qid int64 1 4.65M | metadata listlengths 3 3 | prompt stringlengths 31 25.8k | chosen stringlengths 17 28.2k | rejected stringlengths 19 40.5k | domain stringclasses 28
values |
|---|---|---|---|---|---|
3,777,972 | [
"https://math.stackexchange.com/questions/3777972",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/793349/"
] | Given <span class="math-container">$a$</span>,<span class="math-container">$b$</span>,<span class="math-container">$c$</span> are odd integers Prove that <span class="math-container">$b^2-4ac$</span> can not be a perfect square.
My try:Let <span class="math-container">$a=2k_1+1,b=2n+1,c=2k_2+1;n,k_1,k_2 \in I$</span>
<... | Assume <span class="math-container">$b^2-4ac=d^2$</span>.
Then <span class="math-container">$d$</span> is odd and <span class="math-container">$(b-d)(b+d)=4ac$</span>.
Consequently, there exists odd <span class="math-container">$u,v$</span> such that <span class="math-container">$b-d=2u$</span> and <span class="math-co... | Suppose <span class="math-container">$b^2 - 4ac$</span> were a perfect square. Then the quadratic <span class="math-container">$ax^2 + bx + c$</span> has a rational root by the quadratic formula. By the rational roots theorem, the root can be written as <span class="math-container">$\frac{p}{q}$</span> with <span class... | https://math.stackexchange.com |
509,944 | [
"https://stats.stackexchange.com/questions/509944",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/302966/"
] | I am researching therapy response of melanoma patients based on a number of approximately 80 features with a very small sample size of 60 patients. To eliminate features that do not contribute to the model, I am using <code>train</code> from the <code>caret</code> package and <code>glmnet</code> with alpha = 1 to perfo... | You’re using different loss functions. Of course they’re different. When you do the LASSO, the variables that get set to zero contribute to the loss function. When you do OLS on the “surviving” variables, the loss function only ever sees those variables.
In LASSO, the loss function sees the "dead" variables a... | Define a covariate matrix <span class="math-container">$X \in \mathbb{R}^{n \times p}$</span> with columns <span class="math-container">$\{x_j\}$</span>, where there are <span class="math-container">$n$</span> observations of <span class="math-container">$p$</span> covariates. Define the response <span class="math-cont... | https://stats.stackexchange.com |
180,308 | [
"https://security.stackexchange.com/questions/180308",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/1297/"
] | <strong>ORIGINAL QUESTION:</strong>
We have servers which we want to wipe and sell due to an environmentally friendly scheme, recycling, reducing carbon footprint etc. The servers have a raid configuration.
After doing some research, I am thinking of doing the following:
<ol>
<li>Use a Linux Live CD to boot into se... | There is no need to do full disk encryption in step 2. Simply do
<pre><code>dd if=/dev/zero of=/dev/sda bs=1M
</code></pre>
where <code>/dev/sda</code> is the hard disk device (change it to whatever your disk is called). You might also want to change the block size.
If you don't like the overwrite by 0s (there are p... | If you don't absolutely need to sell the drives, pull them and send them to a recycler for shredding. Physically destroying the drives is a much more secure (and faster) way of dealing with them than all the iterations you're going through. There will be info on each fragment of the drive and it is technically readabl... | https://security.stackexchange.com |
564,571 | [
"https://electronics.stackexchange.com/questions/564571",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/-1/"
] | Why do typical DC motors use brush contacts rather than just the conductors of the wire itself? Wouldn't the wires be more efficient/low wattage dissipation in that region?
| You're not looking at what a brush actually has to do. Brushes slide, need to maintain contact, wear, and arc. So you need spring loading, low friction, resistant to welding and corrosion, and need to be soft and replaceable so they wear instead of the expensive, difficult to replace commutator ring, but not too soft o... | Because the armature reverses polarity each time the brushes switch to the next commutator slot. If it did not switch it would not turn. In DC motors, we need a commutator or something for converting DC power into AC power. The commutator (mounded on armature) is a rotating part of the dc motor. If we connect electrica... | https://electronics.stackexchange.com |
5,316 | [
"https://mechanics.stackexchange.com/questions/5316",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/2714/"
] | I own a 2004 Kia Spectra. It only has 47,000 miles on it (I don't drive much) When I had the transmission fluid changed they said the 3 outer belts needed to be replaced due to dry rot. I am in Texas so guess this is possible. When I called to make the appt to take it in, the guy said I needed 'for maintenance' to h... | Even if the timing belt is "probably" okay, you have to weight the costs and benefits of not replacing it. From what I can tell, this car has an interference engine, meaning if the timing belt breaks, the cylinders will smash into the valves. As long as they don't break off and also tear up the cylinders/combustion cha... | Suggested maintenance on a timing belt is 60k miles.
| https://mechanics.stackexchange.com |
71,600 | [
"https://electronics.stackexchange.com/questions/71600",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/11261/"
] | If I am connecting ICs to both sides of a led matrix, the ICs need to be able to source and sink enough current to light the LEDs? Or just sink?
Let me explain my question with an example:
<img src="https://i.stack.imgur.com/FgvAj.png" alt="Circuit">
In this diagram, I select which row is illuminated on LED1 through... | If you are selecting a column via a 4515 de-multiplexer, <strong>ONLY</strong> one column is active therefore it is <strong>impossible</strong> drive more than 1 LED in the same row at any one moment in time: -
<img src="https://i.stack.imgur.com/ZfhRd.jpg" alt="enter image description here">
This means, if 25mA will... | The issue is that your chosen setup, as explained, will only allow a single LED to be lit at any given time. You said <code>I select which row is illuminated on LED1 through IC12. The column is selected through a demux (IC14). The LED matrix current is sunk through IC13, a ULN2803 transistor array.</code>
Since only o... | https://electronics.stackexchange.com |
681,505 | [
"https://math.stackexchange.com/questions/681505",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/125459/"
] | I need to show that for $0 < q < 1$ that the sequence ${x_n} = q^n$ converges, and to find its limit.
So I need to show that
$\forall \epsilon > 0$ there is $N \in \mathbb{N}$ such that $\forall n>N, |x_n - x_m | < \epsilon$ , or $|q^n - q^m| < \epsilon \\$
Once I show convergence it should be p... | <strong>Hint:</strong> You are trying to prove that the sequence is a Cauchy sequence. It is easier to prove directly from the definition of limit that $\lim_{n\to\infty} q^n=0$.
We have $q=\frac{1}{1+p}$ for some positive $p$. Now by the Binomial Theorem, we have $(1+p)^n \gt np$ if $n\ge 1$. This inequality is eno... | You could think backwards and "guess" the limit. If $q$ is say, 0.2, what is $0.2^{1000}$? It is approximately $0$, so let us use this guess.
We want to show that there is a threshold $N$ beyond which all $n$ satisfy:
\begin{align}
|q^n-0|<\epsilon\\ q^n<\epsilon
\end{align}
So, if you have proved existence an... | https://math.stackexchange.com |
108,686 | [
"https://stats.stackexchange.com/questions/108686",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/20065/"
] | I'm investigating optimal bidding in auctions, and am using logistic regression to predict the probability of winning an auction given a set of explanatory variables (e.g. the price I bid, number of competing bids etc).
One explanatory variable I want to use is the <em>second</em> highest price that was paid. However,... | I just write the answer here, because I have the feeling the comment section is just getting longer without coming to a clear end.
You want to understand the formula
$$p(x=1|\mathcal D) = \int_0^1 p(x=1|\mu)p(\mu|\mathcal D)\mathrm d \mu$$
First, you apply the product rule in the integral. This yields
$$p(x=1|\math... | Just thought I'd add to the above answer by saying that; it makes sense the <span class="math-container">$x$</span> and <span class="math-container">$D$</span> are conditionally independent given <span class="math-container">$\mu$</span>. Since if you know the parameter <span class="math-container">$\mu$</span>, it doe... | https://stats.stackexchange.com |
533,834 | [
"https://stats.stackexchange.com/questions/533834",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/327578/"
] | Currently I'm working on a project involving loan data where I am trying to build a model that will predict a probability of an individual defaulting on a loan. I have binary dependent variable where defaulted loans are denoted with 1. I decided to use logistic regression for this task, but However, I have difficulty i... | Yes, as long as the input for the outcome is failure (0,1) where 0-No 1-Yes (default), then the predicted probability from your logistic regression model will be the probability of defaulting. For your use case of 0.8 or 80% that person does have a default prediction of 80%, so probably not approved. I would think a ... | For the sake of notation, I am using the model with only one independent variable <span class="math-container">$X$</span>. All of the results hold true with more independent variables as well.
In logistic regression, we use the <em>logistic function</em>
<span class="math-container">$$ p(X) = \frac{e^{\beta_0 + \beta_1... | https://stats.stackexchange.com |
728,214 | [
"https://physics.stackexchange.com/questions/728214",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/346006/"
] | Initially, I'm trying to prove if the following is true
<span class="math-container">$$|\psi_{n00}(r=0)|^2 =\dfrac{1}{\pi n^3a_0^3}$$</span>
I'm looking to solve some calculations made in
Introductory Quantum Optics
Christopher Gerry Lehman College, City University of New York
Peter Knight Imperial College London and U... | Think you've got the wrong expression for the wavefunction, the factor with the Lagurre polynomial should be
<span class="math-container">$$L^{2l+1}_{n-l-1}(0),$$</span>
for <span class="math-container">$l=0$</span> this reduces to <span class="math-container">$$L^{1}_{n-1}(0)=n$$</span>
and so <span class="math-contai... | <blockquote>
I would like to know if the following is true
</blockquote>
<blockquote>
<span class="math-container">$|\psi_{n00}(r=0)|^2 =\dfrac{1}{\pi n^3a_0^3}$</span>
</blockquote>
Assuming <span class="math-container">$\psi$</span> is a hydrogen electron wavefunction then yes, it is true.
| https://physics.stackexchange.com |
202,725 | [
"https://electronics.stackexchange.com/questions/202725",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/92715/"
] | I am trying to write a 1 bit shift register with this code
<pre><code>library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;
entity simple_one_bit_serial_shift_register is
port(
clk : in std_logic;
reset : in std_logic;
shiftin : in ... | You are trying to push in a <code>std_logic_vector</code> with two elements (<code>shiftout : out std_logic_vector(1 downto 0)</code>) one single element.
Try to declare it as a <code>std_logic</code> or a <code>std_logic_vector(0 to 0)</code>.
Even if... Why do you need a 1-element vector?
| Looking at these two lines:
<pre><code>shiftout : out std_logic_vector(1 downto 0)
</code></pre>
and
<pre><code>shiftout <= shiftreg(31);
</code></pre>
The first declares <code>shiftout</code> as being two bits wide. The second tries to assign to this a one-bit value. Your two options are:
Redfine <code>shiftou... | https://electronics.stackexchange.com |
241,187 | [
"https://security.stackexchange.com/questions/241187",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/45707/"
] | I am currently making amendments to an IR process and the topic of incident closure has come up. The organisation follows NIST and therefore their IR process has four phases:
<ul>
<li>Preparation</li>
<li>Detection & Analysis</li>
<li>Containment, Eradication & Recovery</li>
<li>Post-Incident activity</li>
</ul... | <blockquote>
My reluctance here is that this will impact SOC performance metrics.
</blockquote>
So, your process of resolving an incident has 2 distinct stakeholders:
<ul>
<li>the SOC team to measure "Time to Resolution"</li>
<li>the infosec team to ensure "Lessons Learned" are properly actioned</li... | In classic Agile parlance, I would consider the post-mortem to Close the incident, while the end of the incident would be declared when the DoD CJCSM 6510.1B incident table category for root/user compromise or malicious logic installation/execution has been Resolved.
