qid int64 1 4.65M | metadata listlengths 3 3 | prompt stringlengths 31 25.8k | chosen stringlengths 17 28.2k | rejected stringlengths 19 40.5k | domain stringclasses 28
values |
|---|---|---|---|---|---|
18,339 | [
"https://dba.stackexchange.com/questions/18339",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/1342/"
] | I believe I understand the reasons behind fenced and unfenced stored procedures.
Fenced run "outside" of the database (in our case DB2) so as to prevent possible corruption of the database engine should there be issues with things like pointers.
Unfenced runs "inside" of the database, which means that performance is ... | To be more precise, <code>NOT FENCED</code> routines run in the same process space as the database manager itself. The engine is written in C, so calling a not fenced routine is just like calling another C function from <code>main()</code>. This is where all the memory corruption and performance aspects come from: a no... | As far as I can tell you are mostly right. The key is that PL SQL functions can't do memory allocation and so there really is no way to treat them specially regarding memory management. In essence PL/SQL is pretty closely tied to the db engine, but the memory management is the db engine's responsibility, not the sto... | https://dba.stackexchange.com |
125,281 | [
"https://cs.stackexchange.com/questions/125281",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/87655/"
] | I have 2 ways of solving Independent Set problem of fixed size <span class="math-container">$k$</span> for graph <span class="math-container">$G = (V, E)$</span>:<br>
- Vertex Cover algorithm running in <span class="math-container">$O^*(1.47^{V - k})$</span> (optimized recursive algorithm)<br>
- Clique algorithm runnin... | For any fixed <span class="math-container">$k$</span>, <span class="math-container">$O(\binom{V}{k}) = O(V^k)$</span> is polynomial, whereas <span class="math-container">$O^*(1.47^{V-k}) = O^*(1.47^V)$</span> is exponential. Exponentials grow much faster than polynomials.
Plotting the curves is not so helpful, since t... | Vertex Cover is fixed-parameter tractable.
There is a simple <span class="math-container">$2^k n$</span> algorithm to find a VC of size <span class="math-container">$k$</span>.
This should beat the naive algorithm.
The current state of the art is something like <span class="math-container">$1.24^k n$</span>.
Under ... | https://cs.stackexchange.com |
305,006 | [
"https://softwareengineering.stackexchange.com/questions/305006",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/207545/"
] | In languages like C and C++, while using pointers to variables we need one more memory location to store that address. So isn't this a memory overhead? How is this compensated? Are pointers used in time critical low memory applications?
| Actually, the overhead does not really lie in the extra 4 or 8 bytes needed to store the pointer. Most times pointers are used for <em>dynamic memory allocation</em>, meaning that we invoke a function to allocate a block of memory, and this function returns to us a pointer which points to that block of memory. This n... | <blockquote>
So isn't this a memory overhead?
</blockquote>
Sure, an extra address (generally 4/8 bytes depending on processor).
<blockquote>
How is this compensated?
</blockquote>
It is not. If you need the indirection necessary for pointers, then you get to pay for it.
<blockquote>
Are pointers used in tim... | https://softwareengineering.stackexchange.com |
108,863 | [
"https://stats.stackexchange.com/questions/108863",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/29500/"
] | I have a data having 2 continuous and 4 categorical variables. Each categorical variable has 3 levels. I want to know how to include the variables in the model. I am using SPSS
Variables:
<ol>
<li>Sales - Dependent Variable</li>
<li>Retail Price</li>
<li>Location : TX, CA, PY</li>
<li>Display Location in Store : DL1... | It has been a while since I last used SPSS, but I am pretty sure that it can handle the creation and inclusion of dummy variables automatically (or mostly automatically). You should not need to create the dummy variables yourself, just try including the categorical variables as predictors when specifying the model and... | If you start with the original categorical variables, the result depends on which procedure you use. REGRESSION treats all variables as continuous, so it would not give reasonable results here. You would need to use the dummy variables.
If you use GLM, you classify the regressors as scale or factor, and it will do t... | https://stats.stackexchange.com |
51,917 | [
"https://datascience.stackexchange.com/questions/51917",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/74169/"
] | I came from a software development background and we have separate servers of the same database (dev, test, prod). The reason for this is because we develop our apps against the dev DB, run tests against the Test DB, and prod is prod. This is so we create a clear separation and won't bring down prod trying to build our... | I've tried this with an sklearn builtin dataset rather than yours, but the only difference appears to be the order of the columns. Switching the order of the elements in the transformer lists produces the same results. (In both cases, the numeric columns and categorical one-hot encoded columns are separated from each... | Both of these methods are used to combine independent transformations (transformers) into a single transformer, by independent I mean transformation (transformers) that don't need to be executed in a defined order. That's because unlike in regular pipelines, one transformer is not applied to the output of another trans... | https://datascience.stackexchange.com |
13,730 | [
"https://dba.stackexchange.com/questions/13730",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/6911/"
] | <strong>How should I name my Tables when creating a new database?</strong>
Singular: <code>Client</code> or Plural: <code>Clients</code>?
| Up to you. Just be consistent though.
<em>Personally</em> I prefer singular based on what each *row" stores: Order, Product, User, Item, etc.
This matches my modelling (via Object Role Modelling) where I use singular entities/types.
Edit:
One reason is that plural fails when you have link tables:<br>
<code>Orders</... | Concerning singular versus plural table names, the subject seems to be controversial, but it shouldn't be.
While a table is a collection of multiple records, a table is named after the definition of the one type of record that it contains. If a table was allowed to have a different name than that of the type of record... | https://dba.stackexchange.com |
6,171 | [
"https://mechanics.stackexchange.com/questions/6171",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/3161/"
] | I have a Hyundai Elantra 2002 and changed its power steering fluid with a turkey baster. Four days after changing the power steering fluid and running 1000 miles I noticed that the power steering fluid is leaking. I filled it up up to Max level when I changed it, but after four days it is leveled at Min. So apparently,... | There use to be a say that you never changed you transmission fluid from whatever to whatever, due to detergents eating up any little bit of soil that might have been holding a leak back. Assuming you used the same fluid type, and the other fluid was filthy enough to have a positive viscosity gain, the new fluid might ... | You definitely have a leak. Get under your vehicle and check the PS hoses on the pressure side. There is a hose that has sections of metal pipe joined by rubber Hose. The rubber hose is for flexibility. Most likely it will be a section of metal hose leaking due to corrosion. As for changing your fluid with a Turkey bas... | https://mechanics.stackexchange.com |
3,793,594 | [
"https://math.stackexchange.com/questions/3793594",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/791229/"
] | Suppose <span class="math-container">$X_t \in \mathbb{R}^d$</span> is a vector valued time series, or in other words a vector valued stochastic process indexed by <span class="math-container">$t \in \mathbb{Z}$</span>. Assume for the moment that <span class="math-container">$X_t$</span> is (weakly) stationary with <spa... | It follows from the spectral measure representation for the covariance matrix. In a nutshell, you have, <span class="math-container">$C_h=\int A(t)e^{iht}\,d\mu(t)$</span> where <span class="math-container">$A(t)$</span> are positive semidefinite and <span class="math-container">$\mu$</span> is some non-negative scalar... | I think the claim is true when you have a WSS process where <span class="math-container">$E[XY^\top]$</span> is symmetric. I have not shown it for general <span class="math-container">$C_h$</span>. We will show two things:
<span class="math-container">$$\frac{E[X X^\top] + E[Y Y^\top]}{2} \geq \frac{E[XY^\top] + E[YX^\... | https://math.stackexchange.com |
88,045 | [
"https://mathoverflow.net/questions/88045",
"https://mathoverflow.net",
"https://mathoverflow.net/users/11145/"
] | <strong>Definition:</strong> Let $B$ be a boolean algebra. Say $X \subseteq B$ is <em>quasi-dense</em> in $B$ if for all $b \in B$, there is $x \in X \setminus$ { $0,1$ } such that either $x \leq b$ or $b \leq x$.
<strong>Question:</strong> Suppose $A \subseteq B \subseteq C$ are atomless boolean algebras, $A$ is qu... | Here is a way to construct an atomless version of Joel´s counterexample:
Let $A_0 \subseteq A_1 \subseteq A_2$ be the algebras in Joel´s example (in his notation $A \subseteq B \subseteq C$) and let $X_0$,$X_1$ and $X_2$ be the corresponding Stone spaces. So $X_0$ and $X_1$ are both just a converging sequence and $... | Well, this still doesn't answer the atomless question, but I've got a violation of the desired implication among atomic Boolean algebras.
Let $A$ consist of the finite or cofinite subsets of $\mathbb{N}$
that take $2k$ and $2k+1$ together, if at all. That is, $a\in A$ if
$a\subset\mathbb{N}$ is finite or cofinite and... | https://mathoverflow.net |
2,079,719 | [
"https://math.stackexchange.com/questions/2079719",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/375407/"
] | Prove that the polynomial $f_n(x)=nx^{n+1}-(n+1)x^n+1$ is divisible by $(x-1)^2$ where $n\in\Bbb{N_1}$.
<strong>My Attempt</strong>
<ol>
<li>I've tried proving it by induction but can't find a way to prove it
for $n+1$ after assuming it holds for $n$;</li>
<li>I've also checked it graphically, it seems that for all ... | <strong>Hint:</strong> A polynomial $p(x)$ has $(x-a)^n$ has a factor iff $p(a)=p'(a)=\cdots = p^{(n-1)}(a)=0$
...or
<blockquote class="spoiler">
Consider $(1-x)^2(1+2x+3x^2+\cdots+nx^{n-1})$
</blockquote>
| Note that $$\left(nx^{n+1}-(n+1)x^n+1\right)-\left((n-1)x^n-nx^{n-1}+1\right)=nx^{n-1}(x^2-2x+1)$$and you should get an induction to work
| https://math.stackexchange.com |
264,358 | [
"https://electronics.stackexchange.com/questions/264358",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/127154/"
] | I'm working on a solar project that involves using 4 100AH LFE (LiFePo4) cells to supply 12 volts. The LFE cells indicate the charge rate should be between 0.3C and 2C, which is a lot of current.
The average 300 Watt solar cell only provides 8 Amps, which is less than 0.1C. Will it do any harm to the LFE cells to ju... | I've only done a lot of reading, but have perceived a consensus on this issue. Supplying lower currents than recommended over longer time periods is in itself unlikely to affect longevity.
However assuming these are "native" LFP4 cells, perhaps with balancing and UVP/OVP circuitry but not "lead drop-in replacement" st... | Generally charging cells slowly means they stay at high charge levels for very, very long, because they have internal leakage that increases with their voltage. Or they may even never reach completely full.
A completely full cell degrades much quicker.
However, LiFePO4 is a bit special, it deteriorates much less diff... | https://electronics.stackexchange.com |
521,895 | [
"https://electronics.stackexchange.com/questions/521895",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/234308/"
] | Why is the voltage of a car battery rated for say 12V around 14V when the car is running? Is it because of the alternator?
| All batteries vary in voltage base on charge state and on loading.
A 12V lead acid battery is 12V nominally. This means that 12V is a about middle of the range of the battery. A fully discharge 12V lead acid is around 11V, fully charged it's about 14 to 15V.
