Playing tabs on a guitar tuned down to C#

Question: I'm probably stupid, but can I play a tab in that is in standard tuning, the same way with a guitar tuned down to C#? Will everything just sound lower? Or do I need to get a tab in that tuning?
Answer: If all the strings are tuned down three half-steps then yes, you can play the tab exactly the same and it will just sound lower — specifically, the song will be transposed 3 half-steps lower.  Naturally, any other instruments would need to play lower to accompany you as well.
If you're playing Drop C# (everything down 1 half-step except the low string which is down 3) then you would need to adjust the tab, most likely by playing everything on the lowest string 2 frets higher than the tab indicates.  If that doesn't work you would probably need to rewrite the tab to fit some other possible way to play the song.
Comment: For the OP: to make explicit what cadmium's comment was pointing out: adjusting the tuning on all the strings the same (scenario 1 in Matthew Read's answer) is the exact same thing as a barre. A barre is *conceptually* moving the entire nut, and a capo is a tool to (temporarily) move it.
Comment: You could also add a capo if you need to use open strings.
Answer: Capo works magic on the stage. Let's say you want to do some Rush and some Sabbath in the same show. Capo gives you the flexibility to quickly switch tunings without the hassle of having the whole band tune up and down.
This can be done on bass, and if set up well with a medium to high action and thicker gauge strings gives a nice thick mellow as molasses guitar tone, heavy as hell and downright mean with distortion.
You can also experiment and play weirder tunings - Soundgarden's Rusty Cage (Drop B), Melvins Boris (Drop A). The answer is to get a capo, they're cheap, and experiment and see if it works for you.
Tab is going to be a lot harder because you have to transpose all notes 3 frets up. It helps to consider the capo on 3 as the open EADGBE and play your F on the 4th fret and think of it as a 1, until you get good at switching beck and forth, a skill that comes with practice and time.
C# is a good tuning because you and the capo get access to some of the most used drop tunings for songs: Nirvana - D standard, Slayer -Eb standard. C#,D,Eb, and E. An increased range on the low end but you will have to use some trickery to fake solos on 21-24 frets in standard tuning.
I've personally always liked the Soundgarden approach of 2 different guitars in 2 different tunings.


How to debug wince6.0 r2 image using KITL?

Question: I am new in wince .I have a image in wince 6.0 r2.I want to debug that image and print messages.I know only that KITL is use for debugging.... but how to use that?
Answer: "How to use KITL" is a very large question, one that isn't easily answered in a format like this.  First, does your target BSP support KITL?  Not all do (though debugging without it is not fun at all) and if your platform doesn't, then trying to get it working is likely way more effort than you want to spend.  So the first step is to talk to the OEM or check the docs.
Next, does the platform support KITL from the bootloader, or from OS startup?  That's another thing the OEM will be able to tell you.  Usually the bootloader has to be told to enable KITL and to look for BOOTME messages from Platform Builder.  How this is done is very platform dependent and, again, you'll want to consult the platform docs or the OEM.
Next, you need to build an OS image that supports KITL.  That's in the properties of the build.  Just turn it on and re-sysgen.
Once that's done, you should be able to tell PB to connect, boot the target and a KITL connection will be made.  The OS image will get downloaded and you're off and debugging.  Of course there are options and different levels of what may or may not be supported, especially if you're trying to do network stuff at the same time.
Most of this is covered in the Platform Builder docs, in MSDN and in the platform team's various blogs.  I'd recommend doing a search for 'KITL' in your favorite search engine.
But again, step one is to ask your OEM about how to set up things on your specific target hardware to use KITL.


Accessing report info from reports stored in the new Fine-Grained Sharing Folders

Question: I use the servlet.ReportList to get report information for reports in folders with AccessType = public. SFDC introduced a new Fine-Grained Sharing for Report and Dashboard Folders (Summer 13 Release Notes), which doesn't seem to have a way to change the new folder types to anything but private access. How do I access basic report information for reports stored in these newfangled folders?
Answer: You can set sharing only through the use of the FolderShare and Folder features of the metadata API. You can set the values through the CRUD- or File-based APIs, but you can read them only through the file-based APIs.


Should the steering wheel of car be on right or left?

Question: What is the user experience of steering wheels placement based on?
I recently visited US and they have steering wheel on the left whereas back in asian countries we usually have it on the right.
What are the factors that decide its placement?
Comment: Have you done *any* research before posting this question?
Comment: *"What are the factors that decide its placement?"* Which side of the road you drive on?..
Comment: I'm voting to close this question as off-topic because the reasons being are well understood and quickly obtainable through a [Google](https://www.google.com/search?q=why+is+the+steering+wheel+on+the+left+or+right+side) or [Bing](http://www.bing.com/search?q=why+is+the+steering+wheel+on+the+left+or+right+side)
Comment: added an image,hope that clarifies the question.
Comment: I haven't really, I am travelling and have limited internet connectivity but was curious to find it out,so just posted it out here.
Comment: more than 70% of questions asked in this forum are easily obtainable through Google and Bing,Would you do the same for those questions as well?
Comment: @NiravChadda "More than 70%"? Really? That's pretty precise statement to make. And questions that are as simple to find the answer to as your one indeed should be closed.
Comment: @JonW : A question still stays a question, it may be simple or stupid and I believe this forum is meant to discussit all.. :)
Answer: I'm pretty sure that has to do with the side of the road you drive on. You didn't specify which Asian countries, but as a quick test I looked at Chinese car interiors (wheel on left) and Japanese ones (wheel on right), and that conforms to right/left side of the road.

Red = Right on road, Blue = Left on road. Via wikipedia.
The question then becomes: 'why is the wheel opposite to the side of the road we drive'.
I don't know if there's a historical reason. I do know that it gives (on average) a better view of the road:

left image = steer opposite to road side, right = steer at same side we ride.
The first thing you'll notice is consistency. Driving in the middle of the road will give the same distance when looking through a curve. When you are on either side of the road, you can see further if you're on the outer curve, but less far if you're on the inner curve. From a usability standpoint consistency is good. So we try to ride as close to the middle of the road as possible.
Second thing you might notice is that how much more/less you see. In my first example you can see the middle of the road during an outer-curve-turn, and the side of the road during an inner-curve turn. In the second example, you can see a bit more (about 15 pixels) during an outer curve, but considerably less (about 45 pixels) during an inner curve. So on average, you're seeing more.
More vision + more consistency = superior.
Another point is passers-by. (both coming towards you and those overtakinh you) If you drive on the right, people will pass on the left, so you need to pay more attention to the left side of your vehicle.
Comment: @AndrewMartin Yeah driving from bottom to top is a right curve, top to bottom is a left curve. A bit cluttered, but otherwise there'd be so many similar images! I made the second chart myself just for this, but feel free to use it elsewhere. The map is from wikipedia, will edit that in.
Comment: It took me a while to figure out what was going on in that second image - I was about to get upset about the road only curving to the right. Closer inspection revealed all though! ;) - What was the source for that image?
Answer: It is simply that countries where you drive on the right side of the road the driver will be positioned on left side of the car. Countries where you drive on the left side of the road the driver will be on the right.

In effect this means that in countries with right-hand traffic, the driver and the vehicle controls would normally be located on the left-hand side of the vehicle. In other words, the vehicle would be described as left-hand drive, LHD. The reverse appears with left-hand traffic, which has right-hand drive (RHD) vehicles.
Wikipedia: Right- and left-hand traffic

Now as to why? It gives the driver the best view of the road: (same article)

manufacturers placed the driving seat on the side closer to the centre of the road to give the driver the longest possible line of sight in traffic

So it stemmed from the UX of the drivers view of the road, but nowadays it is simply the law not a UX decision as to where the driver sits.
Answer: History and origin

In the late 1700s, however, teamsters in France and the United States
  began hauling farm products in big wagons pulled by several pairs of
  horses. These wagons had no driver's seat; instead the driver sat on
  the left rear horse, so he could keep his right arm free to lash the
  team. Since he was sitting on the left, he naturally wanted everybody
  to pass on the left so he could look down and make sure he kept clear
  of the oncoming wagon's wheels. Therefore he kept to the right side of
  the road.

List of left- & right-driving countries

The trend among nations over the years has been toward driving on the
  right, but Britain has done its best to stave off global
  homogenisation. With the expansion of travel and road building in the
  1800s, traffic regulations were made in every country. Left-hand
  driving was made mandatory in Britain in 1835. Countries which were
  part of the British Empire followed suit. This is why to this very
  day, India, Australasia and the former British colonies in Africa go
  left. An exception to the rule, however, is Egypt, which had been
  conquered by Napoleon before becoming a British dependency.
Comment: If there was a compelling reason to drive on the right, what reason did Britain have for doing differently? A huge population of left-handed wagon drivers? The answer doesn't give the reason.
Answer: This is a historical issue that goes back to horse-drawn coaches.
In the UK, coaches would pass on the left so that the coachman (driver) could fend off any attack from the passing coach with their stronger right arm. (Why do some countries drive on the left and others on the right?)
In the US (and other countries) The idea was that if coaches passed on the right it would be more difficult for attackers to attack with their weaker left arm.
Along with this goes the physically wider field of view you get from being closer to the centre of the road - thus, cars that drive on the left have their driver controls on the right and cars that are built to drive on the right side of the road have the controls on the left.
Comment: I guess that once guns became commonplace, a shoulder-width change of distance was not important, but by then, the traffic patterns had been set. It is rather disappointing to find that not only was such a stupid reason chosen for which side to drive on, but that there are two equally stupid arguments choosing opposite sides. Maybe all UX should reduce to choosing the way that someone is less likely to attack? Or, the way that is easier to defend... Shoot! I can't make up my mind!