Resolve incident first; then Close
| https://security.stackexchange.com |
249,764 | [
"https://softwareengineering.stackexchange.com/questions/249764",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/27159/"
] | I am learning about the MVP (Model-View-Presenter) Passive View flavour of MVC. I intend to expose events from view interfaces rather than using the observer pattern to remove explicit coupling with presenter.
<strong>Context:</strong> Windows Forms / Client-Side JavaScript.
I am led to believe that the MVP (or indee... | Well, let's evaluate what you are asking first.
Your application is currently a Model-View-Controller application. What does that mean? It means your application has:
<ul>
<li>A Presentation layer, the View,</li>
<li>An Application Processing Layer, the Controller, and</li>
<li>A Data Management Layer, the Model.</... | Let's look at some questions I ask when I am building a website:
<ul>
<li>Do you expect your website to grow in either views or complexity?</li>
<li>Do you expect there to be more "pages" in the future?</li>
<li>Do you know that you will need a data provider on the back end at some point in the future, even if not cur... | https://softwareengineering.stackexchange.com |
61,025 | [
"https://cs.stackexchange.com/questions/61025",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/9407/"
] | I have a DAG which I want to traverse in a topological order. Wikipedia describes two algorithms for topological sorting, which both work in theory but seem impractical to me from a design point of view: Kahn's algorithm modifies the graph (by removing edges) and the DFS-based one marks nodes, which would require me to... | Instead of seting a 'mark' flag;
<pre><code> node.Marked = true;
</code></pre>
You can maintain a set of marked nodes in a hashtable or similar;
<pre><code> hashTable[node] = true;
</code></pre>
You now have to pass the hash table around, but it's O(n) for space and O(1) to check if a node is marked.
| You can do a topological sort with a DFS and retrieve the nodes order by pushing the node on a stack just before the recursive call ends. This implies extra memory to mark a node as visited though, anyway to transverse a graph you almost always will need extra memory to keep account of visited nodes.
That visited mar... | https://cs.stackexchange.com |
29,553 | [
"https://electronics.stackexchange.com/questions/29553",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/5872/"
] | The Verilog <code>always</code> statement, namely
<pre><code>always @(/* condition */)
/* block of code */
</code></pre>
executes the <code>block of code</code> whenever <code>condition</code> is satisfied. How is such an <code>always</code> block implemented in hardware?
| First, note that not all Verilog designs are synthesizable. Usually, only a very specific subset of constructs can be used in a design that is to be realized in hardware.
One important restriction that pops up is that every <code>reg</code> variable can only be assigned to in at most one <code>always</code> statement.... | An <code>always</code> block is commonly used to describe a flip-flop, a latch, or a multiplexer. The code would be implemented with a flip-flop, a latch, or a multiplexer.
In an FPGA a flip-flop and a latch are generally just two different configurations of a more general-purpose register device. A multiplexer would ... | https://electronics.stackexchange.com |
150,763 | [
"https://cs.stackexchange.com/questions/150763",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/149957/"
] | So, there's a LeetCode problem that has you find a O(log n) solution to finding a target number in a rotated sorted array.
As an example:
<pre><code>array = [5,6,7,1,2,3]
target = 4
</code></pre>
Basically, the trick is that you can find the point of rotation in O(log n) time and then you can do a binary search over th... | I think you essentially answered it yourself (and @Yves Daoust) with the point that there's an O(log(n)) trick.
<strong>We could say that it's the set of problems for which you can modify a known O(log(n)) algorithm by adding O(log(n)) operations.</strong>
You asked for "the conditions" under which an array c... | I would begin by considering the time complexity of an array in absolute worst or best case before concerning with any slight deviations from average. I don't know if you are going to get discernable results.
| https://cs.stackexchange.com |
285,111 | [
"https://softwareengineering.stackexchange.com/questions/285111",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/151252/"
] | This has been bothering me. This is more of a pragmatic problem than technical. Imagine I have a SaveOrderChanges method which, as its name implies, will save the order changes when the user submits the modified order.
But, before saving the order, I need to verify if the order submitted is actually from the current ... | You should choose the latter.
In making my decision, I decided to look at this from the maintenance programmer's perspective. Here's how I'd see each case:
<ol>
<li><code>VerifyOrder(order)</code> is inside <code>SaveOrderChanges(Order order)</code> so the verification is part of what <code>SaveOrderChanges()</code> ... | The first one; <code>SaveOrderChanges</code> should call <code>VerifyOrder</code>. Otherwise, some future coder will call <code>SaveOrderChanges</code> without calling <code>VerifyOrder</code>. An alternative that still prevents such an error is to call <code>VerifyOrder</code> outside <code>SaveOrderChanges</code>, ... | https://softwareengineering.stackexchange.com |
694,839 | [
"https://physics.stackexchange.com/questions/694839",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/297224/"
] | I'm aware that the spin has no classical analogue, and at the same time it is sometimes useful to think of it as a spinning of a small sphere.
When we follow the analogy one would say that the spin momentum will point 'up' or 'down' respect, say, an external field.
My simple question is this one:
<ul>
<li>Does the tota... | In quantum mechanics, there simply are no unsymmetrized states, in the Hilbert space for identical bosons. By definition, all states are completely symmetric between the exchange of identical bosons. There is no arbitrary rule that says that some states are symmetrized, and others not.
Therefore, your friend is correct... | I agree the answer from Andrew: the Hilbert space for identical bosons only has symmetric states. Another point worth making is that if two particles are identical then any Hamiltonian describing their dynamics will be symmetric with respect to exchange of those particles and it follows that the joint state will never ... | https://physics.stackexchange.com |
430,035 | [
"https://physics.stackexchange.com/questions/430035",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/172146/"
] | I know that the universe:
<ol>
<li>It's around 13.772 billion years old</li>
<li>It expands</li>
</ol>
But it's not clear to me if this is not merely the age of the farthest known photons which reached Earth.
| Possibly you are making the mistake of thinking of the universe as expanding from some central explosion? That is not so. All parts of the universe were part of the big bang.
The "oldest" light we can see was emitted about 13.7 billion light years ago, approximately 400,000 years after the big bang. That light has tra... | After the Big Bang the universe was full of hot plasma, which both absorbed and emitted photons. The result was that the oldest photons we can see come from the end of that era (a few hundred thousand years after the big bang); they make up the cosmic microwave background today.
The age of the universe is calculated ... | https://physics.stackexchange.com |
3,715,131 | [
"https://math.stackexchange.com/questions/3715131",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/557708/"
] | Let <span class="math-container">$f$</span> be defined on the rectangle <span class="math-container">$Q =[0,1] \times [0,1]$</span> as follows
<span class="math-container">$$f(x,y) = \begin{cases} 1 \ \text{if}\ x=y \\0 \text{ if } x \neq y \end{cases}$$</span>
Evaluate the double integral <span class="math-containe... | You made a mistake in your substitution. You should have
<span class="math-container">$$\int_{0}^{1} \int_{0}^{1} f(x,y)\,dx\,dy
=\int_{0}^{1} \left(\int_{0}^{1} 1_{\{y\}}(x)\,dx\right)\,dy
=\int_{0}^{1}0 \,dy=0\;. $$</span>
This is because the definition <span class="math-container">$f$</span> tells you that for every... | <h2>Hint:</h2>
<span class="math-container">$\int_{0}^{1} \int_{0}^{1} f(x,y)dxdy=0$</span>
Just observe that the measure of <span class="math-container">$\{(x,y) \in \mathbb{R}^2: x=y\}$</span> has Lebesgue measure <span class="math-container">$0$</span>.
| https://math.stackexchange.com |
149,669 | [
"https://electronics.stackexchange.com/questions/149669",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/64553/"
] | I have a heavy 14.4V 1.5A heavy battery charger I would like to use to charge my car battery (over time, monitored for heat in a well ventilated area).
When I plug the battery to the charger as is, I believe it turns off as the led doesn't turn on and the Voltage I read is 10.8 which is what the battery is at. When... | It looks like you're trying to repurpose a charger that was originally intended for some sort of tool battery, judging from the socket built into the case.
It also appears that said battery leaked at some point into the charger, given all of the crud all over the case, contacts and PCB.
You really need to clean the c... | The charger appears to be unfiltered, so it will produce pulsating DC - this is not a problem for battery charging. Your meter is probably reading a sort of average of the pulsating DC, hence the apparent low voltage.
In any case, a 1.5 Amp charger is grossly undersized for charging a car battery, particularly one as... | https://electronics.stackexchange.com |
61,897 | [
"https://mathoverflow.net/questions/61897",
"https://mathoverflow.net",
"https://mathoverflow.net/users/10446/"
] | Consider some lattice in R^n.
Take some point "P" in R^n (which does not belong to this lattice in general).
What are the algorithms to find some nearest lattice point to "P" ?
"Nearest" - means in the sense of the standard Eucleadian distance.
Lattice - means the standard thing - takes some vectors h_1 ... h_n and c... | This problem is often called the "closest vector problem" for lattices (especially by people in theoretical computer science). The real issue is what sort of lattice you have. For example, for the integer lattice $\mathbb{Z}^n$ the problem is easy, and it's not too hard to do it for other famous lattices, for example... | My guess is that this is going to be hard to solve in reasonable time if you have a large number of dimensions (thousands or more), and don't exploit any particular 'nice' features your lattice might have.
However, I believe it is in NP. The following, while probably impractical, should in theory do what you are askin... | https://mathoverflow.net |
84,726 | [
"https://chemistry.stackexchange.com/questions/84726",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/38667/"
] | My professor says that the most probable point for finding an electron
in a 1s orbital of a hydrogen atom is at its origin.
He explains this by citing the fact that the square of the wave function which gives the probability density is maximum at the origin.
At the same time, we all agree that the Bohr radius is the ... | I provide here a few supplementary comments; the major part of your question has been answered by DSVA.
<ul>
<li>For the electron's position in a 1s orbital, the probability density $\rho(r)$ is maximal at the origin, whereas the radial probability density $p(r)$ is maximal at the Bohr radius.</li>
<li><em>probability... | It makes a difference if you look in a point or in a volume element.
For the radial distribution we sum up the probabilities within (very thin) shells at different distances from the core.
If the radius get's bigger the volume in this shell gets bigger.
Remember that the surface of a sphere goes by $4 \cdot \pi \cdot... | https://chemistry.stackexchange.com |
31,174 | [
"https://dsp.stackexchange.com/questions/31174",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/21251/"
] | If we're to capture an image of a body using four (4) WebCam with a 16 megapixel (1 in the front, 1 in the back and 2 sides(left and right)). Is it possible to make a 3D out of it using image processing?
| Consider a discrete-time input signal of the form:
<span class="math-container">$$ x[n] = \cos(\omega_0 n) ~~~,~~~-\infty < n < \infty, ~~~~~ n\in \mathcal{Z}$$</span>
where the radian frequency <span class="math-container">$\omega_0$</span> is set between 0 and <span class="math-container">$\pi$</span> radians p... | You have probably used filtering a lot already. A moving average is a filter!
Think of general filtering as performing a fancy moving average where instead of averaging every component in a window equally, you weight the components.
If you just wanted to smooth the signal you could weight each value used in the avera... | https://dsp.stackexchange.com |
90,588 | [
"https://biology.stackexchange.com/questions/90588",
"https://biology.stackexchange.com",
"https://biology.stackexchange.com/users/-1/"
] | I have often heard a vague claim that bees help flowering tree populations survive.<br>
As far as I know, bees take nectar and pollen concentrations from the flowers of flowering trees and use at least the nectar as a food source, but they don't take seeds out of these trees, so it's unclear to me how they help these t... | You can put any media in a GasPak or other anaerobic system depending the type of anaerobic growth you are looking for. Sometimes blood is simply added to media to meet nutritional requirements of an organism. I use Columbia Blood agar often as a general purpose anaerobic medium. In a collection of 100+ obligate anaero... | Blood agar is prepared by heating the blood so that there will be lysis of RBC. Blood agar is mostly used to grow pathogenic organisms such as Haemophilus influenzae and Neisseria gonorrhoeae which cannot grow on other media.Neisseria gonorrhoeae can grow in the absence of oxygen. Haemophilus influenzae which is a facu... | https://biology.stackexchange.com |
292,241 | [
"https://mathoverflow.net/questions/292241",
"https://mathoverflow.net",
"https://mathoverflow.net/users/-1/"
] | Let $k$ be a field, $X$ a smooth projective variety over $k$, $\overline{X} := X\times_k {k}^{\rm sep}$ for a separable closure ${k}^{\rm sep}$ of $k$, $\ell$ a prime with $\ell\in k^{\times}$.