Lithium Ion batteries are the same: 3.6V nominally but really... | You are absolutely right, it is because of the alternator. When the car is running the alternator is set to generate around 14 volts which not only charge the battery but also supply all electrical requirements of the car. The battery is only used to start the car or for lighting some bulbs and other accessories when t... | https://electronics.stackexchange.com |
83,062 | [
"https://mathoverflow.net/questions/83062",
"https://mathoverflow.net",
"https://mathoverflow.net/users/11765/"
] | Let $A=C(0,1)$ be the ring of continuous real valued functions on the <strong>open</strong> interval $(0,1)$. It is not too difficult to show that if $\mathfrak{m}\subseteq A$ is a maximal ideal with residue field $A/\mathfrak{m}\simeq \mathbb{R}$ then $\mathfrak{m}=\mathfrak{m}_a:=ker(ev_a)$ where for $a\in(0,1)$,
$ev... | Take any free ultrafilter $U$ on $(0,1)$, and let $m_U$ be the set of functions which are $0$ "almost everywhere", i.e., on a set in the ultrafilter. It seems to me that is a prime ideal, which is in general not maximal. If all ultrafilter sets have, say, the number 1/2 as a limit point, then $m_U$ is properly cont... | For the existence part :
Hint : Let S denote the collection of all polynomials in $C(0,1)$ . Consider $J:=C(0,1) \text{ \ } S$ and all the ideals contained in it. Observe that under usual set inclusion , $(J,\subseteq)$ is a poset. Consider an increasing chain and argue by Zorn's lemma.
| https://mathoverflow.net |
584,545 | [
"https://physics.stackexchange.com/questions/584545",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/247333/"
] | Quoting from my text book - "several attempts were made to predict intensity as a function of temperature/wavelength". This line was preceded by the explanation for blackbody radiations and about how the intensity of radiation of a particular wavelength would be maximum at a particular temperature.
This was f... | In practice there would be a sag. The ideal rigid body can also be invoked. Such a body provides whatever forces are required to stop it bending and squashing. In particular, it can provide sheer forces: forces at right angles to the line along which the body may lie. With a rigid strut fixed to the ceiling by a joint ... | Of cause. there is not really a completely rigid body, so there would be a small displacement. If you calculate with an ideal rigid body, the fastening at ceiling and wall has to take the weight.
| https://physics.stackexchange.com |
410,783 | [
"https://softwareengineering.stackexchange.com/questions/410783",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/341209/"
] | I have an API I wrote that I want to test at the API level.
Given that I'm testing from an external point of view, how can I manage data sets for each tests?
The simplest solution I could come up with is to create a test suite where each test depend on the state the previous one set.
For example to test that a commen... | Yes if you want to actually test a live setup to see if its working you can't avoid having to set state for your tests.
So in your example, you would create a new Post and then add comments and have that dependency and ordering in your test suite.
However! this is why you should also have Delete Posts functionality, ... | Shouldn't a test suite be set up with some test data anyway? Either as part of the build procedure for the application (e.g., test data scripts), or as part of the test's setup/teardown?
I tend to feel that all tests should be "standalone" and not depend on other tests. If you want to test that an Entry goes in, do ... | https://softwareengineering.stackexchange.com |
86,636 | [
"https://mathoverflow.net/questions/86636",
"https://mathoverflow.net",
"https://mathoverflow.net/users/4245/"
] | Dear all, I have some difficulty in understanding the notion of automorphic forms on product of groups.
Let $G$, $H$ be two reductive groups defined over a number field
$F$. Let $\mathcal{A}(G)$ be the space of automorphic forms on $G(F)\backslash G(\mathbb{A})$
and $L^{2}(G):=L^{2}(G(F)\backslash G(\mathbb{A})^{1})... | Even though it is perhaps not surprising for the applications to repns of reductive Lie groups or reductive adele groups, and of reductive p-adic groups, yes, irreducible unitaries of products $G\times H$ are (completed) tensor products of irreducible unitaries of the factors. However, I think this is not "trivially" t... | I think that it is true.
When you look just at irreducible admissible representations over local fields, it's true by theorem of Flath (Corvallis, part 1, pp 179 - 183) - this is the theorem used in decomposing a global representation into a product of local ones.
This of course doesn't answer the global question, bu... | https://mathoverflow.net |
242,393 | [
"https://stats.stackexchange.com/questions/242393",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/135544/"
] | I measured 30 samples each with 3 devices. The devices are the same make and model, just different units. How do I statistically test if the devices measurements are the same or not? If I had two data sets to compare, a simple paired t-test works great. I've read that running three paired t-tests (1vs2, 2vs3, and 3vs1)... | You seem to be conflating the terms paired and pairwise. t-tests are pairwise when you have multiple groups that you compare to each other. They are paired if you have in each group the same number of measurements with matched sample points (within subjects). In your case, it is paired and pairwise, but the concepts ar... | One way ANOVA with a follow up Tukey Test would be a common way to go. The Tukey Test takes the ANOVA object and controls for the familywise error rate.
If you're working in R, you'll use the TukeyHSD function for this.
| https://stats.stackexchange.com |
212,974 | [
"https://electronics.stackexchange.com/questions/212974",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/95368/"
] | The thermal noise power from a resistor is
p = 4kTR
where:
k is the Boltzman constant,
T is temperature,
R is resistance.
Since an open circuit has infinite resistance, it would produce infinite noise--which, of course, is ridiculous. Where has my thinking gone astray? Does it have to do with the fact that any practic... | The only way to develop any noise power from this infinite noise voltage source is to draw current from it.
In other words, to connect it in parallel with a finite load resistance R.
And infinite resistance in parallel wth R is just ... R.
So the voltage noise produced by the overall network is just that of the loa... | I don't think there is a broken corner case or paradox here, either in reality or in theory.
Consider what it means to actually have a very large resistor. Is it that weird to have large numbers of voltage noise in an environment where voltage does little? That is not the same as large numbers of current noise (si... | https://electronics.stackexchange.com |
2,293 | [
"https://scicomp.stackexchange.com/questions/2293",
"https://scicomp.stackexchange.com",
"https://scicomp.stackexchange.com/users/447/"
] | Summary: Are there good algorithms for out-of-core dense matrix transpose if each row of the matrix is separately compressed?
Details: The matrix is about 1 TB uncompressed, and is roughly but not exactly square. An uncompressed row is less than 6 MB, so many of them fit in RAM at once. On disk, I would like to sepa... | If you do not need fast random access to single rows, you can store tiles instead of storing rows. For example, generate $500$ rows at a time and store them in $500\times 500$ tiles (match to a disk block size for best possible performance). These tiles are big enough that reading them off the disk in a different order... | I'd implement it using blocks of rows. If the matrix is $A$, write it as a sum $A=\sum_{b=1}^B A_b$ where each block $A_b$ consists of only some of the rows of $A$. You choose each block to be so that it fits into memory.
Then $A^T=\sum_{b=1}^B A_b^T$: compute the transpose of $A_1$, store it to disk. Read $A_2$, comp... | https://scicomp.stackexchange.com |
123,738 | [
"https://security.stackexchange.com/questions/123738",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/111090/"
] | We're using encrypt-then-mac for authenticated encryption, and recently added a CRC32 to the plaintext. Are there any security problems with using a non-authenticated hash mechanism (for example, CRC32) for error detection (ie ensuring the message wasn't mangled, and it was decrypted with the correct key)?
So the form... | I wouldn't do this and don't understand what problem you are trying to solve (unless this is a purely academic question).
Encrypt-then-MAC where we define <code>ciphertext=encrypt(K_enc, msg)</code> and sending <code>ciphertext||MAC(K_mac, ciphertext)</code> will detect any transmission errors or malicious tampering b... | <h1>This will not harm the encryption, but it doesn't really add anything either.</h1>
What you've described is just encryption. You've only changed what the payload is by making it a little bit larger. This is just as safe.
However a mac also contains a check in it that if it was mangled in transmission in either part... | https://security.stackexchange.com |
492,128 | [
"https://electronics.stackexchange.com/questions/492128",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/225997/"
] | If you apply a positive Vgs value to a P-Channel MOSFET, will the Rds be a high impedance value (assuming that Vgs is within the MOSFET rated spec), or would applying a positive Vgs damage the MOSFET?
| If the voltage is within Vgs rating it will not damage the P-channel MOSFET and the MOSFET will remain off.
Just the mirror image of applying a negative Vgs to an N-channel MOSFET.
| Think about the C-V curves! It has to be part of any university curriculum.
A positive Vgs for PMOS devices is the same as a negative one for NMOS devices. In this case the usually major type of charge carrier are repelled from the gate, and unless the device is using an SOI process, the originally minor carriers wil... | https://electronics.stackexchange.com |
224,735 | [
"https://electronics.stackexchange.com/questions/224735",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/104780/"
] | How can I calculate charging and discharging time of capacitor?
The capacitance is 2100F, rated voltage 2.8V, internal resistance .0158 mohm. Let's say I have 15W of power to feed in the capacitor. how do I calculate charging and discharging time for that? The specific energy is 37 Wh/Kg and specific power 5.6 kW/Kg. b... | If that 2100F is not a typo, so capacticance = 2.1kF, then you can do the sums as follows.
Stored energy at 2.8v = 0.5CV^2 = 8400J
However, you would not be able to charge/discharge efficiently over more than about a 2:1 voltage range, so let's put the minimum voltage at 1.4v. The available energy change by swinging ... | If R is negligible, a fully charged capacitor holds
energy(W-seconds) =0.5 * 2100 * 2.8^2 = 8232 W-sec
and takes (lower limit, not exact value)
8232/15 = 548.8 seconds to charge to 2.8V from zero.
More accurately, the power limit applies to the heat generated in the resistance, as well as to the rate at which the st... | https://electronics.stackexchange.com |
230,719 | [
"https://dba.stackexchange.com/questions/230719",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/173374/"
] | Trying to setup MySQL to run one-way replication. I have the master set to server_id = 1, a replication user setup, binary logging enabled, the Slave server_id = 2 and is connected and waiting for an event. I am also using Workbench.
However, the Master server has the following error...
<pre><code>Fatal error: The sl... | The data of a MV is stored in a regular table, there is no magic to that. But access is typically (much) faster for multiple possible reasons:
<ul>
<li>multiple tables joined already</li>
<li>smaller row size with only relevant columns for common queries</li>
<li>pre-computed values</li>
<li>pre-selected rows, possibl... | Materialized Views help you pre-calculate data. If you don't use that tool correctly, it may be slower to use them.
Here is an example:
<pre><code>test=> create table my_table
(id integer generated always as identity,
time timestamptz);
CREATE TABLE ^
test=> alter ... | https://dba.stackexchange.com |
195,086 | [
"https://softwareengineering.stackexchange.com/questions/195086",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/5094/"
] | We are building an accounting web application. In our database, we store basic data about our customers, like phone number, their login informations, because these things are tied into our web application. Now we need a CRM system to do things like sending marketing mails to users who signed up, but never used the serv... | Off the shelf tools exist to meet customer needs.
Building an off the shelf tool that does everything <strong>any</strong> customer might need is a kind of panacea that a lot of companies try to build.
The problem client companies like yours have is that no "all in one" system will ever do absolutely everything your ... | <blockquote>
Is there any CRM system that can be put upon our PostgreSQL database
and just utilize the data we have and store what we do not have?
</blockquote>
here's your problem - you want a CMS, but you don't want to use the functionality that CMS offers you, you want to bend it to your requirements. Here's a ... | https://softwareengineering.stackexchange.com |
102,209 | [
"https://electronics.stackexchange.com/questions/102209",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/38387/"
] | This is a part of my computer science assignment:
When adding two unsigned binary integers, an overflow can easily be verified by observing
the carry out. Specifically, an overflow occurred if and only if S' · Cout = 1.
