in the intermediate set:
<pre><code>( SELECT id
FROM pixels
WHERE pixel_id='some_pixel_id'
ORDER BY id DESC
LIMIT 1 OFFSET 999
)
UNION ALL
( SELECT MIN(id)
FROM pixels
WHERE p... | https://dba.stackexchange.com |
12,055 | [
"https://engineering.stackexchange.com/questions/12055",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/4088/"
] | What would be some common applications involving high friction and low wear rates? for example, gear-driven mechanisms which require high friction between the gear teeth but ideally low wear between them.
| As mentioned in the comments you don't actually want high friction between gear teeth, the tooth profiles are designed to roll over each other indeed the ideal is to minimise any sliding friction between the teeth.
Obvious examples of devices which use sliding friction are brakes and friction clutches, these will ha... | As mentioned in the comments you don't want high friction between gear teeth, but if you're asking about the materials who exhibits higher friction with low wear rate, it depends on several parameters, such as, the nature of the two counterfaces, the environment, the applied load, the hardness, velocity, etc
In general... | https://engineering.stackexchange.com |
256,384 | [
"https://softwareengineering.stackexchange.com/questions/256384",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/146874/"
] | I tried to explain to a coworker the gravity of having duplicate code in a project, on this piece of code:
<pre><code>+ (void)createIapInParse:(SKPaymentTransaction *)transaction {
Reachability *reach = [Reachability reachabilityWithHostname:@"www.facebook.com"];
if ([Social getFBUser]) {
NSString *iap... | <strong>You're not wrong. It's just psychologically very difficult to convince people of their own limitations.</strong>
The reason we have invented maxims, guidelines etc. that restrict what we should do is that we have found, over time, that behaving in a particular way leads to more success. Importantly, it will le... | <blockquote>
His primary argument was that "he's a good programmer and he can understand and read even the first version fast enough" so he doesn't care if it's written like that or not.
</blockquote>
If that is his primary argument it may be a sign that he is primarily afraid with being not called a good programmer... | https://softwareengineering.stackexchange.com |
84,630 | [
"https://electronics.stackexchange.com/questions/84630",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/30014/"
] | There is a question I can't solve.
<img src="https://i.imgur.com/EraMGsL.png" alt="sat">
I know that \$\beta\ =50\$ and \$V_{ce}\ (sat)\$ \$ =0.2 \$.
I need to find the value of \$ V_1 \$ that the BJT is in saturation.
I've tried some KVL/KCL equation using the \$V_{ce}\ (sat)\$ value but I can't get an answer (\$V_... | <blockquote>
what is the way to approach things like that?
</blockquote>
Since \$V_E = 0 \$, the transistor will be saturated when \$V_C = -0.2V\$. Thus
\$I_C = \dfrac{4.8V}{2k \Omega} = 2.4mA\$
\$I_B = \dfrac{2.4mA}{50} = 48uA\$
Then, by KVL:
\$V_1 = V_{EB} + 48uA \cdot 50k \Omega = V_{EB} + 2.4V\$
So, assu... | The preliminary condition for BJT to be in saturation is that it is not cut-off. This means that you begin by assuming:
$$V_{EB} \approx 0.6V$$
Assumed that, and knowing \$V_{EC_{Sat}}\$, you're calculating the range of collector current such that:
$$V_{EC} < V_{EC_{Sat}}$$
Since you know \$\beta\$, you can der... | https://electronics.stackexchange.com |
14,659 | [
"https://dba.stackexchange.com/questions/14659",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/7214/"
] | Query 1:
<pre><code> SELECT c.class_id,
SUM
(
CASE
WHEN s.student_id IS NULL THEN 0
ELSE 1
END
) as total_students
FROM classes c LEFT JOIN students s ON c.class_id = s.class_id
GROUP BY c.class_id;
</code></pre>
result:
<pre><code>453 100
461 10
462 19
464... | The WHERE clause is checking <code>s.student_type='instate'</code>.
In a LEFT JOIN, everything on the right side is NULL, so the WHERE clause would not evaluate to anything.
If I may, I'd like to suggest a slight rewrite of your query:
Instead of this
<pre><code>SELECT c.class_id,
SUM
(
CAS... | <pre><code>SELECT c.class_id,
COUNT( s.student_id ) AS total_students
FROM classes c
LEFT JOIN students s
ON c.class_id = s.class_id AND s.student_type='instate'
GROUP BY c.class_id;
</code></pre>
| https://dba.stackexchange.com |
34,338 | [
"https://softwareengineering.stackexchange.com/questions/34338",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/-1/"
] | How does an object oriented programmer understand the word "type"? I'm not aware of there being a type theory for object oriented programming because whenever someone mentions type theory it is always in the context of some kind of functional programming language so what does "type" mean in the object oriented context?... | <em>Type</em> is basically the same as <em>class</em> - it defines characteristics and behavior of a family of objects. You instantiate types to create objects of those types.
In practice, <em>types</em> usually refer to a set of predefined classes supplied with the class library of a programming environment - basic p... | A type refers to the identity of a variable. Some variables are integers, some are strings, some are arrays, some are objects, etc. When you have objects, an object's "type" is basically the same concept as its "class," and some type theory starts to be introduced there because you have to deal with inheritance and t... | https://softwareengineering.stackexchange.com |
223,028 | [
"https://physics.stackexchange.com/questions/223028",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/100805/"
] | This is probably very basic but I can't quite find the answer in other questions.
As I understand it we are hoping to create supersymmetric particles at the LHC (in this second run) and these particles could be candidates for dark matter. What I am finding confusing is: If we have to create these particles in the LHC,... | The fact that the neutralino (the common SUSY DM candidate) can be created in a high-energy collisions means that it interacts with other particles. Specifically, it must interact with the protons in the incoming beams, at least indirectly.
