qid int64 1 4.65M | metadata listlengths 3 3 | prompt stringlengths 31 25.8k | chosen stringlengths 17 28.2k | rejected stringlengths 19 40.5k | domain stringclasses 28
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|---|---|---|---|---|---|
4,972 | [
"https://cs.stackexchange.com/questions/4972",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/3121/"
] | I'm currently doing some reading into AI and up to this point couldn't find a satisfying answer to this question: what's the difference between a rule based system and an artificial neural network?
From my understanding both are trying to do inference based on a variety of different inputs.
| The difference is vast, although as Dave wrote, the resulting black box might look the same from outside. Rule-based systems are examples of "old style" AI, which uses rules prepared by humans. Neural networks are examples of "new style" AI, whose mechanism is "learned" by the computer using sophisticated algorithms, a... | Just to give a slightly more general perspective than the other answers: "trying to do inference based on a variety of different inputs" is basically what much of the field is doing and it is a very general problem.
The idea is that you are looking for some simple, general way to explain how data observations are asso... | https://cs.stackexchange.com |
71,949 | [
"https://security.stackexchange.com/questions/71949",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/59802/"
] | So I went over quite a lot of topics here and on the internet.. but I still can't seem to completely understand this issue.
How secure really are services like proxies, VPN or VPS?
VPN is promoted everywhere as being safe. Proxies have different levels of anonymity.
But is there a possibility, that a VPN provider w... | The only defense you can have on a locally encrypted file is the strength of the password used to encrypt it. Also, using a secure encryption algorithm is important (AES is pretty standard right now).
You are absolutely correct that brute-force cracking is 100% successful. The problem lies in the amount of time it tak... | If the file is retrieved from the filesystem to the attacker's system, there is no longer any gateway. The brute force can continue without any impediment.
More complex keys or passwords do increase the time/cost of brute forcing, but 'eventually' (hopefully before the heat death of the universe), it could be cracked... | https://security.stackexchange.com |
25,888 | [
"https://softwareengineering.stackexchange.com/questions/25888",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/9026/"
] | I thought I did okay in the interviews but apparently the interviewers didn't think so. Is it appropriate to ask for a reason after I have received the rejection email? After all I don't want to annoy the HR person.
I am a student, so not so much job hunting experience so far. Bear with me if this question sounds stup... | If you asked it like you just asked us, you'll have a much better shot at getting a useful answer. Emphasize that you are new to the workforce and really value the time the interviewer spent considering you. Ask what you lacked, perhaps that you could have predicted coming into the interview, that affected your consi... | I usually tell people if they call. Common reasons I give are:
<ul>
<li>The position was given to someone with more experience</li>
<li>The position was given to someone who we feel would be a better fit in our team. During our interview, you didn't defend your solution to the [foo] problem very well.</li>
<li>You mis... | https://softwareengineering.stackexchange.com |
455,137 | [
"https://physics.stackexchange.com/questions/455137",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/194517/"
] | I wanted to ask a question. My question is that are the properties of field lines ( number of field lines leaving/entering a point charge is proportional to the charge, field strength between points can be compared using relative field line density etc.) true for any symmetrically drawn diagram. Like if I had charges <... | Here is one argument:
<ol>
<li>Starting from Newton's 2nd law, the Lagrangian <span class="math-container">$L(q,v,t)$</span> is just one step away. </li>
<li>A Legendre transformation <span class="math-container">$v\leftrightarrow p$</span> to the Hamiltonian <span class="math-container">$H(q,p,t)$</span> is well-defi... | To describe the motion of bodies, it is enough to know two variables — the coordinates and velocitys, or the coordinates and momentums, then the initial conditions are determined. In the case of setting other variables, it is necessary to use boundary conditions, which is more complicated. It is necessary to set the in... | https://physics.stackexchange.com |
7,687 | [
"https://security.stackexchange.com/questions/7687",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/396/"
] | We have several smartphone with encrypted data on them (BES, iPhone, Android) and want to prevent an unauthorized person from downloading information from the device via USB.
The visual assumption is that the USB file transfer mode is protected by a password; but then again, it is subject to implementation flaws and... | The kind of attack you are talking is popularly coined as "Juice Jacking".
<ul>
<li>Are there any "known bad" or "known safe" smartphones with regard to USB security?
<ul>
<li>In my knowledge, NO.</li>
</ul></li>
<li>How does a corporation protect from these risks?
<ol>
<li>By making policies (actually spreading awa... | There is an additional piece of protection you can put in place:
On my android phones, I have the default connection type set up to be 'charge only' which prevents access through the USB port until I manually set the charge type to accept a connection. And this can only be done through the on-screen menus.
I think iP... | https://security.stackexchange.com |
166,390 | [
"https://softwareengineering.stackexchange.com/questions/166390",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/34133/"
] | In almost every project I work on with a team, the same problem seems to creep in. Someone writes UI code that needs data and writes a data access method:
<pre><code>AssetDto GetAssetById(int assetId)
</code></pre>
A week later someone else is working on another part of the application and also needs an <code>AssetDt... | Syntax-wise, I'd create an intermediate query-building object with a fluid interface:
<pre><code>// all the basic, cheap to query fields
AssetDto a = AssetRetriever(asset_id).fetch()
// some common expensive fields
AssetDto a = AssetRetriever(asset_id).withOwner().withQuestion().fetch()
// numerous less common fie... | When dealing with large object, this is really common. While adding new methods increases performance, it significantly decreases the maintainability. And again you need to choose between those two.
I suggest you have a method that returns (not necessarily the smallest) commonly used data, another that returns the wh... | https://softwareengineering.stackexchange.com |
384,980 | [
"https://softwareengineering.stackexchange.com/questions/384980",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/100503/"
] | I currently have two derived classes, <code>A</code> and <code>B</code>, that both have a field in common and I'm trying to determine if it should go up into the base class.
It is never referenced from the base class, and say if at some point down the road another class is derived, <code>C</code>, that doesn't have a ... | It all depends upon the exact problem you're trying to solve.
Consider a concrete example: your abstract base class is <code>Vehicle</code> and you currently have the concrete implementations <code>Bicycle</code> and <code>Car</code>. You're considering moving <code>numberOfWheels</code> from <code>Bicycle</code> and ... | Logically speaking, beyond placing the field replicated in subclasses vs. in common in the base class, there is a third option: which is to introduce a new subclass into the hierarchy that has the common properties between the two. @Pete hints at this without fully going there.
Using @Pete's example, we would in... | https://softwareengineering.stackexchange.com |
119,665 | [
"https://mathoverflow.net/questions/119665",
"https://mathoverflow.net",
"https://mathoverflow.net/users/30364/"
] | I am looking for a a description of the algebra of continuous central functions on a group, say a compact simple Lie group $G$, as the algebra of all continuous functions on a "nice" compact Hausdorff space. By central I mean of course constant on the conjugacy classes, i.e.
$f(gxg^{-1}) = f(x)$ for all $x,g\in G$.
B... | If $G$ is compact, then as explained in comments $G/ad$ is $T/W$. If
further $G$ is simply-connected, hence a product of simple factors,
then $T/W$ is a corresponding product of simplices.
The point is that $T/W = ({\mathfrak t}/\Lambda)/W
= {\mathfrak t}/(\Lambda \rtimes W)$, where $\Lambda$ is the kernel of the
exp... | Not an answer as such, but some extended comments with explicit references (posted as community-wiki).
1) As a non-specialist, I'm unsure whether you are asking for new information or for better references than you have. Compact Lie groups have been studied thoroughly for more than a century, going back (as Rober... | https://mathoverflow.net |
130,593 | [
"https://softwareengineering.stackexchange.com/questions/130593",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/38907/"
] | I've noticed that in most technical phone screens, programming questions tend to focus on inheritance. For instance:
<ul>
<li>If a class is intended to be inherited, what should you do with the destructor? (Answer: make it virtual)</li>
<li>What's the deal with public/private access?</li>
<li>What's "protected" for?</... | The goal of a phone screen is generally to figure out which candidates it is worth spending the time and energy to interview in person. So the goal is generally to weed out candidates that aren't worth the time to interview in person rather than to identify the best candidates. That means that questions in phone scre... | Two reasons.
First because, in a phone-screen, you don't want to ask trivia questions. By trivia questions, I mean those that are easy to people who have used those features and difficult to those who haven't. You can't write well in an OO language without knowing about inheritance. You can without knowing about exten... | https://softwareengineering.stackexchange.com |
431,534 | [
"https://electronics.stackexchange.com/questions/431534",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/110116/"
] | I understand that it is common practice in electronic design to simulate a circuit in some spice program before building it. Sometimes a project requires the use of complex ICs, for instance an IC which performs charge control for a Li-Po battery or an IC which acts as PWM controller. Manufacturers generally don't make... | In my experience the widespread use of simulation of entire boards is mostly a myth outside of physics simulations in RF.
Simulation rules for IC design of course, because the prototyping costs are so insane, and for anything involving HDL design, but for general electronics, not so much.
Where the sim really helps... | When using such ICs, I find myself often following the "cookbook" of the manufacturer. This should lead to a working circuit in most cases and often you have a circuit you can more or less integrate into your design as is.
But in some cases, I also build a SPICE model for a part of the circuit with its external compon... | https://electronics.stackexchange.com |
12,655 | [
"https://math.stackexchange.com/questions/12655",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/3595/"
] | Just a quick question about the geometry of Hilbert spaces from an intuitive standpoint. Maybe just assuming we're working with $L^2$ would simplify the situation. Basically, in something like $\mathbb{R}^2$ we have the situation that $\cos(\theta)=\frac{\langle a,b\rangle}{\vert a\vert\cdot\vert b\vert}$, and the ide... | I think in infinite-dimensional spaces one should interpret the angle as a measure of how correlated two functions are. The intuition manifests itself most clearly when the functions are random variables of mean zero; then their inner product is precisely their covariance, which is zero when they are independent (that... | One motivation for the $L^2$ inner product is as follows: Imagine sampling your functions f and g at N equally-spaced points, and putting those values into vectors $\vec{f}$ and $\vec{g}$.
<img src="https://i.stack.imgur.com/Cfal5.png" alt="sample functions">
Then (modulo certain technical assumptions) in the limit a... | https://math.stackexchange.com |
30,176 | [
"https://security.stackexchange.com/questions/30176",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/18331/"
] | While getting a coffee today, a man walked up to me and offered me a kindle. he said he no longer wanted it and that he was looking to give it away. An avid reader, I accepted. It has no accounts on it, for when I start it up it prompts me to make a new account. Obviously, I don't want anyone stealing my credit card/ot... | Sounds extremely strange to me and I believe that you may have received some Stolen Goods.
But none the less this is how you can delete all information.
<ol>
<li><strong>Ensure your kindle is plugged into a power socket</strong></li>
<li><strong>Access The Kindle's Settings Menu</strong></li>
<li><strong>Select Resto... | It is <em>possible</em> that the previous owner was one of these ultra-rich people for whom money no longer has any meaning, and he honestly believed that giving the Kindle away to the nearest stranger would be the easiest and most environmental-friendly way of getting rid of it.
It is <em>also possible</em> that the ... | https://security.stackexchange.com |
18,821 | [
"https://stats.stackexchange.com/questions/18821",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/7571/"
] | When we consider Queueing theory scenarios where individuals arrive to a serving node and queue up, usually a Poisson process is used to model the arrival times. These scenarios come up in network routing problems. I'd appreciate an intuitive explanation as to why a Poisson process is best suited to model the arrivals.... | The Poisson process involves a "memoryless" waiting time until the arrival of the next customer. Suppose the average time from one customer to the next is $\theta$. A memoryless continuous probability distribution until the next arrival is one in which the probability of waiting an additional minute, or second, or ho... | Pretty much any intro to queuing theory or stochastic processes book will cover this, e.g., Ross, Stochastic Processes, or the Kleinrock, Queuing Theory.
