Mean and Variance of subset of a data set

Question: I have a data set of position measurements of an object. However, the data set is split into subsets. The subsets have equal size. I want to find the mean and variance of the whole data set only with access to the subsets, and the not the whole data set at once. How would I go about doing this? Is it correct that the mean of the means of the subsets is equal to the mean of the whole set? What about the variance?
Comment: The answer you accepted is incorrect. Does it make any sense?
Comment: Sorry I misread your post as saying it is split in two subsets. I don't know of a approximation when $k$ is large, but the general expression of pooled variance gives you the exact answer.
Comment: Yes, I have just realized when I got results that did not make sense. I see your answer below is what I am looking for, but I believe I am concerned with the case that k is very large. In particular, my data set is split into a large number of subsets, or groups, and I believe the expression I am looking for seems to be the pooled variance expression in your answer.
Comment: In the context of estimation, one can refer to https://math.stackexchange.com/a/2971563/321264 where the sample sizes are subtracted by $1$ to get unbiased estimates. This is for $k=2$.
Answer: Suppose you have $k$ groups of observations on a variable $x$ (say) where the $i$th group consists of $n_i$ observations, $i=1,\ldots,k$. Let the $j$th observation in the $i$th group be $x_{ij}$ for $i=1,\ldots,k$ and $j=1,\ldots,n_i$.
The $i$th group mean is defined as $$\overline{x_i}=\frac1{n_i}\sum_{j=1}^{n_i} x_{ij}\quad,\,i=1,\ldots,k $$
Then the pooled mean or combined mean is given by $$\overline{\overline x}=\frac{\sum_{i=1}^k n_i\overline x_i }{\sum_{i=1}^k n_i} $$
This is a weighted average with weights being the number of observations in the $i$th group.
The $i$th group variance is defined as
$$s_i^2=\frac1{n_i}\sum_{j=1}^{n_i}\left(x_{ij}-\overline{\overline x}\right)^2\quad,\,i=1,\ldots,k $$
And the pooled variance based on all observations from all groups is given by
$$s^2=\frac{\sum_{i=1}^k\sum_{j=1}^{n_i}\left(x_{ij}-\overline{\overline x}\right)^2}{\sum_{i=1}^k n_i}=\frac{\sum_{i=1}^k n_is_i^2}{\sum_{i=1}^k n_i}+\frac{\sum_{i=1}^k n_i\left(\overline x_i-\overline{\overline x}\right)^2}{\sum_{i=1}^k n_i}$$
You are concerned with the case $n_1=n_2=\cdots=n_k$.
Answer: If ${\cal D} = \{ {\cal D}_1, {\cal D}_2, \ldots, {\cal D}_n \}$, each of the same number of points, then the mean of ${\cal D}$ is simply the mean (expectation) of the individual means:
$${\cal E}[{\cal D}] = \frac{1}{n} \sum\limits_{i=1}^n {\cal E}[{\cal D}_i]$$
The variance sum law states is just the sum of the individual variances (for non-zero variances):
$${\rm Var}[{\cal D}] = \sum\limits_{i=1}^n {\rm Var}[{\cal D}_i]$$


If I drop a leaf twice from the height of a tree in a completely controlled environment, will the trajectory in each case be the same?