However, just because it has interactions, it doesn't mean that it isn't stab... | Just because they are created at the LHC does not mean they are not stable. The LHC is used to create anti-protons, for example, and an anti-proton is just as stable as a proton. Left alone either are expected to last forever (or at least almost). Just because they annihilate if brought into contact does not mean they... | https://physics.stackexchange.com |
35,793 | [
"https://mathoverflow.net/questions/35793",
"https://mathoverflow.net",
"https://mathoverflow.net/users/4298/"
] | It is clear that each maximal ideal in ring of continuous functions over $[0,1]\subset \mathbb R$ corresponds to a point and vice-versa.
So, for each ideal $I$ define $Z(I) =\{x\in [0,1]\,|\,f(x)=0, \forall f \in I\}$. But map $I\mapsto Z(I)$ from ideals to closed sets is not an injection! (Consider the ideal $J(x_0)... | Here is a way to construct a non-maximal prime ideal: consider the multiplicative set $S$
of all non-zero polynomials in $C[0,1]$. Use Zorn lemma to get an ideal $P$ that is disjoint from $S$ and is maximal with this property. $P$ is clearly prime (for this you only need $S$ to be multiplicative.) On the other hand $P$... | There are many prime ideals that are not maximal. You can find some things by Googling "prime ideals in $C(X)$" (e.g. that every maximal ideal is the sum of two proper prime ideals).
The problem is that prime ideals are not closed unless they are maximal.
The closed ideals in $C(X)$ for $X$ compact Hausdorff are in... | https://mathoverflow.net |
2,026,941 | [
"https://math.stackexchange.com/questions/2026941",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/33817/"
] | The countable union of a countable set is countable. Does the same hold for sets with cardinality $|\mathbb R|$. More specifically, if $A_i$ are sets of the same cardinality as the real numbers, and $I$ is an index set also with cardinality $|\mathbb R|$, is $|\bigcup_{i\in I} A_i| = |\mathbb R|$?
| This question can be reduced to the question "is it true there is a bijection between $\mathbb{R}$ and $\mathbb{R}^2$?" The answer is yes.
| The question can be cast into cardinal arithmetic. We can prove the following:
<blockquote>
If $X$ is an infinite set, then $|X|=|X^2|$.
</blockquote>
Moreover, we can prove the following cardinal arithmetic theorem:
<blockquote>
$\left|\bigcup_{i\in I}A_i\right|\leq|I|\cdot\sup\{|A_i|\mid i\in I\}$.
</blockquot... | https://math.stackexchange.com |
157,750 | [
"https://dba.stackexchange.com/questions/157750",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/112547/"
] | I am creating a database structure to represent a <em>football league</em>, but there is a certain part that I do not know how to solve, that is:
<ul>
<li>A <em>member</em> and he can be a <em>referee</em>, a <em>management</em> or a <em>player</em> (but only one of these <em>types</em>).</li>
</ul>
I include the fol... | You can add an attribute to <code>MEMBER</code> that defines the type. Example:
<pre><code>CREATE TABLE MEMBER
( MEMBER_ID INT NOT NULL PRIMARY KEY -- ID is to vague IMO
, MEMBER_TYPE CHAR(1) NOT NULL
, ...
, CONSTRAINT <name> CHECK (MEMBER_TYPE IN ('R','M','P'))
) ;
</code></pre>
I've heard that some DBMS supp... | I assume that the 'business logic' behind this is the conflict of interest where a player (or manager) who is also a referee could potentially help his team cheat. If you truly want each member to only be one type, then you can have an attribute 'memberType' in the member table, which would hold a value of 'R', 'M', or... | https://dba.stackexchange.com |
365,509 | [
"https://physics.stackexchange.com/questions/365509",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/173614/"
] | I was asked to solve the following problem on a test:
<em>A motorist is moving at 70 km/hour on a circular path of radius 500 meter. Determine the normal and tangential components of acceleration.</em>
All I know from high school physics knowledge - centripetal acceleration in uniform circular motion is $\frac{v^2}... | If the speed is constant there is only normal acceleration (from the motorist to the center of the circunference).
To get both accelerations you can make:
1) Get your position vector in polar coordinates:
$$
\vec{r} = x\vec{i}+y\vec{j} =r \cos \theta \; \hat{i} + r \sin \theta \; \hat{j} = r \hat{r}.
$$
Now you can ... | In uniform circular motion the acceleration is radial (normal) of modulus v^2/r.
The tangential component is zero.
| https://physics.stackexchange.com |
330,142 | [
"https://physics.stackexchange.com/questions/330142",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/154644/"
] | I'm studying a toy theory in quantum field theory. There are two free fields: a real massive scalar field $\phi$ with mass $M$ and a complex massive scalar field $\Psi$ with mass $m$.
They are coupled by
$$
\mathcal{L} \subset g \Psi \Psi^\dagger \phi
$$
I'm well aware that this interaction term results in a Lagrangi... | What you found is a very simple example of an <strong>infra-red divergence</strong>, which plague all physical theories with massless particles.
This kind of divergences are already present in the classical case (see for example ref.1), and they usually signal that you are asking an unphysical question, not that the t... | This is a very crude answer. But this will help in your queries. You see the problem with the above method you implied is that at tree level $\psi \psi -
> \psi \psi$ the internal propagator is $\phi$ particle. Now the propagator for massive and massless particles are very different. For massless particle the equati... | https://physics.stackexchange.com |
96,828 | [
"https://stats.stackexchange.com/questions/96828",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/31420/"
] | How can I prove the following lemma?