For an outline of a proof that memoryless arrivals lead to an exponential dist'n:
Let G(x) = P(X > x) = 1 - F(x). Now, if the distribution is memoryless,
G(s+t)... | https://stats.stackexchange.com |
99,606 | [
"https://mathoverflow.net/questions/99606",
"https://mathoverflow.net",
"https://mathoverflow.net/users/13566/"
] | While trying to prove one property of commutative rings with units I can't prove one fact without assuming existence of infinitely many different prime ideals or elements. I tried to test if it was the neccesary assumptions, but I failed, since I don't know any "toy"-examples of such rings.
I know only one example of ... | For the commutative case. Take the set of all rational numbers whose denominators are coprime with a fixed integer $n$. Then the only prime ideals are generated by the prime divisors of $n$.
More generally, take any PID and take its ring of fractions wrt all the elements coprime with some fixed element; you get a desi... | For a noncommutative example you could take the first Weyl algebra $A_1(k)$ with generated over a field $k$ by elements $x$ and $y$ subject to the relation $xy-yx-1$. This is a Noetherian domain which is simple, that is the only two-sided ideals are 0 and the ring itself.
| https://mathoverflow.net |
78,715 | [
"https://physics.stackexchange.com/questions/78715",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/30198/"
] | If our sense of contact temperature is influenced by the thermal conductivity of the material:
<em>Can any solid material with a low heat capacity exist that feels closer to human body temperature than another solid material with a higher heat capacity; where both materials were previously kept in either a mundane ov... | <blockquote>
Can any solid material with a low heat capacity exist that feels closer to human body temperature than another solid material with a higher heat capacity; where both materials were previously kept in either a mundane oven or freezer for a sustained period?
</blockquote>
Let me rephrase to:
<blockquote>... | Yes. Objects from the freezer that feel unusually cold are good at removing heat from your body (and conversely, they will feel hot if they are put in an oven). When you touch a cold object, the part right near your skin (the "surface" layers) warms up and your skin cools down. It's the cooling of skin that you feel.
... | https://physics.stackexchange.com |
54,634 | [
"https://mathoverflow.net/questions/54634",
"https://mathoverflow.net",
"https://mathoverflow.net/users/6761/"
] | There are some nice families of groups as $S_n, A_n$, $GL(n,q)$, $SL(n,q)$, and they are useful; we know their elements, and we can get small groups as subgroups of these groups. Is it possible to get every $p$ group as a <strong>Sylow-p subgroup</strong> of some group in such families of groups? ( For example, the n... | The question is somewhat loosely stated, leading to various answers and comments which are at cross-purposes. Some specific families of finite groups are mentioned, but the list seems to be left open (?) Among these families, the symmetric and alternating groups have no built-in prime $p$ to favor. Moreover, Bu... | No. If the Sylow 2-subgroup of a group is cyclic then the group has a homomorphism onto
its Sylow 2-subgroup. (I don't have a reference at hand, look up $p$-nilpotent groups.
Or just prove that if the Sylow 2-subgroup is cyclic, there is a homomorphism on $\mathbb{Z}_2$ and use induction.) So, a few small cases aside, ... | https://mathoverflow.net |
524,797 | [
"https://stats.stackexchange.com/questions/524797",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/284878/"
] | I have just started learning on the Cox proportional hazards model. I understand that the hazard function is the multiplicative of the baseline hazard rate <span class="math-container">$h_0(t)$</span> and the hazard rates dependence on the covariates <span class="math-container">$\exp(\beta x)$</span> where <span class... | Rewrite your last expression in terms of both the baseline hazard <span class="math-container">$h_0(t)$</span> and the covariate-associated hazard ratios:
<span class="math-container">$$\frac{h_0(t_j)\exp(\beta x_j)}{\sum_k h_0(t_j)\exp(\beta x_k)}= \frac{\exp(\beta x_j)}{\sum_k \exp(\beta x_k)}$$</span>
where <span cl... | The <span class="math-container">$h()$</span> is not a probability, it is a hazard, although they are monotonically related. The Cox model is not a full likelihood procedure, it maximizes a <em>partial</em> likelihood. Even though we don't directly estimate the hazard function as a nuisance parameter (which would be a ... | https://stats.stackexchange.com |
112,466 | [
"https://physics.stackexchange.com/questions/112466",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/41158/"
] | I pierced a hole in a cone shaped cardboard's tip and attached it to my phone speaker. Surprisingly the sound produced when attached is three times louder than the sound when it is removed. I do know that it is something relevant to trumpet loud speaker.What makes it to produce louder sounds?
<img src="https://i.stac... | What you did actually is the so-called horn loudspeaker. And what horns do is to narrow the propagation of sound produced by the loudspeaker. Conventional loudspeaker propagates a lot of sound up, down, left, right, etc. in relation to the axis of the cone. Horns concentrate the sound along the axis, which is therefore... | One effect is, as others have already pointed out, that the cone concentrates the sound power in a narrow direction, thereby making it louder in that direction.
However, that's only part of the answer. Another important part is impedance matching. Whatever little thingy that is vibrating in the phone to make sound i... | https://physics.stackexchange.com |
257,631 | [
"https://electronics.stackexchange.com/questions/257631",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/35875/"
] | AD version is 16.0.6.
I have a simple 2-layer PCB. I'm trying to go to the second (bottom) layer, but everything I tried - did not work: "L", "+", "-", "*", etc. Just nothing happens.
Even <strong>Place -> Via</strong> produces nothing.
For "L" I can hear the Windows... | If you are using an external mouse you can add a via during routing by changing layers. You route, you press CTRL+SHIFT and you use scroll in your mouse to change layers. The VIA will be added automatically.
| The <code>+</code> and <code>-</code> keys along the top of the keyboard (to the right of the <code>0</code> key) will not work to change layers. Altium requires that you use the <code>+</code> and <code>-</code> keys on the number keypad. If you don't have a number keypad you can do what I do and connect a full USB ke... | https://electronics.stackexchange.com |
1,610 | [
"https://mathoverflow.net/questions/1610",
"https://mathoverflow.net",
"https://mathoverflow.net/users/296/"
] | It is known that the binomial coefficient $2n \choose n$ is equal to number of shortest lattice paths from $(0,0)$ to $(n,n)$. The Catalan number $\frac{1}{n+1} {2n\choose n}$is equal to the number of shortest lattice paths that never go above the diagonal. Here, the diagonal may be viewed as a path from $(0,0)$ to $(n... | The answer is (2n)! (2n+1)! / (n)!^2 (n+1)!^2 .
You can get this by the Gessel-Viennot method suggested above. One difficulty is that GV wants to count paths which don't touch at all, even at vertices, while you just want to count paths that don't cross. To solve this, take your lower path and slide it south-east. You... | You should also look up the (Lindström-) Gessel-Viennot theorem for non-intersecting paths, which counts, surprise, sets of non-intersecting lattice paths, and expresses them as a determinant.
| https://mathoverflow.net |
2,852,518 | [
"https://math.stackexchange.com/questions/2852518",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/545219/"
] | <blockquote>
The set of all values of '$a$' for which the function,
$f(x)=(a^2-3a+2)(\cos^2{x/4} - \sin^2{x/4}) + (a-1)x + sin1$ does not posses critical points is:
</blockquote>
I first differented it to find $f'(x)$, then I tried to find out the condition where it becomes zero so that the answer will be $\mathr... | As Daniel Fischer said, you can apply your result for $n=2$ and multiply the square roots of $(z - z_{2k-1})(z - z_{2k})$, $k = 1, \ldots, \frac n2$.
Alternatively, you can show that if $z_1, \ldots, z_n$ lie in the same
component of $\Bbb C - U$ then there is a holomorphic function $g$
in $U$ such that
$$ \tag{*}
g... | Assume that $z_{2k-1}$ lies in the same connected component of $\Bbb C\setminus U$ as $z_{2k}$. Let $w_k(t)$ be a path that connects $w_k(0)=z_{2k-1}$ with $w_k(1)=z_{2k}$. Then the homotopy
$$
h(t,z)=\prod_{k=0}^{n/2}(z-z_{2k-1})(z-w_k(t))
$$
has at $t=0$ a square root
$$
g(0,z)=\prod_{k=0}^{n/2}(z-z_{2k-1})
$$
that h... | https://math.stackexchange.com |
57,902 | [
"https://electronics.stackexchange.com/questions/57902",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/9409/"
] | I've heard people pronouncing the following 'words' in different ways and I would like to know the correct way of pronouncing them.
<ul>
<li>SPI (spy vs s.p.i)</li>
<li>I2C (I.2.C vs I.squared.c)</li>
<li>LED (lead vs L.E.D)</li>
</ul>
I use s.p.i, i.2.c and l.e.d because these are all abbreviations and not really 'w... | I think pronunciation is related to region, laziness and the presence of phonetic pronunciation.
<ul>
<li>Short acronyms are regional - Several answers here indicate this by the variation in SPI pronunciation.</li>
<li>Longer acronyms (4 letters or more) are generally pronounced phonetically due to laziness if they h... | <pre><code>SPI = "Spy" as in "the Spy Bus"
I2C = "eye squared sea" as in IIC = I^2 * C = I2C = Inter-Integrated Circuit Bus
LED = "El Ee Dee" (but Dave Jones does say it like the past tense of "lead" routinely)
</code></pre>
There is, of course, no definitive right answer to this question as you'll hear them spoken ... | https://electronics.stackexchange.com |
124,354 | [
"https://cs.stackexchange.com/questions/124354",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/119697/"
] | I want to create a regular expression for the language:
<span class="math-container">$L=\{w \in \{0,1\}\mid w \text{ does not contain 00 as a substring}\}.$</span>
I've tried various things, but I can't seem to get the correct regular expression.
| First, let's start by enumerating the building blocks of length 2.
<pre><code>S = { 01, 10, 11, 00 }
</code></pre>
We can immediately remove <code>00</code>
<pre><code>S = { 01, 10, 11 }
</code></pre>
Next, notice <code>10 + 01</code> will create a sequence of <code>00</code>. So, let's remove <code>01</code> (10 c... | It should be something like this:
<blockquote>
<span class="math-container">$0?(10?)^*$</span>
</blockquote>
Accepts the empty string.
<blockquote>
<span class="math-container">$0(10?)^*|(1^+0?)^+$</span>
</blockquote>
Does not accept the empty string.
| https://cs.stackexchange.com |
160,249 | [
"https://electronics.stackexchange.com/questions/160249",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/7768/"
] | I would like to understand how the computation process causes the processor to get hot. I understand that the heat is generated by the transistors.
<ol>
<li>How does the transistors generate the heat exactly?</li>
<li>Is the correlation between the number of chips and the heat generated linear?</li>
<li>Do CPU manufac... | A transistor (FET, in modern ICs) never switches instantly from full OFF to full ON. There is a period while it's turning on or off where the FET acts like a resistor (even when fully ON it still has a resistance).
As you know, passing a current through a resistor generates heat (\$P=I^2R\$ or \$P=\frac{V^2}{R}\$).
... | All current flow in anything that isn't a superconductor generates heat. In chips, it's mostly flowing in aluminium "metal" layers (why not copper? Nasty chemical interaction with other parts of the silicon, it turns out).
What causes current to flow? Every time a transistor changes state, this can be modeled as a cap... | https://electronics.stackexchange.com |
706,972 | [
"https://physics.stackexchange.com/questions/706972",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/333557/"
] | I've only scratched the surface of electromagnetism but I figured I might as well ask a question.