Question: Putting my question in other words, can earth form again if a similar initial universe condition is given? The uncertainty principle says that we cannot tell with certainty the position of a particle if we know its velocity with greater surety, and vice versa. But I have always felt that this restriction will vanish for a 'god' who has the advantage of knowing how the particles initially were in the beginning, and how they would interact and how the story would go on.... Therefore, can complete knowledge of the initial conditions of the world completely remove the uncertainty principle?
Comment: @ja72 Chaos theory is the study of systems whose outcomes are very sensitive to the initial conditions.  The systems of study can still be fully deterministic though.
Comment: Nope, because of Chaos Theory. Determinism is a fallacy.
Comment: @ja72 True, but the lack of determinism comes from quantum mechanics, not from the fact that the system is chaotic.
Comment: The uncertainty principle, as far as we understand it, is not 'uncertain' for the reason that our knowledge is incomplete, as you state. Rather, the uncertainty lies in the fact that a particle _really_ has no definite position and momentum at a given time
Comment: Related: http://physics.stackexchange.com/q/24068/2451 and links therein.
Comment: And the initial conditions are subject to quantum mechanics and the uncertainty principle. You need both positions and momenta to completely define initial conditions, which you cannot. There are multiple initial conditions, all superimposed onto each other.
Comment: @BenjaminToueg: Because we're on the winning team?  :)  The two have trouble coexisting, so one of them has to win out.  And if anti-matter had won, it'd be the norm, we'd be made of it, and we'd be calling *it* "matter" -- and the matter we currently know and love would be the "anti-matter".
Comment: @cHao What I mean is that if we were rolling the dice once again, with the exact same initial conditions, are we sure matter would have won over antimatter? If not, then the question is closed.
Comment: This question is really about chaos theory, not about quantum mechanics.  A leaf falling is not about quantum mechanics.
Answer: You are misunderstanding the Uncertainty Principle. The Uncertainty Principle says that a particle cannot simultaneously have a definite momentum and a definite position. This is not due to our incomplete knowledge of parameters. This is a fundamental law of the universe and arises from the fact that the momentum and position operators do not commute in Quantum Mechanics. In your question, the leaf outcome will be the same in both experiments because when you combine a lot of particle wavefunctions together the object does not behave probabilistically anymore. This phenomenon is called Quantum Decoherence. In the earth formation experiment, we simply cannot know. You need the right conditions for the earth to form, and because the Uncertainty Principle and Quantum fluctuations did play an important role in the early universe conditions we can't know for sure if its going to happen again.
Comment: What does UP mean ? Ok, it means Uncertainty Principle. Please do not use acronyms, or define them.
Comment: Theoritically, a coin could flip by itself if you stare at it for a sufficiently long time, but it odd is so ridiculously small that you would have to wait as long as multiple times the age of the universe in order to have a tenth of a hundred chance to see it happen.
Comment: Does that mean there there no quantum fluctuations that could cause macroscopic effects in something as chaotic as air movements?
Comment: Quantum Fluctuations is what caused the big structures in our universe like galaxies, so yes then can form large structures whens stretched to astronomical scales (during inflation for example). But they are not chaotic in the physics sense, they are truly random.
Answer: No. The Uncertainity Principle states the following:
The position and momentum of a particle cannot be simultaneously measured with arbitrarily high precision. There is a minimum for the product of the uncertainties of these two measurements. There is likewise a minimum for the product of the uncertainties of the energy and time. $$\Delta x \Delta p \geq \frac{h}{4\pi}$$
This does not mean that these parameters are impossible to measure because our instruments are not accurate enough yet or maybe some error creeps in. Doesn't matter what the initial conditions are, this uncertainity lies in the very nature of matter.
The main question that you are asking is not really affected by the Uncertainity Principle. The Universe is not deterministic. Hence, the formation of our planet having that tree and that tree having that leaf are just what you may call accidents. Our version of the Universe is just one out of an infinite others where there is no Earth or us.
Answer: The problem with this question is that, even if you perfectly controlled the conditions at the macroscopic level -- including somehow releasing the leaf in exactly the same way every time (nearly impossible), and using leaves in identical starting state (the same leaf may have lost some water by the time you repeat the experiment, and suppressing all pressure waves in the enclosure (absolute silence)... there are going to be feedback effects at the microscopic level which the experiment amplifies and makes visible. Brownian motion could be enough to affect air density -- or leaf flexibility -- enough to start a divergence, and that divergence will affect the leaf's path, which will affect the pressures on it, which will affect how it curls, which will affect its path, which...
This is a highly unstable system, and in practical terms it's probably impossible to control it well enough to exactly reproduce the experiment.
None of which has anything to do with the uncertainty principle.
Comment: I think this is more of a thought experiment; if you *could* put everything back where it started would it play out the same way. Rather than the practicalities of replaying the experiment
Comment: I think the uncertainty principle does set a theoretical bound on how much control is "absolute" control, at least for any experiment set within the realm of known physics. So the trajectory is different each time even in a thought experiment with as close to perfect control as the laws of physics allow.
Comment: @NeilSlater: Uncertainty is a valid issue, and could affect such things as exactly how much surface adhesion there is between the leaf and whatever releases it, but I'm not sure that would be a large enough effect to be visible in this particular experiment. Not impossible, though
Comment: @RichardTingle: OK, if we assume the reset is _COMPLETE_ down to the subatomic level...
Answer: In the case of a leaf's trajectory, yes, it'd be same in both cases if the environment is exactly the same. And you can generalize this to any macroscopic event.
As for the formation of Earth simulating the universe since its beginning, it's complex because it's not a macroscopic event. In the quantum world, everything is probability driven. In a heap of radioactive atoms, all atoms are equally similar and equally unstable. Yet some atoms bleed out their instability at one point, and some after billions of years. See, I haven't even used the uncertainty principle here.
So, given the initial conditions of the universe, the formation of Earth is one of countless possibilities.
Comment: `Yet, some atoms bleed out its unstability at one point and some after billions of years.` And you're sure this has nothing to do with initial conditions? This could simply be deeper chaos theory, and variables that we don't understand where they came from, but that doesn't really imply that it's not determined.
Comment: @Cruncher Providing the nature of this QnA site, my answer is based on facts we have at our disposal. With fictional things, the question would be unanswerable.
Comment: Saying it's a fact without evidence to the contrary, is like saying it's a fact that there's no god because we have no evidence for it.
Comment: @Cruncher In the dimension of physics, those are facts. And, you are free to kill all physics laws based on that logic... in another dimension.
Answer: Different trajectory each time due to probabilistic nature inherent in quantum mechanics and the uncertainty principle. The uncertainty principle is not "removable", it is not a constraint based on practical limitations in an experiment, but inherent to quantum mechanics calculations.
There was an interesting thought experiment, given absolute control over a much simpler system (multiple collisions between 12 billiard balls), it is not theoretically possible to determine the trajectory of the final object: D J Raymond - How Determinate is the "Billiard Ball Universe"?
How different the trajectory ends up will depend on how important this microscopic randomness becomes. I would expect the equations of motion for a floating leaf to have some non-linear elements, such that tiny amounts of difference in speed or position will lead to essentially chaotic motion.
However, that may be constrained within a narrow bound. I cannot really guess whether the chaotic parts of the motion would be one part in a million or completely overshadow the regular predictable motion of the leaf (that you might get from a classical fluid dynamics solution to the equations of motion and fluid flow around the falling object).
Some leaf shapes and airflow may in fact be relatively stable and not show much difference (trivially, with very low air density, the trajectory will be a straight drop). But I suspect that the iconic image of a leaf spinning and rocking as it slowly falls is a highly chaotic system, and it will then be vulnerable to effects of the uncertainty principle, assuming your imagined "perfect" experiment set up is done within the bounds of known physics.
Answer: From my understanding of your questions, you are confusing the "scientific method" and the "uncertainty principle.  The scientific method says that "given the same starting conditions, within a controlled environment, etc., the "results" should be the same (ei. repeatable within some degree of accuracy).  The uncertainty principle "deals" with an entirely different thing.  It tells us that either one of the measurements of a particle's position and momentum can be accurately determined, but not both at the same time.