<blockquote>
Are the Galois cohomology groups $$H^i(\text{Gal}({k}^{\rm sep}/k),H^j_{\rm ét}(\overline{X},\mathbf{Z}_{\ell}... | I'm not sure what's going on with this question, but let me drop a few lines to summarize what the official position should be.
First off, I can't think about any situation these groups may occur beyond that of a Hochschild-Serre spectral sequence, so I hope group cohomology here is meant to be continuous group cohomo... | It is not known, I think. For $X$ a point, $k$ a number field, $j=0$, $i=2$, you get the statement that $H^2(k,\mathbb Q_p)=0$ which is Leopoldt's conjecture.
| https://mathoverflow.net |
286,928 | [
"https://softwareengineering.stackexchange.com/questions/286928",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/26765/"
] | I'm a contractor that has recently started with a firm.
Team is 3 developers consisting of 2 junior to mid level devs, with another at the same level starting soon, and myself (6 Years xp). For both the existing developers it is their first job out of university/college, and they've never had a senior developer overs... | For a team of 3-4 devs, you're proposing WAY too many branches.
Every branch you create is additional overhead that comes with a cost (time spent merging, keeping track of what's where, etc). You need to make sure that the benefit you get from having a branch outweighs the cost.
Keep in mind that the only real ben... | You've written down a few pointers for them, but <strong>you haven't explained why is your approach <em>better</em> than the one they already use</strong>. This may be problematic. If you're in a spirit “We'll do it my way, because I have six years of professional experience, and you don't” (and reading your question, ... | https://softwareengineering.stackexchange.com |
4,731 | [
"https://physics.stackexchange.com/questions/4731",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/622/"
] | 1.In classical mechanics, using Newton's laws, the ellipticity of orbits is derived. It is also said that the center of mass is at one of the foci.
2.Each body will orbit the center of the mass of the system.
My question is : Are the assumptions in 1 and 2 correct?
Follow up question : Assuming the distance from t... | <img src="https://i.stack.imgur.com/6j9DX.gif" alt="Tides & second focus">
The second (empty) focus is relevant in the theory of tides. In an elliptical orbit, the line joining the planet and the empty focus rotates at the same frequency as the mean motion of the planet; therefore, if spin rotation period is equal... | Your assumptions are correct. The classical solution to the two-body problem is that each mass goes in an elliptical orbit, and one focus of each ellipse is at the center of mass.
In the special case that the distance from the center of mass to each body remains constant, that means both orbits are circular, a circle ... | https://physics.stackexchange.com |
1,583 | [
"https://security.stackexchange.com/questions/1583",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/134/"
] | I am dealing with a small business that I have no choice right now but to deal with. I do not work for this business but my personal life dictates that I use them right now. I noticed a few months ago that they have a wireless network setup with WEP encryption (and a really weak key...don't ask), no MAC filter and the ... | No matter what size the business, in my experience the only three ways to get a provider to move on this are:
<ul>
<li>Financial: Tell them you'll take your business elsewhere - I understand this isn't possible here.</li>
<li>Regulatory: If they are dealing with personal information they must provide appropriate prote... | Have pity on the business and find out who their IT person is. Then go the "responsible disclosure" route. Tell the IT person you'll disclose their lax practices publicly (probably without disclosing the business itself) if they don't fix it soon.
| https://security.stackexchange.com |
239,076 | [
"https://security.stackexchange.com/questions/239076",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/243551/"
] | For example, can you reference a customer by their domain in an email?
Each customer in a system can be associated with a domain, and some domains are associated with a single customer.
| The answer, as with all things "data protection" is, "it depends".
It's PII if it can be used to identify a natural person. That's your test.
If enough people share that domain <em>already in your system</em> that it would not be feasible to identify a natural person with it, then it is (probably) n... | Schroeder awnsered this better.
But basically a domain is only considered PII if it’s possible to derive a person from it.
Thereby making it a PII.
Doing this is a really bad idea since the DNS system requires that anyone can cache the data by design.
This means anyone can make copies of the data.
In regards to mail se... | https://security.stackexchange.com |
34,453 | [
"https://dba.stackexchange.com/questions/34453",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/18984/"
] | I really like using sp_whoisactive v11.11 by Adam Machanic. But when then info is displayed, the DB name is at the very end. I would like it to in the very first columns so I don't have to scroll everytime... Does anyone have suggestions to arrange columns
| Edit the line with @output_column_list declared on it and put [database_name] between [dd%] and [session_id].
When I scripted it out it was on line 110.
| Change the code. Or ask Adam Machanic to change it.
| https://dba.stackexchange.com |
41,293 | [
"https://cs.stackexchange.com/questions/41293",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/30523/"
] | In the examples I was given I have the following NFA diagram:
<img src="https://i.stack.imgur.com/wxzQY.png" alt="enter image description here">
Then it gives the conversion process<img src="https://i.stack.imgur.com/qLlDG.png" alt="enter image description here">
Could someone explain to me the process of obtaining t... | This is the standard procedure for converting NFAs to DFAs. The first row should be read as "If you know you're in one of the states $0$, $1$ and $4$ and you read an $a$, you'll have to be in one of the states $1$, $2$ and $4$; if you read a $b$, you'll have to be in one of $1$, $4$ and $5$." The other rows are similar... | You should do
$$\begin{align*}\delta_d(\{1, 2, 4\}, a) &= \delta(1, a) \cup \delta(2, a) \cup \delta(4, a)\\
&= \{1, 2, 3, 4\}\\[2ex]
\delta_d(\{1, 2, 4\}, b) &= \delta(1, b) \cup \delta(2, b) \cup \delta(4, b)\\
&= \{1, 4, 5\}
\end{align*}$$
| https://cs.stackexchange.com |
4,624,896 | [
"https://math.stackexchange.com/questions/4624896",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/1135823/"
] | <span class="math-container">$a$</span>, <span class="math-container">$b$</span> and <span class="math-container">$c$</span> of all Pythagorean triplets can be written in the form
<span class="math-container">$$
\begin{split}
a &= 2mn\\
b &= m^2-n^2 \\
c &= m^2+n^2
\end{split}
$$</span>
where <span class="m... | Hint: For <span class="math-container">$a^2+b^2=2c^2$</span>, observe that <span class="math-container">$a, b$</span> have the same parity. Therefore there exist integers <span class="math-container">$u, v$</span> such that <span class="math-container">$a = u+v$</span> and <span class="math-container">$b = u-v$</span>.... | Noting that
<span class="math-container">$a^2+b^2=2c^2 \Rightarrow a $</span> and <span class="math-container">$b$</span> are of same parity. Hence there exists natural numbers <span class="math-container">$u$</span> and <span class="math-container">$v$</span> such that
<span class="math-container">$$a+b=2u \textrm{ an... | https://math.stackexchange.com |
83,487 | [
"https://mechanics.stackexchange.com/questions/83487",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/65262/"
] | I noticed While driving my car the fuel refills last me a lot longer when I go for the full tank over the half tank. I feel that it takes a lot longer to go through the upper half of the tank than the bottom half of the tank. I felt that keeping a full tank of gas is beneficial over the long run.
Does having air in the... | No. If anything you'll get worse gas mileage with a full tank because you're carrying a heavier load (more fuel = more weight).
What you are most likely experiencing is the top half of the tank is larger than the bottom half (in general terms). In other words, the sending unit (float level) in the gas tank most likely ... | The best way to determine the actual fuel consumption is to brim the tank, drive till nearly empty then brim the tank again.
Then you have an exact volume of fuel and a specific distance.
Repeat over three or four tanks and you will have an accurate fuel consumption figure based on your actual use.
The gauge is not lin... | https://mechanics.stackexchange.com |
61,859 | [
"https://security.stackexchange.com/questions/61859",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/46285/"
] | Is it possible to white list an IP address in mod_security?
I found white ist whole domain name in mod_security. But I want to white list only the administrator IP.
OS: CentOS 6
Server: Apache httpd 2.15
Mod Security: Version 2.7
| Found the way.
<pre><code>vim /etc/httpd/modsecurity.d/activated_rules/modsecurity_crs_10_whitelist.conf
</code></pre>
And add this line:
<pre><code>SecRule REMOTE_ADDR "^192\.168\.50\.1$" phase:1,log,allow,ctl:ruleEngine=Off,id:999945
</code></pre>
| I use modsec version 3 and in my case there wasn't a modsec configuration file in the location <code>/etc/httpd/modsecurity.d/activated_rules/modsecurity_crs_10_whitelist.conf</code> but there was one in:
<pre><code>/etc/modsecurity/crs/REQUEST-900-EXCLUSION-RULES-BEFORE-CRS.conf
</code></pre>
in this file the follow... | https://security.stackexchange.com |
20,616 | [
"https://physics.stackexchange.com/questions/20616",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/5129/"
] | After years of procrastinating i've decided not to "move ahead" with physics without getting this ridiculously trivial question clear!*I know i had asked a similar question as silly and stupid as this one, however for some reason this equation keeps haunting me cause i see it almost everywhere in kinematics!
We know... | Suppose you are holding an apple. You obviously know where the apple is, and as long as you don't drop the apple you can predict it's future position. But suppose you now drop the apple and you want to predict where it will be in one second, two seconds or even ten seconds if you're standing on a tall building. As soon... | Note that the equation you give for position only applies under conditions of <em>constant acceleration</em>.
That is you already have a particle under acceleration.
Now, by definition
$$a = \frac{\mathrm{d}v}{\mathrm{d}t} = \frac{\mathrm{d}^2x}{\mathrm{d}t^2} $$
In other words you care about acceleration and veloc... | https://physics.stackexchange.com |
102,164 | [
"https://mathoverflow.net/questions/102164",
"https://mathoverflow.net",
"https://mathoverflow.net/users/24864/"
] | I think this is not a research question, but in stackExchange remained unanswered.
Let $R$ be a finite commutative ring. For $n>1$ consider the full matrix ring $M_n(R)$ . For a matrix $A\in M_n(R)$ is true that the cardinality of the left annihilator (in $M_n(R)$ ) of $A$ equals the cardinality of the right an... | Let $k$ be a finite field, and let $R := k[X,Y] / (X^2,XY,Y^2)$. Then $R = k \oplus kx \oplus ky$ is a finite ring of order $|k|^3$ with maximal ideal $\mathfrak{m} := kx \oplus ky$ of square zero.