Nikon d3300 "the option is not available in current settings or in the cameras current state"

Question: I have a good condition Nikon d3300 that randomly started giving me the error "This Card is Not Formatted". Then when I try to format, it says "the option is not available in current settings or in the cameras current state". I checked and the card is not manually locked. No damage has happened that I am aware of. Please help! I have wedding photos from my daughters wedding on this card!
Comment: Well, certainly don't format the card!
Comment: The card is not healthy. Your priority is getting as much data off the card as you can: https://photo.stackexchange.com/q/40977/31502 https://photo.stackexchange.com/q/23065/31502
Comment: [How to recover data from a damaged/chewed up SD card?](https://photo.stackexchange.com/q/40977/15871) and [Is there a way to read or recover corrupted/incomplete photos on CF card?](https://photo.stackexchange.com/q/23065/15871)
Answer: It sounds like some communication or compatibility problem with the card.  I would try accessing your photos by putting the card in an external card reader on a computer. The card readers are not expensive. https://www.amazon.com/s?k=sd+card+reader
Comment: Well, not sure of your meaning, but you do have to select the right folder on the card. On a Nikon camera, the first folder name is probably DCIM, and then there will be another folder inside there, which you click to open in the card reader software. It should then show your image files, and the reader can access them.   If you have done that, and still found no images, then the problem appears to be the card, and not the camera.  Cards can fail, and cards are NOT the best long term archival storage.
Comment: I did put in in the computer and it said it could not find any photos on the device to upload
Comment: @claramedland - From the comment above, it sounds like you're using image software - perhaps something that's running automatically. Try using your operating system's File Manager to see what's on the card.
Answer: First use foremost, magic data or any other software for data retrieval and save your photos to your computer.
 Once you saved your photos format the card. It may be locked or corrupted somehow.
Answer: If this is a microSD card, in an adapter to fit an SD slot, then this is classic problem.
If that's your situation, then replace the card with a standard SD card (no adapater), and the problem will go away.
You can also try different card adapters, but it's NOT simply a matter of replacing one bad adapter with ANY other one.  It's more like the fussy camera/microSD card combination will only work with one very specific adapter.  In my case, I had best luck with adapter cards that came with Samsung microSD cards.  Other reliable brands, like SanDisk, did not work.
BTW, this problem showed up for me an a entry-level camcorder (Canon Vixia HF-R800), and no other (out of 8 other cameras/camcorders I've used).


Are private IP addresses the outcome of subnetting a public IP address?

Question: I understand the purpose of both but just verifying if this correlates together at all.
Comment: Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer.
Answer: Private addresses are address ranges set aside specifically for not being used on the Internet by IANA. Anyone can do anything with these addresses except using them on the public Internet.
Subnetting is the process of splitting one address range into two or more smaller ones that are contained within the intial range. Check the excellent answer to this question for how this works.
Both of these are completely unrelated. You can subnet any public or private address range that is large enough. The result doesn't change the public/private property of the initial range.
Answer: Private IPv4 addressing was chosen (somewhat arbitrarily) by the IETF with the cooperation of IANA. It is detailed in RFC 1918, Address Allocation for Private Internets.
IP, itself, has no concept of private or public IP addressing. Private addressing is simply the ISPs adhering to RFC 1918, and agreeing to not route any traffic for the RFC 1918 addresses.
Answer: Private addresses come from three specific ranges of IP addresses specifically reserved for that purpose - to be used on an internal network. They are completely unusable as a public address, as there are potentially thousands of devices having that specific IP as part of their separate network. Communication between those can only happen through public addresses, which are like an "entry point" from outside to anything from a single computer to a complex combination of internal networks, and the request will then navigate through those and end up at a specific device with an internal, private address. There are devices that perform this "conversion", it is called Network Address Translation, or NAT.
For example, if you are on your home WiFi, your PC might have an IP of say 192.168.1.101 - this is in private range. You request the some website, which has a (public) IP of say 188.8.131.52. Your router takes your request, and sends it to wherever it needs to go to reach 126.96.36.199, and makes a note that the return address is actually 22.214.171.124 (that's the router's IP on the Internet, sometimes this translation happens multiple times). When the request arrives at its destination, it also ends up at a router most of the time. This one determines which IP in its internal network the request should actually reach, and forwards it to the private, internal address of the actual webserver (which can very well also be 192.168.1.101). Server then responds with a message destined for 18.104.22.168, the public address of your router (or some other exit point if multiple translations happened). When the response gets there, the router then determines which device originally sent the request and forwards it there.
As far as subnetting goes, this commonly happens with the private ranges, because often networks don't need that many addresses, but more than 3 networks are needed (for multiple reasons like separation of different departments or device types, as well as security).
For example, the 10.0.0.0 range is a /8 range (only the first octet is constant), so that's over 16 million addresses. Often, smaller sections are carved with subnetting, commonly, /24. Then it is possible to have a 10.0.0.0 network, then a 10.0.1.0 and so on.
TL;DR: Private addresses are just specific ranges defined to be only for internal use, allowing the same subset of addresses to be reused again and again to allow more individual devices without exhausting the IP address range. Those private ranges are often subnetted to be able to have many separate networks.
Answer: Private IP addressing pools are similar to public IP pools. It in not like that private pools are derived from public pools. Public and private pools are result of IP subnetting of 32 bit IP. Then, it is understood between the ISPs of the world that they will not advertise private pools from their network towards internet. On the other hand, public pools will propogate through internet and there will be no duplication between public IPs.


Which kind of participle clause does "clarifying ....."stand for?

Question: OP:(See the "How to Ask" page for help clarifying this question. )  does it equal (See the "How to ask" page for help and clarify this questiin) . And plus: It would be more correct if I add a comma before "clarifying" in the OP,right?
Answer: no, See the "How to Ask" page for help clarifying this question. = See the "How to Ask" page for help (on) clarifying this question.
Comment: Could you tell me about redeced preposion grammar? I mean,when should I abbreviate preposition like that?
Comment: Here, HELP is a noun, and "Clarifying this question" is anohter noun clause as the help's topic (purpose)
Comment: It's my own example. (You should read more novels (on) improving your english skill). But I think it also can be like (you should read more novels and improve your english skill)=my example. You know,when the two actions have/modify the sam subject,then I could abbreviate the sentence by using participle clause/ing clause. But I think the OP and the theory I mentioned is not the same thing.
Comment: Maybe it is similar to this example( I have trouble doing sth) or (I am busy doing sth). You know it also can be wrote like ( I have trouble in doing sth)
Comment: I think I get it... I misunderstanded it ... (clarifying ...) functions as an adjective modifying the noun ( help)..


When creating a new solution do I have to run the .\init.ps1 command again to prepare the container environment?

Question: I am going through the Developer Fundamentals training for Sitecore 10 on the SiteCore website.  I created a solution prior to starting the training following my companies documentation.  When creating that solution, I ran  .\init.ps1, init2.bat, and docker-compose up -d.  As I am going through the training, getting-started-template, I ran this command <code>.\init.ps1 -InitEnv -LicenseXmlPath "<path to your license.xml file>" -AdminPassword "<your Sitecore administrator password>"</code> My powershell appears to be stuck at this part, Created a new local CA at "C:\Users\theRestOfMyPath".  I don't know if it is stuck because a certificate was already created the first time I ran the command for the other solution.  Do I just open a new Administrator Powershell window and run the rest of the commands?
Answer: Firstly, you need to run the PowerShell in Admin mode and check the path of the license file. you need to add "license.xml". As shown in below screenshot.

Hope this helps!
Thanks,
Yamini
Answer: Yes, you have to open the powershell in Admin mode.
Try to run the clean script from (clean.ps1) the folder first. It might be a folder deep (depending on how your folder is structured). This will remove everything from previous install. Then try again. I don't think your certificate is an issue here.
Do the following
Open Powershell in admin mode

Go to that directory using
cd [your directory path]/
.\init  [license path] (for me .\init "C:\sitecore\license\license.xml" )
docker-compose build solution
docker-compose build
docker-compose up -d

Don't forget to clean after you do the docker-compose down. Just run that clean.ps1 script from the folder.
There are few things you should know that pre-requisite for docker. Supported version of Windows are Windows 10 pro or Enterprise with version 20H2 is most stable. Also you must have WSL2.
Here is a link that might help.
http://mohammadhoque.com/?p=425
Hope this helps. Thank you.


how to use database mail from SSIS

Question: I try to use gmail in database mail. I have no problem to send out email from it. But how I can configure my send mail task to send out email by using database mail. Thanks
Answer: The SSIS Send mail task connects directly to a SMTP server - it doesn't use database mail.  If you want to use database mail, you would invoke it through an 'Execute T-SQL Statement' task that calls a stored procedure that wraps the database mail facility, or something similar.
Answer: Try this article Sending email from SQL Server Integration Services (SSIS)

how to use database mail from SSIS


Why will dmesg have message from user space?

Question: you can use dmesg -u to see log from userspace.
In my case, I have log from systemd and lvm. Why is this happening, why userspace program can print to kernel buffer ring?
Answer: A root process can write to <code>/dev/kmsg</code>. This is used for logging that occurs very early, before regular logging systems are ready to do any logging.
Answer: Some userspace processes can write to the dmesg because they execute actions which used to belong to kernel-space processes, but which have been moved to user-space to allow easier control by users.
A classic example is udev, which, according to Wikipedia:

it handles ... all user space actions when adding/removing devices, including firmware load.

Another well-know example is FUSE, which is:

Filesystem in Userspace (FUSE) is an operating system mechanism for Unix-like computer operating systems that lets non-privileged users create their own file systems without editing kernel code.

Together with LVM, init, and so on, these tools perform kernel operations in user space; for  this  reason, and possibly also for continuity with the instruments they replaced (devfs, hotplug, ...), their output clearly belongs in the kernel ring buffer.