Why is Frank Burns portrayed as such a child in M.A.S.H?

Question: In the TV show M.A.S.H. why is Frank Burns character portrayed as such a childish person?  Everything he does seems childish.  (I absolutely can't stand the character and feel for the actor who played the part.) (Childish may not properly encompass my feelings, but I can't think of a better word.)
Comment: I think spoiled brat is probably a better description. I don't remember, but I think the character came from money and never had to deal with anything like going to war. Just my thinking, though could be wrong.
Comment: Yes! Spoiled Brat is a much better descriptor.
Answer: To answer this, you have to consider the source material which is the film and the book that came before it. In the original material Frank Burns is a very different creature. While as inept as the character in the series, the film/book version is far stronger in his own personal beliefs and (unwarranted) confidence. Film-Burns goes so far as to blame others for the shortcomings of his lack of surgical knowledge and crushes a young orderly, blaming him for the death of a patient.
The book/film shows the danger created in wartime by drafting doctors to surgical duty who didn't necessarily have the ability yet still got promoted in the chain of command. It further shows the lengths that competent doctors went through to get these people thrown out of the army.
In transitioning to the series which wanted to still be drama mixed with comedy; albeit lighter fare so as to be accessible to 70s audiences; Frank Burns in his film/book state needed to undergo some changes.

He needed to not be so much of a danger that he had to be removed
He needed to be semi-likable

So, ratchet down the incompetence, ratchet up the child-like goofiness and you've still got "A" Frank Burns.
In the long run, the character didn't last the series and left under similar pretenses. Winchester was brought in spinning the film Frank in the other direction. High level of superiority and confidence, but removing most of the incompetence in exchange for cultural snobbery.
One last note on your comments.
Actors will tell you that villains/unlikable characters are far more fun to play. The fact that you find yourself brought to an emotional level over the character on a regular basis is a sign that the actor was succeeding at his work. Linville himself said he had a love/hate relation with the character. The actor himself was a very sweet, bright, well-liked gentleman, but really relished making Frank as conniving as he did.
Comment: Thank you so much!  It is comforting to know that the actor himself enjoyed playing a convincing part!  A toned down version still makes my stomach turn almost every show.  I'm always glad when Frank goes back to the States and get's a job at a VA (I believe) or was it taking up his old practice?  Winchester is a tad more sufferable.
Answer: Flanderization:

The act of taking a single (often minor) action or trait of a character within a work and exaggerating it more and more over time until it completely consumes the character. Most always, the trait/action becomes completely outlandish and it becomes their defining characteristic. Sitcoms and Sitcom characters are particularly susceptible to this, as are peripheral characters in shows with long runs.

Frank didn't start of as a walking punchline and at the start of the series is much more relatable, but was retrofitted with more ineptitude and scorn as the series dragged on.
Divergence from the original source material Characterization Marches On is pretty common - see also Radar O'Reilly whose cute factor was turned up to 10 as the series went on.
I believe the writers caught on that they had reduced the character to a walking punchline a bit too far and hence when Larry Linville left the replacement character played a similiar role, but had more depth ie. Major.Winchester
A lot of characters were Put On A Bus by the writers with Trapper being replaced with BJ Hunnicutt for less womanising and more back story, Henry Blake for Sherman Potter - less bumbling incompetence and more nuance
Answer: Frank was a miserable person. His wife was a cold fish who owned him lock, stock, and barrel. He was, at best, an average doctor, and he couldn't or wouldn't bring himself down to being human. He did show some flashes of humanity, but it was brief. And when Hot Lips Houlihan got engaged, tired of waiting, Burns just became a punchline, and it was the producer's fault. They would not let him grow.
Comment: frank occasionaly would try to get even in one episode he screwed around with the pipes in the shower among other things but hawkeye got even by pulling down the latrine with burns in it but it was rare..