When moving a permanent magnet relative to an electric conductor, a current will form. Say you just move a magnet through a coil of wire for this question. I've learned that current will flow when there is a potential diff... | <blockquote>
I don't understand how the two could really be one and the same. E.g.
we can exert forces <span class="math-container">$F$</span> and <span class="math-container">$-F$</span> on a body and it's acceleration will
not change.
</blockquote>
<span class="math-container">$\vec{F}$</span> in the <span class="mat... | In physics equations (as in mathematics), symbol "=" (equals) means equality in value, not identity of concepts. So in the equation
<span class="math-container">$$
\mathbf F = m\mathbf a
$$</span>
the two sides are not "one and the same". The concept of force is a different concept from the concept ... | https://physics.stackexchange.com |
9,312 | [
"https://stats.stackexchange.com/questions/9312",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/-1/"
] | SPSS returns lower and upper bounds for Reliability. While calculating the Standard Error of Measurement, should we use the Lower and Upper bounds or continue using the Reliability estimate.
I am using the formula :
$$\text{SEM}\% =\left(\text{SD}\times\sqrt{1-R_1} \times 1/\text{mean}\right) × 100$$
where SD ... | The KL-divergence is typically used in information-theoretic settings, or even Bayesian settings, to measure the information change between distributions before and after applying some inference, for example. It's not a distance in the typical (metric) sense, because of lack of symmetry and triangle inequality, and so ... | Another way of stating the same thing as the previous answer in more layman terms:
KL Divergence - Actually provides a measure of how big of a difference are two distributions from each other. As mentioned by the previous answer, this measure isnt an appropriate distance metric since its not symmetrical. I.e. distance... | https://stats.stackexchange.com |
275,313 | [
"https://dba.stackexchange.com/questions/275313",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/71361/"
] | In MySQL, Oracle and PostgreSQL an expresion like <code>1 = 1</code> can be used in where like:
<code>where 1 = 1</code> as well as
<code>where (1 = 1) is not null</code>
In MSSQL, it seem that:
<ul>
<li>a) when an expression is a predicate, it can not be further compared as an expression</li>
<li>b) where requires pre... | It boils down to SQL Server not having a boolean data type. If it did, we could say just:
<pre><code>WHERE myBoolCol
</code></pre>
And since a predicate returns true or false, then such a predicate could be used as an expression. (I'm ignoring the nuances of unknown and null here.) I.e.:
If you can say
<pre><code>WHER... | You can use a case statement (or IIF) to use comparisons in the manner you describe.
<pre><code>SELECT IIF(1=1, 1, 0) WHERE CASE WHEN (1=1) THEN 1 END IS NULL
</code></pre>
Note: A side effect is how NULLs are handled, in that if the expression does not evaluate to TRUE, it will be FALSE, including for NULLs.
| https://dba.stackexchange.com |
37,888 | [
"https://security.stackexchange.com/questions/37888",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/27537/"
] | I'm not sure if the question is eligable for this board as I ask for concrete service providers which can be kind of advertisement, but there is also technical issue involved, so I give it a try.
My concrete scenario is as follows:
I want to use S/MIME for EMail encryption. My decision was made in terms of S/MIME as ... | The theory is that as long as you keep your old keys, your email software will still be able to decrypt your received emails. That the certificate is expired means that <em>other people</em> won't accept to use your old public key to send you new encrypted emails, but reading your mailbox on your side does not entail u... | There are certain rules Certificate Authorities need to follow in order to issue trusted certificates (one of these is that the certificate can not be valid for longer than 3 years)
In the case of archiving you can keep a copy of old certificates (it will show as expired if you try and use it for sending emails after... | https://security.stackexchange.com |
3,007 | [
"https://mathoverflow.net/questions/3007",
"https://mathoverflow.net",
"https://mathoverflow.net/users/493/"
] | If I'm given a division algebra D with Z(D)=F, then how can I view D<sup>x</sup> as an algebraic group defined over F? I'd like to see first how D<sup>x</sup> can be given the structure of a variety defined over F, and then to see how the group law on D<sup>x</sup> is defined over F.
| Choose an F-basis of D. The multiplication is described by certain quadratic functions, with respect to this basis; D* is given by the nonvanishing of a polynomial function (the norm).
So the multiplication can be understood as defining an algebraic group structure on the complement of a hypersurface in an affine spac... | Suppose D splits over a finite extension K/F, i.e., the tensor product of D with K over F is isomorphic to M<sub>n</sub>(K). Then D<sup>x</sup> is the group of F-points of an algebraic group over F that exists as a direct factor (along with all other F-division algebras that split over K, and GL<sub>n,F</sub>) in the ... | https://mathoverflow.net |
379 | [
"https://cardano.stackexchange.com/questions/379",
"https://cardano.stackexchange.com",
"https://cardano.stackexchange.com/users/72/"
] | Two scenarios:
Stakepool owner #1 pledges 10k, stakes 10k and total stake from others is 100k = 110k staked total
Stakepool owner #2 pledges 100k, stakes 10k and total stake from others is 100k = 110k staked total
Do they both have the same odds to generate a block, as long as the pledge amount is maintained <strong>-o... | A high pledge does not increase the chance for the stakepool to get a block, but it does give a higher reward for the stakepool with a larger pledge than the other one. A estimation of assigned blocks per epoch for a pool can be calculated like this:
<em>[stakepool total stake]/[total stake] x 21600</em>
The pledge can... | In your scenario, each pool will have the same chances of getting block and should average to the same amount over time. The pledge amount affects the rewards; however, it is currently only a small amount. The plan from IOG is the update this later in the year to have more of an effect.
Pledge can only be applied from ... | https://cardano.stackexchange.com |
33,006 | [
"https://astronomy.stackexchange.com/questions/33006",
"https://astronomy.stackexchange.com",
"https://astronomy.stackexchange.com/users/-1/"
] | Whenever I read about black holes, it is normally involving how they devour anything that comes too close... regardless of how big anything is.
But what if it were a really small black hole vs something really large? How about something like a large star or neutron star... could a black hole be small enough to get dev... | Black holes don't "devour". They can't "eat" things. But things can "fall into" a black hole. It really is just gravity, but really really intense gravity.
A really small black hole would have a mass of about 3 times the mass of the sun. All neutron stars are smaller than that (or they would turn into black holes).... | That would be a bigger black hole. Black holes are indestructible but a big one can consume a smaller one.
The collision between anything and a black hole results in a black hole plus some optional debris from whatever the other thing is, so the result of a collision between two black holes is simply a bigger black hol... | https://astronomy.stackexchange.com |
465,448 | [
"https://physics.stackexchange.com/questions/465448",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/208833/"
] | Neutron has quark composition udd with spin <span class="math-container">$\frac 12$</span>. <span class="math-container">$\Delta^0$</span> baryon has quark composition udd with spin <span class="math-container">$3 \over 2$</span>.
On Wikipedia it says that <span class="math-container">$\Delta$</span> baryons have mas... | First note that it's the <span class="math-container">$\Delta^+$</span> particle that is <span class="math-container">$uud$</span>. The <span class="math-container">$\Delta^0$</span> is <span class="math-container">$udd$</span> like the neutron.
The <span class="math-container">$\Delta^+$</span> particle is an excited... | In QCD, much as in E&M, there is a chromo-magnetic dipole-dipole contact interaction <span class="math-container">$\propto S\cdot {S}'$</span>, which will obviously differ between spin 1/2 and 3/2 baryons. Bag-modelers have used it to estimate the mass difference between nucleons and deltas with tolerable accuracy... | https://physics.stackexchange.com |
3,863 | [
"https://physics.stackexchange.com/questions/3863",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/977/"
] | I feel this is somehow a stupid question, but I don't know the true answer. What happens to an astronaut who's floating in a spaceship in space when it begins to move? Will the astronaut not move until he smashes onto a wall in the spaceship? Or will he move with the spaceship due to gravity? Or does it depend on the s... | He will start to move with the spaceship due to the air pressure inside (the ship pushes the air, and the air pushes him) and the gravity of the ship pulling him, but unless it is accelerating <em>really</em> slowly he will smash into something, it is not so different from beeing in an accelerating car, infact its exac... | The gravitational force of the spaceship on the astronaut is tiny, effectively zero. It would take a really huge object (e.g. a small moon) to have any appreciable effect on an astronaut or anything else.
If an astronaut is in a spaceship and the spaceship accelerates, for all practical purposes, the astronaut will no... | https://physics.stackexchange.com |
510,167 | [
"https://physics.stackexchange.com/questions/510167",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/107138/"
] | On page 65 of Schutz's A first course in General Relativity, he introduces the notation <span class="math-container">$\phi_{,\alpha}=\partial\phi/\partial x^\alpha$</span>. He then says that <span class="math-container">$x^\alpha_{\ \ ,\beta}=\delta^\alpha _{\ \ \ \beta}$</span>. I understand this, since it's just anot... | First, please update your question and keep your notation clear and consistent.
Second, <span class="math-container">$\{ e_i\}$</span> (in your case) represents the set of "coordinate (holonomic)" basis (i.e., <span class="math-container">$\{ e_i\}=\{ \partial_i := \partial/\partial x^i \}$</span>) and not any basis. ... | <blockquote>
I would get it, if it were <span class="math-container">$\text{d}x^\alpha_{\ \ \ \beta}=\delta^\alpha _{\ \ \ \beta}$</span> ...
</blockquote>
Note that the object <span class="math-container">$dx^\alpha$</span> is a co-vector, so it cannot have two indices, only one. From the normal rules of differenti... | https://physics.stackexchange.com |
367,350 | [
"https://math.stackexchange.com/questions/367350",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/25711/"
] | Suppose I have a highly composite positive integer $N$ with at least $10^{15}$ divisors for which I know the prime factorization.
Given $M$ with $\gcd(M,N)=1$ is there an efficient way to find a divisor $d|N$ with $d>1$ and $d\equiv 1 \pmod{M}$?
(If necessary assume one exists, or if possible determine whether one... | Coppersmith et al. give an algorithm based on LLL lattice reduction in a paper <em>Divisors in Residue Classes, Constructively</em> (2004) that solves this problem if $M$ is not too small relative to N, specifically $M>N^{1/4}$.
For the given example I was able to find a divisor a different way. Since here $M=1999\... | I don't know if this is the sort of thing you're looking for, but here is an algorithm that will take $O(M\phi(M))$ time, and require $O(M)$ storage. We have $N=p_1^{a_1} p_2^{a_2}\cdots p_k^{a_k}$, but instead we take each prime modulo $M$, to give us $r_1^{b_1}r_2^{b_2}\cdots r_s^{b_s}$, where the $r_i$'s are residu... | https://math.stackexchange.com |
2,947,956 | [
"https://math.stackexchange.com/questions/2947956",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/6792/"
] | Let <span class="math-container">$p>3$</span> be a prime, <span class="math-container">$0<k<p$</span>. Then is it possible that <span class="math-container">$pk+1\mid(p-k)^2$</span>?
For <span class="math-container">$k=1$</span>, since <span class="math-container">$(p-1)^2\equiv(-2)^2\equiv4\pmod{p+1}$</span>... | <strong>Claim:</strong> If <span class="math-container">$a,b$</span> are positive integers and <span class="math-container">$q(a,b) := \frac{(a-b)^2}{ab+1}$</span> is an integer, it is a square number. This may be proved by Vieta jumping as follows:
Let <span class="math-container">$k \geqslant 1$</span> be an intege... | Suppose that <span class="math-container">$p$</span> and <span class="math-container">$k$</span> are integers such that <span class="math-container">$p>k>0$</span> and <span class="math-container">$$n=\frac{(p-k)^2}{pk+1}$$</span>
for some integer <span class="math-container">$n>0$</span>. Note that <span cla... | https://math.stackexchange.com |
388,552 | [
"https://physics.stackexchange.com/questions/388552",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/94439/"
] | I have devised a method to isothermally compress a gas without the use of a heat reservoir.