Let $\mathbf{X}^ \prime$ = $ \left[ X_1 , X_2 , \ldots, X_n \right]$ where $ X_1, X_2, \ldots X_n $ are observations of a random sample from a distribution which is $N \left ( 0,\sigma^2 \right)$. Then let $\mathbf{b}^\prime = \left[b_1,b_2,\ldots,b_n \right]$ be a real nonzero vec... | Use Craig's Theorem. Consider the quadratic form on <strong>b</strong>. If two random variables are independent, then any univariate functions of those random variables are likewise independent. The quadratic forms are independent, ergo the linear form on <strong>b</strong> and the quadratic form on <strong>A</stron... | Starting with the univariate case $X=X_1$, we find the correlation:
$\rho(bX,AX^2)=bA\rho(X,X^2)=bA\dfrac{\mathrm{Cov}(X,X^2)}{ \sigma_X \sigma_{X^2}} =bA\dfrac{E[(X-\mu_X)(X^2-\mu_{X^2})]}{ \sigma_X\sigma_{X^2}}$
With $\mu_x=0$, $\sigma_x=\sigma$, and for the expectation we know the distributions of $X$ and $X^2$ (N... | https://stats.stackexchange.com |
310,353 | [
"https://stats.stackexchange.com/questions/310353",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/155650/"
] | I ran the <code>auto.arima()</code>command in R on a set of data and it chose the appropriate model to be ARIMA(0,1,0).
I know ARIMA(0,0,0) is just white noise, but what does ARIMA(0,1,0) mean?
| ARIMA(0,1,0) is random walk.
It is a cumulative sum of an i.i.d. process which itself is known as ARIMA(0,0,0).
| An ARIMA(0, 1, 0) series, when differenced once, becomes an ARMA(0, 0), which is random, uncorrelated, noise.
If $X_1, X_2, X_3, \ldots$ are the random variables in the series, this means that
$$X_{i+1} - X_{i} = \epsilon_{i + 1}$$
where $\epsilon_1, \epsilon_2, \ldots$ is a sequence of centered, uncorrelated random... | https://stats.stackexchange.com |
43,439 | [
"https://softwareengineering.stackexchange.com/questions/43439",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/14788/"
] | Do todays web pages use Web Semantics?
what is the potential in web semantics (i mean potential to enhance web)?
web semantics is all about SEO?
| <ul>
<li>SEO is garbage.</li>
<li>Web semantics is about giving meaning to content by marking it up with the right tags. If something is a heading, mark it up as a heading. </li>
<li>Using semantic markup with meaningful content will get you 99% of the way to good search engine rankings, because the search engines will... | <blockquote>
Do todays web pages use Web Semantics?
</blockquote>
Not really. There is a progressive thinking to promote semantic format but it has failed to attract the masses. The reason for that is there are almost no tangible advantages for the average Joe. Semantic markup is basically a preparation stage for th... | https://softwareengineering.stackexchange.com |
143,111 | [
"https://softwareengineering.stackexchange.com/questions/143111",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/47113/"
] | I just found the following code in our code base:
<pre><code>public String identifyArchitectureName(String platformName, String input) ...
</code></pre>
In my opinion <code>input</code> is one of the most meaningless names for a variable that can be. Is it just me? I can just quietly change it, but should I address t... | It depends on the context to me.
<pre><code>string GetEncrypted(string input)
</code></pre>
quite obviously, <code>input</code> is a string to be encrypted. What would you rename this parameter to?
I also use <code>str</code> for methods that perform conversions or string manipulations
<pre><code>MyEnum Parse(strin... | Part of working with others is educating/teaching/mentoring them, in particular if you have seniority.
By all means, take it up with the developer and come up with a better name <em>together</em>.
| https://softwareengineering.stackexchange.com |
369,564 | [
"https://math.stackexchange.com/questions/369564",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/39537/"
] | I would like to prove this theorem:
Let $A,B \subseteq \mathbb{R} ^3$ be convex, limited sets. $B \subseteq A$. I have a "random line", which intersects A. Probability, that this line also intersects B, should be $surfaceArea(B)/surfaceArea(A)$ .
I would like to "prove" that statement. I will probably need to "measur... | <blockquote>
A <strong>zero</strong> of a polynomial is a value of <span class="math-container">$x$</span> for which <span class="math-container">$P(x) = 0$</span>.
</blockquote>
To show that <span class="math-container">$1 \text{ and}\; 2$</span> are zeros, substitute each value into the polynomial <span class="math-c... | Recall that $(x-a)$ is a factor of a polynomial $P(x)$, if $P(a) = 0$. Hence, to check if $(x-1)$ and $(x-2)$ are factors, find the value of $P(1)$ and $P(2)$ to conclude what you want.
| https://math.stackexchange.com |
408,344 | [
"https://stats.stackexchange.com/questions/408344",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/224017/"
] | Given we have drawn <span class="math-container">$n$</span> samples <span class="math-container">$x_1,...x_N$</span> from a normal distribution <span class="math-container">$\mathcal{N}(\mu, \sigma)$</span>. How do I calculate the probability that eg <span class="math-container">$\mu=1$</span>? ie <span class="math-con... | The probability that <span class="math-container">$\mu=1$</span> given a sample with a non-degenerate prior density is zero.
<span class="math-container">$$\Pr(\mu|X,\sigma^2)=\int_0^\infty\frac{\prod_{i=1}^nf(X|\mu,\sigma^2)\pi(\mu,\sigma^2)}{\int_{-\infty}^\infty\int_0^\infty{\prod_{i=1}^nf(X|\mu,\sigma^2)\pi(\mu,\s... | The probability that <span class="math-container">$\mu=1$</span> is zero: <span class="math-container">$P(\mu=1|X)=0$</span> if you're drawing <span class="math-container">$\mu$</span> from a continuous distribution.