What are some ways to detect the fundamental frequency in a signal using without using FFT?

Question: I am trying to estimate the fundamental frequency in a signal to corroborate the result which I have got by FPGA implementation of an FFT algorithm. Hence, could someone give me some idea how to do so?
Answer:
Count the time interval between zero-crossings (if the waveform/SNR allows...).
Autocorrelation, average magnitude difference function and their variants (YIN...).
Estimating the parameters of a damped sinusoids model (MUSIC/ESPRIT).
Several instances of Goertzel algorithm, or more generally other filterbanks (band-pass, comb) - in case there is only a small number of candidate frequencies that you want to discriminate.
Comment: Could you give me some sources or links to papers using these algorithms ?


Budget drone capable of lifting 0.5 - 1 kg and flying ~2km radius

Question: I'm looking for some budget multirotor drone (up to $300) which can lift 500g-1kg of weight and has long enough range to fly a ~2 km radius, it should also have a small camera just for control. Is there a ready to fly model which I can buy, or can I somehow easily construct a drone with the following parameters?
Comment: Do you need vertical take off and landing? If not, a fixed wing will be faster and cheaper than a multicopter.
Comment: I'll second @RobinBennett's comment. What kind of drone are you looking for? It's critical to include this in the question, either as an affirmative "I want a multirotor" or a less firm "I don't care if it's an airplane, a multirotor, or a helicopter".
Answer: The flight you describe is 100% illegal in the US requiring 107/commercial license + BVLOS waiver.  BVLOS waivers are very rare, 61 issued searching the DB for "107.31" here: https://www.faa.gov/uas/commercial_operators/part_107_waivers/waivers_issued/.  The rules are similar in most countries.
Your budget is off by a zero as well.  Depending on your duty needs, I think minimum \$1k for the core + $ for peripherals.
A Phantom could probably limp that payload - but you need to dig into the powertrain math:

What ratio of thrust do you want? Are you carrying a load form point A to B or will you require some performance?
Weight of unit AUW desired? Payload and performance are correlated to thrust and other performance features.
Flight time desired?

Camera for control at 2km requires high power VTX (FAA HAM license required). A 1 watt VTX in an urban environment will struggle to get you signal without a lot of extra gear (signal tracking from a ground station). Also, 1w is the legal max for a HAM / FCC licensed person, else you are 25mw (0.025 watt) limited and can't mod anything legally.  To get more watts you need to dip into FCC Part 15 regulations, not cheap.
I see you are in Armenia - I don't know the local there laws but my international flight experience informs me that most of the world is either unregulated (3rd world) or as strict or more strict than the US.
Comment: Thank you for a detailed explanation, there should be no problem with law, regarding to the questions: you are correct it's just for carrying a load from point A to B. AUW doesn't matter (whatever is better), drone just needs to correspond the listed requirements. Regarding to flight time - need to find rational balance between speed and cost. As it's for delivery I will need multiple drones perhaps dozens, so you are saying the cheapest solution would be ~$1k for each even in case of not ready to fly/custom build?


What philosophical reason did Al-Jahiz give for preferring Aristotle to the Qur'an?

Question: Al-Jahiz is one of the philosophical superstars of Arab literature. Not only did he write an enormous number of books, but his output was remarkably diverse. Besides a great number of satires, he wrote books on rhetoric and philosophy. And he is well-known for having said that he preferred Aristotle to the Qur'an. Unfortunately, I have not been able to track down the passage where he says that. I'd like to know why, ie what aspect of Aristotle was particularly salient for him, and how he justified philosophically his unusual preference.
Comment: [Francis Edwards Peters](http://en.wikipedia.org/wiki/Francis_Edwards_Peters)'s two accounts related to Aristotle and Arabs may provide clues.
Comment: I can't comment because of low reputation, but this probably would have more response in the Islam Q&A site, http://islam.stackexchange.com/.
Comment: "He is well-known for having said that he preferred Aristotle to the Qur'an" It is no well-kown and it is implausible.
Answer: Al-Jahiz was a Mu'tazilah which was:

an Islamic school of theology based on reason and rational thought that flourished in the cities of Basra and Baghdad, both in present-day Iraq, during the 8th–10th centuries. The adherents of the Mu'tazili school are best known for their having asserted that, because of the perfect unity and eternal nature of Allah, the Qur'an must therefore have been created, as it could not be co-eternal with God. From this premise, the Mu'tazili school of Kalam proceeded to posit that the injunctions of God are accessible to rational thought and inquiry: because knowledge is derived from reason, reason is the "final arbiter" in distinguishing right from wrong. It follows, in Mu'tazili reasoning, that "sacred precedent" is not an effective means of determining what is just, as what is obligatory in religion is only obligatory "by virtue of reason."

Greek rationalism was used here to express how they interpreted the truths of the Qu'ran. Its most unlikely that Al-Jahiz preferred Aristotle to the Qu'ran. Its sounds similar to the myth that above Platos Academy was a sign that said 'Let no one ignorant of Geometry enter here'. What is more likely is that he also recognised the excellence of Aristotle too.


What was the historical motivation for introducing the concept 'gravitational potential'?

Question: As a high school physics teacher, I like to motivate all concepts and terminology with how they were first developed historically. Recently I did some research on the motivation behind introducing the concept of gravitational potential, but I could not really find any clear story on the history of it. Why did people have a need for defining this? I can understand the reasoning for defining a gravitational field, but I do not understand the necessity of introducing gravitational potential.
Any explanations at high school physics level would be appreciated.
Comment: For what it's worth, one science (but not historical) answer to your question is that the potential is a single number, while the full gravitational field (say a vector giving the direction of the acceleration in Newtonian gravity, or the metric in GR) is a set of numbers. It is much easier to solve Poisson's equation for a scalar field and differentiate it, than to solve for a vector field. Also the potential is very intuitive quantity you can visualize, and makes it easy to address questions like stability of orbits.
Comment: This question might be better suited in the history of science stack exchange https://hsm.stackexchange.com/
Comment: Mathematically, every conservative field has a potential function. You don't need to do anything special to "introduce" the potential. Maybe you need to look at the history of vector calculus rather than the physics of gravitation.
Answer: It seems very likely that this question will be migrated to the history of science stack exchange.
The concept of a gravitational potential is associated with the concept of a field. (Not exclusively associated. As pointed out in a comment: the potential function can be defined mathematically anyway (when the force is a conservative force).)
The idea of representing an interaction as mediated by a field originated with the study of electricity and magnetism.
Faraday, for example, proposed a concept of 'lines of force'.
The concept of an electrostatic field that acts as mediator of electrostatic interaction is that it is an entity that is always present, but in the absence of a source of electrostatic interaction the field is in a uniform state.
The presence of electrostatic charge induces a stressed state of the field, a state away from the uniform state.  This stressed state has an associated energy.
A change in the state of stress propagates at a finite velocity.
A charged particle being accelerated by the field is then thought of as interaction with the field at its location (as opposed to interaction directly with other electrostatic charges)
Maxwell formulated a complete field theory of electromagnetism. Maxwell showed that given the properties of the electromagnetic field it follows mathematically that this field also supports propagating waves. These waves continue to propagate independent of whether the original source stil exists. This wave propagation is strong corroborating evidence that the electromagnetic field actually exists, and isn't just a mathematical construction.

As to gravity, I don't know whether before 1905 there was any serious attempt at formulating a field theory of gravity. In effect gravity was treated as acting instantaneously from particle to particle.
Laplace had demonstrated that if Newton's universal gravity would not be instantaneous over distance then momentum would not be conserved. So there were strong reasons to treat gravity as acting instantaneous over distance.
The introduction of special relativity in 1905 made it clear that a new theory of gravity was necessary: one that would have gravity propagate at a finite velocity, while satisfying the conservation laws.
Given that this new theory of gravity would need to have a finite propagation velocity for gravity: formulating a field theory of gravity was the way forward.


Store options in database or in a file?

Question: in a client-server database application, the different options the client needs to read from the server, where you'd store them? In the database or in some file which will then will be transferred on the network, or is there any better way.
Answer: It depends on the specific.
Generally speaking there is very little to store something in a file on the server (apart from files themselves such as images, videos, songs and so forth) rather than a database.
If you're storing, say, client preferences you may store them in a file on the client but this has portability problems (in that the profile settings don't go to another PC with the same user) but it might be appropriate if the client can be used "offline".
Probably the best of both worlds is to store things in a database on the server and cache them on the client (in files probably) to allow offline usage, if that's appropriate to the application in question.
Answer: Depends on how dynamic access to the values has to be.
Putting them in a file means having to edit the file for changes.  You have to edit the file, perhaps repackage the app with the new values, and bounce the server.  If you're using an exploded version of the code on the server, it means giving clients write permissions on the server, which can be problematic.
If you put them in the database, clients can see changes without having to edit a file.  They get to see the values right away.  No server bounce needed.  And you can dole out access using database permissions.
UPDATE: Another thought - are the options for all users or just a single individual?  If it's the former, you have to worry about "oil canning", where one user changes a value and another switches it back.  If it's for a single individual, you'd have to have a file for each user.  A large user base could be a problem.
Answer: The clients need to read just some configuration settings, that's all. Also those options will not be changed from the clients, only from the server.
Comment: Don't create new answers; edit your original post or enter as a comment.
Answer: It depends upon use cases, but my own experience says, it is better to store options in  database. In todays' world, we need to go towards shared-nothing type of architecture as far as we can. In that way, if tomorrow you make your application to be failsafe, you will find, it is better to store all options in database. Because otherwise you need to sync your files accross various nodes which are running the copy of your application. On the other hand, if it is in database, it is all there in db and most of the db supports High-Availability type of use case in which case you do not need to be worried about keeping your application with files running in different nodes in sync.
Answer: That depends on a number of factors:

Do you have more then one Front End
Server, then the database approach
requires less maintainance.
If you have a Dev, QA as well as a
Prod environment then the file
approach makes sense as the config
will not be changed when
copying/restoring a database from
one of the other environments.
Answer: Normally, I would store the configuration settings in a database, if available.  However, in the project I am now working, the client wants multiple distributed copies of the database, updated from a master.  Each installation has it's own configuration, such as printer settings.
The answer in this case is to have a local config file, where the local user settings are stored.  The application generates the default for each setting.  If need be, the file can be edited to update settings on the fly.

