Physical meaning of the Lagrangian function

Question:
In Lagrangian mechanics, the function $L=T-V$, called Lagrangian, is introduced, where $T$ is the kinetic energy and $V$ the potential one. I was wondering: is there any reason for this quantity to be introduced? Does it have any physical meaning?
A professor of mine once said its differential $\delta L=dT-dV$ is "the quantity of energy you must pump into the system to move it from a point $(q,\dot q)$ in the phase space to a point $(q+dq,\dot q+d\dot q)$". Is this interpretation correct? I'm not too convinced…
Comment: Okay. Possibly related: http://physics.stackexchange.com/q/9686 and http://physics.stackexchange.com/q/41138/
Comment: The way I've seen it until know only makes sense if you know the derivation of Euler's Equation in the context of calculus of variations. I recommend you see that if you havent yet.
Comment: Derivation: on a physical path $\vec r(t),$ created by a potential force and constraint force $m\vec a=-\nabla U+\vec F_c,$ we vary the path a little within the bounds of its constraints with a "path-perturbation operator" $\delta$ so $\vec r(t)\mapsto\vec r(t)+\delta\vec r(t),$ etc. Then $\delta U=U(\vec r+\delta\vec r,t)=\nabla U\cdot\delta\vec r$ and $m\vec a\cdot\delta r=-\delta U$ (since $F_c\cdot\delta r=0$ since $\delta$ satisfies the constraints.) Then we can take a time integral and integrate by parts to get $\int dt (-m v\delta v+\delta U)=0,$ or $\delta\int dt(\frac12 mv^2 - U)=0.$
Answer:
is there any reason for this quantity to be introduced?

It is a quantity for which the actual dynamics makes the integral of the thing be stationary with respect to changes of paths when you consider alternate, but nearby changed paths.

Does it have any physical meaning?

One problem is that many Lagrangians give the same equations of motion, so it is like trying to give a physical meaning to a vector potential. It isn't super straightforward. The linked questions might address your question.
But I will point out that the Lagrangian isn't always $L(\vec q,\dot{\vec q})=T-V.$ It is what you need it to be so that the stationary paths are the physically correct paths.

A professor of mine once said its differential $\delta L=dT-dV$ is "the quantity of energy you must pump into the system to move it from a point $(q,\dot q)$ in the phase space to a point $(q+dq,\dot q+d\dot q)$". Is this interpretation correct?

It is not correct. The function could change for instance without you having to do anything. You could consider two equal masses attached by a spring, moving in a line, with the center of mass in chancing. As it oscillates; the Lagrangian, as a function of time, changes. But you do not have to put any energy into it. The Lagrangian is a function of $(x_1,\dot x_1,x_2,\dot x_2).$ And the path through the coordinates $(x_1,\dot x_1)$ moves in a circle as do the coordinates $(x_2,\dot x_2).$ The energy of the system doesn't change, but the Lagrangian is largest when the kinetic energy is high and lowest when the kinetic energy is zero. You can pump energy in and make them move on larger circles or have the circles both translate in some direction over time. So you can put energy in and change the Lagrangian. But the Lagrangian can change without you putting any energy into the system.

I think my professor would reply «The spring is pumping in energy!» :).

I had two particles (instead of a single  particle attached by a spring to an immobile point) exactly so there would be no room to say that. The energy is just sloshing back and forth between kinetic and potential, there is no pumping into the system.

If the energy is sloshing back and forth, I would expect $dT=dU$ and so $\delta\mathcal{L}=0$, so indeed no pumping of energy :). But anyway I got the message: that interpretation is incorrect.

The Lagrangian does change, even when you don't pump energy into the system. That was my entire point.
If $L(\vec q,\dot{\vec q})=T-V$ then $L(\vec q,\dot{\vec q})$=$T+(T-T)-V$=$2T-(T+V)$ so during the actual dynamics $\Delta L=2\Delta T-0.$ So maybe your professor has confused you on other issues too, since it seems like you have the literal same confusion as your professor is claimed. Or maybe you misunderstood all along.
A Lagrangian is different than a Hamiltonian. It increases when kinetic energy increases it is not a constant, it isn't energy. It's a thing, that when stationary under variation, gives the true dynamics.
Answer: As you have already mentioned, L is NOT in general T-V. T-V only holds in classical mechanics. And I will try to motivate the construction of T-V in classical mechanics following "The Variational Principles of Mechanics" by Cornelius Lanczos.
To start out, let's talk about statics. It it well known that the condition for a physical system to be at equilibrium is that $F_{net}=0$.
However, when we consider dynamics, this law is replaced by the famous $F= ma$. While $F=ma$ is very useful in most everyday scenarios, it fails for two reasons: First, it is a vector equation and thus difficult to generalize to general curvilinear coordinates. Second, it does not work in arbitrary reference frames. In the 18th century, Physicist Jean D'Alembert thought about treating dynamical problems as statics problems. Since Newton's law no longer holds in accelerated reference frames, D'Alembert invented a new function called the "effective force":
$$F_{effective}=F_{impressed}+F_{inertial}.$$
Where impressed force is the usual force in Newtonian mechanics and inertial force is what we now refer to as fictitious forces. Then D'Alembert's principle states that the dynamical system follows this particular equation:
$$\sum_i(\mathbf{F}_i-m_i\mathbf{a}_i)\cdot\delta\mathbf{r}_i=0.$$
Where the function inside the bracket is the effective force and the delta Ri's are "virtual displacements". This equation basically says that if you consider the system in some configuration, and you do a virtual experiment where you move the system in some arbitrary directions, the sum of the work done by the effective forces must add up to 0. This is a generalization of the principle of virtual work from statics to dynamics.
But you may be wondering. This is still a vector equation! We haven't solved the problem yet. You are right! Now let's make the jump from vector to scalar through integration.
let us take the integral of this equation with respect to $t$:
$$\sum_i(\mathbf{F}_i-m_i\mathbf{a}_i)\cdot\delta\mathbf{r}_i=0.$$
What you get is this:
$$\int\limits_{t_1}^{t_2}\sum_i[\mathbf{F}_i-m_i\mathbf{a}_i]\cdot\delta\mathbf{r}_idt=0.$$

The first part of the integral, $\int_{t_1}^{t_2}\sum_i\mathbf{F}_i\cdot\delta\mathbf{r}_idt$, can be interpreted as the potential energy for conservative systems. Let's rewrite it as $-\delta\int_{t_1}^{t_2}Vdt$, where $V$ is the potential energy.
Now let's look at the second part. It is clear from integration by parts that:
$$-\int_{t_1}^{t_2}\frac{d}{dt}(m_i\mathbf{v_i})\cdot\delta\mathbf{r}_idt=-\int_{t_1}^{t_2}\frac{d}{dt}(m_i\mathbf{v}_i\cdot\delta\mathbf{r}_i)dt+\int_{t_1}^{t_2}m_i\mathbf{v}_i\cdot\frac{d}{dt}(\delta\mathbf{r}_i)dt.$$
The first term on the right hand side is trivially integral and yields a boundary term: $-(m_i\mathbf{v}_i\cdot\delta\mathbf{r}_i)|_{t_1}^{t_2}$. Since we have the freedom to fix the end points, let us set $\delta\mathbf{r}_i=0$ at $t_1$ and $t_2$. Then we are left with $\int_{t_1}^{t_2}m_i\mathbf{v}_i\cdot\frac{d}{dt}(\delta\mathbf{r}_i)dt$, which we can integrate to obtain $\int_{t_1}^{t_2}\frac12m_iv_i^2dt$. Now the picture is starting to surface. The integral we started with can be expressed as:
$$\delta\int_{t_1}^{t_2}(\frac12m_iv_i^2-V)dt.$$
If we make the substitution $T=m_iv_i^2\cdot\frac12$, the integral reduces to:
$$\delta\int_{t_1}^{t_2}(T-V)dt.$$

Magic!!! $L = T-V$   !! Finally obtained the Hamilton's Principle. Variation of the action is zero!
So the Lagrangian function really came from integrating D'Alembert's principle. It is not arbitrary at all. It is formally different, but mathematically equivalent to D'Alembert's Principle. The remarkable feature of Hamilton's Principle is that $L$ is a scalar quality (a frame-independent quantity). Taking Hamilton's Principle as a fundamental construction, physicists went far beyond classical mechanics. In Standard Model, the Lagrangian is literally a page long instead of just a simple $T-V$. These complicated lagrangians are outside the scope of my understanding. So I will leave it to experts to shed more insight on a general lagrangian formalism.
I hope my somewhat historical account helped to motivate the Lagrangian construction in classical mechanics.
Answer: Now, someone tried to mark this question as a duplicate of this other one. From my point of view, having derived the Euler-Lagrange equations before  even mentioning the least action principle or the action, it didn't seem too related. The point was, I wanted to have a physical interpretation of the Lagrangian, and leave the action and the principle as abstract constructions done for who knows what reason, probably because the principle is equivalent to the EL equations. Because that is basically the way things were presented to me: we start from Newton, introduce general coordinates, make use of the D'alembert principle (What did the teacher call it? Smooth constraint principle, or the likes) to derive some equations, and see they are written in term of this function, $L=T-V$, which we call Lagrangian; oh but then we know those equations are equivalent to this strange abstract principle regarding the integral of the Lagrangian; then transform the Lagrangian and we simplify the EL equations, getting into Hamilton, which is more symmetric in that no total time derivatives of partial derivatives of the Hamiltonian appear, as opposed to EL. So I was a bit biased towards interpreting $L$ physically and keeping the action on another planet.
Luckily, Kyle Kalos posted this link in his last comment. THe turning point was this answer. This tells me the leaast action principle is equivalent to a principle which is much more physical, if the amplitudes are physical enough. SO I looked for that principle, and voilà: I found this, but most importantly this lecture by Feynman, which clearly illustrates the physical relevance of action.
So I conclude that it is action that has a physical interpretation in terms of phases -- and in fact the formula $S=\int(T-V)dt$ need not hold! It is just a case that in classical mechanics, that is the action functional. Unfortunately, I can't go too deep, since I know practically nothing of Quantum Mechanics, and delving into that for a geometric thesis that deals with Hamiltonian fields is decidedly off-topic.
As for the professor's interpretation, I guess I can safely conclude it need not be correct, as $L$ might not be $T-V$. This answer will probably give more details about this point.
Addendum
Potentially related threads: 1, 2 and 3.
Comment: Even when L=T-V it still is not the case that changes in the Lagrangian equal energy pumped into the system from outside. Again as my example of two particles connected by a spring shows.