Now let $A = \begin{pmatrix} 0 & x \newline 0 & y \end{pmatrix} \in M_2(R)$. Then
$\begin{pmatrix} 0 & x \ne... | First note that $R$ as a finite ring is (like any Artinian ring) is a finite product of local rings: $R=\prod_i R_i$. Hence $M_n(R) =\prod_i M_n(R_i).$ So if we write $A=A_1 \times \cdots A_n$ with $A_i \in M_n(R_i)$, then $$\text{Ann}^l(A) = \text{Ann}^l(A_1) \times \cdots \text{Ann}^l(A_n)$$ and analogous for the rig... | https://mathoverflow.net |
1,721 | [
"https://mathoverflow.net/questions/1721",
"https://mathoverflow.net",
"https://mathoverflow.net/users/66/"
] | We all know how to take integer tensor powers of line bundles. I claim that one should be able to also take fractional or even complex powers of line bundles. These might not be line bundles, but they have some geometric life. They have Chern classes, and one can twist differential operators by them. How should I t... | Complex powers of line bundles are classes in $H^{1,1}$, or equivalently sheaves of twisted differential operators (TDO) (let's work in the complex topology). This maps to $H^2$ with $\mathbb{C}$ coefficients, or modding out by $\mathbb{Z}$-cohomology, to $H^2$ with $\mathbb{C}^\times$ coefficients. The latter classif... | To any homomorphism of Lie groups $\phi: G \to H$, and any principal $H$-bundle $P$ over a space $X$, you can associate what I like to call the "gerbe of liftings," namely the stack over $X$ whose objects over $f: Y \to X$ consist of a principal $G$-bundle $Q$ together with an isomorphism $Q_\phi \cong f^* P$. Here $Q... | https://mathoverflow.net |
9,211 | [
"https://dsp.stackexchange.com/questions/9211",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/4580/"
] | I have DSP in my academics and while going through the video lectures i am stuck regarding power of periodic signal.
Its mentioned as
$$P_{\text{avg}}= \frac{1}{N}\sum_{n=0}^{N-1}|x(n)|^2$$
my doubt is why we have to mention $|x(n)|$ as square ?
Note: I am having format issues please edit my Question and put it in... | Power or energy are always squared quantities. If you consider simple circuits as an example, then power is $V^2/R$ or $I^2R$ (with $V$ voltage, $I$ current, and $R$ resistance). For time-varying signals, the power or energy is computed by a time average of the squared signal. For stochastic signals, the power is defin... | Power is proportional to the squared amplitude of a signal. This "power" concept comes from thinking of the signal $x[n]$ as representative of a voltage or current waveform. In that model, the power dissipated by applying $x[n]$ to a one-ohm resistor is the value of $|x[n]|^2$ averaged over one period.
| https://dsp.stackexchange.com |
524,539 | [
"https://physics.stackexchange.com/questions/524539",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/209730/"
] | The Branching fraction formula for a particular decay is <span class="math-container">${\cal {B}}(B \rightarrow X)=\Gamma_{B\rightarrow X/\Gamma_B}$</span>. But experimentally formula is written as <span class="math-container">${\cal {B}}(B \rightarrow X) = N_{obs}/(N_{BB}\times \epsilon)$</span>. Where <span class="... | Here, I change the variable names for more pedagogic ones : <span class="math-container">$X$</span> for the resonance <em>produced</em>, <span class="math-container">$f$</span> for final state (the particle to which <span class="math-container">$X$</span> decays). The couple {<span class="math-container">$X$</span>, f}... | Im not working in this fields, however, I would use a <strong>weighted average</strong> to define the <strong>observed</strong> branching ratio into the <span class="math-container">$i^{th}$</span> decay branch,
<span class="math-container">$$
BR_i^{\textrm{(obs)}}
:= \frac{N_i^{\textrm{(obs)}} }{\sum_i N_i^{\textrm{... | https://physics.stackexchange.com |
146,243 | [
"https://cs.stackexchange.com/questions/146243",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/145802/"
] | I am looking for a reference to a proof that for every list of size <span class="math-container">$n$</span> comparison-based sorting cannot make less than <span class="math-container">$n-1$</span> comparisons. Do you have a reference of a book that covers it (with page specification)? Or a scientific publication that c... | Here is an easy argument that relies on the well-known lower-bound of <span class="math-container">$\log_2 n!$</span> on the number of comparisons needed by any comparison-based sorting algorithm (which you can find in any textbook. See, for example, Theorem 8.1 in Cormen, Leiserson, Rivest, Stein, "Introduction t... | Let us show a different bound, that will suffice for a "loose" bound of <span class="math-container">$n-1$</span>.
On this note, the answer above gives you the tight bound of <span class="math-container">$\Theta(n\log n)$</span>, which is stronger than the one you are trying to prove.
<span class="math-contai... | https://cs.stackexchange.com |
413,172 | [
"https://stats.stackexchange.com/questions/413172",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/250992/"
] | Would the probability of an event A and its complement occurring always be 0? Is there any case it would not equal 0?
| It's <span class="math-container">$0$</span> because <span class="math-container">$A$</span> and <span class="math-container">$A'$</span> are mutually exclusive events. An event cannot result in two different outcomes at the same time. Mathematically, you're trying to find the probability of empty set (since <span clas... | <span class="math-container">$A \cap A^C$</span> is empty, and so <span class="math-container">$P(A \cap A^C) = P(\varnothing) = 0$</span>
| https://stats.stackexchange.com |
10,752 | [
"https://electronics.stackexchange.com/questions/10752",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/1225/"
] | Okay, here's the situation: Currently, I am making a small batch of 100 boards of my project. This is a small order, so start up costs are about 10% of the final cost, and the factory charges $50/hour (they say I can get it done in one or two hours.) These will be made in China. Places in the UK or USA won't even talk ... | <ol>
<li>Most of these local companies in fact will outsource your order to China.</li>
<li>You don't need to print 'Made in China' if you just ordered PCB from China.
'Made in' means place of last significant tech operation, so if Arduino's PCB is from China, but soldering is local - 'Made in Italy' is legitimate.</l... | If you do a 2 sided PCB and plan on doing one sided mounting all SMT except for minimal throughole.
Then, when you order your PCBs, you can order a solder paste template. You can put together a wooden holder with a bottom into which the board fits exactly. Pop in a PCB, place the solder template in there, then put som... | https://electronics.stackexchange.com |
148,736 | [
"https://cs.stackexchange.com/questions/148736",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/147486/"
] | I haven't been able to track down if there is a generally accepted practice for assigning a Big O value when dealing with functions of unknown runtime.
Given the following pseudocode, with two functions that operate in an unknown time, is it typical to assume the processing is constant time, or would it be more correct... | It depends on the situation. Sometimes we treat function calls as "oracle calls", and then we just count oracle calls. Your function makes <span class="math-container">$n$</span> oracle calls to the first function, and one oracle call to the second function.
Another option is to denote the running time of the... | The mathFunction1 and mathFunction2 must not be unknown. Either
<ol>
<li>no known algorithm exists for one or both of them (and it is incumbent on you to provide at least a strawman feeble/naïve attempt at that algorithm) or</li>
<li>one or more algorithms exist for both of them.</li>
</ol>
If the latter situation, th... | https://cs.stackexchange.com |
168,259 | [
"https://stats.stackexchange.com/questions/168259",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/80676/"
] | I have two correlation matrices, one with a condition number of 9 and the other with a condition number of 70. From what i have read, it will appear that the first matrix is better conditioned than the other based on these figures alone, but i am struggling to really interpret how much better one correlation matrix is... | The condition number of a correlation matrix is not of great interest in its own right. It comes into its own when that matrix gives the coefficients of a set of linear equations, as happens for multiple linear regression using standardized regressors.
Belsley, Kuh, and Welsch--who were among the first to point out an... | Super high condition number would mean that some variables are highly correlated. 70 is not that big of a condition number to me.
High or low condition number doesn't mean that one correlation matrix is "better" than the other. All it means is that variables are more correlated or less. Whether it's good or not depend... | https://stats.stackexchange.com |
714,125 | [
"https://physics.stackexchange.com/questions/714125",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/317779/"
] | <em>if the velocity vector <span class="math-container">$\overrightarrow{v}=v\widehat{i}$</span> ,, we define the accelration vector as it's the time derivative of the velocity vector</em> <span class="math-container">$\overrightarrow{a}=(\frac{dv }{dt})\widehat{i}$</span>
We know that when dealing with ... | In rectangular coordinates, the general equation for the velocity (or any) vector is
<span class="math-container">$$\vec v=v_{x}\hat i+v_{y}\hat j+v_{z}\hat k$$</span> where the values <span class="math-container">$v_x$</span>, <span class="math-container">$v_y$</span> and <span class="math-container">$v_{z}$</span> a... | By convention, the magnitude of a vector is always of a non-negative number. So for a vector <span class="math-container">$\vec{a} = (-5) \hat{\imath}$</span> the interpretation is as follows
<span class="math-container">$$ \vec{a}\;\;\; = \underbrace{5}_\text{magnitude}\;\;\; \underbrace{-\hat{\imath}}_\text{direction... | https://physics.stackexchange.com |
44,903 | [
"https://electronics.stackexchange.com/questions/44903",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/14199/"
] | I have been working on this program for a simple controller. I have a prototype all wired up and working however the momentary push button is not very reliable. Sometimes it reads and other times it ignors it.
Here is my code.
<pre><code>/*
* Valve Purge Control/heater control
*/
#include <math.h>
int feedVa... | EDIT: Button is connected like this:
<img src="https://i.stack.imgur.com/khFZk.png" alt="ButtonConnection">
If there was no pull-up, one would put the following in setup()
<pre><code>pinMode(button, INPUT);
digitalWrite(button, HIGH);
</code></pre>
An interrupt is an event that 'pauses' the main program, runs a fu... | The way your code is written, it is spending a <em>lot</em> of time in <code>delay(5000)</code> calls. This could easily explain missed button presses.
Every time the Arduino operating system calls your <code>loop()</code> function, as long as the state of the button is stable, you'll enter the <code>if (val == val2) ... | https://electronics.stackexchange.com |
374,761 | [
"https://mathoverflow.net/questions/374761",
"https://mathoverflow.net",
"https://mathoverflow.net/users/121665/"
] | It is probably an easy question, but somehow I am stuck.
<strong>Question</strong> Is the following statement true? If yes, how to prove it?
<blockquote>
Suppose that <span class="math-container">$f\in C^1(\mathbb{R}^n)$</span> is convex and
<span class="math-container">$$
\langle\nabla f(x)-\nabla f(y),x-y\rangle \leq... | That's a standard result in convex optimization. For example Theorem 2.1.5 in Nesterov's "Introductory Lectures on Convex Optimization" states that the following are equivalent:
<ul>
<li><span class="math-container">$f$</span> is <span class="math-container">$C^1$</span>, convex and the gradient <span class="... | <strong>Yes</strong>
Consider first the case where <span class="math-container">$f\in{\cal C}^2$</span>. Then
<span class="math-container">$$\nabla f(y)-\nabla f(x)=\int_0^1{\rm D}^2f(x+t(y-x))\cdot(y-x)\,dt.$$</span>
There follows
<span class="math-container">$$\|\nabla f(y)-\nabla f(x)\|\le\|y-x\|\int_0^1\|{\rm D}^2f... | https://mathoverflow.net |
36,747 | [
"https://scicomp.stackexchange.com/questions/36747",
"https://scicomp.stackexchange.com",
"https://scicomp.stackexchange.com/users/38115/"
] | I am attempting to create a conditional statement that compares four (4) true/false conditions. Depending on the state of these four conditions (either true or false) the conditional statement will either pass or fail. I have a table that tells me the outcome (pass/fail) of all possible permutations. 2^4 = 16 possible ... | One approach would be to use the direct binary representations of your conditions. That means that, e.g. the first two columns could be represented by:
(A True, B True, C False , D False) --> ( 1100)<br />
(A True, B True, C True , D False) --> ( 1110)<br />
...
You can then define your conditions expressed ... | Note that the if-then-else variant you posted can be shortened further by using the negation "!". If the number of conditions stays relatively low, you can do one-liners like this:
<pre><code>if( A and B and !C and !D) pass();
if( A and B and C and !D) pass();
if( A and B and !C and !D) pass();
if(!A and ... | https://scicomp.stackexchange.com |
190,379 | [
"https://softwareengineering.stackexchange.com/questions/190379",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/56691/"
] | I was recently creating a small technical documentation for an application. The document is to be used by newly hired programmers to get acquainted with the application. It is much friendlier than the Javadocs we have, and includes information that usually isn't being documented.