What do I do with leftover egg whites? How long are they safe for?

Question: I made two Leche Flan the night before last, each calling for 10 egg yolks...so, I was left with about 20 egg whites. I've stored them in the fridge in a tupperware container. How long are they good for? What can I make with them (other than scrambled egg whites and frosting)?
Comment: Hi, I'm afraid both parts of your question would have to be closed. The general shelf life of raw proteins is the same, 3-5 days in the fridge, shared with any other perishable food, and this is described in our canonical question on food safety (which I used as the duplicate parent). "What can I do with X" is a culinary uses question, and our rule for it is: if it is a normal ingredient and would not get thrown away, we don't allow questions about it.
Comment: @rumtscho I thought the rule was no requests for recipes (which this question is not asking for)? I had a feeling that the first part would be duplicate, but considering quantity and that they are stored together, I took a chance on it not being a duplicate.
Comment: @jsanc623 Recipe requests are indeed off topic, but they're not the only thing. We also don't take recipe idea/menu planning questions, i.e. anything of the form "what should/can I make...".
Comment: For "what can I make with X?" see http://meta.cooking.stackexchange.com/questions/740/can-i-ask-about-how-to-use-a-specific-ingredient-aka-culinary-uses-guidelines
Comment: @jsanc623 Jefromi is right, this is a separate rule for off-topic questions. In fact it is a subtype of the "poll" or "opinion based" question type, which is never accepted, just as on any other site on the network. But the culinary-uses questions are so frequent for us that we have discussed them specifically. Beside the question Jefromi linked, there is also http://meta.cooking.stackexchange.com/questions/1058/where-do-we-draw-the-line-on-culinary-uses-questions.
Comment: swallow them all whole all at once!
Answer: I can't really answer the question on what to do with the egg whites but the question how long the egg whites are good: two to four days.
Hmm, what about macaroons?


Reference request for calculus and integration on Banach spaces

Question: I'm looking for some references about calculus and integration on Banach spaces. In particular, I'm interested in some basic results about:

Derivatives and differentiation of continuous functions $f:I \rightarrow X$, where $I$  is a open interval of $\mathbb{R}$ and $X$ is a Banach space on $\mathbb{R}$.
Integration of functions $f:I \rightarrow X$.
Complex differentiation of functions $f:\Omega \rightarrow X$, where $\Omega$ is an open subset of $\mathbb{C}$ and $X$ is a Banach space on $\mathbb{C}$ (simple results about holomorphic functions which takes values in a Banach space).

My background includes calculus and integration in $\mathbb{R}^n$, measure theory, basic complex analysis, and basic results about Banach spaces (Hahn-Banach theorem, open mapping theorem, closed graph theorem).
Could someone suggest me some book or lecture notes where I can briefly recover some information about the topics I listed?
Comment: The book I described in my answer to [Reference Request: Differentials of Operators](https://math.stackexchange.com/a/3565719/13130) might be suitable for *some* of what you're asking about.
Answer: Chapter 1 on Riemann integration in these notes covers the integration of functions part of your question