If two fast asteroids collided, would the temperature and pressure be high enough to cause nuclear fusion?

Question: Some near earth objects travel with speeds of dozens of kilometers per second. Would a head-on collision between two of them create suitable conditions for nuclear fusion?
Comment: I'm only a quarter joking when I say I'm surprised someone hasn't commented with "Fast, you say? Fast relative to what, old chap?".
Answer: A different approach, ignoring any details of the collision. Note extreme simplifications will occur, do not try this at home...
The easiest hydrogen isotope fusion process is D-T, with a cross section that peaks at around 100keV. At 10keV it is more than 3 orders of magnitude lower. Lets ignore the isotope issue, and say we need H (protium) at at least 10keV to produce some fusion in the collision. So, what is the velocity of a 10keV H atom? Since that is non-relativistic, all we need is $E = {1 \over 2} m v^{2}$ and make sure we get all the units accounted for properly. Cranking through that all we get that a 10keV H atom has a velocity of a bit under 1.4 million meters per second, of some 1400 km/sec.
Dozens of kilometers per second doesn't cut it.
Answer: Not even close.
This would have to be a rough "Fermi" estimate,
Lets suppose the asteroids are 50km in diameter and moving at a relative velocity of 50km/s.  And so lets say the collision takes about 1 second.
Such asteroids have a mass of about 4e17 kg and so a momentum of 2e22 Ns  The impulse to cause these asteroids to stop in about a second is 2e22 Ns, and so the forces involve are on the same order of magnitude, but these forces are spread over the whole asteorid's cross section. A rough estimate for the pressures in the collision would be about 1e13 N/m²
The temperature in the collision would be intense.  There is evidence of impact temperatures on Earth being over 2000C.  Let us suppose that the temperature is even higher, 10000C, instantaneously
This is nowhere near the temperature and pressure for fusion.  The centre of the sun has a pressure of 2.5e16 N/m² and a temperature of 15 million C The energy release by an asteroid impact is substantial, but this is spread out over the whole asteroid, and so the temperature is rather less impressive.
These values, especially the value for the temperature, are so much more than the pressure and temperature in an asteroid collision that even though the calculation has been approximate, it is clearly far shorter than that needed to start fusion.
Answer: Fusion is hard; it's really hard (insert paraphrase about a long way to the chemist's down the road).  OTOH,  if these two rocks contained a lot of fissile material,  you might be able to cause a fission-based explosion.
A self-sustaining chain reaction is relatively easy (tho' in reality I can't imagine random asteroids of huge age still being highly fissile), but physically containing the reaction long enough to get more than the initial radiation flash is more difficult. A high-speed collision would emulate the original Little Boy mechanism.
Answer: "If two fast asteroids collided, would…"
We have meteorites from two fast asteroids colliding. Mesosiderites, and likely CB-group, too.
Got that? We have meteorites… which means the meteorites survived. They didn't react via fusion, they didn't plasma-fy, they didn't even vaporize… even liquifying is a bit semantic.
We have hard evidence in our drawers, cases, and gloveboxes that two fast asteroids don't react via nuclear processes. They barely reacted via chemical processes.
We have meteorites from asteroids colliding.
Comment: This just proves that _some_ asteroid can survive the collision, doesn't it? I mean, we could be seeing only the ones that collided slowly enough not to be vaporized ;)
Comment: Don't know when to quit, do you. Jon Custer already showed you are off by ~2 orders of magnitude, yet you still fish for a loophole. ~50,000 catalogued meteorites, of which meteoriticists can study nanogram samples, and you still tell them _how to do their own jobs_. 50,000 meteorites tell us the early Solar System was a billiard-game break, over and over again, for about 500 million years… and you still tell us _how to do our own jobs_.
Comment: Sometimes it is difficult to judge the tone of a written sentence. I will [presume good intent](https://meta.stackexchange.com/questions/335026/we-need-assume-good-intent-back-in-the-code-of-conduct) and interpret you comment as a humourous remark!


Can this year's free extension-to-pay be filed electronically? IRS Form 1127

Question: Does anyone know if IRS Form 1127 can be filed electronically?  I didn't find mention on their site either way so I presume not.  But considering they're pushing to go paperless nowadays like most....
Comment: Just be sure that you understand very clearly that you can request an extension of time to **file** your income tax return, but not an extension of time to **pay the tax due.**  You still have to estimate how much you expect to owe and pay that by the original due date of the tax return (April 15 or soon thereafter depending on weekends, legal holidays in the District of Columbia, etc). When you file your return by mid-October, it might show a refund (which you will get back with interest) or even more tax due (which you will have to pay, together with interest, and possibly, penalties).
Comment: See [here](http://www.ehow.com/how_2156829_use-form-1127-extension-time.html), or the link above from the IRS directly.  What you're referring to is the old form IRS Form 4868: extention to _file_ not pay.  This extension to _pay_ appears new. And penalty-free if you qualify.
Comment: Anyway, for several years already I've been able to electronically file not only Form 4868 when needed but also 1040 and 540(CA) taxes themselves, and not the EZ kind--including Schedule D--very convenient. With payment or refund, using software or directly online. It's true that I've always had to pay at least _estimates_ due April if applicable, even if fully filed later.
Comment: But if you read the start of the web page you refer to, it says that the form is for an extension of time to pay an amount that is shown on your tax return as due, or as assessed by the IRS after it examines your return and comes up with a different number. So until you file your return on October 15, the question of asking for an extension to pay seems moot.
Answer: Form 1127 (updated link) should be filed in paper (with the supporting documents) to the IRS office that has jurisdiction in the area where you live.
From the instructions (see the link above):

File Form 1127 with the Internal Revenue Service (Attn: Advisory Group
Manager), for the area where you maintain your legal residence or
principal place of business. See Pub. 4235, Collection Advisory Group
Addresses, to find the address for your local advisory group.
However, if the tax due is a gift tax reportable on Form 709, send Form 1127
to:
Department of the Treasury
Internal Revenue Service Center
Cincinnati, OH 45999


Is the knock an early sign of Dual Mass Flywheel problem. Main dealer says acceptable noise?

Question: Ford Mondeo 2012 1.6 TDCi DPF SS 115. At 15,500 mls I am experiencing a knocking sound when raising the clutch pedal but only when the engine is running. The sound outside the car is really loud. It is still in warranty. Initially Evans Halshaw said they could hear it but needed the car for 2 days. During that time all they did was a couple of road tests to advise me that the noise was normal and acceptable and a characteristic of the vehicle. They also said there was a small amount of backlash in gear. They suggested they have spoken to Ford who also said it was normal.  So why am I just experiencing the noise? I am concerned as there is so much talk of manufacturers denying responsibility and avoiding warranty work, and a lot of concerns about the Dual Mass Clutch. A problem now will only get worse, what can I do now except put it back in again, to expect the same answer?
Answer: I'm not going to say anything about the dealership you mention that a quick Google of review sites for them wouldn't reveal anyway.
Yes, knocking is an early sign of the dual-mass clutch-flywheel assembly beginning to wear out.  How long you will have between audible knocking and replacement is hard to predict.
If you are unsure or unhappy about your main dealers assertion that the noise is acceptable, take the vehicle elsewhere for an independent assessment.  Presumably the dealership that's assessed it provided you with the car in the first place so would have to shoulder the cost of replacement.  Try another Ford dealership or service centre and see what their opinion of the noise is.


Pantone or CMYK for Product Label

Question: We have redesigned our product labels for our supplement brand and want to know from professional graphic designers and print savvy individuals if most product labels you see in retail stores use pantone or CMYK? The pantone will give us the consistency, but the CMYK may give us a bit more flexibility in color choice and future printers. We are curious to know if most brands that can be found in retail use Pantone or CMYK for their product labels? Thank you very much to all who share their knowledge!
Comment: It depends. How many colours will you be reproducing? What print process will you be using?  Traditional printing such as lithography, or is it digital? CMYK reproduction can look great, but in some cases using spot colours can look much better. Also note that it's possible to use both CMYK and spot colours, however the addition of spot colours will cost more.  There's no one-rule-fits-all here. It's really very dependent on what you want.  I can't really answer for "most brands". You'd need to do some kind of research.
Comment: Each label will have approximately 3 colors and thousands will be printed. Since the runs can be large, most likely lithography printing will be used? We are unsure of the process though. We appreciate your feedback!
Answer: Further to the comments, I think I can answer this now, kind of . . .  I can't answer this for "most brands", because some kind of research would be required.
Anyway . . .
For 3 colour printing, and a large print run, it's likely that 3 spot colours and lithography would be the best option. It may or may not be cheaper though. Ultimately only your printer can give you a cost estimate.
In nearly all cases (depending on the artwork), spot colours will look better than CMYK printing. No halftone screening is required for the colour mixes.  Areas of colour will be sharp, flat, and well defined. And the quality of the colour will far superior.

If you are thinking about using digital printing, then the only real option is probably full colour/CMYK.
CMYK printing can of course still look great, but it uses halftone screening to achieve mixes of colour, which will be visible if you look close enough. Also unless the text on the label is a solid C, M, Y or K, then the text will also be a halftone, which can look pretty awful with small text.
If I were you, I'd ultimately ask your printer for advice. Most are pretty happy to give it. Show them your artwork, and ask them what they would recommend.
Comment: Thank you very much for your in depth answer. We greatly appreciate you taking the time to share your knowledge. We certainly agree that using pantone will give us sharp and well defined colors, especially when using a bright color and some smaller sized text. Thank you again for your feedback.
Comment: @james is confusing "spot" with "Pantone" Pantone Solid are spot colors but not all spot colors are Pantone.
Comment: @Yorik I'm not sure that is true here to be  honest. James didn't mention spot colours, that was me.  When I said spot colours, to be clear, I am talking about solid (100%) Pantone colours.  Tints (less than 100%) of Pantone colours are also a possibility, but without seeing the artwork, I don't if the OP will be using any of these.
Answer: Here are some points to consider.