Consider a container of gas. To compress the gas normally, one would simply move one of the walls of the container inwards, which will do work on the gas when the gas particles collide with the moving wall, increasing its tempe... | As pointed out in the comments, this is just Maxwell's demon in disguise. Why?
Because this is a reversed isothermal free expansion.
Suppose we have an ideal gas trapped in an adiabatic container of volume <span class="math-container">$V$</span>, but all of the gas is compressed by a piston in half of the volume (<sp... | Assuming there is only one particle in the container and you can wisely move the piston without colliding with the particle, you then claim that there is no work done.
But don't miss the other side. Macroscopically, with the space reduced, the frequency that the particle collides with the piston increases. There is m... | https://physics.stackexchange.com |
700,887 | [
"https://physics.stackexchange.com/questions/700887",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/331493/"
] | So as far as I understand time dilation it means that time slows down as an object approaches lightspeed. This is an issue even with for example satellites around earth compared to people on earth (GPS).
Now I am wondering compared to what reference point is this speed measured? Is it absolute speed in comparison to th... | <blockquote>
Now I am wondering compared to what reference point is this speed measured?
</blockquote>
The reference “point” is a system of clocks, all of which are at rest in the chosen reference frame and synchronized. The time on the moving clock is compared to the time on the co-located stationary clock at each mom... | You will get confused if you think that in Special Relativity time slows down in some absolute sense- it doesn't. In SR all motion is relative, and time dilation is relative. So, when you talk about an object moving at close to the speed of light, you have to answer the question 'relative to what?'. As you sit in your ... | https://physics.stackexchange.com |
123,836 | [
"https://electronics.stackexchange.com/questions/123836",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/10884/"
] | In my company we had few earthing related issues. When an consultant was brought in and apart from solving the issue, a suggestion was made to ground the neutral of the UPS and diesel generators that we have.
The situation prevented me to seek clarification from the consultant, but I could not help myself pondering wh... | I am not sure about UPSs, but a diesel generator is built to generate a voltage between its two (four) output terminals. Whether these terminals voltage <em>with respect to earth</em> is high or low is not defined, and can't be. The generator per se is not connected to earth, so its neutral terminal might be some volts... | For the UPS application > If the Neutral - Earth is to be linked, use of a Delta Star (3 Phase to 3 Phase + Neutral) transformer is recommended at the output of the UPS.
It is not approved (in the UK) to bond Neutral to Earth more than once within an installation without galvanic isolation in order to prevent earth c... | https://electronics.stackexchange.com |
124,474 | [
"https://mathoverflow.net/questions/124474",
"https://mathoverflow.net",
"https://mathoverflow.net/users/26659/"
] | Let $\rho : G \to GL(V)$ be an irreducible representation of a finite group. Schur's lemma says if $\pi:GL(V) \to GL(V)$ intertwines with $\rho$, that is, $\pi \rho(g) = \rho(g) \pi$ for every $g\in G$, then $\pi = \lambda I$ for some $\lambda \in \mathbb{C}$.
Is there a similar lemma for $\rho = m_1 \rho_1 \oplus \l... | This is an easy exercise. If $\rho _i$ are "different" (i.e. inequivalent) then by Schur's lemma, $Hom _G(\rho _i,\rho _i)={\mathbb C}I$ and $Hom _G(\rho _i, \rho _j)=0$. Hence
the commutant of $G$ in $End(\rho)$ is easily seen to be the product
$$M_{m_1}({\mathbb C})\times \cdots \times M_{m_k}({\mathbb C}),$$ where... | Schur's lemma has a different generalization when the coefficient field $F$ is not algebraically closed. Then you get $M_{m_1}(D_1)\times\cdots\times M_{m_k}(D_k)$ where $D_i:={\rm Hom}_{FG}(\rho_i,\rho_i)$ is a
division algebra over $F$ by Schur's lemma. If $F$ is infinite, noncommutative $D_i$ can arise. For example,... | https://mathoverflow.net |
12,127 | [
"https://dba.stackexchange.com/questions/12127",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/5412/"
] | I am writting a dynamic sql to drop and create view in different database.
So I wrote:
<pre><code>set @CreateViewStatement =
'
USE ['+ @DB +'];
CREATE VIEW [dbo].[MyTable]
AS
SELECT ........something
exec (@CreateViewStatement)
</code><... | You can use nested <code>EXEC</code> calls. The database context changed by the <code>USE</code> persists to the child batch.
<pre><code>DECLARE @DB SYSNAME
SET @DB = 'tempdb'
DECLARE @CreateViewStatement NVARCHAR(MAX)
SET @CreateViewStatement = '
USE '+ QUOTENAME(@DB) +';
EXEC(''
CREATE VI... | One way I have handled when run into this case is placing GO after use statement.
<pre><code>set @CreateViewStatement =
'
USE ['+ @DB +']; GO
CREATE VIEW [dbo].[MyTable]
AS
SELECT ........something'
exec (@CreateViewStatement)
</code></pre>
| https://dba.stackexchange.com |
70,611 | [
"https://dsp.stackexchange.com/questions/70611",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/36797/"
] | Assume if we have <span class="math-container">$N$</span> OFDM subcarriers represented by results of the inverse FFT of <span class="math-container">$N$</span> data symbols <span class="math-container">$\mathbf x$</span>. As I know, the subcarriers of OFDM should be orthogonal. It means that
<span class="math-containe... | The other answer points out that the DFT is a matrix multiply. The matrix <span class="math-container">$\mathbf{D}$</span> is like this:
<span class="math-container">$$ \mathbf{D}=
\begin{bmatrix}
1 & 1 & 1 & ... & 1 \\
1 & \omega & \omega^2 & ... & \omega^{N-1} \\
1 & \omega^2 &... | Orthogonality is defined as "the inner product of two vectors equals zero".
Now, in OFDM, the transmit vector for a single subcarrier is exactly one row vector <span class="math-container">$\mathbf D_k$</span> of the DFT Matrix <span class="math-container">$\mathbf D$</span>, multiplied by the complex value o... | https://dsp.stackexchange.com |
18,280 | [
"https://physics.stackexchange.com/questions/18280",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/6090/"
] | Why do quantum physical properties come in pairs, governed by the
uncertainty principle (that is, position and momentum?)
Why not in groups of three, four, etc.?
| The duality is a duality because of the notion of canonical conjugation in classical mechanics.
The reason people say that they come in pairs has nothing to do with quantum mechanics, but with the structure of classical mechanics. In classical mechanics, to give you the initial conditions for a system, you need to giv... | Good question! For the properties related by the uncertainty principle, there are two reasons why they come in pairs:
<ol>
<li>Intuitively, the uncertainty principle relates the variance of a function to the variance of its Fourier transform. And, up to a couple of numerical factors, the Fourier transform of a Fourier... | https://physics.stackexchange.com |
69,852 | [
"https://datascience.stackexchange.com/questions/69852",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/14667/"
] | Edit: Removing <code>TransformedTargetRegressor</code> and adding more info as requested.
Edit2: There were 18K rows where the relation did not hold. I'm sorry :(. After removing those rows and upon @Ben Reiniger's advice, I used LinearRegression and the metrics looked more saner. The new metrics are pasted below.
O... | (To summarize the comment thread into an answer)
Your original scores:
<pre><code>Mean Absolute Error: 37216342513.01034
Root Mean Squared Error: 871869805169.7842
</code></pre>
are based on the original-scale target variable and are between <span class="math-container">$10^{10}$</span> and <span class="math-contain... | It seems you are using a the standard scaler twice, once in your pipeline and once more in the <code>TransformedTargetRegressor</code>. Next to that, you are only fitting the scaler, never actually scaling the inputs (i.e. transforming the input).
| https://datascience.stackexchange.com |
31,833 | [
"https://mechanics.stackexchange.com/questions/31833",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/10147/"
] | 1970 Chevrolet C20 Custom Camper Pickup<br>
SBC 350, Quadrajet carburetor<br>
I've been having some issues I believe are float related. Wanted to see if my thinking is correct.
<strong>Issue #1</strong> - takes a bit of cranking to get it started after it's been sitting. I do have check valve in the fuel filter. T... | If the float was sticking you would see black smoke when it stumbles and would clear up when its pinned.You're right with the acc. pump, would be a consistent flat-spot, but check for a steady stream anyway.All little things add up, so if points, plugs and ignition leads are not 100%, start there.
| <strong>Issue #1</strong>
Aren't you supposed to prime the carb by pumping the gas a couple of times before cranking? I think the electrics should be on when doing this. That could at least help.
<strong>Issues #2 and #3</strong>
They're not called Quadra<strong>bogs</strong> for nothing. Bogging can be caused by a ... | https://mechanics.stackexchange.com |
84,627 | [
"https://electronics.stackexchange.com/questions/84627",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/28144/"
] | When using AD9850, I can see a very clean and smooth sine wave but this is not the case by AD9833. In AD9833 multiple steps are visible in the output that gets worse in higher frequencies( > 2MHz) .The output looks as if the DAC never goes under smoothing process. I want to know if this is an inherent nature of this d... | Of course it's possible. There are many companies that provide these services. The real question is whether or not you could do this at home.
You might get away without needing a SEM (Scanning Electron Microscope), that design might be done in ~3u geometry which would imagable using visible light.
You'll need a wet ... | Your last paragraph is basically correct: you can image the chip and then either copy it directly or reverse engineer it to produce a more modern version. The first step might be doable by a university lab with the correct equipment, but the reproduction is not going to be a cheap process (hundreds of thousands of $).
... | https://electronics.stackexchange.com |
16,551 | [
"https://robotics.stackexchange.com/questions/16551",
"https://robotics.stackexchange.com",
"https://robotics.stackexchange.com/users/21379/"
] | I'm trying to build a robot/rover based on Raspberry Pi 3
At the moment I'm straggling with a basic driving in a straight line.
I'm in a process of tuning my PID code andI'm not sure what sampling rate should I choose.
These are the specs of the motors:
<blockquote>
Voltage: DC 6V<br>
Speed: 210 rpm<br>
Encode... | You can only say that the distorted image coordinates are in the range (0-240, 0-180), since that's the image you are starting with. Typically you assume the dimensions of the undistorted image as being the same as the distorted image, and for every pixel in the undistorted image work out the corresponding coordinate ... | Hmm. Have you check the indices used in your code? Simple bugs like swapping i and j happen all the time for rows/columns.
Perhaps its a Hardware issue involving Little Endian vs BIG ENDIAN. in 8 bit 64=64 but 16 BIT 64 is swapped to highorder thus theres rotation in bit order results that the single bit 64 is repres... | https://robotics.stackexchange.com |
576,217 | [
"https://electronics.stackexchange.com/questions/576217",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/291361/"
] | Does I2C have any data loss prevention mechanism? If so, how does I2C recover?
| I2C has several mechanisms to prevent data loss:
<ul>
<li>multi-master collision detection and arbitration</li>
<li>ACK/NACK after each byte</li>
<li>clock stretching (slave slows down the master)</li>
</ul>
SMBus adds a couple of enhancements:
<ul>
<li>Packet Error Check (PEC), a CRC sent after each transfer</li>
<li>... | It doesn't. If you want error correction, you have to implement your own error-correcting code.
| https://electronics.stackexchange.com |
177,751 | [
"https://electronics.stackexchange.com/questions/177751",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/2006/"
] | I've seen reverse-mount LEDs which are meant to have the light shine through a hole in the PCB, instead of straight off. Is it possible to just add a drill hole for normal LEDs and just place them upside down before soldering?
Is it possible the lense/substrate will melt if reflowed on a hotplate? If it matters any, ... | Depending on the package, this can be done.
For my work, we evaluated several types of LEDs, and being mountable "through-PCB" was mandatory.
