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
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341,224 | [
"https://softwareengineering.stackexchange.com/questions/341224",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/128300/"
] | I'm working with particular classes of matrices which admit fast operations without resorting to dense linear algebra. To keep the heierarchy simple, I'm currently doing the following (greatly simplified):
<pre><code>class Matrix:
def mvm() # matrix-vector multiplication
def is_square()
def is_psd()
de... | Given your matrixes are immutable, it is indeed possible to have a general base class <code>Matrix</code> which defines all the operations on matrices you need, and a few specific subtypes of this class <strong>as a form of optimization</strong>, when you know you need this. However, before doing so, I would really thi... | Using a class hierarchy is not generally advisable in such cases, since your subtypes encode specific <em>data constraints</em>.
If your matrices are mutable (i.e. elements of the matrix can be updated), then you run into the circle–ellipse problem. E.g. given a diagonal matrix, I could change an element so that the o... | https://softwareengineering.stackexchange.com |
167,821 | [
"https://chemistry.stackexchange.com/questions/167821",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/127213/"
] | I am attempting to determine whether there is going to be the formation of a <span class="math-container">$\ce{AgCl}$</span> salt precipitate if the following two solutions were to be added together:
<ol>
<li><span class="math-container">$50mL$</span> of <span class="math-container">$\ce{NaCl}$</span>, <span class="mat... | Here is a summary of the steps I would use:
<ol>
<li>Determine the concentration of silver and chloride ions in the mixture, assuming that no silver chloride precipitates.</li>
<li>Compare the solubility product to the product of these concentrations.</li>
<li>If point 2. suggests precipitation, determine the equilibri... | First let's calculate the initial amounts of both reactants, <span class="math-container">$\ce{Ag+}$</span> and <span class="math-container">$\ce{Cl^-}$</span>. They are :
<span class="math-container">$\ce{n(Cl^-) = c·V = 0.05 L·0.04 M = 2·10^{-3} mol}$</span>
<span class="math-container">$\ce{n(Ag+) = c·V = 0.05 L · 0... | https://chemistry.stackexchange.com |
549,712 | [
"https://electronics.stackexchange.com/questions/549712",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/252007/"
] | I was just introduced to the concept of Amplitude Modulation and how it was used for transmitting information between radios.
What modulation technique is used for communication between mobile cell phones and why is AM not used? Also, if newer techniques save more power, why is it still used for radio transmissions?
| <blockquote>
Also, if newer techniques save more power, why is it still used for radio transmissions?
</blockquote>
Legacy. You can't just re-equip all airplanes with new emergency radios, it costs a lot.
That's about the only place where AM is still in used not being currently replaced.
For example, audio AM broadcast... | Airplanes still use AM radio so they can break-in to an existing conversation and say MAYDAY! FM does not allow a break-in because of its "capture ratio".
| https://electronics.stackexchange.com |
638,152 | [
"https://electronics.stackexchange.com/questions/638152",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/315631/"
] | Why do we use BJTs in discrete applications, but prefer to use CMOS in integrated circuits?
| Not necessarily, MOSFETs are very useful components in discrete applications, too.
For example MOSFETs have lower source-drain voltage drop than BJTs have collector-emitter voltage drop if you have reasonable (not too high) currents. Low voltage switched mode power supplies usually use MOSFETs. Also MOSFETs don't have ... | CMOS transistors on an integrated circuit can be much much smaller (1000's of times) than BJTs. That, together with the ease of driving them (no base current; no need for current limiting resistors) makes them easier to use.
BJTs have more precision and specialized uses in some analog circuits, but modern CMOS processe... | https://electronics.stackexchange.com |
256 | [
"https://mechanics.stackexchange.com/questions/256",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/57/"
] | I have a Subaru Impreza WRX wagon with 110K miles on and, naturally, it has developed a few rattles. One that's particularly annoying is coming from the dash near the windshield to the left of the wheel (very near the VIN tag). This is a "sometimes" rattle, making it hard to track down.
What is the likely cause of t... | I just realized that I never followed up on this question:
It turns out that the rattle was coming from the connectors holding down the large trim piece that lines the base of the windshield. It's a long piece of curved plastic with vents for the defroster and happens to have the VIN tag attached to it. If you pull ... | The vin tag can get loose sometimes. It should be up by your windshield on the left side. They are intentionally not made easy to access. Which begs to question why they would also frequently become loose on old cars but I digress. Because of how hard it is to access I would suggest using some clear RTV on each end to ... | https://mechanics.stackexchange.com |
283,206 | [
"https://dba.stackexchange.com/questions/283206",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/221583/"
] | I am very new to postgres so please my apologies in advance if I sound naive. I am still trying to learn. I am trying to create a readonly role and then create a role and assign readonly role to the user. I logged in as postgres user
<pre><code>CREATE ROLE readonly;
GRANT CONNECT ON DATABASE test_db TO readonly;
GRANT... | The <code>ALTER DEFAULT PRIVILEGES</code> statement you ran will only affect tables created by <code>postgres</code>. If a different user <code>creator</code> creates the tables, you need
<pre><code>ALTER DEFAULT PRIVILEGES FOR ROLE creator IN SCHEMA public GRANT SELECT ON TABLES TO readonly;
</code></pre>
| <pre><code> Login : sudo -u postgres psql
Select db : \c yourDbName
View all table \dt;
grant youUserName to postgres;
(permission related error then use this command)
GRANT ALL PRIVILEGES ON ALL TABLES IN SCHEMA public TO {serverName};
</code></pre>
| https://dba.stackexchange.com |
66,341 | [
"https://security.stackexchange.com/questions/66341",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/50051/"
] | I have 2 or more web applications that need to be able to communicate together using a web service interface.
Information
<ul>
<li>All applications are using TLS/SSL (https)</li>
<li>All applications have access to the same database and that database can only be access by these applications</li>
</ul>
My problem is ... | <blockquote>
My problem is that I don't want anyone else to be able to use the web
service. Meaning that only the applications should be able to call the
web service to get information or execute an action on another
application.
Is there any "simple" way to do that?
</blockquote>
There are several ways. ... | If you were using WCF you could use authentication to only allow specific users run specific methods. I use this in an intranet envoironment. I am not 100% but this might be a good starting point to use WCF or find an equivalent method in whatever technology you are using to call methods.
| https://security.stackexchange.com |
125,671 | [
"https://mathoverflow.net/questions/125671",
"https://mathoverflow.net",
"https://mathoverflow.net/users/4298/"
] | I was wondering if the sum $TS^{2n}\oplus TS^{2n}$ is a trivial bundle?
The same is true for spheres of odd dimension (one can find a nowhere zero section of the second bundle, add it to the first, the first becomes trivial and the rest of second bundle plus trivial bundle of rk 2 is trivial too).
It seems that one sh... | Yes. Let $V$ be a real vector bundle whose base is a $d$-dimensional manifold or cell complex, and whose fibers are $r$-dimensional. Then (1) if $r>d$ then $V=W\oplus \epsilon$ where $\epsilon$ is a trivial rank one bundle, and (2) if $r>d+1$ then the rank $r-1$ bundle $W$ is determined up to isomorphism by $V$. ... | [[Edit]]: I hastily interpreted "sum" as the "direct product", although $\oplus$ is almost surely (or surely) referring to Whitney sum:
No. $\chi(S^{2n}\times S^{2n})=\chi(S^{2n})^2=4$ and so the Euler class of $S^{2n}\times S^{2n}$ is nontrivial (it pairs to the Euler characteristic under Poincare-duality). But that ... | https://mathoverflow.net |
427,776 | [
"https://physics.stackexchange.com/questions/427776",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/165613/"
] | If I push an object in space, will any strain/stress happen within the object, though there is only 1 force rather than a pair of opposite forces on the object?
Can be any (even if trivial) stress/strain under the effect of a single force?
| IchVerloren, welcome to Physics SE!
The thing isn't temperature changing the electromagnetic field. In its most fundamental form, temperature $T$ is the relationship between lack of information (entropy $S$) and total energy $U$:
\begin{equation}
\frac{1}{T}=\frac{\partial S}{\partial U}.
\end{equation}
It is a stat... | You are here- und deshalb bist du nicht verloren! Here is why:
The surface of a hot body can be thought of as consisting of a huge number of tiny electromagnetic oscillators which can be excited by incoming photons. They can absorb the energy in those photons, and then by oscillating they can radiate that energy away ... | https://physics.stackexchange.com |
194,248 | [
"https://electronics.stackexchange.com/questions/194248",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/88506/"
] | I have a problem when I send some character from an hyperterminal through an uart frame, I receive the wrong character. I use a PIC 18F46K80. In some test I did, I got these results :
<strong>Test 1 :</strong><br>
Character sent : <code>'A' (=1000001)</code><br>
Character received : <code>'_' (=01011111)</code>
<st... | The important number isn't 524288, it's \$2^{16}\$ 65536, or hex 10000.
An m x 8 memory will return 8 bits when it gets a m-bit wide memory address. So your 16-bit wide address bus memory chip will be able to provide the contents of all of its memory locations using only 16 address bus signals.
That memory's 16-bit ... | I think this is really an address decoding question.
You want to map the memory to occupy the upper half of the 17 bit processor address space (A weird processor, but anyway) (10000 - 1ffff).
This is probably most easily done by gating the chip select signal with A16 (Which if you think about it will only be high for... | https://electronics.stackexchange.com |
239,201 | [
"https://security.stackexchange.com/questions/239201",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/238316/"
] | I was wondering... if antiviruses store virus definition files that contain virus signatures then why wouldn't they get detected as malware by themselves or Windows Defender or any other AV out there?
| That's a good question, and the answer is they do, or at least <strong>they did</strong>.
It used to be a common problem and was one of the reasons it was recommended not to install multiple virus scanners, because they would trigger on the other vendors signatures.
Currently nearly all signature files are encoded or p... | Well, I would assume that the antivirus is just using a virus signature, and as such couldn't mistake it for a virus. It's like Schroeder said, the antivirus is just using a signature, it's not actually a virus, merely a way to identify the virus and remove it quickly.
| https://security.stackexchange.com |
25,120 | [
"https://physics.stackexchange.com/questions/25120",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/6136/"
] | Given the rather huge price differences between eye pieces at the same focal length. How exactly does the AFOV affect the view seen through the eyepiece?
Are higher / lower AFOV better for certain situations? or is higher always better?
| Simply, a larger FOV provides a wider hunk of sky in the eyepiece. This is useful for capturing entire objects at higher magnifications than could be obtained with cheaper eye-pieces. It doesn't provide more light, just a wider view. As for better, if you've gone to the expense of buying one for a given focal length, i... | There are actually two <em>different</em> fields of view to consider. The <em>apparent</em> field of view is the apparent view you see in the <em>eyepiece</em>, typically 35° to 110°. The <em>actual</em> field of view is how much of the <em>sky</em> you are actually seeing, typically from a few degrees to a few arc min... | https://physics.stackexchange.com |
21,526 | [
"https://electronics.stackexchange.com/questions/21526",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/6337/"
] | I have the circuit of the amplifier below. I want make the DC analysis and find the gain the amplifier produces and the cutoff freq(high-low).