Number of colors.
Type of paper, absorption, roughness.
Details on the label, mainly small text.
Stile of the label. Gradients, flat colors.
Special colors, metallic, fluorescent, bright colors.
Print method and Finish. Puffy inks, engraver, silk print.
Budget.

Sometimes we look for cheap alternatives for our prints. But cheap also means easy falsification, so, if your brand uses normal paper on an inkjet printer, they can easily be forged.
Using a spot ink, means, at least that it needs a bit more effort than a home printer.
You need to define what you mean when saying:

flexibility in color choice and future printers.

You define your colors and production cycles. Period. Normally a brand is not changed on the fly.
Answer: From a print and brand perspective - your logo and brand name should be in spot/PMS color to maintain consistency across your product line and branding/marketing materials.
If you change printers, change machines, etc, the PMS color should remain constant. If you decide you want to go with process colors, then establish a standard CMYK mix for your logo and brand so no one has to guess what formula to use. If you're going online with your materials, also establish your RGB percentages. Consistency is key to making your brand recognizable as well as making the reproduction process as smooth as possible.
Just as a random pick, here's how FedEx sets it up:
https://usbrandcolors.com/fedex-colors/
Answer: (Active in packaging and labels artwork for 25 years)
Spots colors are still very common in packaging, especially (but not exclusively) with A-brands as they have larger order sizes and they are less willing to compromise design, quality and consistency. Six, seven or eight color prints are more rule than exception (CMYK + spot).
For cost and time-to-deliver reasons, CMYK label printing is slowly making a rise, made possible by digital printing presses (where spot colors are not possible and every color is to be composed) and halftoning advancements in offset printing.

Pantone or CMYK for Product Label


Is there a bus from Tbilisi, Georgia to Thessaloniki, Greece?

Question: While it appears that information is available about the bus from Thessaloniki to Tbilisi in a previous question, I'm curious about the reverse? What Georgian companies (or Greek companies operating in Georgia) service this route?
Comment: @hippietrail Wouldn't the same companies that operate Thessaloniki->Tbilisi operate the reverse?  Buses do have to get back somehow.
Comment: I don't think it's a good idea to close this question as a duplicate yet. It specifically asks for the return route that was not addressed in my previous question and about which I also have no information. If it's closed now the missing info is unlikely to appear in the other question. But if this question is answered then merging the two would not be a bad idea.
Comment: possible duplicate of [What are the bus (coach) connections between Thessaloniki, Greece and Tbilisi, Georgia?](http://travel.stackexchange.com/questions/2759/what-are-the-bus-coach-connections-between-thessaloniki-greece-and-tbilisi-g)
Comment: @Karlson: Yes I would expect so. But seeing how difficult it was to find the names and offices of the companies when I was in Thessaloniki and the fact that none of them own their own buses but do charters, it's going to be just as difficult to find in the opposite direction. Maybe harder because in Greece I could look for Georgian expats but I'm not aware of Greek expats here in Tbilisi.
Comment: Likely we need someone locally in Tbilisi to go to the bus station to get info.
Answer: I don't know about direct, but you could do it in two legs.  There are plenty of buses from Tbilisi to Istanbul and then there are more from Istanbul to Thessaloniki which cost around 95 lira.


I am Learning to play Bach 846 prelude on piano but when I play the second note of the triplet it doesn't always sound why

Question: I am trying to use the rolling hand method but sometimes the second note of the triplet doesn't always sound why
Comment: Presumably because the technique you are using isn't actually hitting the key hard enough! You could post a video of what your hand's doing...
Answer: There are no triplet.
But you mean the middle finger:

Play the prelude slowly
Try to play it with bowed fingers and with stretched fingers. Find out the optimal stretching position of the middle finger.
Pay attention to the weight of the arms. Vary the weight.
As the middle finger is longer it is normally nearer to the torque of the keys and this would need more strength and power. Play in front of the keys. (You'll  see you have to turn the wrist.)
Play the arpeggio in a dotted rhythm.
Play it through by accenting each time a different note (=finger) of the basic figure (motif).
Play it f and as p and fast as possible.
Play it in different octaves. R.h. Very high and very low.


Problematize and building a paradox over the repression drug use, its debates and issues

Question: At the extraordinary session held from 19 to 21 April 2016, the UN General Assembly acknowledged the failure of the "war on drugs". I wanted to find a paradox to create a philosophical problem on the following topic the repression of drug use: debates and issues from the French topic I was given to reflect about (la repression de l'usage des drogues : débats et enjeux).
Here is a definition of a philosophical problem by the French Association of professors of philosophy of public education:

What is a philosophical problem? Vast question, that it would be right to problematize. Can we answer it without philosophizing, and can we philosophize universally? In other words, is there a single definition of the philosophical problem? Does the way in which problematization is conceived in philosophy imply a particular philosophy? If this were not the case, one would expect to almost agree, because this definition would come under the observation. Now it is precisely a fact that philosophers do not agree on the nature of the philosophical problem. But if the conception of the philosophical problem is philosophical, there are as many as philosophies. This risks degrading the philosophical problem into a false problem, because its formulation would already contain its "solution" (implied by the particular philosophical framework within which it is formulated). A problem which, in its formulation, engages a certain philosophy, would be less a problem than a similar problem, an appearance of a problem. But the opposite would also be embarrassing, because a problem that would not lead to any solution would not it be rather aporia, the observation of a blind spot of thought, the statement of the limits of philosophical reflection? - from appep.net consulted 5-7-2019

I wasn't sure to use drug or narcotic term for the French word "stupéfiants". I used the first one as far as it seemed more generic.
Definitions

Drugs are substances that have physiological effects on the consumer when ingested or otherwise introduced into the body. "The end result is that the experience of using the substance is so pleasurable, relaxing or energizing that it triggers your internal reward system, making you want to repeat that experience again and again." one can read on luxury.rehabs.com. Some say activities can be drug but they won't fall in my reflection. In our context drug use is most of the time illegal. Using drugs may be in different ways. One can have a recreational use, another may be an addict, other like may use it to foster their creativity or as experiences like Henri Michaux and Mescaline or Gérard de Nerval to write Aurélia. Other may only use drugs to sell them, the drug dealer, but I would call it drug traficking.
Repression is the process of punishing people doing a prohibited activity and impeding them to do it. It is different from legalizing something use. It can be by law enforcement by the police but it can also be arbitrarily. In our case, the repression of drug use had several aspects such as preventive actions but also the drug war: designed to drastically reduce the supply of narcotics, the mobilization of important military and police means did not produce the desired effects.
Debates and issues about the repression of drug use are everywhere as drug has no geographic or social boundaries. The main drug issue is addiction. If drugs like heroin, cocaine and alcohol couldn't cause dependence and addiction, the issues of substance abuse and ban from societies might not exist. The main debates seem to be about decriminalization and setting up of shoot room.

I'm not very happy with my definitions as I don't feel like they help me to build a paradox.
Paradox building
I thought about the next two contradicting truths:

If the debates tend to be oriented to decriminalization, it creates a risk of losing awareness that it is a public health problem. Yet if the debates also tend to take care of this public health problems such as setting up of shoot room to help drug user to do it responsibly, but maybe these centers would be another issue as incentives.

Therefore the paradox lead me to this question:

What debates make it possible to go beyond a counterproductive repression without favoring the development of a public health problem?

I'm not sure my paradox is strong enough ...
Answer: See if you can do something with these three types of "wrongdoing":
1. Things I do to myself:
These would relate to issues surrounding the integrity of my right to determine what happens to my own body, crimes of use and acquisition...
2. Things I do to other people: This may involve practices such as supply of inferior/substitute product. Or infringement of principles such as willing buyer willing seller.
3. Things I do against the public interest: Think safety: drunk driving, standards and regulatory... Or state crimes like tax evasion and illegal trade.


How many must you sample with no negatives to conclude there is no negatives in the population?

Question: If I have 1000 widgets made in my factory and I want to know that none of them are defective, how many must I sample to expect that there are no defects in the whole 1000 at 95% CL.
Comment: Related: [How to tell the probability of failure if there were no failures?](https://stats.stackexchange.com/q/134380/7290)
Comment: In a comment to an answer you express scepticism about the simplicity of the answer (or maybe about its obviousness). For a rigorous demonstration, note that when $k$ of the widgets are defective, the chance that a sample of size $n$ contains none of them is $\binom{1000-k}{n}/\binom{1000}{n}.$ In the worst case where $k=1,$ then, your chance of *not* detecting it would be $$\binom{1000-1}{n}/\binom{1000}{n}=\frac{1000-n}{1000}.$$ The smallest $n$ that reduces this to $100-95=5\%$ or less is $950.$
Comment: Do you know the rates of false positives and false negatives for the process you use to test samples?
Comment: Its safe to assume that there is not error on the test for the sample.
Answer: As explained in the Wikipedia link, the "Rule of Three" is for (binomial)
sampling with replacement or sampling from a theoetical infinite distribution. I am skeptical that this rule applies to your question.
Of course, to be 100% sure not even one of your 1000 widgets is defective, you will
have to look at all of them.
If there is one defective widget among 1000, then your chances of finding
it by looking at 750 randomly chosen widgets is only
$\frac{{1\choose 1}{999\choose 749}}{{1000\choose 750}} = 0.75,$ a hypergeometric probability. In R,
dhyper(1,  1, 999,   750)
[1] 0.75

If you want to be 95% sure to find the one defective among 1000, you will need to sample 950 widgets (without replacement).
dhyper(1,  1, 999,   950)
[1] 0.95

If there are two or more defectives among the 1000, then it would be (almost) good enough to look at 750.
sum(dhyper(1:2,  2, 998,  750))
[1] 0.9376877
sum(dhyper(1:2,  2, 998,  775))
[1] 0.9495495
sum(dhyper(1:2,  2, 998,  777))
[1] 0.9504444