The right LED shown in the picture can be mounted normal and through-PCB, the second is exclusively for through-PCB, and the LED in the middle is a standard and very common 060... | You can make through hole and is ok
Normally they are a little bigger than 0805
I don't see issues
| https://electronics.stackexchange.com |
110,896 | [
"https://dba.stackexchange.com/questions/110896",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/72714/"
] | I prepared a script to create a table with 800 columns but SQLPlus and SQL Developer are not reading the whole script as they probably read only 7499/2499 characters max. As an alternative I am thinking to divide the script into an initial create script with 200 columns and then alter table to add remaining columns in ... | The best way to run a very long script is not to load it into the editor, any editor.
Just reference it via @ and run it
So @my_script.sql and execute that.
| I had to try it myself, because I did not believe SQL*Plus can not handle this. Apparently, it can.
Script for generating the create statement:
<pre><code>[oracle@ora71 ~]$ cat generate.sql
set echo off feedback off heading off pages 0
spool create.sql
select text from
(
select 'create table t1 (' as text, 0 ... | https://dba.stackexchange.com |
2,204,079 | [
"https://math.stackexchange.com/questions/2204079",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/395958/"
] | I am starter at Topology.
I have found a definition of $T_0$ as;
"A topological space $X$ is said to be a $T_0$ space if for any $x,y \in X$, $x \neq y$ there exist an open set $U$ such that $x \in U$ but $y \notin U$"
For $X=\{a, b, c\}$ $\mathcal{T}=\{\emptyset, \{b\}, \{c\}, \{a,b\}, \{b,c\}, \{a,b,c\}\}$ is know... | For $a$ and $b$ we take $S = \{b\}$, then $b \in S$ and $a \notin S$.
We cannot do it the other way round (any open set that contains $a$ also contains $b$) but for $T_0$ we only need to be able to do one of them, otherwise the space is called $T_1$.
| Ohh I understand now. So the thing that I tried to find was T1 and we can say it's not T1. Thank you so much for answers
| https://math.stackexchange.com |
76,995 | [
"https://dba.stackexchange.com/questions/76995",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/28954/"
] | Hi guys I have question about how two different Hard disk setups can possibly affect performance of my database.
I have two Options.
<h2>Option 1:</h2>
One Physical Harddisk and then Multiple Virtual hard drives for SQL Server's Database files (.mdf , .ndf),Log files, TempDB, Backups etc
<h2>Option 2:</h2>
One P... | There is no appreciable difference in performance when the underlying hardware is the same, assuming we're talking about a single physical disk.
However, separate logical drives might help you maintain your sanity, and could result in lower physical fragmentation of the SQL-related volumes
| It will be very difficult to guess in advance exactly how big each of your virtual drives should be. If you get it wrong you will run out of space for, say, data files while log and TempDB have plenty of unused space on their logical disks. You will not be able to assign this unused space to data files without creati... | https://dba.stackexchange.com |
67,318 | [
"https://mathoverflow.net/questions/67318",
"https://mathoverflow.net",
"https://mathoverflow.net/users/13363/"
] | I believe this may be a standard algebraic topology problem, so I apologize in advance if this belongs in stackexchange (it's not a homework problem, however, and came about in a research context). I've got a continuous map $f$ from the $n$-simplex to itself, such that the image of every strict sub-simplex is itself. ... | Given such a map $f:\Delta_n\to\Delta_n$, put $f_t(x)=(1-t)x+t f(x)$. This gives a homotopy between $f$ and the identity, and each map $f_t$ also sends every subsimplex to itself. In particular, each $f_t$ preserves $\partial(\Delta_n)$ and so induces a self-map $\overline{f}_t$ of the space $\Delta_n/\partial(\Delta... | Neil Strickland's answer is very nice. Let me add a slightly different answer, which might be useful in a similar situations, when a homotopy can't be given as easily.
Notice that the homotopy between $f$ and the identity implies that the map of $f: (\Delta_n,\partial\Delta_n)\to(\Delta_n,\partial\Delta_n)$ is of deg... | https://mathoverflow.net |
612,233 | [
"https://physics.stackexchange.com/questions/612233",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/274216/"
] | I'm wondering what's the steady state for an oscillator.
Is it a system without driving force so without external force to disturb the system?
If a system oscillates without driving force can we say the system is in the steady state?
| <blockquote>
Is it a system without driving force so without external force to disturb the system?
</blockquote>
<blockquote>
If a system oscillates without driving force can we say the system is in the steady state?
</blockquote>
These two questions aren't phrased properly. Steady state is not a property of the system... | Oscillatory dynamical systems return many times in the neighborhood of some reference configuration. In the particular case of a periodic evolution, we speak of steady oscillations. Notwithstanding the opinion of who voted for closing this question as "opinion-based," this definition is not an opinion at all.... | https://physics.stackexchange.com |
419,902 | [
"https://mathoverflow.net/questions/419902",
"https://mathoverflow.net",
"https://mathoverflow.net/users/146942/"
] | In his book <em>Topological Function Spaces</em> Arhangel'skii says that "it is well known that every nontrivial locally convex linear topological space <span class="math-container">$X$</span> is homeomorphic to a space of the form <span class="math-container">$Y \times \mathbb{R}$</span>, for some space <span cla... | I guess that <em>non-trivial</em> means that the locally convex space <span class="math-container">$X$</span> is not endowed with trivial topology <span class="math-container">$\{\emptyset,X\}$</span>.
This implies that <span class="math-container">$X\neq \overline{\{0\}}$</span> (since this closure does have the trivi... | This fact is a consequence of Hahn-Banach separation theorem (HBST). Such a space admits a continuous linear functional.
Let us be more specific: let <span class="math-container">$V$</span> be a Hausdorff HLCTVS (Hausdorff locally convex topological vector space) over <span class="math-container">$\mathbb{R}$</span>. L... | https://mathoverflow.net |
16,710 | [
"https://electronics.stackexchange.com/questions/16710",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/-1/"
] | I want to achieve 0.05C stability in closed space to fit 24 bit ADC and voltage reference. Is it a good idea to use Peltier and heater together ?
| The Peltier can be used as a <strong>heater</strong> as well, just invert the power connection. But this kind of precision is very hard to obtain, no matter how you heat or cool down. The reason is the <strong>thermal inertia</strong> of your system: switching on the Peltier if the temperature rises won't result in an ... | First, a Peltier device <em>is</em> a heater. It is also a cooler. Which it is at any one time depends on the direction of the current flow.
Yes, a Peltier device would be appropriate if you think the ambient temperature could be both above and below the desired temperature.
Controlling anything to .05C is not triv... | https://electronics.stackexchange.com |
254,221 | [
"https://physics.stackexchange.com/questions/254221",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/116535/"
] | I am currently studying IGCSE Physics, and have the following question: Why aren't upthrust and normal reaction force not the same.
I understand that upthrust only occurs in fluids, and normal reaction forces only occur on a surface, but what is the actual, theoretical difference?
| At the beginning I found this question a bit naive. But now I think it is worth to think a little bit about it.
They definitely share some properties, at least at the microscopic level. Both have the same microscopic origin: the electromagnetic interaction. The upthrust requires gravity to create a pressure gradient o... | To some extent I agree with @diracology : The question does at first seem naive, but on reflection it is insightful. And there are similarities at the microscopic level, in that both are contact forces which originate from the same electromagnetic repulsion between the outer electrons of atoms or molecules which are f... | https://physics.stackexchange.com |
215,935 | [
"https://electronics.stackexchange.com/questions/215935",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/72429/"
] | I am interesting in getting a device, (bare metal micro-controller with sensors), to communicate to an android phone.
The device is not wearable and the power difference between Bluetooth and wifi as a consequence is of no import.
The range only needs to be a maximum of 3m with a low data rate (<2.1 Mbit/s), so bl... | Bluetooth (BT) will be overall more reliable. The android device can connect to more than one Bluetooth device but usually only one WiFi device and this you likely want to be a device providing Internet access such as a WiFi Access Point (AP). The Android device will "randomly" connect to more advantageous WiFi signals... | Wifi allows for multiple connections. A standard wifi device, connected to a wifi router, and likely the Internet through it, can communicate with anything on the network (and with proper routing, the internet). A Bluetooth device is typically just node to node, as in only one device can directly talk to it, without a ... | https://electronics.stackexchange.com |
4,769 | [
"https://mechanics.stackexchange.com/questions/4769",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/2427/"
] | I need to replace a broken section of exhaust. Should I replace the gaskets also? one of the gaskets is directly between the engine and the new part. The other is between the new and an old part of the exhaust.
| You should replace any gaskets that will be disturbed by replacing the pipes. Clean any old gasket material off the surface that the gasket sat on with a putty knife or something similar. You want a nice clean surface for the new gasket to seal against. After everything is reassembled start the engine and place your ha... | gasket surface prep is an art and a science. yes, always replace gaskets when adjacent parts are disturbed. it is important to have a clean, even, sealable mating surface on each part so that the gasket can do it's job. different materials and shapes will require different approaches. i would avoid using a putty kn... | https://mechanics.stackexchange.com |
24,024 | [
"https://security.stackexchange.com/questions/24024",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/11892/"
] | I use AES encryption on a website. At the moment, the key is stored in the source of the PHP script that does the encryption/decryption process thanks to openssl.
I know that it isn't secure, so I want to put parts of the key in different places:
<ul>
<li>first part in PHP source</li>
<li>second part as server environm... | Essentially what you're attempting to do is backdoor each user's account in a way that allows only the user and a single administrative user to access their data. This can be achieved as follows:
<pre><code>us = User salt = Random unique value (not the same salt as used for authentication)
as = Admin salt = Random ... | To put what Polynomial is saying another way, if you are trying to make it so that encryption works for user data so that only the user and administrators can get to it, the critical piece is to not store the ability to get the information on the server. For users, this is done via their password, for administrators, ... | https://security.stackexchange.com |
464,470 | [
"https://physics.stackexchange.com/questions/464470",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/181243/"
] | I've always seen older books talking about relativistic mass all over their special relativity introduction <span class="math-container">$m=\gamma m_0$</span>. But I can't stand it. It makes no sense to define this quantity at all.
To explain myself, mass can't be measured for a moving object, so why even bother bring... | It is now common to assert that mass is invariant, and what changes as an object is accelerated to near the speed of light is not its mass but instead the relationship between that object's mass and its <em>momentum</em>- and this is how the topic is currently taught.
This does not mean, however, that the results of ... | It's a matter of definition. Everybody (I hope.) agrees that E=m\gamma (with c absent).
The argument is over what to do with \gamma. Unfortunately some (even serious) people put the \gamma into the mass, thus calling relativistic mass M=E. This has lead to confusion and arguments over language (although some call it... | https://physics.stackexchange.com |
35,801 | [
"https://physics.stackexchange.com/questions/35801",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/-1/"
] | Here is one task below.
How to solve equation
$$
m\ddot {x} + ax = F(t), x(0) = \dot x (0) = 0
$$
in quadratures by using two methods?
