NTP: How to know a complete time sync is happened in NTP

Question: Here is the scenario:
I have a two node machine. The master node synchronizes its time with some external source and then sets a reference time source for the slave node to sync its time.
I wanted to know how to check that the time is synchronized on the master node and reference time source is set and now ntpdate command can be run on slave node.
I read about NTP and found out that if ntpq -p  shows an asterisk in the output like below:
remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
10.20.94.1      10.20.78.3    6 u   13   64  327    0.407  893.508  770.685
*127.127.1.0     .LOCL.       0 l   16   16  377    0.000    0.000  0.001

which means the master node is ready.
But it is working sometimes and sometimes not.
I want to know where i am going wrong or there is some specific pattern to look for in the ntpq o/p.
Answer: Run ntpq -c rv. In the first line of the output, you should see clock_sync if the clock is synchronized. A full description of the first line of the output can be found here: http://www.eecis.udel.edu/~mills/ntp/html/decode.html#sys


Euler's equations and free rotating symmetric top

Question: For a free rotating symmetric top, where there is no torque, in the body fixed frame, am I correct in saying that the angular momentum $L$ is not constant because the angular velocity in the body fixed frame $$\omega = Acos(\Omega t+\phi )E1 +  Asin(\Omega t+\phi )E2 + \omega _{3}E3$$ (where E1,E2 and E3 are the basis vectors in the principle axis direction) changes with respect to time and the angular momentum is also not parallel to the angular velocity because $$M=I\dot{\omega }+(\omega \times I\omega )$$ and so because the torque is 0 and the rate of change of angular velocity is also not 0 then the cross product is not 0? However the component $\omega _{3}$ is parallel to $L _{3}$ because Euler's equations say that for a free symmetric top with no torque, when $I_{1}=I_{2}$, $\dot{\omega _{3}}$ equals 0 and so $\omega _{3}$ is parallel to $L _{3}$. Is this correct? Thanks
Comment: What you write is a bit unclear. Freely rotating – in which kind of frame? By "freely rotating" do  you mean that the torque is zero (which seems to contradict what you write afterwards)? Also, in the frame of the (rigid) top the angular momentum should be zero.
Comment: Thanks for you comment. Yeah I mean that the torque is 0, and I think I mean the lab frame because Euler's equations use the torque in the inertial frame.  I don't see how I have contradicted that the torque is non 0. I was just stating Euler's equation and then setting the torque to 0. I guess my question is how does the angular momentum change in the rigid body frame. I don't see how it can be 0 because it is precessing?
Answer: The angular momentum, seen from the inertial frame,  is constant.  The angular velocity is not constant.
The curve traced out by the endpoint of the angular velocity vector $\omega$ of a freely rotating rigid body is called the herpolhode The endpoint of the angular velocity moves in a plane in absolute space, called the invariable plane which  is orthogonal to the angular momentum vector ${\bf L}$. The fact that the herpolhode is a curve in the invariable plane appears as part of Poinsot's construction.
As described in Goldstein's Classical Mechanics:  "The polhode rolls without slipping on the herpolhode lying in the invariable plane."
Answer: This is only an addendum to Mike's answer, which is correct.
This may clear up some confusion:
You may be following Taylor's Classical Mechanics, which seems to be the case from your wording. If so, he writes the Euler equations in terms of the body frame. In this frame, L (angular momentum) is moving in a loop about $ \hat e_3 $ much like $ \omega $ (the vector) and $ \hat e_3 $ move around in a circle about L in the lab/inertial frame.
Consequently, you are correct that $ L_3 $ is constant when you work out the equations, but that the $ L_2 $ and $ L_1 $ components are not, so $ L $ the vector consequently rotates around $ \hat e_3 $ in the body frame. $ \omega $ does too.
(this is assuming body-fixed means "the body is fixed in this frame".)
Finally, saying $ \omega_3 \hat e_3 $ is parallel to $ L_3 \hat e_3 $ is correct, but I'm not sure why you bring it up.
Comment: I actually don't remember the M equation; I guess its the equation for torque but frankly I've forgotten. I'm unsure what you mean by $ \omega_1 \times L_1$. L is a vector, $ L = ( L_1, L_2, L_3) $ and likewise for $ \omega$. Consequently, saying $ \omega_1 \times L_1$ would be interpreted as $ \omega_1 e_1 \times L_1 e_1$, if you use $ \times $ to indicate cross product. However, I think you have the right picture in your head, because as a whole, $ L $ is not parallel to $ \omega$ since the moments of inertia differ for the $ e_3 $ versus $ e_2 $ and $ e_1 $ axes.
Comment: to be clear, $ \omega \times L \ne \omega_1 \times L_1 + \omega_2 \times L_2 ... $ etc. you may be confusing dot product with cross product?
Comment: Thankyou very much,  that makes more sense. Just one thing, by using the equation in the OP if $M=I\dot{\omega }+(\omega \times (I\omega ))$ then if torque is 0 does that mean that if we take the first and second components (as opposed to the 3rd) then because $\dot{\omega }_{1}$ and $\dot{\omega }_{2}$ don't equal 0 and $M_{1} $ and $M_{2} $ equal 0 then $\omega _{1}\times L_{1}$ and $\omega _{2}\times L_{2}$ are non 0 and therefore $\omega _{1}$ is not parallel to $L_{1}$ and likewise for the second component? Is that true-I'm not sure if that is correct mathematically.


use MBP as external screen

Question: I've done some search about it, leading me to this link which provide support for using it with another mac. What I'd like to do is use it with another device (like a ps3) via HDMI & Thunderbolt. I've got a late 2011 mbp 15"
Answer: I've researched this topic myself, and everything I've found says that the HDMI port and/or Thunderbolt port on Macs is not meant as a display input. You can't use it for that purpose.
However, something that may work, if you're willing to spend money, is a capture card. I've used them for recording video game footage before. The one I use has a noticeable lag. It's split from the TV to the capture card, and what happens on the TV takes 1 or 2 seconds to display on the input from the capture card.
If you could find one without lag, or with very minimal lag, it'd be usable for gaming purposes. Of course, if you're trying to hook up something that doesn't need to be lag free, such as a movie player, or anything else that plays non-actively controlled media (actively-controlled media would be video games, and pretty much nothing else), you could do with a capture card that has some lag.
This is a capture card that advertises OS X compatibility: http://www.blackmagicdesign.com/products/intensity/
It has probably any input you could need. I'm not sure if it lags or not, as I have not used it. Also, you have to consider the fact that they may use proprietary software for recording. If they do, and there's no way to display a video stream without recording, it's probably not a good solution for you.
Some quick searching seems to indicate there is no noticeable lag with Blackmagic's Intensity capture cards. It also seems to suggest that their software can display without recording. I don't know if you can full screen it or not. Or if you can display a video stream in a program of your choice.
Edit: I just noticed on their site, they said it supports streaming. And doing so with "all leading streaming software" too. Which would suggest that it does provide a video stream, which you could utilize in a program of your choice, and also display in full screen.
Comment: At this price, I can afford a lovely HD screen :)
`everything I've found says that the HDMI port and/or Thunderbolt port on Macs is not meant as a display input` what about the link I provided?
Comment: It's a bit different. Sorry I didn't say anything about that. I missed the link apparently.

Anyways, this works for computer-to-computer displaying. If you're going to use your MBP as a monitor for another computer, you can. This likely works because they can talk to each other using a specially designed protocol for this purpose. The Thunderbolt and/or HDMI port on Macs though, does not support standard HDMI or other video input, in regular format. From a computer, it can be done in a way that works.

Also, there probably are cheaper capture cards out there. I just clicked the first one.
Answer: as far as I know, Target Display Mode are supported only on iMacs, which means only iMacs can accept input from other Macs.
Older iMacs with Mini Display Ports are able, through third-party adapter of course, to receive input from devices like PS3 or Xbox. That feature or hack no longer work as new iMacs feature Thunderbolt which requires the other end of the device to be a Thunderbolt-equipped Mac.
That being said, I will say capture cards would be your best option, as what superriku11 suggested.

use MBP as external screen


"Two are better than one" or "Two is better than one"?

Question: I just came across the phrase "Two are better than one", but I had always heard it in my head as "Two is better than one". This is partially due to the Boys Like Girls song. Which one of these is actually correct?
Comment: They are both correct in different contexts.  "Two [heads] **are** better than one."  and [Having] two **is** better than one.  It depends on what is being elided in your sentence.   @Yaje, No. :  "How many men are coming?" "Five hundred is coming."!?!
Comment: "Two is better than one" is the correct one. Numbers are always considered singular
Comment: @Yaje- What I mean to say is numbers *are* singular when being discussed as a number: "312 is a large number." But not all occurrences of numbers in a sentence refer to the number itself.
Comment: @Jim Well said, the hidden context really does drive it. Thanks!
Answer: TL;DR: Usually choose are.

The question asks which of these two  "is actually correct":

Two is better than one.
Two are better than one.

Unfortunately, there can be no answer to that question.  It's a leading question.   The problem is that the question by its nature forces the answerer to concede that only one of them is "correct", necessarily leaving the other in some "incorrect" category.
But that isn't how English works: English isn't a multiple choice quiz with one "correct" answer. Both versions occur in print by native speakers, and so both versions (can) have their place.
The clearest case for choosing the singular is when one is talking about the numbers themselves, such as saying:

Two is greater than one.

Then you really must use the singular form, since you are really just saying that 2 > 1 — or in other words:

The number two is greater than the number one.

However, in most other circumstances, you are talking about two somethings, and two somethings are more likely to take a plural verb than a singular verb.

I just read a series of three books, and I find that the first two are better than the third.