<em>Does anybody know what this S might represent? is it the sum? if it is how is this expression ma... | 256K x 8 means 256 kibi-locations, each location holding 8 bits. There are 18 address lines (2<sup>18</sup> = 256 * 1024) and 8 data lines.
| 16k x 9 means that the memory chip has a total of 16k locations in which it can store a binary number that consists of 9 bits. It will have a 14 bit address structure (14 bit gives you 16,384 locations in decimal). It may be a serial device but the address lines will still be there but internal to the device.
| https://electronics.stackexchange.com |
3,524,868 | [
"https://math.stackexchange.com/questions/3524868",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/729518/"
] | Let <span class="math-container">$X, Y$</span> be closed oriented smooth manifolds of dimension <span class="math-container">$(n+1)$</span>, where <span class="math-container">$Y$</span> is also connected, and let <span class="math-container">$F: X → Y$</span> be a smooth map. As usual, the degree <span class="math-con... | <blockquote>
Is there anything that can be said about the degree of <span class="math-container">$\tilde{F}$</span>? Do we have <span class="math-container">$\deg \tilde{F} = \pm \deg{F}$</span>?
</blockquote>
I will show below that without further assumptions, the answer to this is no.
<blockquote>
For each <spa... | While Jason DeVito posted a nice counterexample to my question in the
general case, I've managed to prove the special case I was interested
in:
<blockquote>
Let <span class="math-container">$X^{n+1}, Y^{n+1}$</span> be smooth, compact and oriented manifolds, with
<span class="math-container">$Y$</span> also being ... | https://math.stackexchange.com |
109,912 | [
"https://mathoverflow.net/questions/109912",
"https://mathoverflow.net",
"https://mathoverflow.net/users/10791/"
] | Suppose I have some random variable X with probability distribution P(.;theta). Suppose I have a single sample x from this distribution.
Does it make any sense to ask for the derivative of x with respect to theta?
I believe it does not, but am having trouble convincing some of my colleagues.
| It does not because $x$ is just some element of your state space. You could conceivably choose $x$ as your sample point for any or all of the $\theta$'s. So what it would make sense to differentiate with respect to $\theta$ is $$\mathbb{P}_{\theta}(X=x)$$ as long as you have a discrete distribution. For a continuous di... | What might make sense is if $X$ is a function $g(U,\theta)$ of some underlying random variable $U$ (with distribution not depending on $\theta$) and $\theta$, where the differentiable function $g$ is chosen so that $g(U,\theta)$ has the given (continuous) distribution. Then you could say $\dfrac{dX}{d\theta} = \dfrac{... | https://mathoverflow.net |
14,463 | [
"https://astronomy.stackexchange.com/questions/14463",
"https://astronomy.stackexchange.com",
"https://astronomy.stackexchange.com/users/9124/"
] | How large and bright would Betelgeuse appear if it were as close to Earth as Sirius, before and after it goes supernova?
| The distance to betelgeuse is poorly known, so we don't actually know how bright it is with much accuracy measurements of its parallax by satellite give a distance of 197 parsecs <em>+/- 45 parsecs</em> (1 parsec is 3.26 light years). The absolute magnitude (the brightness if it were 10 parsecs distant) is estimated to... | Given a distance of $d_1 = 640~\mathrm{ly}$ for Betelgeuze and $d_2 = 8.6~\mathrm{ly}$ for Sirius the difference in the apparent magnitude for Betelgeuze at distances $d_1$ and $d_2$ that is given by
$$m_1 - m_2 = 5~\mathrm{mag} \cdot log_{10}(\frac{d_1}{d_2})$$
is $9.4~\mathrm{mag}$. With magnitude $m_1 = 0.45~\math... | https://astronomy.stackexchange.com |
554,663 | [
"https://physics.stackexchange.com/questions/554663",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/257479/"
] | Let's say that a body <span class="math-container">$A$</span> possesses a charge of <span class="math-container">$-1 \text{ e}$</span> (electron) and another body <span class="math-container">$B$</span> is electrically neutral (has a charge of <span class="math-container">$0 \text{ e}$</span>). Now, if we bring any two... | Few points to note:
<blockquote>
Let's say that a body <span class="math-container">$A$</span> possesses a charge of <span class="math-container">$-1 \text{ e}$</span> (electron) and another body <span class="math-container">$B$</span> is electrically neutral (has a charge of <span class="math-container">$0 \text{ e... | Well the thing is the whole transfer scenario depends on electron affinity values of the materials A and B. Just like SchrodingersCat elaborated. Different materials will have different 'attractions' for electron. In this case, if B has a greater electron affinity than A, the transfer is plausible of course. So now B w... | https://physics.stackexchange.com |
173,055 | [
"https://electronics.stackexchange.com/questions/173055",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/11709/"
] | A project I just read gave their consumption data in µW. The main component was a microcontroller, which has stated in its datasheet what different current consumptions it has in different modes (nRF51422).
Since P = U*I, should I have any reason to believe that the datasheets current numbers are actually larger when... | <blockquote>
consumption data in µW. The main component was a microcontroller [...] nRF51422
</blockquote>
This NRF µC has a step-down DCDC included, which draws less current at higher voltages - resulting in almost constant power consumtion for the controller.
Note that this DCDC can be switched off in the user f... | Microcontrollers do not work with constant power, so they should take less current with lower voltages. Think about them as a bunch of charging and discharging capacitors (gates). The lower charge voltage is, thevlower energy is stored. This is, by the way, one of the reasons to go to very low voltages in faster circui... | https://electronics.stackexchange.com |
71,252 | [
"https://stats.stackexchange.com/questions/71252",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/29547/"
] | I'm perplexed by some vertical lines that show up in these scatter plots on a log scale. Population is on the y-axis and the proportion of the neighborhood with the attribute mentioned in the panel label on the x-axis. Is this just an artifact of the transformation? (I thought perhaps this was due to digit preference o... | I see that the lines are always at $\log( y ) = a - <log( x )$, e.g. in the lower left panel, proportion of $10^{-4}$ corresponds to population of $10^4$. I think that the population was used when calculating the value.
For example, maybe the census did not record "what is the proportion of Chinese in the neighbor... | It's due to integer effects with low counts for the class membership.
Consider the "Not Filipino" graph at the lower left. Note how the lower left line goes through the point (-3,3). That point would correspond to 1 observation of a Not Filipino out of $10^3$ people in the neighborhood. Note also that for the Chi... | https://stats.stackexchange.com |
58,843 | [
"https://mathoverflow.net/questions/58843",
"https://mathoverflow.net",
"https://mathoverflow.net/users/4333/"
] | Let $\pi:Y\longrightarrow X$ be a finite morphism of smooth projective geometrically connected curves over a number field $K$. Let $h:\mathcal{X}\longrightarrow \textrm{Spec} \ O_K$ be a regular integral flat projective $O_K$-scheme with generic fibre $X$. Here $O_K$ is the ring of integers of $K$.
I would like to ex... | The vertical ramification can't be seen from the branch locus $D$. For example, consider
$$ Y : y^2 = f(x), \quad f(x)\in O_K[x]$$
(say with $f(x)$ monic and separable in all residue fields of $O_K$) and
$$ Y' : y^2 = tf(x), \quad t\in O_K.$$
Then $Y\to \mathbb P^1_K$ extends in an obvious way to $\mathcal Y\to \ma... | Yes, the normalization $\mathcal Y$ of $\mathcal X$ in $K(Y)$ will give you such an extension. Since $\mathcal X$ is regular and $\mathcal Y$ is normal, purity of the branch locus shows that the branch locus is a divisor on $\mathcal Y$ (as you probably know). However, my feeling is that it is difficult to say much m... | https://mathoverflow.net |
1,783,831 | [
"https://math.stackexchange.com/questions/1783831",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/301198/"
] | Obviously assuming $f$ integrable. The standard proof seems to integrate by substitution(substitute $x$ by $-u$, $dx$ by $-du$,...etc.). Nevertheless, in the proof of the theorem of substitution, we assume(at least in the proof I know) that for
$$\int _{g(a)}^{g(b)} h(x) dx=\int _a^b h(g(t))g´(t)dt$$ to hold, we need ... | Yes it is true. Let me outline a proof.
First note that if $f$ is integrable on $[a,b]$ and $c\in [a,b]$ then (by theorem):
$$\int_a^b f(x) ~dx=\int_a^cf(x)~dx+\int_c^b f(x)~ dx$$
Applying this to $[-b,b]$ and $c=0$ we get:
$$\int_{-b}^b f(x)~dx=\int_{-b}^0 f(x) ~dx+\int_0^b f(x)~dx$$
Note that:
$$\int_0^b f(x)~... | Yes, it is always true. (Assuming the integral makes sense). First, notice that
$$\int_{-b}^b \mathrm f(x)~\mathrm dx = \int_{-b}^0 \mathrm f(x)~\mathrm dx + \int_{0}^b \mathrm f(x)~\mathrm dx$$
If we make the substitution $x = -u$ then $\mathrm dx = -\mathrm du$ and so
\begin{eqnarray*}
\int_{x=-b}^{x=0} \mathrm f(... | https://math.stackexchange.com |
247,080 | [
"https://physics.stackexchange.com/questions/247080",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/83081/"
] | My book says that the electric field due to infinite long plates doesn't depend on 'r', so does it mean that no work is done in moving a point charge towards or away from it?
Also considering the situation of parallel plate capacitors , even here the electric field between the 2 plates doesn't depend on the distance f... | Radioactivity occurs (with the exception of k-capture in which the nucleus captures an orbiting electron) inside the nucleus of atoms, not in the electron shells. Yes, the product has one extra proton, and thus is now a different element, jumping up one in the Periodic Table. No nucleus is electrically neutral. Whether... | Radioactive materials are studied in bulk matter. The electron that left with beta decay will become part of the conduction band electrons for the lattice the atom is in, and another electron will be drawn in very fast from the conduction band.. To remain an ion the atom should be isolated from bulk matter, and usual... | https://physics.stackexchange.com |
798,363 | [
"https://math.stackexchange.com/questions/798363",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/119537/"
] | <img src="https://i.stack.imgur.com/Vcpr8.png" alt="enter image description here">
[ORIGINAL PROBLEM] You are given hat the Green's function $g(x,t,\xi, \phi)$ is
$\frac{\partial^2g}{\partial t^2} - \frac{\partial^2g}{\partial x^2}=\delta(t-\tau)\delta(x-\xi)$
with
$g(x,0,\xi, \tau)= \frac{\partial }{\partial t} ... | Part a) After performing a Fourier Transform we obtain:
$$ \partial^2 _t G+k^2 G= \delta( t - \tau) \exp(i k \xi)$$
using the opposite signed Fourier Transform(please note:you made a sign mistake on the $k^2G$ term), then let $ G(x,t) = \exp(ik \xi) f(x,t)$ so we only have:
$$ \partial^2 _t f+k^2 f= \delta( t - \tau... | To avoid contradiction, I use the notation mentioned in the problem. As your work, $G$ solves the following IVP of $t$:
$$
G_{tt}(k,t)+k^2G(k,t)=\delta(t-\tau)e^{-ik\xi}\\
G(k,0)=0,G_t(k,0)=0
$$
A quick way to solve this equation is to use Laplace's transform in $t$. Let $\mathcal{L}:t\rightarrow s$ be the Laplace tran... | https://math.stackexchange.com |
411,428 | [
"https://softwareengineering.stackexchange.com/questions/411428",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/368068/"
] | Everyone creates bugs, including me and my teammates. When bugs are pointed out to them, they're friendly and try to fix the bug. But their fix is 'wrong' and just creates a more subtle bug. Usually this takes the form of them thinking that the bug is an edge case, and they put some special check in.
Sometimes they w... | <h2>Test your code</h2>
Have an actual regression testing, so that when a bug is introduced, the programmer finds it right away.
This doesn't mean that you should just write the actual tests. Instead, it means that you need to work on the culture of the team to understand that without regression testing, the project ... | Start by inviting people to pick apart your work.
You don't need management to create a command structure to fix this problem. You need teammates that trust you.
You build trust by showing you're not just some power hungry jerk that's looking to get out of work by spending all day approving other peoples work.
