Why isn't Higgs coupling considered a fifth fundamental force?

Question: When I first learned about the four fundamental forces of nature, I assumed that they were just the only four kind of interactions there were. But after learning a little field theory, there are many other kinds of couplings, even in the standard model. So why isn't the Yukawa Higgs coupling considered a fifth fundamental force? To be a fundamental force, does there need to be a gauge boson mediating it?
Comment: Doesn't look like this has been mentioned yet: intuitively, forces are vectors and impart momentum, whereas the Higgs field is a scalar field that generates mass. If a fundamental interaction isn't mediated by a gauge boson, then it loses it's most force-like quality of being a vector field.
Comment: For absolutely no good reason at all.
Comment: I think you're more or less right; what have been (sociologically) canonized as the fundamental forces (minus gravity) roughly correspond to the factors $U(1)$, $SU(2)$, and $SU(3)$ in the famous "$U(1)\times SU(2)\times SU(3)$" gauge symmetry of the standard model.  But this is really a historical question, in my opinion.
Answer: The Higgs exchange between matter particles can certainly be called a force. Whether it can be viewed a fundamental force, is a matter of taste. But there is one important distinction between the force due to the Higgs exchange and the usual fundamental interactions. The strong and electroweak interactions are described as gauge interactions. It means that they are not put by hand but arise automatically when you require that the matter fields be invariant under local certain internal transformations (phase rotations, color transformations, etc.). In contrast to that, the "Higgs force" is put into the model by hand, as its presence is not driven by any symmetry consideration. You can equally nicely consider a model with zero Yukawa coupling.
Comment: The catch here being that the symmetries themselves are "put into the model by hand." The Higgs coupling is driven by experimental results, and so while you could consider a model with no coupling, you'd have to explain spontaneous symmetry breaking some other way. Is your suggestion that some higher energy theory may in fact have some further symmetry that at low energy gives us the Higgs interaction, and that the higher level symmetry is the fundamental force, making the Higgs in some sense non-fundamental (like electric and magnetic separately)
Comment: As for the second question, I just say that you can construct a theory with Higgs bosons but zero Yukawa couplings (no "direct Higgs force"), but you cannot construct a locally U(1) invariant theory without electromagnetic interactions.
Comment: Concerning putting by hand, let's consider electromagnetism. You start from free field theory with complex field describing matter. Complex fields are put by hand, but after quantum mechanics this is not that unnatural. The lagrangian has the global U(1) invariance, so that the global phase is unobservable. This is rather expected. What you ask in addition is to make the phase unobservable locally. This also seems a rather reasonable requirement. That's it, the electromagnetic interactions follow. For non-abelian groups I agree that the initial global symmetry is put by hand.
Comment: You can certainly send the gauge coupling to zero. Notice also that you can write down theories in which the Higgs comes from additional components of gauge fields in extra dimensions. Given that, it is hard to argue that there is a fundamental difference between these interactions.
Comment: @IgorIvanov "_You can equally nicely consider a model with zero Yukawa coupling._" Though mathematically consistent, that wouldn't describe the Universe we live in!
Comment: @IgorIvanov: Really? Are you sure you can't zero out the charges on all fundamental particles?
Answer: Scalar fields do transfer momentum in classical physics. Just take a look at acoustic signals in a gas. A strong sound can cause your windows to rattle. A well known example of energy transference by means of sound (pressure waves) is demonstrated with tuning forks. Quantum theory speaks of sound as particles (phonons), the discrete quanta of quantized mechanical vibrations of a christal lattice, whose longitudinal mode corresponds to our macroscopic perception of sound. In quantum field theory all fields need to be quantized in the end. If I've understood it correctly, the Higgs particle represents the discrete quanta of the quantized Higgs field. Since the Higgs field is a scalar field, its quanta are bosons. They carry kinetic energy, and this energy can be transmitted to all quantum fields that the Higgs field interacts with. You just need to take a look at the Lagrangian to see all the fields that the Higgs interacts with. Alternatively, look for the various Feynman diagrams that include Higgs lines. You can then easily see all the particles it interacts with.
Comment: Exactly the same can be said about all 4 fundamental forces: they make waves which transfer energy and momentum, they are quantized and make particles, also bosons (though of other spins, 1 and 2, as they are vector and tensor fields).
Answer: Forces and interactions are similar, so maybe for the purposes of this discussion we should define force as "interaction with a massless particle," as this gives the possibility of macroscopic-range "forces" (barring impeding effects such as confinement or symmetry breaking).  After all, gravity is a massless but non-Yang-Mills force (mediated by spin-2, not spin-1, particle).  There are some constraints on which spins (representations) of massless particles are possible in quantum field theory, but I'm not familiar enough to try to cite them off-hand, sorry.
Answer: The theory of particle physics is mathematically organized as a gauge theory with the group structure of SU(3)xSU(2)xU(1).  These have exchange bosons, which before weak symmetry breaking have a zero mass, and after symmetry breaking have been  associated with the three fundamental forces , electromagnetism, weak, strong. This association comes from the mathematical continuity that is necessary going from the microscopic frame of quantum mechanics to the macroscopic of classical electrodynamics, extended to the strong and weak forces.
A force in the micro world of Feynman diagrams is any dp/dt, momentum transfer,  in an interaction exchanging particles, for example in this Compton scattering diagrams which is for calculating the crossection of a photon scattering off an electron:

There is a dp/dt, and the virtual exchange particle is the electron. It is an electromagnetic interaction because the incoming vertex is electromagnetic and has the coupling constant of electromagnetism. The electron exchange between vertices is not a fundamental force.
Fundamental are the exchanges associated with  the gauge bosons, as the lower order diagrams which give most of the probability for the interaction are  the simple exchange of a gauge boson, when it is allowed by quantum numbers. It is the simple exchange of virtual photons that will build up the classical electric and magnetic potentials of the classical electromagnetic interaction.
The Higgs field which is associated with the existence of the mass of the elementary particles  does not transfer momentum, and thus is not a force; the exchanges of the Higgs boson are on the same level as for example the exchanges of electrons, (as seen in the diagram above,)  in the appropriate diagrams, i.e. a simple transfer of dp/dt. Thus the Higgs mechanism is not related to a new fundamental force.
At the quantum level it is the coupling constants that define the type of interaction and are fundamental. The Higgs boson is in the electroweak sector and, as a neutral elementary particle, interacts only with the weak coupling constant at the vertices.
Comment: There is a Higgs-exchange force, as discussed [here](http://resonaances.blogspot.com/2016/01/higgs-force-awakens.html).
Comment: @benrg interesting, nevertheless it is not counted in the three fundamental forces of the standard model. In a sense all virtual particle exchanges in a Feynman diagram carry a dp/dt and can be called a "force", imo
Answer: I agree with tparker's comment: it's for absolutely no good reason at all.
As discussed in this Résonaances blog post, there is a Higgs-mediated force between particles, which is a bit like scalar gravity, but with a weak-force-like range. Its Feynman diagrams look just like those for other forces. I can't see any good reason to deny fundamental-force status to this interaction in light of the fact that:

The nuclear force, which is carried by non-gauge bosons (pions), is called a force. Not a fundamental force, since pions aren't fundamental, but it's similar to the Higgs force otherwise. There's even a pion version of the Higgs mechanism.

The electromagnetic force is called fundamental even though its force carrier is a weird mixture of the fundamental SU(2) and U(1) gauge fields.

The weak force is called a fundamental force even though it barely has the qualities you'd normally associate with a force, and its force carriers are weird mixtures of the fundamental SU(2) and U(1) gauge fields and the fundamental Higgs field.

The Higgs force shares the weak force's weakness of not being quite fundamental because the Higgs that we see isn't quite the fundamental Higgs field. But it's not a composite particle either. I'm inclined to say that gravity, SU(3), SU(2), U(1), and the fundamental Higgs force are the five fundamental forces of our current standard model, and electromagnetism, the weak force, and the low-energy Higgs force should be classified as "dwarf fundamental forces".
Comment: Right, I find it laughable when people say the Higgs doesn't qualify when three components of the Higgs field literally make up some of the degrees of freedom of the W and Z. I would also point out that Higgs mediated interactions are one of the primary targets of dark matter direct detection experiments, so if the Higgs doesn't count as a force... what would one say these experiments are looking for?
Answer: The Higgs field is not a vector field like, say, the vector potential of EM is. It arises from the observed coupling of massive particles to the weak field. So the Higgs boson is not a force-exchanging gauge boson in the same way as the other bosons of the Standard Model.
Comment: The gravition wouldn't be a vectorial (it would have spin 2), but I would still be a force boson. Right?
Answer: If gravity is a fundamental force, then the Higgs mechanism is also.  This is is true whether they are related or not.  The Higgs mechanism is certainly the source of the inertial mass that inspired Newton to quantify what a force is, and how it behaves.
Gravity, like the Higgs mechanism, can add mass/energy to matter in bulk (like constant acceleration), bend or even confine other force carrying bosons (photons) in space.  This happens in the event horizon of black holes.
Not only is the Higgs mechanism a fundamental force, but the way it interacts is unquestionably unique among the fundamental forces.   It slows down and limits the range of electroweak force carriers (W,Z) by breaking local symmetry, giving them mass without violating conservation of mass/energy.
Comment: The Higgs mechanism is certainly **a source** of the inertial mass, but [the only source it is not](http://physics.stackexchange.com/questions/64232/your-mass-is-not-from-higgs-boson).

A rare occasion where English helps to get a thought precisely, a correct one or not.


Script that send Public/Global IP On restart

Question: I own a server at my Parents house and recently there has been a lot of power cuts and when our Router comes back online it changes its Public/Global IP address which makes me unable to connect to it (SSH, FTP, HTTP) ,is there any way that I could make a script that when the power goes out on my server and it reboots it send an email with my Global/Public IP to me.
Comment: Hi, Joiie, I think [**this is the right answer**](https://askubuntu.com/a/907784/566421) for your question. I can create step by step 'manual', but later today :)
Answer: You could try using sendmail.
install
sudo apt install -y postfix

choose internet side and enter your server's hostname
Write a script e.g. in sudo nano /usr/local/bin/sendIPmail:
#!/bin/bash

# 1. gets the primary IP
#from https://stackoverflow.com/a/25851186/7111561
IP=$( ip route get 1 | awk '{print $NF;exit}' )

# 2. send it using sendmail
#from https://stackoverflow.com/a/13390926/7111561

#--- adjust those ---
recipients="your.mail@address,email@example.com"
subject="some subject"
from="firstname.lastname@example.com"
#--------------------

/usr/sbin/sendmail "$recipients" <<EOF
subject:$subject
from:$from

New IP is $IP
EOF

exit 0

make it executable
sudo chmod +x /usr/local/bin/sendIPmail

and call it on every reboot
run
sudo crontab -e

(select your editor e.g. 2 for nano)
Add the line
@reboot /usr/local/bin/sendIPmail

This does not require any external webpages or complex scripts/setups and uses only packages from the official Ubuntu repos.