I tried to create a system of equations
$$
\begin{matrix} \dot v = F(t) - w_{0}^{2}x \\ \dot x = v \\ \end{matrix},
$$
but I don't know, what to do next without using some vector $\... | You might not like this answer, but you want to solve for $x\left(t\right)$ in
$$
m \ddot{x} + \omega^2 x = F\left(t\right),
$$
with $\dot{x}\left(0\right) = x\left(0\right) = 0$. A Laplace transform gives you
$$
x\left(t\right) = \mathcal{L}^{-1}\left\{\frac{\mathcal{L}
\left[F\left(t\right)\right] \left(s\right)}{m s... | First solve
$$
m\ddot {x} + ax = \delta(s)
$$
With BC
$$x(-\infty) = 0$$
$$\dot x(-\infty) = 0$$
The solution will be sine wave starting at t=s. (zero before that)
Lets call this solution G(s)
Then integrate this solution to find
$$x(t) = \int_0^t F(s)G(s) ds$$
| https://physics.stackexchange.com |
15,317 | [
"https://softwareengineering.stackexchange.com/questions/15317",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/5605/"
] | What are the risk factors that we need to consider while planning for a software project.
| <ul>
<li>Is your team adequately trained?</li>
<li>Is your team large enough? </li>
<li>Do you have contingency in case
someone leaves the project, and how
would it affect the schedule? </li>
<li>Is your team too large? </li>
<li>Do they have the resources they need?</li>
<li>Might a competitor bring a product to
marke... | I would add to @Graham's list:
<ul>
<li>Are some of the requirements out of your control (eg the laws about calculating sales tax) and might they change?</li>
<li>Are you using a tool for the first time and how confident are you the tool will work for you? (It might be brand new, eg Azure, or just new to your team)</l... | https://softwareengineering.stackexchange.com |
63,243 | [
"https://softwareengineering.stackexchange.com/questions/63243",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/14363/"
] | I'm thinking of things like:
<ul>
<li>designating a developer having say 6 hours out of their normal 7.5 hour day dedicated to the project, the rest for other work/company related activity (meetings, emails, calls etc), maybe a senior dev is less.</li>
<li>building in 20% contingency time to estimates.</li>
</ul>
Wha... | A pet peeve of mine are arbitrary deadlines.
<strong>Project Deadline: the problem</strong>
Project estimation invariably leads to a date which becomes an implicit deadline. Missing that date, regardless of cause, often feels like a failure if it is not outright characterized as such. When you give a date you set ex... | Previous performance is the best predictor assuming you have valid data. It still may not be accurate enough, but the more cumbersome you make gathering data to gain accuracy, you risk not capturing it at all.
IMHO - being focused on what is important is the best way to manage your time and hit due dates.
| https://softwareengineering.stackexchange.com |
3,285,242 | [
"https://math.stackexchange.com/questions/3285242",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/395670/"
] | I want to ask for a proof-reading of my solution to the following problem.
<blockquote>
For any closed subset <span class="math-container">$X$</span> of <span class="math-container">$\mathbb{R}^n$</span> prove that there is a
countable subset <span class="math-container">$S$</span> of <span class="math-container">... | No, this is not quite correct yet. Think about what happens for <span class="math-container">$n=1$</span> and <span class="math-container">$X=[0,1] \cup \{\pi\}$</span>. Even more striking, for <span class="math-container">$X=\{\pi\}$</span> the set <span class="math-container">$S=X\cap\Bbb Q$</span> is empty, while th... | Note that <span class="math-container">$\Bbb R^n$</span> has a countable base: all finite products of open intervals with rational endpoints, or all open ball around rational points with rational radii. Enumerate them as <span class="math-container">$\{B_n: n \in \Bbb N\}$</span>, say.
Now for any (not just closed) su... | https://math.stackexchange.com |
111,680 | [
"https://mathoverflow.net/questions/111680",
"https://mathoverflow.net",
"https://mathoverflow.net/users/27871/"
] | Let $X$ and $Y$ be complete curves over a field $k$ of characteristic zero. Let $S = X \times_k Y$. Assume that Y has a $k$-rational point and use this point to consider $X$ as a divisor (also denoted by $X$) on $S$. Is this divisor ample?
If yes, for which $m_0$ do we have that the higher cohomology of $mX$ vanishes ... | There is an excellent reason why the exponential term and the division by $n$ are there, although they look a bit mysterious at first.
Firstly, a correction to your formula: it should be $|C(\mathbb{F}_{q^n})|$, the number of solutions over the field with <em>q</em> elements, not $|C(\mathbb{F}_{q})|$. (Notice that t... | One justification for this is the Euler product expression. To find the Euler product expression for the Hasse-Weil function, you have to ask yourself what the appropriate analogue of a prime is. It turns out to be a closed point on the variety. The analogue of the size of the prime is the size of the residue field of ... | https://mathoverflow.net |
2,689,574 | [
"https://math.stackexchange.com/questions/2689574",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/492610/"
] | I was asked to determine for what $x\in\mathbb{R}$ does $\displaystyle \sum_{n=1}^\infty \frac{1+x^{2n}}{n^6}$.<br>
My attempt is:<br>
$\displaystyle \frac{1+x^{2n}}{n^6}=\frac{1}{n^6}+\frac{x^{2n}}{n^6}$.
I was told the "two out of three" rule:
<blockquote>
If $c_n=a_n+b_n$, then $\sum C_n=\sum a_n +\sum b_n$, p... | I think the reasoning is not good enough. Actually one should assume first that $(x_{n})$ is Cauchy in $|\|\cdot\||$ and $\|\cdot\|$ is complete. Then there is some $\|x_{n}-x_{m}\|\leq C|\|x_{n}-x_{m}\||\rightarrow 0$, so $(x_{n})$ is Cauchy in $\|\cdot\|$. Then there is some $x\in X$ such that $\|x_{n}-x\|\rightarrow... | Assume <span class="math-container">$m\|\cdot\| \le |\!|\!|\cdot|\!|\!| \le M\|\cdot\|$</span> for some constants <span class="math-container">$m,M > 0$</span>.
Take a Cauchy sequence <span class="math-container">$(x_n)_{n=1}^\infty$</span> in <span class="math-container">$\|\cdot\|$</span>.
Then we have
<span class... | https://math.stackexchange.com |
1,324 | [
"https://mechanics.stackexchange.com/questions/1324",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/783/"
] | Anyway, I have a Grand Am 2003 V6. It only has 80k miles. My car ran great when I got it(used), but at some point it began to have minor temperature problems. It would always run a little bit hotter than it should. This basically just meant I couldn't keep it idling forever. At some point I took a drive for about an ho... | This actually ended up being a very simple problem. Something so simple that I'm almost in disbelief.
My car has been running nearly straight antifreeze.(I'd say about 90% anyway) Everyone I'd talked to locally has said it should run <code>even cooler</code> doing that... but they're wrong. I emptied my expansion tan... | First, if it runs hotter during slower speeds (the 25mph-50mph you mention), I would think this is a sign that you're not getting enough airflow through the radiator. This might be a fan issues, but it might also be some other obstruction that prevents sufficient airflow.
You said you hit a deer and had the radiator r... | https://mechanics.stackexchange.com |
106,150 | [
"https://mathoverflow.net/questions/106150",
"https://mathoverflow.net",
"https://mathoverflow.net/users/2720/"
] | <blockquote>
Let $G$ be an algebraic group over an
algebraically closed field. If $H$ and
$K$ are closed subgroups and one of
them is connected, then their
commutator $[H,K]$ is also connected.
</blockquote>
Is there an easy way to see this fact?
The proof that I see in Springer's book on Linear Algebraic G... | The case for $G$ a topological group doesn't look hard; it just comes down to two facts:
<ul>
<li>A union of connected sets which have a point in common is also connected. For example, suppose $K$ is a connected subgroup and $H$ is any set. For each fixed $h \in H$, the set of commutators $[h, K]$ is the image of $K$... | It seems to me that in a topological group $G$ if $H$ is a connected subset containing the identity and $K$ is any subset then the subgroup generated by all commutators $hkh^{-1}k^{-1}$ is connected. $G$ does not to be Hausdorff, and $H$ and $K$ do not have to be closed or to be subgroups.
The ingredients in the proo... | https://mathoverflow.net |
61,139 | [
"https://dba.stackexchange.com/questions/61139",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/4325/"
] | How can I get list of stored procedures/Function which are compiled for debug?
I do not see relevant column in following tables.
<ul>
<li>DBA_PROCEDURES</li>
<li>DBA_OBJECTS</li>
</ul>
| Thanks for Phil's answer, following query do what I need, compile all debug compiled objects.
<pre><code>SELECT 'ALTER ' || object_type || ' ' || owner || '.' || object_name || ' compile;'
FROM SYS.ALL_PROBE_OBJECTS
WHERE DEBUGINFO = 'T'
ORDER BY owner, object_type, object_name;
</code></pre>
| I think DBA_PLSQL_OBJECT_SETTINGS gives more appropriate information.
| https://dba.stackexchange.com |
57,490 | [
"https://mathoverflow.net/questions/57490",
"https://mathoverflow.net",
"https://mathoverflow.net/users/9714/"
] | From Cantor we know that |R| = 2^|Z|. That is, |R| is equal to the number of subsets of Z. Is it also true that |R| is equal to the number of <em>infinite</em> subsets of Z?
| Yes, because there are only countably many finite subsets of Z.
| The set of subsets of $\mathbb{Z}$ can be seen as the set of all functions $f:\mathbb{Z}\to\{0,1\}$. And this last set can be seen as the set of all sequences of 0 and 1. With this last point of view, it is easy to see that there exists a bijection between this set and, for instance, the interval $[0,1]$.
| https://mathoverflow.net |
413,782 | [
"https://physics.stackexchange.com/questions/413782",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/167103/"
] | I just finished my class on circular acceleration and I learnt that centrifugal force (outward force) is a psuedo force. It doesn't really exist.
Now suppose I am going round in my car or a merry go round or whatever. I feel like a force is pushing me from the center and towards the window of my car which is in the o... | If you think about the car scenario, there are two possible scenarios.
1) The turn is very small, friction will provide enough centripetal force which is equal to centrifugal force (outward force) and you will stay still.
2) The turn has a high curvature. Then the friction will not be enough to match the centrifugal ... | <blockquote>
If centrifugal force isn't real then why am I being pushed on a merry go rournd?
</blockquote>
It is not you who are accelerating outwards away from the car seat or the merry-go-round - <strong>it is the car seat or merry-go-round that accelerates away underneath you</strong>.
And as it moves away unde... | https://physics.stackexchange.com |
39,423 | [
"https://electronics.stackexchange.com/questions/39423",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/-1/"
] | I want to know the basic/fundamental difference between AM and FM radio. Why nowadays FM radio has replaced AM and has become more popular?
| Short answer: FM is far less susceptible to disturbance of the signal.
<img src="https://i.stack.imgur.com/0NiP8.png" alt="enter image description here">
This is an AM modulated signal. The contours are the baseband signal which we recover by demodulation. Notice that there's a spike in the signal, which may be cau... | AM radio is amplitude modulated, meaning that the <strong>amplitude</strong> of the carrier frequency is varying in the same manner as the audio signal you are transmitting.
FM radio is frequency modulated, meaning that the <strong>frequency</strong> of the carrier frequency is varying in the same manner as the audio ... | https://electronics.stackexchange.com |
3,416,629 | [
"https://math.stackexchange.com/questions/3416629",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/54398/"
] | Let <span class="math-container">$S_n(R)$</span> and <span class="math-container">$V_n(R)$</span> denote the surface area and volume of an <span class="math-container">$n$</span>-sphere with radius <span class="math-container">$R$</span> respectively.
It is well known that
<span class="math-container">$$S_n(R) = \fr... | Let <span class="math-container">$x$</span> denote the number of blue boxes that get filled and <span class="math-container">$y$</span> the number of red boxes that get filled. Then there are <span class="math-container">$5x$</span> red boxes and <span class="math-container">$5y$</span> green boxes. Hence,
The total n... | Let <span class="math-container">$r$</span>, <span class="math-container">$b$</span>, and <span class="math-container">$g$</span>, be the nubmers of red, blue, and green boxes respectively.