If you want to apply inference techniques, then it's usually for intervals, such as <span class="math-... | https://stats.stackexchange.com |
16,987 | [
"https://mechanics.stackexchange.com/questions/16987",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/10501/"
] | Today, my car didn't start. I think that the crank was turning over because I could hear the loud sound a car makes just before starting up but the car was not starting.
I called a mechanic. He changed the battery and the car works now. Coming to the point, I initially thought that since the crank was turning, there w... | For starting an engine, the battery should have a minimum voltage of 9V and above. if that is not available, then starter will be able to crank the engine, albeit weakly but would not be able to start the car. Low battery voltage can happen due to a defective battery or because of quiescent current consumption that dra... | When a starter is energized and cranking the engine, it will pull more power than any other electrically operated part on the vehicle. You say you <em>think</em> the car was cranking over ... I'd submit that maybe what you thought you heard was not what was actually happening.
| https://mechanics.stackexchange.com |
2,959,890 | [
"https://math.stackexchange.com/questions/2959890",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/601649/"
] | This question got me thinking and confused on how to solve it.
If <span class="math-container">$$\begin{align}k(x-a)+2x-z&=0\\k(y-a)+2y-z&=0 \\ k(z-a)-x-y+2z&=0\end{align}$$</span>
Show that <span class="math-container">$$x = \frac{ak(k+3)}{k^2+4k+2}.$$</span>
So far so good, I could only solve it simult... | We have that
<span class="math-container">$$\sum\limits_{n=0}^{N}x^{n}=\frac{1-x^{N+1}}{1-x} \implies \sum\limits_{n=1}^{N}x^{n}=\frac{1-x^{N+1}}{1-x}-1=\frac{x-x^{N+1}}{1-x}=x^{N+1}\frac{x^{-N}-1}{1-x}$$</span>
and then
<span class="math-container">$$\sum\limits_{n=1}^{N}\frac{x^{n}}{x^{N+1}}=\frac{x^{-N}-1}{1-x}$... | We need to show <span class="math-container">$$\sum\limits_{n=-N}^{-1}x^{n}=\frac{x^{-N}-1}{1-x}$$</span>
Note that <span class="math-container">$$\sum\limits_{n=-N}^{-1}x^{n} = x^{-N} + x^{-N+1} +... + x^1$$</span>
<span class="math-container">$$= x^{-N}(1+x+x^2+...+x^{N-1}) = x^{-N} (\frac {1-x^N}{1-x}) = \frac {x... | https://math.stackexchange.com |
583,480 | [
"https://stats.stackexchange.com/questions/583480",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/254244/"
] | I'm reading <em>Performance Modeling and Design of Computer Systems</em> which contains some analysis of Markov chains. In particular, it emphasises various analytical methods for finding the stationary distribution of a Markov chain.
Here's what confuses me: when I have formally studied computer-intensive statistics (... | The book I was reading pointed out in a later chapter the obvious that I had missed.
By learning to work on Markov chains analytically, it's possible to derive probabilities that are functions of inputs of high dimension, and answer more interesting counterfactuals in the form of "if I vary this one parameter out ... | In theory, some Markov chains will not have a stationary distribution. Hence, using theoretical approaches deriving the stationary distribution from the transition matrix itself should identify this issue, while simply running simulations could make it more difficult, especially if you are not careful about this potent... | https://stats.stackexchange.com |
415,104 | [
"https://softwareengineering.stackexchange.com/questions/415104",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/367426/"
] | While I know this is the tight coupling example:
<pre class="lang-py prettyprint-override"><code>class User:
def __init__(self):
pass
def get_status(self):
api_client = APIClient()
status = api_client.get_user_status()
return status
</code></pre>
And this is the loose coupling e... | Which ones break when <code>APIClient</code> doesn't exist?
Being able to override <code>APIClient</code> is nice. It's handy to have a known good default. But it's still more coupled than having no idea that <code>APIClient</code> exists.
| Coupling in python is more prevelant at the import level.
If you have a <code>User</code> class in <code>./user.py</code> like so:
<pre class="lang-py prettyprint-override"><code>class User:
def __init__(self, api_client):
self.api_client = api_client
def get_status(self):
status = self.api_cli... | https://softwareengineering.stackexchange.com |
749,105 | [
"https://physics.stackexchange.com/questions/749105",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/297351/"
] | I'm studying the Lagrangian
<span class="math-container">$$
\mathcal{L} = \frac{1}{2}\partial_\mu\phi \partial^\mu\phi+\lambda\phi\partial_\mu\phi\partial^\mu\phi
$$</span>
And am trying to work out the Feynman rule for the 3-point function of this interaction term. The massless free part makes sense to me, but I don'... | The term <span class="math-container">$\lambda\phi^3$</span> would render a vertex in Feynman diagrams that would contribute to amplitude as <span class="math-container">$\lambda$</span> only. In contrast, <span class="math-container">$\lambda\partial_\mu\phi\partial^\mu\phi$</span> would render a vertex with the same ... | If you work through the derivation of the Feynman rules (for example by using path integral methods), you will find that the cubic vertex you have written down will contribute a factor of <span class="math-container">$\sim \lambda k_{1, \mu} k_2^{\mu}$</span> (up to factors of <span class="math-container">$2$</span>, <... | https://physics.stackexchange.com |
2,270,306 | [
"https://math.stackexchange.com/questions/2270306",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/406287/"
] | <blockquote>
There is a 6 digit number $abcdef$. Given that it is divisible by $7$, show that $abc-def$ is also divisible by $7$.
</blockquote>
Attempt at solution:
$abcdef=10^5a + 10^4b + ... + f=7x$.
Therefore, $7|a, 7|b, ...$.
Hence, $abc=7m, def=7n$ and $7(m-n)$ must be divisible by $7$.