Store options in database or in a file?


How do I create a speckled textured background?

Question: How do I get this sort of background texture? Short of time-consumingly adding them bit by bit with a brush I have no idea how to get this effect.
Comment: You can probably find a free texture / brush somewhere in the internet. Or: scan a piece of speckled paper and use it as a texture.
Comment: I realized that I answered a similar question not too long ago: http://graphicdesign.stackexchange.com/q/66630/2332
Answer: Brush would be one way and depending on the brush, not that time consuming, as you could do it in one swoop, but the first thing that comes to my mind is using a photo of a specific texture.
This is a concrete texture I googled for this example.
I chose this one specifically, cause it's got those air bubble holes that are like dark speckles waiting for you to harvest them.

Turn the image gray: Image > Adjustments > Black & white...
With levels: Image > Adjustments > Levels...

Bring the upper white arrow to the left as far as you can, so that it's almost all white. Then slide the grey arrow closer to the white. The goal is to get rid of most of the grays and and be left with black speckles on a white background. ( Every image will be different. )
It might be easier to get it kinda close, apply that and do Levels again. This gives you finer control over those last few gray pixels you wish to push to black.

To easily blend it to the colored background:

Set it on top of the background color ( in its own layer of course )
Set its Blending mode to Multiply. This gets you half way. You could potentially just lower the opacity at this point and be done with it, but I'd keep the opacity at 100% and do the following:
Image > Adjustments > Hue & saturation...

Turn on Colorize
Set hue to your liking
Add some saturation if needed
Add some light

Remember that you can also stack these textures. For example, If you want to have more of the bigger speckles, you might be left with just a few of them, but you can compensate by either duplicating them or adding more textures to the mix... or just find a texture that is perfect to begin with.
Comment: Obviously, if I wanted to keep the texture uniform, I'd erase the big dark  splotches and replace them with the smaller speckles. Also, you can blur the texture, if you feel like you had to push the levels too far to get the amount of speckles you wanted.


Compact normal subgroups of connected groups

Question: We know that for a connected locally compact group $G$ there exists a compact normal subgroup $K$such that $G/K$ is a Lie group. Now, if $G$ is compact, could we find a proper compact normal subgroup $K$ with that property?
Answer: The answer is no when $G=\{1\}$, and yes otherwise, as a consequence of the Peter-Weyl theorem. The latter ensures that $G$ has a nontrivial finite-dimensional representation $G\to U(k)$. The image of the latter is a nontrivial Lie quotient of $G$.
More precisely, a consequence of the Peter-Weyl theorem is that every compact group is projective limit of its Lie quotients.


Visible Light Communication Signal Transmission

Question: Im working on a VLC project where Ill need to transmit encoded data through an LED using an Arduino board to a photodiode receiver that somehow demodulates the signal and extracts the data. Im looking for a transmission rate of atleast 1Kbps where anything higher is bonus points. The problem is there will be ambient light present and my LED cant be a distinct red or green color to resemble a common lighting fixture. So one solution Im considering is to modulate the LED at two set frequencies, say 30kHz and 35kHz, where and connect the photodiode to a bandpass filter designed for 35kHz so that the output of the filter is a logic one when my LED is modulated at 35kHz and a logic 0 when its mod at 30kHz(this is simplified, id do something where a logic 1 is a certain duration of 35 followed by a certain duration of 30). Pretty much this idea is modeled from the NEC protocol used for remote controls. Id like to know if this setup would work before I start putting it together as I cant find any simulator that reasonably simulates LED/Photodiode interactions. Also, since im a beginner and im sure you all have wonderful ideas, is there anything I can do better or differently? Any input would be golden!
Comment: Must it be visible light instead of infrared, what will be the distance between the LED emitter and the photodiode, and will it be operated indoors or  outdoors?
Comment: It has to be visible light. The goal is anywhere in a small room,so approximately 20 ft but to prove the concept I can start at 6in distance, and it will be indoors.
Comment: If you must use a LED for visible light, you should consider a narrow band optical filter for the receiver. The filter will block most of daylight and other ambient light.
Answer: Your research has pointed to methods used by TV remotes, which have refined data transmission that is robust. A visible-LED link has little optical difference from the infra-red optical link universally used by all remotes. Perhaps some research into those excellent IR-remote receiver chips would be time well-spent. Vishay describe internals in a bit more detail in this note:circuit description of IR receiver remote
 Too bad that those IR-remote receiver chips are all optically opaque to visible light (they only accept infra-red wavelengths longer than about 750nm). This optical filter is the only reason why these chips can't be used with a visible red LED light source.
Your proposal of alternating between 30-35 Khz. modulation is also a reasonable approach. A  photodetector, bandpass filter, limiter, into a PLL detector like LM567 or 4046 could process the received signal. In the presence of no signal, you're likely to get garbage data, so a data protocol with checksum or CRC packets would be appropriate. Here's an idea for optical receiver "front-end" that could feed the PLL demodulator...

simulate this circuit – Schematic created using CircuitLab
If you can, choose a high-efficiency RED led (not green) that has tight beam width like 8 degrees or less, with clear (not diffused) plastic lens. You'll have to point it fairly carefully at the receiving photodetector. You can easily modulate this LED with a 30/35 KHz. square wave from a digital source.
 Silicon phototransistors have best efficiency for infrared, but still detect visible RED light sufficiently well, but not so much GREEN light from your LED. A standard clear-lens phototransistor could be used, with a tuned load comprising a L-C tuned circuit (tuned to 33KHz.). A large bias resistor (3.3MEGohm) helps improve AC response at 33KHz. Ambient room light provides additional bias too. Loaded Q of the L-C bandpass should be less than ten for your application.
Answer:
Im considering is to modulate the LED at two set frequencies, say 30kHz and 35kHz, where and connect the photodiode to a bandpass filter designed for 35kHz so that the output of the filter is a logic one when my LED is modulated at 35kHz and a logic 0 when its mod at 30kHz

You could save power by simply turning the LED off altogether to transmit a 0, rather than transmit a signal and throw it away at the receiver.
Or ou could improve the effective SNR if you use a receiver that can detect both 30 and 35 kHz, but can tell the difference between them.
Comment: I'm pretty sure he meant NE567
Comment: Try an NE756, since it'll reject pretty much out of its passband
Comment: @EMFields, could you double check that part number or give a link to a datasheet? It's not a known pn on Octopart.
Answer: If you can manage to correctly modulate and demodulate the signal, you shouldn't have much of a problem. Infrared LED-Photodiode pairs help reduce interference, especially if you chose them so that one emits at peak sensibility of the other. Also, if you use some kind of amplifier for the photodiode signal, make sure to stabilize the system, as they tend to oscillate if not carefully implemented (particularly at ever higher frequencies, when the gain starts to roll off).
Answer: An alternate approach to this problem is to read in analog data and do the processing in the digital domain.
Using a technique like cross-correlation would probably work well, it might be a bit overkill for this application but should be fairly robust. The typical way to apply this would be to subtract the result of two cross correlations, and using a single cycle of the two frequencies as the windows for the two cross correlations. (this could also easily be expanded to recognize more frequencies or patterns for more complex encoding)
Answer: The modulation you are talking about is Binary Frequency Shift Keying. I think that is something similar to what the TSOP sensor does. But it works in IR. And I frankly feel it is overkill for VLC.
If you really want "visible" light communication, you just need a good enough photodetector. I have used a few photodiodes which work reasonably well even at 9600 baud (I was using UART as my modulator/demodulator). The receiver circuit used was a transimpedance amplifier to get a voltage waveform from the photodiode current, followed by a comparator. You would only need a bright enough LED to increase the range. I had to set the comparator threshold manually but you could implement automatic gain control to overcome that issue.
One very simple filtering method is to cover your sensor with tinted plastic (If you are using Red LEDs, cover your sensor with green and blue filters). You are effectively bandpass-filtering the light signal. On the circuit, if you are working with a data rate of 10kHz then a passive RC highpass filter to block out 50Hz/60Hz noise should be enough. Because if you think about it, ambient light is either from the sun/DC source like a torch i.e. its DC or from a mains-powered light source i.e. its at 50Hz/60Hz wave. A high pass filter should do the trick of removing noise.
Answer: When I did design and build a similar system (well, simple pulsing ("0-1-0...etc") of the transmitter, nothing more) back when dinosaurs roamed the earth, I found a 25mm diameter piece of matt black plastic pipe, maybe 50mm-75mm long, with the transmit and receive devices at the far ends of these short tubes, solved all of the problems I had with the electronics picking up stray input from daylight or artificial lighting.
Before an editor leaps to delete this, I suggest that this is the epitome of an electronics answer because at one "blow" my bits of plastic pipe filtered out every unwanted source of electromagnetic interference sufficiently. Perfect solution. Just don't point the receiver at the window or the light fittings.
A short piece of pipe in my case also determined the amount of freedom in the overall electronic design. And isn't all electronics tailored specifically to the environment it is to be used in? A chunk of pipe determines the electronics - everything normal here...
Why did I use the pipe shield on the transmitter?  Solely because of the specific requirements of that particular installation.  I wouldn't have bothered with a transmitter pipe shield in many other circumstances.