Get o... | https://softwareengineering.stackexchange.com |
357,414 | [
"https://softwareengineering.stackexchange.com/questions/357414",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/73508/"
] | For reasons lost in the mists of time, your project has a code coverage standard. Unfortunately, some new code has gone in which takes the coverage below this figure. John Doe is duly assigned to write more tests (since Jane Doe is off snowboarding). John is unfamiliar with the code and drags the coverage over the line... | Yes, I'd say these are technical debt. Test code is not different than the code being tested in that it must also be maintained and understood. The fact that you don't understand the point of the testing code is a maintenance problem as it doesn't help you understand the code which is being tested; a large component ... | Do the new tests constitute technical debt?
Yes. Eventually, these horrible tests will need to be modified, probably by Jane when she returns from snowboarding. At which time, she will struggle with understanding the tests.
<hr>
What should be done about them (if anything)?
If the horrible tests are acceptable for ... | https://softwareengineering.stackexchange.com |
23,304 | [
"https://earthscience.stackexchange.com/questions/23304",
"https://earthscience.stackexchange.com",
"https://earthscience.stackexchange.com/users/22632/"
] | Call it hair splitting, if you want, but I see at least three numbers in the latest IPCC report (e.g. on pages 7-51–7-52). The first one, "the total human forced GSAT change from 1750–2019", is 1.29°C. The second one, "the total (anthropogenic plus natural) emulated GSAT between 1850–1900 and 2010–2019&q... | Some of the relevant AR6 headline values are:
<ul>
<li>+1.09 °C = Observed GMST and GSAT change between the periods 1850-1900 and 2011-2020
</li>
<li>+1.06 °C = Observed GMST and GSAT change between the Chapter 7 attribution assessment periods 1850-1900 and 2010-2019
</li>
<li>+1.14 °C = Emulated GSAT change between th... | There has been a component of natural cooling over that period - not warming. 1.14C is the modeled amount of warming overall, which comes from 1.29C of anthropogenic, less 0.15 of natural cooling. There appears about 0.8C of difference between modeled and assessed from actual temperature data - which is almost certain... | https://earthscience.stackexchange.com |
14,774 | [
"https://stats.stackexchange.com/questions/14774",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/5969/"
] | Suppose I have samplings from two distinct populations. If I measure how long it takes each member to do a task, I can easily estimate the mean and variance of each population.
If I now hypothesise a random pairing with one individual from each population, can I estimate the probability that the first is faster than ... | <h3>Solution</h3>
Let the two means be <span class="math-container">$\mu_x$</span> and <span class="math-container">$\mu_y$</span> and their standard deviations be <span class="math-container">$\sigma_x$</span> and <span class="math-container">$\sigma_y$</span>, respectively. The difference in timings between two ride... | Suppose the two data sets are $X$ and $Y$. Randomly sample one person from each population, giving you $x,y$. Record a '1' if $x > y$ and 0 otherwise. Repeat this many times (say, 10000) and the mean of these indicators will give you an estimate of $P(X_{i} > Y_{j})$ where $i,j$ are randomly selected subjects fro... | https://stats.stackexchange.com |
511,698 | [
"https://physics.stackexchange.com/questions/511698",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/211437/"
] | When a goalkeeper stops the ball he does the work but how he only stops the ball but dont displaces the ball please explain
| <blockquote>
Does the goalkeeper do Work while stopping the ball?
</blockquote>
The amount of Work done by the goalkeeper’s mass equals the amount of kinetic energy lost by the ball.
Computing the velocity of the mass-plus-ball system after the goalkeeper captures the ball gives us a quantitative answer as to the... | The goalie uses his arms, legs and body to <em>absorb</em> the kinetic energy carried by the ball. At the moment when its velocity towards him is almost zero, he grabs onto the ball with his hands and arms so the ball cannot bounce back away from him.
| https://physics.stackexchange.com |
293,980 | [
"https://math.stackexchange.com/questions/293980",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/15283/"
] | How to integrate $\;\large \frac{2x}{1+x^{2}}\;?\;$ Do I need to use u-substitution for $\,(1+x^2)\,$?
| That's the most straightforward way.
Let $u = 1 + x^2,\;$ then $du = 2x \,dx.\; $ Now you're all set to substitute:
$$\int \dfrac{2x\,dx}{1+x^2} \;\;=\; \;\int \dfrac{du}{u}\;\;=\;\; \ln |u| + C \;= \;\ln(1 + x^2) + C$$<br>
<hr>
<em><strong>Added</em></strong> (to address comment below): <br>Note that we can <em>o... | $\textbf{Hint:}$ You don't need any fancy technique. Look at an antiderivative table and try to work it out.
Scroll over the grey area for the solution.
<blockquote class="spoiler">
Note that $\displaystyle \int \frac{2x}{1+x^2}dx=\int \frac{(1+x^2)'}{1+x^2}dx=\log {\bigl(|1+x^2|\bigr)}=\log {(1+x^2)}$
</blockquote... | https://math.stackexchange.com |
207,078 | [
"https://electronics.stackexchange.com/questions/207078",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/56529/"
] | So I'm trying to make the following simulation work properly to verify some hand solving for a circuit. The circuit is an LC tank with some diode clamping, and an initial capacitor voltage of -50V.
I tried both with and without a switch to see if that helped...it didn't.
<img src="https://i.imgur.com/KECRGlt.png" al... | I actually got the numbers to make a bit more sense, although I don't fully understand why. I set the simulation options to not do an initial operating point solution and suddenly the currents started to match my hand calculations.
In addition a total summary of the fixes that were contributed by folks here:
<ul>
<li... | Suffixes in LTspice are not case sensitive, so your switch's off resistance <code>Roff=1M</code> is actually 1 <em>milli</em>ohm not 1 Megohm. Change it to <code>Roff=1Meg</code> and it will work.
Without a switch you get several thousand Amps because the initial conditions are calculated at DC and inductors are consi... | https://electronics.stackexchange.com |
157,440 | [
"https://softwareengineering.stackexchange.com/questions/157440",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/47328/"
] | In c++, the * operator can be overloaded, such as with an iterator, but the arrow (->) (.*) operator does not work with classes that overload the * operator. I imagine that the preprocessor could easily replace all instances of -> with (*left).right, and that would make iterators nicer to implement. is there a practica... | The rule that <code>foo->bar</code> equals <code>(*foo).bar</code> only holds for the builtin operators.
Unary <code>operator *</code> doesn't always have the pointer dereference semantics. I could make a library in which it means matrix transposition, zero-or-more parser matches, or pretty much anything.
It would... | As a general rule, C++ is designed to favor flexibility, so overloads of <code>*</code> and <code>-></code> are separate. Though it's fairly unusual to do so, if you want to badly enough you can write those overloads to do entirely different things (e.g., might make sense for a domain specific language implemented i... | https://softwareengineering.stackexchange.com |
11,088 | [
"https://datascience.stackexchange.com/questions/11088",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/17699/"
] | I have started learning data science using R, however I have C++ as a subject this semester, and my project is to predict the outcome of a game using C++.
I have not come across many instances (close to none, I did find libraries like Shark though) of implementation in C++.
Is it to do with the fact that C++ isn't as ... | Yes, you're correct -- it's that C and C++ are harder to use and are more burdened with boilerplate code that obfuscates your model building logic. When you build models, you have to iterate rapidly and frequently, often throwing away a lot of your code. Having to write boilerplate code each time substantially slows yo... | <strong>Advantages of any modern interpreted language over C++.</strong>
Like any tradeoff, these are advantages in some situations and disadvantages in others. Situations where you don't want these conveniences are becoming more rare, though, as hardware gets even faster and high-level language implementations get ev... | https://datascience.stackexchange.com |
92,072 | [
"https://softwareengineering.stackexchange.com/questions/92072",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/-1/"
] | How much experience do you need in a language before you can put it on your resume? There is one language I'm in proficient in (Java) which I would definitely put on the resume but say I took I couple of semester courses in college which involved extensive programming in C or self-taught myself C# but have written no m... | You can always list languages (as well as other skills) in tiers on a resume:
<pre><code>Proficient: Java, Lisp
Familiar with: Perl, C++
</code></pre>
As a guy looking at a resume, I will appreciate both the honesty and the effort; and when bringing you in the first question you usually get asked is to rate your i... | I include any language which I have used as a professional; i.e. any language I used while paid to write in it. And I don't list competance levels. A resume is an introduction; If I say "Computer languages: Algol, Basic, C, C++, Cobol, Fiemaker, Fortran, and Foxpro", it's up to the interviewer to ask "Just how much Alg... | https://softwareengineering.stackexchange.com |
114,965 | [
"https://physics.stackexchange.com/questions/114965",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/14220/"
] | In ultracold atomic gas experiments, the optical lattice provides a periodic optical potential to trap the atoms, why an extra trap, usually a harmonic trap is needed to trap the atoms?
| If you only have the lattice, the atoms can wander around and won't stay together. If you are interested in their interaction (for example to study many-body physics), you need to keep them together. That's what the additional trap is doing.
The harmonic potential induce inhomogeneities, which one might want to get re... | Modified: after 4 years in cold atom experiments I found my original answer of this question to be super naive.
There are quite a few types of trapping in cold atom experiments. Such as a periodic trap which we called optical lattices, a magneto-optical trap (MOT) where most experiments use for a very powerful coolin... | https://physics.stackexchange.com |
80,817 | [
"https://dba.stackexchange.com/questions/80817",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/106/"
] | I will migrate from a database. There is one column of type <code>image</code> that I would like to export to binary files on the file system. One file for each record. How can I do this with SQL Server?
| This is the solution I came up with:
<ol>
<li>Enable <code>xp_cmdshell</code> with
<pre><code>EXEC sp_configure 'show advanced options', 1
GO
RECONFIGURE
GO
EXEC sp_configure 'xp_cmdshell', 1
GO
RECONFIGURE
GO
</code></pre></li>
<li>If needed create a directory with <code>xp_cmdshell</code> to get the needed permissi... | I had the same problem with the extra 4 bytes being added to the beginning of all of my files as well. Instead of using -N option in my bcp command, I changed it to -C RAW. When you do this, bcp will be prompted with the following questions:
<pre>
Enter the file storage type of field FileData [image]:
Enter prefix-l... | https://dba.stackexchange.com |
350,942 | [
"https://physics.stackexchange.com/questions/350942",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/77283/"
] | <blockquote>
A raindrop absorbs water as it falls vertically under gravity through
a cloud. In a model of the motion the cloud is assumed to consist of
stationary water particles. At time $t$, the mass of the raindrop is
$m$ and the speed of the raindrop is $v$. At time $t = 0$, the
raindrop is at rest. The r... | Let's be precise here. The 'invariance' in question is invariance of the spacetime interval under Lorentz transformations. Lorentz transformations here relate the coordinates of an event as measured by Alice with that of Bob, where they have a boost velocity with respect to each other. As such, Alice measures some time... | Well, let the thing that the two people observe be a clock -- a mechanical clock. If they disagree about the proper time on its worldline between two events, then they also disagree on its physical state at at least one of those events in general. That means that, say, if the two observers and the clock meet at some ... | https://physics.stackexchange.com |
512,704 | [
"https://physics.stackexchange.com/questions/512704",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/244685/"
] | I have seen countless examples where Gauss' law is applied to state that the electric field in a region is zero. For example, taking any Gaussian surface inside a spherically conducting shell where there are no charges inside, we find the the surface integral is zero by Gauss' law, but then it is always claimed that th... | You are exactly correct. In general
<span class="math-container">$$\iint\mathbf E\cdot\text d\mathbf a=0\nrightarrow\mathbf E=0$$</span>
However, in special instances of symmetry (like your spherical cavity), you can argue that the field must have the same magnitude and point radially outwards at all points on your G... | The argument uses a spherical Gaussian surface whose center coincides with that of the sphere. Spherical symmetry then means that any nonzero field would be radial and only a function of the radial coordinate. Thus the flux integral reduces to <span class="math-container">$4\pi E_r$</span>. The only way it can be zero ... | https://physics.stackexchange.com |
32,675 | [
"https://electronics.stackexchange.com/questions/32675",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/9978/"
] | This question might sound silly, but it is very serious (although geeky, I must admit).