If you look at historical usage, the singular version was virtually unknown until comparatively recently, at least in this Google N-gram:

You do still have to dive into the actual citations for the two is case and the two are case separately.
The singular choice is nearly unknown in the 1800s, although there is this example dating from the Annual Register of 1800:

I have seen that two is better than one, and that a threefold cord is not easily  broken, and have therefore cultivated friendship with much zeal and disinterested  tenderness: but I have found this also vanity and vexation of spirit, though it be of the best and noble sort.

That is example of nominal agreement, where the collection of two together is the thing being considered.
In contrast, the far more numerous plural examples are thinking of two items separately.  Certainly when the number is just a cardinal number used in a noun phase, like saying two people are at the door, then there is never any question of the plural being the only grammatical choice.
However, it is really only in the last 50 years that the singular version has caught on much.  Also, if you change the search to look only in (allegedly) British sources versus (allegedly) American sources, you will find that the British sources have a higher ratio of plural to singular than the American ones have.  Note however that in both cases, the plural is still more common.
If you look at the Corpus of Contemporary American English 1990–2012, it has 3 citations of the singular two is better than one (2 spoken and 1 fiction) compared with 2 citations of the plural two are better than one (1 spoken and 1 fiction).  That isn't really much to go on.  If you relax the constraint by dropping the than one part, then there are 7 citations for the singular and 4 for the plural.
If it were me, I would in most cases go along with most writers not just of yesteryear but also of today and choose the plural version just like they did.
That is the best I can do for answering the leading question of which one is "actually correct": a long exposition demonstrating that the question is itself flawed, and that while both can have their place, usually the plural version works better.
Comment: The problem is that the question by its nature forces the answerer to concede that only one of them is "correct", necessarily leaving the other in some "incorrect" category.

But that isn't how English works: English isn't a multiple choice quiz with one "correct" answer.
This is what's wrong with the test questions that pop up on this site. Assuming you don't cheat and try to figure out what answer is wanted rather than what answer is "correct," you too would have trouble with the questions, and the experts would have more trouble than the rest of us.


How can we trace problems of crashing programs in Linux?

Question: If an application crashes in Windows we can check the Event Viewer in the Administration tools to see what has crashed. Sometimes it has useful information others not, but it is a start.
In linux if an application (any) crashes how one starts to trace what happened?
Is there e.g. some central log or something similar?
Comment: The standard way of debugging this kind of thing is to launch the problematic application from a terminal manually. That way you can see any error messages printed.
Comment: 64-bit versions of Linux will log a short description of a crashed process (one that died due to a signal) in `/var/log/syslog`.  Linux provides a way for a daemon to be notified of process crashes. Ubuntu's [apport](https://wiki.ubuntu.com/Apport) and Red Hat's [abrt](https://github.com/abrt/abrt/wiki/overview) use this to provide centralized logging and report-generation facilities. Generally a core dump is saved so that you can invoke a debugger on the crashed program.
Comment: I would have upvoted this question, but the OP does not seem to want to help the community by accepting, or posting, an answer, so I will find a similar question which does accept an answer and upvote  that, in the hope that it will rise to the top of search results and help future searchers
Answer:
Is there e.g. some central log or something similar?

The normal place for system logs is /var/log/.  What gets put in each log depends on the syslog configuration, but commonly everything except logins goes to /var/log/syslog.
This is no guarantee that individual applications will have left any clue there in the event of a problem.  But they, or the shell, will likely spit something to the standard out/standard error streams, and if you run a troublesome application in the foreground from a terminal you'll be able to see that stuff.
Comment: If you can make the crash happen, do so, then see which file under /var/log was most recently changed. With `ls -lart`, the last file in the listing was the most recently changed.
Comment: What should one look for in `/var/log`?Which log file?Is there some convention?
Comment: There are convention*s* -- linux is much more heterogeneous than windows.  [Syslog](http://en.wikipedia.org/wiki/Syslog) refers to the system logger, but there is not a universal implementation, and the variations can then be configured in different ways.  The general logic is that messages are sent to syslog by the application, and these messages are then sorted into different files.  As mentioned, commonly everything ends up in `/var/log/syslog`, but different distros do things differently.  If you know what which syslog you are using, you can examine its configuration to determine this.
Answer: On Ubuntu segfaults get written at /var/log/kern.log. I tested it by creating a program that segfaults:
void main() {
    int *a=0;
    *a=0;
}

After it segfaulted there was this line in /var/log/kern.log:
a.out[534]: segfault at 0 ip 08048432 sp bfaec8c0 error 6 in a.out[8048000+1000]

Answer: In Ubuntu if you are launching your application from a .desktop launcher file, add the option Terminal=true to your .desktop file.
Answer: Run the daemon exec barely in the command line, instead of being taken over by systemd, then you will get the full crashing stack info from the stdout when the crash is reproduced. It will save lots of time to blindly adding trace log everywhere.


what is a thyristor

Question: As part of my 2330 lv3 am required to know about thyristors.
I just want to confirm my understanding is correct. A thyristor is basically similar to a transistor, only it stays switched on when it's trigged for as long as there isn't a break in the circuit it's switching. Am I correct?
Answer: You are basically right, but as Majenko said, it's not about there being a break in the circuit but rather whether current keeps flowing.
Here is a simple way to think of how a SCR works:

A SCR isn't just two transistors hooked up like this, but this isn't bad as a mental picture of how one operates.  You can even build this and have it work like a SCR as long as you keep the currents low.  Note that all current in this circuit ultimately flows thru one of the bases.  These don't have much current capability in normal transistors.  A SCR is a sandwich of P and N regions such that the "bases" are intended to handle the current.
Anyway, think about this circuit or even build it.  Once current starts flowing in one transistor somehow, it turns on the other transistor, which keeps the first transistor on.  Once on, this thing will stay on until there is too little current to keep it on.
Answer: Pretty much correct.
It's not while there is no break in the circuit, but while the thyristor is forward biased.
So, while there is a positive voltage potential across the Anode/Cathode terminals.
That means that if an AC signal is fed through it the thyristor will switch on when the gate is driven high (as long as the AC signal is currently in the positive phase), and stay on until the end of the current positive phase of the signal - when the potential drops to zero or below - thus creating a zero-crossing switch-off.
Answer: Wikipedia has a detailed yet simple explanation of what a thyristor is.
Comment: Just a link is not a good answer.

what is a thyristor


HP server delayed boot

Question: I'm currently using HP Proliant DL120 G5 servers running VMWare ESXi 4 to run server VM's.  They are connecting to an iSCSI SAN for the shared storage.  I'd like to implement a delayed boot of these hosts servers so that they don't boot up and try to connect to the SAN before the SAN is ready for connections after a power failure. Does anyone know of a good way to do this?
Answer: HP Blades let you do this but the DL100 series don't - what I'd do is delay the startup of Guests, this will allow time for your ESXi host to connect to your storage.
If you really want to delay the OS booting then HERE is a guide of how to do this with ESXi 3-3.5 - not tried it with 4 yet however.
Comment: SYSLINUX. Good to know.
Answer: Many bootloaders have some sort of configuration option that gives a timeout before running the default selection. For lilo this is the delay= setting, and for grub this is the timeout setting. All you need to do is add it if not present, and give it an appropriately high value. ESXi's bootloader should have a similar option, if it's not one of those two.
Answer: This should help: http://www.vm-help.com/esx/esx3i/boot_delay.php

HP server delayed boot


Can cat urine corrode stainless steel?

Question: My cat has a habit of urinating in the bathroom sink. It is unsanitary, but can it corrode the stainless steel plumbing hardware? My friend believes it will, but I disagree. I could believe that if the urine were left to sit over time it could possibly affect the electropolished layer, but it is generally cleaned up within 24 hours.
Comment: You do not have a stainless steel sink drain. It is 70:30 cartridge brass with nickle/chrome plating ( or equal; admiralty metal , muntz metal, etc) .
Answer: Well, infact yes, cat urine can corrode stainless steel plumbing.
Urine of any mammals contains quite a lot of ions, and the chloride ion concentration is quite high. Chlorides attack the passive layer of steel, exposing the reactive iron underneath.

Pitting corrosion - The passive layer on stainless steel can be attacked by certain chemical species. The chloride ion Cl- is the most common of these and is found in everyday materials such as salt and bleach. Pitting corrosion is avoided by making sure that stainless steel does not come into prolonged contact with harmful chemicals or by choosing a grade of steel which is more resistant to attack. The pitting corrosion resistance can be assessed using the Pitting Resistance Equivalent Number calculated from the alloy content.[1]

While you may clean up the urine quickly, if your cat does this frequently, it can add up to corrosion very quickly. I'd suggest doing whatever you can to make your cat from urinating in the sink.

"BRITISH STAINLESS STEEL ASSOCIATION Making the Most of Stainless Steel." What Forms of Corrosion Can Occur in Stainless Steels?, www.bssa.org.uk/faq.php?id=9.
Answer: I would be surprised if you have stainless plumbing  ( cost >>> brass ). Any urine produces ammonia. Ammonia causes stress corrosion cracking in any brass and some other copper alloys. In the UK it may be called "season cracking" ( for the rain season in India ). So, if you have brass , I would keep it rinsed. Urine would most likely cause only cosmetic damage to stainless. These factors ( cracking of brass - no problem for stainless) have resulted in the flex tubing for connecting gas home appliances being made of stainless today when 30 + years ago they were brass. Footnote : Years ago, I had a gas space heater in a garage , a dog urinated on the brass flex tube and it cracked and leaked .

Can cat urine corrode stainless steel?


How can I access to "shared with me" folders?