Why does Parity mapping allow 2 qubit reduction?

Question: when mapping from fermionic to qubit hamiltonian, using Parity mapper allow us to reduce 2 qubit in the final hamiltonian. I would like to understand which kind of symmetries are being used and how it is done. Thank you in advance!
Answer: There is a relatively intuitive way to understand 2-qubit reduction using the parity mapping. It uses that the number of $\alpha$ (spin up) and $\beta$ (spin down) electrons are conserved (because the Hamiltonian commutes with the particle number operator).
In the Jordan-Wigner mapping, we represent a Slater determinant as
$$
|k_1^\alpha,k_2^\alpha,\dots,k_{M}^\alpha,k_1^\beta,k_2^\beta,\dots,k_{M}^\beta\rangle$$
where
$\sum_{p=1}^M k_p^\alpha=N_\alpha$ and $\sum_{p=1}^M k_p^\beta=N_\beta$.
Going from the Jordan-Wigner mapping to the parity mapping, the following transformation is applied
$$    |{k_1^\alpha,k_2^\alpha,\dots,k_i^\alpha,\dots, k_M^\alpha,k_1^\beta,k_2^\beta,\dots,k_i^\beta,\dots, k_M^\beta}\rangle \rightarrow |{k_1^\alpha,k_1^\alpha+k_2^\alpha,\dots,\sum_{p=1}^i k_p^\alpha,\sum_{p=1}^M k_p^\alpha+k_1^\beta,\dots,\sum_{p=1}^M k_p^\alpha+\sum_{p=1}^M k_p^\beta} \rangle$$
where all sums are taken mod 2.
Now, as the number of alpha-electrons and beta-electrons is conserved, we know that $\sum_{p=1}^M k_p^\alpha=N_\alpha$ and $\sum_{p=1}^M k_p^\beta=N_\beta$ . This is true for ANY Slater determinant that preserves the number of alpha-electrons, and we know that the exact ground state is a linear combination of only those Slater determinants. But then, in the parity mapping, the M-th qubit takes the value $N_\alpha \text{ mod } 2$ and the 2M-th qubit takes the value $(N_\alpha+N_\beta) \text{ mod } 2$. But that means that we already know the correct value of 2 (out of 2M) qubits, and do not have to simulate them, e.g. they can be tapered off.
Comment: Now I understand the physical meaning of the 2-qubit reduction. Thank you very much for the very clear explanation!!!
Answer: The Parity mapper 2-qubit reduction uses the Z2Symmetry logic in Qiskit. For any qubit operator the Z2Symmetry logic allows a search to find any symmetries that may be present. In the case of a Fermionic Operator, where we have the block spin mapping and know the number of particles in the system, we know from the mapping itself that it will produce symmetries.
Since the symmetries are known the Z2Symmetry logic can be used to taper the operator without any need to search for them. There may be other symmetries present that the Z2Symmetry logic might find though. If you do Parity mapper, without 2-qubit reduction, and then use Z2Symmetry to find the symmetries it will do so to - the 2-qubit reduction avoids the search since we know they will exist. You can see the code here for the 2-qubit reduction to find out more detail if you want.


Adding a newborn child to US tourist visa (B1/B2)

Question: My wife and I have a 3 year B1/B2 US visa and we got it before having a child. Now since we have our newborn child, we'd like to travel to US again. So somehow we need to add our child to our visas.
Do we need to apply for a dedicated application for a child?
Do we need to go in person with a child to embassy for this? Somewhere it was mentioned for applicants <14 there is no need to be in person for this.
Thank you!
Answer: You need a new application for your child, you cannot add your child to an already approved visa.
It makes sense to carry the child along to the interview although they indicate it is not mandatory. In theory you do not have to take the child along, however in practice it's sometimes different and they will ask for the child.
In theory you don't have to carry a bank statement or indeed any documents (except those listed below) along for a USA B visa interview. In practice very very very few people get approved without some documents.
You are the legal guardians of the child I assume and you will have to prove you are actually his parents via a birth certificate or other means.
Required Documentation per Department of State

Gather and prepare the following required documents before your visa
  interview:
Passport valid for travel to the United States – Your passport must be
  valid for at least six months beyond your period of stay in the United
  States (unless exempt by country-specific agreements). Each individual
  who needs a visa must submit a separate application, including any
  family members listed in your passport.
Nonimmigrant Visa Application, Form DS-160 confirmation page.
Application fee payment receipt, if you are required to pay before
  your interview.
Photo – You will upload your photo while completing the online Form
  DS-160. If the photo upload fails, you must bring one printed photo in
  the format explained in the Photograph Requirements.
Comment: "It makes sense to go to the interview with the child although they indicate it is not mandatory." I interpreted this as "your newborn is permitted to attend the interview alone but it might make sense to accompany them" and was briefly fascinated by this kid's precociousness.
Comment: Perfect, fully answered my requests.
Comment: We say thanks you here by voting the answer (using the vote tab) and then clicking on accept for that best answer (using the accept tab).
Comment: In some usa embassies the child must attend the interview.
Answer: Yes, to enter the US, all children, including infants, needs his/her own valid travel document/passport and visa. Citizens of countries eligible for the Visa Waiver Program would apply for the ESTA. As you did for your visa, you would need to file a DS-160 and pay the applicable fee.
Generally, children under 14 do not need to appear for an interview. The website of the US Consulate that serves your country or area should have the specifics.


Do sharks fart?

Question: My son is 5 and I'm encouraging him to be curious and ask questions of the world around him.
He asked if sharks fart and how does it smell?  He feels that it would smell of fish and be disgusting.
He was also asking how anyone would know or be able to check. I don't know the answers and am teaching him how to research.
Comment: https://www.thenakedscientists.com/articles/questions/do-fish-fart
Comment: Nice first question, welcome! What have you tried to asnwer that question?
Comment: Thank you very much, had much hilarity explaining the answer    he is particularly  taken by thr idea of herfing communicating by farting!
Comment: @Cameron Well done for encouraging your son. If I were you, I'd try to get him to think about how we sense the qualities that constitute a fart and what mechanisms create the fart. A fish may well fart but will we hear it? Will we smell it through the water? Linking back to the creation of the fart (production of gases in the intestinal tract), would we see a new effect like a bubbling in the water?
Comment: I thought that anaerobic decomposition will definitely cause methane in any animal which has an intestine. Why isn't that so for all species?
Answer: Excellent question. Via Southern Fried Science: According to Daniella Rabaiotti, a postdoctoral researcher at the Zoological Society of London, sand tiger sharks are the only shark known to fart.
They gulp in air at the surface, store it, and when at depth let the air our in the form of a fart to alter their buoyancy. Air lets them float instead of sink, so when they want to sink, that's when they release the air. Shark fart source
There is also a book of species known to fart, confirmed by scientists.
Book of farting animals on Amazon

Do sharks fart?


How to write summaries for literature survey?

Question: My professor wanted me to write a short summary (one or two paragraphs max) on each paper. Focus on the salient of the method.
could I use the abstract sentences exactly or should I change the words and write with my own words?
I was wondering if you could tell me whether it is necessary to read whole the papers or it is enough to read abstract and conclusion part?
Comment: I'm voting to close this question as off-topic because we cannot know what your professor wants. However, I'd guess that if your professor asked you to write a summary, they expect you to write the summary in your own words.
Answer: He has asked you to write a summary of the works. I expect he wants to assess how you write, as well as your understanding of the papers themselves.
Copying the abstracts verbatim not only obstructs this goal, but is also plagiarism. The ideas and words are not your own and you should not try to pass them off as such.
Read the papers carefully and summarise them in your own words.
Comment: I ask my students to do exactly the same thing.  I use the summaries to assess their writing and technical skills.  By 'copying' or 'paraphrasing' sentences from papers will show that you have a shallow understanding of a paper, and that your English level is poor.  I can very easily tell the technical depth of a student by reading their writing or listening to how they explain technical concepts.
Comment: @nikki2 If you study with such an attitude, you may be well stop here. Don't you think that by reading those papers you might actually learn something?
Comment: should I read whole the papers? What will happen if I just summarize the abstract and conclusion?
Comment: @ Massimo Ortolano. I do think so. but I have just started finding articles related to my master thesis and I am going to read 60 articles. I need to find top 10 articles among those 60 articles.


Maintiaining SQL Transactions over web service calls in .Net

Question: How do I perform a database transaction where I create a new record then make a call to a web service using the new record ID returned from the database which will also manipulate the same database? I could obviously update all tables directly from the same SQLConnection object but the logic within the web service call is subject to change and I really need to ensure that the changes my code makes are committed alongside those changes introduced by the called web service.
Answer: If the web service has the responsibility to manipulate the database, I would extend the web service to perform the actions that your code is doing.  The point of using the web service is (ought to be) to separate your code from having to deal with the database directly.  Introducing direct DB manipulation into your code is just going to make things much more convoluted and harder to maintain.
Answer: This isn't something that you want in an actual transaction. Transactions should be as short as possible, which means no user interaction in the middle of it or in this case waiting for a web service to respond.
As to your problem,if you have control of the web service then change the web service to make a stored procedure call that performs the whole transaction. If there are actions that MUST be completed every time the service is called then they should be part of the service.
My guess is that you don't have control over the web service though, or this wouldn't be an issue. How is the web service accessing the database? If it's using a stored procedure already then you should be able to add the necessary logic in there. Again, I'm guessing that's not the case or it wouldn't have been a problem. My suggestion is that you try to change the web service to fit that architecture if at all possible.
Assuming that the web service accesses tables directly (yuck), you will need to put code into your calling code that does the insert, calls the web service, then checks to see if the web service did what it was supposed to do, and if it didn't then your code takes the necessary actions to undo everything. It's basically like a home-grown transaction engine. It's also very messy and tends to be bug-prone and difficult to maintain. Not to mention, it's not 100% full proof.