When I use my electric toothbrush in front of my alarm clock (one of those with a big red LED display), the numbers seem to break apart. Why?
With my current alarm clock the first 3 segments (a,b,c) make one group and the other 4 m... | Yes, it sounds like you are seeing artifacts of toothbrush frequency vibrating your head and therefore your eyes, and that beating against the LED refresh frequency.
This is a similar effect to eating potato chips (actually anything crunchy) while watching the LED display. In that case the head vibrations are more ra... | This can be experienced with any vibration of the head in front of certain LCD displays - usually microwave ovens for some reason - most amusingly by vibrating your lips the way you would as a kid when imitating a car or motorbike sound - no oral hygiene technology necessary.
If you purse your lips and modulate your ... | https://electronics.stackexchange.com |
384,653 | [
"https://physics.stackexchange.com/questions/384653",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/183984/"
] | I am studying Lasers and I am very confused regarding radiationless transition. Why electron does not emit photon while downward transition from higher state to metastable state and in which form the energy is released ?
| If I'm not mistaken and we talk solid-state lasers you really mean non-radiative transitions.
In this case excess energy is dissipated in various manners, but the simplest is phonon (or multi-phonon) relaxation. This means energy transfer to the crystal lattice. This causes heating of the laser medium.
This is usual... | This is a so-called Auger transition. The first electron making a transition from a higher state into the vacant hole releases energy $\Delta E$. This energy is transmitted - via a virtual photon - to another electron, which then makes a transition into the continuum (under the condition that the binding energy of this... | https://physics.stackexchange.com |
49,887 | [
"https://electronics.stackexchange.com/questions/49887",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/9287/"
] | Im looking at some spring probes, such as are used in test fixtures (NOT on multimeters or scopes).
All the catalogues (Ingun, Coda-Pin, etc) seem to organise by a dimension they call "centers" but never seem to show a matching dimension on diagrams... what is a "center" in this context?
Ta
| I think it's how close together you can crowd the pins in your test fixture. If your test pads are 2mm apart, you need probes that work at 2mm centres or smaller. The max diameter has to be somewhat smaller than this...
| Since IC's come in a variety of standard pitches (measured from pin to pin center), spring probes are designed to match the typical pitch of IC's used on the board.
Often they are defined as "grid" spacing which is same as pad "centers" or "pitch".
The diameter of the pins are just over 50% of the minimum grid space ... | https://electronics.stackexchange.com |
352,197 | [
"https://physics.stackexchange.com/questions/352197",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/152429/"
] | I was recently looking at a physics problem and it kind of confused me:
A 1 kg ball is shot out of a 5m long cannon directly upwards. A constant force of 15 N is used to accelerate the ball out of the cannon. What is the ball's velocity as it leaves the cannon?
I understand how to do this problem with work-energy pr... | It sounds like you have a slight misunderstanding with acceleration. In the problem, the ball is propelled out of the cannon with 15 N of force, and gravity is trying to pull it down with 9.8 N of force. These two forces never change: the acceleration of gravity will always be the same no matter how long it is applied ... | According to the question as you quote it, as long as the ball is in the cannon, there are two forces acting on it: the 15 N upwards, and 10 N down (from gravity). This should lead to constant acceleration of 5 m/s$^2$.
Not sure what is confusing you.
| https://physics.stackexchange.com |
185,342 | [
"https://softwareengineering.stackexchange.com/questions/185342",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/79891/"
] | I understand that the model should generally consist of data manipulation and the view for data display from the model, but how do I keep my model and view layers decoupled?
My simple view has a few tables that display data. Its associated model manipulates the data based on the view's type of <code>TableModel</code>.... | The easiest metric is to ask, "when was the last time this integration test <em>legitimately</em> failed?" If it has been a long time (there have been a lot of changes) since the integration test failed, then the unit tests are probably doing a good enough job. If the integration test has failed recently, then there wa... | Units tests are not the holy grail of testing, they are only one tool of many than should be used to test a code base. Therefore no amount of unit tests should ever be considered safe to replace other tests. If you have a bad integration test you should work to make it a good integration test, not replace it with somet... | https://softwareengineering.stackexchange.com |
471,230 | [
"https://physics.stackexchange.com/questions/471230",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/209648/"
] | I have a problem (that I am not asking you to solve) where it takes <span class="math-container">$4s$</span> for an object to travel upward to its maximum height, and we have to determine how far the object travelled. If the acceleration of gravity is <span class="math-container">$9.8\,\rm ms^{-2}$</span> downward, do... | That depends on your axis. A <strong>sign</strong> is nothing but a mathematical tool showing direction according to an <strong>axis</strong>, which is also just a mathematical tool. Without an axis, signs don't mean much.
<ul>
<li>So, is the axis pointing upwards? Then the downwards-pointing acceleration is negative,... | The kinematic equations of constant acceleration which you will use to solve your problems are relationships between components of vector quantities.
Assume that you define unit vector up <span class="math-container">$\hat u$</span> which in effect is you defining up as positive because a vector quantity in the down... | https://physics.stackexchange.com |
34,464 | [
"https://stats.stackexchange.com/questions/34464",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/8013/"
] | I have encountered in swathes of medical literature the use of the terms "case-mix" and "risk" adjustment without any citations or explanations of their exact usage and motivation from a modeling perspective. I understand the principles of covariate adjustment in multiple regression modeling to address confounding (bia... | I've seen the two terms are sometimes used synonymously, and they're both an attempt to control for a particular type of confounding, namely that some patients have a set of covariate risk factors the predispose them to the outcome.
Generally speaking, I've found "case-mix" most often used in studies where the unit of... | I do not think there is any real difference between "case-mix adjustment" and "risk adjustment" in this context. I would say the terms are used interchangeably.
They refer to adjusting for confounding due to patient ("case") mix, or the patients' risks of the outcome being examined.
Funders often want to compare hosp... | https://stats.stackexchange.com |
515,094 | [
"https://physics.stackexchange.com/questions/515094",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/218022/"
] | How can we distinguish between the metric expansion of space and the speed of light slowing over time?
I understand that the universe is expanding. But it seems that our main measurement techniques involve assuming the speed of light is constant over time. I know that we <em>define</em> length in terms of a constant... | If the speed of light were variable, it would affect plenomena at all scales from microscopic to cosmological. However the expansion of space has no effect on matter bound by forces, such as on anything within a galaxy. The expansion of space is observed (based on the FLRW metric) only on the intergalactic cosmological... | Type 1a supernovae explode with a fixed luminosity, then fade over a fixed time.
If the speed of light varies over cosmic time, the light will be redshifted for more distant supernovae, but the duration of the fading will on average be the same. Cosmic expansion, on the other hand, will increase the wavelength of the... | https://physics.stackexchange.com |
3,527,698 | [
"https://math.stackexchange.com/questions/3527698",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/707633/"
] | Suppose there are 10 people apart of a club: A, B, C, D, E, F, G, H, I, and J. They decide to go to a restaurant for a club outing, but there isn't one table to seat all of them, so they decide to take one table that seats four people and two tables that seat three people. Based on this, what is the probability that Pe... | As pointed out in the comments, it depends whether the 3-persons tables are distinguishable or not.
<strong>If the 3-persons table are distinguished</strong>
There is Three cases to look at.
<ul>
<li>If <span class="math-container">$G$</span> and <span class="math-container">$J$</span> sit at the 4-persons table, we... | Here is another approach. We assume that the <span class="math-container">$10$</span> people arrange themselves in some random order and then sit down, so there are <span class="math-container">$10!$</span> possible orders, all of which we assume are equally likely, with the first <span class="math-container">$4$</spa... | https://math.stackexchange.com |
55,405 | [
"https://stats.stackexchange.com/questions/55405",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/23964/"
] | I have two different time series both length = 100 and I need to know what is the best test (non-parametric, if possible), that return how much these two series are same or similar shapes.
Here are two examples: first one the two series are very similar shape, not matching perfectly but overall trends and tops and bott... | I don't think the $u_i$s will go to infinity. If $C$ is set to zero this effectively disables the inequality constraints, so the optimisation problem is just to minimise the squared norm of the weights, which has a trivial solution at $w = 0$. Substituting this into $y_i(w \cdot x_i + b) \geq 1 - u_i$ gives $y_i b \g... | Actually, the slack variable $u_i$ means the tolerance of inconsistent labeling with $y_i$ by the linear function $(wx_i +b)$. The factor $C$ "adjusts" the weight of total tolerance. Therefore, setting $C$ to zero might be problematic in the case that the set $\{x_i,y_i\}$ is <strong>not</strong> linearly separable!
| https://stats.stackexchange.com |
399,342 | [
"https://softwareengineering.stackexchange.com/questions/399342",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/167042/"
] | I'm wondering how best to handle the scenario of releasing a mobile app that includes an incomplete feature behind a feature flag in one version and then the completed feature behind the flag in a subsequent version - and making sure users with a previous version don't encounter incomplete functionality.
Let's say I'm... | The old client version can’t handle weather data. Therefore it mustn’t even try, whatever the server says. So If you want most of the code present but not operational, your client itself must contain a feature flag, set at compile time.
The client displays weather data if the client feature flag allows it (changed at... | Instead of a flag, the backend could return an app version that the client must have in order to use the feature. Example: <code>"show-weather":">=2.0.0"</code> could be used to indicate that clients starting with version 2.0.0 may use the feature.
| https://softwareengineering.stackexchange.com |
261,451 | [
"https://electronics.stackexchange.com/questions/261451",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/110946/"
] | I was wondering if a battery charger rated at 240V 60 Hz 3 phase input can be somehow made to work properly if I only have 240V 60 Hz single phase available. I know there are expensive phase converters available on the market but I want to try to avoid those because of cost reasons. So would 240V single phase possibl... | A simple (e.g., no power factor correction) 3-phase charger or power supply generally has a 6-diode bridge as the first item (perhaps after some filtering components) on the input side to create an internal DC bus. You'll want to verify this before proceeding.
If you connect a single-phase source (of the appropriate p... | It is extraordinarily unlikely that you could get enough CURRENT (Amps) out of a single phase to properly supply a circuit that was designed for 3-phase input. You did not mention any current specifications, either for the mains supply, or for the rated output of the charger, or for what you need for your proposed use... | https://electronics.stackexchange.com |
412,989 | [
"https://math.stackexchange.com/questions/412989",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/65982/"
] | Can anyone give me a hint / help with the next integral? Thanks!
$$\displaystyle\int_{0}^{t}{x^{a-1}(t-x)^{b-1}dx}$$
| Note that $K[x_1,x_2,\dots]=\bigcup_{n\in \Bbb N}K[x_1,x_2,\dots,x_n]$.
I'm going to denote these rings in the union by $R_n$ to save typing time.