<img src="https://i.stack.imgur.com/hxmsd.png" alt="enter image description here">
My problem is that it's been 15 years since I was student and I remember nothing. I will ap... | I did the DC analysis by hand:
<img src="https://i.stack.imgur.com/ehXtC.jpg" alt="enter image description here">
<img src="https://i.stack.imgur.com/gsnyf.jpg" alt="enter image description here">
<strong>Summary:</strong>
Theoretical:
Ib = 5.963uA
Ic = 895uA
Ie = 900uA
Vce = 7.362V
Spice:
<pre><code> ... | Simplistic but possibly useful starter:
<img src="https://i.stack.imgur.com/nHypM.png" alt="enter image description here">
<strong>1. Gain</strong>
The load current flows in both the 4k7 and the 220r resistors.<br>
So relative voltage ratio between THE two resistors is proportional to their resistances<br>
as V=IR... | https://electronics.stackexchange.com |
339,641 | [
"https://physics.stackexchange.com/questions/339641",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/68549/"
] | <blockquote>
A two-level system is governed by $\mathcal{H_0} = E_0 \left( {\begin{array}{cc} 2 & 0 \\ 0 & 4 \\ \end{array} } \right)$. A small perturbation $\mathcal{H^{'}} = \epsilon \left( \begin{array}{cc} a & b \\ c & d \end{array} \right)$ is applied. So what is the first order correction to t... | In theory you can obtain exactly the eigenvalues of any Hamiltonian - for a $2\times 2$ Hamiltonian, this is equivalent to solving a quadratic equation - but in practice this is computationally impossible. What perturbation theory does is to write the eigenvalues (and also eigenvectors) of a Hamiltonian of the form $\m... | <em>Additional Comment</em>
The nice thing about small matrices is you can easily check the first computation using the pertubative formula $\langle \psi_n | \Delta \hat{H} | \psi_n \rangle$ with a direct expansion, and they should match!
Hint:
compute the eigenvalues directly using
$$\det [\left( {\begin{array}{... | https://physics.stackexchange.com |
385,792 | [
"https://electronics.stackexchange.com/questions/385792",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/102846/"
] | I have a power supply from a broken 3d printer. I want to test if it is still okay. It is specified as 24V, 15A (360 W). It is giving me perfect 24V at idle, but I wanted to test if it is still performing well under (almost) full load.
But what could I use to dissipate 360W at 24V? And: my multimeter is only specified... | @sunny-lan, even if you write the pin to be INPUT, there's still a protection diode from the IO pin to VDD inside the microcontroller. So if your VDD is 3 volts, you're basically still pulling the pin low to 3.6 volts even if you set the pin as INPUT. If you set it as OUTPUT, LOW then you're pulling it low to zero volt... | Do you have space for 3 components? they are tiny.
Please choose the values and part numbers as per your application need. just for representation.
Drive <strong>LOW</strong> from MCU to <strong>disable</strong> the external control circuit (active low)
Drive <strong>HIGH</strong> from MCU to <strong>enable</stro... | https://electronics.stackexchange.com |
566,046 | [
"https://physics.stackexchange.com/questions/566046",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/164488/"
] | I always found Legendre transformation kind of mysterious. Given a Lagrangian <span class="math-container">$L(q,\dot{q},t)$</span>, we can define a new function, the Hamiltonian, <span class="math-container">$$H(q,p,t)=p\dot{q}(p)-L(q,\dot{q}(q,p,t),t)$$</span> where <span class="math-container">$p=\frac{\partial L}{\p... | Legendre transformation is necessary to switch to new <em>independent</em> variables: <span class="math-container">$q, \dot{q}, t\rightarrow q,p,t$</span>. The differential of <span class="math-container">$H$</span> is:
<span class="math-container">$$dH = \frac{\partial H}{\partial q}dp + \frac{\partial H}{\partial q}d... | When you switch from Lagrangian mechanics to Hamiltonian mechanics, you are not just making a change of variables, but you are moving from a problem set on the tangent bundle <span class="math-container">$TM$</span> to a problem set on the cotangent bundle <span class="math-container">$T^*M$</span>. Furthermore, you ar... | https://physics.stackexchange.com |
185,071 | [
"https://softwareengineering.stackexchange.com/questions/185071",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/79782/"
] | In our software environment, we often run a/b tests, as is probably good practice. However, our environment is set up such that, in very short order, the code starts to become very crufty with dead tests. The testing registry is little more than a collection of internal wiki pages.
I thought of a "dead man's switch" s... | I'd be worried about a system that automatically <em>removes</em> code. Unless your team is very well diciplined, I can only see this as a road to tears and pain. Things happen: people go on vacation, get sick, leave the company, forget what the code that's about to expire does, ... and having code be automatically cle... | This system creates a problem of orphaned tests: if someone who wrote a suite of tests and a set of production code associated with it departs the company, the tests are in danger of being removed prematurely by omission of their new owner.
I do not think that "too many tests" is a problem: as long as tests are automa... | https://softwareengineering.stackexchange.com |
178,734 | [
"https://electronics.stackexchange.com/questions/178734",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/79628/"
] | I am trying to figure out how electricity works and I wonder why do electronics components have the maximum voltage limit?
Why does the voltage matter? Isn't it the current that can 'kill' the component?
For example if I have an LED with a maximum voltage of 2V powered by a 5V source.
If I put enough resistance in th... | You most probably don't have a LED 'with a maximum voltage of 2V when powered from a 5GV source', but a LED that is rated for a maximum of 20 mA.
Components that have a low resistance, and particularly ones that approximately drop the same voltage over a wide current range, are rated for a maximum current, not a maxi... | From what it sounds like you are saying, You are putting resistance in series to lower the current to the LED. The LED and resistors are seeing 5V but the LED is not seeing the 5V now. At the appropriate current it will only be seeing 2V. The resistor will be seeing 3V and the circuit will be balanced 2+3=5. When devic... | https://electronics.stackexchange.com |
18,394 | [
"https://mechanics.stackexchange.com/questions/18394",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/1115/"
] | I am not a car mechanic so please excuse my ignorance but... my manual Saab 9-5 has increasing problems starting. The symptoms are as follows.
When I turn the ignition the lights on the dashboard come on. Sometimes there is just complete silence.
Sometimes I can hear the start motor.
Sometimes the car actually star... | I've a 93 and have had what sounds like the same problem, that is the ignition turns on but when the key is turned further to start the engine it does not always crank the engine. In my case it was the ignition switch and being one not to through money away I took it all apart and cleaned the switch contacts and it's b... | The following could be the reason for your car not starting, based on the symptoms you have stated.
<strong>Car does not crank at all</strong>
<ol>
<li>Drained/Dead battery ,Try Jump starting the car, if it starts then it can be the battery, the electrical come on since they don't use as much electricity as the start... | https://mechanics.stackexchange.com |
172,345 | [
"https://electronics.stackexchange.com/questions/172345",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/77308/"
] | I am doing a development board for a IC with 36 WLCSP package. My PCB layout has 16 via over pads, minimum 0.1mm drill holes, 4-layers. I need to fabricate my PCB. And I could not find a exact pricing for PCBs in the required design quality. I sent sample Gerber file for some PCB manufacturers. And they replied with ex... | I would recommend <strong>envelope step response</strong>. It's not terribly elegant, but it does convey the meaning you're trying for. The other possibility that seems possible is <strong>tone burst response</strong>.
| <blockquote>
“response to a step change in the amplitude of the input waveform”?
</blockquote>
"Response" implies a reaction to an "input change" making your sentence now: -
“response to a step ” or "step response"
| https://electronics.stackexchange.com |
241,238 | [
"https://electronics.stackexchange.com/questions/241238",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/114015/"
] | What is the the physical meaning of inductance? We know that the resistance "R" of a conductor is how easily the electrons flow through it, etc., but what about the inductance "X"?
| In addition to the other answers, the symbol for inductance is L, not X. The symbol for inductive reactance is \$X_{L}\$, and for capacitive reactance is \$X_{C}\$.
<blockquote>
What is the the physical meaning of inductance?
</blockquote>
Hugh Young, in his textbook <em>University Physics</em> [1], states the fo... | When we use the term 'inductance', we're usually shortening what should actually be called 'self-inductance'.
When a current flows through a wire, a magnetic field is produced around that wire, with its field strength in proportion to the current strength, changing as the current changes.
We also know that a chan... | https://electronics.stackexchange.com |
3,607,909 | [
"https://math.stackexchange.com/questions/3607909",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/676808/"
] | <blockquote>
Let <span class="math-container">$p\in\Bbb{Z}[i]$</span> be an irreducible element. Prove that for any positive integer <span class="math-container">$n\ge0$</span> the ideal <span class="math-container">$(p^{n+1})$</span> is an ideal in <span class="math-container">$(p^{n})$</span>, and prove that multip... | There are a few problems with what you have written:
<ol>
<li>If <span class="math-container">$p$</span> is an integer then indeed <span class="math-container">$\Bbb{Z}[i]/(p)$</span> is a field of order <span class="math-container">$p^2$</span>. However, if <span class="math-container">$p$</span> is not an integer th... | The map defined by
<span class="math-container">$\sigma:x-> p^nx$</span> is an isomorphic map from <span class="math-container">$Z[i]/(p)->(p^n)/(p^{n+1})$</span>.
We first try to see whether the map is homomorphic or not
<span class="math-container">$\sigma((a+ib + c+id)) = p^{n}(a+c) + p^{n}(b+d)i = \sigma(... | https://math.stackexchange.com |
46,011 | [
"https://dba.stackexchange.com/questions/46011",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/24713/"
] | I am setting up MySQL Master-slave replication and I am trying to figure out how to handle the failover situation where I promote the slave to master (in the event that the master goes down).
My application server needs to direct all writes to the current master, but I cannot use server level HA between the master an... | @RolandoMySQLDBA has answered the question accurately ... but he also pointed out that his solution was "quick-and-dirty."
And that is a very true statement. :)
The thing that concerns me here is not with that answer, but rather is that the original question appears to make an incorrect assumption:
<blockquote>
I ... | If you are using Master/Slave only, here is something quick-and-dirty:
<pre><code>SELECT COUNT(1) SlaveThreadCount
FROM information_schema.processlist
WHERE user='system user';
</code></pre>
What does this tell you?
<ul>
<li>If <code>SlaveThreadCount</code> = 0, you have the Master</li>
<li>If <code>SlaveThreadCount... | https://dba.stackexchange.com |
112,715 | [
"https://mathoverflow.net/questions/112715",
"https://mathoverflow.net",
"https://mathoverflow.net/users/10446/"
] | Classification of simple finite-dim Lie algebras for char >=5 has been accomplished not so long time ago, and char p=2,3 is open problem.
I wonder what is known/expected for char p=2,3 ?
More vague and soft question is the following - look at some famous classification problems: simple finite-dim Lie algebras, simple... | According with the introduction of Strade's book "Simple Lie algebras over fields of positive characteristic. Structure Theory", it seems that a possible list of known finite-dimensional simple Lie algebras over algebraically closed fields of characteristic 3 could be close to complete. A discussion on this topics can ... | (This is too long for a comment). There is a recent surge of activity around (attempts of) classification of simple finite-dimensional Lie algebras in $p=2,3$. It is my understanding that the common view among experts is that the case $p=3$ might be in sight, while situation in $p=2$ is still chaotic. The main current ... | https://mathoverflow.net |
391,070 | [
"https://softwareengineering.stackexchange.com/questions/391070",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/334932/"
] | I have been learning about stateful apps vs non-stateful, but I am still a bit confused on this topic.
For example, let's say I have an app running on Node where users are assigned to random rooms as soon as they connect through socket.io. These are rooms of 4 and not persistent in any way, but they are stored in a gl... | In the context of web applications, we call the server stateful if it maintains transient state <em>in memory</em>, rather than storing any data externally (e.g. in a database).
Stateful applications have a number of problems, for example:
<ul>
<li>you can't have more than one server running without pinning sessions ... | If you are storing state on the server that is needed in order to process an incoming request from the client, then the server is stateful. Said another way, it has state that it stores and needs to access in order to process requests from clients. So, your hashmap is state so your server is stateful.
Now, there are... | https://softwareengineering.stackexchange.com |
361,212 | [
"https://softwareengineering.stackexchange.com/questions/361212",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/79557/"
] | <h2>Summary</h2>
Our development/support team creates applications for company employees (invoicing, task management and the likes).
We have a recurring issue where users misuse the applications they're provided, using workarounds, stepping outside of <em>business</em> process boundaries, leaving data or automated p... | First of all: <strong>if your software allows to mess things up, it is not the fault of the users!</strong>. The only effective way to prevent this is to fix the software, so it won't allow workarounds, or only with some pain. If that's not possible, find a way to mitigate the consequences of these software issues. Of ... | You (perhaps your whole department) need to change your attitude towards users.