Question: Obviously, shared with me folders are visible on the Google Drive web, but I cannot find them on my local Google Drive for Desktop. One suggestion online was to create a shortcut on my own Google Drive, but it didn't work. Any idea?
Comment: I'm voting to close this question because questions about installable clients of Google Drive belongs to [su] or [apple.se], [android.se].
Answer: This is a recent change (from around April 2020). Previously, one was able to add files and folders from "Shared with me" to one's Drive. This made syncing other people's files with one's computer's hard drive easy. However, items can no longer be placed in more than one folder. This does simplify syncing, as far less data is used to sync a shortcut, compared to large items.
In addition, it prevents people from believing that other people's files are permanent. It is always possible for the other person to permanently delete their files (often this would simply arise from technical reasons, such as deleting their account, reducing storage, or accidents, rather than an unkind decision). To ensure that you keep someone else's files permanently, make a copy. If its parent is "Shared with me", right-click on the file and select "Make a copy". If its parent is a shared folder, select the files you want to copy, right click on the selected files and select "Make a copy". In both cases, the copies will be placed in "My Drive", which you should move to a sub-folder. Unfortunately, entire folders can't be copied at once using the features in the Web app, although you could download the folder, then upload it to your Drive, instead.
For files that are not Google Docs editors, when edit access is granted to other people's files, it appears that Google Drive now expects users to manually upload edits, through the Web app. (This is done by right-clicking on the file > Manage versions > Upload new version.) In my opinion, this makes collaboration more difficult compared to before, when items could be added to My Drive. An alternative is to use Github, or to use G Suite's shared drives.
Comment: yes, thanks! That would make a copy of files and moving things much easier, but make a copy option does not work on folders.
Comment: Thanks @ahorn! Your answer and comment were both helpful, unfortunately my points are not enough to upvote your answer.  I will mark it as accepting answer.
Comment: @Rubén, yes I have just tested that by creating a shortcut to a .txt file, and when I open it on my hard drive, the file opens locally. This might be an improvement from before.
Comment: Yes, not having access to shared folders only on web app is a pain. So, I am concluded that it is not possible, and I ended up uploading files to my own drive.
Comment: @Mahdiar do you know about the "Make a copy" option for files, in the right-click menu?
Comment: Please consider upvoting and/or accepting my answer if I have given you useful information. :)
Comment: I can't downvote because just joined, but this requires downvoting: The other answers are correct! No need to copy, or do weird version uploading: You can just add a shortcut.
Comment: @Georg, the question is asking about syncing offline files locally, not online Google Docs. Think about where the data is stored. :)
Comment: Updates to files using non-google formats could be handled with the help of Google Drive installable clients (Google Drive for Desktop for macOS and Windows, and the Android and iPhone and iPad apps for mobile devices).
Answer: Hallelujah.  The article about the changes that Google made was my answer!
In the online UI in Google Drive, I navigated to the folder (not created by me) with the shared data.  I right clicked the folder and selected "Add Shortcut to Drive."  From there I navigated into My Drive, and then clicked "Add Shortcut."  Voila, now I can use my windows folders to see all the shared data!
Comment: What type of account do you have: G-Suite or a regular free account? And what sync client are you using: Backup & Sync or Drive File Stream?
Answer: Drive File Stream does not show the shared shortcut if it is placed in the My Drive root folder, but it will show and sync if it is placed in a My Drive subfolder.
Create a folder in My Drive, for example 'SharedShortcuts'.
From 'Shared with Me', right click on a shared folder and choose 'Add shortcut' and place it into My Drive/SharedShortcuts.
Now you can see the shared folder link in the SharedShortcuts folder from your PC. When you click on the shared folder link it will create a temporary folder in .shortcut-targets-by-id hidden folder and you'll be able to see and open the shared files.
Comment: Interesting! Are you using mac or windows?
Comment: Drive File Stream is now **Google Drive for Desktop**. I'm not sure that this problem is still happening. Anyway, issues with the installable clients are better suited on [su], [apple.se] and [android.se] sites, depending on the platform used.


How to effectively use CloudKit daily transfer limit of of 25mb

Question: I'm creating a highly picture oriented app that might end up using a lot of ckassets. But I read that there is a 25mb limit on daily data transfer per user. My question is is this data transferrable? If one user uses 0 then some other person can use 50?
I feel like 25mb limit on data transfer seems so small since one pic is 100k so one can only play w 250 pics max per day. It just seems like such a drastic limitation.  Thank you.
Answer: The data transfer limits for CloudKit are monthly and are based on the number of active users.  You get 50MB/month per user with a minimum of 2GB.
The 50MB/month/user is only used to calculate the free quota; it is not an actual per-user limit, so if some users transfer 150MB and some transfer 0 that is fine.  You only pay if your total transfer for all users exceeds 50MB*number of users (or 2GB if you have less than 40 users)
In your question you quote 25MB/day but the limit is actually monthly, so if every user used 50MB a month that would mean they could transfer about 16 images per day.
Extra data is fairly inexpensive though.  Say you had 40 users and they transferred 50 images each per day, that would be 6GB per month, which would cost you $0.40
Note that the maximum free transfer is 200TB/month so above 4,000,000 active users the 50MB/user no longer applies, the available transfer is less on a per-user basis but the 200TB is still applied as an aggregate across all users.
Comment: The calculator is difficult to use for low numbers, but you can see that you get 50 MB per use per month and below the calculator you can see that amounts over your quota are 0.10 per GB so if you transfer 6GB in a month with a free quota of 2GB it will cost you 0.40
Comment: where did you find the online pricing info that yielded you $0.40? I can find the scope of the "free" services here: https://developer.apple.com/icloud/ but couldn't find the calcutor to simulate what it would cost me if my traffic grew out of the free tier service. Thank you.


Asphalt career performance isn't synced between my PC and Android phone

Question: I am playing asphalt 8 airbone on my pc which runs on windows 8.1 pro and on my android smartphone. I connected Asphalt 8 with my same facebook account but it doesn't show same career performance, my car pack, etc. Help me out with this.
Comment: Does the game offer cross platform saves? It might be worth asking the developer. Is there cloud saving, any option in game to import a save from the cloud? I doubt it does to be honest, but worth a look.
Answer: According to Ryan from Gameloft, writing on the Touch Arcade iOS forum, Asphalt 8: Airborne doesn't sync save games between different platforms:-

no, Asphalt 8 doesn't have cross-platform save functions. You won't be able to play on an iOS device and then load that progress on an Android device.

He's writing about iOS and Android, but it's easy to see why the same would apply to Android and Windows too.
Answer: Both are being played on different platforms and machines. Whenever you are playing the game from your PC, the player-specific data would probably come somewhere from Users directory in your C drive, however, for your mobile, it will be stored on your mobile storage in a specific folder. You won't be able to see the same progress since those details are stored locally on the respective storage drives and doesn't get fetched online.


Visual studio 2008 crazy debugger skipping

Question: I'm developing my C# 3.5 ASP.NET MVC web app, same as I do all day every day. Not doing anything clever, just standard methods on classes calling other methods.
I build my project, fire up a URL in Chrome, and get the response I expect. I attach the debugger to w3wp.exe, set a breakpoint and f5 in Chrome. The debugger stops at the breakpoint as I'd expect.
I hit f11 to step through the code, and it will move to the next line/part line, do it a few times and it will randomly skip to an arbitrary line in the execution path!
The line it skips to is a line that would have been executed, it doesn't skip to any old line, it just decides to miss out a whole bunch of lines in between.
I've never seen this before, how do I debug what's going on?
For a while I thought perhaps Chrome is making two requests, and the debugger isn't really skipping, its just swapping between request threads making it look like it's jumping about, but that's not it! If i set a breakpoint on every single line I can partially prevent it, but take the following:
1. public string Method()
2. {
3.     string s;
4.     s = OtherMethod();
5.     return s;
6.
7. }

The type of behaviour I'm seeing (with a breakpoint on every line above) is 1,2,3,4,5,6,7 (i.e. it won't step into OtherMethod()).
Other behaviour I'm seeing is 1,2,3 and then that's it, off back to wherever called Method() or even further away.
Answer: Have you tried cleaning your solution?
 - (the bin and obj folders in your project folder)
Delete files from the temporary asp.net files folder?

(usually C:\windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files)
You probably will need to run "iisreset /stop" at the command prompt first, then re-enable with iisreset /start
Comment: doing all this and Atom's suggestions seems to have fixed it, thanks
Answer: Hey, you probably found a workaround on this by now but many people (I was one) still struggle with it. It's a VS 2008 problem and this fix should be applied:
http://support.microsoft.com/?scid=kb%3Ben-us%3B957912&x=9&y=14
Answer: Not sure if this will help. I have run into issues before where the compiled code in a related assembly doesn't match up with what the debugger thinks I have. The way I always solved it was to frist shutdown VS, then restart and reload the project, then do a full rebuild of the solution. Then change build mode from debug->release or release->debug, and do one last rebuild. I've honestly never figured out what causes it. Only happens on occasion.
Comment: doing all this and Jeff's suggestions seems to have fixed it, thanks
Answer: Sounds like you are trying to step through a binary that's been optimized.  The optimizer can do lots of things that make it hard to debug including but not limited to:

Reordering statements
Inlining functions
Answer: I've seen something similar in 2.0 when I don't ensure that my browser cache is clear.
Answer: Turn on disassembly and see if your stepping makes more sense. If you're certain that you aren't jumping between threads, then the compiler has probably decided that some of your code isn't important enough to step to (i.e., does nothing).


How would I best express this time-dependent scenario in Cucumber?