NOTE: Alternatively you really should consider using a static IP address for a server!
Answer: use my script.

Clone the script from my github repo:

git clone https://github.com/el-beth/sendExternalIPAddress.git

then move the sendexternalip.bash file from the directory sendExternalIPAddress to /usr/lib - use the following command to do so.

 sudo cp sendExternalIPAddress/sendexternalip.bash /usr/lib

now make the script executable:

sudo chmod +x /usr/lib/sendexternalip.bash

for the first time, to install all the necessary packages and dependencies:
sudo /usr/lib/sendexternalip.bash
now to make the script run automatically on startup run the following command:

sudo printf "start on startup\ntask\nexec /us/lib/sendexternalip.bash\n" > ~/.config/upstart/sendexternalip.conf
This will make your Linux box email it's current external IP address to the email address specified in the script.
N.B. The script - by default - sends the External IP address to the email address "firstname.lastname@example.com", however, you can change the customReceiverEmail variable on line 9 of the script to any @grr.la address of you choosing and the IP address will be sent to that address instead.
Comment: I think one of the issues here is if they don't have GoeillaMail - the entire thing seems to rely on that based on your answer.
Comment: I have edited the answer and fixed a bit. would you be so kind as to go through the answer - from the top - once more and up-vote the reply when it works .. lol .. btw, really sorry for the hassle - but the improved answer will work. Also gorilla mail is a free and anonymous messaging service. google it.  no sign up or subscription is needed. in your case you just insert the email address "firstname.lastname@example.com" in the box at the homepage and voila, you can see all the emails that are sent to that account. these are disposable email addresses.


Seeking Open Source Training Materials?

Question: The question Are Online Certs worth their weight? made me wonder if there are any open source training materials for GIS.
By this I don't mean training specifically for open source software - of which I know there are some - but a set of general training materials for GIS and geographic data that are developed as an open source project.
i.e. a set of training materials that are community developed, freely available, and with an open license. That anyone could take and use for general GIS training.
If there isn't, does anyone think this would be a worthwhile project?
Please add license info for the material you're suggesting.
Comment: This sounds like a great project. I'm trying to get started in FOSS4G and am finding it really hard to know where to begin. (GIS.SE users have been very helpful in giving pointers)
Answer: OpenGeo have really great material on their site. Some of it is training for their particular software combination (which is not free AFAIK), but they run through a bunch of other tools and methods that are.
For example, here is a PostGIS tutorial; they also provide everything rolled up in this useful zip.
This work is licensed under a Creative Commons Attribution-Share Alike 3.0 United States License.
Answer: The OSGEO Education group have a searchable collection of educational materials (some of which it hosts, others are links to materials hosted elsewhere).
(Licenses vary between different tutorials.)
Ultimately the plan is to develop a handbook and course materials - feel free to join the effort at http://wiki.osgeo.org/wiki/Edu_goals_and_to_dos
Answer: There is the FOSS GIS Academy
The FOSSGIS Academy is a joint venture between Linfiniti Consulting cc, AfriSpatial cc and Geograph (Pty) Ltd. FOSSGIS Academy was formed with the aim of creating a formalised FOSS GIS training curriculum to provide the needed injection of FOSSGIS skilled workers into the geospatial workplace.
Has some 'Resources'
Though most of the actual courses do charge a fee for the course online.
For Mark Ireland:
Maybe Safe Software can invest some resources (or some open source datasets) for OpenFME?
(A web based lite version of Desktop/Server)
*have just made OpenFME up
Have enjoyed FME Training Online and there is a potential for Open GIS Resources - there is just a cost for setting all of this up - with governments freeing up geospatial datasets and open source GIS software and databases it can be possible.
Comment: There is also the http://www.foss-academy.eu/
Answer: There is GIS Commons, a free textbook being developed by a Sacramento State professor. It covers high-level GIS topics, not any particular software.
This work is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License
Answer: The Boston GIS site (bostongis.com) has tutorials and reference material for a few different OS software packages.
Answer: Possibly out-of-date for some topics, and not exactly what you're looking for but there's the Geographer's Craft site. They have materials on ethics, intro to GIS, map projections and datums, etc.
Comment: out-of-date but still very useful.
Answer: ELOGeo Project has couple of good pointers in its repository, and let's hope it will grow larger.
Answer: Dr. Nicholas Short's Remote Sensing Tutorial
This tutorial on remote sensing is excellent. It is essentially a textbook on remote sensing for free on the web. It's produced by a NASA employee as part of his job so it is in the public domain.
Answer: Take a look at Geospatial Analysis. Not exactly "Open Source" in the true sense of the term, but freely available.
Answer: Have a look at this repository, it's a list with all the online resources to learn CartoDB, a open-source geospatial platform. From their Map Academy and tutorials to related programming languages such as SQL, CartoCSS or Javascript. The repo is in Spanish, but all the links are in English.

Seeking Open Source Training Materials?


How do "lecturers" differ from "professors" in large universities?

Question: I notice that some universities have academic positions known as lecturers. Are these positions different from professors? Are transitions from instructors to the professor track relatively easy. This position seems similar to the adjunct professor position.
Note that I am talking about universities in the USA.
Answer: I used to be a lecturer at a university in the southwest USA.  As a lecturer, I was charged with only teaching lower division undergraduate courses (freshman & sophomore level).  In general, research and service is not a requirement for lecturers (unlike professors), but we are required to teach a larger load than professors.  And we were generally yearly appointments with no chance of tenure.
Comment: A lecturer is effectively a contractor who happens to be a university employee rather than working for another company. A lecturer position may also be part-time, and can sometimes be called an "adjunct" position.
Comment: @Suresh: I think it means that you are employed as needed for a period of time, but are not guaranteed employment year to year.
Comment: @aeismail, it depends.  There are universities that have lecturers with the equivalent of tenure (they may call it something else, like "security of employment", but it is functionally equivalent).  So, I agree with all of Paul's answer, except for the last sentence -- in practice there is considerable variation from university to university on the specifics of how lecturers are hired or retained, and what degree of job security they enjoy.
Comment: Note: Some universities have a career lecturer/teaching professor track. At such universities, you can be promoted to "senior lecturer", and although this doesn't come with tenure, it switches over to something more like a 5 year contract instead of a 1 year contract, and the intent is to allow people to stay at the university long term.
Comment: What does it mean to be "effectively a contractor" ?
Comment: Question "How do lecturers differ from professors". Answer: "Yes!"
Comment: @Suresh: Regarding Paul's comment, it should be noted that in the US, this is the norm for employees in all sectors: employment is generally "at will" and university professors are among the very few employees, in any industry, who have any sort of guaranteed job security.
Comment: Where I work (Canada) a Lecturer gets promoted to Senior Lecturer and then has bit more job security. We can/are teaching all years (1-4, which in US is freshman all the way to senior). Unlike Professors, we don't have graduate students, have a higher teaching load, are expected to have the same service load as the professors and don't have to do research (which is a big one).
Answer: In the US, I've mostly seen the title "Lecturer" applied to non-tenure-track, mostly non-research teaching positions. For what it's worth, wikipedia agrees with me on this.
Answer: In many places in the US, thinking of research-oriented universities, "lecturer" or "instructor" is not at all like assistant, associate, or full prof, and is not tenure track. "Lecturer" and "instructor" are closer to "adjunct", and are teaching-oriented. Sometimes the positions are effectively long term, but most often just year-by-year, or even term-by-term. Any transition from these positions to tenure track would be unusual, although in the more recent economic upheaval, sometimes people take such positions just to be employed for a year, waiting out the job market.
Comment: I agree with most of this answer, though in my experience lecturers are usually pretty different from adjuncts (lecturers are often full-time employees, adjuncts are typically part-time and in some ways may be more like contractors than employees).
Comment: @D.W., yes, what you note can be true, and/but adjuncts often have a better chance at long-term employment, even if without long-term contract, than lecturers, whose employment may have a definite end. Depends on the situation and the economic times.
Answer: I can give the Australian context.
"Lecturer" is a rank in Australia.
The typical hierarchy is "Associate Lecturer", "Lecturer", "Senior Lecturer", "Associate Professor", "Professor" (see this discussion). Thus, on the academic ranking scale from A to E, lecturer is B.
However, it is also common for anyone who gives lectures in a university to describe their job in terms of "being a lecturer". In this sense "lecturer" is an often informal job title that may be used by an academic at any academic rank. For example, someone might ask you what you do for a living and you might answer "I'm a lecturer at a university". Such a response could be given by someone at any academic rank.
Comment: This is a reasonably important answer to the extent that applying your local ranking system to other University systems' ranking system may result in embarrassment or offence.
Answer: Agreeing with the other answers, "Lecturer" is often the title given to full-time non-tenure track (i.e. contractual) faculty who typically only have instructional duties. Depending on the style of the institution, it may or may not be possible to move into the tenure-track. Lecturer, however, is not always a "dead-end". Some schools have a separate promotion system to reward and promote their non-tenure track faculty (similar to the way you would reward and promote staff). At these institutions there might be ranks, like Lecturer I, Lecturer II, Senior Lecturer, etc.
Disagreeing with the other answers, the term "adjunct" usually refers to a part-time instructor. Adjuncts usually have few if any opportunities for advancement. At many institutions, adjuncts may be distinct from Lectures (as a Lecturer is a full time appointment). My institution confusingly calls full-time and part-time instructors "Lecturer", but then proceeds to treat them as very different types of employee.
Comment: At the University of California, there is such a thing as "Lecturer with Security of Employment", which offers tenure-like protections to instructional faculty.
Answer: The terminology of positions differ from country to country. Lecturer has its origins in the British system. I know that when positions in other (non-English speaking) countries are announced internationally they may use this terminology. This is of course because each language have their own words for different positions. There is no straight translation between these systems including the system used in for example the US consisting of Assistant, Associate and Full Professors. The form of the employment also varies from country to country for historical reasons. A Lecturer is probably similar to an Assitant Professor, whether it is a permanent position or not probably varies.
Comment: The question specifically asks about universities in the US.
Answer: I am teaching in University (Mongolia). In our country calling every person who is teaching in university, first "Lecturer". We are starting from assistant lecturer, lecturer, senior lecturer going on. If you have PhD degree you can go to next level: Associate Professor and Professor. But in generally all calling like lecturer. If you are already in Professor position your teaching hours is reducing and increasing hours for research and projects.
Different between Lecturers and Professors in our meaning sounding like, have academic degree or not. But not every body can become Professor who have PhD degree. You have to be lead some main research direction or field, you have to write books about your field.
Big difference from European countries Professor position in our university is not lifelong. After every 3 years you have to be accredited. If you are enough good by this process you can keep your position, if not your level is reducing.
I am agree that Professor have to concentrate more to research and Lecturers can be focused for teaching.
Answer: I'm a staff member at an American university.  Lecturers here don't take on graduate students (Research Assistants) to advise for their thesis, guiding their research, etc. which is a major component of a professor's duties and legacy.
Comment: This question has been really interesting to follow. Clearly there is a huge breadth of definitions for lecturer positions. I am a full-time lecturer and my responsibilities are to teach graduate level courses. A significant portion of my responsibilities also includes admission decisions and advising masters students including their MA theses, projects, and research. No tenure track, but the trend here is a more long-term career / relation with the institution. Non-faculty, but with many faculty duties. Even within a particular institution, there can be some variations.