Your software is there to help the users to get the job done - not the other way around! If the users are not able to get the job done, or they have to jump through hoops to do it, then is <strong>a fault in the software</strong>, not a fa... | https://softwareengineering.stackexchange.com |
34,367 | [
"https://quant.stackexchange.com/questions/34367",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/13990/"
] | I'm still confused on how to provide liquidity on the forex market using passive or resting orders and get the spread from that (selling at ask and buying from bid)
And what's the dynamics on the LOB using them.?
Anything that could lead me to this will be appreciated.
Thanks
| The only way you can use limit orders to provide liquidity is to post prices that are the same as the prices of the limit orders, and then you will not be earning any spread. In other words, what you are asking is not possible, since to earn spread you would have to quote a bid that is lower than the price of your clie... | With a resting order the market maker's client takes (buys) at the offer, or gives (sells) at the bid. The market maker prices the deal that way as with any other order type. A resting order is simply another type of order and the client pays the market maker's spread like with any order type. I am not sure I agree wit... | https://quant.stackexchange.com |
69,906 | [
"https://math.stackexchange.com/questions/69906",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/947/"
] | What is the most specific word that describes both? As in "all theorems and conjectures are ..." ?
| A Proposition.
Or perhaps a '(mathematical) assertion'
| The term "Mathematical statements" is perhaps slightly too general for many intended purposes. Though theorems and conjectures form a subset of all mathematical statements, theorems must be true and we hope for conjectures to be true, while there are many mathematical statements which are false. This distinction is ver... | https://math.stackexchange.com |
2,458,211 | [
"https://math.stackexchange.com/questions/2458211",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/215714/"
] | I want to estimate big-O notation for $\frac{\log(8n^2)}{\log(n)}$.
I think the big-O notation is constant. am I right?
in case of $\frac{\log(N+1)}{\log(N)}$, is it the same and O(1)?
and what about $\frac{\log(N^3+7n+1)}{\log(N^4+N^2)}$, is it O($\log$ $n$)?
It would be appreciated if somebody could generalize th... | To show that something is less than the <em>greatest</em> common divisor of $ca$ and $cb$, it is enough to show that is a common divisor of $ca$ and $cb$, since obviously the $\gcd$ is the greatest divisor.
Now, $\gcd(a,b)$ divides $a$, hence $c \times \gcd(a,b)$ divides $c a$. Similarly, it divides $cb$. Hence, $c \... | $gcd(a,b)$ divides $a$ implies $cgcd(a,b)$ divides $ca$ since ${ca\over cgcd(a,b)}={a\over {gcd(a,b)}}$, $cgcd(a,b)$ divides $cb$ so $cgcd(a,b)$ is a divisor of $ca$ and $cb$ and by definition is inferior to $gcd(ca,cb)$.
| https://math.stackexchange.com |
586,951 | [
"https://physics.stackexchange.com/questions/586951",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/275176/"
] | I recently saw a Walter Lewin lecture on YouTube, and he proved how solid cylinder rolls down faster due to a smaller moment of inertia.
In one of the steps we get,
my step:
<span class="math-container">$$ma=mg\sin\theta−\mu mg\cos\theta$$</span>
his step:
<span class="math-container">$$ma=mg\sin\theta-Ia/R^2$$</span>
... | In your step, you are assuming that the maximum value of static friction is acting, but that is not the case. Static friction can have variable values, with a limit that it canot cross. When a solid cylinder is rolling down, lesser frictional force acts on it than if a hollow cylinder is rolling down, while you have as... | Taking moments about the centre of the cylinder we have
<span class="math-container">$I\dot \omega=FR$</span>
where <span class="math-container">$F$</span> is the frictional force. But <span class="math-container">$\omega = \frac v R$</span> so <span class="math-container">$\dot \omega = \frac {\dot v} R= \frac a R$</s... | https://physics.stackexchange.com |
169,371 | [
"https://security.stackexchange.com/questions/169371",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/76546/"
] | I realize this is often described as a bad idea. So first of all I'll state motivation - feel free to critique this.
Creating a product for an industry which tends to be overly concerned with security. The product needs to store and return user files but they do not need to be readable server side.
I feel that by enc... | (To be clear: this only protects users in situations that the attacker only gets read-only access and protects users who haven't used the site since an attacker replaced the javascript with a malicious version. It does not protect users from you being malicious from the start unless the user painstakingly verifies / re... | If using asymmetric encryption from openpgp.js, the private key is stored encrypted by default and then briefly decrypted to decrypt or sign a message with the users passphrase.
It is never stored un-encrypted and relies on the user remembering the passphrase he used to create the key pair.
In this case even if the... | https://security.stackexchange.com |
283,007 | [
"https://stats.stackexchange.com/questions/283007",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/150154/"
] | In a (including convolutional) neural network, suppose I get a fair accuracy (say, $\approx 80\%-90\%$) on my validation/test data, but extremely good accuracy ($\approx 100\%$) if I run it back on my training data.
Does this <em>necessarily</em> mean that my network is overfitting, and I should apply some techniques ... | The training error is always going to be somewhat smaller than the validation error (because you're actively trying to minimize the training error) - that in itself is not a sign of overfitting. Overfitting means you decreased the training error <em>at the expense of</em> a higher validation ($\approx$ generalization) ... | I'd say very highly likely. A training accuracy of 100% is acceptable only if the data isn't noisy (which is definitely not the case for image recognition). If not, you probably are learning unnecessary noise, which is not going to allow the net to generalize well, since it "belongs" only to that particular training se... | https://stats.stackexchange.com |
187,910 | [
"https://physics.stackexchange.com/questions/187910",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/75538/"
] | I'm having some problems on notation for indices:
<ol>
<li>I've found in Goldstein, 3rd edition, that the Kronecker delta satisfies
the following property:
$$\delta_{ij}\delta_{ik}=\delta_{jk}$$
But imagine that $i \neq j$ and $j=k$. In this case,
$$\delta_{ij}\delta_{ik}=0$$
but,
$$\delta_{jk}=1.$$
So how does this... | You're getting tripped up by summation notation. Whenever you have a repeated index, this means that that index is to be summed from 1 to 3:
$$
\delta_{ij} \delta_{ik} \equiv \sum_{i=1}^3 \delta_{ij} \delta_{ik}.
$$
You're right that there are two terms in this sum where $i \neq j$, and so the contribution to the sum ... | I think you're tripping on repeated indices/Einstein notation here. If an index is repeated, you're supposed to sum over it. So $\delta_{ij} \delta_{ik}$ seems like it would be zero, except that one term in the sum will have $i = j$ and another will have $i = k$. If they're the same, you get a $1 \cdot 1 = 1$ term, if ... | https://physics.stackexchange.com |
289,459 | [
"https://physics.stackexchange.com/questions/289459",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/72314/"
] | Statistical phase space distributions are related with Wigner functions defined by:
$f(x,k,t) = \int \frac{d^3x'}{(2 \pi)^3}e^{ikx'}\psi^*(x+x'/2,t)\psi(x-x'/2,t)$.
This definition holds only for nonrelativistic quantum mechanics. In relativistic quantum field theory I can't use this definition, since it is not Loren... | <blockquote>
So what happens when the mass M and the distance are set so that $2M/r=1$? If you are at $r=2M$ distance from a $M$ mass black hole then $(1-2M/r)=0$ and what will that mean? This will be zero $−(1−2Mr)dt^2$.
</blockquote>
The correspondence between the Schwarzchild metric and the flat scale metric impl... | <blockquote>
What does that mean?
</blockquote>
It <em>means</em> that for $r \gt 2M$, an infinitesimal displacement $\mathrm{d}r$ is <em>space-like</em> while for $r \lt 2M$, an infinitesimal displacement $\mathrm{d}r$ is <em>time-like</em>. The horizon is the boundary.
Put another way, inside the horizon, moving... | https://physics.stackexchange.com |
136,570 | [
"https://softwareengineering.stackexchange.com/questions/136570",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/17599/"
] | For instance, I have a file with poor indentation (at least incoherant with the rest of the project).
If I correct the indentation and commit, there will be a serious change in the file at a certain point in time, causing the diffs between versions before and after that serious change to be hard to read.
How do you h... | I will handle it in this way:
<ol>
<li>Make one commit ONLY involving the indentation correction</li>
<li>Define a label to categorize this kind of "minor logical modification causing major diffs" behaviors (e.g. <code>[CodingStandard]</code>), and include such label in the comment on that commit (e.g. <code>[CodingSt... | You need to do it, so do it.
However, isolate it to that commit. Make one commit fixing the whitespace and making no other changes to the code. That will be easiest to work with later if you need to revise the repo history or bisect, etc.
| https://softwareengineering.stackexchange.com |
29,255 | [
"https://electronics.stackexchange.com/questions/29255",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/5780/"
] | I may be called upon to write a feasibility study report for consumer hardware (to be manufactured) and/or a service to be offered to clients in the near term. What is the proper technique here? Google says I need to start by suggesting alternate solutions and talking about how my solution is the best one; however my i... | Make a breakdown of the task in separate sub-problems and explain for each of them how you solve them. Make cost calculations. Comparing with alternate solutions you've studied is a good way to take away the wind from the client's sails: if <em>you</em> don't come up with alternatives (which you dismiss with good argum... | Tackle the situation in a organized manner.
For example, your not going to say "my idea is: your information here."
You want to come clear as possible with your claim as possible, but acknowledge the fact that there is other solutions, but yours is more outstanding because ( insert evidence here ).
| https://electronics.stackexchange.com |
18,164 | [
"https://dsp.stackexchange.com/questions/18164",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/5108/"
] | Consider how the Hanning window is defined:
<pre><code>0.5 - 0.5 * cos(n*2*Pi/(N-1))
</code></pre>
By this definition, it has a gain of 0.5, which is simply the average value of the coefficients. By contrast, Flattop windows, as defined, have unity gain, presumably by design.
It would seem appropriate to scale the ... | Yes, it is customary to correct for the gain of a window, except for some cases I refer to later. (If you are interested only in the relative amplitude, of course you do not need to correct for the gain.)
Because the window reduces the gain of the original signal (time domain), the amplitude obtained through FFT need... | one way of <em>"correcting the gain of a window"</em> is to do that in the definition of the window. what would this mean? correcting the gain <em>where</em>? at <em>which</em> frequency? at DC? if you're correcting the gain, at DC, of a window, it means that all coefficients add to 1.
$$ \sum\limits^{+\infty}_{n=... | https://dsp.stackexchange.com |
3,265,143 | [
"https://math.stackexchange.com/questions/3265143",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/356308/"
] | My projective geometry textbook says the following:
<blockquote>
<strong>Degrees of freedom (dof).</strong> It is clear that in order to specify a point two values must be provided, namely its <span class="math-container">$x$</span>- and <span class="math-container">$y$</span>-coordinates. In a similar manner a line... | We have that <span class="math-container">$x, y, z \le 2 \implies (x - 2)(y - 2)(z - 2) \le 0$</span>
<span class="math-container">$$\iff xyz - 2(xy + yz + zx) + 4(x + y + z) - 8 \le 0$$</span>
<span class="math-container">$$\iff 4 \cdot 3 - 2(xy + yz + zx) \le 8 - xyz \implies - 2(xy + yz + zx) \le -(xyz + 4)$$</spa... | Let <span class="math-container">$x\geq y\geq z$</span>.