Question: I've been trying to learn about Cucumber in Ruby and I thought that the best way to do that would be to make my own project. However, I'm wondering what constitutes a good "Given" clause.
As far as I understand, "Given" is basically a set up, "When" is the function under test, and "Then" is the expected result.
For example, let's assume I am making a Minecraft scenario based on an entity stepping in lava. My current G-W-T looks like this:
Scenario: Take damage when I stand in lava.
  Given an entity is standing next to a block of lava with 10 health
  When the entity steps in the block of lava
  Then the entity should take 2 damage

However, this "Given" step seems fairly 'off'. It doesn't make sense that I should have to be standing next to a block of lava for this scenario to work. Similarly - how would I write (and test) a GWT for a scenario that should always happen - for example, how could I ensure that as long as my entity remains in lava, that it will keep taking damage? I find it hard to write code that will test how long an entity has been standing in lava. How is the system to know how long the entity has been sat in lava? it seems to me that testing that sort of thing would require me almost writing the rest of the world in order to be able to say "this entity has been in the lava for x seconds, advance the simulation, how much hp have I lost"
Thoughts?
Answer: You don't have to rewrite the world. You just have to be able to fool your tests about the state of the world (in this case, time). The usual way to control time in tests is to stub.
I would write that scenario like this
Scenario: Take damage when I stand in lava.
  Given I have 10 health
  And there is a block of lava next to me
  When I note the time
  And I step in to the block of lava
  And I wait 5 seconds
  Then I should have 8 health

and implement the time steps like this:
When /^I note the time$/ do
  @start = Time.now
end

When /^I wait (\d+) seconds$/ do
  Time.stub(:now) { @start + 5.seconds }
end

When I note the time is kind of artificial, so you might fold that in to another step if it made sense. (I don't see an appropriate step in this case, but you might in a longer scenario.) When I wait 5 seconds is perfectly appropriate to the domain, though.
Other niceties:

It's concise and appropriate to the domain to use first person.
Given is for conditions that are true before the scenario starts. One way to think about it is that time might have elapsed between when the Given becomes true and when the actual scenario starts, during which other things might have happened that aren't relevant to the scenario.
Health doesn't have much to do with standing next to lava, so those are better set up in separate steps.
Testing that you've taken two damage (as opposed to that your health is 8) would require a dependency between the assertion step and the Given that initializes your health. Minimizing such dependencies makes Cucumber steps more reusable. So as long as it doesn't hurt understandability (which I don't think it does in this case) just assert the final state at the end.
Comment: As the system under test (i.e. Minecraft) is a sealed entity, then you will note be able to "stub" (or mock) it's time component.
Comment: OP says he's writing the server. Regardless, you don't need to own code to stub it.
Comment: Hey, I forgot I didn't accept an answer and I'm not sure why this got so much attention as it's old! Either way, I actually used TimeCop and used something similar to this.
Answer: Interesting question!

"It doesn't make sense that I should have to be standing next to a
  block of lava for this scenario to work."

If an entity is NOT standing next to lava, then it won't be able to step into lava. What exactly don't you like about your scenario?
Now regarding testing how much damage gets inflicted on an entity, if you were writing this scenario to test the actual Minecraft game, then you'd have to enable some kind of browser based timer to count the monitor the amount of time that passes (if it were being played in a browser). This would indeed be awkward.
However if you were writing your own version of Minecraft, then you could write you scenario so that it would test the code itself (i.e. not test the code running in a browser). For instance:
Scenario: Take damage when I stand in lava.
  Given an entity is standing next to a block of lava with 10 health
  When the entity steps in the block of lava
  And remains there for a unit of time
  Then the entity should take 2 damage

If this test was exercising the code you'd written, you would be able to accurately control the amount of time that the entity would be spending in the lava region (hence the use of "unit of time")
Similarly:
Scenario: Take fatal damage when I remain standing in lava.
  Given an entity is standing next to a block of lava with 10 health
  When the entity steps in the block of lava
  And remains there for 5 units of time
  Then the entity should lose all health

You are right when you say:

"it seems to me that testing that sort of thing would require me almost writing the rest
  of the world"

You hit the nail on the head when you say "almost". The key to this BDD approach is to take an evolutionary approach and mock as much as possible initially to satisfy the test. Once the test goes green, then implement the mocked areas using TDD.
Comment: I would be writing the server, rather than the actual game. Writing the game? PFT. too much work for me ;) interesting answer, food for thought.

Also, a entity does not have to stand next to lava to end up falling into it. They could be, for example, teleported into it, or they could fall into it. :b
Comment: I just mentioned the difference in approach to testing a pre-written game (e.g. Minecraft) compared to testing a game you would write (yeah, writing your own version would take some time! :) ). As for an entity not having to be next to lava to be placed in it, I forgot that in a game world you can be more creative. However, I still think it would be valid to write scenarios for some of the ways you can be plonked into the hot red stuff e.g. teleported, dropped.
Comment: Actually, using tables (examples) can make the scenario's more compact and readable. I prefer an absolute outcome rather than relative (i.e. Then Health should be 8 (instead of 2 damage). Also, I'd split the Given and use I instead. (as minecraft world is observed from the avatar=I)
Answer: Like said above, a Give clause indicates some sort of setup.  Most of my Given clauses can be found in my Background.  For example:
  Feature: A New User
  Background:
    Given I am a new user

  Scenario: Writing a new Feature
    And I add "text" to my new feature
    Then I should have a new feature named "feature.feature"

In this case, the background validates that "I am a new user".  In feature files, the background step(s) get ran before each subsequent Scenario.
Answer: I've tried to improve readability of Fresh' answer. I'm currently learning Gherkin (using the excellent The Cucumber book). Code can be downloaded from minecraft_gherkin_example
Feature: Take damage when I stand in lava.

In minecraft, lava is bad for your health.
    Every unit of time, damage reduces your health.

Scenario Outline: Step into lava
    Given my health level is <Health>
    When I step into the lava
        And I wait <LavaTime> unit of time
    Then my new health level is <NewHealth>
        And the outcome is <Outcome>

Examples:
  | Health | LavaTime |  NewHealth | Outcome   |
  |  10    |    1     |     8      | Alive     |
  |  10    |    4     |     2      | Alive     |
  |  4     |    1     |     2      | Alive     |
  |  2     |    1     |     0      | Game over |

Comment: If you were writing many tests then I agree that using "Examples" is the way forward. However, I would not use "-" as an outcome as it is not obvious what "-" means. I'd possibly use "Still alive" (or something similar) instead.
Comment: In the step files you could replace 'step into' by (?:step into|teleported into) to allow stories with different ways into the lava. The stepping out of lava is missing; assumed to be part of the wait step.


Embedding Python in LaTeX

Question: As of today, what is the best package for embedding functional Python code in LaTeX? I've searched this site and others, which recommend the python, pythontex, and sympy packages, amongst others, but the information is somewhat dated. I want to know what users suggest as the best alternative now.
Comment: The abstract and the introductory section of the user guide of the `pythontex` package pretty much address the questions and concerns you're expressing. Type "texdoc pythontex" at a command prompt to bring up the user guide document.
Comment: Don't forget `sagetex` if you happen to want a fully equipped mathematical engine. That said, I swear by `pythontex`. Incidentally, its author @GPoore is a member of  tex.sx and gives quick and sound support.
Answer: You might want to try out Pylatex (https://github.com/JelteF/PyLaTeX), the documentation is not the best you can find out there, but once you get a hang of it, it is pretty neat. Personally, I love the fact that you can do your analysis(using Python) and the the documentation of the analysis together. And as it always goes, do split your programs into lots of small functions to make your work easier!
Comment: Isn't PyLaTeX the opposite of what NVaughan is asking about? This is a python package to create a LaTeX document not a way to embed python code into LaTeX.
Comment: Well, something like pythontex, lets you call python from within the latex, which then runs your python script and you can display whatever output it generates in the latex document. Whereas using PyLatex, you write a python script which generates the latex document using the Pylatex. the script you write,  can have your own code and you can send the output of that code into the latex document. So yeah it is different, but if what you aim is to eventually fasten your workflow by combine the coding and the documenting part together, either of these work fine.
Comment: Let me introduce you to my good friend...sorry our good friend 'Google'!
Answer: Disclaimer: This answer is referring to a github repository that I wrote.

I have recently been working on a github repository that does what you are asking. It can be found here: https://github.com/QuantumSpaghettification/QS-TEX and works as follows (you need to be able to run python2.7):

Download the FUNC and LANG directories along with editor.py and place them into a directory e.g. QS.
Download  QS.config and place into the directory of you .tex script.
Edit the QS.config file to include the path to the directory QS and if you want to use the Listings package define a style else empty all other variables.
In your tex document use the following notation:
< script=python2.7:action={}\>
Your script here.
output(string you want to output in place of script)
< /script>

(there should be no space after the open angle bracket)

Using python2.7 run the script editor.py on your tex file and then your standard LaTeX program on your standard compiling program.

Embedding Python in LaTeX


Is there any way to get around the rule that drag $ \propto v^2$?