When describing a function, I first br... | Post-edit #1 - my answer works equally well for argument names or specifying the variable type, which is what I first read your question as. My answer is driven in part because I had a similar discussion recently with the use of C#'s <code>var</code> auto-typing keyword and a code sample we received.
In my answer"it"... | If you ever intend to generate documentation from the header files it might be a good idea to include the names
| https://softwareengineering.stackexchange.com |
206,358 | [
"https://electronics.stackexchange.com/questions/206358",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/94631/"
] | Currently, I'm doing my wind turbine electrical project. Let me get straight to the topic, wind turbine, with a small generator in it. Lets say it can produce 2V and less than 1A . It is connected to an inverter to increase its voltage. Now my idea is to connect the output to a load, where I will need more than 30A. D... | You can't cheat physics. You can convert between different voltage and current tradeoffs, but you can't make more power out than in. Power is Volts x Amps, so whatever Volts x Amps you convert to can't exceed the Volts x Amps you have coming into the converter. Actually the output will be a bit less due to inevitabl... | <blockquote>
Let say it can produce 2v and less than 1A
</blockquote>
That's a power of 2 watts in
<blockquote>
It is connected to an inverter to increase its voltage. Now my idea is
to connect the output to a load, where I will need more than 30Amps
</blockquote>
If voltage increased to 2.0000001 volts the po... | https://electronics.stackexchange.com |
3,522,288 | [
"https://math.stackexchange.com/questions/3522288",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/657147/"
] | <span class="math-container">$Problem:$</span>
Let <span class="math-container">$$\sum_{n=0}^\infty c_nx^n$$</span>
be convergent when <span class="math-container">$x=-4$</span> and divergent when <span class="math-container">$x=6$</span>. What can we say about the convergence or divergence of the following series?
... | Yes, the solutions you provided itself are correct. Well done!
Maybe one remark can be useful here: <span class="math-container">$I= |a_{n+1}/a_n| < 1$</span> doesn't make much sense, because <span class="math-container">$I$</span> is an interval (not depending on <span class="math-container">$n$</span>). This happ... | The ratio test doesn't always work to determine the radius of convergence. That it exists is clear, because we can define it as the supremum of all positive numbers <span class="math-container">$x$</span> such that the series converges absolutely. If this supremum <span class="math-container">$R$</span> is <span class=... | https://math.stackexchange.com |
9,912 | [
"https://chemistry.stackexchange.com/questions/9912",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/302/"
] | Ok, so the following question is given in my text book.
<blockquote>
Of the molar conductance value of $\ce{Ca^2+}$ and $\ce{Cl^-}$ at infinite dilution are respectively $118.88\times10^{-4}$ and $77.33\times10^{-4}$ then that of $\ce{CaCl2}$ is (all have same unit)
</blockquote>
So what I did was I added the mol... | Yes, the process is correct, but do you understand why?
| You are calculating limiting molar conductivity
<blockquote>
limiting molar conductivity = V<sub>+</sub> A<sub>+</sub> +
V<sub>-</sub> A<sub>-</sub>
V<sub>+</sub> = number of cations per formula unit of the
electrolyte
V<sub>-</sub> = number of anions per formula unit of the
electrolyte
A<sub>+</sub> = molar cond... | https://chemistry.stackexchange.com |
129,456 | [
"https://dba.stackexchange.com/questions/129456",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/57174/"
] | There is a table in my database that starts with the <code>@</code> symbol. I am able to query it successfully using the following query:
<pre><code>select * from [@tablename]
</code></pre>
This format works in SSMS and Crystal Reports.
However, I have a C# application where the same query give an 'invalid object... | I do not believe that there is a specific problem with referencing tables, in C#, having names starting with <code>@</code>. I was able to create a table with a name of <code>@TableName</code> and was able to execute <code>SELECT SUM(Col1) FROM [@TableName];</code> successfully. I used <code>SqlConnection</code> and <c... | <pre><code>con.Execute("SELECT H.DocEntry, DocNum, LineId, CreateDate, Creator" +
" FROM \"@RETURNABLEGP_H\" H" +
" INNER JOIN \"@RETURNABLEGP_R\" R ON H.DocEntry = R.DocEntry" +
" WHERE CreateDate = '2022-01-06'&quo... | https://dba.stackexchange.com |
138,690 | [
"https://physics.stackexchange.com/questions/138690",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/60433/"
] | A stone is released from an elevator going up with acceleration of $g/2$. What is the acceleration of the stone just after the release?
The answer is $g$. Shouldn't the stone carry the acceleration of the elevator and be $-g/2$?
| While the stone is still travelling on the elevator, there are two forces acting on it, the force from the elevator to the stone, as well as the weight due to gravity.
<img src="https://i.stack.imgur.com/6T6BJ.png" alt="enter image description here">
The moment the stone leaves the elevator, it becomes a free falling... | Acceleration only happens if a force is acting on an object. When you are holding the stone, the force which is accelerating the elevator is transmitted to the stone through your grip and you, the elevator and the stone form a single rigid collection of objects all accelerating at g/2.
When you let go the only force ... | https://physics.stackexchange.com |
14,162 | [
"https://softwareengineering.stackexchange.com/questions/14162",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/2294/"
] | I'm trying to decide if I need to reassess my defect-tracking process for my home-grown projects. For the last several years, I really just track defects using <code>TODO</code> tags in the code, and keeping track of them in a specific view (I use Eclipse, which has a decent tagging system).
Unfortunately, I'm starti... | Fogbugz (free individual license) if its a longish project or a simple to do list (using Google tasks)
| I usually use a web based revision control system(Github, Bitbucket, Redmine, Google Code, ...) to store my source code and track bugs. If you think there's a bug in a specific code, you can create an issue with the revision number/changelist/changeset and specify which file and the range of lines you suspect.
| https://softwareengineering.stackexchange.com |
815,951 | [
"https://math.stackexchange.com/questions/815951",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/-1/"
] | How do I show that $\lim_{x \rightarrow \infty}(1+\frac{a}{x}+\frac{b}{x^{3/2}})^x = e^a$? Actually, I had to deal with something similar yesterday and after thinking about it for quite a while I did it with L'Hospital's rule, but this was very unsatisfactory for me. I am rather interested in a more algebraic proof th... | I am expanding the hint in comments. In dealing with limits of expression of type $\{f(x)\}^{g(x)}$ it is much better to take logs rather than write complicated exponents. Let the limit be $L$. Then we have $$\begin{aligned}\log L &= \log\left\{\lim_{x \to \infty}\left(1 + \frac{a}{x} + \frac{b}{x^{3/2}}\right)^{x}... | HINT:
$$\left(1+\frac ax+\frac b{x^{\frac32}}\right)^x=\left[\left(1+\frac{a\sqrt x+b}{x^{\frac32}}\right)^{\frac{x^{\frac32}}{a\sqrt x+b}}\right]^{\frac{a\sqrt x+b}{\sqrt x}}$$
| https://math.stackexchange.com |
16,779 | [
"https://stats.stackexchange.com/questions/16779",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/5407/"
] | I have a sort of philosophical question about when multiple comparison correction is necessary.
I am measuring a continuous time varying signal (at discrete time points). Separate events take place from time to time and I would like to establish if these events have a significant effect on the measured signal.
So I c... | Technically, when you do a visual preselection of where to do the test, you should already correct for that: your eyes and brain already bypass some uncertainties in the data, that you don't account for if you simply do the test at that point.
Imagine that your 'peak' is really a plateau, and you hand pick the 'peak' ... | Long ago, in one of my first statistics classes, I was reading about this in a text (I think it was an old edition of Cohen's book on regreession) where it said "this is a question about which reasonable people can differ".
It is not clear to me that anyone ever needs to correct for multiple comparisons, nor, if they ... | https://stats.stackexchange.com |
90,194 | [
"https://softwareengineering.stackexchange.com/questions/90194",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/15574/"
] | I work in a small development group with 3 developers. We are loosely managed and have no structure to the team. There is no designated team leader and the manager is fairly hands off. The Senior developer has been with the company for 4 years, in that time he has had a huge hand in setting up systems and keeping th... | Management won't change anything if they don't feel any pain.
If you allow management to be hands off (by fixing things and being successful) then you will be expected to continue fixing things and being successful.
After all -- from management's view -- things are fine. Stuff is getting done. You may feel stresse... | Next time he threatens to leave, ask your manager if you should start a knowledge transfer so you can get familiar with the parts of the system only he knows about.
If he's bluffing, your manager won't have any idea what you're talking about and you can inform them that he told you he was leaving in x weeks, then let ... | https://softwareengineering.stackexchange.com |
441,949 | [
"https://physics.stackexchange.com/questions/441949",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/52363/"
] | A rather obvious question perhaps but if I have a Hilbert space of dimension <span class="math-container">$d$</span> and <span class="math-container">$d$</span> is prime, I cannot possibly write my state as <span class="math-container">$$\rho = \sum_i p_i\rho_a\otimes\rho_b$$</span> simply because the dimensions don't ... | If the dimension is prime, there is no point in talking of two subsystems (which would be entangled), and thus no point in talking about entanglement (which is a property between two subsystems). Since, if subsystem 1 has dimension <span class="math-container">$d_1$</span> and subsystem 2 has dimension <span class="mat... | If the dimension of the Hilbert space is prime then the state is guaranteed to be <em>un</em>entangled, simply because it can't have any tensor factor spaces to count as subsystems.
| https://physics.stackexchange.com |
31,612 | [
"https://dba.stackexchange.com/questions/31612",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/8185/"
] | The failed job is a Litespeed transaction log backup, but also happens to fulls and diffs occasionally.
This same setup works on other servers without issue, and it's only a few times overnight that the error occurs, but it does happen every night at some point:
Error in SQL Server Agent Log:
"Logging on to SQL Serv... | I've seen this happen both with network DC issues and also with a system that had too many connections and not enough memory.
| There might be something useful in the SQL Server ERRORLOG file but probably not. It is probably a network timeout between the SQL Server and the domain controller.
| https://dba.stackexchange.com |
5,630 | [
"https://dba.stackexchange.com/questions/5630",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/2992/"
] | I have a legacy database server. The person who wrote it is long gone. There is no documentation at all just some comments in the code. Luckily, it is not that complicate but if I want to fix it (requests from users), it takes time to investigate all related database objects (tables, views, or stored procedures).
Rece... | If you don't:
<ul>
<li>it will be unmaintainable at some point because of OS, version, patch, whatever</li>
<li>hardware failure may force an upgrade at the wrong time</li>
</ul>
What you gain:
<ul>
<li>older code can be simplified with new constructs (eg ROW_NUMBER)</li>
<li>far better error handling (TRY/CATCH)</l... | GBN is spot on with his analysis - I'd just add that something that can buy you time, if your company has the technology, is to virtualise this legacy database server, either as a new build or as a clone/P2V. This will buy you time in that you'll be better protected against hardware failure.
| https://dba.stackexchange.com |
12,788 | [
"https://quant.stackexchange.com/questions/12788",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/2161/"
] | Self-financing is an important concept in financial product replicating, normally used in pricing.
I read about several ways to derive Black-Scholes-Merton (BSM) formula. Seems some approaches actually rely on replicating, implying the self-financing prerequisite. But it turns out that such approaches missed to check... | OK, I think now I got the point, after comparing to Shreve's "Stochastic calculus for finance I, The binomial asset pricing model", the simpler case.
The pricing theory in continuous time is:
<ol>
<li>Define the wealth process $X(t)$, by definition, it is self-financing: $$d X(t) = \Delta(t) dS(t) + r (X(t) - \Delta... | It is true that the self-financing property of the replicating portfolio seems not explicitly presumed nor shown in Shreve's derivation of the Black-Scholes formula. One may note that a replicating portfolio is by definition a self-financing portfolio which replicates the payoff.