Thus, <span class="math-container">$$(2,1,0)\succ(x,y,z).$$</span>
Indeed, <span class="math-container">$$2\geq x,$$</span>
<span class="math-container">$$2+1\geq x+y$$</span> and <span class="math-container">$$2+1+0=x+y+z.$$</span>
Also <span class="math-contai... | https://math.stackexchange.com |
13,779 | [
"https://dsp.stackexchange.com/questions/13779",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/5014/"
] | I was reading on windowed fourier transform and wavelet transform, and i was thinking that the windowed fourier transform is a subset of wavelet transform. Is that true?
| Define the Fourier transform as $$ x(t) = \mathcal{F}^{-1}\big\{ X(\omega) \big\} \triangleq\frac{1}{2 \pi} \int_{-\infty}^{\infty} X(\omega) e^{j\omega t} \ d\omega $$
and $$ X(\omega) = \mathcal{F}\big\{ x(t) \big\} = \int_{-\infty}^{\infty} x(t) e^{-j\omega t} \ dt $$.
Define the real-valued and non-negative w... | Wavelets commonly factor the frequency of the basis vectors into their temporal widths, some with more than one temporal location. Windowed FFTs fix the temporal width of each basis vector to the length of the FFT, thus independent of any bin frequency, and with the basis location fixed to the center of the FFT.
I su... | https://dsp.stackexchange.com |
7,494 | [
"https://physics.stackexchange.com/questions/7494",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/2740/"
] | $\alpha$ radiation consist of positive charged helium nuclei, $\beta$ radiation of negative charged electrons. So why don't the $\alpha$ particles take those electrons to get neutral?
| I agree with jwenting but in some sense, I feel that he is not answering the question: why there's no "combined $\alpha$ plus $\beta$ decay in which a nucleus emits e.g. a helium atom?
Well, let me start with the $\beta$-decay. Nuclei randomly - after some typical time, but unpredictably - may emit an electron because... | when they meet, it might happen. But calculate the chances of 2 particles meeting that have the right energy levels to actually combine. You'll find those chances are miniscule.
| https://physics.stackexchange.com |
3,316,749 | [
"https://math.stackexchange.com/questions/3316749",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/496514/"
] | One of my classes has online notes containing theorems. One of the theorems is "Assume that <span class="math-container">$R=[a,b]\times[c,d]$</span> is a rectangle in the <span class="math-container">$xy$</span> plane. Let <span class="math-container">$f$</span> be a function on <span class="math-container">$R$</span... | This is a consequence of Fubini's theorem. A proof for Riemann integration follows.
Consider a partition <span class="math-container">$P$</span> of <span class="math-container">$R$</span> into <span class="math-container">$mn$</span> rectangles <span class="math-container">$I_j\times J_k$</span> where the intervals <... | Here is another way of looking at the issue:
We know that <span class="math-container">$\iint_DfdA$</span>, for a <span class="math-container">$0$</span>-form scalar function <span class="math-container">$f$</span>: D <span class="math-container">$\Rightarrow$</span>R, represents the volume under the graph of <span cl... | https://math.stackexchange.com |
52,492 | [
"https://dba.stackexchange.com/questions/52492",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/29782/"
] | I have a simple mysql table which I use as a server booking system. A user can log in to a server, if he has a valid booking for that server. A sample data might look like this:
<pre><code>+----------+----------------+---------------------+---------------------+
| server | user | start | end ... | This script will provide you with detailed information on SQL Server Agent Jobs and their schedules. This doesn't include any scheduled task that may exist in Scheduled Tasks for Windows.
<pre><code>USE msdb
Go
SELECT dbo.sysjobs.Name AS 'Job Name',
'Job Enabled' = CASE dbo.sysjobs.Enabled
WHEN 1 THEN '... | USE
<ul>
<li>select j.name, s.next_run_date, s.next_run_time
from sysjobs j
inner join sysjobschedules s on j.job_id = s.job_id</li>
<li>Select jobsched.next_run_date, jobsched.next_run_time, sched.name, sched.<em>,jobsched.</em> FROM msdb.dbo.sysschedules AS sched
inner Join msdb.dbo.sysjobschedules AS jobsched ON sc... | https://dba.stackexchange.com |
338,400 | [
"https://softwareengineering.stackexchange.com/questions/338400",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/234573/"
] | I'm creating an ASP.NET MVC application to work with data from an API that has a couple of different endpoints for different geographical regions. Each region has a name, an alphanumeric ID and a host URL. e.g.: <code>Western Europe - WE1 - we.api.com</code>.
There are less than a dozen regions and their values won't ... | You could do that like this:
<pre class="lang-cs prettyprint-override"><code>class Region
{
public string name { get; private set; }
public string id { get; private set; }
public string url { get; private set; }
// private constructor
Region() {}
// static members
public static Region Wes... | The answer all depends on your requirements over time.
If your only requirement is clean code that's easy to understand, I would suggest a straight forward class like this:
<pre><code>internal static class regionStrings {
static public string Ireland { get; private set; }
static regionStrings()
{
Ireland ... | https://softwareengineering.stackexchange.com |
75,404 | [
"https://datascience.stackexchange.com/questions/75404",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/98492/"
] | E.g. In detriment of a smaller mean error, I want to have fewer big mistakes
I'm working on a time series forecasting task and in some specific cases I don't need perfect accuracy, but the network cannot by any mean miss by a lot.
Any suggestions of loss functions or other methods to solve this issue?
| As you increase the harshness of big misses, you make the model less willing to miss big.
For instance, absolute loss considers missing by <span class="math-container">$2$</span> to be twice as bad as missing by <span class="math-container">$1$</span>, but square loss considers missing by <span class="math-container">... | You could consider something like the relative error
<span class="math-container">$$L(y,\hat{y}) = \sqrt[]{\sum\big\vert (y_i - \hat{y}_i) / y_i \big\vert^2}$$</span>
| https://datascience.stackexchange.com |
43,748 | [
"https://stats.stackexchange.com/questions/43748",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/16849/"
] | I have the following problem: two groups A and B.
The proportions of married and single are ($p_1$) and ($p_2$) respectively, and the standard deviations ($s_1$) and ($s_2$). The sample consists of ($n_1$) A and ($n_2$) B observations.
Now I want to test whether the proportions are equal. I use the following formul... | There are two differences for a usual linear regression model (<code>lm</code>) between <code>AIC</code> and <code>extractAIC</code>:
<ul>
<li><code>AIC</code> accounts for the estimation of the unknown variance of the error (i.e., scale) while <code>extractAIC</code> does not, hence <span class="math-container">$k$</s... | According, to the help for these two function (use ?AIC and ?extractAIC) this is expected.
Note that the AIC is just defined up to an additive constant, because this is also the case for the log-likelihood. This means you should check whether
<pre><code>extractAIC(full.modell) - extractAIC(null.modell)
</code></pre... | https://stats.stackexchange.com |
220,224 | [
"https://physics.stackexchange.com/questions/220224",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/99439/"
] | A $65\,\mathrm{kg}$ object slides down a $30^\circ$ slope at a constant speed. Air resistance is negligible. Find the coefficient of friction and force of friction.
The normal force equals $F_\text{normal} = 637 \ \mathrm{N} (=Gravity * Mass) \cos{(30^\circ)}$. But this does not yet give the coefficient of friction.... | Thank you both for the help. I were able to find a, better I think, solution myself, but only partially why it works. Maybe you could help me with that? If I break the rotation down into three components that each will satisfy the rotation for each vector, I can add the components together to find the total rotation ax... | The rotation velocity vector $\vec \omega$ must be in the plane perpendicular to the vector difference $\vec a - \vec a_0$ and also be in the plane perpendicular to the vector difference $\vec b - \vec b_0$. Consequently, unless these two vector differences are parallel to each other (and provided neither is zero), the... | https://physics.stackexchange.com |
664,705 | [
"https://physics.stackexchange.com/questions/664705",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/652/"
] | This is not a homework question. I attempted to draw a free body diagram for a person pulling or pushing a cart.
Based on Newton's third law, the following forces act on the body of the person:
<ul>
<li>forward reaction force done by the ground because of friction between the person and the ground.</li>
<li>downward fo... | Probably the easiest way to analyze it is in terms of torque balance.
So, you already know that a rigid body which happens to have a constant momentum, this constancy requires all of the external forces to sum to zero: this is force balance. (It is sometimes confused with Newton's third law; Newton's third law just say... | <h3>It adds a horizontal component to the vertical force exerted by your legs.</h3>
When you're standing straight up, the forces exerted by your legs are straight up and down. Your legs are designed to exert a force to counter your bodyweight and allow you to stand like this, so they're quite strong at countering this ... | https://physics.stackexchange.com |
233,175 | [
"https://security.stackexchange.com/questions/233175",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/236549/"
] | I am in the process of developing a web-application which requires MFA on every login. (On the first login, before you can do anything, you are forced to setup MFA. Due to monetary restrictions and development time restraints, the MFA chosen is a simple TOTP solution, but in the future I may include other providers suc... | So from what I gather here, the "best practice" is to keep the recovery / changing of MFA completely separate from the password reset / recovery.
That's what I thought, but it's nice to hear others say it too.
| I would not make that assumption as it would undermine the security of having a second factor to a certain degree. A malicious factor who manages to reset a user's password (such as by exploiting a vulnerability in the password recovery flow) will then be able to take over the account by resetting MFA as well.
The pas... | https://security.stackexchange.com |
83,680 | [
"https://mathoverflow.net/questions/83680",
"https://mathoverflow.net",
"https://mathoverflow.net/users/9550/"
] | <ol>
<li>Is it possible to prove without Continuum Hypothesis that for every uncountable subset $S$ of $\mathbb{R}$ there is a real number $x$ that splits it into two parts of the same cardinality, i.e. $\left|S \cap (-\infty,x)\right|=\left|S \cap (x,\infty)\right|$? </li>
<li>(if the answer to the first question is n... | No, the statement cannot be proven in ZFC without assuming continuum hypothesis or something similar. In fact, it is equivalent to the statement that there are finitely many cardinalities between $\aleph_0$ and $2^{\aleph_0}$, so it is strictly weaker than the continuum hypothesis.
Suppose that there were infinitely m... | Suppose that the continuum is larger than $\aleph_\omega$. Choose a subset $S_n$ of $(n,n+1)$ of cardinality $\aleph_n$ and let $S=\cup_{n=1}^\infty S_n$. Then for each $x$, $S\cap (-\infty,x)$ has cardinality smaller than $S\cap (x,-\infty)$.
| https://mathoverflow.net |
40,560 | [
"https://chemistry.stackexchange.com/questions/40560",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/16851/"
] | This is what I understand about three electrode electrochemistry (correct me if I am wrong):
<ul>
<li>The working electrode is where the reaction of interest happens, e.g. copper ions reduced to solid copper.</li>
<li>The auxiliary/counter electrode supplies the current to the working electrode, i.e. it is the source ... | The way a three electrode potentiostat works is to
<ul>
<li>read the potential difference between the Reference electrode and the Working electrode using a very small DC current(generally pA level). (Just like MaxW mentioned)</li>
<li>Compare this potential to the desired voltage level as input by the user or a funct... | <blockquote>
<blockquote>
The reference electrode lets you control the potential difference so you don't apply too much driving force to the working electrode and end up reducing water etc. <strong>No current passes through it.</strong>
</blockquote>
</blockquote>
You have the basic idea but if <em>absolutely ... | https://chemistry.stackexchange.com |
738 | [
"https://quant.stackexchange.com/questions/738",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/35/"
] | I built risk models using cluster analysis in a previous life. Years ago I learned about principal component analysis and I've often wondered whether that would have been more appropriate. What are the pros and cons of using PCA as opposed to clustering to derive risk factors?
If it makes a difference, I'm using the r... | I've played around with both schemes, but not for portfolio optimization.
I used PCA on some interest rate models. That turned into a Partial Least Squares scheme, then into some non-linear thing. I wasn't impressed with the results.
My Cluster Analysis scheme morphed into a classification scheme, and it turned ou... | They are not mutually exclusive. PCA and clustering are similar but used for different purposes. You could use PCA to whittle down 10 risk factors to say 4 uncorrelated factors, and you could combine securities with different FACTORS into different clusters with offsetting returns and variance characteristics. However... | https://quant.stackexchange.com |
73,879 | [
"https://physics.stackexchange.com/questions/73879",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/23816/"
] | I have a question regarding the magnetic moment of an atom.