Q.E.D
I still feel this... | My first reaction to "If $abcdef$ is divisible by $7$ then $abc-def$ is divisible by $7$" is "really, I had no idea that was true!". Then I'd think well, gee, if that's true then how could that be true and what would it imply. How can I get from $abcdef$ to $abc-def$?
$abcdef = 1000abc + def$ is a start.
and $1000a... | Since $1000\equiv -1\pmod{7}$, we have $$abcdef=1000abc+def\equiv -abc+def\pmod{7}$$ and if the given number is divisible by 7, then by above result $-abc+def$ is divisible by 7.
| https://math.stackexchange.com |
23,247 | [
"https://mathoverflow.net/questions/23247",
"https://mathoverflow.net",
"https://mathoverflow.net/users/318/"
] | Let $\mathrm{Hol}^d(\Sigma, \mathbb{C} \mathbb{P}^n)$ denote the space of holomorphic maps of degree $d$ from a Riemann surface $\Sigma$ to complex projective space of dimension $n$. Let $\mathrm{HolEmb}^d(\Sigma, \mathbb{C} \mathbb{P}^n)$ denote the subspace of those holomorphic maps which are also embeddings, so ther... | I will assume that <em>d</em> is the degree of the pull-back of $\mathcal{O}(1)$ to $\Sigma$ and that it is sufficiently large with respect to the genus <em>g</em> of $\Sigma$. In this case, the dimension of the space of holomorphic maps of $\Sigma$ in $\mathbb{P}^n$ is
$$
D_n := (n+1)d + n(1-g) ,
$$
while the dimens... | At least for CP^2, HolEmb is empty unless g=(d-2)(d-1)/2 by the adjunction formula.
| https://mathoverflow.net |
340,334 | [
"https://stats.stackexchange.com/questions/340334",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/204232/"
] | I am experimenting with the Bayesian Naive Classifier and I have come across a situation for which I wasn't able to find a solution on the net.
Suppose you have a dataset with a few attributes that takes real values. The values of the observations varies around a mean as they typically do -- except for a particular at... | The PDF is the probability <em>density</em> function. What you're describing doesn't have a <em>density</em> of 1 at the mean, it has a probability <em>mass</em> of 1 at the mean. If you really are certain that the variance of machine cookies is zero, then you should classify all cookies that don't have the mean of ma... | Within statistics, all is uncertain, also the class membership of each pattern. Probabilities that are purely 0 and 1, that indicates a <strong>deterministic mechanism</strong>, for which statistics was not developed. As soon as uncertainty comes into play, a deterministic paradigm is left and it becomes statistics and... | https://stats.stackexchange.com |
208,926 | [
"https://physics.stackexchange.com/questions/208926",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/17338/"
] | <ol>
<li>Say I have a wire, and I connect a current source on its left end, and a ground to its right end. Then using my power supply I source a positive current, does this mean that electrons will move from left to right or from right to left?</li>
<li>Also, what about joule heating? Is the direction of the temperatur... | <ol>
<li>If your power supply is sourcing a positive current toward the ground, that corresponds to a flow of positive charge from the supply to ground. This is equivalent to a flow of negative charge from the ground to the power supply. In a real wire, only negative charges can flow, so the second thing will happen: e... | Given a particle of charge $q$ placed into an electric field, the equation of motion is $m \mathbf{\ddot{r}} = q\,\mathbf{E}(\mathbf{r},\mathbf{\dot{r}})$.
The direction of the electric field comes into play in the difference of potential $V_A - V_B$, according to whether your ground is at a lower or higher voltage (... | https://physics.stackexchange.com |
316,911 | [
"https://stats.stackexchange.com/questions/316911",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/182615/"
] | I have a trivial problem but I do not understand fully the k-armed bandit theorem from chapter 2. My question is based on Sutton's "<strong><em>Reinforcement Learning: An introduction, second edition</em></strong>". The exercise is as such:
<blockquote>
Consider a k-armed bandit problem with k = 4 actions, denoted
... | From what you posted, I don't see where the rewards are constrained to 0,1. Generally rewards can be real-valued.
To understand the algorithm, let's write down the estimates after each iteration. I'll use the format Iteration: estimate of Q(1),Q(2),Q(3),Q(4)
0: 0, 0, 0, 0
1: 1, 0, 0, 0
2: 1, 1, 0, 0
3: 1, 1.5, 0,... | Let's start the table of Zhang Kin from one, not zero. Because in this question, it's given <span class="math-container">$Q_1(a)=0$</span> for all <span class="math-container">$a=1,2,3,4$</span>.
By using the table starting at one since the action of <span class="math-container">$A_2=2$</span>, this action can be an ex... | https://stats.stackexchange.com |
359,014 | [
"https://softwareengineering.stackexchange.com/questions/359014",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/248300/"
] | The company I work for now doesn't implement continuous delivery yet. We still deploy the project manually to server, file by file. Which is best practice: to manually deploy one project artifact for each deployment or keep doing the file-by-file deployment?
| <blockquote>
Which is best practice? to manually deploy one project artifact each deployment or keep doing the file by file deployment?
</blockquote>
Neither.
Best Practice is to <em>automate</em> your deployment, completely and exclusively.
That means <em>nobody</em> gets to put <em>anything</em> onto a server ma... | Manual steps take a lot of effort and are risky: you might forget a necessary file. Maybe not everyone in your team knows which files need to be copied. All of these issues make deployments big, daunting, and rare – completely unnecessarily. Automation addresses these.
Even the simplest automation step can have big be... | https://softwareengineering.stackexchange.com |
24,717 | [
"https://engineering.stackexchange.com/questions/24717",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/12586/"
] | I am curious about the design considerations for a hydraulic system.