Go Ethereum (GETH) Node Error

Question: I'm trying to get smarter on blockchain broadly so downloaded Bitcoin Core / Geth nodes recently and got them both working but admittedly I hardly know what I'm doing. I didn't realize that I needed to shutdown geth in a particular way (as opposed to just exiting out of CMD), so I did an unclean shutdown and then received an error that keeps repeating directly after that. The error is 'Section processing failed, type=bloombits, error ="canonical block #12597521"'. Searching around I've seen this error occur to others that improperly closed geth, but I've failed to find a fix and if it actually makes an impact to my node. My chain is still up to date.
Would appreciate any advice/insight to this error.
Thanks!
Answer: In go-ethereum repo there are a couple of related issues. In issue #22471 Ligi suggest a couple of solutions

Try PR #21650
Sync from scratch

Go Ethereum (GETH) Node Error


On rotation table cells do not take up the full width of the table

Question: When the app first loads the table and cells are correct. When you rotate to landscape mode the table cells look like they are still set up for portrait mode. When you rotate back to portrait the table cells are set up for landscape mode.
Is there any way to manage this in the code?
Thanks
Answer: Looks like I spend for ever looking for an answer and when I break down I ask a question, then 5 min. later I find the answer.
Well here you go.
Hope this helps out someone.

<code>
-(void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation{
    [self.tableView reloadData];
}
</code>


In Ruth 1:2 what is the meaning of אפרתים (commonly translated "Efrathites")?

Question: In Ruth 1:2, Naomi, Elimelech, Machlon and Kilyon are referred to as אפרתים, or Efrathites.  To me, the simplest understanding would be that they come from Efrat (see Genesis 35:19, 1 Samuel 17:12, Micah 5:2).  What other possible explanations are there, and what might motivate them?
Comment: בראשית מח ז: ואני בבאי מפדן מתה עלי רחל בארץ כנען בדרך בעוד כברת ארץ לבא אפרתה ואקברה שם בדרך אפרת הוא בית לחם
(Genesis 48:7 MT)
Comment: @AbuMunirIbnIbrahim I'm not sure I understand what you are adding.  I already quoted וַתָּמָת רָחֵל וַתִּקָּבֵר בְּדֶרֶךְ אֶפְרָתָה הִוא בֵּית לָחֶם. (Genesis 35:19).
Answer: There appear to be two possibilities to the meaning of this term. Let me explain.
The term Ephrath, means 'fruitful'. The people living around Bethlehem (House of Bread) were called Ephrath, or Ephrathites. The area surrounding the city is/was known to be productive agriculturally.
This term could have come from ...
1. A family or clan from Israel who first settled the area.
2. Ephrath was an acient name of the area (a Canaanite city) before it was named Bethlehem.
When the term, Ephrath, is used in scripture, it is always associated with Bethlehem of Judea.
Comment: Can you please point me where אפרת means fruitful (פורה)? I agree that the base is פר but can't find any פ.ר.ה/פ.ר.ת changes on other words (that is not plural end like cow פרה-פרות or fruit פרי-פרות)
Answer: Mark 7:34 has the translation of Ephratah as :

And looking up to heaven, he sighed, and saith unto him, Ephphatha, that is, Be opened.

If 'be opened' is the meaning of Ephphatha (Ephrata) then I would say it is a matter of the fruitfulness of the womb, as in its connection with Bethlehem and the bringing forth of the child Jesus, and the fruitfulness of the opening of the ear to rightly hear and understand the word of God.
Both the fruit of the womb and the fruitfulness of the open ear are brought together in Mark's record of the incident in 7:34.
The opening of flesh - the bringing forth of that which is spiritual and Divine - is what I understand in the word Ephrata.
Comment: Why is it justified to reconstruct the meaning of אפרתים using the root פתח? How did the ר sneak in and where did the ח get lost? There are some personal names based on פתח (yiphtaḥ, nephtoaḥ, naphtuḥim), but to go to אפרתים seems quite a leap doesn't it?


How do I trim the grass that's growing between the links of a chain link fence?

Question: I have a long stretch of chain link fence, and there is some grass that grows into the links.  When I try to trim it using a basic lawn trimmer, all that ends up happening is I chew up trimming wire and the grass stays put.  Is there anything I can do to trim this down easily?
Comment: Trim it with systemic weedkiller. Then plant something that will climb up the fence, if you want to make it look nicer.
Comment: It's a *lot* of fence, something like 100 feet or more.  Is there anything that can be planted easily that would do that climbing without needing to  plant dozens of vines?
Answer: One solution is to examine why the fence is there, and if the purpose permits it to raise the fence up on its support so that there is a clear space between the bottom links and the ground. Then when you pass with the trimmer the only obstructions will be the posts which are easier to avoid than the less visible chain links.
A slight modification would be to arrange the bottom of the fence so that it can be detached from its posts and temporarily held out at an angle, perform the trimming and then replace the fence. Perhaps you can find some snap clips at the hardware store that would enable this.


How to print ALL the elements of a List<>?

Question: I would need  to print all the elements of a list so to be able to copy them (CTRL+C) . In Debug Log , I can see only the first 10, or something similar .  (a temp solution I'm using is to store them in a Long Area Text field, but I think there's a more efficient solution).
Answer: You could use JSON serialization to format all the records in the collection.
E.g.
List<Account> accs = new List<Account>();
for(integer i = 0; i < 50; i++) {
    accs.add(new Account(Name='Account-'+i));
}
System.debug(JSON.serializePretty(accs));

Comment: Definitely the best answer - no need for a loop to print the List
Answer: I do it like this, if I want to see records in the debug log. Or query for them directly in execute anonymous and debug them from there.
string s = '';
for (record__c r : listOfThings) s += '\n' + r;
system.debug(s);

Answer: you don't need to change code for this. There is a Chrome plugin which shows debug log nicely formatted.
This is the link to that plugin:
https://chrome.google.com/webstore/detail/apex-debugger/mpckkbblhbfngaininanfjpdfjhbncjo?hl=en
Comment: This won't change the fact that, for Lists that are printed, only 10 values are sent to the debug log.
You can see this if you view the raw log - no amount of 'pretty printing' is going to 'expand' the 3 little dots at the end of  a line into actual values.

Still, looks an interesting plugin so I'm gonna give it a try anyway - just not for the reason you suggest ;)