To see that an irreducible $p$ of $R_n$ is irreducible in $R_m$ for $m\geq n$, suppose you have an equation $p=ab$ where $a,b\in R_m$. By evaluating $x_1,\dots, x_n$ all a... | They key idea is that each successive polynomial ring extension $\,D\subset D[x]\,$ is factorization <strong>inert</strong>, i.e. the ring extension introduces no new factorizations, i.e. if $\, 0\ne d\ \in D\,$ factors in $\,D[x]\,$ as $\,d = ab\,$ for $\, a,b\in D[x]\,$ then $\,a,b\in D.\,$ From this one easily deduc... | https://math.stackexchange.com |
1,023,124 | [
"https://math.stackexchange.com/questions/1023124",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/179201/"
] | The question is
<blockquote>
Solve the inequality $ax > |x-a|$ where $0 < a < 1$
</blockquote>
| Note that $[a,b]=([a,b] \cap \mathbb{Q}) \cup ([a,b] \cap ([a,b] \setminus \mathbb{Q} ))$ and $([a,b] \cap \mathbb{Q}) \cap ([a,b] \cap ([a,b] \setminus \mathbb{Q} ))=\emptyset$, so:
$$b-a=\lambda([a,b])=\lambda(([a,b] \cap \mathbb{Q}) \cup ([a,b] \cap ([a,b] \setminus \mathbb{Q} )))= \\= \lambda([a,b] \cap \mathbb{Q}... | Measure is additive:
$$
m([a,b]\cap\mathbb Q) + m([a,b]\setminus\mathbb Q) = m([a,b])=b-a.
$$
If one of the two terms on the left is $0$, then you can find the other.
| https://math.stackexchange.com |
136,483 | [
"https://mathoverflow.net/questions/136483",
"https://mathoverflow.net",
"https://mathoverflow.net/users/36814/"
] | I am wondering whether the following SDE can be solved explicitly?
$$
d X_t = X_t^2 d t + X_t d B_t
$$
where $B_t$ is a standard Brownian motion. If not, can we say some thing about the moments of the solution, i.e., $E(|X_t|^n)$?
Thank you very much for any hints!
Anand
| Solutions do exist locally. Globally they MAY blow up as you already know.
The blowup will be dominated by the deterministic system. You did not write what is your initial condition - note that $0$ is a perfectly fine solution to your equation. If your initial condition is say $X_0=1$, then it may blow up, but with p... | Actually your SDE may be solved explicitly. Look at the more general SDE,
\begin{align}
dX_{t} = (a X_{t}^{n} + b X_{t}) dt + c X_{t} dW_{t}
\end{align}
where $n > 1$ and $a,b,c \in \mathbb{R}$. It has a solution given by
\begin{align}
dX_{t} = \Theta_{t} \Bigl( X_{0}^{1-n} + a(1-n)\int_{0}^{t} \Theta^{n-1}_{s} ds \... | https://mathoverflow.net |
90,677 | [
"https://electronics.stackexchange.com/questions/90677",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/16307/"
] | When we cut a power supply's DC output tips we need to be careful how we feed the circuit since one side is negative one side is positive. But why doesn't the same apply when we plug for example a laptop charge, mobile phone charger to a wall outlet? Is that because alternating current has no one sided direction? What ... | Note that you can imagine the AC from wall outlet as as 2 stages DC power supply (that is a huge simplifcation but you may understand it better). Imagine that in a given moment the 2 holes in the wall give us a voltage difference of 120VDC between them, like a DC power supply of 120v (if exists). But in the next moment... | You said it. Standard AC supplies around the world alternate positive and negative at 50 or 60 times per second (hertz or Hz). This makes it suitable for a transformer and what comes out of a transformer is also AC but at a lower voltage and this is suitable for a bridge rectifier. Some bridge rectifiers can also be co... | https://electronics.stackexchange.com |
77,049 | [
"https://biology.stackexchange.com/questions/77049",
"https://biology.stackexchange.com",
"https://biology.stackexchange.com/users/45742/"
] | We know that <strong>Phosphatase</strong> is a type of enzymes that <strong>removes</strong> a phosphate group.
Why can't phosphatases <strong>add</strong> a phosphate group if we know that all <strong>enzymes reactions</strong> are <strong>reversible</strong> ?
| I think the description of enzymatic reactions as 'reversible' is potentially a bit misleading. It might be better to think of enzymes as <em>agnostic to reaction direction</em>.
The big missing piece is the difference in free energy of the reaction itself. Reactions that remove a phosphate group are energetically fav... | Not all enzyme catysed reaction are reversible reactions .reversible reactions are those which have free energy change between product and reactant sholud approximately or exactly equal to zero. Phosphatase canot do the reverse of the reaction because if both the reactions where done by the same enzyme in both the dir... | https://biology.stackexchange.com |
529 | [
"https://cardano.stackexchange.com/questions/529",
"https://cardano.stackexchange.com",
"https://cardano.stackexchange.com/users/255/"
] | This might be a novice question, but please bear with me :)
I'm working towards becoming an SPO and have a question regarding setting up the two types of nodes:
<ul>
<li>I have a Raspberry Pi 4 and an AWS, which should I (ideally) configure to be the relay node and which, the BP?</li>
</ul>
Regards
| You would probably want to use the AWS node as relay. This way you don't have to distribute the IP address of the Raspberry Pi in the Cardano network. (I assume you want to run the Raspberry from your home).
You also need to figure out if you have a static IP where you setup the Raspberry or if you get a dynamic IP fro... | The minimum RAM requirements are 8gb. You may think that the Raspberry may fall short in the short term. If you use it as a Relay you can disable the Tracemenpool to save resources.
| https://cardano.stackexchange.com |
152,268 | [
"https://electronics.stackexchange.com/questions/152268",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/65839/"
] | I have an ATX power supply which has got multiple 5v outputs (at a maximum 40 amp current). I am willing to use it to power up a moving mechanical system 5-10 meters away. The problem is that since the current can be so high I need a thick wire which obviously lacks flexibility. I am looking for a way to "carry" the lo... | Power companies get around it by increasing the voltage and decreasing the current. There's nothing you can do to reduce the total gauge of wire needed to transfer a given current, but if you can reduce that current then you can reduce the total gauge needed.
Instead of feeding the 5V direct from the ATX supply you c... | I would just extend the existing cables one by one. Using the same gauge as the existing cable may lead to a high voltage drop over this distance, so you should look for thicker cables (or splice e.g. one existing wire to two extension cables). This is simple math.
However, it also depends on your needs for flexibili... | https://electronics.stackexchange.com |
52,627 | [
"https://datascience.stackexchange.com/questions/52627",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/74855/"
] | I am applying both class_weight and oversampling (SMOTE) techniques on a multiclass classification problem and getting better results when using the class_weight technique. Could someone please explain what could be the cause of this difference?
| You should not expect class_weight parameters and SMOTE to give the exact same results because they are different methods.
Class weights directly modify the loss function by giving more (or less) penalty to the classes with more (or less) weight. In effect, one is basically sacrificing some ability to predict the lowe... | Probably not the answer you're looking for, but don't go crazy! Different class weight strategies give different results.
The follwing drove me almost crazy! The following should give the same results, but it doesn't.
class_weight = "balanced"
class_weight={0:0.85, 1:0.15}
I learned to live with it ...
| https://datascience.stackexchange.com |
224,638 | [
"https://dba.stackexchange.com/questions/224638",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/151018/"
] | <pre><code>SELECT
ROW_NUMBER() OVER(ORDER BY c.FullName ASC) AS No#,
a.AcctBranchName,
c.FullName,
c.BirthDate,
c.Age,
a.StartDate as 'Account Start Date',
c.CustStartDate as 'Customer Start Date',
c.CustomerNum,
a.Currency,
a.AccountNum,
a.ProductType as 'Product Name'... | Based on your comment to the question of whether multiple rows could come out of your subquery for a given account number, you indicated that was not possible. If that's true, I don't see why you can't simply <code>LEFT JOIN</code> by account number against a derived result of your subquery.
Not tested, but basically... | <pre><code>SELECT
ROW_NUMBER() OVER(ORDER BY c.FullName ASC) AS No#,
a.AcctBranchName,
c.FullName,
c.BirthDate,
c.Age,
a.StartDate as 'Account Start Date',
c.CustStartDate as 'Customer Start Date',
c.CustomerNum,
a.Currency,
a.AccountNum,
a.ProductType as 'Product Name'... | https://dba.stackexchange.com |
616,243 | [
"https://physics.stackexchange.com/questions/616243",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/196626/"
] | I wish to generalise the equations governing electromagnetic induction. Consider a loop whose size is changing, and is subject to a changing magnetic field. Then,
<strong>Definitions:</strong>
<span class="math-container">$$\phi \equiv\int_{S(t)}\mathbf{B(t)}\cdot d\mathbf{a} \tag{1.1}$$</span>
<span class="math-contai... | A conceptual error: The parallel axis theorem is used to find the inertial moment about an <strong>rotating axis</strong> which is not the CM. In this problem, the disk is not rotating about the CM (for rock and disc joint system) but it rotates around the center of disk.
Therefore, it should be think in decomposing th... | This problem has a major difference from many similar textbook problems dealing with the conservation of angular momentum.
In many of the textbook problems the axis of rotation of the disk about its center of mass (CM) is fixed by a constraining force/torque and does not move. If that were the case here, the axis of r... | https://physics.stackexchange.com |
255,129 | [
"https://physics.stackexchange.com/questions/255129",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/16223/"
] | <blockquote>
As air moves from high to low pressure in the northern hemisphere, it is deflected to the right by the Coriolis force
</blockquote>
They use an example of a merry-go-round, which makes sense intuitively. An object pushed from the outer edge inward is deflected to the right if the merry go round is spinn... | I never did like the merry-go-round explanation for the Coriolis Effect. It may be intuitive for some, but I never could wrap my head around it. (And it's properly the Coriolis Effect, not Force. It's no more a "force" than the "force" pushing you against your car seat as your car accelerates.)<br><br>This works better... | <blockquote>
In physics, the Coriolis effect is a deflection of moving objects when
they are viewed in a rotating reference frame. In a reference frame
with clockwise rotation, the deflection is to the left of the motion
of the object; in one with counter-clockwise rotation, the deflection
is to the right.
</... | https://physics.stackexchange.com |
223,637 | [
"https://electronics.stackexchange.com/questions/223637",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/104174/"
] | Basically we give a PWM wave to the control input, but what will be the input for the error detector...?<br>
How is this PWM wave converted to some voltage value that can be compared from the potentiometer output....?<br>
What is the average value of the current drawn by the servo motor, is it same as that of the dc mo... | <strong>How is this PWM wave converted to some voltage value that can be compared from the potentiometer output....?</strong>
It's not.
In the simplest version of the servo's position control, the servo output shaft drives a potentiometer, which is the control resistor in a monostable pulse generator. The monostable ... | PWM control of the setpoint is specific to hobby radio controlled products. Servo motors are ubiquitous in a wide range of e.g. automation, vehiclular and consumer electronics applications, but they do not generally use the RC PWM protocol.
<img src="https://upload.wikimedia.org/wikipedia/commons/7/7b/ServoPwm.png" a... | https://electronics.stackexchange.com |
9,700 | [
"https://mechanics.stackexchange.com/questions/9700",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/3474/"
] | I was driving normally (no problems, everything going smoothly; never had felt any problems with the clutch, was catching on well etc.) and <strong>all of a sudden</strong>, with no warning sign or anything (no shock, no bang, nothing), the <strong>clutch pedal doesn't go far enough anymore</strong> to engage the gears... | After your last edit and a few minutes of thinking about your situation I have one more question.
<em>When he vehicle is in gear and moving is there any noise? With the pedal fully depressed is there any noise?</em>
I am going to assume the answer to those are both no and there is simply just difficulty switching ge... | If it is hydraulics double pumping the clutch should notice some improvement.
I am going with throw out bearing myself though. or the pressure plate fingers bent in.
So once you eliminate the master and slave cylinders of leaking, you are going to need to pull the transmission to find which is bad.
At that point change... | https://mechanics.stackexchange.com |
250,463 | [
"https://physics.stackexchange.com/questions/250463",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/114731/"
] | If $X$ and $Y$ are two observables and $\rho$ is a density operator, is it true that for every complex number $z$ the quantity
$$
\mathrm{tr}[\rho (X+zY)^*(X+zY)]
$$
is non-negative?
| Yes it is. Use the fact that the operator in the trace different from $\rho $ is positive and compute the trace using a basis of eigenvectors of $\rho $, whose eigenvalues are also positive. (By positive I actually mean nonnegative).