Let's say you have a 3HP 1200RPM motor
you also have a hydraulic pump that's rated 4LPM and pressure of 40MPA rated for 40RPM MAX
You can put many different types of gear box on the 3HP motor to get it to operate in the N-40RPM range
Let's forget a... | you should think first about the whole structure, and then look into each joint. Apply the sum of the forces on the horizontal, the sum of the momentum and vertical forces must all be equal to zero to the structure as an object, similar to what you have been doing all the course.
I have found a mistake on your solutio... | Using method of joints we can calculate the maximum compression according to the values given being 6kN. As that strain is greater than 8kN we should assume 6kN to be achieved first.
Force P should not exceed the maximum compression value of 6kN at the vertical component of the truss CD.
<span class="math-container">... | https://engineering.stackexchange.com |
10,337 | [
"https://stats.stackexchange.com/questions/10337",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/3903/"
] | What would be <span class="math-container">$\operatorname{Var}(X^2)$</span>, if <span class="math-container">$\operatorname{Var}(X)=\sigma^2$</span>?
| Error propagation via Taylor's rule (aka "delta" method) --
<span class="math-container">$$\operatorname{Var}(X^2) \approx 4\operatorname{\mathbb{E}}(X)^2 \operatorname{Var}(X)$$</span>
| As a simple example of the responses of @user2168 and @mpiktas:
The variance of the set of values 1,2,3 is 0.67, while the variance of its square is 10.89. On the other hand, the variance of 2,3,4 is also 0.67, but the variance of the squares is 24.22.
These are just variances for finite sets of data, but the idea ext... | https://stats.stackexchange.com |
2,933,843 | [
"https://math.stackexchange.com/questions/2933843",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/593845/"
] | I am trying to determine the generating function for the sequence <span class="math-container">$a_n$</span>, where <span class="math-container">$a_n $</span> is the number of words of length n over the alphabet {0, 1, 2, ..., q-1} that do not contain the subword <span class="math-container">$0^k$</span>.
I came up wit... | Suppose you do have
<span class="math-container">$$a_{n+k}=(q-1)\sum_{i=n}^{n+k-1}a_i$$</span>
for all <span class="math-container">$n$</span>.
Then
<span class="math-container">$$a_{n+k+1}=(q-1)\sum_{i=n+1}^{n+k}a_i$$</span>
and so
<span class="math-container">$$a_{n+k+1}-a_{n+k}=(q-1)(a_{n+k}-a_n).$$</span>
We get th... | Let's say <span class="math-container">$f(x)$</span> is the generating function for a string of characters from <span class="math-container">$\{0,1,2,\dots,q-1\}$</span> with no substring of <span class="math-container">$k$</span> or more consecutive <span class="math-container">$0$</span>s.
An acceptable string is
... | https://math.stackexchange.com |
29,087 | [
"https://datascience.stackexchange.com/questions/29087",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/47813/"
] | The original string is like this "965 - Vehicle parking area", how do I get rid of the "965 - " part in R? (There are two spaces before and after the dash.)
Thank you!
| One possibility is to use gsub function to find the first ' - ' and remove everything before and also remove the dash with the space before and after that.
<pre><code>> tmp
[1] "965 - Vehicle parking area"
> gsub("^.*? - ","", tmp)
[1] "Vehicle parking area"
</code></pre>
If there are two spaces:
<pre><code>&... | Use <code>str_replace</code> function in <code>stringr</code> library. You just need the alphabets and spaces between them, so this will work-
<pre><code>> str_replace("965 - Vehicle parking area", "[^A-Za-z]+", "")
[1] "Vehicle parking area"
</code></pre>
| https://datascience.stackexchange.com |
115,978 | [
"https://stats.stackexchange.com/questions/115978",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/56055/"
] | I am reading this statistics books and it keeps on repeating same expression over and over again $P(\theta_1,\theta_2,\theta_3) \propto 1$
What does the above expression mean?
| If the density is proportional to a constant, then it has the same value at each point in the domain being considered (not stated in your question).
That is, the density is uniform over whatever subpace <span class="math-container">$(\theta_1,\theta_2,\theta_3)$</span> is defined to have support on.
Presumably this i... | That they follow an uniform distribution (proportional to a constant, with the adequate normalization)
| https://stats.stackexchange.com |
593,355 | [
"https://physics.stackexchange.com/questions/593355",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/248292/"
] | It is said that a magnetic moment is always associated with angular momentum. For a particle, the magnetic moment <span class="math-container">$\boldsymbol{\mu}$</span> and angular momentum <span class="math-container">$\boldsymbol{l}$</span> are related by
<span class="math-container">$\boldsymbol{\mu}=\gamma \:\bolds... | The magnetic moment could be the sum of that from many small rotating or revolving charges. Then the magnet as a whole doesn't have to rotate.
It could be atoms spinning inside crystals. It could be electrons spinning around atomic nuclei. It could be electrons spinning like tops.
We can make up lots of stories to expl... | A permanent magnet actually has angular momentum. As it is <em>electron</em> angular momentum, mostly spin, the crystal itself does not rotate. A iron magnet, for example, has 5/2h of spin angular moment per iron atom. For 1 mole of iron it is 10<span class="math-container">$^{-9}$</span> Nms of AM. If the magnetic ord... | https://physics.stackexchange.com |
338,487 | [
"https://electronics.stackexchange.com/questions/338487",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/168108/"
] | They seem like two words for the same thing, but I also see some sources have different configurations for them.
| When we talk about common emitter, common base, and common collector configurations, the terminal that's named as "common" is the one that isn't used for input or output. It's the one that's used as a ground or "common" terminal by both the input and output of the circuit.
An emitter follower has input into the base a... | Common Emitter can produce voltage gain >> one.