There are seven blue boxes. A blue box is either empty or filled. If it is filled, it is filled with <span class="math-containe... | https://math.stackexchange.com |
97,224 | [
"https://dba.stackexchange.com/questions/97224",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/62897/"
] | I installed Squirel SQL on Ubuntu and a downloaded and put a MySQL driver into the <code>lib</code> folder of the Squirel folder. Then I chose this driver in the "extra class" tab when configuring Squirel MySQL driver. Connecting to the database and viewing data works but when I try to rename a column in Squirel it sug... | Works for me with the latest version of SQuirreL. Make sure that you change the dialect to MySQL in the Alter Column dialog. Its just below the column name.
| OK - the syntax for changing a column name in MySQL is
<pre><code>ALTER TABLE table_name CHANGE old_col_name new_col_name COL_DATA_TYPE;
</code></pre>
However, it appears that the syntax generated by SQuirreL SQL is
<pre><code>ALTER TABLE table_name ALTER COLUMN "old_col_name" RENAME TO "new_col_name";
</code></pre... | https://dba.stackexchange.com |
310,547 | [
"https://softwareengineering.stackexchange.com/questions/310547",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/124477/"
] | I need to write a function to detect if a set of strings needs delimiters when concatenated in any order.
For example, the strings <code>("A","B","C")</code> do not need a delimiter: <code>"ABCBB" -> ["A","B","C","B","B"]</code>.
However, the strings <code>("Pop","corn","Popcorn")</code> <em>do</em> need a delimit... | After some thinking, there is a simple algorithm.
Assume you have two strings x and y, and neither is a prefix of the other. Nothing you could append to them would make them equal, so they are of no interest. What you are interested in are strings x and xa, where xa has not been created by adding strings to x: We mig... | I think the structure you are looking for is a 'Trie' commonly used for auto complete, spell checking etc.
In your case a trie which is flat, ie no node has a child node, should equate to none of the words being a substring at the start of any of the others and hence your ablity to ommit a delimiter.
In the case of '... | https://softwareengineering.stackexchange.com |
99,179 | [
"https://softwareengineering.stackexchange.com/questions/99179",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/21104/"
] | First off, I'm not looking for this answer: "learn PHP/MySQL, JQuery, HTML/CSS...."
My background, I wear many hats, and do many things. Currently I manage investment accounts with a business partner who is also a friend. He happens to be attending business / law school perusing a joint JD and MBA. As a result, we're ... | A lot of what small businesses need can be served with a content management system (CMS) such as Joomla, Drupal, or Wordpress, with some customization written in PHP, HTML, JS, and CSS. For $2k/month, you need a CMS as a starting point.
| Try to get into SugarCRM or Magento everybody and their mom is in the CMS (wordpress, drupal, ...) and you will always be undercut in price. You want something with a pretty heavy ramp up time that's hard for people to just pickup. Then you can charge a much more reasonable rate.
| https://softwareengineering.stackexchange.com |
57,738 | [
"https://mechanics.stackexchange.com/questions/57738",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/40615/"
] | My bicycle tires go to 60 psi, and I can easily fill them up from nothing with less than 10 pumps.
My car tires are at 32 psi, so shouldn't they be even easier? Yet I have never heard of anyone hand pumping their car tires. Why not?
| People do that. Sometimes, at least.
I have a high quality (high volume) bike pump at home, and occasionally I use it to check the pressure on the car, or to top off if it's obviously missing something. I find it 100% hassle free and not in the least problematic. But then I have a really good volume on that pump; also... | There is no theoretical reason why you couldn't use a bicycle pump to fill car tyres. Indeed I used a double barrel foot pump to pump the tyres on my wifes' bicycle last night that I usually use for car tyres.
What you have to consider though is that the volume of air in a car tyre is significantly more than that of ... | https://mechanics.stackexchange.com |
92,041 | [
"https://softwareengineering.stackexchange.com/questions/92041",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/12961/"
] | I see a lot of .NET job postings that list XML as a required skill.
What should one be able to do in/with XML to have confidence that this requirement is satisfied?
Modeling?
Work with XPATH?
Familiarity with serialization?
What is specific to .NET?
| As well as non-.NET-specific things like XSDs and XPATH queries:
You'd want to be familiar with the different ways of handling XML that the .NET framework has provided - the old <code>System.Xml</code> namespace (<code>XmlDocument</code> et al) from .NET 1.1, and the new <code>System.Xml.Linq</code> namespace (<code>X... | Well these days I would say having a good understanding of how to create a well structured XSD is enough to mark you as competant in XML in the context of .Net considering there are so many XSD -> .Net Object data binding packages avaialable, which handle stuff like serialization and XPATH.
But I would recommend some ... | https://softwareengineering.stackexchange.com |
398,317 | [
"https://softwareengineering.stackexchange.com/questions/398317",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/346477/"
] | I am trying to split down user stories for a brand new system. This system will record weight readings from a balance connected to a serial port.
Due to regulatory data integrity requirements - the data must be attributed to the user who produced it. The business cannot possibly use the software without meeting this r... | Each story should be valuable independently. But don't get too hung up on it.
The idea is to avoid partial functionality. ie spending ages doing something and being unable to demonstrate any progress towards the project goal.
So for example say I have an ecommerce site project with a Login story and a Purchase story.... | Context is king.
A story that happens after authentication is dealt with <em>somehow</em> is still a useful story. You do not have to bake a fully detailed authentication story into every user story simply because you're required to always authenticate.
Also, your authentication requirement is only "always" in certai... | https://softwareengineering.stackexchange.com |
302,348 | [
"https://physics.stackexchange.com/questions/302348",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/140669/"
] | If particles can be either matter or anti-matter, and particles are (supposedly) made up of strings, is it possible so that those strings and have anti-matter or matter properties or is it another variable affecting the matter or anti-matter properties?
| Without loss of generality, in bosonic string theory, particle states arise as excitations of the string. Specifically, in light-cone quantisation, we can expand the string embedding as,
$$X^i (\tau,\sigma) = x^i + \frac{p^i}{p^+}\tau + i\sqrt{2\alpha'} \sum_{n \neq 0} \frac{1}{n}\alpha^i_n e^{-\pi inc\tau/\ell} \cos ... | Particles are not "made up of strings" in string theory. The quantum states of the string (often called "excitations" or "modes") correspond to particle states. There is only <em>one type of fundamental string</em>, it is not the case that there would be "different" strings for matter or anti-matter - different states ... | https://physics.stackexchange.com |
97,778 | [
"https://softwareengineering.stackexchange.com/questions/97778",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/27796/"
] | A software project that I am working on involves me and another programmer. The project involved an engine backend with an MVC front end. Initially I did alot of the work on the project and so setup some simple design methodologies mainly surrounding abstraction and template strategy.
For quite a while I have been o... | From supervising maybe upwards of 200 developers over the last 25 years, I reckon - the proportion of developers who are intuitively comfortable with the kind of design abstractions you are talking about - is something like a third. My approach has evolved from expecting to fix this with coaching, training and encourag... | Abstract classes, class factories, don't get me wrong, but sounds like an artillery to kill a bird. Patterns are there to solve problems not to create them. You admitted that the project is 2 people project.
What your colleague is doing wrong, though, is that he's not following the guidelines. It will cause some mess ... | https://softwareengineering.stackexchange.com |
25,323 | [
"https://dba.stackexchange.com/questions/25323",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/13128/"
] | I'm trying to create a relationship between two tables where one column in TABLE A is the foreign key for a column in TABLE B. However, there is one row in TABLE B that is currently null in that column and it's giving me an error. However, from Googling the issue, the general consensus seems to be that null is an accep... | For anyone who stumbles here with the same question. An empty cell is not the same as a NULL cell. Empty cells are '' not NULL!
| <pre><code>update TABLEA set COLUMN1 = NULL where COLUMN1 = '';
update TABLEB set COLUMN2 = NULL where COLUMN2= '';
</code></pre>
If you changing your "NULL" values to none and it works, it might just be that there's an empty string or a hidden character in there.
Try recreating your FK after that.
| https://dba.stackexchange.com |
632,744 | [
"https://physics.stackexchange.com/questions/632744",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/297709/"
] | I have a question about a convention from Peskin & Schroeder, namely that
<span class="math-container">$$\int d\theta^{*}\, d\theta \, (\theta \theta^*) = 1,$$</span>
where <span class="math-container">$\theta$</span> and <span class="math-container">$\theta^*$</span> are independent Grassmann numbers. Always refer... | The answer already posted by Pavlo B. is not wrong, but I think it obscures the most important element of the explanation.
You have implicitly assumed that you can simply apply a linear operation to make a differential out of a complex Grassmann number. However, this is not correct. Consider, just
<span class="math-co... | Integrating Grassman numbers does not work in a naive way. It is exactly opposite to the naive way. Consider
<span class="math-container">$$
\int d\eta\, \eta =1
$$</span>
Under the change of variables <span class="math-container">$\eta=2\eta_1$</span>, the top expression would naively become
<span class="math-contain... | https://physics.stackexchange.com |
1,297 | [
"https://mechanics.stackexchange.com/questions/1297",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/768/"
] | I installed a car stereo a few months ago and it seems to forget all of its settings whenever it loses power. The stereo the car came with didn't have this issue. I am familiar with electronics so I am assuming it needs a constant power source to keep the memory in-tact, however the ponytail connector is different than... | Typically car stereos do require a constant voltage source in order to keep settings - they may have a supercap which keeps settings for a short while (for changing batteries over etc), but over time this may degrade, and in any case is only designed to last for a few minutes.
In order to do this you usually have an u... | Before you go to a lot of time and effort I recommend that you check the ground connections. Make sure the negative battery terminal is clean and tight. Make sure the other end of the negative cable well attached and not rusty or corroded.
Also check the ground you used on the stereo, be sure it is well connected and... | https://mechanics.stackexchange.com |
63,931 | [
"https://cs.stackexchange.com/questions/63931",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/58940/"
] | I'm fairly new to heaps and am trying to wrap my head around why min and max heaps are represented as trees when a sorted array appears to both provide min / max properties by default.
And a follow up: what is the advantage of dealing with the complexity of inserting into a heap given an algorithm like quick sort hand... | $\small \texttt{find-min}$ (resp. $\small \texttt{find-max}$), $\small \texttt{delete-min}$ (resp. $\small \texttt{delete-max}$) and $\small \texttt{insert}$ are the three most important operations of a min-heap (resp. max-heap), and they usually have complexity of $\small \mathcal{O}(1)$, $\small \mathcal{O}(\log n)$ ... | To answer your questions, you have to define which different actions you will perform and how often, and you have to evaluate the time complexity of each action.
Which method is performing better overall will depend on the individual complexities and how often each action is performed.
Sorting an array has a very h... | https://cs.stackexchange.com |
315,829 | [
"https://physics.stackexchange.com/questions/315829",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/82630/"
] | In studying the the interaction of a single mode electromagnetic field in a coherent state with a two state atomic system (initially in its ground state), the problem is reduced to evaluating the following expectation value:
$$\langle 1,n| \left[\frac{2}{\hat\Omega^2}\left(\hat{H} - \omega\left(\hat{N_e}-\frac{1}{2}\r... | If $\hat H$, ${\hat N}_e$, and $\hat \Omega$ all commute, the simplest idea is to take their common eigenstates as a basis for the identity decomposition. If
$$
{\hat H} |\lambda\rangle = E_\lambda |\lambda\rangle\;, \;\;\;
{\hat N}_e |\lambda\rangle = n_\lambda |\lambda\rangle\;,\;\;\;
{\hat \Omega} |\lambda\rangle =... | You might want to consider inserting the unit operator:
$$
\hat 1= \sum_{n_1n_2} \vert n_1 n_2\rangle\,\langle n_1 n_2\vert
$$
or a complete set of eigenvectors between your operators. Also, since $\hat \Omega$ commutes with $\hat H$ and $\hat N$, you can act move it to the right.
| https://physics.stackexchange.com |
1,069 | [
"https://electronics.stackexchange.com/questions/1069",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/142/"
] | The datasheet for the ATTiny13A, for instance, lists Min frequency of 0 MHz. Does this mean the clock can be run at any arbitrarily low frequency with no ill effects? I'm assuming it draws lower current at lower clock speeds? Does 0 MHz mean you can stop the clock completely, and as long as power is still applied, i... | Yes. If the datasheet says "fully static operation", then you can clock it at any speed, even 0 Hz. A "dynamic" chip needs to have a clock at a specific rate or it loses its state.
| I am posting another answer, just because the last question you had was not answered before.