Here is the proof (assuming the first version of the question regarding $tr(\rho (X+... | Assuming $(X + zY)^*$ is the conjugate of $X + zY$, a counter-example is:
$$z=0, Y=\begin{bmatrix} 0&0\\0&0 \end{bmatrix}, X=\begin{bmatrix} 0&-i\\i&0 \end{bmatrix}, \rho = \begin{bmatrix} 1/2&0\\0&1/2 \end{bmatrix}$$
Because:
$tr[\rho(X+zY)^*(X+zY)]$
$= \text{Tr}\left[I/2\left(\begin{bmatri... | https://physics.stackexchange.com |
269,334 | [
"https://softwareengineering.stackexchange.com/questions/269334",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/78270/"
] | modern dynamic programming languages like Python, Ruby and Javascript all take the approach of treating everything as an object, what's the benefit of this approach, and what's the curse of it?
Benefit I can think of: first class functions, duck typing.
Drawbacks:performance issue, especially performance of primitiv... | It's not entirely clear whether you are talking about the semantics or the pragmatics here. Your question reads more about semantics, but in the comments you say you are asking about pragmatics. I'm going to answer about both.
<h1>Semantics</h1>
<ul>
<li>Pros: simplicity. Why have two concepts when one will do?</li>
... | Performance doesn't matter. Or rather: compared to providing developers the best tool with which they can express and model what they want the computer to do, performance is the easier problem to solve.
Types, classes, objects, functions, lambdas - all those concepts help organize your thoughts and your code. At this ... | https://softwareengineering.stackexchange.com |
1,072 | [
"https://mechanics.stackexchange.com/questions/1072",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/649/"
] | I've got a '66 Datsun Fairlady (called a Roadster in the USA) and the locking mechanism on the boot (trunk) is broken. If the correct key is inserted into the lock the mechanism turns but with no resistance and nothing happens. And without a key inserted the mechanism also turns with no resistance. I can tell that at s... | If you can get through the license plate hole on the left side of the trunk key and simply press down on the back of the latch mechinsm while holding pressure down on the trunk lid it just might open up for you.
The lock simply has a small arm that performs the same task. Keep in mind, the key for this lock must be in... | Do you have a workshop manual or parts book for the car? These should at least give you an idea of what the mechanism looks like.
The best option I can see would be to find someone else with another Fairlady (is there an owners club?) who would let you have a look at theirs, or email you photos if they aren't local. I... | https://mechanics.stackexchange.com |
80,599 | [
"https://stats.stackexchange.com/questions/80599",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/2676/"
] | While I was reading Torgo's Data Mining with R, I found that the description of precision/recall curve was different compared with other approaches. Usually, these curves are based on a threshold that determines which probability value is good enough to decide when an event has occurred, so we can classify future event... | Short answer: Torgo describes the usual method of generating such curves.
You can choose your threshold (= cut-off limit in the cited text) at any value. The cited text refers to one such choice as a working point.<br>
That is, for a given working point, you'll observe exactly one (precision; recall) pair, i.e. one <... | For your aim, precision/recall curves are not that relevant. Yours is a probability estimation problem, something that logistic regression and its many variations can do quite nicely. There is nothing magic about a probability threshold of 0.5 nor is it needed. You can choose $k$ based on cost and inspect the units ... | https://stats.stackexchange.com |
110,585 | [
"https://stats.stackexchange.com/questions/110585",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/24515/"
] | After multiply imputing data, it is natural to estimate regression models on the data. When multiple predictors are available, sometimes stepwise regression is used for model building (forward inclusion or backward elimination of covariates). My question is how to use a similar procedure on multiply imputed data sets (... | Avoid stepwise regression due to the many issues indicated in many other threads.
If you search Google.Scholar for methods that are more appropriate for variable selection (e.g. cross-validation approaches) + "multiple imputation" you will find many suggestions. For example:
<ul>
<li>Heymans, M. W., van Buuren, S.... | One way to pool the stepwise analyses of individual imputations is to identify the predictors that most frequently appear in them.
For example, <code>names(coef())</code> applied to output from <code>stepAIC()</code> (MASS package) applied to a linear regression gives the predictor names retained in the final stepwis... | https://stats.stackexchange.com |
316,407 | [
"https://softwareengineering.stackexchange.com/questions/316407",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/225483/"
] | I often find myself struggling to decide which of these two ways to use when I require to use common data across some methods in my classes. What would be a better choice?
In this option, I can create an instance variable to avoid the need of having to declare additional variables, and also to avoid defining method pa... | I'm surprised this hasn't mentioned yet...
<strong>It depends if <code>var1</code> is actually part of your object's <em>state</em></strong>.
You assume that both of these approaches are correct and that it's just a matter of style. You are wrong.
This is entirely about how to properly model.
Similarly, <code>priv... | I don't know which is more prevalent, but I would always do the latter. It more clearly communicates the data flow and lifetime, and it doesn't bloat every instance of your class with a field whose only relevant lifetime is during initialization. I would say the former is just confusing, and makes code review signifi... | https://softwareengineering.stackexchange.com |
352,196 | [
"https://electronics.stackexchange.com/questions/352196",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/1240/"
] | So I have a display which has an integrated LED driver for backlight. The driver expects PWM input with frequency between 10 kHz and 100 kHz. The only other information I have are the maximum voltage and current and that there are two LED strings.
Most of the research results I found concern themselves with PWM freque... | <blockquote>
So are there any other important factors, other than EMI concerns, which need to be taken into account when selecting the PWM frequency?
</blockquote>
Yes.
The higher the switching frequency, the more you have to charge / discharge whatever MOSFET that is being used for switching. So the larger input c... | May or may not be a serious issue in practice, but:
Choose 38kHz and your infra-red remote controls may get a lot less sensitive...
It's certainly true that the first overhead LED room lights (GU10 bulbs) I installed jammed the remote control of anything in the same room.
Whether the same would apply with a LED ba... | https://electronics.stackexchange.com |
195,388 | [
"https://softwareengineering.stackexchange.com/questions/195388",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/83306/"
] | We have lots of user-generated images on our site. When users upload their images, we only store the original. However, depending on the page, we show different sizes of those images (small, medium, large, original). Is it necessary to store all sizes of these images or is there a better way? Currently, we are resi... | Storing multiple copies of the image at the required sizes is probably your best bet, for a few reasons:
<ol>
<li>Disk space is relatively cheap,</li>
<li>As @Jalayn commented, downsizing images doesn't require much processing power,</li>
<li>As @Dan Pichelman commented, serving smaller images when possible will save ... | There's a lot of way you can handle this, and I think the "right way" depends.
However I think we can all agree that storing the different sizes is the best way.
Your site might not be setup in a way that 3 sizes work for you though (such as small, medium, large) and of course storing every possible combination is un... | https://softwareengineering.stackexchange.com |
323,025 | [
"https://softwareengineering.stackexchange.com/questions/323025",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/156202/"
] | The problem is maintaining in .net a list of rows that have a specific sequence where rows can be inserted, moved and deleted, and being able to save and restore that sequence from disk.
In memory I can use a .net list with insert and delete by index position. The alternatives that I see for converting that to a dis... | You are concerned about the performance of bulk-updating a sequence number, but I suspect this is premature. Bulk updating sequence numbers (e.g. increment a field for all items in a section of a list) can be done in a single SQL update. I if the average set is 200 items performance will most likely not be an issue.
A... | <blockquote>
being able to save and restore that sequence from disk
</blockquote>
Are we talking about a file system, here, or a "DB", as in your posting's Title?
In the file system, just write your list items into a file. They will be stored in the order you want them and you can read them back in the same order... | https://softwareengineering.stackexchange.com |
22,593 | [
"https://quant.stackexchange.com/questions/22593",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/15782/"
] | I am trying to understand the relationship between two methods of pricing callable bonds in the risk-neutral pricing framework.
<h2>Problem statement</h2>
Let's consider zero-coupon bond with face value 1, expiring in 1 year and callable at 6 months with strike $K =0.4$. I am going to work in the Ho-Lee model in whi... | <strong>Transformation to Heat PDE</strong>
First define $T_1$ to be the call date and $T_2$ to be the maturity date. We start by making a change of variables. Let
\begin{equation}
\tau = T_1 - t, \quad x = r - \frac{1}{2} \sigma^2 \tau^2, \quad g(t, r) = \exp \left\{ -r \tau + \frac{1}{6} \sigma^2 \tau^3 \right\} h(... | Can you try to plug your analytical solution obtained Method 1 into the PDE and show that it satisfies the PDE with boundary conditions ?
| https://quant.stackexchange.com |
418,809 | [
"https://mathoverflow.net/questions/418809",
"https://mathoverflow.net",
"https://mathoverflow.net/users/172051/"
] | For <span class="math-container">$n\in \mathbb{N}$</span> with prime decomposition <span class="math-container">$n=p_1^{r_1}\cdots p_k^{r_k},p_i\neq p_j$</span>, let <span class="math-container">$A=\{p_1,\cdots,p_k\}$</span>; then the following holds:
<span class="math-container">\begin{equation}
|\{q\in \mathbb{N},q&l... | Let <span class="math-container">$q<Q$</span> be such that all its prime divisors are in <span class="math-container">$A$</span>. We can write <span class="math-container">$q=q_0\times r_1^{n_1}\cdots r_s^{n_s}$</span>, where all prime factors of <span class="math-container">$q_0$</span> are <span class="math-contai... | Here is a proof that its at most <span class="math-container">$\exp(O(\log Q\log\log\log Q/\log \log Q))d(n,Q)$</span>, which suffices for the paper.
Let <span class="math-container">$S(n,Q) = \{q<Q: q|n\}$</span>. Clearly <span class="math-container">$|S(n,Q)| = d(n,Q)$</span>.
Now consider <span class="math-contai... | https://mathoverflow.net |
12,374 | [
"https://chemistry.stackexchange.com/questions/12374",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/5424/"
] | I am confused, should it be 2 or 4?
If I consider $\ce{BeCl2}$ as a chain structure the coordination number is 4, and in the gas phase it is 2.
| Coordination number is determined by compound. It is normal for an element to have several different CN. Preferable CN can change for an element depending on the atom's neighbors. For example, Fe has preferrable CN=6 for fluorine anions, but CN=4 for chloride anions. When heated or under extreme pressure preferable CN ... | Beryllium is the most electronegative of the Group 1 and Group 2 elements (excluding hydrogen) and so rather than lose 2 electrons (and become $\ce{Be^{+2}}$ - a lot of charge on such a small atom) it can often bond covalently. Just like with carbon, the covalent bonding will involve mixing of beryllium's $\ce{2s}$ an... | https://chemistry.stackexchange.com |
102,829 | [
"https://cs.stackexchange.com/questions/102829",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/81234/"
] | Wikipedia says that "a dense graph is a graph in which the number of edges is close to the maximal number of edges." and "The maximum number of edges for an undirected graph is <span class="math-container">$|V|(|V|-1)/2$</span>". Then why do even use <span class="math-container">$ |E| = \Theta (|V|^2)$</span>?, under... | It only really matters in the limit: for small sizes, the difference isn't really important.
But if you're doing a large number of each operation, <span class="math-container">$O(\log n) + O(\log n) = O(\log n)$</span> is asymptotically faster than <span class="math-container">$O(n) + O(1) = O(n)$</span>.
| We have a simple equation: Number of insertions = number of removals + size of priority queue. If the number of insertions is n, then the heap will be faster as long as the number of removals is at least n / log n. And if the number of removals isn't that large, then your priority queue will grow in size very, very qui... | https://cs.stackexchange.com |
484,557 | [
"https://physics.stackexchange.com/questions/484557",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/204775/"
] | Consider a railway carriage. It is moving in +ve x-axis with a velocity, v, relative to the platform.