Deterring Mobile phone Tethering in the workplace

Question: How do you put in controls to prevent a staff using his/her mobile phone to tether 3G/4G connection and download unauthorized files onto the office PC?  Of course minimally there must be an AV in place to check for viruses and stuff. But how to stop the tethering in the first place? Any recommendations?
thanks
Comment: Don't give them admin rights and restrict the access to network control. Only enable the network connection that you generally use on those machines.
Comment: fyi - Blocking USB isn't the answer, I can tether my MacBook with an iPad over Bluetooth
Answer: There are potential technical options you can pursue, and several of those have been mentioned in other answers, such as global policies or BIOS settings to disable the USB ports, or physically disabling the USB ports.
However...
My suggestion is that if you have a systemic problem with this sort of thing, it isn't, in fact a technical problem at all, but a policy or people issue instead, and you should be looking for ways to deal with the underlying issue, and not the symptom of mobile tethering.
The most likely cause, is in fact you.  (You being inclusive of the IT department, management, and the policies in place.)   If your policies are too restrictive, and people are having a hard time doing their jobs because you've removed or disabled the tools that they need, good employees will become frustrated, and they will find ways around your restrictions in order to accomplish their duties.   With good employees, productivity always wins the day, no matter how hard you try and prevent it with policy and technology.   As the saying goes, security at the expense of usability comes at the expense of security.
So, if that is in fact the issue at play here (and in order to find out you'll have to actually talk to the employees!) then you need to figure out how to change your policies in order to enable them while still effectively managing risk to the business.  There will have to be trade-offs, but such is life.
There are other less likely possibilities, such as perhaps this behavior is limited to users who don't know that it isn't allowed, or who would rather goof off at work with things that have no business purpose than do their jobs.   If that is the case, it's still a human resource issue, not a technology issue, and the solution is not to crack down on tethering, but to crack down on those employees and educate them or show them the door.
In any case, don't jump straight to a technical solution for a behavioral issue.  You likely aren't going to solve the problem, but may in fact make it worse.
Answer: The problem with this is the availability of USB ports... if the USB ports no longer work, then they will stop trying it.
I know there are group policies that disallow the use of USB ports through the OS, but I'm not too familiar with if there is a policy that will disable them entirely. If not, then you might be able to either A) disable USB in BIOS or B) glue them shut (effectively ruining the computers, which corporate won't like).
Answer: This is where company and security policies can come in handy if you don't want to get all too technical. However if you do not require the need to write to mass storage devices via USB then you can simply edit the registry to only allow for devices to read via USB. Although, if you're staff do need the ability to read/write there are other registry related options but if you're using a group policy; You can use the 'Group Policy Object Editor' to control what a user can and cannot do via USB. including that of preventing the ability to install any device drivers. ... Sorry This is a bit vague, I'm currently at work waiting for a build to finish :)
Answer: I guess the policy is there to prevent virus infections because the computers are a Group resource and not a personal resource (eg, employees can take any PC that is available, the employee does not have a assigned "own" PC for the whole employment period).
In this case, I would recommend running some sort of kiosk/readonly solution. One example is booting the PCs over iSCSI with iPXE, where the iSCSI target is read-only. There is a bit complicated setup where you must make the first few megabytes of the read-only partition read-write and then reset this part to original each bootup, else Windows 7 BSoDs at startup.
If you can live with a Linux OS - EXCELLENT then you can host a live distro on a HTTP server and then have iPXE boot them up.
If you want to stick with drives in the computers, then Another solution is to use one of all these HDD protection cards that exist, that ensures a computer is reset to a "pristine state" each reboot.
When you have implemented a read-only/"live" solution, then you can give you employees administrator rights. It wont matter, they can download the worst trojans ever - reboot - trojans gone. If a large trojan infection happens to come, then shut down all work PCs - then start up all PCs again. infection guranteed gone.
If the policy instead is because of sensitive material on the PCs that can be leaked, I would instead recommend moving that sensitive material to "secure terminals", eg hardened PCs where the PC machine is locked into a cabinet, nothing is accessible except screen, keyboard and mouse. And then employees that want to access sensitive materials have to go to a secure terminal. In this case, secure terminals can also physically be locked in and require a access card swipe - where this swipe also unlocks the terminal, for maximum security.
If the PCs are "personal", eg the employee get a own "assigned" PC that is his for the whole employment period, and then that PC is returned or become vacant for the next employee, then I would suggest a policy where "you are responsible for your own PC". Let them do whatever they want, if their PC no longer boot, its their fault. For reformatting you could have a service fee for lets say 50$. When employee leaves, then you reformat PC for the next employee free of charge.
Of course, in ALL these cases, I assume theres user isolation in the network switch activated so PCs cannot "talk" with each other.
Answer: Glue the usb connector shut. No BYOD. Put it in writing, and have a workshop.
Comment: Gluing the USB connector shut is not feasible for most workplaces - too many legitimate uses, including USB keyboards/mouses.
Answer: Alright, ultimately the sensible answer is to provide charging points for everyone at the desk, so noone gets tempted.
And, I'm sure you have a group policy in place that stops you from doing anything right? In linux, you could probably implement this as one of the udev rules.


How do i ask questions?

Question: I read ( or have read) a lot of English tenses until I mess up.
So please what is the differences between these sentences?

have you finished the homework?
are you finish the homework?
do you finish the homework?
Answer: If you want to know whether the person concerned has completed their homework, you might ask:

Have you finished your homework?

You might also ask:

Did you finish your homework?

This construction is often used with a time reference:

Did you finish your homework before you went to bed?

If you want to know whether the person is completing their homework, you might ask:

Are you finishing your homework?

NOT: Are you finish your homework.
You would not ask:

Do you finish your homework?

except when you are asking a general question, such as:

Do you finish your homework on Friday evenings to leave the weekend free?
Answer: @Ronald Sole's answer is correct -- but maybe I can explain a bit more of the "why".
As you're probably finding, tenses in English can get weird. There are many ways to refer to the place of an action in time.

Have you finished the homework?

This is correct. It's in the present perfect tense. This tense is used for actions that happened at an undefined time in the past.
Present perfect is also used when describing actions that started in the past and continue into the present, such as "I have lived in the city for 10 years".

are you finish the homework?

This is incorrect. The word "are" implies that you are trying to use the present continuous tense. This tense is used for actions that are going on right at this moment.
The present continuous tense is formed by the present tense of the verb "be" and the present participle of the main verb. The present participle is usually the base verb plus "ing": "finishing", "drawing", "riding", "talking", etc.
So this sentence, written in present continuous tense, would be:

Are you finishing the homework?

This question is asking whether the person is finishing their homework right now. If they have already finished their homework, the correct answer to this question is "no". If they are doing something other than their homework, the correct answer to this question is also "no".

do you finish the homework?

This sentence may or may not be correct. It depends on what you are asking.
My guess is that this sentence is likely intended to be using the simple past tense. In that case, you should use the past tense of the verb "to do", which is "did".

Did you finish the homework?