How to isolate $x$ when $\cos(x/2)\cos(3x)/2−3\sin(x/2)\sin(3x)= 0$

Question: Asked to find all relative and absolute extrema of  $f(x) = \sin\left(\frac{1}{2}x\right)\cos(3x)$ on the interval $[0,\pi]$. I've gotten the derivative, $$f'(x)=\frac{\cos(\frac{x}{2})\cos(3x)}{2} - 3\sin(\frac{x}{2})\sin(3x),$$  just fine, but how would I proceed to isolate x after this? I noticed that the situation is similar to the sine angle sum identity, but I don't know if there's an identity for an equation with the form $$h\cos(\alpha)\cos(\beta) - k\sin(\alpha)\sin(\beta)$$ and can't find anything online. I don't have much experience working with Euler's Formula in this context but know enough that I could probably follow an explanation based on it.
Comment: [Wolfram Alpha](https://www.wolframalpha.com/input/?i=Solve+cos(x%2F2)+*+cos(3x)%2F2+-+3sin(x%2F2)+*+sin(3x)+%3D+0) seems to solve it the way I feared: by turning the whole thing into a degree six polynomial. This question appears to be unreasonable for a first year calculus course.
Comment: Just wondering, is this a book problem? Which class?
Comment: Taking Calc BC online through UC Scout; this is an open response assignment so just Wolfram Alpha without explanation isn't really good enough (and I also need exact answers when everything I've seen just approximates with polynomials).
Comment: Since $f'(x)/(\cos x/2)$ can be written as a cubic polynomial in $\cos x$, you could conceivably use Vieta's trig solution to the cubic to get $x=\arccos(\tfrac{2}{7}+\tfrac{\sqrt{37}}{7}\cos \theta)$, $\cos 3\theta = -\tfrac{104}{37\sqrt{37}}$.
Answer: Expanding and varying my own comment:
$$\begin{split}
f'(x)&=\tfrac{1}{2}\cos\tfrac{x}{2}\cos 3x - 3\sin\tfrac{x}{2}\sin 3x\\
&=\tfrac{1}{2}\cos\tfrac{x}{2}\left(\cos 3x - 6\frac{\sin\tfrac{x}{2}\sin x}{\cos\tfrac{x}{2}} \frac{\sin 3x}{\sin x}\right)\\
&=\tfrac{1}{2}\cos\tfrac{x}{2}\left(\cos 3x - 6(1-\cos x) \frac{\sin 3x}{\sin x}\right)\\
&=\tfrac{1}{2}\cos\tfrac{x}{2}\left(T_3(\cos x) - 6(1-\cos x) U_2(\cos x)\right)\\
\end{split}$$
where
$$\begin{align}
T_3(y)&=4y^3-3y \\
U_2(y)&=4y^2-1\text{.}
\end{align}$$
Thus,
$$f'(x)=\tfrac{1}{2}\cos\tfrac{x}{2}g(\cos x)$$
where
$$g(y)=28y^3-24y^2-9y+6\text{.}$$
Now, we "cheat" a bit and use a CAS to find an optimized representation for $g(y)$. Let
$$y=\frac{z+2}{2(z+4)}\text{.}$$
Then
$$g(y)=-\frac{h(z)}{(z+4)^3}$$
where
$$h(z)=z^3-66 z -172\text{.}$$
Using the trigonometric solution to the cubic, we find
$$\begin{align}
z&=2\sqrt{22}\cos\theta&\cos 3\theta&=\frac{43}{11\sqrt{22}}\text{.}
\end{align}$$
That is,
$$\begin{align}x&=\arccos\frac{1+\sqrt{22}\cos\theta}{2(2+\sqrt{22}\cos\theta)} \\
\theta&=\tfrac{1}{3}\arccos\frac{43}{11\sqrt{22}}+\frac{2k\pi}{3}\end{align}$$
Comment: Yes, you can. I just prefer to work with the [normal form](http://www.lmfdb.org/NumberField/3.3.87804.1) of an algebraic extension. If you depress the cubic with $y\mapsto y+c$ you get the expression for $x$ given in my comment on the question.
Comment: Like it! but can't you turn g(y) into $t^3+pt+q=0$ directly instead of 'cheat'?
Comment: You made it ! Great and $\to +1$. Cheers.
Answer: Trying approximate solutions.
First, using trigonometric formulae, the derivative can write
$$f'(x)=\frac{1}{4} \left(7 \cos \left(\frac{7 x}{2}\right)-5 \cos \left(\frac{5
   x}{2}\right)\right)$$ Forget the $\frac{1}{4}$ and plot the function. You should notice that, for the range of concern, the solution are "close" to $\frac \pi{12}$, $\frac \pi{3}$, $\frac {2\pi}{3}$ and the last one is exactly $\pi$.
So, around each of these values, build Taylor expansions to get successively
$$f'(x)=\left(7 \sin \left(\frac{5 \pi }{24}\right)-5 \cos \left(\frac{5 \pi
   }{24}\right)\right)+\left(x-\frac{\pi }{12}\right) \left(\frac{25}{2} \sin
   \left(\frac{5 \pi }{24}\right)-\frac{49}{2} \cos \left(\frac{5 \pi
   }{24}\right)\right)+\left(x-\frac{\pi }{12}\right)^2 \left(\frac{125}{8} \cos
   \left(\frac{5 \pi }{24}\right)-\frac{343}{8} \sin \left(\frac{5 \pi
   }{24}\right)\right)+O\left(\left(x-\frac{\pi }{12}\right)^3\right)$$ and we know the values of the trigonometric functions of $\frac{n \pi }{24}$. Solving the quadratic will give $x_1=0.286024$ (while the "exact" solution would be $0.286061$).
$$f'(x)=-\sqrt{3}+\frac{37}{2} \left(x-\frac{\pi }{3}\right)+\frac{109}{8} \sqrt{3}
   \left(x-\frac{\pi }{3}\right)^2+O\left(\left(x-\frac{\pi }{3}\right)^3\right)$$
Solving the quadratic will give $x_2=1.13170$ (while the "exact" solution would be $1.13265$).
$$f'(x)=1-\frac{37}{2} \sqrt{3} \left(x-\frac{2 \pi }{3}\right)-\frac{109}{8}
   \left(x-\frac{2 \pi }{3}\right)^2+O\left(\left(x-\frac{2 \pi
   }{3}\right)^3\right)$$
Solving the quadratic will give $x_3=2.12520$ (while the "exact" solution would be $2.12525$).


how to show views for particular language

Question: I have simple problem - there is a view that is aggregating some info and it has a link in the main menu. I'm also using i18n and would like to have that particular view only in one language, but it looks like that it's impossible to make it - I can't find any option how to make the view just in one language - the main menu item appears in both languages and I can't figure out how to disable it.
I'm using D7 and newest Views.
Answer: Have you tried to use filters? When you create your view, you add a new filter and select "Node translation" from the "Groupes" list and the check "Node translation: Language" and click "Add". Then you can chose language(s) on which you want the view to show
Comment: Yes, I can filter it away and therefore the content of it is not shown on any other languages. But the problem is that the menu link is still there and it is not translated - is on my original language. If I use filters then I have this link and clicking on him while being on some other language I'm getting an empty (filtered page). So let's say it's ok - I will have content for all the languages, but how can I translate the View's name to be seen in the correct language and is it possible to hide it in general?
Comment: Maybe you can try to use one different menu for each language?That's the solution we have used on one of our project with 3 different languages : each language has his own menu , then we add a block for each menu and we select the language in which this block will appear so only one menu would display for each language but others will be hidden
Comment: we used menu-translation and menu-block modules for that ..
Comment: Well it could be a solution, I have done this in my previous project, but I think there should be something more simple - it's ok if I use one View, but if I would like to use couple different views it could be very complicated. I'm pretty sure, that there should be some other workaround, or maybe something in views functionality that I don't know.
Comment: At the end I've solved this issue by creating separate menus for different languages. Actually there is another more intelligent solution, but it is not working with D7/Views3 - it's called i18nViews (Internationalization Views) - with this it is possible to translate headings of views, but I had to disable it as it crashes the system at the moment.

Now I have another problem - when I have two different menus for each language for some reason the menu title that is clicked is not highlighted and I can't find why...
Comment: I have never worked using i18nViews but I will have a look at it..it seems to be really interesting..have you reported the bug so they can fix it?


What is a proof for the principle of deferred measurement?

Question: Does anyone know of a proof for the 'principle of deferred measurement'?
Comment: Can you take the hints from problem 5 of [O'Donnell's homework set](https://www.cs.cmu.edu/~odonnell/quantum15/homework/homework1.pdf)?  I always intuited it as a consequence of the no-communication theorem; a violation of the principle of deferred measurement may allow Alice to take some of qubits, and make a measurement of her qubits whose results were contingent on whether or not Bob waited until the end to measure his qubits, or instead measured his qubits *in-situ* during the running of the circuit.
Comment: Related: [this answer](https://quantumcomputing.stackexchange.com/questions/15349/are-there-any-algorithms-that-take-measurements-in-an-intermediate-step/15355#15355) of mine works through two important cases.
Answer: I'll assume the "principle of deferred measurement" refers to the equality shown in the figure in the relevant Wikipedia page: the possibility of writing a "classically conditioned" operation as a standard conditional operation followed by a measurement (where measurement basis and basis used for the conditional operation are presumably the same).
(Measure and then conditional operation)
Consider a physical situation where one register is measured, and a channel is applied to another register conditionally to the measurement outcome.
We can actually model this situation in full generality for quantum channels and POVMs.
If you only care about pure states and unitary evolutions, you can replace in the following POVMs with standard projective measurements (i.e. $\mu(b)=|b\rangle\!\langle b|$), channels with unitary gates (i.e. $\Phi_b(X)= U_b X U_b^\dagger$), and generic operators/density matrices with pure states (i.e. $X=|\psi\rangle\!\langle\psi|$).
In fact, if only pure states are of interest, you can outright skip this section and jump the next one, as I'll specialise the formalism to pure states there anyway.
Assume a bipartite space $\newcommand{\Tr}{\operatorname{Tr}}{\cal X\otimes Y}$ for some finite dimensional vector spaces $\mathcal X,\mathcal Y$. Denote with $\operatorname{Pos}(\mathcal X)$ the set of positive semidefinite operators on $\mathcal X$, with $\Sigma$ some finite set labeling measurement outcomes, and with $\mathrm C(\mathcal X,\mathcal Y)$ the set of channels from $\mathcal X$ to $\mathcal Y$.
Suppose you measure on ${\cal X}$ with some POVM $\{\mu(b):b\in\Sigma\}\subset\operatorname{Pos}({\cal X})$, and the overall input state is some $\rho\in\operatorname{Pos}(\mathcal X\otimes\mathcal Y)$.
If the measurement gives the outcome $b$, which happens with probability $p_b\equiv \operatorname{tr}[(\mu_b\otimes I)\rho]$, the residual state on the other register "collapses" to
$$\rho_{\cal Y}(b)=\frac{\operatorname{tr}_{\cal X}[(\mu_b\otimes I_{\cal Y})\rho]}{p_b}.$$
If a channel $\Phi_b\in\mathrm C(\mathcal Y)$ is applied to the second register conditionally to observing the outcome $b$ on the first register, then the overall final state, disregarding the measurement
outcome, is going to be
$$\sum_b p_b \Phi_b(\rho_{\cal Y}(b))
= \sum_b \Phi_b(\operatorname{tr}_{\cal X}[(\mu_b\otimes I_{\cal Y})\rho]).$$
A concise way to rewrite this is as
$$\sum_b (\mu_b^\star\otimes \Phi_b)(\rho),$$
having defined the quantum map $\mu_b^\star\in\mathrm C(\mathcal X,\mathbb{C})$ as $\mu_b^\star(\sigma)\equiv \langle\mu_b,\sigma\rangle$.
This is but a formal trick to get a concise expression for the channel $\Psi$ describing the overall measurement+channel evolution, which can therefore be concisely written as $\Psi=\sum_b \mu_b^\star\otimes\Phi_b$.
If on the other hand the observed measurement outcome is remembered, then we can write the final state as
$$\sum_b p_b \mathbb{P}_b\otimes\Phi_b(\rho_{\cal Y}(b))
= \sum_b (M_b\otimes\Phi_b)(\rho),
\qquad \mathbb{P}_b\equiv |b\rangle\!\langle b|,$$
where I defined the quantum maps $M_b(\sigma)\equiv \mathbb{P}_b \langle\mu_b,\sigma\rangle$.
Note that $M\equiv \sum_b M_b$ would be the (entanglement breaking) measurement channel describing the act of measuring with the POVM $\mu$ and remembering the result in a classical register.
(Conditional operation and then measure)
Our goal would be now to show that we can equivalently perform some operation on the state and only afterwards measure the first register, and obtain the same identical final state.
Working in the general formalism of quantum channels, however, actually makes this a bit of a trivial question. The reason is that a channel might itself model an evolution involving a measurement, which would make the question moot.
In fact, we could simply define the "conditioned channel" $\tilde\Phi\equiv\sum_k |k\rangle\!\langle k|\otimes\Phi_k$, and trivially find that performing a computational basis measurement after applying this channel is identical to what we obtained before measuring and then applying the channel.
But this $\tilde\Phi$ corresponds in practice to applying $\Phi_k$ conditioned to a measurement outcome on the first register, and so this solution is useless in this context.
To get a better idea of how and where exactly measurements are involved, let's specialise our formalism above to pure states, unitary evolutions, and projective measurements.
Let $|\Psi\rangle$ be the input state. Say we measure in the computational basis the first register (we don't lose any generality assuming computational basis measurement: it amounts to a specific choice of basis to describe the states). Then the possible post-measurement states on the second register are
$$|\Psi_b\rangle\equiv \frac{1}{p_b} (\langle b|\otimes I)|\Psi\rangle,
\qquad p_b\equiv \|(\langle b|\otimes I)|\Psi\rangle\|^2,$$
and $|\Psi_b\rangle$ is found with probability $p_b$.
If the unitary $U_b$ is applied conditionally to observing the $b$-th outcome, the final state is
$$U_b |\Psi_b\rangle\equiv \frac{1}{p_b}(\langle b|\otimes U_b)|\Psi\rangle.$$
Suppose we instead deferred measurement to the end, and replaced the classically-conditioned unitary operation with the controlled-unitary operation $U\equiv \sum_b |b\rangle\!\langle b|\otimes U_b$.
This unitary gives the evolution
$$|\Psi\rangle\to U|\Psi\rangle
= \sum_b (|b\rangle\!\langle b|\otimes U_b)|\Psi\rangle
= \sum_b p_b |b\rangle \otimes U_b |\Psi_b\rangle.$$
This last expression makes the conclusion immediate: if we now measure the first register of $U|\Psi\rangle$ in the computational basis, we'll get the $b$-th outcome with probability $p_b$, and the corresponding post-measurement state on the second register is going to be $U_b |\Psi_b\rangle$, which is exactly what we got doing the measurement and then applying the unitary $U_b$ conditionally to the classical outcome.
Comment: @R-XZhao sorry, can you rephrase that? I don't really understand what you're trying to say. Anyway, rereading this I do think there were some issues in the answer. I reworked most of the derivation, so it should be solid now
Comment: +1 It's cool to know the principle applies to channels and POVMs, too. However, I think it's more general than the ability to commute measurements through controls. It says that for *any* circuit $C$ with intermediate measurements there is another circuit $C'$ where all measurements are terminal and that agrees with $C$ on all inputs, e.g. measurement sandwiched between two unitaries can be made terminal too (by adding ancilla, see 2nd example [here](https://quantumcomputing.stackexchange.com/questions/15349/are-there-any-algorithms-that-take-measurements-in-an-intermediate-step/15355#15355)).
Comment: @AdamZalcman I see. I suppose "circuit with intermediate measurements" could be modeled in general as a channel with Kraus operators corresponding to the different possible measurement outcomes (or more precisely, the different possible combinations of measurement outcomes). Then a possible corresponding matching unitary evolution with measurements only at the end should be the isometry obtained putting all the Kraus operators one above the other, with the measurement outcomes "selecting" a corresponding block in this isometry.
Comment: I'm not sure whether one can also control the gate decomposition with this type of argument though. That is to say, the isometry/unitary thus obtained might not admit a gate decomposition resembling the original one. Though I guess that might make sense, after all, removing intermediate measurements from a circuit potentially makes for a completely different type of dynamics
Comment: I'm sorry I haven't missed the detailed steps of the above mathematical derivation. First not quite sure what each symbol, and parameter means. Second how to derive the next step, I can't figure out yet. Third, the significance of delayed measurement and what the advantages are cannot be seen from the two equations above.