Question: I was looking at a question on aviation.stackexchange and an interesting answer I found included that even today, we have no physical way to get around the fact that drag of a body is roughly the square of velocity. Theoretically is there any way to get around this?
Comment: What does it mean to "get around" it?
Comment: If you can make the surface porous and blow air out of the pores, you can lower the drag.
Comment: To echo Steeven's comment I don't know what you mean by getting around the $v^2$ law. Are you asking for drag reduction as Chester points out? A simplistic picture would be to represent drag $D$ as Taylor series in $v$: $D=a_1v+a_2v^2+a_3v^3+\ldots$ so the question really becomes "which term is dominant at what speed $v$?"
Comment: Yes that was what my question was aimed at sorry about the confusion.
Answer: It comes from the Navier-Stokes equation.
More specifically, it's the ram pressure term which goes as $ -\nabla (\frac{1}{2}\rho u^2)$. This gives a force per unit mass, since the LHS o the N-S equation is usually $\rho \frac{\partial \mathbf{u}}{\partial t}$.  The ram pressure is also referred to inertial terms.
Physically, in order to move at speed $u$, you need to "move away" the air in front of you, i.e. you need to provide it with kinetic energy $\frac{1}{2}m u^2$.
--
Maths
Let's consider the total derivative of the fluid velocity $\mathbf{v}$ in the presence of a pressure gradient $\nabla P$ and an external field $\phi$, which could be gravity:
Let's use tensor notation:
$$ \frac{\mathrm{d} (\rho v_i)}{\mathrm{d} t} = \rho \frac{\mathrm{d} v_i}{\mathrm{d} t}  + v_i \frac{\mathrm{d}\rho}{\mathrm{d} t}. $$ The equation of motion is $$ \frac{\mathrm{d}(\rho\mathbf{v})}{\mathrm{d} t} = -\nabla P - \rho \nabla \phi,$$ and the total derivative $\mathrm{d}_t = \partial_t + v_i \partial_i$.
Hence we get:
$$ \frac{\partial \rho v_i}{\partial t} =  -\rho v_j \partial_j v_i - \partial_i P -\rho \partial_i \phi - v_i \partial(\rho v_j) \\ = -\partial_j(\rho v_j v_i + P\delta_{ij}) -\rho \delta_i \phi$$ so that $$   \frac{\partial \rho v_i}{\partial t} = -\partial_j T_{ij} - \rho \partial_i \phi.$$
$T_{ij}$ is the stress energy tensor, the first term of which is the ram pressure due to the bulk motion of a fluid, and the second term is the pressure introduced by thermal effect (e.g. denser regions).
Answer: Inviscid drag due to lift (induced drag) of a wing or similar lifting body follows a different trend. It is roughly proportional to the inverse of the velocity squared, so it actually decreases with speed.
The total drag of the wing includes both viscous and inviscid components. The inviscid component dominates at very low speeds, while the viscous component dominates at high speeds. As a result, the drag-versus-speed curve is roughly parabolic, with a minimum at some value of speed greater than zero.


Setting best SVM hyper parameters

Question: I have a non linear data set, and I am using SVM (RBF kernel) to build a classification model, but not sure how to set the best hyperparameters of the SVM, C and gamma in Matlab fitcsvm.  And is it acceptable if it is trial and error approach setting arbitrary values, until finding the best performance?
Answer: Well, there is a bunch of articles that tries to tackle this problem but basically, to guarantee a good solution you will need to do Grid Search (sklearn tutorial on it)
You can use various techniques for that, for example:

Binary Gridsearch: Try the maximum and the minimum value in the interval you want, and the middle point, check which side is best and set the minimum or the maximum as your previous middle point according.

That can help you find an average solution fast, but remember that this comes without warranty.

Exhaustive Grid Search
Randomized Parameter Optimization
Genetic Algorithms

Check the link for sklearn for more information. I research on kernel methods and this is aways a bit annoying thing to tackle.
Note: If you're only going to try RBF I would advise to use $\sigma$ as a value betwen the norm of your training samples $\pm 80\%$. You could also normalize you vectors to norm 1 and limit the search to $0.2$ to $1.8$. Usually too small $\sigma$ gives high sensibility to noise while too big aproximates a straight line (loses non-linear power)
Comment: what do you think of using  'OptimizeHyperparameters' function to get best parameters https://www.mathworks.com/help/stats/bayesian-optimization-case-study.html
Comment: Never used it before, but you should try
Comment: tried it and it works fine. I would like to ask about soft mragin SVM, i believe it needs tunning the C value as well, correct?
Comment: You should post it as a separated question as this may help others. But remember to search for an previously answered question on soft margin parameter tuning
Answer: Sadly, there is no easy solution for hyperparameter tuning. Basically, you have two options:

Manual Adjustment: Read the documentation of the SVM and dive into the corresponding literature. Try to understand how the different kernel functions work and which functions are appropriate for your classification problem. Set the hyperparameters to the best of your knowledge and then observe what difference slight deviations make. Of course, there will still be some degree of trial and error in this approach.
Grid Search: For all categoric parameters (e.g. kernel function), set up a list of all possible categories and for all metric parameters (e.g. epsilon), define a range of reasonable values. This is your hyperparameter space. Subsequently, run a multitude of SVMs with randomly selected parameters from the hyperparameter space. In the end, you choose the hyperparameter combination with the highest accuracy. (Note: there are also other approaches with more sophisticated methods than random selection)

Both methods are widely used, however, if you are not very familiar with SVM's, I highly recommend the manual adjustment. Of course, it is very tempting to simply set up a grid search, grab something to eat and later pick the best performing hyperparameter combination. But in the end, you will not learn anything and you will not know if these hyperparameters are a reasonable choice for your problem. Broadening your knowledge will be beneficial in the future, both because it reduces the effort for future manual adjustments and because in the future you will be able to narrow down the hyperparameter space for the grid search, which will significantly reduce computing time.

Setting best SVM hyper parameters


How to upload URL to IPFS API

Question: I'm working on a project where I wish to upload some images to IPFS, but the issue is I have the URL for the images, is there any way to upload the image using the URL? Like I was searching for ways to do this but all I could find is I can use images in jpeg, png etc formats for the IPFS API. Please help me out with this query
Answer: if you want to stay purely decentralized, do not do this under any circumstances UNLESS your url is another IPFS reference:
{
"image":url
}

I've seen some NFTs rugpulling due to the centralized factor. If your IPFS is going to point to an image on the standard web, why even bother to use IPFS?
You haven't explained which technology stack you are using so can't give you an exact answer, however your solution will look like this:

Make a GET request to the URL you wish to get the image from (if you're using nodejs, you can easily do this via axios)
Store it as base64 format in your state
Upload it on IPFS

Again, assuming you're using Nodejs, it's pretty easy to upload over IPFS a base64 string image
import { fromString } from 'uint8arrays/from-string'

const data = fromString(base64_string, 'base64')
const { cid } = await ipfs.add(data)

console.info(cid)

Reference for code above here.
Comment: hey, thanks a lot, i will try this
Answer: Why not simply download the image from the link and upload it to IPFS?
Otherwise, you could do similar to what people do with NFTs, which is to create a JSON with an image tag in which you insert the link and store that on IPFS. You can store any type of file on IPFS.
Comment: So instead of using the IPFS url of the image you're suggesting me to just add the normal url to the object and upload that object to IPFS? will that be okay?
Comment: It will work, but it depends on what you want to achieve. It will store the file with the URL to your image on IPFS.For example, if you want Opensea to be able to see your image it will work. You can read more about Opensea metadata here: https://docs.opensea.io/docs/metadata-standards
Answer: In case of NFT, if you already have images uploaded somewhere then this is a good news because the NFT contract looks up at metadata. Just prepare metadata json files and upload those files to the ipfs. You can just use image url in metadata image field.
Eg. in metadata:
{
  .....
  image:"image url"
  .....
}

Answer: You dont have to reupload your images, you can upload the metadata and use the image URL inside the image: field.
Here is an example on how to upload metadata to IPFS using Moralis IPFS API.
https://docs.moralis.io/web3-data-api/evm/how-to-upload-nft-metadata-to-ipfs
Let me know if you need any help!
Disclosure: I work at Moralis

How to upload URL to IPFS API


Cohen-Macaulay monomial ideal

Question: Let $R=K[x_1,...,x_n]$ be the polynomial ring over a field $K$ and $I[x_1,...,x_n]=(u_1,...,u_t)$ be a Cohen-Macaulay monomial ideal of $R$.  If $m<n$, could we say that $I[x_1,...,x_m,0,0,...,0]$ is Cohen-Macaulay in $K[x_1,...,x_m]$?
Comment: @WlodAA An ideal $I$ of $R$ is Cohen-Macaulay if $R/I$ is a Cohen-Macaulay ring.
Comment: Not all of us are ring-theory specialists. Would you provide the C-M ideal definition?
Comment: Oh, well, a reader here has to be either young or a specialist,
Answer: No, we can't say that. For a counterexample, take $n = 3$, $m = 2$, and let $I = (x_2^2, x_1x_2, x_1x_3)$.
To see that $I$ is Cohen-Macaulay, note that the Krull dimension of $R/I$ is 1. Cohen-Macaulayness is then equivalent to $I$ having no associated prime $P$ with dimension $R/P$ equal to 0. Since $I$ is homogeneous, its associated primes are homogeneous, and so the only possible example of such an associated prime is $P = (x_1,x_2,x_3)$, which is easily seen not to annihilate any element of $R/I$, hence is not associated with $I$.
On the other hand the restricted ideal $I' = (x_2^2, x_1x_2) \subset K[x_1,x_2]$ is not Cohen-Macaulay, since $x_2$ is annihilated by $(x_1,x_2)$ in $K[x_1,x_2]/I'$, and so $(x_1,x_2)$ is an associated prime of $I'$.
Comment: Thank you so much for your nice example.
Comment: For another example, take $I=(x_1x_3,x_1x_4,x_2x_4)$. This is Cohen-Macaulay since it is the face ring (aka "Stanley-Reisner ring") of a connected graph. (It's also easy to check Cohen-Macaulayness directly.) But $I=(x_1x_3,x_1x_4)$ is not Cohen-Macaulay since it's the face ring of a nonpure simplicial complex. (The face ring of any nonpure simplicial complex has depth 1.)

Cohen-Macaulay monomial ideal


Can we think of an address a mini-account, and is re-useable and disposable?