Comment: It is informative to think about trying to find a single defect in 1000 but a slightly different question. I will update if I make progress on the Bayesian approach.
Comment: In your calculation are you sure that you accounted for the ones you checked. If you look at 750 then you know those are good so you only need to check the 250 remaining. The 250 can act as the prediction set and the 750 is some sort of prior information. Perhaps there is a Bayesian formulation which makes this more clear.
Comment: Hypergeometric probabilities are based on sampling without replacement, which is what one would do in your case. // A Bayesian approach might be a good idea.
Comment: If you were to cheat and consider sampling with replacement, then the number of $k$ of defectives $n$ trials with defective probability $p$ is $\mathsf{Binom}(n,p).$ Then choose a noninformative Jeffreys prior $\mathsf{Beta}(.5,.5)$ on $p.$ If you have $k = 0$ successes in $950$ trials, Bayes Thm gives posterior $\mathsf{Beta}(.5,,950.5)$ and from R code `qbeta(.95, .5, 950.5)` gives Jeffreys posterior upper bound  0.002019247 on probability of defectives. // More properly for you, the issue is what convenient prior to use for hypergeometric data.
Comment: However, it seems to me you may want to test a hypothesis of no defectives at the 5% level, given the minimal single defective among 1000 as alternative. That is the context of my Answer. // For CIs, it is easy to say 95% ("everyboty" uses that), but not so easy to say what upper bound you'd want to have for a one-sided CI.
Answer: Suppose we want to expect that there are no defective widgets at the 95% confidence level. What this means is that we must test enough widgets that if there were a defective widget, then we would have a 95% chance of finding the defective one in our tests.
Of course, if we want to have a 95% chance of finding the defective widget, that means we must test 95% of all widgets. So the answer, unfortunately, is that you have to test 950 of the 1,000 widgets.
And that's it, that's the entire answer to your question. But let me talk about practical considerations, because in practice, there isn't really any situation in which you'd want to test 95% of all widgets.
Scenario 1: You're building a chain out of 1,000 links. For some reason, you've decided to buy each link from a different person, so you have 1,000 different people supplying chain links to you. All of the links have to be strong in order for the chain to be strong; having even one weak link is unacceptable.
In this scenario, the problem is that testing some of the links doesn't tell you anything about the remaining links. Even if you test 999 of them, you still haven't learned anything whatsoever about the remaining link. So, testing (say) only 750 of the links is definitely not enough.
As I mentioned, in order to conclude at the 95% confidence level that none of the links are weak, you need to test 950 of them. At this point, you might be wondering, "Why should I stop at 950? Why not just test all 1,000 of them?" And the answer is that you're absolutely right. You should probably just test all 1,000 links, so that you know that all of them are strong.
Scenario 2: You have a machine that makes chain links, and you've just made a batch of 1,000 chain links using that machine. As above, all of the links have to be strong in order for the chain to be strong. How many chain links should you test in order to be sure that you'll have a strong chain?
If you're faced with this scenario in the real world, then you should try to find out more information about the machine. The best case is that there are two types of machines: ones which produce only strong links, and ones which produce only weak links. In this case, you only need to test one link in order to know that all of the links are strong!
A more realistic case, perhaps, is where some machines produce only strong links, and other machines produce 50% strong links and 50% weak links. In this case, in order to achieve your 95% confidence level, you only need to test 5 links and see that they're all strong.
Another interesting case is the case where these machines are known to be very reliable, and 99.9% of them produce only strong links. In this case, if this machine was chosen randomly out of all machines, then you don't need to test any links in order to reach the 95% confidence level that all of the links are strong.
I can't describe all possible practical situations, of course, but hopefully this gives you an idea of why 950 is the correct answer to the original question, as well as why that answer isn't likely to be very useful in practice.
Comment: This seems too simple to be correct but I do not have a good argument against this way of thinking.
Comment: @Keith Sometimes, the answer is simple. This is one of those times. That said, there are some practical considerations that I haven't talked about in my answer. I think I'll edit my answer to talk about those.
Comment: The connection this made for me was that 95% confidence of 100% being good is the same as 100% confidence of 95% being good.
Answer: I looked at a version of this problem back in April, to see what we could say about Covid elimination based on reasonable numbers of tests (spoiler: not a lot).
As @keith's answer shows, if you want to be sure there isn't even one failure in the population, you need sample a large fraction of the population. That's obviously not sensible in most cases.
As @BruceET says in his comment, a Bayesian solution makes sense. However, because there's very little information in the data about very small numbers of failures in the population

it will matter what prior you put on very small numbers of failures
if you think small numbers are plausible a priori, and don't sample a big fraction of the population, you will inevitably still think that a posteriori, so you won't end up with high posterior probability on zero

Suppose you take a $Beta(a,b)$ prior for the probability of failure.  The posterior after no failures out of $n$ is $Beta(a+0,b+n)$. So you can look up the quantiles of that distribution and see when it's concentrated close enough to zero for what you want to use it for.
Comment: This is useful. Can you add more. Perhaps an example. We know the probably of defect is small (<1%) and would want to not assume much more than that.

I was thinking to take the only prior information to be the sample but could not sort out the formulation.
Answer: The Rule of three states that if I sample N then I know I have a rate less than 3/N at 95% CL
My expectation, E, is my rate times the number of total events, T.
E =  T*3/N
The total events remaining is just the number unsampled T=1000-N
E = (1000-N)*3/N
I want to expect at most 1 so E=1
Solving for N gives
N = 10003/(1+3) = 10003/4 = 750
Sampling 3/4 seems like a lot so I have some doubts but this is a pretty strict requirement.
The general case for any confidence can also be given where the multiplayer is -ln(α) with α being 1 minus the confidence level.
With a population size P the general case is
N = P*ln(α)/(ln(α)-E)
Comment: I think you've calculated the wrong thing. By setting $E = 1$, you've calculated the number of widgets that would need to be sampled in order to expect that *no more than 1* widget is defective. But we want to ensure that there are 0 defective widgets, not no-more-than-1 defective widget.
Comment: I do realize that. I think that this works for my situation but you are rigorously correct. I thought about putting it to 0.49 then I could round down to 0. I am unclear how to handle the discrete nature of this problem.


How can I install GNOME 3 on CentOS 6.3?

Question: Would be possible to install GNOME 3 (instead of 2.28 that ships with CentOS) on a minimal CentOS 6.3 install? Is there any repository that provides packages for the new version?
Answer: You can download it from the Gnome website
Haven't tried this yet, although I will do so in the next couple of days. If you get it working, could you say how and I'll do the same.


Property and time evaluation of Gaussian wavefunction

Question: I faced some problems while learning the time evolution of Gaussian wavepacket . I started the part with a wavefunction in momentum space which was like $ \ \phi(p) = c.e^\frac{-(p-p_0)^2}{2.\sigma_p^2} \ $ . Then found the position space wavefunction by Inverse Fourier transform . And found a $\psi(x) \ $. I was asked to find out the $\psi(x,t)$. I thought that like the bound state problems I will multiply the $ \ \psi(x) \ $by $ \ e^\frac{-iEt}{\hslash} \ $and find the time evolution of the wavepacket. But in the solution they invoked a solution with integrals like :  $ \ \psi(x,t) = (2\pi \hslash)^\frac{1}{2}.\int_{-\infty}^{+\infty} e^{(kx-\omega t)}.\phi(p) \ dp \ $ and solved this to find the time dependent wavefunction . Can anyone tell me that why they followed this approach ? I am suspecting that the Gaussian case is not always bounded so they didn't followed the $ \ e^\frac{-iEt}{\hslash} \ $ approach . Can the Gaussian wavepacket represent a free particle ?
Comment: The gaussian wavepacket is a superposition of infinitely many energy eigenstates, so each frequency component has to be weighted separately to yield the time evolution of the whole packet. Regarding the physicality of the wave packet, it is useful to represent realistic free particles that occur in experiments in which there is a spread in the momentum distribution  (we can't have a delta function in Nature).
Answer: The time evolution of a system is actually given by $e^{-iHt/\hbar}$ operating on the initial condition, where $H$ is the Hamiltonian describing the system.  You have to know how the Hamiltonian operates on the state your system is in.  IF your system is in an energy eigenstate, then the $H \phi_E = E \phi_E$ and you get the term you were expecting.  However if its not, then you need expand the state in the basis of energy eigenstates.  This can involve an integral over all the energy eigenstates. IF the momentum eigenstates are also energy eigenstates, and you know the relationship between the momentum in a given eigenstate and the energy in that eigenstate, then that integral can become an integration over all possible momenta.
Try to figure out what the momentum eigenstates are for your system.  Can you write your initial condition in terms of an integral over all the momentum eigenstates?  Do you know what the energy is when you operate your Hamiltonian on a single momentum eigenstate?
Comment: Yes I understood your point . And I think it's a correct approach . In this problem as you can see I can find the space wavefunction by inverse transform easily and hence the momentum also can be found . But the potential energy term is not described anywhere . It can be a free particle or it's not impossible to be a bound particle . As potential energy term is unknown how the hamiltonian H can be calculated for a single momentum eigenstate ? Only I can work with the kinetic energy term .
Comment: The fact that they gave you an initial wavefunction in momentum space does imply that they probably meant it to be a free particle.  One can choose to write a wave function in momentum space even if there is some potential that means momentum is not conserved, but you probably wouldn't.  But the point is you need to write your wave function in terms of the energy eigenstates to evaluate the time evolution, which happen to also be the momentum eigenstates if you have a constant potential.


Forest canopy structure

Question: Optical remote sensing technology is commonly used for forest biomass estimation. The NDVI is used to define greenness. But how can we tell about biomass after capture only canopy area from above? Is it only outermost layer, right? Can only NDVI represent the all biomass of tree?
Answer: Not an expert in this field but I found this in quick Google search:

Reference: https://doi.org/10.2307/1942049
I think from line 8 the answer to your question begins.
Comment: Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer).

Forest canopy structure


How does federalism in the United States work?