If you just have one atom, and you apply an external magnetic field in lets say the z-direction. Then the magnetic moment will precess around the direction of the magnetic field applied, and depending on the quantum numbers it can precess in different quantize... | The reason is simple. With the existence of external magnetic field, the coupling involve the magnetic moment quantum number $m$ and the z-component of angular momentum $L_z$:
$$\mathcal{H}\propto \vec{B}\cdot \vec{L_z}$$
However, in quantum mechanics, the magnitude of possible $L_z$ are strictly less than magnitude of... | corresponding to magnetic moment of atom there is magnetic field so when a atom is placed in external magnetic field there is interaction in magnetic moment and external magnetic field and energy depends upon the angle btw these two so mag moment try to align in B direc.but theta can not be changed because if it will ... | https://physics.stackexchange.com |
119,326 | [
"https://mathoverflow.net/questions/119326",
"https://mathoverflow.net",
"https://mathoverflow.net/users/29273/"
] | Apologies in advance if this is a bit too simple to ask here, but I think I'm probably more likely to get an answer here than at stackexchange.
I've been trying to learn the basics of the Langlands program over the last couple of months, and I've reached a funny point where I <em>think</em> I understand the rough idea... | I would disagree with your last two points just as wccanard does in his comment: automorphicity of $L$-functions is part of global Langlands functoriality, not the local conjectures (although the two are related).
I would also disagree with your third point: instead of nonabelian harmonic analysis, it is automorphicit... | To complement the answer from GH from MO:
Your first two bullet points, about Tate's thesis and Hecke characters are completely correct.
Your third point should be made more precise as follow. Yes we can prove the functional equation for the L-function attached to automorphic representations of $GL_n$, and a bunch of... | https://mathoverflow.net |
718,762 | [
"https://physics.stackexchange.com/questions/718762",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/339229/"
] | The statement "Uncertainty principle is valid for macroscopic objects" is (empirically) unfalsifiable: no macroscopic measurement is going to detect.
Yet, the majority of scientists insist that UP is valid at macroscopic level...
| Reusing the photons to produce more electron hole pairs is sometimes called photon recycling, and some photons do get reabsorbed in a productive way, but if the photon energy is already near the bandgap it may not produce an electron hole pair if there is no available state to be excited.
Then if you think about absorp... | When photons strike electrons, the electrons get excited to a higher energy level. Then, spontaneously (randomly), they release this excess energy and return back to their original position. In doing so, they release a photon and some heat into the surrounding area.
When there is total internal reflection, this photon ... | https://physics.stackexchange.com |
3,907,194 | [
"https://math.stackexchange.com/questions/3907194",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/547331/"
] | I am trying to understand the proof of the following theorem :
<blockquote>
Let <span class="math-container">$A$</span> be an <span class="math-container">$n\times n$</span> matrix such that it has only negative eigenvalues and let <span class="math-container">$f: \mathbb{R}\times \mathbb{R}^n$</span> continuous and lo... | The logic of this kind of continuation argument goes like this. What has been shown is that supposing <span class="math-container">$\|x_0\|<\frac\delta M$</span>, if <span class="math-container">$\|x(t)\|<\delta$</span> for all <span class="math-container">$t$</span> in <em>any</em> interval <span class="math-con... | The constant <span class="math-container">$M$</span> is there as guard for the behavior of <span class="math-container">$e^{(A+αI)t}$</span> in the case of eigenvalues with "proper" multiplicities. Then the matrix exponential may also have polynomial terms, and as one can see in examples like <span class="mat... | https://math.stackexchange.com |
308,040 | [
"https://softwareengineering.stackexchange.com/questions/308040",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/-1/"
] | I have the following code:
<pre><code>subroutine foo(int index)
{
// Check A.
// Critical: Check A must precede Check B below.
if (index == 1)
{
return true;
}
// Check B.
if (index - 2 < 0)
{
return false;
}
return true;
}
</code></pre>
The code is a simpl... | Anyone who can edit the source code can remove anything that you might put in there to "protect" them. You can do two things:
<ol>
<li>Choose a good name for the function that conveys your intention</li>
<li>Provide Unit Tests that will break if someone ever changes what the function does</li>
</ol>
Both do not pre... | In probably all relevant languages, the statements are processed in order.
And that's valid for the whole program code. Even the simplest programs wouldn't work otherwise.
If someone is allowed to change the code but doesn't understand anything about it, there's not much you can do about it, except removing his right... | https://softwareengineering.stackexchange.com |
173,213 | [
"https://softwareengineering.stackexchange.com/questions/173213",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/38606/"
] | Friend of mine said that not every interface is abstract. I haven't chance to discuss that with him but it get me thinking of not abstract interface in any type of language.
Is there a non abstract interfaces?
| Simple answer to your question : No, your friend is wrong.
An interface provides no implementation of the methods it defines. Would it make sense if we could instantiate one of those? Of course not. Interfaces are only that, an abstraction.
This is obviously assuming that when you say <code>interface</code>, you thin... | Yes.
The <em>idea of an interface</em> (ie, a description of facilities provided and their semantics) is inherently abstract.
However, the question appears to confuse this with the mechanism by which such an interface (small <em>i</em>) may be reified into certain languages which provide an <code>Interface</code> (bi... | https://softwareengineering.stackexchange.com |
18,773 | [
"https://engineering.stackexchange.com/questions/18773",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/14437/"
] | I've come across this phenomenon several times and never found any real reason for this.
When I consider a cylindrical object like a rod, I need to calculate several things. One of those is the stress tensor in cylindrical coordinates represented by $r$, $\theta$, and $z$ directions.
Now, in many books and in my lect... | I don't know if its a driver, but an advantage to rail is that you can run parallel lines very close together and in close proximity to structures and such.
I don't think you'd want buses approaching each other at 100+mph on a paved road that would fit in the space of an existing rail corridor.
| The primary advantage is a sense of prestige and permanence that encourages more ridership and more development than buses. Technically heavy rail can achieve larger passenger volumes with minimal headway compared to buses (which can achieve smaller headways but are more limited in size), but commuter trains cannot ach... | https://engineering.stackexchange.com |
271,404 | [
"https://stats.stackexchange.com/questions/271404",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/130693/"
] | Suppose you have a binomial experiment with 1 million trials and chance of success 0.25. At the end of the 1 million trials you record the number of successes. You repeat this experiment 100 million times, independently. What should you estimate the sample mean of succeses and sample second moment of success to be?
I ... | let $X_i\sim Binom(N,p)$ and n be number of simulations
we know
$E(\bar{X_i})=E(\frac{\sum X_i}{n})=\frac{\sum E(X_i)}{n}=\frac{n*E(X_i)}{n}(because~X_i's~are~identical~for~each~simulation)=Np$
and
$E(\bar{X_i^2})=E(\frac{\sum X_i^2}{n})=\frac{\sum E(X_i^2)}{n}=\frac{n*E(X_i^2)}{n}(because~X_i's~are~identical~for~e... | First - n∗p∗(1−p) is not .00188 - it's much larger (n is a million!). Second - of course the numbers you get are large - a million is a large number, and the variance is the square of the standard deviation and therefore is very large.י
| https://stats.stackexchange.com |
294,246 | [
"https://softwareengineering.stackexchange.com/questions/294246",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/13154/"
] | In practical terms it means using an custom (immutable) <code>class</code> over a <code>string</code> or some other primitive type.
Examples:
<ol>
<li>Publishing: International Standard Book Number.</li>
<li>Finance: International Securities Identification Number.</li>
</ol>
Advantages:
<ol>
<li>Can ensure the form... | If you can give the class enough useful functionality to justify the added complexity of not being a string, then do it. For identifiers like ISBN and ISIN, I suspect this is not the case.
For an identifier class to be useful, I'd expect it to look something like this:
<pre><code>class ISIN {
fromCUSIP()
from... | I would say go for it. I would argue that the advantages outweigh the disadvantages in this case. The extra code is likely to be pretty minimal and the persistence issue can be solved pretty easily be providing some sort of converter between your new Class and the type the database expects (I've never used Entity Fra... | https://softwareengineering.stackexchange.com |
1,530,447 | [
"https://math.stackexchange.com/questions/1530447",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/290335/"
] | Can you help me to proof that the nth derivative of $9\sqrt{x}$ is $$ (-1)^{(n-1)} \cdot \frac{9(2n-2)!}{(n-1)!} \cdot (4x)^{\frac{1-2n}{2}}$$
I've tried induction but didn't go very far.
Many thanks
| Induction is a very good way. For the induction step,
Say $P(n)$ is true for $n=k$ <br>
For $P(k+1)$, $$\frac{d}{dx^{k+1}}(9\sqrt x)$$
$$=\frac{d}{dx}\left(\frac{d}{dx^{k}}(9\sqrt x)\right)$$
$$=\frac{d}{dx} \left[(-1)^{(k-1)} \cdot \frac{9(2k-2)!}{(k-1)!} \cdot (4x)^{\frac{1-2k}{2}}\right]$$
$$=(-1)^{(k-1)} \cdot \fr... | Firstly, the 9 is unimportant. Induction is the correct way to proceed, but perhaps we can disguise it in a computation:
$$\begin{align} \frac{d^n}{dx^n} \left( x^{\frac{1}{2}} \right) &= \frac{d^{n-1}}{dx^{n-1}} \left( \frac{1}{2} x^{\frac{1}{2} -1} \right) \\&= \frac{d^{n-2}}{dx^{n-2}}\left( \frac{1}{2} \le... | https://math.stackexchange.com |
265,939 | [
"https://stats.stackexchange.com/questions/265939",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/137200/"
] | If I have given distribution family, say normal, is there a way how to derive what are the location and scale parameters based on the probability density function (PDF)?
I know in case of normal distribution, it is $\mu$ and $\sigma$ respectively. I know how to show, that these two are in fact location and scale para... | Let's talk about what a location parameter is. (The discussion of scale parameters will exactly parallel it and offers little new.)
The setting concerns a set $\mathcal{F}$ of probability distributions $F_\theta$ indexed by a parameter $\theta \in \Theta \subset \mathbb{R}^p$. "Indexed by" not only means each $\thet... | Consider a random variable $Z$ with any density function $f_Z(z)$. You can define a location–scale family with the transform $X=\phi Z +\theta$, & the new density function is given by
$$f_X(x;\theta,\phi) = \frac{1}{\phi}\cdot f_Z\left(\frac{x-\theta}{\phi}\right)$$
So any family of distributions whose dens... | https://stats.stackexchange.com |
41,874 | [
"https://dba.stackexchange.com/questions/41874",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/23597/"
] | What I'm trying to do is running a job on more than 100 million domains which haven't processed before.
I have two tables, "<strong>domain</strong>" and "<strong>domain_setting</strong>", on every batch (10.000 domains per batch) I'm getting a list of domains from domain table by checking their status on "<strong>doma... | Since <code>is_keyword_checked</code> can take only two possible values, <code>0</code> or <code>1</code> (and it's not nullable), you can try the rewriting. There is no <code>OR</code> and the index on <code>(is_keyword_checked)</code> will be used:
<pre><code>SELECT *
FROM domain
WHERE domain_ID NOT IN
( SEL... | If I'm reading your query correctly your asking for anything NOT in domain_setting EXCEPT for those with is_keyword_checked = 0. You should be be able to just get rid of that first not in check.