Question: Can we think of an address as a mini-account, and we can keep on using one, or we can use many to add privacy to our activities, and we can transfer or sell the bitcoins in it and make them empty and dispose of them any time?
Answer: No, you should not reuse addresses/treat them as a "mini-account". You should create a new one for every transaction and not re-use old addresses.
Your wallet software will generally handle this automatically for you -- just remember to request a new receive address each time you receive new bitcoin, and it should give you a new address that you should only use once.
Comment: Perhaps also important to note that under no circumstances this has any effect on fees. Reusing an address is not cheaper than creating a new one.
Comment: You should *not* consolidate addresses. But yes, when we say "single use" we mean receive once and send once -- if you only use it to receive once, your wallet software should handle the rest automatically.
Comment: Isn't it I have to at least use an address twice?  The first time when the address is created, it has 0 bitcoins.  So when 0.001 bitcoins go into it (is associated with it), then it has 0.001 bitcoins, and ... at least you need to use it again to consolidate it into your bigger account (address), or that you need to send to another person, so that in either case, the address becomes empty (0 bitcoins), so that you can stop using it forever?
Comment: Or, one other way is: the time you spend that 0.001 bitcoin is the time you dispose of it.  So if I have 12 addresses with 0.001 bitcoin, and now I need to buy something or transfer 0.01 bitcoins to Coinbase, now, out of the 12 addresses, 10 of them will be transfer to Coinbase, and then immediately thrown away by my wallet?  So basically we only use the address twice: when bitcoins come in and when it goes out
Comment: @nonopolarity I find this abstraction most useful: you have a single wallet, and it has multiple "entry points" that are addresses, which are used to receive coins into the wallet. But once received, those coins are held and managed by the wallet, and it's the wallet that sends them - not the individual addresses. In this abstraction, addresses are indeed single use.
Comment: so we can think of, one address, receive once, and send out once, and abandon it


Android app that shows WiFi password

Question: I need to share WiFi password with my notebook, because it has better antennae. Is there an open source Android app that allows see the WiFi pass of existing connection?
Comment: Only on rooted devices. Are such answers acceptable? If so, take a look at my app listing on [WiFi Password Recovery](https://android.izzysoft.de/applists/category/named/network_wifi_config#group_423). Though the only one I see that definitely is open source requires Xposed and wasn't updated for a while…
Comment: If answer explains why no such app exists for non-rooted devices - this is a good answer. And if adb can still fetch the info - it is good to know.
Answer: On Android devices, WiFi passwords are stored in an area no "normal" app can access (if you are interested in details, it's file system permissions behind this). Thus, if an app shall access stored WiFi passwords, it requires root access. Without root powers – no way, to my knowledge not even via ADB¹.
If you take a look at my app listings on WiFi Password Recovery you will see that all those apps require root access. And if you have root access, you don't need an app for that – you can simply access the /data/misc/wifi/wpa_supplicant.conf file directly and see the password (psk) for each network (ssid) you connected, plain text.
That said, I don't know of any up-to-date open-source app for this.

¹ only place that could work would be examining a full ADB backup, but I doubt it's in there

Android app that shows WiFi password


Are there any better asymptotics than Liouville for how fast a series of rational terms needs to converge to guarantee the sum being transcendental?

Question: So the title basically says it all: A Liouville number is a number $x$ such that for any $n$, there exist integers $p,q$ with $q > 1$ and $0 < |x - p/q| < 1/q^n$. This implies that the number $x$ can be arbitrarily well approximated by rationals, to an increasing definition of accuracy. Liouville numbers are transcendental by theorem. My question is: Are there any conditions WEAKER than the Liouville condition given above, which guarantee that a series of rationals converges "fast enough" to make the limit sum transcendental?
Answer: Yes there are.
A generalization of Liouville numbers involves defining the irrationality measure of a real number $x$, which measures of how "closely" $x$ can be approximated by rationals. Formally, this is the least upper bound of the set of real numbers $μ$ for which the inequality $0< \left| x- \frac{p}{q} \right| < \frac{1}{q^{\mu}} $ is satisfied by infinitely many integer pairs $p, q$ (where $q > 0$).
Clearly, Liouville numbers have infinite measure while rational numbers have measure 1. Roth's Theorem states that all irrational algebraic numbers have measure of 2. Therefore, any number with a measure greater than 2 is approximated "too closely" by rationals to be algebraic and is therefore transcendental, just like the Liouville numbers.
Examples of such numbers include the Champernowne constant 0.1234567891011..., which has a measure of 10. Unfortunately, nearly all transcendentals have an irrationality measure of 2, and it's usually difficult to calculate the measure even for numbers known to be transcendental.
Comment: The irrationality measure  is the least upper bound of the set of real numbers $μ$ for which the inequality $0< \left| x- \frac{p}{q} \right| < \frac{1}{q^{\mu}} $ is satisfied by  at most finite many integer pairs $p, q$ (where $q > 0$).


laplace transform with heaviside step function

Question: There are some similar questions around but they didn't help me much.
I've got a graph that I'm supposed to perform a laplace transform on. From $0<t<2$, it's a ramp function from $f(0)=0 to f(2) = 10$ (slope of 5) and then from 2 to 6 it's a -2.5 slope from $f(2) = 10$ to $f(6) = 0$.
Another way to solve this, I think, would be to take derivatives until it's in the form of impulse functions and then do the laplace using the transformation for a second derivative, but this is what I was doing first and I got stuck ...
I translated the intervals into $5tu(t) -7.5tu(t-2) + 2.5tu(t-6)$, where $u(t)$ is a heaviside step function.
I did this thinking I could use the time shift transform, but got stuck with the $t*u(t-2)$ part. The time shift transform is $f(t-a)u(t-a) = e^{-as}$, but in all but the first case, t is not shifted, only the step function is.
Would I have to use the integral definition of the transform from this point, or am I missing something?
Comment: If anybody knows how I can draw a graph in these questions, that'd be helpful :)
Comment: Also bear in mind I'm coming from a rudimentary crash course in these transforms from an engineering textbook, I haven't taken differential equations yet.
Answer: The cleanest way to handle such problems is to write
$$ t u(t-2) = (t-2+2) u(t-2) = (t-2) u(t-2) + 2 u(t-2)$$
Now take Laplace transforms and use the time shift property you wrote.
You are almost there.
Comment: I ... wow. Um what just happened? Oh, I see, distributive. Clever :D But ... what do I do with the 2u(t-2)? I can't use the transform for u(t) on that can I?
Comment: Yes. $u(t) \to 1/s$ Hence $u(t-2) \to e^{-2s}/s$.
Comment: It'd be ... 2*integral(e^(-st) from 2->infinity ... *scribble scribble*
Comment: Use time shift property! see my comment above
Comment: Oh hey. You responded ... Oh right, because u(t) is a special case of u(t-a) where a is zero, right? I don't see that on my little chart. I'm allowed a cheat sheet on my exam, I should put that on there.
Comment: Good luck! Time for me to head to bed...it is 1:30 AM here


What's the name of the trope where a character answers the phone expecting someone and it's someone else?

Question: Often used in horror movies, when the female victim answers the phone, jumping straight into conversation assuming it's their girlfriend, and it ends up being the killer.
Answer: If we go by TV tropes, this trope would be a variant of the Evil Phone trope. I would call it The Reverse Evil Phone. In the Evil Phone trope the character thinks it's the killer calling, but it ends up being someone else, which then guarantees the next call will be from the killer but the character think it's the first caller calling back. The scenario you describe would therefore be a Reverse Evil Phone trope.
Comment: oddly enough, I cannot find a TV Tropes entry for the sit-com variant of this, where a person answers the phone and starts cursing at the caller (assuming it is the previous caller, whom they are angry with, calling back) and it turns out to be their grandmother.
Comment: Sounds about right. I wondered this after watching this situation *not* happen in How Do You Know, and found myself relieved because I'm so fed up of seeing it happen!


Why is CBD legal in UK, Ireland, etc but it is Illegal to advertise it?

Question: Why can't you advertise CBD on Facebook, Google, etc., considering there is no THC and it is not a drug?
Comment: "illegal to advertise" is not the same as "This advertiser refuses my business".
Answer: CBD most definitely is a drug and a chemical derived from marijuana. It may be a legal medicinal drug under the laws of the UK and Ireland (two completely separate sovereign countries by the way) which just set their respective policies on the subject earlier this year, but that doesn't mean that it isn't a drug, and like many drugs it will require a prescription.
In any case, the UK and Ireland are not bound by the vigorous first amendment protections of the USA, and even the U.S. heavily regulates the advertising of medicinal drugs in order to protect the public from misleading claims in this commercial form of speech.
Comment: Perhaps you need to have ads pre-approved by their respective versions of the FDA before they can be used. Also, enforcement systems don't have to be flawless. There gap be enforcement gaps and loopholes due to inadvertence and all sorts of other means.
Comment: Thank you for the reply!

I understand how that works and the different laws. What I'm not understanding is how some places sell it as a food supplement [fruugo](https://goo.gl/XgDfFF) and if you search for CBD oil in Google, they show up as ads in the sidebar. From what I can see the website is UK based.

Yet I've tried to place an ad in Ireland with google for [fightstore](https://fightstoredublin.ie/product-category/brand/canavape-brand/) and it was turned down. Then I've tried to do the same with Facebook and they came back saying I was promoting illegal drugs.
Comment: After I messaged them asking for an explanation, they came back with the same message 'You are promoting illegal drugs... and we will not reply to any of your messages'. They can't tell me why... that's odd.
Comment: Thanks for the reply. Will try and see if I can find a loophole around it.


Room temp batter for cheese cake?

Question: Does the cheese cake batter have to be at room temp before cooking? I'm using batter I saved in the fridge and just didn't want cracks if I put it in before it was room temp.
Comment: You need to be clear about what sort of cheesecake you're making.  It sounds like maybe a baked one, but that's not clear.  You may want to post the full recipe
Comment: it's doesn't have to be anything, but the slower you change temp the less cracking you'll have. I find a baking sheet on top of the pan for the first 20 mins helps a lot, as does slightly lowering the temp and cooking slightly longer, broiling at the end if needed to give it the right color. That said, cracked cheesecake tastes good, don't worry too much about it, it will get eaten regardless.
Answer: If you're using refrigerated batter, you'll need to increase the cooking time.
Cracking is more related to how you cooled the cheesecake than how you heated it up, so I wouldn't expect this to affect cracking either way.

Room temp batter for cheese cake?