Common Collector (aka emitter follower) produces voltage gain slightly less than one.
| https://electronics.stackexchange.com |
110,098 | [
"https://electronics.stackexchange.com/questions/110098",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/38769/"
] | Eigen functions are the origin for Laplace transform while eigen vectors is for state space representation.Can we relate the eigen concept in these two?
The complex exponential functions, are eigen functions of any LTI system. Also there are infinitely many such linearly independent eigen functions.Then why do we say... | <blockquote>
Then why do we say a second order LTI system has only 2 eigen
values/vectors?"
</blockquote>
Consider the following 2nd order system:
$$a\ddot y(t) + b\dot y(t) + cy(t) = x(t)$$
We can write this as
$$\mathbf Dy(t) = x(t) $$
where \$\mathbf D\$ is the 2nd order <em>operator</em>
$$\mathbf D = a\f... | The confusion arises because of the different uses of the concept <em>eigenvalues</em> in control theory and in signal and system theory. In control theory I've come across the use of <em>eigenvalues</em> for the poles of a transfer function. This is why if used with this meaning a second order system has only two eige... | https://electronics.stackexchange.com |
18,390 | [
"https://mechanics.stackexchange.com/questions/18390",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/9982/"
] | Bike got tipped over by a random person, handlebar got bent, and throttle is really hard to move now so I decided to try to take it out to see what I could do. Here is a picture of the bar:
<img src="https://i.stack.imgur.com/5bsPe.jpg" alt="enter image description here">
You can see where it's bent, and I wanted to ... | I don't know for sure, but would bet your best option is the last one. I know straightening tubes of any sort is a <em>very hard option</em>. There should be an Allen head bolt which is clamping to the forks. You don't want to take the fork loose if you can help it, as getting alignment back right could be a huge pain ... | You're going to need to take that off.
Can't see from your picture, but usually there's one or two clamp bolts and maybe a positioning bolt running vertically (maybe from the triple clamp area to the clip on mount) After this it looks like you can just take it off the top of your fork.
IF the only damage in that area... | https://mechanics.stackexchange.com |
276,836 | [
"https://stats.stackexchange.com/questions/276836",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/159524/"
] | I am working on a Network Meta-analysis that is aimed at comparing different treatments (medical vs surgery vs percutaneous approach) on short as well as long-term outcomes (including cardiovascular morbidity and mortality at 1 year).
We have completed a first pass literature review identifying many studies involving ... | The idea of how one can use single arm trials is that you assume that outcomes vary across trials, but that they are somewhat similar (assumption of exchangeability). If you have multiple single-arm trials with the same treatment, then you can estimate how much outcomes vary for the same treatment. You might for exampl... | I will answer your questions labelled as you have them
(a) there is no statistical reason for excluding cohort studies from your analysis but there might be substantive reasons if they are performed on people with a very different case-mix from these in trials (randomised or not). So it is perfectly in order to includ... | https://stats.stackexchange.com |
318,427 | [
"https://electronics.stackexchange.com/questions/318427",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/132863/"
] | I have a few types of solder. One of them is 0.4 mm and the other is around 0.8 (not very sure). Which one should I use for SMD, and which is good for general purpose?
I have heard that it is best to learn with a thinner wire. Is this true?
| The primary way of controlling how much solder you feed into a solder joint is by the length of solder you shove in.
Thus if you assume a certain "length accuracy" of your hand, the overall volume accuracy of a thinner wire is higher.
I personally use .5mm or less for most work, even non SMD, unless the solder joints... | Thinner solder allows you to control the amount of solder added more precisely. <strong>If you use too-large solder, then</strong>
<ul>
<li>you may have to remove excess solder, and try again after removing too much as desoldering is even less precise.</li>
</ul>
Thicker solder allows you to add more volume of solder... | https://electronics.stackexchange.com |
337,085 | [
"https://physics.stackexchange.com/questions/337085",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/36601/"
] | How it can be seen that the quantity
$$u_{ij}={1\over2}(\partial_iu_j+\partial_ju_i)$$
is rotationaly invariant?
I've tried to use
$$u_i=R_{ij}u_j',$$
where $R_{ij}$ is the rotation matrix.<br>
Here is my attempt:
$$ {{\partial u_j} \over{ \partial x_i}}={{\partial u_j} \over{ \partial x'_k}}{{\partial x'_k} \over{ \... | It's not rotationally invariant. It's a <em>tensor</em> after all, not a scalar.
| let us denote rotated system with primes
$$u'_{ij}={1\over2}(\partial'_iu'_j-\partial'_ju'_i)$$
We have transformation rule
$$u_i'=R_{ij}u_j.$$ From above relation I guess the transformation rule for derivatives is
$$\partial'_i= \partial_i R^{-1}_{ij}.$$
Plug in the relations
$$u'_{ij}={1\over2}(\partial_i R^{-1}_{ji... | https://physics.stackexchange.com |
61,039 | [
"https://softwareengineering.stackexchange.com/questions/61039",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/17722/"
] | Regarding pointers which are members of classes. Should they be of a smart pointer type or is it enough to simply deal with them in the destructor of the class they are contained in?
| No, it's not enough to deal with the raw pointer in the destructor. You also have to deal with it in the copy constructor and assignment operator functions. It's usually not enough to simply copy the pointer (which the compiler will happily do for you); you probably really want to make a copy of the resource it point... | Well if they are only members, I prefer not bother with delete and use boost::scoped_ptr. For me that's the simpler way to manage it.