Further subqueries are not always as efficient as you might think. You could rewrite the query to be
<pre><code>SELECT * ... | https://dba.stackexchange.com |
466,707 | [
"https://math.stackexchange.com/questions/466707",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/90220/"
] | I would like to have some examples of infinite dimensional vector spaces that help me to break my habit of thinking of <span class="math-container">$\mathbb{R}^n$</span> when thinking about vector spaces.
| <ol>
<li>The space of continuous functions of compact support on a locally compact space, say $\mathbb{R}$.</li>
<li>The space of compactly supported smooth functions on $\mathbb{R}^{n}$.</li>
<li>The space of square summable complex sequences, commonly known as $l_{2}$. This is the prototype of all separable Hilbert s... | <ol>
<li>$\Bbb R[x]$, the polynomials in one variable.</li>
<li>All the continuous functions from $\Bbb R$ to itself.</li>
<li>All the differentiable functions from $\Bbb R$ to itself. Generally we can talk about other families of functions which are closed under addition and scalar multiplication.</li>
<li>All the inf... | https://math.stackexchange.com |
279,886 | [
"https://electronics.stackexchange.com/questions/279886",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/135732/"
] | I'm working on adding some LED's to some electric train engines that can have a variable power input up to 13V. I was hoping that under 5V, the power could go directly to the LED (with an inline resistor) for variable brightness, but limit the circuit to 5V as the input voltage increased beyond 5V so the maximum LED br... | <img src="https://www.circuitlab.com/circuit/5fzbnwrpa27p/screenshot/540x405/" alt="circuit">
I ended up building my own AMS1117 module with a diode rectifier. It achieves full brightness at the point the train starts moving. Perfect! Thanks for the tip on the 1117, @FakeMoustache!
| <strong>NEVER EVER</strong> connect a LED directly to a supply unless it is specifically designed for that. Almost all common LEDs are not.
<strong>ALWAYS</strong> use a series resistor.
If you make 20 mA flow at 13 V then at 5 V the LED will still work but at a lower brightness. For that 20 mA you need a 500 ohm res... | https://electronics.stackexchange.com |
96,235 | [
"https://chemistry.stackexchange.com/questions/96235",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/63628/"
] | I'm a computer science with only a weak undergraduate chemistry background, but have recently become interested in simulation methods for computational chemistry. Many simulation methods, such as DFT, make the Born-Oppenheimer approximation (nuceli are static) and solve for some properties of the electrons (in the case... | Yes, these methods (both wavefunction-based and electron density-based) typically solve a <em>purely electronic</em> system defined by an electrostatic potential which is produced by the nuclei; the Born-Oppenheimer approximation can be understood as treating the electronic system as a function of nuclear geometry, whi... | As far as Quantum mechanics is concerned, there is no such thing as bonds or bond order. Any QM method is just dependent on finding the wavefunction that satisfies the Schrodinger (or Dirac if concerned with relativity) equation (or some approximation of it). Within the Born-Oppenheimer approximation for a particular m... | https://chemistry.stackexchange.com |
2,919,303 | [
"https://math.stackexchange.com/questions/2919303",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/109135/"
] | I want to calculate the maximum likelihood estimation of $P(x|\theta) = 1/(1-\theta)$ for $\theta<= x <=1$.
I end up with $log1 - nlog(1-\theta)$ and when I want to take the derivitie I end up with $-n*-1/(1-\theta)$ how should I proceed? Because I cannot set this equal to zero and get a value for $\theta$
I kn... | When you cannot set derivative to zero, it means the maximum occurs at the boundary. Indeed, it is clear the maximum occurs at $\theta=\min x_i$ if you actually kept the indicator in your likelihood function:
$$P(x\mid\theta)=(1-\theta)^{-1}1_{\theta\leq x\leq 1}$$
So with independent $x_1,\dots,x_n$, we get
$$L(\thet... | So lets write down the PDF of $n$ independent samples generated from $x \vert \theta$, i.e
\begin{equation}
f(x_1 \ldots x_n \vert \theta)
=
f(x_1 \vert \theta)
\ldots
f(x_n \vert \theta)
=
\frac{1}{(1 - \theta)^n},
\qquad
\theta < x_k < 1, \quad
k = 1 \ldots n
\end{equation}
The log likelihood is the lo... | https://math.stackexchange.com |
44,053 | [
"https://mathoverflow.net/questions/44053",
"https://mathoverflow.net",
"https://mathoverflow.net/users/10416/"
] | This may seems to be an elementary question, but I found no answers on MO nor google.
I have always heard "polynomials are easier to handle with than integers". For example:
<ol>
<li>When $n$ is quite large, maybe 200 or more, it's relatively easier to factorize a polynomial $f$ of degeree $n$ than to factorize an in... | How Halloweeny can you get with your questions? The norm on $Z$ is Archimedean and the norm on $F[X]$ is non-Archimedean, and, in general, non-Archimedean maths is easier than Archimedean...
| In the Euclidean division of polynomials, quotient and remainder are uniquely defined, and compatible with addition. This fails for integers.
There is no integer analogue of constant polynomials. I guess that the search for the "field with one element" is in a sense motivated by this.
| https://mathoverflow.net |
457,028 | [
"https://physics.stackexchange.com/questions/457028",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/208011/"
] | I know that the conditions for constructive/destructive interference are given by the following equations:
<span class="math-container">$$\text{Constructive:} \space \space \space d\sin{\theta}=n\lambda \\ \text{Destructive: }\space \space \space d\sin{\theta}=(n+\frac{1}{2})\lambda$$</span>
for <span class="math-con... | <strong><em>I was wondering that the density of electric field lines determine the strength of the electric field</em></strong>
First we need to realize that electric field lines are used to visualize and analyze electric fields and therefore should be considered as a pictorial tool as opposed to a physical entity. Fo... | It is <strong>not</strong> true that if <span class="math-container">$E \rightarrow \infty$</span> then it should be the case that <span class="math-container">$\Phi_E \rightarrow \infty$</span>.
Notice that in your example, the surface area of your sphere tends to zero <span class="math-container">$A \rightarrow 0$<... | https://physics.stackexchange.com |
1,534 | [
"https://security.stackexchange.com/questions/1534",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/176/"
] | There are some websites and even programs that I use that have ridiculous password restrictions. Lots of forums for instance restrict passwords to ~32 characters. Others enforce a restricted charset.
What would cause a developer to put in such restrictions? As long as you do the initial hashing of a password on the c... | I think the reason is the same as for any other input validation; to make sure it doesn't cause any problems during processing and storage. Now, for passwords this is of course completely misguided since they should be hashed and therefore neither stored nor really processed in cleartext.
I'd take any such limitation... | I'm going to go with: the same old reasons people do strange things.
<ul>
<li><strong>Because it seemed like a good idea at the time.</strong> Developers might be well-intentioned but poorly informed. There's no need to limit password length, but maybe developers aren't aware of that. Maybe developers didn't even t... | https://security.stackexchange.com |
88,650 | [
"https://mechanics.stackexchange.com/questions/88650",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/71946/"
] | I bought a second-hand 2005 Nissan Almera 1.5 just under 6 months ago, and apart from an early issue with the catalytic converter, seemed to be running okay.
However, a month or so ago, I was out running errands and the car refused to start again after my first stop. Battery and starter motor all checked out okay, and ... | There's a few things that come to mind which match hard starting when hot and a loss of fuel economy:
<ol>
<li>Bad coolant temperature sensor: if your car's ECU (Engine Computer) doesn't know what temperature the engine is it will not know the correct air-fuel ratio to inject into the cylinders. This is where an OBD re... | There were a ton of Hondas that had fuel pump relays on a circuit board that failed after a few years. And they would fail when it warmed up, so the first drive was fine, but a quick stop would leave the car not able to start.
No idea if Nissan had a similar problem, but relay should be relatively easy to test (or rep... | https://mechanics.stackexchange.com |
476,197 | [
"https://electronics.stackexchange.com/questions/476197",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/225886/"
] | The manual for my HV probe tells me to connect my ground clip to the chassis. I can see how this would be good advice for say a 12V car, because the chassis is made the ground and every component uses the same power that's hooked to ground.
However this can't be the case with say a CRT circuit. The way I see it, whe... | Things at different voltages often share the same ground.
When you say "If I wire the ground wire of a 30VDC LED and the ground wire from a 200VDC motor to a sheet of aluminum and turn it on, things are going to spark." you are making an assumption that is not necessarily true. This is where you are getting off track... | Not everything is "grounded" to chassis. It is normal, allowable <em>and often necessary</em> to have a circuit entirely floating from "ground".
<blockquote>
Take the electrical controls and accessory loads on a subway train or light rail. You have two separate systems: 600V-3000V line voltage, which propels the... | https://electronics.stackexchange.com |
156,028 | [
"https://dba.stackexchange.com/questions/156028",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/111154/"
] | My issue is as follows:
I'm trying to create a global temp table using data from DB1, then use that temp table in a query executed in DB2 and then have the results imported into a new table on DB2. Since the query is a bit more complicated a simple Merge join won't do as I need to transform the data and add an extra c... | There are two methods available, either use ZIP archive to install or you may have to change the datadir variable in my.ini after installation. You can use following steps
<ol>
<li>Complete the installation </li>
<li>Identify the config file and then look for related datadir being used, you may used mysql>show varia... | You can make the following steps:
<ol>
<li>Manually create folder <code>C:\Program files\MySQL\MySQL Server 5.7</code> (this is in 64 bits version)</li>
<li>Run the installer normally </li>
</ol>
Create an empty folder, although is empty folder, makes the installer allow you to choose another location.
| https://dba.stackexchange.com |
151,334 | [
"https://stats.stackexchange.com/questions/151334",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/76577/"
] | I have a question about hypothesis testing.
How can I test a hypothesis like the following for example:
<strong>People prefer chicken to beef.</strong>
And for example, the data that I have is that I've asked from 1000 people "do they prefer beef or do they prefer chicken?" 80% said chicken, and 5% said beef and 15%... | "People prefer chicken to beef" is not quite precise, so we need to 'unpack' the concept a bit:
"The proportion of people who prefer chicken to beef is larger than the proportion of people who prefer beef to chicken"
If that's what you really mean, that's something we can work with.
You also have a sample which -- ... | In hypothesis testing, you come up with...a hypothesis! So if the statement was
<blockquote>
People prefer chicken to beef
</blockquote>
Maybe you try to quantify it by saying, "hmmm, I think over 50% of people prefer chicken to beef". It doesn't actually matter if people say they are indifferent, after all you wa... | https://stats.stackexchange.com |
116,540 | [
"https://stats.stackexchange.com/questions/116540",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/56318/"
] | I am a newcomer to survival analysis, although I have some knowledge in classification and regression.
For regression, we have MSE and R square statistics. But how we can say that survival model A is superior to survival model B besides some kind of graphical plots (K-M curve)?
If possible, please explain the differ... | The main problem with statistics like the Cox model $R^2$ (described in another answer) is that it's very dependent on the censorship distribution of your data. Other natural things you might look at, such as the likelihood ratio to the null model, also have this problem. (This is basically because the contribution of ... | Cox proportional hazards regressions for survival data can be thought of as corresponding to standard regressions in many respects. For example, Cox regressions also provide residual standard errors and R-square statistics. See the <code>coxph</code> function in the R <code>survival</code> package. (You can think of K-... | https://stats.stackexchange.com |
123,310 | [
"https://mathoverflow.net/questions/123310",
"https://mathoverflow.net",
"https://mathoverflow.net/users/31760/"
] | Let $S^2$ be the 2-sphere and $g$ some metric on it. Is it possible
<ol>
<li>to construct embedding $\iota:S^2\rightarrow \mathrm{R}^3$ s.t. $g=\iota^* g_{\mathrm{R}^3}$ and</li>
<li>decide when given $(S^2,g)$, there is such an embedding as above?</li>
</ol>
With $\iota: S^1\rightarrow \mathrm{R}^n$ ($n=2,3$) consta... | Although, as jc says, this question was addressed in earlier questions, the answer is scattered among the accepted answer as well as the comments. So here is a summary:
<ol>
<li>By the Nash-Kuiper theorem (which I believe is one of the original uses of the so-called h-principle), there always exists a global $C^1$ iso... | In general, the answer is no. This is a difficult problem and there was a lot of research on it.
For example, for a metric with positive curvature there is also an embedding.