Let A',B' be end points and M' be the exact middle of the carriage.
Let the platform observer be O.
The observer situated at M' at rest relative to the carriage be O'.
When O and O' cross each other I set the clocks... | Neat paradox. The flaw is in the innocent-looking line
"At time 0 (when O and O' cross) I shoot 1 photon each from A',B' towards M'."
The reason is that setting <span class="math-container">$t=t'=0$</span> when the origins coincide only applies at <span class="math-container">$x=x'=0$</span>
For other values they ar... | observer O is not necessary, unless you would have stated that he was in the exact center of a and b. if the photons are sent when O' is at the exact center of a and b (which was not specified) then the light will be off, by the time the rear photon hits the carriage will have moved ahead and already hit the front pho... | https://physics.stackexchange.com |
136,390 | [
"https://softwareengineering.stackexchange.com/questions/136390",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/48292/"
] | So I'm trying to make my Unit Tests as by-the-book as possible, but it becomes troublesome when I'm testing some simple Add/Delete methods.
For the add method, I basically have to create a dummy object and add it, then after the test is successful, I have to delete the dummy object.
And for the delete test, I obvious... | Well, there's nothing wrong with what you're doing. Multiple tests can cover the same code; it just means that one problem will cause several tests to fail. What you want to avoid is tests that depend on the results of other tests. I.e., your delete test depends on the add test having run, and thus if you run your dele... | Use transactions.
If you are using a database that supports transactions, then run each test in a transaction. Rollback the transaction at the end of the test. Then each test will leave the database unchanged.
Yes, to cancel an order you will first have to create one. That's fine. The test will first create an ... | https://softwareengineering.stackexchange.com |
230,107 | [
"https://stats.stackexchange.com/questions/230107",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/127850/"
] | I am confused!
I have two dummy variables (3 groups) and a third predictor, $Age$, which is continuous. What I don't understand is: why do I get different results (p-value and coefficient) for $Age$ when I include the two dummy variables in the model vs. when I run the model over the reference group only (without the d... | In your analysis with three groups $\beta_1$ captures the average relation of age and $y$ in the three groups. In you second analysis with only one group $\beta_1$ captures the average relation of age and $y$ in that group. If the relation between age and $y$ is different across your three groups, you will have differe... | If you want to run your analysis on reference group only, your equation would be y= b0 + b1*age + b4*d3
NOT
y= b0 + b1*age
The second equation essentially doesn't know of the existence of any grouping variable, whereas the previous versions have information from the dummy variables. As a result there will be a change ... | https://stats.stackexchange.com |
154,483 | [
"https://softwareengineering.stackexchange.com/questions/154483",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/57828/"
] | I'm trying to compare two graphs using hash value ( i.e, at the time of comparison, try to avoid traversing the graph )
Is there a way to make a function such that the hash values compared can also lead to determining at which height the graphs differ?
The comparisons between two graphs are to be made by comparing chi... | <strong>A cobbled together solution:</strong>
You could probably cobble something together where each level of the graph affected a different portion of the hash value. What you'd essentially be doing here is creating a separate hash value for each level and appending them in sequence.
e.g. For a 32-bit hash and grap... | No there is no way to do what you are asking, the purpose of a hash value is to take something and make it something else with no apparent relation to what it was. This means hash values are only useful to tell you if to things are the same, not what is different between them.
It is theoretically possible to reverse e... | https://softwareengineering.stackexchange.com |
113,977 | [
"https://softwareengineering.stackexchange.com/questions/113977",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/1130/"
] | This is probably a stupid question, but do I need to Clean/Rebuild before Debugging or Publishing a Visual Studio project?
I see other developers doing it all the time, and at some point I started doing it without even thinking. It seems habit to always go Clean, wait, Rebuild, wait, Publish.
I know I didn't always ... | You don't <em>have</em> to, but I find that Visual Studio sometimes looses track of what assemblies were built when. When that happens, you end up with stale assemblies and a bad debugging experience (when the code and symbols don't match).
As result, I simply do a re-build every time (this does a Clean + Build). This... | It is not "required," but you might want to do the Clean+Build before a major release and/or after you get files from other resources.
VS sometimes fails to identify the modified files and thus bypasses the necessary re-compilation. In my case, this usually happens when the files are updated via some overwriting behav... | https://softwareengineering.stackexchange.com |
615,419 | [
"https://physics.stackexchange.com/questions/615419",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/-1/"
] | Very simply put, I don't understand why SHM happens.
If a spring or a pendulum can attain lowest potential energy by stopping at the mean position, why don't both of them stop at the mean position itself? ( Assuming that there are no damping forces)
| The spring or pendulum does not stop at the lowest point having lowest energy because it still has kinetic energy at that point and hence goes up in which in loses its kinetic energy and gains potential energy and this cycle continues in vacuum as there is no damping.
| to enlarge slightly upon Black Thunder's answer, the inertial forces and compliance forces in a mechanical oscillator are <em>out of phase</em> which causes the inertance (mass) in the system to <em>overshoot</em> its rest position. The system then oscillates.
| https://physics.stackexchange.com |
2,532,827 | [
"https://math.stackexchange.com/questions/2532827",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/293908/"
] | Let $f:K\subset R^n \rightarrow R$ be a continous function and $K$ a compact set
Proof the following statement about the lebesgue integral.
<blockquote>
$$\int_K fd\lambda =\lambda(K)f(\epsilon)$$ for some $\epsilon \in K.$
</blockquote>
I am stuck with this problem and would appreciate a hint
| Yes, for $\|f_{n}-f\|_{\infty}\rightarrow 0$, then for some $N$, if $n\geq N$, $\|f_{n}\|_{\infty}\leq\|f\|_{\infty}+1$. Note that $f$ is also continuous by the uniform convergence. As $f$ is continuous on the compact set, so $\|f\|_{\infty}=\max|f|<\infty$. So $\|f_{n}\|\leq\max\{\|f_{1}\|_{\infty},...,\|f_{N-1}\|_... | <strong>Hint</strong>. There exists an $N$ such that for all $n>N$ we have $\sup_x|f_n(x) - f(x) |<\epsilon$ (conclude your self why this implies boundedness for $n>N$). Since $f_n$ is continuous we have for all $n\leq N$ there exist a $M_n$ such that $|f_n(x) |<M_n$ for all $x$ in the domain by Weierst... | https://math.stackexchange.com |
137,230 | [
"https://electronics.stackexchange.com/questions/137230",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/54791/"
] | Just wondering how with DC measurements you could measure a diodes saturation current and the Emission coefficient factor N. I was thinking a basic DC circuit varying the voltage taking voltage measurements, then plot the V-I and then try fit the diode equation to the graph?
| Two measurements should be enough for the basic Shockley model.
<ol>
<li>Measure current with fairly large reverse bias, to give you Is. (for example, -20V for a 1N4148)</li>
<li>Measure forward voltage with fairly large forward current (for example, 20mA for a 1N4148) and calculate the emission coefficient:
\$n = \... | I was going to suggest measuring Vf at several current's with decade type steps.
100nA, 1uA, 10uA, 100uA... at higher currents there is a resistive term that creeps in.
And plot that against the diode equation.<br>
(at higher currents the diode can heat up too.)
I've never had any luck trying to measure the Is in reve... | https://electronics.stackexchange.com |
157,995 | [
"https://electronics.stackexchange.com/questions/157995",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/69083/"
] | Trying to find the Thevenin equivalent voltage for the circuit on the picture below.
This voltage is supposed to be found at the round dots to the very right in the circuit.
According to the answer sheet the answer is supposed to be 16V for the Thevenin voltage.
However I keep getting the wrong answer and I don't und... | We ignore the R10 because effectively there is an infinite resistor across the two output terminals. Which means you have the same voltage drop at the output as is dropped across R9 which is 16volts 22*(R9/(R9+R8))
(Just think of it as another voltage divider of an infinite resistor and R10. The infinite resistor gets... | You don't need to find Rth. Note that R10 is immaterial since the Thevenin voltage is found with the output open circuited so no current flows in R10. Without R10, the Thevenin voltage consists of a voltage divider, R8 and R9, and a source voltage of 22 volts. Just calculate the output voltage based on that configura... | https://electronics.stackexchange.com |
116,318 | [
"https://softwareengineering.stackexchange.com/questions/116318",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/18170/"
] | I really like pair programming for particular projects or features. It can act as an immediate sanity check and increase code coverage across your development team. That said I always seem to run into an issue regarding editors. I primarily code Ruby and I personally like to use VIM whereas other developers on my team ... | <ul>
<li>Hour one: you program, the other person watches and helps thinking.</li>
<li>Hour two: the other person programs, you watch and help thinking.</li>
</ul>
You can switch editors when the other person starts programming.
| I've started using the homesick gem to track my .vimrc, .vim, etc
Now I can checkout my dot files to any machine, no worries! hooray!
I do tend to keep my customized vim pretty light (CommandT, some whitespace stuff, matchit) that way I learn how to do stuff the standard way instead of the really cool way that only m... | https://softwareengineering.stackexchange.com |
4,268 | [
"https://physics.stackexchange.com/questions/4268",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/1677/"
] | I'm in the process of working on a physics related game. I'm looking to find the maximum velocity of an object given it's mass and the force acting on it when it is traveling horizontally. I believe there must be a method of calculating this but I'm unaware of it. Is there a formula for this scenario? I'm unaware i... | Suitable for game physics and BoTE calculations:
<ol>
<li>Assume a functional form for the frictional resistances (all the apply from rolling, sliding and fluid (wind or water)), and solve for the total resistance equal to the driving force.</li>
<li>If that does not limit the speed to a reasonable velocity and this e... | Assume the object is moving on a frictionless surface in the absence of a gravitational field with a certain velocity or it is at rest. Calculate the kinetic energy of this object as a result of its uniform motion or rest. The formula for kinetic energy is:<br><br>$K.E \ =\ \Large \frac{1}{2} \large mv^2$<br><br>
Appl... | https://physics.stackexchange.com |
11,722 | [
"https://mechanics.stackexchange.com/questions/11722",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/876/"
] | I brought my car in because the starter died. During the multipoint check, they also discovered that the timing belt and the 'package' (all other components related to it) has not been changed since the previous owner had it. (I have a 2003 Accord w/ ~90k miles).
They told me that the timing belt needed to be changed ... | Yes, they have to be changed along with the timing belt. The tensioner pulley doesn't last very long (only as long as the timing belt, or not as long as two timing belts, at any rate) and the water pump is cheap enough anyway. If one of these things decide to break, it will also break your timing belt, which will damag... | It's not necessary, but VERY recommendable to change all the related things. I had often enough, that the old water pump got leak after change of timing belt because of different tension. You may be lucky, and nothing will happen. But if, you will have to pay almost the same high price just to change only a water pump,... | https://mechanics.stackexchange.com |
107,186 | [
"https://physics.stackexchange.com/questions/107186",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/23179/"
] | Since neutrons have no electric charge will an anti-neutron annihilate when it comes into contact with a regular neutron as protons and anti-protons do? if so what causes it to annihilate?
| Neutron and antineutron have also an internal structure formed by quarks.
A neutron is composed by 2 down quarks, each with a charge -1/3, and one up quark with a charge of 2/3. This gives a total charge of 0.
Antineutron are different, they have 2 anti-down quarks (each with a charge of 1/3) and one antiup quark (-2/... | Yes it will. Annihilation is a form of interaction which only happens between a particle and its anti-particle. You can sort of imagine it even though its not completely true I think, as destructive interference of the same particle field. Its independent of charge.
| https://physics.stackexchange.com |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.