Simultaneous synchronisation of several QField files

Question: I would like to synchronise several QField files using one command in QGIS. Is this possible with a Python script?
I would like to use the plugin QField sync but for the data of 10 tablets. So that I don't have to synchronise each tablet individually, a script would be very time-saving. Has anyone tried this before?
Comment: I use rsync over wi-fi. On android side dropbear ssh server. Then it's just a matter of opening multiple terminals.
Answer: I am not aware of this, but you can try using Mergin service (https://public.cloudmergin.com/) and Input app which is also based on QGIS.
To achieve that using https://inputapp.io and Mergin, you need:

Upload your project to Mergin (using Mergin plugin in QGIS)
All your users need to have their own accounts
Share your projects on Mergin with your users
Install https://inputapp.io
Each user can access the same project from Input under Projects >
Shared with me
Download the project and make changes
Sync the changes from Input, Projects > Home


Something is wrong with my Wien Bridge

Question: I want to create a wien bridge oscillator to use in my later projects so I tried to simulate a schematic I found online. Its stated that R1 = R2 and C1 = C2 should be true in order to circuit to oscillate. Ironically, thats the only situation that my circuit does not oscillate. I chose C1 = 1uF and C2 = 1.1uF and that is the closest I can get to a clear sine wave. While C1 = C2 my circuit does not oscillate. I tried C = 1n which is useless too. I even tried charging one of the capacitors beforehand to kickstart the sim but it doesnt work either, the wave just flattens in time. If I remove C2 I get square wave which is more interesting. Later on I decided to try the working one (C1 = 1uF/1nF, C2 = 1.1uF/nF) on my bread board which didnt oscillate, but created a steady voltage. I formed a voltage divider and powered it with my dc power supply, used the middle node as my virtual ground. Im lost and I need help.
Answer: The minimum gain to start oscillation of a Wien Bridge Oscillator is three. So, if your circuit negative feedback resistors are in the ratio 2:1 then theoretically this is sufficient to start an oscillation.
However, it may take a year to build-up and, with slight losses (op-amps are not actually ideal) or tolerance issues on the two feedback resistors, then your oscillator may not start at all. For this reason, the feedback resistors need to be chosen such that your value for R1 is slightly greater than twice the value of R2.
Then it will start but then you'll encounter the next problem; the amplitude of the sine wave will continue to grow until the op-amp output clips the sinewave. And now you have a distorted sinewave which is not usually desirable.
For this reason, anyone designing a practical Wien Bridge Oscillator incorporates a variable gain stage that attempts to stabilize the amplitude at a fixed and fairly undistorted level. Traditionally this has been done with filament bulbs as per this wiki article: -

There is also this circuit that uses back-to-back diodes to slightly clip the sinewave as amplitude grows beyond a certain point: -

You can also use a JFET to provide amplitude stability: -

Picture from here.
So, take your pick.
Comment: Oh I had no idea I have  to do that sorry. I am new.
Comment: Thank you, I tried with a higher gain and it worker. I realized that when I choose C1 slightly higher than C2 ı get a clean sine wave without the clipping problem. How is this possible? Is this applicable to a practical application? I thought that since there is about %20 error rate in my capacitors, one of them must have slightly higher capacitance then the other but it doesnt work.
Comment: Also when I choose 1nF instead of 1uF, I get a very high frequency unclipped wave. This is both amazing and confusing.
Comment: The 741 is pretty crappy and it's likely there was some subtle distortion that you may not have seen that was slightly limiting the gain. Typical of this might be slew rate limiting of the sinewave i.e. making it appear slightly more triangular. In other words, there will be distortion that is limiting the gain. If you want a decent wideband oscillator use at least the back-to-back diode version AND use a decent op-amp and not a dinosaur.
Comment: Would 1458 be okay? I lack knowledge thus I dont know how the diodes affect the circuit in a good way. Im a student so I am still learning :D thank you.
Comment: @Tombeki The [LM1458](https://www.ti.com/lit/ds/symlink/lm1458-mil.pdf?ts=1618283890254&ref_url=https%253A%252F%252Fwww.google.com%252F) choice depends on what your power supply rails are and how high in frequency you expect your oscillator to work to. Unfortunately the 1458 data sheet does not provide great information about how well it might work so, look for a more "supported" device like the [TL08xx](https://www.ti.com/lit/ds/symlink/tl082.pdf) is my recommendation.
Answer: Total gain around the loop (loop gain) should be 1 at oscillation. There is a gain of 1/3 through the RC network which is why the negative feedback gain is required to be 3 at oscillation. 1/3 * 3 = 1.
But there needs to be a loop gain of greater than 1 at power-up in order to start oscillation and then reduce the loop gain to 1 when the required amplitude of oscillation is reached. Therefore the negative feedback gain needs to be greater than 3 at power-up and reduce to 3 when oscillation amplitude has grown to required amplitude.
One way of doing this is to use a jfet which will reduce the gain as the amplitude grows until the loop gain is equal to unity when the oscillation amplitude will be steady.

EDIT
The gain of the amplifier must be greater than 3 at power-up, reducing to 3 when the oscillation amplitude has grown to some significant level.
The JFET acts as a variable resistance. When the gate is equal in voltage to the source terminal voltage the JFET is at its minimum source-drain resistance.
The gain of the amplifier = 1 + (VR1/(resistance of JFET))
At power-up the JFET's gate is equal to the source voltage (C4 is discharged) and so the gain of the amplifier is at a maximum.
As the output oscillation grows in amplitude C4 is charged negatively by the amplifier's output via the diode, taking the gate of the JFET negative with respect to the JFET's source voltage which increases the effective resistance of the JFET, reducing the amplifier's gain.
The output oscillation amplitude will stabalise at a voltage where a balance is achieved. If the output were to increase any more, the gain reduces further reducing the output amplitude and if the output amplitude were to decrease, the gain increases, increasing the amplitude.
A steady state amplitude has been achieved, an equilibrium.
Perhaps you could do some reading around the subject of operation of JFETs to improve your understanding of this automatic gain control (AGC).
Comment: I barely understand the logic of wien bridge, this circuit is far complex than I can understand ım afraid. I can assemble it ofcourse, but the point is learning so can you give me a more tuned down answer please? Thank you :)

Something is wrong with my Wien Bridge


How to decide if a potential is a scalar?

Question: I know that ${\vec E}=-{\vec \nabla} V$. If a potential is scalar, I can find its electric field strength. The question is how can I know if a potential is scalar? Do all point charges result in scalar potential? Multiple point charges in a space still gives scalar potential? Can you give examples when the potential is not scalar?
Comment: The electric potential is additive. Addition of two scalars results in a scalar. Is that your question? Other than that, I think you should go back to the definition of potential energy and think about it for a while.
Comment: If the potential is not a scalar, what is $\nabla V$ supposed to mean?
Comment: Well gradient of a vector field is a rank 2 tensor field...its just not as useful here.
Answer: There is always a scalar potential $V$ and a vector potential $\vec A$. The vector potential always determines the magnetic field $\vec B$ but if your magnetic fields are not changing in time then you don't need the vector potential to determine the electric field $\vec E.$
You can get $\vec E = -\vec \nabla V -\frac{\partial \vec A}{\partial t}$ and $\vec B=\vec \nabla \times \vec A.$
Then if your magnetic field isn't changing in time then you can pick a vector potential that isn't changing in time and then $\frac{\partial \vec A}{\partial t}$ is zero so you didn't need it.
$\vec B=\vec \nabla \times \vec A$ gives us $\vec \nabla \cdot\vec B=0$ and $\vec E = -\vec \nabla V -\frac{\partial \vec A}{\partial t}$ and $\vec B=\vec \nabla \times \vec A$ together gives us $\vec \nabla \times \vec E =-\frac{\partial \vec B}{\partial t}$
Answer: If you have a vector function let's say $\bar E $, the you can prove that if:
1) $\nabla \times \bar E =0 $ then $\bar E =\nabla \cdot  V $ where V is a scalar function.
Assume another vector field function B,then if:
2) $ \nabla \cdot \bar B =0 $ then $\bar B =\nabla \times \bar A $ where $\bar A $ is a vector potential function
The above all of course have mathematical proves. If non of the above two statements hold, then in general you can express a vector function as a function of a scalar and a vector function. From here, for the electric and magnetic field, one begins to find different potentials to describe the fields and from here comes the gauge invariance in EM.
Hope this helps.
Answer: The term "scalar potential" is OK when applied to electrostatics, but it is somewhat messy when applied to electromagnetism in general, as "scalar potential" is actually not a scalar function, but a component of the 4-potential. So point charges at rest create electric field that can be described by a "scalar potential", but moving point charges create magnetic field as well, which cannot be described by the "scalar potential". Let me also note that the "vector potential" $\mathbf{A}$ can always be used to describe arbitrary electromagnetic field using the so called Weyl gauge.