Now, if you don't have access to boost, or don't want to use it, you can make you own simple smart pointer that simply does the delete for you in it's destructor. It's really easy and I... | https://softwareengineering.stackexchange.com |
35,429 | [
"https://stats.stackexchange.com/questions/35429",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/13702/"
] | Is it possible to do model selection in this way? Suppose I need to select a good (logistic) model among three variables (var1, var2, var3). The deviance D* (-2*log-likelihood) of this full model would be the minimum among all possible models. Then I could try all 6 combination of sub-models(1,2,3,12,13,23) and compute... | Normally looking at all subsets as you do in your example is not done because there are so many. In your example with just three variables it can be done and would usually be done. Rather than use the deviance which gives the smallest value to the full model, criteria like AIC or BIC are used as they penalize the log... | Here's a somewhat longer answer, to complement my comment and @MichaelChernick's answer.
You can do this. With only 6 models - sure.
BUT
<ol>
<li>What about interactions? Even with only 2 way interactions, your number of possible models goes up fast. You now have null model, 1, 2, 3, 1 + 2, 1 + 3, 2 + 3, 1 + 2 + 3 ... | https://stats.stackexchange.com |
57,477 | [
"https://cs.stackexchange.com/questions/57477",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/47900/"
] | <blockquote>
Prove that $T$ is MST $\Leftrightarrow$ for any edge $uv \notin T$, $uv$ has the maximal weight on the cycle created by adding $uv$ to $T$.
</blockquote>
It's my attempt to prove $\Rightarrow$:
Consider the cycle $path(v, u) \in T \cup E(v, u)$. If $(v, u)$ is not maximal, replace the maximal edge on t... | <em>Note:</em> The original answer has a flaw in "without loss of generality". The following one is based on Section 8.2.3 of the book "Computer Algorithms" (3rd edition) by Sara Baase and Allen Van Gelder.
<hr>
The right part of the theorem is called the MST property.
<blockquote>
<em>MST Property:</em> Let $T$ b... | Assume that there is a minimum spanning tree $T'$ with smaller weight than $T$. Since $T\neq T'$ there has to be an edge $uv$ in $T'$ but not in $T$. Now remove $uv$ from $T'$. This splits $T'$ into two trees $T'_u$ and $T'_v$. We denote the vertices spanned by $T'_u$ by $U$ and the vertices spanned by $T'_V$ by $V$. L... | https://cs.stackexchange.com |
281,442 | [
"https://electronics.stackexchange.com/questions/281442",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/134435/"
] | With a Tesla coil being a high-frequency, high voltage device, and the secondary coil connected to ground, is there a way to prevent the high frequency signal from interfering with other electrical devices when connected to mains ground, such as some sort of low pass filter? I know I can simply avoid this by connecting... | A Tesla coil is going to make a lot of RF. That's its job. How you ground one end of the output doesn't change this. At best it moves around where exactly this RF noise will be seen.
If you ground one side of the output to the ground in a wall plug, then the high frequency current runs along the ground wire, eventu... | Yes, there's a magic way to filter out the RF from ground connection. Don't connect it to mains ground. Think like this:
What if your TC was sitting on an infinite horizontal conductor-sheet? In that case any connection between Earth and the <em>other side</em> of the sheet (the bottom,) will have zero current. An... | https://electronics.stackexchange.com |
610,021 | [
"https://math.stackexchange.com/questions/610021",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/47820/"
] | Suppose $a$,$b$,$c$,$d$ be the points of set of all complex no$(C)$. with $c$ not equal to $0$ and $ad$ not equal to $bc$.$f$ be a function such that
$f(z)$=$(az+b)$/$(cz+d)$.
how to prove that $f$ defines a bijection between $C$-{d/c} and $C$-{a/c}?
how to show that it takes circles into circles?What about circles th... | Indeed, you are correct in your intuition. Moreover, we also have
$$
|x-y|\ge \left|\; |x|-|y|\; \right|
$$
| The proof of the "reverse triangle inequality" requested in the other comments: given the basic TE,
$$\def\abs#1{\lvert#1\rvert}\abs{x + y} \leq \abs{x} + \abs{y},$$
subtract $\abs{y}$ from both sides:
$$\abs{x + y} - \abs{y} \leq \abs{x}.$$
Now replace $x + y$ with $x$, and thus $x$ with $x - y$ (if you don't get this... | https://math.stackexchange.com |
29,196 | [
"https://dba.stackexchange.com/questions/29196",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/6499/"
] | I would like to optimise the query below because it's actually taking 40% of the time in the real one. I HAVE to get the first line in the table 2 for each line in the table 1. The relationship is 1 to N between the tables.
I also tried with a <code>MIN()</code> for the subquery but I did not had any gain.
I'm open... | I'd try
<pre><code>SELECT *
FROM TABLE1 T1
CROSS APPLY
(
SELECT TOP 1 * FROM TABLE2 sT2
WHERE sT2.FK = T1.PK
ORDER BY sT2.DATE_X
)b
</code></pre>
| I can't tell exactly what you're doing. I can't tell if you're trying to <code>CROSS JOIN</code> Table1 with a subset of Table2, or if there's actually a relationship there.
The query you listed looks like it's doing a complete implicit <code>CROSS JOIN</code> of Table1 and Table2 because your join condition ends u... | https://dba.stackexchange.com |
90,753 | [
"https://security.stackexchange.com/questions/90753",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/54158/"
] | When using 3G or 4G internet on my phone, is this running over the SIM card or is this similar to WLAN traffic?
Can a mobile network provider assign my mobile internet traffic to my phone by either the SIM card number or the IMEI of my phone?
| All the things in mobile operators are assigned per SIM card. You have stored in HLR 3 parameters: MSISDN (your phone number), IMSI (internal customer identifier) and ICCID (SIM card serial number). Based on those parameters in different subsystems of mobile operator are created CDR (call detail record) for voice and d... | SIM card is basically a smartcard with authentication data on it. The traffic doesn't go <em>through</em> the SIM card physically, the card is merely used for authentication and "logging in" to the provider network and is used by the operator for billing and other subscriber-specific operations. The traffic itself is t... | https://security.stackexchange.com |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.