Tattoo removal video effect

Question: Is there a video editor that has a video effect where tattoos on human skin can be motion tracked and filtered out frame by frame, either by blurring them, or replacing the tattoos with surrounding skin pigment?
Comment: You can do it in Premiere Pro. Google for "premiere pro mask tracking", you'll find loads of videos and tutorials. Usually people do it to blur faces, but in the same way it can be done with a tattoo
Answer: Assuming that it's not changing perspective or moving around too much, I would use a tracker on the tattoo and a clone stamp from another area of skin.  More elaborate removal could be done with Mocha, or using a mesh warping tracker like Lockdown, which has a demo of tattoo removal in their showreel at 0m24s:
Comment: Could you edit with a link to mocha
Comment: good idea - added
Comment: Might want to also mention AE's new content aware fill.
Comment: Could you go in more detail about what clone stamp is and settings for tracking skin pigment to mask the black tattoo with

Tattoo removal video effect


What is this tubing in the basement?

Question: I saw a house for sale today and my realtor and I couldn't figure out what this was attached to the water heater, some kind of water piping/tubing. We'll get to the bottom of it with the inspection, just impatient to know what on earth this is. House built in 1984.
Comment: Your realtor has never seen that before? It's an incredibly common plumbing material usually called PEX.
Comment: Why not put your answers in the box labeled "answer" instead of the one labeled "comment"?
Comment: Are the red ones hot then?
Comment: Those are your water pipes. The material in question is called PEX. It is becoming increasingly common to see it used in homes. I just got done re-piping my entire downstairs with PEX. The short white one with the shut off valve and thin copper is likely a line for the ice maker in your fridge.
Comment: I'll note that this "manifold" scheme is rarely used with regular copper or glued plastic piping, but with PEX it's a lot easier to install (fewer joints) and, for the hot water, it delivers water at temp a lot faster.
Answer: That would be your water distribution system, aka supply plumbing. Cross linked polyethlene, or PEX for short; Using a manifold arrangement.
Most likely the red ones are hot water, the white ones are cold.
Only gets confusing if there's also a hydronic heating system also using PEX, but no more so than when they were all copper, or iron.
Comment: Might be worth mentioning you can "Google" for "PEX Manifold" to see various types of manifolds like these.
Comment: @DerKommissar - Actually, that should be "manifold types of manifolds".
Comment: Well done, @HotLicks :)
Answer: It looks like PEX and has the white ring things that go over Uponor ProPEX style connectors. Here is a video of the material in use, pay attention to the expansion tool: https://www.youtube.com/watch?v=AXYONkaxzv8
You should confirm this observation by noting any markings printed on the tubing, they should say PEX somewhere. The house was built right in the middle of the polybutylene era, you want to be absolutely sure it is not that.
PEX would definitely not be original to the house as it did not exist in 1984. Why the piping was replaced would be a good question for the seller, it might actually be replacing polybueylene. https://www.nachi.org/pb.htm

What is this tubing in the basement?


Can we pick a cheaper starting ship and add mods to it at the start?

Question: Can a group pick a cheap ship with mods as a starting ship in EotE, as long as the total cost doesn't exceed the 120.000 maximum credit amount for starting ships?
Comment: Hi Nyllcode, and welcome to RPG Stack Exchange. I see from your Informed badge you've already checked out our [tour]; thanks for doing that. If you have any site about the site itself or how to use it you can ask on [meta], and whenever you reach 20 rep you're welcome to join us in [chat].
Answer: It's up to your GM
The rules say that the group starts with a ship with a cost of up to 120,000 credits, but not that you have 120,000 credits to spend on a ship and it's accessories.

As part of their Obligation, each group starts the game with a starship. This is the final part of character creation. The GM can choose one of these three ships as his group's starter vessel. Alternatively, experienced groups can select their own ship, so long as that ship costs no more than 120,000 credits and is approved by the GM.

So the players start with one of three possible ships presented by the book, or pick their own ship as long as it doesn't cost more than 120,00 credits. But makes no mention of modifications or equipment inside the ship.
However, as long as that ship costs no more than 120,000 credits and is approved by the GM you can start with any ship you want.
The GM has the final say on what ship your group starts with, he has all the power to allow or disallow a specific ship. If you check Age of Rebellion (p. 111), characters are presented with three different options instead of a single ship worth 120,000 credits:

A stolen imperial Lambda Shuttle, which is worth 140,000 credits;
A Y-Wing squadron, worth 80,000 each. Yes, that's right, one Y-Wing for every two members of the group (four PCs = two y-wings);
A base of operations, which has no listed value but will grant an additional 1,000 worth of gear for every PC. This can be expanded by the supplements published, though;

With that said, when I ran my first Edge of Empire campaign, set in the Old Republic, the players didn't start with a ship at all, but ended the second session stealing a Pathfinder, a ship worth 135,000 credits.
Comment: I don't see how the quoted text disallows mods. The mods would be part of the ship, they're not "accessories". If I buy a car with built-in GPS, that just adds to the value, it doesn't mean I bought a car and a GPS.
Comment: @Theik, modifications are *vastly* different from built-in GPS. They are more like stuff you add to your car *after* you bought it. A GPS would be part of the factory mods, and many ships already come with installed weapons, or better engines, heavier armor plating, or even stealth technology, those aren't installed by the user, they are *built-in*.
Comment: A YT1300 comes with many "open" mod slots because its a big ship made for transporting cargo, when you install additional weapons, you are using that space for a new purpose not intended by the designer. There are many ships that come with fewer (or no) hard points for modifications, but that is made up by all the systems that come installed on it.


Is this normal Wireshark behavior?

Question: I'm running Wireshark in Windows inside a virtual machine. Wireshark keeps reporting network activity, even though I don't have anything running in there that's accessing the network.
Comment: It depends, you'll need to examine the ports, protocols, and packets to determine what the activity is. Start with the ports and protocols; that's easiest. Is it TCP, UDP, ICMP? Is it a known port or an ephemeral port?
Comment: They're mostly TCP with some UDP. All the local ports are ephemeral ports.
Comment: **1.** Wireshark should also show the higher-level protocol names (e.g. DNS, NBNS, ARP) along with every packet. Or does it just say "TCP" and nothing else? **2.** Which direction are the packets travelling? **3.** Do the addresses (IP, Ethernet) match the virtual machine's? There's a slight possibility that you could be seeing your host's or another VM's traffic. **4.** Are _both_ ports in the "ephemeral" range? If yes, P2P is a possibility. (I keep receiving BitTorrent traffic _long after_ I close the client.)
Answer: Windows constantly broadcasts NetBIOS node information, just as OSX constantly broadcasts mDNS (Bonjour) information.
Comment: But, you can turn it off if not needed…
Answer: If you have an ethernet network and any hosts running IP, then you will see occasional ARP (Address Resolution Protocol) messages, even if you aren't actively using the network.
ARP is the protocol that hosts use to figure out which IP addresses match to ethernet addresses (MAC).
For example:
<code>Host 1: Who has 192.168.1.2?

Host 2: I have 192.168.1.2 and my MAC is aa:bb:cc:dd:ee:ff
</code>
Now host 1 knows that any packet which has 192.168.1.2 as its destination can be sent in an ethernet packet that has aa:bb:cc:dd:ee:ff as its destination.

Is this normal Wireshark behavior?


TeXnicCenter not working with Acrobat Reader

Question: Even after updating to R20 in the PDF section, TeXnicCenter is not opening Acrobat Reader. I'm using Adobe Acrobat Reader DC version 2020.013.20074. The old trick does not seem to work.
Comment: Try with a lower case V: `AcroviewR20`.
Comment: Welcome to TeX SX! Acrobat Reader is not recommended for use with latex documents: it locks the .pdfs, and before you can re-compile, you have to close the resulting .pdf.
Answer: I have the Acrobat Pro DC version 21 (not acrobat reader). In order to find the version of the server I looked at the following registry entry:
HKEY_LOCAL_MACHINE \Software\Classes\acrobat\shell\open\ddeexec\application
In my case I found that the server was AcroViewA21. Also in my case the executable that I was calling was the "Acrobat.exe", and not the "AcroRd32.exe".
It worked perfectly.
Answer: To confirm the previous answer, after my Adobe Acrobat automatically updated to 64 bit my TeXnicCenter failed to view - it hung. I changed the viewer comand line to that which appears in the Adobe icon properties target, which uses Acrobat.exe rather than AcroRd32.exe. This still failed to view, but did when I changed the viewer from AcroViewR21 to AcroViewA21 as suggested in Answer 1. Thank you very much Answer 1.
Comment: Welcome to TeX.SE!
Answer: New version of Adobe Reader was released and new server version is required.
Adobe Acrobat Reader DC
Continuous Release Version 2022.001.20085 64Bit
Executable: Acrobat.exe
Server version: AcroViewA22


Camera of AR Application flipped in Vuzix M300 glasses

Question: I am trying to install an AR application build using unity and Vuforia to vuzix m3000 glasses, but the camera of the application is flipped vertically and the contains of the screen is in the right way. I have tried to rotate the AR camera in unity but the view in the glasses is still flipped. Is there any other way to correct the camera view?
Answer: I've run across a similar problem before; in my case, it was the HoloLens.
Try disabling MSAA on your camera object.
Essentially the post processing effect (the antialiasing in this case) messes with the camera's UVs and they get flipped (because one thing has the V=0 at the top, the other has V=0 at the bottom). It's a long-standing problem across multiple platforms.


Is there any finished tutorial on how to develop and package unity web apps?