How to fold a tesseract from L-unfolding?

Question: I came across an image, that show really simple unfold of 4-dim cube. https://arxiv.org/pdf/1512.02086.pdf here at #2.1, and 120 here https://page.mi.fu-berlin.de/moritz/mo/198722/unfoldings.html. Does anyone know how to fold it? Thanks for the help!
Answer: Since your first link is to my own paper, I will try to respond to your
slightly unclear question:

Does anyone know how to fold it?

Our paper showed various hypercube unfoldings that tile $\mathbb{R}^3$,
including the Dali cross, and one unfolding that further unfolds to tile the plane.
I gather you are seeking additional unfoldings of those unfoldings into $\mathbb{R}^2$.
In which case, this correspondence from Andrew Winslow,
triggered by our paper, may help:

"Stefan Langerman and I have found some unfoldings of the Dali cross that tile the plane. Attached are pictures of three examples. They all tile the plane isohedrally using $180^\circ$ rotations, i.e., they satisfy Conway's criterion."

Below I show one:

Added. In case what you seek is how to fold the $L$-shape
from 2D to 3D, Fig.16 is explicit:

Or perhaps you are asking how to fold the 3D $L$-shape to
the 4D hypercube, i.e., which faces glue to which?
Comment: Mark McClure's Mathematica calculation and display of the $261$ hypercube unfoldings: [3D models of the unfoldings of the hypercube?](https://mathoverflow.net/a/199003/6094).
Comment: Excuse me for misunderstanding. At wikipedia https://en.wikipedia.org/wiki/Tesseract, in image gallery block you can see gif with unfolding projection of 4-dim cube into Dali cross. And I asked about something similar. I can't understand which edges we need to glue, if we want get tesseract.
Comment: @MichaelKhoroshikh: Of course you cannot fold to get a tesseract except in 4D. I'll add another image, but I still may be misunderstanding your question.
Comment: @MichaelKhoroshikh: I apologize for misunderstanding your question. I now see that what you must be asking is: How can that $L$-shape in 3D be refolded to form the 4D hypercube? Which faces glue to which? You want instructions on how to reverse the unfolding from 4D to 3D. That I don't know. You could use McClure's Mma program to see how the $L$-shape is achieved, and reverse-engineer from there.


Unable to access new installed theme

Question: Bear with me as I am new to this.I am running 13.10 desktop.
I installed Wordpress LOCALLY on my computer. I already have a website that will eventually be replaced and want to create the site myself then load to our hosting servers.
I am unable to access the theme that I purchased and installed through my Dashboard. The theme file is located with the other theme files that already come with WP. The new Theme file has the same read/permissions as the rest of the themes. I can access the new file and see all its contents but unable to access through Dashboard and customize.
Mysql and PHPMYADMIN are all current.
Any idea?
Answer: This is typically a file ownership problem -- in a normal install, WordPress runs as the webserver user (www-data in the default Ubuntu install of apache). When you create files or copy them into your web directory, they're owned by your normal user account. sudo chown -R www-data your-theme-directory should take care of it.
Comment: Thank you for your response. I am learning the commands. I know I replace "your-theme-directory" with where the files are located, What about the "www-data" is that replaced with something? Thank you in advance.
Comment: Nope! www-data is the actual name you need (again, assuming you're running the default apache you can get out of the box, which it sounds like you are). Chown is short for "change owner"; you're saying that instead of your normal login owning these files, they should belong to the same account as the rest of your WordPress install. More info on the chown command: http://www.linfo.org/chown.html
Comment: I was able to chown the themes dir using the input you gave me. Now I am UNABLE to get access to any of the theme files. How can I reset?
Comment: You can revert by issuing the same command, but using your normal username instead. But this is all getting pretty off-topic for this SE -- your issue, at heart, is that you need to understand the basics of file ownership and permissions a bit better; you'd be having exactly the same problems running any system other than WordPress. You might want to take a look at some of the many tutorials out there, like this: http://blog.pluralsight.com/linux-file-permissions

Unable to access new installed theme


Open Source Publishing?

Question: If an author is not concerned about making money from her story, but rather would like to publish the story to protect the story from copy right yet allow others to read and review the story for critical improvement, is there such an open source website or facility that promotes such a peer review environment?
Comment: When you say "read and review," do you mean like a wiki, where anyone can edit?  Or do you mean like a web-enabled version of TrackChanges, where anyone can suggest changes and/or insert comments keyed to the text?  Or do you just want reviews/comments, separate from the text?
Comment: Publishing doesn't protect it from copyright. You need to register the work to get copyright protection.
Answer: Create an ebook and distribute it through Amazon's Kindle Direct Publishing (or other ebook selling platforms) for $0.

Note:
Amazon KDP allows to give away your book for free for some limited time, after that you have to sell it for at least $0.99. But you can publish it for free elsewhere, and since Amazon always wants to have the cheapes prices, once you report that your book is available for free elsewhere, you can lower your price to free on Amazon, too. I never tried this, just read about it in forums and blogs. Google to find a more detailed how to. Of course you can always ignore Amazon and just use other platforms, but Amazon has the widest reach, so I would try to be on there, if I could.
Also:
Don't be hasty and throw away your idea just yet. Take some time to evaluate all options, let some experienced readers read it and give you feedback (find bloggers doing reviews in your genre and ask them for feedback), if they are even half positive, either educate yourself to write well or find a co-author, etc. You can always publish your book free, but maybe some better ideas come along in the next weeks or months.
Comment: Thanks for the additional notes. I was able to speak with the second English professor today. She stated she was engaged in the characters and took notice that the document was more of sample summary of world build then an actual well crafted story. She did say that there is potential in the story. I like the idea to wait, practice, learn, revise, evaluate approach. It is too early to rush to conclusions. Thanks. I am in an unusual position where I am not financially dependent on the success of the story, which puts me in a position to buy time for a more polished work.
Comment: Isaac Asimov published several of his best sci-fi books originally as separate (but related) short stories in sci-fi mags.  Later he collected them, did some revising, and published them as books.  "I, Robot" would be the best example.  Many of Asimov's peers worked similarly.
Comment: Sounds good. If you want to stay within your creation instead of inventing something new, you could take one small event in your world and develop it into a story. Or write one scene or chapter. It does not matter how many pages this has, just that the whole thing is limited, and that you don't focus on developing the huge arch, but on how the characters think, their inner conflicts, the small scale development of the events. Take your favourite book and look at it: what is told on one page? What do the protagonists say? How do they say it? Stuff like that. Then try doing that.
Answer: github.com, gitlab.com. They offer to create a license file for you. I use non-copyleft licenses like MIT, BSD or Apache.

Open Source Publishing?


Creating a text report detailing attributes on several GIS layers within a polygon

Question: I am trying to create a text report listed by area (taken from a polygon layer) that details any features from other layers (points, lines and polygons) that fall within the listed area.  I have QGIS and FME but I cannot find anything that creates what I need.  Do any of you have any experience of creating this type of output please?
Answer: What you describe is imho called a "query" (SQL Query) :
you're able to query any of your currently opened tables using (for example) the DB Manager.
You choose Database/Database Manager/Database Manager then Virtual Layers/Qgis Layers you can then try queries like the following :
<code>select info_a,info_b, info_c from point_layer, area_layer
where st_intersects(area.geometry, point.geometry)
</code>
In a query you'll be able to use any spatial operator (the one used here is "intersection" ...)
This query is just an example (not based on any of your data structure) using two layers of a qgis project
Answer: In FME there are two different aspects to this: assessing the data and creating the report.
To assess the data, you'd use a transformer like SpatialRelator or SpatialFilter. Here I am testing park features against a set of other data, to see which intersect, overlap, fall inside, etc:

The key is to create a list of which features are spatially related (with whatever predicates you chose to test) because they will form the basis of your report.
So, the report can take many forms. The simplest is to explode the List you created (ListExploder transformer), format the content (AttributeManager probably) and just pipe the data into a Textfile writer. The CSV format writer is another good choice.
However, you could go further and use the HTMLReportGenerator transformer and HTML writer to generate a report that is more elegant than just plain text.
This should get you started. Basically you have a case whose solution ranges from the very simple to the very complex, depending on how you need to assess the data and how you want to style your output.
For further information check out the Common GIS Operations tutorial on the FME Knowledgebase (for info on assessing spatial relationships). For the report the Textfile writer is fairly self-explanatory, but for HTML reports there are a couple of blog posts (here and here) and this project on Github is a good example that generates such a report.


does anyone knows how to make spiral clouds (hurricane) for a planet?

Question:
Does anyone knows how to make spiral clouds (hurricane) for a planet? i want to make a planet with spiral clouds like in the image but here is the thing online tutorial on youtube show you how to make hurricane but sadly they don't work with planets because they use some kinda angle tricks meaning if you moved the camera you will break the illusion
Comment: Are you talking about this tutorial ? https://www.youtube.com/watch?v=-Xr6FDJiCLw
Comment: yes that it is ..
Answer: You can use material nodes to create this spiral-like pattern on curved geometry. With cycles you can make use true displacement, which is important with light from acute angles.

Unwrap your object or use object coordinates if possible. With a distance node, we can create a gradient, starting at $0$ in the center and increasing outward. If we use this value as the angle for a Z rotation (with a mapping node) you can twist the texture coordinates into spiral.

These spiral mapping coordinates can be used as the input for any texture, for example a noise texture. I will use it to color a diffuse BSDF.

You can also use the diffuse texture to create a displacement of the surface by connecting it to a displacement node. Use a colorramp or rgbCurves node to shape the ridges and valleys of the displacement.