This is correct. This question is asking if the action "finish the homework" happened in the past.
As you've probably noticed, both the simple past and the present perfect refer to an event in the past. In this particular case, there's not much difference between the simple past and the present perfect; as long as you are talking about an action in the past, either tense is correct. Many native speakers use the present perfect tense to talk about the recent past, and use the simple past tense to talk about something in the more distant past, but that's not a strict rule.

However, just to make things more complicated, "Do you finish the homework?" might be correct. It is a grammatically correct sentence, just maybe not in the way you (might) mean it.
Consider these sentences:

Do you live in the city?
Do you pay your taxes?

Both of these sentences are in the simple present tense.
The first question is asking whether I am living in the city right now. The reason this is correct is because "live in the city" is a continuous action, and the simple present is used to describe continuous actions.
The second question is asking whether I pay taxes in general. This sentence is not asking if I've paid my taxes for a specific year. The simple present is correct here, because the simple present is used when the exact time is unknown, indefinite, or doesn't matter.
Here's a conversation where "do you finish the homework?" is correct:

STUDENT: I don't understand why I am failing math class!
PARENT: Do you finish the homework?
STUDENT: No...
PARENT: Well, that's why you're failing!

In this case, the parent is asking if the student ever finishes their homework (or finishes their homework in general).
The parent is not asking if the student finished yesterday's homework, or last week's homework -- the simple present tense means the parent is not talking about a specific time.
My guess is that your 3rd sentence was meant to be in the simple past tense, in which case "did" is correct. But the simple present is also correct, depending on what you mean to ask.

How do i ask questions?


Shut down when asked without terminal help

Question: My system has Ubuntu 11.10, and it will not shut down when asked to. It will reboot to the sign-in page. I have been using sudo shutdown -h now to shut down, but is it any way to put this into the program so ask to shutdown it will without going to terminal?
Answer: The shutdown and reboot options can only be used by a non-privileged user if they are the only user logged in to the system.  Chances are that your system thinks that there is another user on the system.
You can get a list of the active sessions using the ck-list-sessions command:
$ ck-list-sessions
Session2:
    unix-user = '1000'
    realname = 'James Henstridge'
    seat = 'Seat1'
    session-type = ''
    active = TRUE
    x11-display = ':0'
    x11-display-device = '/dev/tty7'
    display-device = ''
    remote-host-name = ''
    is-local = TRUE
    on-since = '2012-04-05T23:36:58.278097Z'
    login-session-id = '1234567890'

If you see more than one session listed, then this is the reason why the shutdown and reboot options fail and you get returned to the login screen instead.
I once had a problem where ConsoleKit believed that one of the daemons running on the system represented a user session and causing this problem, so that could be your problem.
Alternatively, if you've logged in multiple times consider logging out of your other sessions before trying to use the shutdown or reboot options.
Answer: What is the reason makes your Ubuntu not shutdown with buttons?
Try repairing your Desktop Env. from software center. This may help, may be.


How use strongarm with domain access?

Question: Lets say I have 2 domains, A (Site A) and B (Site B). I achieved this with domain access module. Then with features and strongarm I would like to export site_name variable from both domains. How can I do it?
Answer: What you want is the Domain Conf module which is a sub-module of Domain Access and provides you per-domain configuration.

The Domain Access: Site Configuration module (called Domain Conf), is
  an optional extension of the Domain Access module.  Domain Conf
  provides options for configuring basic settings of your affiliate
  sites to be different.

How use strongarm with domain access?


How does mass spectrometry detect histone methylation?

Question: In this research paper they talk about the methylation of histone.  They use mass spectrometry to identify which peptide position is methylated. Does the number yielded by the spectrometer calculate the mass of the amino acid with and without the mass of methyl group? I wonder because I saw some introduction saying the number present the molecular mass of the molecular. I also would like to ask the mechanism of it and how you interpret this data? Thank you!
Comment: Can you provide link to that paper ?
Comment: The link is http://www.sciencedirect.com/science/article/pii/S1931312813001145 Thanks
Answer: It is not simple MS, it is tandem MS. They send the sample through multiple MS and they fragment it between them. So they can get info about the molecular structure as well, not just the mass/charge of the molecule.
A quote from your article:

MS/MS spectra of the methylated H3 protein (top down) and fragments
  upon electron transfer dissociation fragmentation. Fragments of the
  methylated H3 have a mass shift of 42 starting at C14, indicating a
  modification site at the K14 at the N terminus of the peptide.
  Normalized collision energy = 35%, activation Q = 0.250, activation
  time = 100 ms, accumulation time = 5 min.