Multipage form not multistep

Question: Can anyone help me to make multipage form not multistep.
Suppose On front page i have two fields select service and select location and a button and after selecting both clicking on button opens a new form on new page.
Answer: You can use Webform module and create multiple separate forms.
On submission of first (on front page), you can redirect users to another page (another webform) based on their selection using custom redirect in webform settings and tokens <code>[submission:values:?]</code> that use data from webform that has been submitted. You just have to set "key" on selects in your form properly.
Comment: Thanks for you answer. Can you pls explain about keys ie field key(I guess) and how i will get form 1st data to next page form.
Comment: When you create form element with multiple options (select list for example), each item on that list is defined as pair KEY | VALUE. User can see value while you work with keys when processing results. So you can set one of your "field_service" options to "foo | I need Foo service". User then selects "I need Foo service" and after submission, that form redirects to custom url of specific Foo service form (www.example.com/foo-service-form) by `[submission:values:field_service:key]-service-form`
Comment: How i will use this data in next form
Comment: Adn since those two forms are completely separate, if you need to prepopulate some fields of second from first, you can pass values in URL (by using tokens in redirect url again) and set default values in second form to read those from url query - see http://drupal.stackexchange.com/q/81182/38635

Multipage form not multistep


Is it just me or does Windows 7 index-based searching still not work as well as Agent Ransack?

Question: It really seems that this is the case....am I wrong?  Or an I not understanding something about Windows 7 search and just don't know how to properly use it?
And as far as I can tell Agent Ransack doesn't use an index...how is this possible?
Comment: Can you specify the exact problems with the Windows 7 indexing in your question? As in: Does it lack performance, results or something else?
Answer: Just to confirm your suspicion Agent Ransack does not use indexes there's actually a KB article on indexing (although for the bigger brother FileLocator Pro it's still valid):
http://www.mythicsoft.com/kb/Does%20FileLocator%20Pro%20use%20indexing.ashx
Whether Agent Ransack performs better is down to the type of searching you're doing and the type of documents you're searching through. Windows Search normally does a good job of indexing Office type documents (e.g. Word, PDF, Excel etc) and if you're searching for a whole word the speed of indexed search is MUCH faster than a non-indexed search product like Agent Ransack, especially if you are searching the whole drive.
Where Agent Ransack will beat indexed search is on file types not indexed (or files not YET indexed), which quite often includes code files, logs etc. Also, non-indexed search works well for partial matches especially when the match isn't at the start of the word boundary, e.g. searching for 'companyname' in an email address like firstname.lastname@example.com (not to mention other features like print preview and export). Then you have all the security issues of indexes containing sensitive data that isn't easily controlled.
Personally, I recommend indexed search to my non-technical friends and family, who generally have no idea where things are saved, and Agent Ransack to tech-minded friends.
One final note, if you mainly just search by file name lots of people rave about a free indexed based tool called Everything by Void Tools.
Comment: "Everything" by Void Tools is a fantastic file search app for power users.  I use it even though the built in search function on Win11 works well.
Answer:
Or an I not understanding something about Windows 7 search and just don't know how to properly use it?

Assuming you have indexed all the locations that you want to search, I find the search index to be quite useful. However, I have seen cases where it just fails to find files even when the index is up to date and the file is in an indexed location.
See here for instructions for Vista/Windows 7 to add locations to the index.
Remember that the Windows Search Index contains meta information and file contents information as well, so if you search for "xyz", you might get a file called "abc" authored by "xyz".
Answer: Windows 7 Indexing should work perfect and provide the results you are looking for in a reasonable time, if I look for "Test" it shows me the folders and files I used for testing things in under a second.
If your performance is bad then you should reduce the locations that are being indexed and deselect the file types that you don't want to be indexed, this could need a bit of organization if you store things you do and don't want to serach together. It's like comparing a big pile of trash with a super market, where would you find anything quick?
If your results are bad then there are locations that are probably not being indexed or important file types that are deselected, this should not be an issue at first unless you are working outside the folders where you are supposed to be working in.
Microsoft provides you with C:\Users\Username and shortcuts to it and it's contents so that you don't have to go all the way to C:\Whatever and place things there. Why should C:\Intel, C:\Program Files\VLC or C:\Windows be indexed anyway?
If you adjust your question then I can produce a more specific answer,
check the comment to your question for that.
Answer: It's not your imagination.  I discovered Agent Ransack about 2 years ago and never looked back.  Windows Search, to me, has been hopelessly broken since going to Windows 7.  It fails to find files and the user interface is just plain clumsy.
When people complain that Windows search fails to find files, MS always has the same suite of useless answers: "You must have turned off certain file types.  Your indexing must not be up to date".  Nonsense.  Everybody who has struggled with Windows Search knows this isn't the problem.  It can't find JPGs, it can't find .cpp, movie files, text files, you name it.  It has nothing to do with disabling types.  It can't find files that have been on my drive for months.  It just plain doesn't work.
In contrast, I never have to do anything, configure anything, or worry about anything when I use Agent Ransack.
Honestly, something as simple and basic as search for files?  How could they break it and turn it into such a complicated problem?
The old XP file/contents search function on the Start Menu was so much simpler and more intuitive.  They should have just left it alone.
Comment: This is a rant not an answer.


Vagrant: Error: Could not resolve host: (nil); Host not found

Question: I am getting "Could not resolve host" error while trying to create a vm using vagrant and VirtualBox. I followed the instruction from http://docs.vagrantup.com/v2/getting-started/
Executed the below 2 commands

vagrant init hashicorp/precise32
vagrant up

Below is the error message.

C:\Users\xyz123>vagrant up Bringing machine 'default' up with
  'virtualbox' provider...
  ==> default: Box 'ubuntu/trusty32' could not be found. Attempting to find and in stall...
      default: Box Provider: virtualbox
      default: Box Version: >= 0 The box 'ubuntu/trusty32' could not be found or could not be accessed in the remote catalog. If this is a
  private box on HashiCorp's Atlas, please verify you're logged in via
  vagrant login. Also, please double-check the name. The expanded URL
  and error message are shown below:
URL: ["https://atlas.hashicorp.com/ubuntu/trusty32"] Error: Could not
  resolve host: (nil); Host not found

All the help appreciated
Comment: Have you checked that in your VagrantFile config.vm.box is set to `hashicorp/precise32`?
Comment: hello,
my bad. I copied the VagrantFile content after i edited it to try to download precise32.  But i get same error with hashicorp/precise32 and ubuntu/trusty32.
Answer: Following commands fixed the problem for me with vagrant 1.7.2 on Mac
brew install curl
export DYLD_INSERT_LIBRARIES=

Answer: Uncomment below line in Vagrantfile..

config.vm.box_check_update = false

Source: https://github.com/mitchellh/vagrant/issues/3391
Answer: Setting up the proxy command worked for me
export https_proxy=http://username:password@proxy_ip:proxy_port

Then
$ vagrant up
Bringing machine 'default' up with 'virtualbox' provider...
==> default: Box 'ubuntu/trusty64' could not be found. Attempting to find and install...
    default: Box Provider: virtualbox
    default: Box Version: >= 0
==> default: Loading metadata for box 'ubuntu/trusty64'
    default: URL: https://atlas.hashicorp.com/ubuntu/trusty64
==> default: Adding box 'ubuntu/trusty64' (v20170202.0.0) for provider: virtualbox
    default: Downloading: https://atlas.hashicorp.com/ubuntu/boxes/trusty64/versions/20170202.0.0/providers/virtualbox.box
    default: Progress: 8% (Rate: 302k/s, Estimated time remaining: 0:26:21)

Answer: You are calling a box inside a box you will you don't need to init again just vagrant up,you will need to start afresh