The problem as I see is that Shreve is... | https://quant.stackexchange.com |
115,177 | [
"https://softwareengineering.stackexchange.com/questions/115177",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/38976/"
] | During last year, several of the projects of the company where I work failed.
We develop web software, that are not especially complicated (the most are CRUDS and search form about this data).
One of the problems that management has identified is the test phase.
Putting simple, our protocol is:
<ol>
<li>Analysis ... | P. Brian Mackey is right about TDD being useful - and any unit tests will improve things dramatically. As a tester, I can tell you that a thorough unit test suite dramatically decreases the number of bugs, <em>and</em> limits the remaining functional bugs to mostly a few predictable areas where I can focus my testing ... | Use Test Driven Development. This way you continually test and integrate functionality. In CRUD based development, I like to use a iCRUD interface. This makes it easy to setup my tests. Just create <code>ConcreteItemX</code> which implements <code>iCRUD</code> and setup the 4 tests (Create, Read Update Delete). Im... | https://softwareengineering.stackexchange.com |
52,318 | [
"https://datascience.stackexchange.com/questions/52318",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/74589/"
] | A group I work with wants to create its own plants data set that will be used for multiple projects like plant type classification and leaf segmentation for starters.<br>
They are willing to provide all the means necessary for the creation of this data set. A partner agriculture company is willing to assist with planti... | Yes, in deep learning (image classification) more is merrier and there are several ways to do this. The approach you have mentioned of taking N images every X days is ok if you have the workforce to complete this task. Another method would be to artificially blow up your dataset using image augmentation. This augmentat... | <h3>Well, it all depends on what you plan to accomplish with this dataset:</h3>
<ul>
<li>If you are planning on using drones to identify crops in the wild then you should use a drone to take the images and get images in the wild. (By in the wild I mean a free environment that differs from a lab or something like it)</... | https://datascience.stackexchange.com |
31,361 | [
"https://security.stackexchange.com/questions/31361",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/10574/"
] | Which is better?
<ol>
<li>Create tamper-proof encrypted password reset token which contains the user id and the expiration time within the encrypted token.</li>
<li>Generate a random token and store it in the database with the user id and expiration date. Look up the token when the user clicks the link.</li>
</ol>
An... | Creating a random token containing absolutely no information and linking it in the database with a username and an expiration time is by far the best solution.
Encryption (and hashing) is used to store and transfer data that absolutely must be sent. If there is any way to do something without having to send that da... | You could encode the expire time into a token and use an HMAC, but generally a password reset involves visiting a specific URL. Usually to make things easier for the user, one includes the token in the URL as a GET field.
Wanting to keep the URL relatively small and only made of printable characters, you'd probably en... | https://security.stackexchange.com |
20,800 | [
"https://electronics.stackexchange.com/questions/20800",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/5963/"
] | I'm trying to do find the voltage over R1 in the following circuit, where L1/L2 is an ideal transformer. LTSpice complains that the "Matrix is singular". Why? I've tried to play around with lots of different values in order to see if it's a problem with approximation.
<img src="https://i.stack.imgur.com/fWmpT.png" alt... | You need a DC path between the two circuits. Put a high value resistor between them, say 10M.
I checked that it worked using Pulsonix (actually SIMetrix) SPICE. I got a singular matrix error without the resistor.
| There is a SPICE parameter called RSHUNT which adds shunt resistors to GND on every node. By default it is usually set to ZERO (that meaning no shunt resistors). If you make this a very high value (1e12) then it won't affect the simulation, but it will provide a finite resistance between all nodes, avoiding the singu... | https://electronics.stackexchange.com |
80,582 | [
"https://softwareengineering.stackexchange.com/questions/80582",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/3792/"
] | Being the creator of a program, you are probably in a better position than anyone to be aware of security vulnerabilities and potential hacks. If you know of a vulnerability in a system you wrote, is that a sign that increased security MUST be added before release, or should this be evaluated on a case by case basis to... | I would say it should be done on a case-by-case basis. You are the author, you know <em>many</em> of the holes. Some vulnerabilities might only be known to you. Of course that means that if any of them are exploited, you might have some difficult questions to answer so it might be a good idea to reduce these vulnerabil... | I've had the unfortunate experience of being in the situation twice. The business in both cases were putting out products with <em>serious</em> security problems with very sensitive data.
In both cases the business did not seem to care, despite my best efforts to make them aware of the risks that they were taking.
... | https://softwareengineering.stackexchange.com |
200,055 | [
"https://electronics.stackexchange.com/questions/200055",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/90657/"
] | I'm using an <strong>Atmega32</strong> to read various sensors using its ADC.
Using digital logic and a few multiplexers, I've multiplexed the entirety of PORTA, using PA0:6 for address and PA7 as the input. Therefore, I can have a maximum of 128 inputs from just a single PORT.
Now, since the user will be operat... | Bit fields don't work like that. Cventu's answer shows a correct way to use them, but in this case, I recommend avoiding them altogether.
Instead, create an array of 8-bit values and use shifting and masking to access it:
<pre><code>uint8_t flags[16];
//Initialize the flags
void init_flags(void)
{
for (i = 0; i ... | It sounds a bit confusing, but maybe something like this can help:
<pre><code>struct bits_field {
unsigned char bit_7 :1;
unsigned char bit_6 :1;
unsigned char bit_5 :1;
unsigned char bit_4 :1;
unsigned c... | https://electronics.stackexchange.com |
1,474,644 | [
"https://math.stackexchange.com/questions/1474644",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/277442/"
] | There are two sentences $\varphi(u), \psi(u)$ with common variable $u$. Are they equivalent: $\forall u[\varphi(u) \rightarrow \psi(u)]$ and $[\varphi(u) \rightarrow \psi(u)]$?
| $\forall u[\varphi(u) \rightarrow \psi(u)]$ doesn't have any free variables. It's either true or false, depending on what $\varphi$ and $\psi$ say.
On the other hand, $[\varphi(u) \rightarrow \psi(u)]$ has a free variable (namely $u$). It doesn't have a set truth value untill you give it a concrete $u$ to evaluate, an... | By definition: <br>
We say that formulas $\phi (x_1,x_2, \dots , x_n)$ and $\psi (x_1,x_2, \dots , x_n)$ are equivalent, if: $\forall_{x_1}\forall_{x_2} \dots \forall_{x_n} \ \phi (x_1,x_2, \dots , x_n) \leftrightarrow \psi (x_1,x_2, \dots , x_n)$ is a rule of logic. In other words two formulas are equivalent if theirs... | https://math.stackexchange.com |
100,203 | [
"https://physics.stackexchange.com/questions/100203",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/41077/"
] | My friend puzzled me with this: Say I have a container that contains a vacuum and another container inside. And this inner container contains air. Also the outer container material is just barely strong enough to not implode due to the vacuum. If I remove the air from the inner container to outside of the outer cont... | If the volume between the two containers is a true vacuum (by definition no molecules present), taking away the air inside the inner container would have no effect.
The net pressure on the outer container would be atmospheric pressure, since the internal pressure is zero.
If the volume between the two containers ... | Building upon DavePhD's answer:
"If the volume between the two containers is a true vacuum" the inner container does not have any effect. Assume the complete inner container was miraculously just "beamed" away. What would remain in the "hole" we have created? Vacuum. Which is, by definitio... | https://physics.stackexchange.com |
326,738 | [
"https://electronics.stackexchange.com/questions/326738",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/160345/"
] | Could you explain to me the differences between a tachometer and a tachogenerator? For example, is a tachometer just a tachogenerator attached to a dial to display RPM rather than voltage or are they two completely different devices?
Thank you.
| Tachometer is an instrument to display RPM of some rotating shaft.
A tachometer consists of tachogenerator (a sensor on the rotating shaft), and an electronic circuit that displays the sensed input.
The tachogenerator might generate either analog voltage proportional to RPM ("analog tachos"), or square pulses with p... | Tachogenerator is usually referred as permanent magnet DC brush generator. It has many slots and very fine brush collector. They usually output +/-10V at full RPM. Nowadays are being replaced with digital encoders, resolvers, ...but they were long time used as velocity feedback in servo drives.
Tachometer is a device ... | https://electronics.stackexchange.com |
594,476 | [
"https://physics.stackexchange.com/questions/594476",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/280025/"
] | In general relativity, if there is a line element of the form <span class="math-container">$$ds^2 = [f(u, v)]du^2 + [h(u, v)]dvdu + [w(u, v)]dv^2$$</span> which I believe corresponds to metric coefficients <span class="math-container">$$g_{00} = f(u, v)$$</span> <span class="math-container">$$g_{01} = \frac{1}{2}h(u, v... | Simple answer yes,
Think about taking two extreme cases :
How much does a slinky extend in a gravity-free space? None at all
How much would it extend if it was on perhaps Jupiter or even a black hole ?It should extend by a large amount.
Gravity does play a role.
| If a slinky is hanging vertically in a gravitational field, the amount of stretch in any short section depends on the weight of the coil hanging below that section. Less gravity will produce less stretch.
| https://physics.stackexchange.com |
2,674,136 | [
"https://math.stackexchange.com/questions/2674136",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/323580/"
] | <blockquote>
Let $b ≥ 1$ and $c ≥ 1$ be integers. Elisa’s neighborhood pub serves $b$ different types of
beer and $c$ different types of cider. Elisa invites $6$ friends to this pub and orders $7$ drinks,
one drink (beer or cider) for each friend, and one cider for herself. Different people may get
the same typ... | $\binom{6}{4}$ is the number of ways to choose the 4 of Elisa's friends who will get a beer.
$b^4$ is the number of ways those 4 friends can choose their beers: Each of those friends can choose one of $b$ different beers, so there are $b^4$ different assignments of friends to beers.
$c^3$ is the number of ways Elis... | Elisa must order a cider, thus we need to choose $4$ out of her friends to order beer. Which gives $\binom{6}{4} $ choices. For each of those $\binom{6}{4} $ choices, we must decide on the type of beer. Each choice implies $4$ orders of beer and $3$ orders of cider, which is where the answer came from.
Hence, to addres... | https://math.stackexchange.com |
55,550 | [
"https://mathoverflow.net/questions/55550",
"https://mathoverflow.net",
"https://mathoverflow.net/users/12730/"
] | Let $k$ be an algebraically closed field, and consider some subscheme $X\subset \mathbb{P}_k^n$. Let $x$ be a closed point of $X$, and $H$ a general hyperplane containing $x$. There is a regular map $\phi:\mathbb{P}^n\setminus{\{x\}}\rightarrow \mathbb{P}^{n-1}$ gotten by projecting from the point $x$.
My question: I... | <strong>EDITED</strong> to match clarifications in the question and in Sándor's answer.
The question is equivalent to asking whether the tangent cone at $x$ of the hyperplane section coincides with the hyperplane section of the tangent cone:
Blow up $x$, and denote $\tilde{\mathbb{P}}^n$, $\tilde X$, $\tilde H$ the r... | I will use the notation that if $S\not\subseteq\{x\}$ then $\overline{\phi}(S):=\overline{\phi(S\setminus \{x\})}$.
Assume that $X\neq \{x\}$ and it is not a union of lines through $x$. See below for an explanation that this is equivalent to $X\cap H\not\subseteq \{x\}$. In this case the statement is true.
A general... | https://mathoverflow.net |
17,622 | [
"https://stats.stackexchange.com/questions/17622",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/7089/"
] | I have done some AI projects involving inference, neural networks, etc., but I'm not sure what the right algorithm would be for this problem.