A reference from your article:

Frese et al., 2011 C.K. Frese, A.F. Altelaar, M.L. Hennrich, D.
  Nolting, M. Zeller, J. Griep-Raming, A.J. Heck, S. Mohammed
Improved peptide identification by targeted fragmentation using CID,
  HCD and ETD on an LTQ-Orbitrap Velos
J. Proteome Res., 10 (2011), pp. 2377–2388
Answer: The numbers yielded by any mass spectrometer are always the mass divided by charge (m/z).
Figure 2B in the paper shows the peaks from a peptide that was isolated and then fragmented inside the mass spectrometer. The ideal scenario is that each peak has an m/z that corresponds to a potential fragment of the peptide (or whatever is being analysed).
The fragment ions that indicate the methylation include the monoisotopic mass of three methyl groups (~42). These ions (C14 - C21) also carried two electrons. The machine provides m/z so add the monoisotopic mass of peptide + monoisotopic mass of three methyl groups + mass of two electrons and then divide by the charge (2).
The effect of the charge state can be seen when you look at C13(+;1360.79 m/z) and C14(++;766 m/z).
I didn't know how to address the "mechanism of it".


Arduino GSM Module with network GPS

Question: I have looked through the AT command set of Arduino GSM Shield boards. I dont find any AT command that provides network GPS. I wonder what I am missing. Why isn't it possible for GSM module to provide NetworkGPS (the one that is not really accurate) ?
Comment: A very simple answer could be that the firmware does not support it.
Comment: I believe the SIM900 has a command for it: http://www.puntoflotante.net/SIM900-Gsm-Location-AT-commands.pdf
But other manufacturers may have it aswell. (EDIT: the answers seem to differ and I must agree that it may not work depending on which carrier you use)
Answer: Simple answer is that it is function of cellular network (phone company) instead of the module.
More informative answer is, Position is calculated by network via

serving cell base station ID and location
when phone on standby, it monitors signal strength from multiple base stations and signal strength is roughly related to distance
when phone on transmitting, base station has one more piece of information. It calculates distance through time taken for signal to travel to multiple base stations (called 'time advance' in original GSM)

US E911 utilizes these to locate the phone.
Good technical paper with diagrams
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0CEUQFjAF&url=https%3A%2F%2Fwww.fig.net%2Fpub%2Fcostarica_1%2Fpapers%2Fts08%2Fts08_01_schwieger_2407.pdf&ei=Ms3bU8-DItfr8AXT7oLQCg&usg=AFQjCNHImn4G34WC0Naw8IH6g1gfLzykuQ&bvm=bv.72197243,d.dGc
http://en.wikipedia.org/wiki/Positioning_%28telecommunications%29
Comment: I would agree that much of the functionality is in the carrier's network infrastructure, but that wouldn't explain why it's not available on a module that is almost certainly a network who's phone clients do receive this service.
Comment: The AT command set follows international technical standard, now 3GPP, was GSMMOU. The function you want is not there, according to the standard.  Individual network use what i describe above, also in the detailed tech paper I quote, for their own use, like E911 and other commercial LBS (locate based service). Some network make the info available on commercial terms. For example, one actual implementation is auto advertisement for long distance phone call (to call home) when user pass to a new country border.
Comment: You are right in that info is available as part of the overall structure, but, not via the module AT command.  If you like more detailed tech info. http://www.telecomsys.com/products/location-based-services/infrastructure-gsm/smlc.aspx  http://en.wikipedia.org/wiki/Location-based_service  http://en.wikipedia.org/wiki/GMLC
Answer: This is a very complicated situation.  In short, the module itself does not provide Assisted GPS without both the handset's help, and the help of the carrier.
Since the module is sold as an OEM or embeddable object, the manufacturer either hasn't included such functionality, or hasn't enabled it, or hasn't documented it.
Even if it were included, enabled, and documented, it has to work with the carrier, and each carrier provides different services for different modules.  Some locate solely based on triangulation using cell towers and the module's command channel.  Others depend on the module capturing a short sequence of RF from the GPS network, sending it to the carrier's AGPS server to be processed, which then reports back a very accurate position.
At any rate, this is not a standardized function for embedded cellular modules because cellular networks and carriers vary in how they've chosen to implement AGPS.
If you want to use AGPS in an embedded cellular module, you'll need to work with both the module manufacturer and the cellular carrier to enable that functionality.  It usually involves additional charges - renting an AGPS server, for instance.  These often involve a monthly fee in addition to a per-request fee.  Some companies set up their own AGPS servers to do the processing, but the cellular company still has to provide gross location information based on the tower signal reception.
Suffice to say, this is not something that is common or cheap enough for low volume projects.  Unless you're going to be working with thousands of these devices it's typically cheaper to integrate a standalone GPS chipset in your device.

Arduino GSM Module with network GPS


Has the US government done everything it can to prove the votes were counted correctly? If not, why not?