Question: How does federalism in the United States work? Why are there States within the country? What do they do?
Comment: We already have [a canonical question on state vs federal law](https://politics.stackexchange.com/questions/26252/in-the-us-what-is-the-role-of-and-relationship-between-federal-law-and-state-la).  Do we need this one too? How does this question differentiate itself, other than using "federalism" in the title?
Comment: Oh ! - it doesn't.
Answer: Background on Federalism itself:
Federalism is a method of organizing a country where there are two "levels" of government: the country and its constituent parts. Unlike provinces or departments in a so-called unitary state, these parts have, in theory and practice, significant self-government. They cannot be easily abolished or changed by simple decision of the country's government. In a unitary state this may occur. For example, in New Zealand in 1870 the provinces were completely disbanded by act of the legislature.
Background on federalism in the United States:
In the 1600s and 1700s, England and then Great Britain colonized the eastern coastal part of the north American continent, from what is now Georgia in the south to what is now New Found Land in the north. This was not a unified effort. Each colony was governed separately and had its own charter issued by the monarch of Great Britain at the time of founding. These charters varied, but all had provisions for a elective part of a legislature and a governor from either the monarch (such as in Massachusetts) or the company that owned the colony (such as Pennsylvania). These latter were termed "proprietary" colonies, governors, etc.
At the time of the Revolutionary War, thirteen of the colonies declared themselves independent of their colonial mother country (Great Britain). This was done via extra-legal means: the royally appointed governors refused to countenance the elected assemblies treasonous (to them) declarations, so the assemblies met as "provincial" congresses and declared themselves the lawful assemblies and independent States.
Critically, although the thirteen colonies banded together immediately under the first constitutional document of the United States, the Articles of Confederation, they did this of their (provincial congress's) free will. After the war and some trouble with the existing confederal* government, they, again individually, agreed to replace the Articles of Confederation with the new, current, Constitution.

Do not confuse the confederal union here with the much later Confederate States that fought and were defeated in the Civil War.

Because of this history, the States of the Union are the originators of the powers of government in the United States. When they ratified the Constitution, they agreed to mutually cede equal amounts of power to the new Federal government. These powers are listed in article 1, section 8 of the Constitution and are termed the "enumerated powers".
Although written in quaint terms, they essentially comprise what the authors of the Constitution (termed "framers") thought a country on the international and internal stage needed to be able to do. Similarly, they listed a few things that the States could NOT do, like have foreign relations. These were to be the domain of the Federal government alone.
Various amendments were added to the Constitution soon afterwards in order to protect the people from the Federal government. Ten of these twelve were ratified and made a part of the Constitution to be termed the "Bill of Rights". The last one was ratified approximately 200 years later.
Current affairs:
Although not given the power to do so explicitly, the Supreme Court of the United States is by all agreed to have the power to determine "what the law is". Persons regularly think that laws the Federal or State governments have passed are against the Constitution. They bring law suits against the persons who are, by law, required to enforce them, and seek to have the Federal court system, possibly the Supreme Court, declare them "unconstitutional". When the court does so, it declares the law in question to be unenforceable and void. The only ways to change this are via a change to the law, so it is constitutional now, a change to the Constitution or a later decision of the court.
Comment: Nitpick: There were actually 12 amendments originally proposed by Congress. Ten of those became the Bill of Rights, and one became the 27th Amendment in the 1990s.
Comment: Since you ask:  "Federalizm" shouldn't have a Z.  It's spelled "Federalism".   It's used in your first 3 paragraphs.
Comment: Also comprise, not comprize.
Comment: @DM: Fixed. Any others?


Do Ferengi have any colonies outside their home system?

Question: Aside from Ferenginar, have the Ferengi ever settled or occupied planets from other systems in large numbers?
Comment: http://memory-alpha.wikia.com/wiki/Inhabited_planets#Ferengi_Alliance
Comment: It's probably worth mentioning but hasn't yet that the reason this question exists are various lines of dialogue about Ferengi woman not being allowed to travel off world.  (Which is in addition to not being allowed to own property, do business, or wear clothes.)  Now of course this is no way to set up a galactic franchise so generally everyone assumes Ferengi colonies exist with women that have traveled off world with their male owners.  But it is an assumption and really a necessary one because the alternative is silly.
Comment: @lucasbachmann- I always assumed male Ferengi settling on other planets got permission from the Nagus to take their women with them.
Answer: Yes
The most clear canonical example is Lappa IV. From the transcript for "Ménage à Troi" :

WORF: When you have finished here, survey in that direction.
CREWWOMAN: Aye, sir.
GRAX: I wish I had some answers for you, Lieutenant Worf.
WORF: Mister Homn was no help?
  GRAX: None. He last saw them as he was leaving this clearing. When he
  returned, all three of them were gone.
DATA: Lieutenant Foley discovered this in the pond. (Tog's bouquet)
  The species is Zan Periculi. It is not indigenous to Betazed, but to
  Lappa Four. A Ferengi world.

There are several other examples, as list on the list of Ferengi planets1, but they are more ambiguous. For example, Volchak Prime has ports that are owned by Ferengi:

QUARK: Is something wrong?
KRAX: You can't seat Turot next to Hoex. They've been bitter rivals
  ever since Hoex bought out Turot's controlling interest in the cargo
  ports on Volchok Prime.

However, this does not necessarily imply that the planet is under the control of the Ferengi alliance, merely that certain Ferengi do business there.
1. Credit to @Valorum
Comment: Quark's cousin owns a moon.
Comment: @Valorum - One cannot really say. It seems exceedingly likely to me that a planet owned by the Ferengi also has significant Ferengi presence, but there is always some uncertainty.
Comment: @xantec - I suspect there's a technical definition of what constitutes a colony *planet*, but my personal definition is that there has to be an intention to raise a self-sustaining population and the near total absence of other races.
Comment: @Valorum would a single Ferengi constitute a colony?
Comment: I'm not certain that being a "Ferengi world" is the same as being a colony. It might simply be a possession


"To delete" is to "deletion" as "to discard" is to what?

Question: "To delete" is to "deletion" as "to discard" is to what?
Comment: There's a reason those character count requirements are in place. The question you're asking should always be included in the body of the text, not only in the title. And adding a bit of verbosity, rather than ranting and raving inappropriately, is not that difficult. -1.
Comment: It also reduces the quality of the prose.
Comment: Discard is like any other verb: you get a noun by adding *-ing*.
Answer: The thing that is deleted is a deletion; the thing that is discarded is a discard.
The act of deleting is a deletion; the act of discarding is a discarding.
If you like using incredibly rare words, you can use discardure for the act of discarding, as Jon Hanna's answer says. Expect people to think it's not a real word.
Comment: Isn't this attitude the one that cements the extinction of already rare words?
Comment: If we go by usage, it's not clear to me whether *discardal* or *discardure* is the correct noun. Using search tools, they seem roughly equally frequent, with *discardal* having a slight edge. (See [Google Ngrams](https://books.google.com/ngrams/graph?content=discardal%2Cdiscardure+&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cdiscardal%3B%2Cc0).) I don't know why one appears in dictionaries and the other doesn't.
Answer: Discardure, though it is not a common word, used primarily in legal contexts.


powershell displaying output from an invoke-espression

Question: I have a powershell windows form which has a button which uses the invoke-expression to call a batch file which then calls another powershell script. the script runs fine but i do not see an output from the second script in the powershell command window.
Button which when clicked calls the second powershell script:
<code>$run = New-Object System.Windows.Forms.Button
$run.Location = New-Object System.Drawing.Size(133,430)
$run.Size = New-Object System.Drawing.Size(75,23)
$run.Text = "Run"
$run.Add_Click({ Invoke-Expression \\$pc\c$\users\$user\desktop\a\test.bat;

 })
 [System.Windows.Forms.MessageBox]::Show("Changes Saved. Now click RUN.") })
</code>
Batch file used to call the second powershell script:
        c:\Windows\System32\WindowsPowerShell\v1.0\powershell -ExecutionPolicy RemoteSigned -   File "C:\Users\kam\Desktop\a\Powershell.ps1"
The second script itself just copys files to a remote host, and displays output by using the write-host command. If i run this script by itself it shows the output but when i run it using an invoke expression it shows a blank powershell command window.
any help would be appreciated.
Answer: Fixed,
it was because i was calling the bat file to call the powershell, i just called the powershell script directly and output gets displayed.
<code>$run = New-Object System.Windows.Forms.Button
$run.Location = New-Object System.Drawing.Size(133,430)
$run.Size = New-Object System.Drawing.Size(75,23)
$run.Text = "Run"
$run.Add_Click({ Invoke-Expression \\$pc\c$\users\$user\desktop\a\powershell.ps1;

 })
 [System.Windows.Forms.MessageBox]::Show("Changes Saved. Now click RUN.") })
</code>


Powering an LED matrix

Question: I am building an led matrix having 75 SMD 2835 60mA leds. I am connecting 3 in series with a resistance and then connecting the 25 series parallely to a 12V power source supplying 3A@12V. This means that 120mA will be divided among the 25 series, will this set up burn up the leds. Also what value of the resistance will i need to connect to the 3 leds in series?
Comment: It would help to know the exact models of LEDs, as we don't know the specific forward voltage.
Comment: Forward voltage of an led is 3.2-3.3v
Answer: If forward voltage is 3V DC, the drop across 3 diodes is 3*3V=9V. The remaining voltage is the battery voltage V_battery-9V. The resistance needed (for each series connection of 3 diodes) is (from Ohm's law) : R=(V_battery - 9V)/60mA. E.g. 50 Ohm.
Answer:
I am building an led matrix having 75 SMD 2835 60mA leds

I am going to assume you mean you want to light up approximately 75 white LEDs with a test current of about 60 mA.

To get the resistance value use an online calculator such as Hobby Hour LED Series Resistor Calculator

Forward voltage of an led is 3.2-3.3v

This is not true.  The IV curve and temperature determines Vf.
Today typical Vf for a 60mA white LED is 2.75-2.85V.

a 12V power source supplying 3A@12V

Is there any particular reason you are using 12V?
A 48v or 54v constant current would be better than using resistors. Recommended: Mean Well HLG-40H-54B

In the 60 mA area I would use a Samsung LM561C (2.75V @ 65 mA) with an efficacy of 212 lm/W.