Three mothers of Agni/Rudra; Tryambaka

Question: Who are the three mothers, Tryambaka, of Agni/Rudra, and where are they mentioned in the Vedas?
Comment: Does [What does the word "Tryambakam" mean in Vedas?](https://hinduism.stackexchange.com/q/20321/277) answer to your question?
Answer: Rig Veda itself in its 5th mandala uses the term त्रिमाता - trimātā́ to denote three mothers, so there is no need for Triambakam to become 3 mothers in any sense. Yet, some Western scholars associated the Triambakam with 3 mothers for a lack of better vocabulary. Finally, 3 mothers of Agni/Rudra is a very unusual question as none of the Native Acharyas have given an explanation as such. However, if one does have such a reference, we urge you to share it with us in the comments so an exchange of valuable information can take a page. Now for those who are interested to deep dive into vocabulary and Sandhi (the junction of Sanskrit building blocks) here is some analysis and a conclusion from the literate itself:
Vocabulary: Ambā/Amba means mother. Especially the southern regions influenced with such literature its Amma, so the 'म्ब' became just 'म्'. The short form of Amma is just "Mā" the preceding 'ā' became silent in regular usage, but mātā denotes respect. Hence the title Uma = 'U' + 'Ma' or the title Sambha = 'Sa' + 'Ambā' (meaning along with Ambā). Hope we are clear till now. Rig Ved itself in its 5th mandala uses the term त्रिमाता - trimātā́ to denote three mothers so there is no need for Triambakam to become 3 mothers or 3 sisters. Further South of India Amma became Amman/Amme (Hence the song "Amme Narayani"). Ambā is a respected term given to women irrespective of age. Ambi  is a term used with affection towards a mother or daughter, since Uma is a princess she was called with a derivative Ambika (Ambi + Ka). Hence, Ambaya/Ambada and Ambala/Ambali are all derivatives given to the term mother based on the context. Since the prevalence of Devi Uma is high in Kashi the King of Kashi named his 3 daughters: Amba, Ambika, Ambalika. Ambi+ka is given to sister, and Amba+lika is given to mother. Ambā is not equal to Ambakam. Two separate words. Hence, ambakam denotes eyes and has no relevance to the mother. One is welcome to open Sanskrit Lexicon and see of themselves. I am attaching an image and one can see no synonyms used other than eye.  It's only when you convert the sandhi as Amba+ka+am or Amba+kam which many try to interpret in relation to mother, but contextually there is no reason for such a sandhi (decoupling) in the context of this hymn especially when there is a term trimātā́ used in Rig Veda. Hence Vedic Ghana Patana chant says "त्रि अम्बकं इति त्रयम्बकं" (reference from Tezz ji's post). Ambu can also denote water in a few cases.
Having explored the vocabulary with various derivations and Ghana Patana, is there any explicit reference that can conclude the title trayambakam and its origin? Well, Rśi Vyāsa explains the significance of 3 and its association to Rudra in Mahabratam Drona Parva 203, the following should clarify any remnant questions:
And since Maheswara by means of his two eyes closed (in meditation), created through sheer force of will the third eye on his forehead, he is for that reason called the trayambakam...And since three goddesses adore and have recourse to that Lord of the universe, viz., Firmament, Water and Earth, he is for that reason called Tryamvaka.The Ordainer of the three worlds (Triloka), he is the sole refuge of the three worlds.... O son of Kunti, seek the protection of that boon-giving Lord of the universe, the lord of Uma, that God of three eyes (trayambaka), that destroyer of Daksha's sacrifice....When, however, the three cities came together in the firmament, the lord Mahadeva. pierced them with that terrible shaft of his, consisting of three knots. (Tripurantaka/Tripurari)....And since the solar and the lunar rays of light that appear in the world are spoken of as the hair on the Three-eyed one, he is for that reason called VyomakesaMahabratam Drona Parva 202-203

Image:
Now, coming to the 2nd part of question where Agni and Rudra are Tryambakam. Both Agni and Rudra take the mantel of Tryambakam.
trikāgnikālāya meaning the 3 fires which blaze at all times, are garhapatya, ahavaniya, and agnihotra. Time is always burning or is exhaustive, meaning it doesn't stop, and trik+āgni+kālāya also depicts the three dimensions of time, which are the memory of the past, the present moment at hand, and the upcoming imaginative future. One might think of past and future as linear events and so are non-existential, but we will address this soon. The second title is kālāgnirudrāya (कालाग्निरुद्र) meaning fire that devours time, why? Because Rudra itself is TIME, hence the title Kālāya Namaha"कालाय नमः" TA10.18 meaning, I bow to you oh time. This finally landed in Svetasvatara Upaniṣhad wherein it says "अन्त:काले सञ्चुकोच"SU3.2 meaning He dissolves all beings into Him at end of time. Similarly, the association of Agni with time is clear in Muṇḍakopaniṣad with the title Kāli.
Source: 1. Vedic Rudra-Agni
2. Appearance of Rudra

Three mothers of Agni/Rudra; Tryambaka


How to make Thunderbird open links in Firefox?

Question: I'm trying to use Thunderbird again, but I can't make it use Firefox to open links. I'm using KDE and Firefox is my default browser. I tried the network.protocol-handler method but it doesn't work.
Answer: To open links in thunderbird so that they will open firefox or chrome or opera, you open preferences, attachments, and click on use other and navigate to the browser that you want to use.
Comment: I have already tried that, but there is nothing to select. http://goo.gl/KafD
Comment: I'm accepting this answer, but I decided to use Opera for mail, instead of Thunderbird, so will no longer testing other options.
Answer: It seems that thunderbird uses sensible-browser, that actually tests for the following alternatives: gnome-www-browser and x-www-browser; so what you need to do is manage your altenatives with:
<code>sudo update-alternatives --config gnome-www-browser
sudo update-alternatives --config x-www-browser
</code>
And the choose Firefox for those.
Probably you'd only need to update x-www-browser since you're using KDE.


Does registering a second domain name with the dashes help SEO?

Question: If I have a site registered and running on ThisIssomething.com for example, does registering This-Is-Something.com and redirecting it actually help SEO?  Or is it mainly to protect your brand?
Answer: It's mainly to protect your brand. The dashes don't help search engines determine keywords unless the words are ambiguous like expertsexchange.com or whorepresents.com. In those cases it may help although anchor text in hyperlinks (internal or external) most likely removes the ambiguity.
See this related question for more information on why it doesn't help.
Answer: I'm just venturing a guess, but 2 domains pointing to the same site might actually be bad for SEO. You'd be competing against yourself.
Comment: If you do a 301 redirect from the site with dashes to the one without it will not hurt your SEO at all.
Comment: Duplicate content issues would be the biggest problem. Pages from both sites might be included in the index when you only really want one site to be represented.
Comment: Yea, a lot of sites are accessible from multiple domains. As long as you're using a 301 redirect, search engines will only look at your canonical domain. It'll confer no benefits or penalties.
Comment: We have a few clients who have a lot of domains all pointing to the same site. 301 redirects are the norm for them.
Comment: I guess I was referring more to literal duplicate sites, not one that points to the other. As in they both point to the same code/structure but are coming out from different domains.
Answer: There is quite a lot of power in domain names that include your keywords, at least according to an article on SEOMoz - Exact Match Domains from last week.
That said, my own opinion is that buying additional domains that will be only used for 301 redirects will not affect your ranking at all. Since these domains will never appear in the search results (if the 301 is done properly).
So just pick a good domain name, with or without dashes, and stick to it.


Can I claim Croatian citizenship by descent if my mother left Croatia before it became independent?

Question: My mother was born in Rijeka, currently in Croatia, and held citizenship while under Yugoslavia. She then emigrated to the US before Croatia gained its independence. Do the laws regarding citizenship by direct descent apply or is there an exception in this case? I am under 21 years old.
Answer: Your first task is probably to determine whether your mother is a Croatian citizen.  As I understand it, Yugoslavia had a concept of concurrent citizenship (like the US and Switzerland, and probably some other federal countries), so Croatian citizenship existed before independence and persists after.  If your mother is a Croatian citizen, or, more precisely, if your mother was a Croatian citizen when she gave birth to you, then you may well have been a Croatian citizen all your life without knowing it.  More likely, you may be eligible to register as a Croatian citizen because you are under 21.
If your mother naturalized in the US before you were born, she may have lost her Yugoslav and/or Croatian nationality at that point.  Some countries have provisions to that effect in their nationality law; I do not know about Croatia.  (Whether such a provision exists now is not relevant; what matters is whether it existed when your mother naturalized.  Similarly, whether she could pass Croatian citizenship to you depends on the law as it existed when you were born.)
If you are not already a Croatian citizen and you are unable to register, then you may be able to naturalize.  As the descendant of an emigrant, you are exempt from the most burdensome requirements: to renounce your other citizenships, to have lived in Croatia for eight years, and to be proficient in the Croatian language and Latin script.
More detailed information is available on the relevant page of the ministry of the interior.  An application from outside of Croatia would be submitted through a consular office of the ministry of foreign affairs; see their website for more information.


Is hearing a curse word like the f-word haram?

Question: So I was watching a youtube video and the Youtuber kept on saying curse words and my parents heard it. I kept on watching because the video was entertaining and really didn't pay attention but my parents told me that listening to any curse words regardless of the usage is haram. So can anyone explain to me if it's haram or not?
Comment: The main issue is you hearing them. While nothing really wrong, but think `influence`. You are listen to that content when you could listen to Quran or something more clean. However if you "spoke" them, then this answer will help you: https://islam.stackexchange.com/a/23901. The question also talks about influence, so reading it will be beneficial.
Answer: You're being too literal.
If, say, you are watching a film  about gangsters, and they swear. Then that's in character - for them - and it's not haram.
Secondly, listening is a passive and not active act. You have no control over your environment and who may, or may not swear in your hearing distance.
Swearing, as an active act, is haram. It's against al-'Ird, the dignity and honour of a Muslim.


Data Structures in Python

Question: All the books I've read on data structures so far seem to use C/C++, and make heavy use of the "manual" pointer control that they offer. Since Python hides that sort of memory management and garbage collection from the user is it even possible to implement efficient data structures in this language, and is there any reason to do so instead of using the built-ins?
Comment: Most C/C++ structures "heav[ily] use manual pointers" because they have to, rather than because it's more efficient to do so.
Answer: Python gives you some powerful, highly optimized data structures, both as built-ins and as part of a few modules in the standard library (lists and dicts, of course, but also tuples, sets, arrays in module array, and some other containers in module collections).
Combinations of these data structures (and maybe some of the functions from helper modules such as heapq and bisect) are generally sufficient to implement most richer structures that may be needed in real-life programming; however, that's not invariably the case.
When you need something more than the rich library provides, consider the fact that an object's attributes (and items in collections) are essentially "pointers" to other objects (without pointer arithmetic), i.e., "reseatable references", in Python just like in Java. In Python, you normally use a None value in an attribute or item to represent what NULL would mean in C++ or null would mean in Java.
So, for example, you could implement binary trees via, e.g.:
class Node(object):