<ul>
<li>Say there is a set of pills, where each type is visually unique. So, for example, a pain reliever might be a red pill and an allergy medication might be a blue pill. On... | First look at the scatterplot shows that the problem is in a few very high values of the second variable:
<img src="https://i.stack.imgur.com/1RBcv.png" alt="enter image description here">
Log scale on V2 shows some subtle decreasing relationship, so you can start from there:
<img src="https://i.stack.imgur.com/JYVk... | I am with @mbq on this, but would suggest plotting in logscale in <em>both</em> dimensions:
<img src="https://i.stack.imgur.com/T01Xi.png" alt="scatter fit in log/log">
The correlation coefficient is now like -0.44.
| https://stats.stackexchange.com |
29,845 | [
"https://electronics.stackexchange.com/questions/29845",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/8647/"
] | What I am trying to do is set pin PC0 of PORT C as output to light an LED.
The code I am using for that is:
<pre><code>//SET PORT C
//PC0 = RELAY STATUS LED - O/P
//PC1 = RELAY CTL LINE - O/P
//PC2 = PUSH BUTTON - I/P
//PC3 = SPARE - O/P
DDRC |= _BV(PC0) | _BV(PC1) | _BV(PC3) & _BV(PC2);
//SET PC0 = HIGH
PORTC ... | <h2>Your problem:</h2>
Your DDR setting is incorrect: You've written
<pre><code>DDRC |= _BV(PC0) | _BV(PC1) | _BV(PC3) & _BV(PC2);
</code></pre>
but you want
<pre><code>DDRC |= _BV(PC0) | _BV(PC1) | _BV(PC3)
DDRC &= ~_BV(PC2);
</code></pre>
You say you want more detail because you just kinda emulated othe... | What microcontroller you are using? is it Atmega32 or 16 or any other?, than check its Datasheet, either they have JTAG interface or not. If they have JTAG, than you may not be able to use PortC Few pins as JTAG is enabled by default from factory.
For this you have to Disable JTAG from Fuses, by disabling <strong>JTAG... | https://electronics.stackexchange.com |
221,582 | [
"https://softwareengineering.stackexchange.com/questions/221582",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/13833/"
] | I'm writing a Java class, part of an opensource game development framework under the Apache 2.0 license.
There is another framework, under the same license, that happens to also have a Java class that addresses the same subject as mine. I recently checked it out, and my implementation is extremely similar to that. Hec... | You developed the code in isolation of the other code, the code is not a derivative work of the other. Do nothing that would claim that yours is a derivative of the other.
Writing code that does similar things will often be implemented the same way. An anecdote of this is I was working on some software to handle arb... | Why not contact the other project and offer to pool your resources?
Such "project merges" are reasonably common for open source projects.
| https://softwareengineering.stackexchange.com |
52,933 | [
"https://dba.stackexchange.com/questions/52933",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/29940/"
] | Quite often it is necessary to do some repetetive operations / few line queries against set of objects. Let's say you have a list of accounts to unlock via
<pre><code>alter user %username% account unlock
</code></pre>
and instead of typing the same line multiple times for each user I believe some cycle construction ... | You can generate this sort of statements using dynamic SQL, e.g.
<pre><code>select 'alter user ' || username || ' account unlock' as cmd
from dba_users
where account_status = 'LOCKED';
</code></pre>
Following up on your latest comment, if you want to manually enumerate the usernames you can use a PL/SQL collection... | <pre><code>set serveroutput on size unlimited
for i in (select 'alter user '||username||' account unlock' cmd
from dba_users
where account_status = 'LOCKED'
)
loop
dbms_output.put_line (i.cmd);
-- execute immediate i.cmd;
end loop;
end;
/
</code></pre>
This works. Be careful, I ha... | https://dba.stackexchange.com |
1,948,097 | [
"https://math.stackexchange.com/questions/1948097",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/111883/"
] | <em>(old question: the usual proof of Well-founded induction uses Dependent choice. Is it necessary?
I've heard that Well-founded induction is equivalent to dependent choice - I highly doubt that, but I couldn't find any references.)</em>
<strong>EDIT</strong>: Hagen's answer suggests, that I have a different definiti... | The assumption that those two definitions of "well-founded" are equivalent implies the axiom of dependent choice. I will show the contrapositive; assuming the failure of dependent choice, there is a partially ordered set which is well-founded in one sense but not the other.
Let $X$ be a nonempty set and let $R$ be a b... | Recall that we define a set $X$ to be <em>well-founded</em> by the binary relation $R$ if every non-empty subset $Y\subset X$ has an $R$-minimal element, i.e., there exists $a\in Y$ such that $R^{-1}a\cap Y=\emptyset$. (Here, we write $R^{-1}a:=\{\,x\in X\mid xRa\,\}$).
The principle of well-founded induction states: ... | https://math.stackexchange.com |
330,526 | [
"https://physics.stackexchange.com/questions/330526",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/89955/"
] | Since static friction helps in the movement of rolling motion, not opposes it, Why do we say we need more torque to get the car to move from rest if we have the rolling friction coefficient static and the torque = mass * acceleration * wheel radius, surely the mass and radius do not change. So, why do we need more tor... | There are two factors I know of. First, and less important, overcoming static friction requires more force than kinetic friction. This applies to all of the internal parts that have to get going/moving past each other, and probably to the rolling friction of the tires.
The major reason, though, has to do with how cars... | The power you can transmit (force times velocity) depends on velocity. To get any power when velocity is small, you need a lot of force. And force is just torque divided by distance (distance = radius of wheel), times whatever scale factor the gear box supplies.
So all the horse power in the world won't move your car ... | https://physics.stackexchange.com |
391,042 | [
"https://softwareengineering.stackexchange.com/questions/391042",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/330348/"
] | When testing an API (with, for example, Java), what parts should I actually be testing when calling methods of my Controller class (e.g. a Spring <code>RestController</code>)?
For example, lets say I've got a <code>logIn</code> method in my controller.
Said method calls some methods of another class (i.e. my Service c... | Test functionality not implementation.
Testing implementation details kills refactoring. You can't change anything without breaking a test.
Correct headers, cookies, and token validity shouldn't be defined by the test. They should be defined by the code that creates them and uses them. What you test is if a user atte... | I advise creating an end to end test which uses a client to connect to your api as a user would.
You want to be able to point these tests at your live api and ensure its working.
There are always implementation details that can go wrong with the hosting layer, such as ports, firewalls, caching etc which unit tests on... | https://softwareengineering.stackexchange.com |
155,482 | [
"https://dba.stackexchange.com/questions/155482",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/110718/"
] | I'm struggling to get data from a JSON column in my PostgreSQL database.
In our <code>users</code> table, we have a <code>known_ips</code> column, which is a JSON column, holding a flat array of IP addresses known for the given user, like this:
<pre><code># select email, known_ips from users limit 3;
email ... | Double quotation marks are name delimiters. They are reserved for delimiting names (column names, table names etc.) that contain non-standard characters or those that you want to explicitly make case-sensitive (because that is their effect in PostgreSQL, which is according to the standard, too).
So, that is why all at... | I know that there can be better solution but this sql should work;
<pre><code>SELECT *
FROM users u
WHERE u.known_ips::TEXT LIKE '%192.168.1.2%'
</code></pre>
| https://dba.stackexchange.com |
57,868 | [
"https://softwareengineering.stackexchange.com/questions/57868",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/9135/"
] | I'm redesigning the website for my academic library and am examining other sites to determine to identify the technologies used. Things like:
<ul>
<li>Web frameworks</li>
<li>Javascript frameworks</li>
<li>Server-side technology</li>
<li>Content management system</li>
</ul>
Now I've had some real success in Firefox ... | Fundamentally, you can't tell. No matter what CMS you use, you can always strip the identifying information from it. Plone, for example, is currently themed using a system called Diazo (a subset of Deliverance) which basically plugs chunks of content into any given CSS + HTML theme. Tons of other web applications re... | One way is to inspect HTTP response headers. Lots of frameworks include a custom header, like <code>X-Powered-By</code> which contains the name of the CMS or framework. Although I don't think you'll get good results with this as there's a big change these kind of headers are only included in development mode.
| https://softwareengineering.stackexchange.com |
63,440 | [
"https://mathoverflow.net/questions/63440",
"https://mathoverflow.net",
"https://mathoverflow.net/users/5000/"
] | The action of a group $G$ on a topological space $X$ can be viewed as a functor $F: G \to \mathcal{Top}$ with $F(*)=X$. (Here I'm viewing a group as a category with one object, $ * $, and the morphisms are isomorphisms labeled by the group elements.)
We can extend this idea and define the action of a groupoid $\mathca... | Perhaps the most natural example is given by universal covers?
Let $X$ be a "nice" space. For a point $x\in X$ let $\tilde X_x$ be the universal covering of
$X$ taken at $x$ (the fiber at $y \in X$ is the homotopy classes of paths $[0,1]\to X$ which start
at $x$ and end at $y$, where we are taking homotopy classes re... | There is a nice overview of Moerdijk and Mrcun in the proceedings of the PQR 2003 conference on groupoids and their actions and stuff. So this might provide quite a number of examples from (differential) geometry. They mainly investigate Lie groupoids.
In the setting of Lie groupoids, there are also more refined notio... | https://mathoverflow.net |
66,475 | [
"https://electronics.stackexchange.com/questions/66475",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/-1/"
] | In Jal, it's possible to do something like this:
<pre><code>var word the_var = 0x1234
var byte the_array[2] at the_var;
</code></pre>
Now you can easily access the bytes of the word <code>the_var</code> with <code>the_array[0]</code> (<code>0x34</code>) and <code>the_array[1]</code> (<code>0x12</code>). Can something... | One C equivalent is to use a anonymous union, there are a few ways to use them so it's worth researching them further but an example is:
<pre><code>static union {
word the_var;
byte the_array[2];
};
the_var = 0x1234;
some_value = the_array[0];
some_other_value = the_array[1];
</code></pre>
Another way to go about... | In C, you can always get a pointer to the data structure and cast it to some other type (such as <code>uint8_t</code>, like this:
<pre><code>long myLong = 123456;
uint8_t* bytePtr = (uint8_t*)(&myLong);
uint8_t seventByte = bytePtr[6];
</code></pre>
The first line is your non-byte data, of type <code>long</code> ... | https://electronics.stackexchange.com |
3,564,156 | [
"https://math.stackexchange.com/questions/3564156",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/728796/"
] | Let <span class="math-container">$E$</span>, <span class="math-container">$F$</span> be two topological spaces and <span class="math-container">$f:E\to F$</span>. Let <span class="math-container">$(\omega_i)_{i\in I}$</span> be some open sets of <span class="math-container">$E$</span>. Under what condition (on the func... | Always. Unions of sets commute with images (no topology needed).
Proof: <span class="math-container">$y \in f[\bigcup_i \omega_i]$</span> iff
<span class="math-container">$\exists x \in \bigcup_i \omega_i: f(x)=y$</span> iff
<span class="math-container">$\exists j \in I: x \in \omega_j \land f(x)=y$</span> iff
<... | <span class="math-container">$f(\cup_i A_i)= \cup_i f(A_i)$</span>, where <span class="math-container">$i \in I$</span>.
1) <span class="math-container">$f(\cup_i A_i) \subset \cup_i f(A_i)$</span>.
Let <span class="math-container">$y \in f(\cup_i A_i)$</span>.
There is an <span class="math-container">$x \in \cup_... | https://math.stackexchange.com |
257,151 | [
"https://softwareengineering.stackexchange.com/questions/257151",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/122844/"
] | For example, if I have two classes "Director" and "Follower". I want the Director to tell the follower where to go (ex: <code>follower1.go(direction.LEFT)</code>), and I want the Director to know what directions it can tell the Follower to go when coding in an IDE that gives completion suggestions.
I know I can alread... | I <em>think</em> if you remove <code>public</code>, it will work:
<pre><code>enum Direction{LEFT, RIGHT, UP, DOWN};
</code></pre>
though I believe it that this enum will only be accessible to other classes that are in the same package as <code>Follower</code>.