Using the 561C's Vfmax 3.0V you can drive strings of 18 LEDs using 54V LED driver.  I would drive 18 sets of four parallel LEDs wired in series.
To drive these at 65 mA.  You will need 4 x 65 mA = 260 mA.
72 x 37 lm @ 65mA = 2,664 lumens
With a $25 HLG-40H-54B you can run them up to 750mA (≈8,000 lumens) without exceeding the max current (200 mA) for a 561C.  Current is easily adjusted with a variable or fixed resistance.

Powering an LED matrix


Do gibbons have a monogamous sexuality?

Question: the question is already in the title. If possible, it might be extended to:
Have animal taxa (mammal) who tend to live in a family structure have a monogamous sexuality? Or are there cases of these taxa, where the sexual partner is not the social one.
Answer: Regarding gibbons, yes. According to National Geographic:

Gibbons are monogamous and live in family groups consisting of an adult pair and their young offspring.

There isn't a generalized answer for "family living", although specific family types are indicative of relationship type. Nuclear families (parents and children) tend to be monogamous, families with multiple males and one female tend to be polyandrous, and families with one male and multiple females tend to be polygynous. See this page on primate social structure for more information.

Do gibbons have a monogamous sexuality?


Philosophical works on Privilege

Question: I read the book "Caste", and can't recommend it highly enough. Are there any philosophical works that directly address the historical causes and current 'benefits' to society of what ended up resulting in privilege? Successfully? Any answers, beyond just trying to treat people more fairly?
Comment: History-via-biography, not philosophy, but you might be interested in *Joe Louis: Hard Times Man* (R Roberts, 2010), which does directly address the topic of interest as regards race in the global cultural West and especially the US.
Comment: Are you referring to this https://en.wikipedia.org/wiki/Caste:_The_Origins_of_Our_Discontents ?
Comment: @Rusi Yes. One of the best books I have ever read.
Comment: Oooo I'll be careful
Comment: @Rusi Yes, it might change your mind on some things, quite dangerous :-)
Answer: Note: the question has been significantly altered since this answer was posted. Applied out of context to the current edition of the question, the below answer may be nonsensical or false.

Why do you assume that these ideas are rational, and not based off of ignorance, false beliefs, desire for social prestige, avoidance of short-term psychological distress, etc? Very few people, including intellectuals, on any side of any issue, are motivated by honest interpretation of the totality of available evidence.
What you want is introductory economics. Framing questions about behavior in terms of incentives and constraints is usually more useful than asking for defensible arguments.
Comment: @ScottRowe: Have you read primary texts, like the above paper? Most of the criticism, like of 'woke' & 'CRT' comes in bad faith from those who haven't read & don't understand it, & cherry-pick people misrepresenting the ideas.
Comment: Yes, I know only enough Economics to manage my own finances. So that might give me a warped view of people's personal control over their circumstances.
Comment: So address the arguments. See seminal early paper on privilege discourse "White Privilege and Male Privilege: A Personal Account of Coming to See Correspondences Through Work in Women's Studies" https://www.collegeart.org/pdf/diversity/white-privilege-and-male-privilege.pdf Which makes points like No. 21: "I am never asked to speak for all the people of my racial group." No. 24: "I can be pretty sure that if I ask to talk to the 'person in charge,' I will be facing a person of my race." The people reacting against this generally don't know their history, eg Freedom Riders, Red-Lining
Answer: NOTE: This answer was composed in relation to a previous version of the question, which has undergone a substantial revision (most of the original has been edited out). Please see edits prior to March 25, 2023 before downvoting.

This answer constitutes a shallow, layman response to an issue that attracts substantial academic interest, in fields including, but not limited to:

Race
Rights
Identity politics
Feminist ethics
The 'Common good'.

Recent discussion of privilege has centred around 'White Privilege'. For some examples of white privilege, see here. Even though it is perhaps not merely white privilege which you are most interested in, this link provides interesting examples of how privilege exerts itself in dominant cultures, in many places in the world.
But privilege of course permeates almost every aspect of our existence, across many levels of society, between almost any subset you care to identify. It exists in the relationships between ethnicities, socioeconomic classes, genders, sexualities, geographies, education and religion to name a few.

"But I of myself didn't create the circumstances I benefitted from.

No. You didn't. This is a key point. Most of us, regardless of our circumstances (particularly in developed cultures and communities) hold privileges that are bestowed upon us not on our own merits, but because of circumstance, circumstances which inevitably have historical roots; prior inequalities and injustices.

"Is that someone's fault?".

We cannot be reasonably blamed for the circumstances we inherit, but according to many, we can be blamed for not acknowledging the various privileges we inherit, and for failing to take steps to redress any injustice our privilege affords us; see San Francisco board open to reparations with $5M payouts.

"If I saw someone complaining about the weather in Alaska, I would suggest that they move to a better climate".

A reasonable suggestion, on the face of it, but it hints at the ignorance to which you frankly admit in your question; and ignorance of circumstances which prevent people from easily manipulating their circumstances, including by making a 'simple' move.

"Why then do some folks who live here already, think it is so bad? Instead of drilling holes in the ship, maybe people should try to improve it?".

For many, especially those who are growing up with an increasing awareness of privilege and phenomena such as intersectionality, I suspect they would clarify such a statement by acknowledging the relative excellence of many developed nations such as the U.S.A., but by simultaneously bemoaning the injustice, inequality and failure that pervade them; by regretting the potential of such nations is not more thoroughly accomplished. See OECD Better Life Index for relative standards of various nations by topic (interactive), and World Quality of Life ratings.

"Without the revolution of culture that began there [in the U.S.A.] about 500 years ago, it appears that life would be little better now than it was then. And for much of the world it is far worse. So, the folks who improved things are at fault? Why are we blaming the successful people?".

Much of the success of a relative few has indisputably be gained at the expense of many. It is possible to attack unjust privilege whilst simultaneously acknowledging positive outcomes that have been achieved by societies in which privilege exists. It is not an 'either/or' proposition. It is simply to say, "Let's acknowledge how certain privileges came to be. Let's celebrate our successes, but also recognise those who have not been fortunate enough to come along for the ride. Let's try to even the playing field a bit". One counter to this might be economic rationalisms such as trickle-down economics, in which inequality is 'justified' by claiming that "tax breaks and benefits for corporations and the wealthy will trickle down and eventually benefit everyone", in effect raising the 'poverty line'.
By calling privilege an 'invisible ocean', we may well be proving the point of those who are trying to illustrate just how privileged we are. Many of us are so accustomed to our privileges that we fail to see and/or acknowledge them, thus perpetuating/prolonging cycles of injustice.
Comment: Although a shallow answer I think it went to the core of the issue.
Comment: @NikosM. Good to hear. Perhaps someone else will provide an answer with some more specific references.
Comment: @ScottRowe. I see what you mean. It's a word that can be counterproductive
 too, in that many of us find it difficult to acknowledge - given all of our troubles - that we are nonetheless fortunate and in a position to do more than we currently do.
Comment: Thank you. The 'Ocean' reference was to the old, *What the heck is water?* story. You said, "But privilege of course permeates almost every aspect of our existence" and that is what I am getting at. Calling that by a specific word like Privilege seems to me to sharpen the point too much. There seems to me to be a visible ocean of problems, that I have been well aware of since I was a child. For me as a programmer, if I saw an old, messy program full of poor design choices and fixes, calling it something like 'technical debt' obscures and misleads. I think 'Privilege' hides more than reveals.
Comment: Not important, but the *revolution of culture* 500 years ago that I referred to was Europe, not the US. It was so sweeping a change as to dwarf pretty much all of human history before that. To consider it all to be a big mistake is hard to accept. So we were better off as serfs and peasants in thatched huts?
Answer: I'll just throw a few philosophical works out there related to privilege.
Famously, economic privilege is covered by Karl Marx in Das Kapital. From WP:

Das Kapital proposes an explanation of the "laws of motion" of the capitalist economic system from its origins to its future by describing the dynamics of the accumulation of capital, the growth of wage labour, the transformation of the workplace, the concentration of capital, commercial competition, the banking system, the decline of the profit rate, land-rents, et cetera.

Thus, why someone might have the privilege of buying a jet and jet setting and why someone else may not have the privilege of eating is explained in terms of fiat currency, market forces, and fractional lending, among others.
Privilege conceived more broadly is discussed by John Rawls in his A Theory of Justice. From WP:

the author attempts to provide a moral theory alternative to utilitarianism and that addresses the problem of distributive justice (the socially just distribution of goods in a society). The theory uses an updated form of Kantian philosophy and a variant form of conventional social contract theory. Rawls's theory of justice is fully a political theory of justice as opposed to other forms of justice discussed in other disciplines and contexts.

Hence, privilege is discussed in the broader notion of social justice which covers ideas far beyond mere economics including ethical considerations.
Economy and Society by Max Weber is famous for giving a series of essays that explores notions, among others, of the monopoly on violence that the state has which might be seen as how the state reserves itself a privilege for administering justice. From WP:

Much like in other works, Weber makes it a point to mention the state's role in legitimizing and perpetuating violence. Weber writes that legal norms exist when they are kept through "...normally directly physical, means of coercion of the political community". This legal norm can extend into further arms of the government and the public as described when Weber writes, "In the case of certain events occurring there is general agreement that certain organs of the community can be expected to go into official action, and the very expectation of such action is apt to induce conformity with the commands derived from the generally accepted interpretation of that legal norm….

Jean-Jacques Rousseau famously creates and defends the notion of the social contract in the The Social Contract. In this way, when a person participates in society, they accede privileges. From WP:

Social contract arguments typically are that individuals have consented, either explicitly or tacitly, to surrender some of their freedoms and submit to the authority (of the ruler, or to the decision of a majority) in exchange for protection of their remaining rights or maintenance of the social order.

Berger and Luckmann attempt to describe the mechanism by which individuals are inculcated into a society including norms such as privilege in their The Social Construction of Reality. From WP:

The Social Construction of Reality: A Treatise in the Sociology of Knowledge (1966), by Peter L. Berger and Thomas Luckmann, proposes that social groups and individual persons who interact with each other, within in a system of social classes, over time create concepts (mental representations) of the actions of each other, and that people become habituated to those concepts, and thus assume reciprocal social roles.