  __slots__ = 'payload', 'left', 'right'

  def __init__(self, payload=None, left=None, right=None):
    self.payload = payload
    self.left = left
    self.right = right

plus methods or functions for traversal and similar operations (the __slots__ class attribute is optional -- mostly a memory optimization, to avoid each Node instance carrying its own __dict__, which would be substantially larger than the three needed attributes/references).
Other examples of data structures that may best be represented by dedicated Python classes, rather than by direct composition of other existing Python structures, include tries (see e.g. here) and graphs (see e.g. here).
Answer: For some simple data structures (eg. a stack), you can just use the builtin list to get your job done. With more complex structures (eg. a bloom filter), you'll have to implement them yourself using the primitives the language supports.
You should use the builtins if they serve your purpose really since they're debugged and optimised by a horde of people for a long time. Doing it from scratch by yourself will probably produce an inferior data structure.
If however, you need something that's not available as a primitive or if the primitive doesn't perform well enough, you'll have to implement your own type.
The details like pointer management etc. are just implementation talk and don't really limit the capabilities of the language itself.
Answer: C/C++ data structure books are only attempting to teach you the underlying principles behind the various structures - they are generally not advising you to actually go out and re-invent the wheel by building your own library of stacks and lists.
Whether you're using Python, C++, C#, Java, whatever, you should always look to the built in data structures first. They will generally be implemented using the same system primitives you would have to use doing it yourself, but with the advantage of having been tried and tested.
Only when the provided data structures do not allow you to accomplish what you need, and there isn't an alternative and reliable library available to you, should you be looking at building something from scratch (or extending what's provided).
Answer: How Python handles objects at a low level isn't too strange anyway. This document should disambiguate it a tad; it's basically all the pointer logic you're already familiar with.
Answer: With Python you have access to a vast assortment of library modules written and debugged by other people.  Odds are very good that somewhere out there, there is a module that does at least part of what you want, and odds are even good that it might be implemented in C for performance.
For example, if you need to do matrix math, you can use NumPy, which was written in C and Fortran.
Python is slow enough that you won't be happy if you try to write some sort of really compute-intensive code (example, a Fast Fourier Transform) in native Python.  On the other hand, you can get a C-coded Fourier Transform as part of SciPy, and just use it.
I have never had a situation where I wanted to solve a problem in Python and said "darn, I just can't express the data structure I need."
If you are a pioneer, and you are doing something in Python for which there just isn't any library module out there, then you can try writing it in pure Python.  If it is fast enough, you are done.  If it is too slow, you can profile it, figure out where the slow parts are, and rewrite them in C using the Python C API.  I have never needed to do this yet.
Answer: It's not possible to implement something like a C++ vector in Python, since you don't have array primitives the way C/C++ do.  However, anything more complicated can be implemented (efficiently) on top of it, including, but not limited to: linked lists, hash tables, multisets, bloom filters, etc.
Comment: I'm not familiar with the implementation of the C++ vector but the Python list type *is* implemented as an array (http://bytes.com/topic/python/answers/101848-list-implementation) rather than a linked list. Isn't that what a vector basically is?
Comment: Yes, a Python is implemented as an array (same as a C++ vector).  What I'm saying is you couldn't implement your own list *in* Python, except on top of the existing one.
Comment: Well, the python list type is really more like Java's ArrayList (ie. an array of pointers to Object).
Comment: True, but that's because Python and Java have reference semantics (ignoring Java's handling of primitives).

Data Structures in Python


Can a new Android app replace existing app in the play store?

Question: I have an android app developed in native Android, which is released in the Play store. I am wondering if I should rebuild the app in Flutter as I want both Android and iOS apps. However, I am not sure if the new android app developed using Flutter will be able to replace the current app. I want to use the same package name and release key. Also, most importantly preserve my users.
Thank you!
Comment: Does this answer your question? [How to Update a flutter app on already published native android using java app in play console](https://stackoverflow.com/questions/64005603/how-to-update-a-flutter-app-on-already-published-native-android-using-java-app-i)
Answer: Yes, it is possible if you sign the new flutter app with the same release key and with the same package id.
Comment: That is fantastic. Thank you!
Comment: What about existing database and login details
Answer: Yes, you can replace already existing app with Flutter app but you need to take care of few points to be able to do this.
Please take care of following things:

The package name must be identical with the old application. Please take a look into Manifest file of old app and replace the package name in new application AndroidManifest.xml file with the package name from old application.

Now take care of the versionCode and versionName, this info can be retrieved from AndroidManifest file of old application and upgrade it in  Flutter's pubspec.yaml file with version attribute as it is must to keep it greater than previously released application. This attribute has the form of 0.1.1+3 where 0.1.1 corresponds to versionName and 3 (the number after + sign) to versionCode.

Here's the crucial part, the keystore file used to sign New Flutter's version must be the same used to sign the Android's native release.

If you follow all these steps then you can update the new version of the application irrespective of the programming framework you are using i.e  Kotlin, Flutter, React Native or any other technology.
Answer: That should indeed be possible. Afaik a play store "update" is just a new apk. I have had plenty of apps that have done this, so it is definitely possible, you'll just want to make sure package names and other important config objects are the same.
Comment: That is fantastic. Thank you!
Comment: What about existing database versions and updates?
Answer: Yes, You can do that. You just need to take care of Package name, Version name and Version code of you application (if applicable).


How to change the Home directory of the currently logged In user

Question: I am currently logged in into a CentOS server and I would like to change my home directory from /home/myuserName/ to /var/www/html/
I tried the below command :
> sudo usermod -d /var/www/html myuserName

But this gives me an error:
usermod: user myUserName is currently logged in

Comment: I am unsure what you meant, `HOME=/var/www/html` will change *for the session* your home dir.
Comment: That helps, But i would like to change my home directory permanently, not for just the current session.
Answer: short answer : you can't.
long answer:
HOME dir is set in /etc/passwd, 6th field. It is read upon login; your shell is started with this home dir.
The proper way to change home dir for joe is :

have joe log off.
use usermod -d /new/home joe  to change home dir for subsequent session.

Once session is run, you must do two things:

edit $HOME to change home dir for session (to be repeated on all active session).
use sudo vipw to edit home dir for next session

Also, be aware you might have an issue with permissions/ownership on /var/www/html.
Comment: edit /etc/passwd always worked for me. See @7171u below
Comment: editing /etc/passwd without logoff/logon ?
Comment: editing /etc/passwd for an account that is logged in, and then start a new session with that same account, and it obeys the new home dir. For the already logged in account, that session still has the old home location in the Environment.
Answer: You need to edit the /etc/passwd file to change home directory of users that are currently logged in.
Edit the /etc/passwd with sudo vipw and change home directory of the user.
vipw highly recommended other than vim or other editors since vipw will set lock to prevent any data corruption.
Answer: The usermod command won't work if you're logged in with the user you are trying to make changes on.
From the manual page on usermod it says:

CAVEATS
         usermod will not allow you to change the name of a user who is logged in. You must make certain that the named user is not executing
  any processes when this command is being executed if the user's
  numerical
         user ID is being changed. You must change the owner of any crontab files manually. You must change the owner of any at jobs
  manually. You must make any changes involving NIS on the NIS server.

Try logging in with a different user and running the command again.
If that isn't possible then you can manually edit the /etc/passwd file (which is actually what the usermod command is doing). If you do that make sure you back the file up in case you inadvertently do something silly.
Answer: A couple possible workarounds, depending on what you're hoping to solve:
Option 1. Add HOME=/var/www/html to your .bashrc
Option 2. Rename /home/myusername and then create a symlink to the desired directory.
mv /home/myusername /home/myusername-old
ln -s /var/www/html /home/myusername

Comment: bad habbit. after that, myusername-old can not be used by other user
Answer: You can only do this temporarily. This means that every time you login as that user you have to run this one command:
export HOME=/var/www/html

This way, you can make most applications think that your home directory is whatever location you use above.
~ will also start to point to /var/www/html.
The applications this worked with for me were NPM and Maven.


How to view Windows' equivalent of Unix Swap usage?

Question: How do I find out available and in-use virtual memory usage on Windows?
Answer: You can view this information by opening up the Resource Monitor and selecting the Memory tab:

"Used Physical Memory" is your RAM, while "Commit Charge" is the sum of RAM and the paging file, or the maximum available virtual memory. (This comes from a display of how much virtual memory windows has "committed" to being able to provide - the sum of every allocation request it has granted.)
Windows and Linux manage their paging/swap space differently, however. With Windows, a paging file with 0% utilization is not good for performance; rather, Windows will try to mirror every page from RAM onto the paging file if it can. This will allow it to quickly drop pages out of RAM when it needs to reuse them for something else. This is why Windows will try to create a paging file at least as big as the physical RAM you have installed on your machine. It's less of a swap file, and more of a backing store.
Comment: "Windows will try to mirror every page from RAM onto the paging file if it can" this can't be true, if it was, it would be non-stop writing data to disks. It doesn't. It only pushes pages that weren't used for long time into there, just like Linux does.
Comment: Thank you! So can I assume that commit charge - 2 * working set = swap usage of a process?
Comment: Having no swap is not good also on Linux. This part is being done pretty similarly in both OSes.
Answer:
How do I find out available and in-use virtual memory usage on
  Windows?

At first, we need to invoke the Performance Options:
%windir%\system32\SystemPropertiesPerformance.exe

After selecting the Advanced tab, the frame Virtual memory reports the Total paging file size.

Q1: in-use virtual memory

.

Q2: available virtual memory

This is set / displayed by clicking on the Change... button (see above)

Q3: virtual memory usage

About this last question, the resource monitor might help now.
%windir%\system32\resmon.exe

Here, the Hard Faults/sec parameter shows the expected info (column values and graph)

When should I buy more RAM memory for this machine… is another story.
Or not.
:)
Answer: THE ANSWER
Note: These are the exact steps for Win 7. I think is the same on Win 8.
To get the actual amount of PageFile usage, start 'Performance Monitor' (perfmon.exe), and 'Add Counters' -> 'Paging File' -> 'Usage'.
It will give you the answer in %, but you know the total amount of paging file so you can calculate the exact amount of USED paging file (in MB).
To read the total amount of paging file:
Press Win+Break to open 'System properties'. Go to: 'Advanced' -> 'Performance' -> 'Advanced' -> 'Virtual memory' -> 'Total paging file size' (in MB) ).
Answer: This is easily found in the Windows Task Manager under the Performance tab.


What type of files/documents we can edit in SharePoint standard 2013?

Question: I just want to know that what type of files/documents (word,excel...) we can edit in SharePoint 2013?
Answer: It depends where you want to Open & edit documents, in the browser using the Office Online server or you want to edit them on the local machine.
Office Online Server is not configured by default, you have to setup a separate farm and connect it to the SharePoint server.
Office Online Server Support Word, Exel, PowerPoints file types.
if you have other 3rd party files to edit in SharePoint(browser) then you have to add their editor as a package in SharePoint i.e Mindjet is an example.
Answer: According to a website I have found it's:
Supported files for viewing:

    Word files: .doc, .dot, .dotx, .docx, .docm, .odt
    Powerpoint: .pot, .potm, .pps, .ppsm, .ppt, .pptm, .pptx, ppsx, .odp
    Excel .xls, .xlsx, .xlsm, .xlsb, .ods

Supported files for viewing & editing:

    Word: .docx, .docm, .odt
    Excel: .xlsx, .xlsm, .xlsb, .ods
    Powerpoint: .pptx, ppsx, .odp

Source: https://support.edmodo.com/hc/en-us/articles/210209948-What-file-types-are-supported-by-Office-Online-
Answer: The answer is none.
As @Waqas pointed out you need the Office Web App server, which is a separate product from SharePoint.  If you were running Enterprise - you would have access to Excel and Visio services, Standard edition come with none of that.
By default when you attempt to open a file it will it open in the supported desktop applications (i.e. work, excel, etc).  This, however, is no longer in SharePoint, you are editing in the office or other client and then will save it back to SharePoint.