Why does <code>Direction</code> need to be contained <e... | There are two ways you can with this.
As FrustratedWithFormDesigner pointed out, you can make the enum a top level entity.
The other option is to leave it as a inner-member of one of you classes. To do this, you can either qualify the enum with the host class name:
<pre><code>go(Follower.Direction.LEFT);
</code></pr... | https://softwareengineering.stackexchange.com |
556,720 | [
"https://physics.stackexchange.com/questions/556720",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/143038/"
] | The Fourier transform of <span class="math-container">$1$</span> is the (one-dimensional) Dirac delta function:
<span class="math-container">$$\delta(x) = \frac{1}{2\pi} \int_{-\infty}^\infty dp\ e^{-i p x}. \tag{1}$$</span>
Now I would like to replace the RHS with:
<span class="math-container">$$\frac{1}{2\pi} \int... | The answer provided by roshoka is correct. I only want to briefly discuss why the time dependence can be "ignored" in this case.
As the question asks for the probability of obtaining a particular energy eigenvalue at a later time, then you must first understand what the wave function looks like at a later time t. For ... | A fundamental postulate of QM is (From Shankar chpt. 4)
<blockquote>
If the particle is in a state <span class="math-container">$|\psi\rangle$</span>, measurement of the
variable (corresponding to) <span class="math-container">$\Omega$</span> will yield one of the eigenvalues
<span class="math-container">$\omega... | https://physics.stackexchange.com |
3,943,262 | [
"https://math.stackexchange.com/questions/3943262",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/845249/"
] | Suppose <span class="math-container">$E\subseteq [0,1].$</span>
<span class="math-container">$C$</span> is some positive number and <span class="math-container">$\mu$</span> is Lebesgue measure.
My approach:
Assume <span class="math-container">$\mu(E)<\frac{q}{p}<1$</span>.
We know <span class="math-container">$E... | There's this nice proof using Lebesgue's differentiation theorem, at least assuming <span class="math-container">$E$</span> is measurable:
Let <span class="math-container">$I_{\varepsilon, x} := [x - \varepsilon, x + \varepsilon]$</span>. We know that for almost every <span class="math-container">$x \not\in E$</span> ... | The premises imply that <span class="math-container">$E$</span> is measurable because <span class="math-container">$\mu (E)=\mu(E\cap I)$</span> exists when <span class="math-container">$I=[0,1].$</span>
Let <span class="math-container">$E'=E\setminus \{0,1\}.$</span> I found it easier to show that <span class="math-co... | https://math.stackexchange.com |
442,588 | [
"https://physics.stackexchange.com/questions/442588",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/187139/"
] | What is the shape of a gravitational wave as it hits the Earth, particularly the time portion.
Does time start at normal speed, then slow slightly, and then return to normal speed?<br>
Or does it start at a normal speed, slow down slightly, then speed up slightly, and then return to normal speed?
Those other ques... | A simple monochromatic gravitational plane wave has two possible transverse polarizations. If the wave is traveling in the <span class="math-container">$+z$</span> direction, then the metric for one of the polarizations can be written in the simple form
<span class="math-container">$$ds^2 = -dt^2 + (1+h_+)\,dx^2 + (1-... | This is written as if the metric for a gravitational wave was something like <span class="math-container">$ds^2=(1+f(t))dt^2-dx^2-dy^2-dz^2$</span>. It isn't. A metric of that form is just Minkowski space described in unusual coordinates. General relativity doesn't really even offer us any way of describing the notion ... | https://physics.stackexchange.com |
384,007 | [
"https://electronics.stackexchange.com/questions/384007",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/27682/"
] | I have a 12v/22A DC switching power supply and 9 peltier elements rated for 12v/6A.
I would like to limit current to 2A per peltier element.
I don't know how to calculate the impedance (in ohms) that I need.
Intuitively, by ohm's law, every peltier element's impedance is 12v÷6A=2Ω and the impedance I'm aiming for is... | If the Peltiers are rated at 12v/6A, then I would try measuring the current taken by 3 in series. If you can tolerate that your resulting current isn't exactly on target, then job done!
This is far more efficient than burning excess power in resistors, especially as you're starting from an SMPS.
While the Peltier cu... | The Peltier Device has a nonlinear rise in resistance with lower power applied, which you must derive from datasheet graphs. So it must be regulated with a constant current source or an active current limiter.
The reason for this is the resistance and power absorption changes with temperature difference.
It may mean... | https://electronics.stackexchange.com |
24,503 | [
"https://mathoverflow.net/questions/24503",
"https://mathoverflow.net",
"https://mathoverflow.net/users/259/"
] | This is quite possibly a stupid question, but it is pretty far from what I normally do, so I wouldn't even know where to look it up.
If $X$ is a projective variety over an algebraically closed field of arbitrary characteristic and $Y\subset X$ a smooth divisor. Under which conditions can I contract $Y$ to a point, i.e... | For a smooth $Y$, a necessary condition for contractibility is that the conormal line bundle $N_{Y,X}^\*$ is ample. It is also sufficient for contracting to an algebraic space. The reference is <em>Algebraization of formal moduli. II. Existence of modifications.</em> by M. Artin.
$Y$ can be contracted to a point on a... | In the case of smooth surfaces, this is already a tough question :
If E is a rational curve, then E can be contracted to a point in a smooth variety if the self-intersection $E\cdotp E=-1$ (thm of Castelnuovo).
If you don't impose the smoothness of the variety, then a sufficient condition is $E\cdotp E<0$.
Moreov... | https://mathoverflow.net |
126,061 | [
"https://softwareengineering.stackexchange.com/questions/126061",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/42827/"
] | I work for the State of California. Our programming team in my opinion is not really a 'team' in that we usually work solo on projects throughout the application/systems complete life-cycle.
The end result is a lot of developers are 'reinventing the wheel'... writing their own data layers, even though the vast majorit... | The trouble is...
<blockquote>
the obvious benefits
</blockquote>
may not be so obvious to the people around you, especially if they are not devs. I've worked for both State governments and the Federal government so I can empathize with your situation. In my experience you need to <em>show them the money</em>. Sta... | Could you consider teaming up with one or two of your co-workers to help start building a common framework? That would be my suggestion for a starting point as you will need allies and some of the benefits may reveal themselves after some time working together so that things aren't so isolated. You may have to have a... | https://softwareengineering.stackexchange.com |
470,663 | [
"https://electronics.stackexchange.com/questions/470663",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/175381/"
] | How optical sources having narrower spectral width '<span class="math-container">\$ \Delta \lambda \downarrow \$</span>' gives higher data rates '<span class="math-container">\$ R_B \uparrow \$</span>'?<br>
For example: Laser having lower spectral width gives higher data rates ,similarly LED having higher spectral widt... | You're probably missing one thing : the transmission medium.
Optical sources for high bandwidth communications normally use glass as the transmission medium, in the form of optical fibre. Now the glass is carefully chosen, and I expect one of the factors they optimise for is low dispersion, yet I don't believe the di... | Narrow line width sources don't necessarily have higher (digital) bandwidth, but they tend to be much more useful because:
<ol>
<li>Usually you're going to use the laser a carrier for a signal that will be introduced onto it by a modulator, and so having a very narrow signal <strong>before modulation</strong> means yo... | https://electronics.stackexchange.com |
183,840 | [
"https://softwareengineering.stackexchange.com/questions/183840",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/40518/"
] | I'm working a small-to-medium legacy codebase and when working on a ticket I will come across code that should be cleaned-up or that I <em>need</em> to clean-up just to be able to understand the follow of the application.
A real example is:
<pre><code>if( !a && b ){
doSomething1();
doSomething2();
... | I follow a process similar to Karl's answer. I prefer a separate commit of the cleanup / refactoring prior to the feature changes for a few reasons:
<ul>
<li>Separating the two commits will explain your process and thinking better to others who look at the logs. </li>
<li>It provides a specific set of changes useful ... | I prefer the extra commit before the fix. This clearly separates the two tasks you are doing, and allows other people to see what was cleanup versus what was a bug fix. Also, cleanup (for me at least) is usually a lot faster, so if I commit a cleanup fix, I don't have to worry as much about someone making a difficult... | https://softwareengineering.stackexchange.com |
262,556 | [
"https://security.stackexchange.com/questions/262556",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/279062/"
] | I recently installed the AdGuard app on Windows and Android. It wants to enable HTTPS filtering and install a certificate. I've seen antivirus do similar things. How exactly does this work and what security implications does this have? I'm guessing it's a compromise, but if the app wanted to do something malicious it w... | I you specified your ciphersuites using the <code>tls-ciphersuites</code> options, this is not enough. This option specifies which ciphersuites are enabled for TLS v1.3: this options <strong>does not</strong> configuration the ciphersuites used for TLSv1.2 and below.
For TLS v1.2 and below, you must use <code>tls-ciphe... | TLS 1.3 has other benefits besides just ciphersuites. Mostly in the name of performance but also patching up some latent security issues in the handshake (encryption/signing).
Is it enough to merely restrict ciphersuites?
Depends on the threats one is worried about but most likely yes for an individual user.
Is there ... | https://security.stackexchange.com |
78,729 | [
"https://physics.stackexchange.com/questions/78729",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/8123/"
] | If not always, how much "most of the time" could it get?
Or would a multi-satellites setup be more suited?
| Yes, but the satellite(s) would be orbiting the sun instead of the earth. You place a satellite at either L4 or L5 Langrangian points on the Earth-Sun two-body system--these are points 60 degrees to either side of earth on her orbital plane around the sun where you can place a satellite. Throughout earth's entire orbit... | The best way to minimise loss of sight would be to have the satellites orbiting at a very high altitude, e.g. beyond the distance of the moon. It would then be very rare for the satellites to be eclipsed by the planets, or moon. Such eclipses could also be easily avoided with a small orbit correction or by synchronizin... | https://physics.stackexchange.com |
2,185,571 | [
"https://math.stackexchange.com/questions/2185571",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/413861/"
] | The Polish notation of the expression a + b * c + d ( where "+" is left associative):
A/ + + a * b c d
B/ + a * bc + d
C/ + + * a b c d
D/ + * bc + ad
Can anyone explain why the answer is A please? What is the best way to solve this kind of problem though?
Thanks
| Let $S^{(N)}$ be the sequence such that $x_0=-1$ and $x_n=\frac{1}{N}$ for any $N+1\leq n\leq 2N$, zero otherwise.
This sequence belongs to $G_2$ and $\{S^{(N)}\}_{N\geq 1}$ is a Cauchy sequence in $\ell^2$, but $\lim_{N\to \infty}S^{(N)}$ is not a zero-sum sequence. This disproves completeness.
| To work out the closure of $G_2$, we could use the fact that $\bar{G_2} = (G_2^\perp)^{\perp}$.
But $G_2^\perp = \{ 0 \}$. [For instance, if $y_n \in G_2^{\perp}$, then the fact that $y_n$ is perpendicular to $(1,-1,0,0, \dots)$, $(0,1, -1,0, \dots)$, $(0,0, 1,-1, \dots), \dots$ means that $y_1 = y_2 = y_3 = \dots$, a... | https://math.stackexchange.com |
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I drive a 2011 F-150 with the 5.0 motor in it and after cranking it up this morning it's driving fine but the circled pulley at the front of the block (with arrow pointing towards the front of the truck) is wobbling rather aggressively ... | I'm not familiar enough with that engine to say for sure, but the circled pulley might be the water pump. The wobbling is <strong>not</strong> a good sign, it indicates that a bearing is failing.
There are four accessories that are likely to be driven by a belt or belts at the front of the engine:
<ul>
<li>The water ... | That is the water pump I just changed one on a 2014 with a 5.0 and if the pulley is wobbling that means the bearing r bad in the water pump
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