John Searle explores how 'privilege' as a shared linguistic entity comes from processes in the philosophy of language in his The Construction of Social Reality (GB). What is a privilege can be explored by how society negotiates meanings to begin with.
Those are big philosophical works. I think you might find lots of exploration of 'privilege' in any body of work of critical theory (SEP) which explores why some have privileges over others which might be understood as domination. From SEP:

Because such theories aim to explain and transform all the circumstances that enslave human beings, many "critical theories" in the broader sense have been developed. They have emerged in connection with the many social movements that identify varied dimensions of the domination of human beings in modern societies. In both the broad and the narrow senses, however, a critical theory provides the descriptive and normative bases for social inquiry aimed at decreasing domination and increasing freedom in all their forms.
Comment: Wow, this is great list, thanks! I suppose I am naive in thinking that people shouldn't coerce each other, and also that the state has to reserve the option of violence when faced with violence. Why is there any question about that? What is the alternative supposed to be?
Comment: @ScottRowe Not naive at all. Violence has a cost. It's economical to avoid violence and coercion. There's a very rational basis for psychological altruism. Of course, sometimes violence ensures survival or maintains order. Intelligence might be seen as the ability to make choices to avoid violence by preventing the conditions of violence from manifesting.
Comment: @ScottRowe And as for avoiding violence, some people prefer it. It does have survival value under certain circumstances. Pinker discusses the notion of the [Hobbesian trap](https://en.wikipedia.org/wiki/Hobbesian_trap) and the economics of in-group-out-group violence in uh... [*The Blank Slate*](https://en.wikipedia.org/wiki/The_Blank_Slate) if you're interested in the science that leads to peace and violence.

Philosophical works on Privilege


What does "people of the concrete steppes" mean?

Question: I read this on an economics blog (http://econlog.econlib.org/archives/2014/02/in_the_1930s_it.html) and tried to google it, but the results seem to just be people using it, no one explaining it.
Thanks for any help!
Comment: In my opinion, out means city people.
Answer: The steppe is a large prairie region that is mostly located in Russia and central Asia. "Concrete steppes" appears to be a pun mixing steppe with concrete steps. From context, I would guess that it's a derogatory reference to Marxist-Leninist economic thinkers in academia or in large cities, both of which are places where one might expect to encounter concrete steps.
Comment: This answer is partially correct.  The steps are not stairs, though.  They are steps toward improvement.  [See this here](http://www.themoneyillusion.com/?p=13472)
Answer: I invented the term. Kenneth Duda and Thomas Lumley have it right (though phenry and GenericJam gave good guesses).
It's a play on words. The "people from the concrete steppes" think of the economy (and the effects of monetary policy in particular) like a mechanism, where the central bank moves one lever, which causes another lever to move, and so on. They forget the economy is composed of people, whose actions depend on their expectations of other people's (future) actions, including expectations about counterfactual conditional actions (what you would do if I did something that I won't do, because I expect you would do something if I did do it).
Comment: My goodness, this might actually be authentic! +1 either for being you or for giving that impression. :)
Answer: No no, this has nothing to do with Marxism.  "People from the concrete steppes" means people who focus exclusively on actions and consequences, what people are actually doing and what happens as a result.  In doing so, "people from the concrete steppes" neglect counterfactuals and expectations and their impact on dynamics and what actually happens.
A beautiful example comes from Nick Rowe.  People from the concrete steppes look at the Federal Reserve quintupling the monetary base plus the lack of actual inflation, and conclude that money printing either does not cause inflation at all, or causes it after a significant time lag.  They are neglecting the expectations channel, the way the expectation that the Fed will tighten money as soon as spending picks up causes people to not spend the money.  We are in this amazing situation where people's expectation about what would happen if something that won't happen did happen (an expectation of a counterfactual!) is what gives rise to credit deadlock, the ballooning of bank reserves, and the utter failure of money printing to cause inflation or move the economy.  "People from the concrete steppes" find this hard to understand, because they are only looking at what is actually happening, rather than reasoning through the impact of people's expectations of what would happen if something that's not happening were to happen.
Boy.  Hope that was clear.
Kenneth Duda
Menlo Park, CA
Answer: I believe the original example was this one by Nick Rowe, in http://worthwhile.typepad.com/worthwhile_canadian_initi/2011/10/engdp-level-path-targeting-for-the-people-of-the-concrete-steppes-/comments

"But what concrete steps will the Fed actually take to raise Nominal GDP? Can anyone tell me that?"
I must have heard that question a hundred times over the last couple of years. And a dozen more times in the last day, ever since Paul Krugman endorsed the proposal to target NGDP. I always imagine it being asked in a gruff Yorkshire accent, by some middle-aged no-nonsense practical man of business with a background in mechanical engineering.
So this is written for the people of the concrete steppes.

The use of "steppes" isn't a metaphor for anything, it's just a play on words. The people of he concrete steppes are those who believe economic interventions must involve concrete steps (eg, printing money) and that just announcing targets couldn't have any impact.
Answer: I just briefly skimmed those articles, but it seems to me, especially in reference to the 1930s it is talking about a sense of stagnation. The 'steppe' is a plain and is therefore flat. The pun is replacing step (growth) with steppe (flatline). I suppose you could extend the metaphor to include the 'concrete' policies being put in place which are intended for long term growth are actually solidifying stagnation.


In terms of Jewish status, what is the difference between a person who has a sheilah and being plainly non-Jewish?

Question: A person says he's Jewish. Deeper inquiry reveals that there are sheilos. For Halachically significant areas (e.g. aliyas, minyanim), he's not considered Jewish. But what's the difference between a person who is not Jewish and a person for whom there is a sheiloh that they are Jewish. Are the latter usually from mixed families, and that there is murkiness even though overall it's Jewish. Is the latter more of an honest mistake? A person who claims to be Jewish when there is a sheilah, is he considered a liar?
Comment: No I'm not saying he pretends he knows. He might just be ignorant that he can't do such a thing
Comment: I doubt you can consider someone who is getting interested in Yiddushkeit but unaware of the exact criteria to be considered Jewish, to be a 'liar'. He might have good intentions but is simply not knowledgeable of what is required.
Comment: It sounds like your mind filled in the gaps of my text correctly. The man is an am hararetz but pretends to know.
Comment: I'm not sure what you are asking. Are you asking what halachic differences does it make between a person who has doubtful Jewish status and a non-Jew? You already noted that some people of doubtful Jewish status cannot be included in a minyan? What else are you asking?
Comment: I'm not saying you are saying he pretends to know. I'm just saying in addition to not knowing he pretends to know
Comment: So they are the same. They are both non-Jews.
Comment: @mbloch if he marries a Jewish girl, does she need a get?
Comment: @Heshy if that is the question, the OP should state it clearly
Answer: Someone who is definitely non-Jewish can marry another non-Jew, and has no obligation to keep the specific commandments of Jews. Someone who might be Jewish and might not can't really marry anyone: they can't marry a Jew because they might be non-Jewish, and they can't marry a non-Jew because they might be Jewish. And whether and how they keep the commandments applying to Jews would be a tricky question a competent rabbi would have to answer for their specific circumstances.


How to calculate shipping cost based on "City" instead of "State"?

Question: I am looking for a solution to modify Magento 1.9.3 in order to calculate the shipping cost according to City when checkout. Could anyone give me some pointers?
Comment: Which shipping method used ?
Comment: It depends on shipping method you use
Comment: are you using onepage checkout ?
Answer: UPS and FedEx shipping methods both calculate the cost of the shipping based on the zip code.
If you are using flat rate or matrix shipping, you would need to calculate this yourself.
Answer: You can use event/observers approach for this.

Create a hook on the event sales_quote_address_collect_totals_after e.g.
<events>
    <sales_quote_address_collect_totals_after>
        <observers>
            <meteorify_observerexample_model_observer>
                <type>singleton</type>
                <class>Meteorify_Observerexample_Model_Observer</class>
                <method>setShippingCost</method>
            </meteorify_observerexample_model_observer>
        </observers>
    </sales_quote_address_collect_totals_after>
</events>

Below function is the example to set shipping price based on any logic you apply, write this function in your observer model class:
public function setShippingCost($observer)
{
    $events = $observer->getEvent();
    $address = $events->getQuoteAddress();

    if ($address->getAddressType() == 'shipping') {
        //Here you can get all shipping information on checkout
        $shippingInfo = $events->getQuoteAddress()->getData();
        $price = 0;

        $address->setShippingAmount($price);
        $address->setBaseShippingAmount($price);
        $address->save();
        // Find if our shipping has been included.
        $rates = $address->collectShippingRates()
            ->getGroupedAllShippingRates();

        foreach ($rates as $carrier) {
            foreach ($carrier as $rate) {
                $rate->setPrice($price);
                $rate->save();
                // print_r($rate->getPrice());

            }
        }

        $address->setCollectShippingRates(true);
    }
}

Answer: You can use default shipping method "Table Rate" for this.
In this shipping method you can import CSV file for that zip codes. and set your rates and shipping label there.
OR
You can use web shop matrix shipping method for this.
Both are same in functionality of working.


Why to use ARMA model as a time series is either over-differenced or under-differenced?