Todbot is completely correct. It will also draw lower power at lower speeds. It also means if you supply it's clock from another processor, for example, you could stop supplying it at any point and then start clocking it later... | https://electronics.stackexchange.com |
392,718 | [
"https://softwareengineering.stackexchange.com/questions/392718",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/337714/"
] | I am wondering about the correct architecture to work with a progress bar in C#. But maybe it applies not only to C#, because I need an architectural look at this.
I'll explain my question with an example. The user presses a button and then the program starts to work on a huge algorithm. One part of the algorithm is t... | A long running algorithm certainly could use some method of indicating it's progress. But it would be inappropriate for the algorithm to know that it's talking to a progress bar.
The algorithm should be able to talk to adapters that can take what the algorithm says about it's progress and turn it into a progress bar,... | This is how I have approached this problem. There are a few points I find important.
<ol>
<li>Possibility to subdivide the progress into parts. It seem fairly common to either have separate phases in the work, or that each work item takes a considerable amount of time, so each work item should also report progress.</l... | https://softwareengineering.stackexchange.com |
23,455 | [
"https://softwareengineering.stackexchange.com/questions/23455",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/4688/"
] | It seems like most of the jobs I'm receiving, and most of the Internet, is still using standard HTML (HTML 4, let's say) + CSS + JS. Does anyone have any vision on where HTML5 is as a standard, <strong>particularly regarding acceptance and diffusion?</strong> It's easy to find information about inconsistencies between ... | I'd say definitely get in there and start learning some of the technologies involved. Just be aware that 'HTML 5' right now is actually really a marketing term!
HTML 5 has not been ratified as a standard yet and although all of the major players are throwing their support behind 'HTML 5' they're all actually just imp... | Because of Mac/Steve Jobs, "HTML5" is a public term. Meaning, that non-programmers (AKA clients) can recall it, and are often asking for it. So, in that sense, even though it doesn't really exist in a standardized form, but rather WebKit and Firefox's own versions, it already is relevant.
Unfortunately, the inconsis... | https://softwareengineering.stackexchange.com |
99,683 | [
"https://stats.stackexchange.com/questions/99683",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/35574/"
] | I was wondering if anyone could elaborate more on this statement which I came across whilst reading a book on non-linear mixed effects model. I know that you can have linear, generalised linear and non-linear mixed effect models.
The book says
<blockquote>
mixed models are non-linear statistical models, due main... | Hopefully the amount of notation suppressed and corners cut in what follows still leaves something intelligible:
<strong>On what 'mixed' means</strong>. Imagine somewhere at the heart of the model we have a line looking something like this.
$$\eta = \beta_0 + \beta_1 x_1 + ... + \beta_p x_p$$
Where the $x_k$ are o... | And, here's a "street" version of the above:
a) what is a linear model? It's one which can be expressed in the form of sums and scalar products of the inputs (y = ax + b at the simplest). If "a" is a function of some other factor ("z" not "x") perhaps a random function, A(z), then we have y = A(z)x + b which is no lon... | https://stats.stackexchange.com |
4,359 | [
"https://dba.stackexchange.com/questions/4359",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/2498/"
] | Below is the my.ini file of one of my PC running MySQL 5.5 with 1 GB RAM. It is not using concurrent connections and we are using a stand-alone PC for a single application and single user.
<pre><code># MySQL Server Instance Configuration File
# ----------------------------------------------------------------------
# ... | One area that stands out is the way you are accessing the BillDetails table. All queries appear to be using MONTH and YEAR operators on BillDate. For example:
<pre><code>SELECT SUM(GROSSAMOUNT) FROM BILLDETAILS WHERE MONTH(BILLDATE) = 8 AND YEAR(BILLDATE) = 2011;
</code></pre>
This approach requires accessing every r... | First off, most of these seem to be 'slow' because they're not using indexes. You need to analyze how you're accessing the data in your tables to determine proper indexes. But a few pointers from this file:
<pre><code>SELECT * FROM REMARKSETTINGS;
</code></pre>
and
<pre><code>SELECT * FROM BILLINGSETTINGS;
</code><... | https://dba.stackexchange.com |
283,070 | [
"https://physics.stackexchange.com/questions/283070",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/65592/"
] | I am reading some of Schwartz's quantum field theory book, and I have come across a passage I find confusing. It states that
<blockquote>
When the coupling is small, the theory is perturbative, and then the coupling must either increase or decrease with scale. (p442, 1st edition)
</blockquote>
I think I am confus... | I'd agree that the sentence is not correct (in a sense that the author should't have written <em>"must"</em>). There are actually three possibilities:
First:
<blockquote>
If the coupling increases with $\mu$, as in QED, it goes to zero at long distances.
</blockquote>
Second:
<blockquote>
If it decreases wit... | Perturbation theory and the fact that couplings run in most quantum field theories are not actually directly related to each other. As long as the coupling is small enough, one can use perturbation theory. The smaller the better of course.
The coupling runs, because the strength of the interaction differs at differen... | https://physics.stackexchange.com |
51,657 | [
"https://physics.stackexchange.com/questions/51657",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/20019/"
] | I just started learning physics 3 days ago and am having trouble understanding what I am doing wrong. Can someone please explain my error(s)? Thanks!
We have a 1kg object on a plane at a 30 degree angle from horizontal. Force of friction is 1.5N. We are asked to calculate the net force.
I assume the object is moving... | An object of mass $m$ on an incline with friction experiences the following three forces:
<ol>
<li>Gravity</li>
<li>Normal force</li>
<li>Friction</li>
</ol>
The normal force points away from the incline's surface and is perpendicular to it. The force of friction is parallel to the incline and points in the directi... | It's easier to understand if you ignore friction for a minute.
Suppose you're on a road on a hill which has iced over. Anything that goes on the road, slides down because there's no friction. It is gravity that is pulling the objects down, even though they're following the surface of the hill, instead of going straigh... | https://physics.stackexchange.com |
164,693 | [
"https://stats.stackexchange.com/questions/164693",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/84119/"
] | I want to model a logistic regression with imbalanced data (9:1).
I wanted to try the weights option in the <code>glm</code> function in R, but I'm not 100% sure what it does.
Lets say my output variable is <code>c(0,0,0,0,0,0,0,0,0,1)</code>.
now I want to give the "1" 10 times more weight.
so I give the weights argu... | Ching, You do not have to make your data set balanced in terms of 1’s and 0’s. All you need is sufficient number of 1’s for the maximum likelihood to converge. Looking at the distribution of 1’s (100,000) in your dataset, you should not have any problems. You can do a simple experiment here
<ol>
<li>Sample 10 % of t... | Weighting is a procedure that weights the data to compensate for differences in sample and population (King 2001). For example, in rare events (such as fraud in credit risk, deaths in medical literature) we tend to sample all the 1’s (rare events) and a fraction of 0’s (non events). In such cases we have to weight the ... | https://stats.stackexchange.com |
13,989 | [
"https://mathoverflow.net/questions/13989",
"https://mathoverflow.net",
"https://mathoverflow.net/users/3757/"
] | Suppose $E_1$ and $E_2$ are elliptic curves defined over $\mathbb{Q}$.
Now we know that both curves are isomorphic over $\mathbb{C}$ iff
they have the same $j$-invariant.
But $E_1$ and $E_2$ could also be isomorphic over a subfield of $\mathbb{C}$.
As is the case for $E$ and its quadratic twist $E_d$. Now the question... | Question 1: Putting both curves in say, Legendre Normal Form (or else appealing the lefschetz principle) shows that if the two curves are isomorphic over <span class="math-container">$\mathbf{C}$</span> then they are isomorphic over <span class="math-container">$\overline{\mathbf{Q}}$</span>. Now we could say that for ... | The answer is a bit more complicated if $j=0,1728$ because the corresponding elliptic curves have a bigger automorphism group, so I'll leave those out and let you (or others) deal with this case. If $j \ne 0,1728$, then the automorphism group of $E$ is of order $2$ and all other elliptic curves isomorphic to $E$ over a... | https://mathoverflow.net |
59,101 | [
"https://softwareengineering.stackexchange.com/questions/59101",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/20393/"
] | For example, some library (in my case it's ruby gem) became deprecated. And my app is using this library. It's ok and I have not any problems with how it works. When should I switch from deprecated open-source library to something new? Or should I at all?
| What was the reason for the deprecation? You have a responsibility to balance keeping your technology fresh with the demands of stable software. Every time you make a big change, you introduce a decent amount of risk that you'll break something doing that change. So evaluate the following for your situation:
<ul>
<... | Deprecation today means that bugs will not be fixed tomorrow, unless you do it yourself.
If you do not mind that, then no need to worry.
| https://softwareengineering.stackexchange.com |
498,826 | [
"https://electronics.stackexchange.com/questions/498826",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/252060/"
] | I know that in motional emf V=Blv where B,l,and v are perpendicular to each other. When one of them isn't, then there would be no emf. What formula supports this?(mathematical evidence)
Can anyone help?
| <blockquote>
I know that in motional emf V=Blv where B,l,and v are perpendicular to each other. When one of them isn't, then there would be no emf. What formula supports this?(mathematical evidence) Can anyone help?
</blockquote>
No mathematical formula supports that other mathematical formula. There is no mathemati... | I believe what you are asking about is the mathematical vector expression that both your scalar expression and Fleming's Left Hand Rule comes from:
This would be the equation for the Lorentz Force. Of course you could also just say Maxwell's equations.
Basically ripped off Wikipedia:
<span class="math-container">\$ ... | https://electronics.stackexchange.com |
4,331 | [
"https://physics.stackexchange.com/questions/4331",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/1588/"
] | If the S-Matrix is the only observable, that rules out both generalized free fields and Wick-ordered polynomials of generalized free fields as interesting Physical models, because both result in a unit S-matrix. Neither possibility has been developed since the 1960s when these results were proved, and when the S-Matrix... | Do I understand your question correct? You ask: if the S-matrix is the only quantity which really can distinguish interesting models from free models?
Then I would say no. But there are no interesting models in 4D, fullfilling let's say the Wightman axioms, are there?
In lower dimension for example conformal field the... | Correlation functions of local operators are the other observables that field theorists talk about most of the time: things like $\left<{\cal O}_1(x_1) {\cal O}_2(x_2) \ldots\right>$. But there's no shortage of observables in quantum field theory.
The situation where you'll hear people say that the S-matrix is t... | https://physics.stackexchange.com |
102,137 | [
"https://dba.stackexchange.com/questions/102137",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/66932/"
] | If I set 'Auto Update Statistics' to 'False' and 'Auto Update Statistics Asynchronously' to 'True'
What the DB will do?
Also - If I set 'Auto Create Statistics' to 'True', It will be 'Async'?
| The user account that is running the SQL Server agent might not have permissions to use the database mail profile you can check that with EXECUTE msdb.dbo.sysmail_help_profileaccount_sp;
But you are having some issues with the agent account security, please try the following steps.
<ul>
<li>Remove all extra privilege... | Possible cause you may be seeing this error is:
Either The <code>BUILTIN\Administrators</code> has been removed from the Logins (Security-> Logins) section or <code>BUILTIN\Administrators</code> does not have sufficient priviliges to access the SQL server.
As per MS
<blockquote>
The issue does not occur if the SQ... | https://dba.stackexchange.com |
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