The answer also depends on the degree of the smoothness of the metric.
Here is a recent survey:
MR2261749
Han, Qing; Hong, Jia-Xing
Isometric em... | https://mathoverflow.net |
85,349 | [
"https://softwareengineering.stackexchange.com/questions/85349",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/7251/"
] | From everything I have learned about "Aspect-Oriented Programming" or "Aspect-Oriented Software Development," labeling it as a programming paradigm or methodology appears to be inaccurate. From what I can tell it is not a fundamental technique for programming.
To nail down what is meant by "paradigm" and "methodolo... | I think this is a really iffy issue because the definition of a "methodology" and "paradigm" and "-oriented programming" is potentially a bit loose in this context, but I'm going to play devil's advocate and go with "<strong>yes, it's a misnomer</strong>".
Even if you didn't use AOP or AOP features to solve a problem,... | All development methodologies are merely ways of thinking about organization of code. Each development methodology may produce very different looking code, or they may produce similar code. They may also require libraries or language features for support.
In C++ for instance, AOP is typically implemented using traits ... | https://softwareengineering.stackexchange.com |
17,187 | [
"https://dsp.stackexchange.com/questions/17187",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/7103/"
] | I want to match a small template to a larger image, that the distance between the template and the subimage with the same size of the template is minimized. It can be solved directly or by applying 2D cross correlation, and both methods have an O(n^4) time complexity. Are there any method to simplify the algorithm by e... | If your template or kernel is small, then straight convolution might be the fastest approach. There's a crossover point when performing convolution in the frequency domain is faster than straight time/spatial domain convolution and it can be hardware dependent, but usually when the kernel (template) approaches 1/4-1/2 ... | ya know, i've never done 2D signal processing other than using MATLAB's <em>surf( )</em> function naïvely, but i would bet that if you 2D-FFT your 2D data (possibly doubling both length and width by mirror reflecting the data to reduce edge effects, or maybe you should zero-pad), pointwise multiply the FFT of the data ... | https://dsp.stackexchange.com |
419,106 | [
"https://mathoverflow.net/questions/419106",
"https://mathoverflow.net",
"https://mathoverflow.net/users/117282/"
] | Let <span class="math-container">$G$</span> be a <span class="math-container">$d$</span>-generated group. Then my first question is how to see free reduced group <span class="math-container">$FV(G)$</span> in the variety containing <span class="math-container">$G$</span>. What I understood is: "Let <span class="ma... | I'll give a more detailed answer. My comment above about your first question was wrong because I read it too quickly and didn't catch the difference between <span class="math-container">$m$</span> and <span class="math-container">$d$</span>. Your description of the free object in question 1 is off.
Take the cyclic gr... | The relative free group of rank <span class="math-container">$n$</span> corresponds directly to a set of maps from <span class="math-container">$G^n\rightarrow G$</span>. These maps are the coset representatives of <span class="math-container">$F_n/K$</span> where <span class="math-container">$K$</span> is the group of... | https://mathoverflow.net |
406,901 | [
"https://mathoverflow.net/questions/406901",
"https://mathoverflow.net",
"https://mathoverflow.net/users/78539/"
] | Let <span class="math-container">$(X(t))_{t \in [-1,1]}$</span> be a centered non-stationary smooth gaussian process with covariation function <span class="math-container">$\rho(t,s) = \mathbb E[X(t)X(s)]$</span>. For <span class="math-container">$t_0 \in (-1,1)$</span> and <span class="math-container">$\epsilon \in (-... | <span class="math-container">$\newcommand\ep\epsilon\newcommand\si\sigma\newcommand\th\theta$</span>In your concrete example,
<span class="math-container">$$p_X(t_0,\ep)=P\Big(m_1<\frac VU<m_2\Big),$$</span>
where
<span class="math-container">$$m_1:=\min_{t\in[t_0-\ep,t_0+\ep]}r(t)
=r(t_0+\ep),\quad
m_2:=\max_{t... | <strong>Disclaimer.</strong> <em>This is just to push the accepted answer a bit further and obtain an explicit upper-bound, valid for small <span class="math-container">$\epsilon$</span>.</em>
<hr />
As shown by user Iosif, <span class="math-container">$M:=U/V$</span> has Cauchy distribution with CDF <span class="math-... | https://mathoverflow.net |
22,043 | [
"https://physics.stackexchange.com/questions/22043",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/8016/"
] | I have another question on the notation in Shankar. I think it's sloppy, but I also may just be misunderstanding it. Again, this is at the very beginning of the math intro.
He has:
<blockquote>
$$a\left| V \right\rangle \to \left[ {\begin{array}{*{20}{c}}
{a{v_1}}\\ {a{v_2}}\\ \vdots \\ {a{v_n}} \end{array}} ... | As others have said, a heat pump with an efficiency greater than unity doesn't have any problem with the laws of thermodynamics. There are still a few problems with this which mean that it isn't as good as it seems.
The efficiency of a heat pump depends on the temperature difference - you can get higher efficiencies ... | I can only hypothesize that the extra energy is due to cooling of environment. As there is some input of energy, that would not contradict the second law of thermodynamics.
| https://physics.stackexchange.com |
161,978 | [
"https://stats.stackexchange.com/questions/161978",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/82604/"
] | I have three correlated variables for 18 cases. I would like to construct a composite index using PCA, where each case has a score. Basically to reduce three dimensions to one, and use that dimension to construct an index that presents most of the variability of the original data.
Here are some of the results:
<pre><... | <blockquote>
Does the PC score itself provide the composite index value for each case?
</blockquote>
Yes, this is correct. You just take the scores of PC1 and that's it.
This is exactly what PC1 <em>is</em>: it is a composite variable (linear combination of the original three variables) that has the maximal possib... | <pre><code>$loadings
PC1 PC2 PC3
V1 -0.6055294 0.3894576 -0.6940151
V2 -0.5086870 -0.8600761 -0.0388151
V3 -0.6120226 0.3295328 0.7189134
</code></pre>
That means:
<pre><code>V1 = -0.6055294*PC1 + 0.3894576*PC2 -0.6940151*PC3
V2 = -0.5086870*PC1 - 0.8600761*PC2 -0.0388151*PC3
... ... | https://stats.stackexchange.com |
60,403 | [
"https://math.stackexchange.com/questions/60403",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/13174/"
] | Let $n$ be a positive integer and $p$ a prime, how can I prove that the highest power of $p$ that divides $\binom{2n}{n}$ is exactly the number of $k\geq1$ such that $\lfloor 2n/p^k\rfloor$ is odd?
| Let us write out this binomial coefficient a bit more
$$\binom{2n}{n} = \frac{2n \cdot (2n-1) \cdot \ldots \cdot (n+1)}{n \cdot (n-1) \cdot \ldots \cdot 1}$$
Above we have all numbers between $n + 1$ and $2n$, while below we have all numbers from $1$ to $n$. Now suppose $\lfloor 2n/p\rfloor = 2m + 1$. Then there are ... | <strong>HINT:</strong>
This is a useful general approach to questions regarding the divisibility of factorials and binomials. What is the highest power of $p$ that divides $n!$? Well $p, 2p, 3p,...$ and all further multiples up to $n$ divide $n!$, so at least $ \left\lfloor \frac{n}{p} \right\rfloor $. But that was no... | https://math.stackexchange.com |
1,302 | [
"https://physics.stackexchange.com/questions/1302",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/230/"
] | If you shake a soda bottle before opening it, and then open it, you get the fizz.
That is the compressed CO<sub>2</sub> releasing to the atmosphere which is at comparatively low pressure value.
Two questions (related)
<ul>
<li>Why does shaking a bottle make the compresses gases <em>un</em>-dissolve?</li>
<li>Why can... | This is what I think that happens. The bottles with the soda have the liquid inside under pressure. Under these conditions you have an amount of CO$_2$ dissolved in the liquid. If you shake it then it will make some bubbles but not a lot and it will return to the previous state. If you don't disturb the liquid and open... | I cannot see, above, the correct answer to the first part of the question. They all have the second part right.
The first part: Why does shaking the bottle make it fizz when you open it?
The gas is in solution in the closed, unshaken bottle. The solubility of that gas in that liquid at that temperature and that pres... | https://physics.stackexchange.com |
713,312 | [
"https://physics.stackexchange.com/questions/713312",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/337932/"
] | Let's say I'm heading towards a star 10 ly away but I am traveling at 298289729 m/s (~99.49% of light), so that I will reach the star in 1 year from my perspective. This would cause the length to contract in the direction of motion.
If I were to peer out the front windshield at the beginning of my journey, I would stil... | I am afraid that you are misunderstanding the implications of SR. You have said that you can complete your journey to the star in 1 year. That means the star is about a light year away from you in your frame of reference at the start of your journey. The fact that it might be some other distance away in some other fram... | Actually talking about what you would <em>see</em> in special relativity is pretty complicated. Way too many books and resources use the term "see" or "observe" to talk about what is being referred to when things like length contraction and so forth are discussed and this really makes it misleading.... | https://physics.stackexchange.com |
1,224,051 | [
"https://math.stackexchange.com/questions/1224051",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/153357/"
] | I am having a small problem recalling how to factor with exponents and roots.
For example, I understand $\sqrt{16t^2+4t^4}$=$2t\sqrt{4+t^2}$
But I have issues when it is factoring not with a square root, but say a (3/2) for example.
For instance , in my book it writes $$(4e^{2t}+4e^{4t})^{3/2}=8e^{3t}(1+e^{2t})^{3/... | At all times, $V=\frac43 \pi r^3$. So $\frac{dV}{dt}=4\pi r^2 \frac{dr}{dt}$.
At the moment of interest, you have a value for the radius and a value for $\frac{dV}{dt}$ (be careful here--the volume is decreasing). This should allow you to plug into the derivative equation above and find $\frac{dr}{dt}$ at the moment... | You started correctly with
$$
V = \frac{4}{3} \pi r^3
$$
But your time derivative misses $\dot{r}$, that is the quantity you want
$$
\dot{V} = 4 \pi r^2 \dot{r} \iff
\dot{r} = \frac{\dot{V}}{4\pi r^2}
$$
You had
$\dot{V} = -0.2 \,\mbox{m}^3/\mbox{min} = \mbox{const}$
and $r = 0.5 \,\mbox{m}$ which gives
$$
\dot{r} = ... | https://math.stackexchange.com |
5,804 | [
"https://physics.stackexchange.com/questions/5804",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/72/"
] | In a lot of laymen explanations of general relativity it is implied that the four dimensions of the space-time are equivalent, and we perceive time as different only because it is embedded in our human perception to do so.
My question is: is that really how general relativity treats the 4 dimensions?
If so - what are... | That statement, that space and time are equivalent, is not really correct. In special relativity there is a distinction between spacelike and timelike events, those are events that cannot or can (respectively) be causally connected. This replaces the notion of "simultaneous" and "before or after" to something all inert... | The formal statement would be that there is no <em>one</em> notion of time, and that one persons definition of time may be intermixed with another's definition of space. What is not correct is that time and space are wholly interchangeable, as Moshe says--there is a distinction between events separated in time and eve... | https://physics.stackexchange.com |
228,799 | [
"https://electronics.stackexchange.com/questions/228799",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/107086/"
] | I'm trying to simulate a simple pulse generator that gets activated by a voltage source <code>vs</code>.
<code>vs</code> starts at <code>0V</code> and switches to <code>5V</code> at <code>10us</code> where it remains at 5V for the duration of the simulation.
When I run the simulation and <code>plot v(in)</code>, the ... | I figured out what I overlooked: (re)sourcing the modified netlist file.
There must have been errors when I first sourced the file into ngspice. Changes made to the file are not taken into account unless sourced again.
<pre><code>source pulse-generator.cir
run
plot v(in) v(out)
</code></pre>
| There are different version of SPICE, and rather than delve deeply in this specific version I can suggest the following.