Question: Knowing that a time series is over-differenced or under-differenced, and  adding an AR term to the model means that we are partially differencing the time series if it's underdifferenced till a white noise remains, and adding MA term means that we are removing the effect of over-difference time series till we get also to white noise.
Thus as adding MA terms has an effect that oppose to the effect of adding AR terms to our model why are combining the two into ARMA model as the series is either over-differenced or under-differenced??
Comment: Why is a time series over- or underdifferenced, is that an assumption? And why do you think that AR or MA terms work as differencing or anti-differencing (they do not, at least in terms of the common definition of differencing)? Could you give some background for that?
Comment: https://people.duke.edu/~rnau/411arim3.htm  Rule 6 and 7 in the precedent link answer your question
Comment: Thank you! OK, I see these are written in quotation marks, that makes sense. You could loosely say that some forms of AR and MA do something like differencing or antidifferencing. But these are rather constrained cases and the argument could even be reversed by reversing the signs of AR and MA coefficients. But OK, thanks for the reference!
Answer: The whole idea is to combine AR , DIFF and MA structure in a parsimonious way incorporating pulses,level/step,seasonal pulse and local time trends as needed following http://docplayer.net/12080848-Outliers-level-shifts-and-variance-changes-in-time-series.html and others .
Careful iterative steps should be taken to insure that no unnecessary and/or redundant structure is incorporated. Model building is not a 1 stop process but rather a sequence of steps culminating in an equation that may have needed complexity but doesn't have unnecessary structure. Comments like "the significance of variables is irrelevant" is self-serving due to software limitations which doesn't' enable necessity and sufficiency checking and appropriate remedies and flies in the face of "good statistical practice"
Software that simply tries to "fit without testing significance"  and avoiding the treatment of deterministic structure often over-parameterizes requiring some of the steps you alluded to in your question ARIMA Time series analysis forecasting and How to determine order of sarima?.
So the suggested "logic" goes ..  STEP 1:... use auto.arima to identify the ARIMA portion assuming no interventions ( one form of deterministic structure) are present in the data which erroneously misidentifies the noise if deterministic structure is present. This explains the unwarranted and extremely complex over-parameterized model selection typically reported. See Coefficient Significance in Regression with Arima Errors for a very recent example of this.
The model should be complex enough but not too complex. The residuals from the final model should be free of autocorrelation and have a constant mean and variance throughout time.


Local strong convexity of a strictly convex function

Question: Is there a formal way to characterise strong convexity about the optimum value of a strictly convex function? I have an objective that looks something like this: $J(p,q) = \sum_{i=1}^{n}d(\pi_{i},q_{i}) + \alpha\sum_{i,j}w_{ij}d(p_{i},q_{j})$ where d is a jointly convex Bregman divergence (like KL or squared Euclidean) and $\pi_{i}$'s and $w_{ij}$'s and $\alpha$ are given parameter values. At the optimal value $(\bar{p}, \bar{q})$, neither the first term, nor the second term becomes zero (this comes from the practical usage of this objective). Is it possible to show strong convexity of this function around $(\bar{p}, \bar{q})$. My objective is to show positive definiteness of the Hessian around $(\bar{p}, \bar{q})$ and I think it is easier to prove strong convexity compared to proving positive definiteness of Hessian.
Comment: Do you wish to do this because strong convexity implies strict convexity? Or are you looking to see to what extent does the reverse direction hold?
Comment: Suvrit, I want to see to what extent strict convexity implies strong convexity around the minimizer. My final objective is to show positive definiteness of Hessian around the minimizer. Strong convexity $\Leftrightarrow$ positive definite Hessian, and positive definite Hessian around minimizer is going to help me in convergence rate analysis.
Answer: Well, not a full answer, but in general a strictly convex function does not need to be strongly convex around its minimizer. An obvious example is $f(x) = x^4$ in the real axis. While this is "locally strongly convex" away from $x=0$, its "local modulus of strong convexity" decreases to zero for $x\to 0$.
However, I am not sure if one can produce this situation in is your case of Bregman divergences but I would guess it could be possible.
Comment: Actually, I worked out the details and it turned out the showing positive definiteness of Hessian is easier for some special cases. However, I would really like to have a more "general" solution. Is anyone aware of any such theorem in convex analysis?


Does a radiologist adjust the amount of radiation for each individual?

Question: When performing an x-ray (in the UK specifically) does a radiologist use different settings based on which body part they are x-raying? Or do they have the machine on one setting for everyone? I'm curious because I would like to think that they adjust the x-ray dosage for each individual (and each body part) in order to minimise the amount of radiation the patient receives.
Answer: According to this Harvard Medical article, in order to x-ray an arm or leg the average dose is 0.001mSv with a range reported in literature of 0.0002—0.1mSv.
A lumbar spine x-ray would require an average of 1.5mSv with a range reported in literature of 0.5—1.8mSv.
Therefore, it would be safe to say that dosages are adjusted according to the part of the body needing an x-ray image.
Comment: @BenClarke - No radiologist here is going to answer a question that has already been answered correctly. The dose isn't dictated by the radiologist; it's dictated by protocol, which the technician follows for *every* Xray, or the image would be sub-par. Little people get less; larger than normal people may need more. See https://www.epa.gov/radiation/who-regulates-radiation-used-medical-procedures; "Using only as much radiation dose as is required to achieve adequate image quality should be the goal."
Comment: Thanks Chris. The information you provided would definitely indicate that the radiation levels of most x-rays are indeed adjusted based on the body part being x-rayed — this is good to know. However it would be nice to hear first hand from a radiologist if this is strict practice for every x-ray, or just done every now and then. For example, does the x-ray machine explicitly require the body part to be specified before each new x-ray is performed, or is there room for human error if the radiologist simply forgets to adjust it from the previous patient?
Comment: Thank you @anongoodnurse - your comment helped to further clarify the previous answer. It would still be good to hear from an actual radiologist though, just to get some finer detail about how the protocol is followed in terms of the user interface on the machine.
Comment: @BenClarke - Not gonna happen. Your expectations are way too high. The tech presses buttons, enters info, et voila! Ask a radiology tech you might know.


Close question when answer is not possible

Question: I have asked a question that has no possible answer due to a flaw in the underlying system that hasn't been resolved and won't get resolved. That flaw isn't completely analyzed and won't be in the future, so the given answers, though all might have helped, weren't the solution to the specific problem. I can't answer my own question as the problem hasn't been solved and won't be solved. How can I close that question (to have that question not killing my acceptance rate)?
Comment: I'd say the answer is that the problem is unsolvable for X reason. Share your research so the next person with that problem doesn't waste their time.
Answer:
You can answer your own question to state what you have discovered via your research. If the question is unsolvable, the answer is that it is unsolvable. Post the appropriate documentation that has led you to this conclusion.
Forget your accept rate. It's less important than finding the right solution. If the right solution never arrives despite other people's best intentions and your own followup, then it simply never arrives. Do not feel obligated to accept an imperfect or incorrect answer just because somebody nags you over some metric.
Comment: I object strongly to #2: If it is literally impossible then the accepted answer should lay out why that is the case. Don't let future users suffer because you know something is impossible, show them via an accepted answer and your research.
Comment: @BenBrocka, strongly agree to #1 then. #2 is a related offshoot inspired by his comment about his acceptance rate and recent comments I have seen added to questions on Stack Overflow where the comment *literally* said "nothing works below but accepted an answer to keep my accept rate high." I obviously want him to provide his own answer when he finds out what it is, even if that answer is "no soup for you." I do not want him feeling pressured to accept *the wrong thing* just to keep some stupid metric at some meaningless level. Make sense?
Comment: Answered my own question, providing one more fact we found on the way, just before it was decided to workaround the issue with the provided hint until the next hardware version is out.


Can a PhD thesis use only data that other people collected?

Question: If another PhD student created a dataset, can I use it for my own PhD thesis, with permission and attribution, and not collect any data myself? Or it is usually expected that a PhD student should collect at least some data?
Comment: I'm sure this is field-specific: neither myself, nor any of my fellow statistics PhD students came anywhere close to collecting our own data :)
Comment: Ask your advisor.  He/she will know the answer in your specific case much better than anyone here.
Answer: Yes, in principle there is no issue with not generating your own data. The general requirement is that a PhD provides an advancement of knowledge in a particular field, not necessarily generate novel data.
However this is likely to be subject-dependent. My PhD was based on developing a new statistical method to analyse data, and for that I applied to data other people had collected, not data I had generated. However, if your field was experimental plant sciences, I imagine there may be an expectation (but not necessarily requirement) to collect your own data.
Comment: Yes, my field is Stats&ML, and I tend to use readily available datasets as well (other than artificial data)
Answer: There is no ethical problem with using data from others with permission and attribution. However, what is acceptable in a dissertation is up to your advisor and your institution.
Since one major purpose of a PhD is to give you training and experience in research, some will expect that collecting the data yourself might be required. There are problems that can arise in collection that you avoid by using the data of others in some cases.
Work this out with your advisor if the question isn't purely theoretical. The research question itself might be important enough that the source of the data is less of an issue. There are lots of possibilities.
Answer: You should be fine not collecting the data and instead use widely used data if there is no regulation against it (which generally does not). Moreover, using others' data has a good side that might increase the impact of your work.
First, people in the field will know right away what to expect. For example, in the digit recognition work, using MNIST data would be the no-brainer choice for this task as people in the CS would have known it by heart. Or if it is an RNA sequence, you might not need to do sequencing again if it is on NCBI.
Second, using the already existing data would benefit you in benchmarking your method. This includes the performance of your method and the correctness of your work. Now, given that you are using another Ph.D. data and assume that it is not yet published or it is not a well-known dataset. If your results are in the same direction, that will tremendously increase your work and another Ph.D.'s work impact.
That said, you might need to look into the purpose of the data you are using and whether it will take the crucial part of your work. Nevertheless, please review with your advisor and university to get a more decisive answer on whether the data inclusion is ok.
Comment: Indeed, using public data is convenient for comparing your result with others'. DNN papers seem to be fond of public data.
Comment: Good answer, though your MNIST digit example is a bit out of date, that challenge problem is [pretty much solved](https://paperswithcode.com/sota/image-classification-on-mnist).
Comment: @cag51 Look at it another way - it is a *timeless classic* now :)
Answer: Yes. Also: depends on your PhD.
Whole areas of physics rely on data retrieved by someone else (or layers of "someone elses"). Particle physics is one of them.
I used the experimental data of other people because I am not interested in the experimental part and they were interested in the theoretical / analysis one. We made a few papers together.
I wrote a paper after asking someone else for their data (they published an article based on them) because I wanted to analyze them differently. That person did not want to be a co-author but was happy to share their data (and more).
I gave the data I received to another PhD student so that she does not lose time gathering more.
All of this, of course, assumes that the exchanges and relationships are clearly acknowledged (or co-authored).
And then comes the second sentence of my answer: your PhD may require you to actually retrieve your data. I do not think that this is a hard rule but the spectrum of research is so wide that everything is possible.
Answer: Ph.D. theses, like other publications, can use data other people collected. A meta-analysis or meta-study is a statistical analysis combining the results of pre-existing published scientific studies.
Comment: While this is true, a meta-analysis is not usually an acceptable PhD thesis, at least in fields I'm familiar with