The reference seems to have some ridges and noise in its outer areas. We can replicate that with a radial stripe texture. Create a radial gradient first with the gradient node. Then multiply it by a whole number and use the fraction node. The result is a radial-symmetric gradient which goes from black to white any number of times. Use a colorramp or RGBcurves to shape the gradient and make it goes from black to white to black again. Hence, we get a seamless transition. I use a noise texture to create some variation for the initial texture coordinates.

There seems to be less noise in the center of the spiral. Add another distance node using the same input coordinates and shift its black-white transition outwards with a mutliply-add math node. I checked clamp to limit the highest number to one. Multiply the result with the previous stripe pattern and we get the stripe pattern, but with black in the center.

This is good, because we don't want to add noise to the center.

For the alpha channel, I used a duplicate of my original spiral noise with slightly different settings. Then I shifted the distance gradient and subtract it, making the alpha fade to black further from the center.

The complete node setup looks like this.
Comment: thanks man !! this is unbelievable
Answer: If I needed to do it I'd find an image, give it a feathered alpha channel in Photoshop and import it into Blender as a plane and position it. You could create normal and specular maps from the image.
Creating it in Blender, as far as I can see, means modeling it, using a particle system or perhaps nodes though that would be beyond myself. You might somehow animate smoke emitters to form a spiral then take one frame of that against an alpha background (the same as getting an image).
Hope that helps.
Rusty


Why did Duryodhan go to heaven?

Question: While I have found some speculative answers to this question, I would like to know something more accurate and philosophical rather than the usual clichés. I personally don't think he was a villain and Draupadi was not molested
Answer: All the answers for these questions can be found in Sabha parva and Swargarohana parva.
Why Duryodhana attained heaven?
Duryodhana attained heaven due to his practice of Kshatriya dharma on the battlefield.
Sage Narada mentions this to Dharma raja as part of their conversation in heaven

"Narada, smiling, told him, 'It should not be so, O king of kings. While residing in Heaven, all enmities cease. O mighty-armed Yudhishthira, do not say so about king Duryodhana. Hear my words. Here is king Duryodhana. He is worshipped with the gods by those righteous men and those foremost of kings who are now denizens of Heaven. By causing his body to be poured as a libation on the fire of battle, he has obtained the end that consists in attainment of the region for heroes. You and your brothers, who were veritable gods on Earth, were always persecuted by this one. Yet through his observance of Kshatriya practices he has attained to this region. This lord of Earth was not terrified in a situation fraught with terror.

I personally don't think he was a villain?
Sage Narada enlisted the mistakes done by Duryodhana and why Dharma raja should forgive him in the following conversation in heaven

"'O son, thou shouldst not bear in mind the woes inflicted on thee on account of the match at dice. It behoveth thee not to remember the afflictions of Draupadi. It behoveth thee not to remember the other woes which were yours in consequence of the acts of your kinsmen,—the woes, viz., that were due to battle or to other situations. Do thou meet Duryodhana now according to the ordinances of polite intercourse. This is Heaven, O lord of men. There can be no enmities here.'

Defeating another king using magical dice. Asking wife of your brother who is equivalent to your mother to be brought into the sabha. Not returning the kingdom back to his brothers once they held their end of bargain. Trying to kill them using wax house and lighting it. I think after enlisting all these things there would be no one saying he is not a villain.
Draupadi was not molested?
First we need to understand that Matha Draupadi is never lost in dice game. The following question by her goes unanswered because she has asked the right question and there is no right for any one to put his wife as stake once he lost himself first.

"Draupadi said,--'O son of the Suta race, go, and ask that gambler present in the assembly, whom he hath lost first, himself, or me. Ascertaining this, come hither, and then take me with thee, O son of the Suta race.'

So technically Dharma raja did so only on insistence of Shakuni who is playing on behalf of Duryodhana who has become the master of Dharma raja due to previous bet. Respecting the wish of master is another part of Dharma and Dharma raja obliged with that.
So there is no right for anyone to bring Draupadi devi to sabha and they did so against her wishes which attributes to molestation. There is no evidence say anything contrary to this and it is blatant case of molestation without any doubt.
Will Duryodhana stay in heaven forever?
The following words of Indra will give an insight of what will happen next to people who commit a lot of sins

'O Yudhishthira of mighty arms, come, come, O chief of men. These illusions have ended, O puissant one. Success has been attained by thee, O mighty-armed one, and eternal regions (of felicity) have become thine. Thou shouldst not yield to wrath. Listen to these words of mine. Hell, O son, should without doubt be beheld by every king. Of both good and bad there is abundance, O chief of men. He who enjoys first the fruits of his good acts must afterwards endure Hell. He, on the other hand, who first endures Hell, must afterwards enjoy Heaven. He whose sinful acts are many enjoys Heaven first. It is for this, O king, that desirous of doing thee good, I caused thee to be sent for having a view of Hell. Thou hadst, by a pretence, deceived Drona in the matter of his son. Thou hast, in consequence thereof, been shown Hell by an act of deception. After the manner of thyself, Bhima and Arjuna, and Draupadi, have all been shown the place of sinners by an act of deception. Come, O chief of men, all of them have been cleansed of their sins. All those kings who had aided thee and who have been slain in battle, have all attained to Heaven. Come and behold them, O foremost one of Bharata's race.

So there is definitely going to be hell for mistakes done and it will be delivered once all the result of good acts is complete.
Comment: In my personal opinion based on some research  I did it came to my attention that Draupadi episode is later interpolation also biased interpretations. All problems they face are also those faced by tapasvis who reach highest chakras. But above are more widely accepted today.
Comment: @Sona Parivraj can you please share the research material names that you might have used to come to that conclusion. No need for links. Just the author names or books studied will suffice.
Comment: An intuitively compiled article could answer questions of Tej and others. Please read https://www.esamskriti.com/e/Spirituality/Philosophy/Draupadi-colon-S-Abuse-And-Other-Myths--1.aspx

Why did Duryodhan go to heaven?


How can I find out which 21:9 Monitors will charge my MacBook Pro 15"?

Question: I know the LG UltraFine 5K monitor has the  ability to supply enough power to charge a 15" MacBook Pro (https://support.apple.com/en-us/HT207448) but is there a way to tell if a different monitor supports this function?
Answer: Your Mac has a power charge requirement (i.e. 85W or 67W).  To properly charge your Mac, you need a monitor that supplies at least this amount of power.
For example, looking at the support page you referenced, they state that

When you connect the display using a single Thunderbolt 3 cable
(included), it provides up to 85W of charging power to your MacBook
Pro with Thunderbolt 3 (USB-C) ports.

87W (watts) is the highest power rating that Apple power supplies will deliver (at the time of this post).  Those power supplies come with the 2015 through 2018 15" MacBook Pros.  Everything else uses a smaller wattage adapter (i.e. MacBook Air uses 30W).
What this means is the LG supplies more than enough power to charge and use pretty much any MacBook notebook with the only exception that it's just 2W shy of providing full power to the 15" model.  In other words, those will charge and work just fine; it just won't charge as fast as the native charger.
What to Look For

...but is there a way to tell if a different monitor supports this function?

If the monitor can deliver approximately 85W of power (or greater) then it will support this function.
If it cannot deliver enough power to both charge and run the MacBook, it will draw power from the battery and discharge it.


iPhone calendar app is stuck on Add Event page

Question: In Calendar app, I clicked the + button to add an event. When I'm done filling all the event details out, I click the blue Done button in upper right corner. It adds my event but it won't leave the Add Event page. I'm stuck on that page whenever I'm in the Calendar app.
Answer: This problem likely can be remedied by restarting the app (Double Tap the home button, tap and hold the calendar app icon until an X icon appears, tap the X icon). If that doesn't work, I would reboot the phone (hold the power and home button down until you see the Apple logo).
If this doesn't help, I would recommend posting screen shots.
Answer: Here's an easier way: hold down the power button when this happens, but don't turn off the device. Hold the home buttom until your calender app unfreezes. You should still have the event in your calender after that!
Answer: Switch the view from landscape to portrait. It will revert.
Answer: I was able to send myself a message from the event that was blocking my email, this changed my view to email and I deleted the email. It unblocked it for me.


Disable chrome.exe Volume Control

Question: I recently got new update from windows.
It really annoys me the new look of the audio sound display.
Its really big and i get unnecessary information like from where audio comes and to have next and previous button.
The previous one was simple and much better.
Is there a way I can roll back to the old one, just to display the sound bar ?
the new audio look
Answer: You would have to stop updating, and Microsoft releases updates to fix bugs and to update features. Things like this happen on almost any OS. The only way you might be able to do this is if you go into the settings app, Update and Security, Recovery, then go back to the previous build, or you could go into Windows Update, view update history, uninstall updates, and uninstall the one that was installed. Be aware though that if you do this your computer will most likely not be as secure, as that is what a lot of the updates are for.
Answer: I found the solution online.
I was wrong, this new look was from google chrome update not from windows.
At the fallowing link there are 2 steps to disable and get back the old simple look.
Disable chrome.exe Volume Control

Disable chrome.exe Volume Control


Normalizing document numbers for multiclass perceptron

Question: If I have a multiclass perceptron that I'm using for document classification, and the dataset I'm using has different numbers of documents for each class, is there any normalization that has to be done to account for this? Because right now the model seems to be overfitting to the more common classes, which I suppose makes a little sense from a logical perspective because the a priori probability would be higher anyways, but it doesn't seem like an ideal outcome.
Answer: Normalization is always needed for the perceptron. In your case maybe you could try to preprocess further the data by having approximately the same number of documents per class.
Obviously if you have two classes with hundreds of docuw each and other two classes with just a couple documents your model will not even consider those classes.
Apart fron that, if you are using different sets of data for training and test, be sure that the percentage of documents of each class in each set is similar. This can be done by making a set per class and then creating the test and training set for each class, finally getting all the training sets together and all the test sets together and randomizing at least the final training set.
Comment: Did yoy get better results with any of these changes?