<ul>
<li>Capitalize the source "V" 's
so instead of vcc is should at least be Vcc or even better VCC</li>
</ul>
Your DC source really should be
VCC 4 0 DC 5V
That may be what was causing the prob... | https://electronics.stackexchange.com |
3,960,902 | [
"https://math.stackexchange.com/questions/3960902",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/829251/"
] | I need help with this problem if anyone can contribute to solving this I would much appreciate it:
<blockquote>
Find all polynomials <span class="math-container">$P$</span> that satisfy <span class="math-container">$P(1)=210$</span>
and for every <span class="math-container">$x\in \mathbb{R}$</span>: <span class="math-... | If the sequence converges to <span class="math-container">$L$</span>, taking the limit on both sides of the recurrence shows that
<span class="math-container">$$L=\frac1{4-3L}\,,$$</span>
or <span class="math-container">$3L^2-4L+1=0$</span>. The quadratic factors nicely: <span class="math-container">$(3L-1)(L-1)=0$</sp... | <strong>Update:</strong> Thanks Brian M. Scott for your insight.
I'll add the case where some <span class="math-container">$a_k=\frac 43$</span>. Per Brian, we need to solve for the sequence <span class="math-container">$b_k$</span> such that <span class="math-container">$b_1=\frac 43$</span>, <span class="math-contain... | https://math.stackexchange.com |
1,838,276 | [
"https://math.stackexchange.com/questions/1838276",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/-1/"
] | Let $G$ be a group and $H$ be a normal subgroup of index $p$ ( a prime ) ; suppose $K$ is a subgroup of $G$ not contained in $H$ , then is it true that $G=HK$ ? ( I know that the fact is true if $p=2$ , but I don't know for the general case . Please help . Thanks in advance )
| By Lagrange's,
$$[G : HK][HK:H] = [G:H] = p$$
since $K \not\subset H$, $[HK:H] > 1 \implies [HK:H] = p$, so $[G:HK] = 1 \implies G = HK$.
| Let $p:G\rightarrow G/H$ be the projection, there exists $x$ in $K$ not in $H$ this implies that $p(x)$ is a generator of $G/H$ since it is a non trivial element of $Z/p$. Let $y\in G$, $p(y)=p(x)^n=p(x^n)$, this implies that $p(yx^{-n})=1$ and $y=hx^n$, $h\in H$.
| https://math.stackexchange.com |
464,699 | [
"https://stats.stackexchange.com/questions/464699",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/235199/"
] | I'm reading a paper on the use of pseudovalues in survival analysis and am trying to derive the pseudovalue for the restricted mean lifetime function. We have,
<span class="math-container">$$ \hat{\mu}_{\tau_i} = \int_{0}^{\tau} \hat{S}_{i}(t) ~ dt $$</span>
where <span class="math-container">$\hat{S}_i(t)$</span> is... | The notation <span class="math-container">$\hat{\mu}_{\tau_i}$</span> is bad notation, since there is no variable <span class="math-container">$\tau_i$</span>. Using the alternative notation <span class="math-container">$\hat{\mu}_i(\tau)$</span> for the same thing (which is better notation), you should have:
<span c... | Okay I've figured it out.
My indicator function is
<span class="math-container">$$ I(X_i > t) = \begin{cases} 1 ~,~ t < X_i < \infty \\ 0 ~,~ otherwise\end{cases} $$</span>
I can rewrite this as a function of t instead of <span class="math-container">$X_i$</span>,
<span class="math-container">$$ I(t \leq X... | https://stats.stackexchange.com |
284,581 | [
"https://dba.stackexchange.com/questions/284581",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/222992/"
] | I have a table with an "e-mail address" and "P2PMail address" column. The user is required to either enter an e-mail or P2PMail address.
If I set both to <code>NOT NULL</code>, then both must be filled in for a record to be created.
If I allow both to be <code>NULL</code>, then a user would be entir... | You need a table-level check constraint:
<pre><code>alter table <name>
add constraint either_email
check (email is not null or p2pmail is not null);
</code></pre>
If you're only allowed to enter one, but not both:
<pre><code>alter table <name>
add constraint either_email
check (email is null <... | I like using <code>num_nonnulls</code> for this:
<pre><code>alter table the_table
add constraint check_at_least_one_email
check (num_nonnulls(email, p2pmail) > 0);
</code></pre>
I prefer this because it can easily be extended to multiple columns.
If you also want to deal with empty strings:
<pre><code>alter tabl... | https://dba.stackexchange.com |
234,989 | [
"https://softwareengineering.stackexchange.com/questions/234989",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/125930/"
] | What is the industrial practice on how to separate html and php code in a web project? Using echos to generate html is considered bad but what is the standard way to achieve the sought separation? Using template engines like twig?
| Lets look at two little C programs that do a bit shift and a divide.
<pre><code>#include <stdlib.h>
int main(int argc, char* argv[]) {
int i = atoi(argv[0]);
int b = i << 2;
}
</code></pre>
<pre><code>#include <stdlib.h>
int main(int argc, char* argv[]) {
int i = atoi(arg... | The existing answers didn't really address the hardware side of things, so here's a bit on that angle. The conventional wisdom is that multiplication and division are much slower than shifting, but the actual story today is more nuanced.
For example, it is certainly true that multiplication is a more <em>complex</em> ... | https://softwareengineering.stackexchange.com |
150,795 | [
"https://softwareengineering.stackexchange.com/questions/150795",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/55099/"
] | The data in my website is stored in many different tables(friends,relatives,etc) and every-time I have to query each and every table. But all this data is subject centric. E.g. data for a person is of the form
<pre><code>data[301]={
"pid"=>301,
"friends"=>array(),
"relatives"=>array(),... | I don't suggest you to use another table as a cache.
If you want to cache data, It's more appropriate use a technology like memcached (http://memcached.org/).
This specialized storage should operate <em>near</em> your data access layer.
In addition I'll use a <strong>IoC/DI</strong> framework to integrate the code de... | You could store is in any serialized form, json or PHP serialize() when you are using PHP.
I think you always need the whole blob of data when reading and using the cache so it does not care if you store it this way. Also it is fast accessible when you have a good primary key.
You could also consider using memcache w... | https://softwareengineering.stackexchange.com |
4,433,188 | [
"https://math.stackexchange.com/questions/4433188",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/561028/"
] | Define each i.i.d. indicator variable <span class="math-container">$X_i$</span> as Bernoulli with <span class="math-container">$p = \frac{\pi}{4}$</span>. If we want to find the variance of <span class="math-container">$X$</span>, which is defined as the mean of <span class="math-container">$n$</span> of these indicato... | One way to see this is to note that the sum of the eigenvalues <span class="math-container">$\sigma_1 \geq \cdots \geq \sigma_d$</span> must satisfy
<span class="math-container">\begin{align}
\sigma_1 + \cdots + \sigma_d &= \operatorname{tr}\Bbb E[\phi(x)\phi(x)^\top] = \Bbb E(\operatorname{tr}[\phi(x)\phi(x)^\top... | Hint: What's the trace of <span class="math-container">$\phi(x)\phi(x)^T$</span>. With the assumption given, you can bound it by <span class="math-container">$1$</span>. The trace of a diagonalizable matrix is the sum of its eigenvalues. You can show that the sum of the eigenvalues is less than or equal to 1. You have ... | https://math.stackexchange.com |
300,754 | [
"https://physics.stackexchange.com/questions/300754",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/116030/"
] | Usually, for christmas , I have lunch with my family and a couple of other families. Most of the people got a Phd on chemistry, or molecular biology, and are high academics (they're in they 50-70). On the other side, i'm the only one who studies physics there, and 2 years ago, in the same situation, they told me that p... | It is sometimes better to find an answer by a different route and then consider what went wrong or right using the initial problem solving equations.
<hr>
Let $N$ be the force exerted by the rod, length $l$, radially inwards and the speed of the mass $m$ be $v$ when the angle between the rod and the horizontal is $... | OK it looks like you have<br>
1) integrated a tangential expression for acceleration due to gravity to get<br>
2) an expression for tangential velocity due to gravity.<br>
The change from cos to sin is due to the integration, not a change in direction.
Which you have<br>
3) then substituted into a radial expression fo... | https://physics.stackexchange.com |
100,290 | [
"https://security.stackexchange.com/questions/100290",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/24339/"
] | I'm toying with the idea of creating a pair of OpenPGP keys, and I'm wondering if I should include a picture or two. I know it will make my key a lot bigger, but is it still worth it?
I'm thinking of adding a passport-photo of myself.
I'm also wondering if I should also add a picture of a scan of my signature (you kn... | Pictures would add additional information on your identity: similar to providing information on your name, location, place and date of birth, they might <strong>help others in identifying you</strong> (and distinguishing from people with similar names). A picture of you (and your signature, which seems an interesting i... | Whether or not it increases risk depends on what you consider risk. Adding photo may make identifying your key easier. If you add photo to your public key though, you need to consider that your photo will be public, some people consider that to be a privacy issue.
| https://security.stackexchange.com |
86,856 | [
"https://stats.stackexchange.com/questions/86856",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/27779/"
] | With all the media talk and hype about deep learning these days, I read some elementary stuff about it. I just found that it is just another machine learning method to learn patterns from data. But my question is: where does and why this method shine? Why all the talk about it right now? I.e. what is the fuss all about... | The main purported benefits:
<em>(1)</em> Don't need to hand engineer features for non-linear learning problems (save time and scalable to the future, since hand engineering is seen by some as a short-term band-aid)
<em>(2)</em> The learnt features are sometimes better than the best hand-engineered features, and can... | Another important point in addition to the above (I don't have sufficient rep to merely add it as a comment) is that it is a generative model (Deep Belief Nets at least) and thus you can sample from the learned distributions - this can have some major benefits in certain applications where you want to generate syntheti... | https://stats.stackexchange.com |
146,727 | [
"https://softwareengineering.stackexchange.com/questions/146727",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/53022/"
] | I am new to event driven development, and I feel lost when I try to implement events that should pass the core/UI boundary.
In my program I have the following (example in c#):
<pre><code>UI.RuleForm Core.RuleList UI.ResultForm
Cell 1 Rule 1
Cell 2 Rule 2
Cell 3 Rule 3
</code></pre>
What I ... | <blockquote>
What I want is: when a RuleForm cell changes, it will update the corresponding rule in RuleList. And when the RuleList changes, the resultFrom will be recalculated from the rules.
My current thought is that, in order to keep core logic separated from UI logic (i.e. core should know nothing about UI)... | By core do you mean business layer, presentation layer, etc? By presentation I don't mean UI. Depending on the pattern, the UI might raise events to the presentation layer who would then interface with the business layer. Typically your middle tier will respond to UI events and communicate back with the view via a view... | https://softwareengineering.stackexchange.com |
202,712 | [
"https://mathoverflow.net/questions/202712",
"https://mathoverflow.net",
"https://mathoverflow.net/users/-1/"
] | Let $\overline{M}_{g,A}$ the moduli stack of pointed genus $g$ stable curves with weights $A = (a_1,...,a_n)$ introduced in
Brendan Hassett, Moduli spaces of weighted pointed stable curves, Adv. Math. 173 (2003), no. 2, 316–352
In this paper the author proves that $\overline{M}_{g,A}$ is indeed a smooth DM-stack endo... | There is probably not an isomorphism.
First, note a reason to be suspicious - if you had such an isomorphism, couldn't you just iterate it to get an isomorphism $\overline{M}_{g,A}=\overline{\mathcal M}_{g,n}$. This would make the work of Brendan Hasset in his paper somewhat superfluous.
I claim there is a natural ma... | As Hassett notes in Section 2.1.1, the universal curve $\mathcal{C}_{g,A}$ can be identified with the slightly generalized Hassett moduli space $\overline{M}_{g,A\cup \{0\}}$, where weight zero markings are allowed to lie on singular points. This is clear since the moduli problem is identical.
As Will Sawin notes (and... | https://mathoverflow.net |
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