Question: I want to create unity web-app for my new website.So,is there any up to the mark tutorial.I've read Ubuntu's official tutorial on this topic but that is not even complete.I've developed the code but don't know how to package the code
Comment: I found this tutorial:http://quickmediasolutions.com/blog/9/using-the-unity-web-api
This is quite nice but still dont know how to compile ".js" file I've created.I did "make" but that didn't do anything. :(
Answer: Actually packaging a webapp isn't really different from packaging any other application. Take a look at resources in this answer and especially at existing integrations, e.g. LinkedIn, Feedly and (shameless plug) This Is My Jam.
Basically, you need debian/ directory with at least the following files (see the guide for details):

control with basic description for package manager (see example) Three keys are important for webapps in particular: XB-Ubuntu-Webapps-Includes, XB-Ubuntu-Webapps-Name and XB-Ubuntu-Webapps-Domain.
compat
copyright
install specifies which files should be installed where
rules
changelog specifies the resulting version of the package and must follow a very specific format; can be managed using e.g. dch command

You can generate these files using e.g. dh_make command or just copy the debian directory from other webapps project and change package names, filenames, and domains.
Once you have the files in place, you should be able to generate package using e.g. dpkg-buildpackage command (from the dpkg-dev package). The resulting package is generated in the parent directory.
If you are using version control such as Git or Bazaar, take a look at git-buildpackage or bzr-builddeb respectively (both available in Ubuntu repository). I've found especially the git dch command useful for maintaining the changelog. There's a nice HowTo on packaging with Git and uploading to PPA.
Answer: I'd take a look at this link: http://developer.ubuntu.com/resources/technologies/webapps/ seeing it's the official guide.
Comment: Unfortunately there's no information on how to create a package for the webapp. Documentation covers only webapps APIs.


how do i get a flash builder 4 window on my other monitor?

Question: I read online that with Eclipse (which FB is built in) you can reposition an editor onto a different screen however I am unable to do so.. I get an X whenever dragging it anywhere outside the main application frame.
I am on OSX.
Comment: Flash Builder is such a miserable piece of (work).
Answer: This is not supported AFAIK.
You can, as a workaround, create a new window  (Window, New Window), move your desired document/editor into that window, and maximize the editor to hide the panels around it (Cmd-M).
Comment: That would be a useful enough alternative, unfortunately I don't seem to have that option in my 'Window' menu... I can get at 'new editor' by right clicking on the open files bar, but it just puts that right in the same row.
Comment: @Damon Sorry, I don't use Flash Builder. It's in the newest version of Eclipse (Java developer variant) -- you could try combining your Flash Builder modules with the newest Eclipse; otherwise you'd have to wait for a more recent release of Flash Builder.


Is it legal in England to use adjacent road to move building materials to your property?

Question: I'm in this situation. Builders coming to my street (small cul-de-sac) to move bulky building materials to a property that is located on neighbouring street and its garden backs onto my street. They destroyed some vegetation on my street to create a pathway and opened up part of a fence. There are builders' vehicles coming to my street. Can I legally stop them from doing that? I also have been sworn at when I  was taking pictures of their vehicle and company logo.
Comment: I'd say "having no other reasonable access" is a pretty important reason for using a public road this way. You have no evidence that they weren't allowed to break the fence or that they aren't going to repair the vegetation (by which you should mean more than a bit of grass).
Comment: Who owns the fence?
Comment: What do you mean with *your street*? Are they only using public roads and areas, or are they using and destroying your property, for example your driveway?
Comment: "My street" means here "the street I live at and where I expect to feel undisturbed without an important reason". They are using (and damaging) public land, not my driveway.
Comment: Andy: The fence is ancient iron spiky railings, I don't know who put it there. Maybe it was there before the area was built-up. Nij: They have reasonable way of access through the other road, it's just easier for them to use the street where we are living. They have cut down a tree and a number of self-set sycamore saplings thus creating a gaping hole in what used to be a nice green screen of plants and left a half ton of builders sand on the ground. Children used to have a den right there.Generally they behave like a invading army, having no regard for the proper residents.
Answer: Summary: More information needed, but I have listed out some legal claims available to homeowners when they have similar concerns.
There are several issues here which need elaboration before deciding if you can take legal action.
The first is: "the destroyed some vegetation on my street."
If the by "my street" you mean that the street is part of your property, you may sue the builders for trespass and/or damage to property.
If the street isn't your property, but the vegetation  is your property, you may sue them for destruction of your property.
What you are probably looking for, however, is a prohibitive injunction. This is a court order forcing the builders to avoid doing something, e.g. An order forcing them to avoid using roads adjacent to your property.
To obtain such an injunction you will have to prove that what they are doing is violating your rights, is somehow harmful to you or your property, or inevitably will do either of those things. One way to demonstrate this is if you can show that you have a claim under nuisance, or damage to property, or trespass.
On the description you have given us, there isn't enough to say your rights are being violated, or that your property has come to harm or will come to harm because of their actions.
You should also be aware of claims under nuisance. Nuisance is when someone is doing something that prevents you from "peaceful enjoyment of your land".
It appears from your question that the actions of these builders have, in your mind, done this. However there are several aspects that have to be satisfied for this to amount to private nuisance:
What the builder are doing must be a "continuing state of affairs." They may have annoyed you by trampling over vegetation, but if this is a "one-off" event, it is unlikely to amount to nuisance.
A reasonable person must find the conduct to interfere with the enjoyment of their land. That is to say: it isn't enough that their conduct is making you unable to enjoy your land peacefully, you have to show that any reasonable person in the same situation would find this conduct unacceptable.
Finally, the context of your neighbourhood matters: if the behaviour is something expected in a residential area, then it will not amount to a nuisance. For example, heavy drilling in an industrial location will not amount to a nuisance, while the same may do so in a normally quiet neighbourhood.
Comment: I suspect that the prohibitive injunction requires not just inevitable damage, but additionally a lack of reasonable alternatives.  Part of that relates to the "any reasonable person would find it unacceptable", though.


shake sensor in android

Question: I am developing an android application which involves shaking sensor in android emulator.I have implemented functionality and 4 screens.Now I am facing problem how to implement shake listener in android.Can anybody tell me in advance.Regards Tushar
Answer: You have to use the motion sensor. Here is a good tutorial that describes how to do that:
http://www.clingmarks.com/?p=25
Answer: Few weeks ago I had the same question as you and first thing I did was google
"android shake listener" and found several nice tutorials. This one might be what you're looking for, isn't it?

shake sensor in android


Violation of Derrick's theorem for finite energy, time independent solutions?

Question: How are vortices the finite energy time independent solutions for 2+1 dimensions abelian Higgs model? Doesn't it violate Derrick's theorem that there are no finite energy time independent solutions in dimensions higher than 1+1?
Answer: No, it's not a violation. The conclusion of Derrick's theorem is modified in the presence of gauge fields, cf. e.g. this Phys.SE post.
Answer: No, it does not violate. Derrick's theorem is actually very restricted. It says that there is no finite energy time independent solution for
$$L=\frac{1}{2}\partial_\mu\phi\partial^\mu\phi-V(\phi),$$
in dimensions larger than $1+1$. The vortice in the Abelian-Higgs model appears for the lagrangian
$$L=-\frac 14F_{\mu\nu}F^{\mu\nu}+(D_\mu\phi)^*D^\mu\phi-\frac{\lambda}{4}(|\phi|^2-v^2)^2,$$
in $2+1$ or $3+1$. This is a gauge theory and the gauge field provides "more structure" to the theory, allowing for finite time independent solutions.
The intuition is that the for the first theory, there is a term $\int rdr\partial_i\phi\partial_i\phi$ in the energy density of the possible vortex but this diverges logarithmically. The corresponding term for the second theory is $\int rdr (D_i\phi)^*D_i\phi$ and the presence of the gauge field $A$ turns it possible that $D_i\phi=\partial_i\phi+ieA_i\phi$ decays sufficiently fast.


What are blood group determinants?

Question: I am trying to understand if they are the same as the blood antigens. The books I have tried to read say something about them being the antigens on the surface of the red blood cell.
Answer: Blood group A expresses A antigens and anti-B antibodies etc etc, see the next figure:

Taken from the wikipedia entry on blood groups.
Answer: In immunology, determinant is another name for epitope (the portion of an antigen recognized by a BCR/Ab or TCR).

What are blood group determinants?


What is the antonym of "feathering" in lighting?

Question: If I have to tell someone to move "unfeather" the light and point it towards the subject, what verb should I use? Gather?
Answer: The edge of most luminary output [beam] spread is more diffuse than the centre. A lighting technician will sometimes point a source "off-axis" to get a more or less indirect beam to "feather" it.
The term(s) I would use is to aim, point, or direct the beam of the light more towards the subject. You want to "harden" the light rather than "soften" (another term for feather) it.
Sometimes a "barn door" or "gobo" [go-between] is used in the path of the light so as to cause a light shadow that does the job. In this event, you would turn your attention to the accessory that's causing the [un]desired effect.
Thin translucent screens or "scrims" are also used directly in the path of the light to soften the harsh direct beam of a light to feather it. In this case, you would use less material or thinner diffuser or even remove the "flag" entirely. Flags, which are normally opaque are used to block light like a "barn-door," can also be made of other materials. A flag is called such due to being attached to an independent support not part of another lighting fixture in the set-up. It looks like a flag.
A white or crushed-foil reflector can be used to feather a light. In this case you would use a more "specular" reflection material or a smoother-surfaced foil reflector.
All of that pedantry aside, I would say, "Could you harden the light a bit." Then, more if that wasn't enough to satisfy me.
Answer: I would say "slightly defeather" the light, or just say to point it a bit more directly toward the subject. Since feathering (in this context) is not a term covered by any dictionaries I've consulted (and I did just check a few), I think that the term meaning to move in the direction opposite of feathering is still to be established. ;-)
Answer: Probably "Turn the light that way" will work.

I am so dumb. I first read "Anatomy"... And made this sketch. Now I realize it was not the question. I'll post it anyway n_n
Comment: What do you call the area where feathering occurs in your diagram?
Answer: The antonym of feathering is "full".
Comment: Could you provide a reference? I could not find any relevant search results for "full the light".