Configuring logging for ActiveMQ 5.5 on Tomcat 6 with web app using SLF4j and logback

Question: I would like my web app to log using SLF4j and logback. However, I am using ActiveMQ - which then requires that some if its jars go in /usr/share/tomcat6/lib (this is because the queues are defined outside of the web app so the classes to support them must be at container level).
ActiveMQ 5.5+ requires SLF4j-api so that jar has to go in to. Because SLF4j is now starting it needs to have a logging library added or it will simply nop. Thus, logback-core and logback-classic go in too.
After quite some frustration I got this working well enough that I can tidy it up shortly. I needed to configure logback to use a JNDI lookup to get the context. Then it can lookup logback-kenobi.xml in my web app and have a separate configuration there.
However, I'm wondering if this is the best way to do this. For one, the context handling appears not to support the groovy format. I did have a logback.groovy in my web app that logged to console when I was developing locally (which means that Eclipse WTP works nicely) but logs to file and to Splunk Storm when everywhere else. I'm going to want to do something similar with this setup but I'm not sure if I should do that by overwriting the logback-kenobi.xml or some other method.
Note that I don't, currently, need Tomcat itself to log with slf4j although I am planning to do that. Nor do I really need ActiveMQ to log with slf4j but I did need it to stop spewing debug messages every 30s as it was doing. I am aware of tomcat-slf4j-logbak but I don't believe it is directly useful as it is ActiveMQ requiring logging which is the issue.
Answer:
However, I'm wondering if this is the best way to do this.

Best is an opinion, working is a fact.


How to solve Hot Upstairs but cold basement

Question: I have central air in my house(20 year old house). In my basement it gets cool, and cold air is coming from a vent in the ceiling. My upstairs gets really warm and humid even though central air is on. What should I do to resolve this? I was suggested to replace windows, fill attic/crawl space. I heard there could be a tool to help even out the air but the technician wouldn't share the secret.
Comment: If the vent has a way to restrict air flow, use that.  If not think about taping a piece of cardboard or material over the vent for a temporary test.   If it helps, block some or all of the airflow with a more permanent solution, like plexiglass screwed to the ceiling over the vent or other creative and attractive measure.
Comment: Duct tape works very well also.
Comment: Unless it was built badly (too often the case) a 20 year old house should not need windows replaced, and should have been insulated when built. What is the insulation situation? Do your ducts leak, or are the upstairs ones poorly insulated in a hot attic?
Answer: George Anderson is right. Balancing air flow is the easiest and most cost effective solution. Obviously, cold air is heavier than warm air. In the summer you need to direct AC air flow to higher floors and restrict it on lower floors. In the winter you reverse this directing heat to the downstairs and letting it rise via convection to upper floors.
Ceiling fans also help if used properly. To cool use mid to high speeds blowing down in the summer. In winter use slow speeds blowing up in order to bring warm sir from the ceiling down the walls.
Comment: Dang, you turned my comment into an answer!  Stupid me!  LOL  NP!!!!  Upvote my comment to make up for it!
Comment: Well actually...making the answer "community wiki" is the traditional approach to turning someone else's comments into an answer.
Comment: Sorry. Well I did expand on it a little. Put it in as an answer and I'll give you an upvote. BTW - what is "community wiki"?
Comment: I already upvoted and would have answering with a similar answer as I have in the past, simple dampers can easily help winter summer heating / cooling. Close or restrict lower floors open upper floors in summer in winter close upper floors and open lower floors ant take advantage of heat rising and cool air dropping many don't add the trunk dampers a very small expense that can do this in 1 minute if properly set up in the trunk.+
Answer: Is there sun shining on the upstairs moreso than the basement?  It sounds like part of your problem could be solar gain.   The sun applies 1000 watts per square metre (about 100 watts per square foot, or 300 BTU/sf), almost all of it turns into heat.  A light colored wall or roof will reject some of that, the lighter the better - my preferred white paint has 91% albedo (reflection of solar energy).
So most of your A/C capacity is going to reject that "solar gain".  However, solar gain falls only on parts of the house, and this changes through the day. In the morning, your east-facing rooms take the brunt (but they're usually cool from the night before, so not much of a factor).  In the afternoon, south and west facing rooms take the brunt.  If clouds roll over, solar gain is reduced, and now the house is being heated evenly by the outside air which is warm.
Let me guess, you're trying to counter that with a "1-zone" system. That is, the system cools all rooms equally, and is not mechanically able to redirect the cooling to where it is needed most.   Further, I bet that same system is used to distribute heating. Heat turns the formula upside-down, because now, "solar gain" is your friend! The solar-gain rooms require less heating than the rest of your house, and may get too much heat.
So how do you want your system balanced?

Afternoon sun during A/C
Evenly, ignoring all solar load
Afternoon sun during heating

Whatever choice you make, you'll have to adjust registers to accommodate that choice, and then, you have to live with it.  That's what a 1-zone system means.  This is why multi-zones are becoming popular, particularly with "mini-split heat pumps" which both air condition and cool.
It's also possible you could use any adjustment features on the registers to adjust it "on the fly" hour by hour, but then you'll a) need to have a strong grasp of the problem, and b) go around and do it all the time.
Another, simpler option is to install a window A/C on the room in question.
Comment: Thank you for the explanation. I am very certain the heat is primarily caused by solar gains. Which is why I wanted to find out would more insulation be a proper solution to help reduce the amount of heat coming in. We rent out half the basement, so covering registers aren't an option.


AC behavior of a capacitor

Question: While under DC current capacitors cause open circuit as time goes to infinity but under AC current they flow through capacitor. As I know Maxwell described this behavior as "Aether current". Is this current under AC source actually caused by microwaves or how is it possible for current to pass through it and how AC current can pass while DC can't?
Comment: Do you understand the concept of impedance and how it varies with frequency? Note that DC has a frequency of zero.
Comment: As I know impedence is vectoral sum of resistance and reactance and reactance causes phase shift. But I could not fit these two in my mind to associate with current flowing through capacitor under ac circuit.
Comment: @PhilFreedenberg Can you follow up on why impedance creates different behaviors for AC and DC voltage sources for capacitors?
Comment: Go google "displacement current".
Answer: The current does not actually "pass through." Charge flowing into one terminal of a capacitor accumulates and forces charge to flow out the other terminal of a capacitor causing that side to have a deficit of charge. In effect, that is current, but the current stops when the capacitor is charged to a voltage that equals the source voltage. When the source voltage reverses, the accumulated charge reverses direction of flow. With AC current, the process in continuous.
Answer: Think about what AC is conceptually. It's a constant change in the direction of current, right? This alternating behavior constantly charges and discharges a capacitor. The current doesn't literally flow through the capacitor with an AC source but the constant charging and discharging of the capacitor makes it seem like current is passing through the capacitor. This doesn't happen with DC because... well... it has no cyclic behavior, hence why it seems like DC creates an open circuit.

AC behavior of a capacitor


Does circuit switching know any information about the networks topology?

Question: I've been stuck with this question for a while. I'm aware of the fact that in circuit switching all the packets use the same path, but does circuit switching need to know the network structure in order to function properly?
Comment: Circuit switching creates a point-to-point link between the two ends.
Comment: Circuit switching doesn't have a brain, and circuit switching doesn't even have a CPU, so circuit switching can't know things. Perhaps you meant to ask whether the hosts which are trying to communicate need to know the network structure? Or the routers in-between?
Answer: Depending on the the specific technology, circuit switching doesn't have "packets."  The circuit is a direct point to point link between the endpoints.  In the case where data is packetized, there is still a single point to point link.  In either case, there is no need for the data to "know" how to get from one end to the other.
Circuit switching requires an initial step - called signaling - which is used to set up the circuit. Signaling does need to understand the topology so the correct devices can be configured to create the point to point circuit.  Once the circuit is established, the data flows along the circuit.  Signaling is used again at the end to tear down the circuit and make the resources available for another use.
Answer: With circuit switching, all packets that belong to an established connection use the same path (if packets are used at all). Of course, there needs to be some kind of routing = finding the path from one connection partner to the other. The methods can vary significantly, depending on the protocol. Routing is often hierarchical, ie. it takes place in central nodes that control the infrastructural, subordinate nodes.
With circuit switching, a connection is only really routed while it is established. Once the connection is established, the transit nodes know which way to forward each packet. This is in stark contrast to packet-switched networks where the transit nodes (bridges and routers) are essentially stateless and forward each packet individually, without using a connection concept.


How to solve black screen issue on polychromatic

Question: Recently I ran into a black screen issue while setting up polychromatic. There was a small note on the page that said:

*Desktop environment needs to support AppIndicator. Some distributions
  (such as elementaryOS) require additional steps.

Once I installed the program by following the guide here, I was met with a black screen.
Answer: You need to install GNOME AppIndicator by following the guide here


What are admin hooks

Question: I'm trying to write a new plugin and I get so confused about wp hooks to use.
What is the difference between init hook and admin_init hook, which one is fired first?
Answer: The init hook is triggered a little earlier than the admin_init. Between them is triggered wp_loaded and few hooks related to updating the DB.
The init hook fires when WP is finished loading (viewer-facing and administration side).
The admin_init hook fires on administration side only (/wp-admin/*), therefore is triggered also by front- and back-end ajax requests (/wp-admin/admin-ajax.php) and POST handler (/wp-admin/admin-post.php).
Comment: thanks for the help @nmr, I've found a comprehensive list of action hooks available in WordPress https://codex.wordpress.org/Plugin_API/Action_Reference

What are admin hooks