Question: Some Trump supporters (including Trump himself) claim that votes were counted in an unfair way. Has the US government done everything possible to prove that Biden is the legitimate winner of the election, such as recounts in all contested states? If not, why not, if it could restore peace? Is it that everything that reasonably could be done to prove that the count was done correctly, has already been done and these people are akin to conspiracy theorists who go buy a different set of logic?
Comment: Re *Is it that everything that reasonably could be done to prove that the count was done correctl?* Yes. This was a very secure and very fair election. People who only talk to fellow conspiracy theorists cannot imagine that anyone else cannot think the same way. People do occasionally vote in the name of the dead, or in the name of others. This is highly criminal, but these crimes are extremely small in number. Pennsylvania found after the fact that three of the millions of people who voted in the last election were in the names of dead people. All three of those dead people voted for Trump.
Comment: In the US, the states have the responsibility to oversee elections. To ask if "the US government [has] done everything ..." is to suggest the states haven't; thus discrediting the states.
Comment: @RickSmith While it is true that the Constitution explicitly delegates responsibility for elections to the states, the federal government can do some things to help the states conduct secure and fair elections, and the federal government does do some of those things.
Comment: This is a badly framed q as @Rick notes, but it has been argued on the left that e.g. Pence or McConnell took too long to speak out against the conspiracy theories. https://edition.cnn.com/2021/01/06/politics/mitch-mcconnell-trump-electoral-vote/index.html
Comment: … been unable to find *a single example* of widespread fraud, and only extremely tiny and irrelevant examples of individual fraud or even just honest mistakes, many of which actually *benefiting* Donald Trump is probably going to be the best we will get until there is a new administration.
Comment: I think the down votes were a bit harsh considering there were good answers given in comments and the main body
Answer: Trump has been claiming the election would be fraudulent since at least April of last year. He also claimed that the 2016 election was fraudulent, even though he won. At no point has he or any of his supporters provided any evidence of the widespread fraud he has been claiming. Everything necessary to confirm the results has been done, but Trump refuses to accept the result and continues to spread misinformation and false claims of fraud. He is not interested in restoring peace, and has been actively stoking division and riling up his supporters.
At this point there really is no controversy about the election result (there never was a controversy other than that manufactured by Trump himself) and the fraud narrative is being pushed only by Trump and sycophantic Republicans and media outlets who seem to think this will benefit them by ingratiating themselves with Trump's base, who won't just go away once Biden is president.
Aside from all of that, it is not the US (Federal) Government's responsibility to carry out elections. That is the responsibility of the individual state governments, each of which have certified that the results are accurate (after recounts where necessary) according to their own laws and processes.
Comment: @EkadhSingh Thanks. Normally I would agree that it's unnecessary and could be interpreted as bias. However in this case I think it's important to stress that there is no basis in reality for the fraud narrative and the only reason it's *still* being pursued is to appease Trump and his supporters.
Comment: @EkadhSingh I disagree with your edit. The word "sycophantic" was doing a lot of heavy lifting. It's not all Republicans and media outlets that are pushing the fraud narrative, only those that are sycophantic to Trump to the extent that they are denying reality.
Comment: Okay, my bad. You can roll back the edit.


Microphone should work and yet it doesn't?

Question: Testing it through windows and realtek with the "listen to voice" option on makes it work perfectly and I can hear my own voice. However when talking through it in another software such as discord and skype, no sound can be picked up because its apparently too quiet. Drivers are up to date and the sound is maxed out from the "Sound device" options.
Answer: I've used discord in the past, not so much recently, but I remember having to change my input device so it was using the right device for audio in. Even with other programs like Audacity or Adobe Audition, I've always had to select the audio in device. So check in the settings for the voice channel and see if it's using the right device. Might even try and make sure the microphone is set as the default communication device.
Regards,
Chris
Answer: Your signal path is interrupted somewhere.
Trace every link in the chain, being clear that it is passing the signal.


Multiple perpendicular cross sections

Question: I am working with QGIS and I have a DTM of a river. I need to extract multiple cross sections (one every 10m), and they must be perpendicular to the river center line.
Can you tell me how to do that, with the passages?
Comment: Hi Elena, welcome to GIS SE! Try to divide your project into atomic, specific, or non-trivial tasks. Do you have already the center line of the river? Do you have it densified with a vertex each 10m? Do you have perpendicular lines? If yes, you can ask about how to extract the cross sections from the DEM. If not, you can ask about the specific step where you are stuck.
Answer: Try Cross Profiles tool in the Processing Toolbox > SAGA > Terrain Analysis - Profiles.

(1) Make sure to reproject your DEM to XY(m) coordinates.
(2) Prepare your river center line(s), perhaps by digitizing manually.
(3) Start the tool and set each parameters:

DEM: Your DEM layer
Lines: Your river line(s) layer
Profile Distance: 10m
Profile length: The length of profile you need.
Profile Samples: Number of sampling points along the cross profile. Please calculate this number beforehand by profile length(m) * 2 / sampling interval(m).

Multiple perpendicular cross sections


I'm new to learning Korean, and I'm really excited, but, I'm not sure where to start. Does anyone have any tips for a newbie like me?

Question: I started trying to learn Korean like 2 days ago, but it doesn't make any sense to me at all. I tried learning it because I heard it's super easy to learn. Does anyone have any tips for a beginner like me?
Answer: I would suggest learning hangul first (the Korean alphabet). Then, I would learn grammar (there are many websites and courses where you can learn it) and then pick up vocabulary along the way :)
Besides that, I think consistent exposure to Korean is important for you to learn how the different grammar points are used.
good luck!
Answer:
I tried learning it because I heard it's super easy to learn.

I can't see in your bio where you're from, but if you're a native English speaker, I don't think any Asian language is going to be super easy to learn... The alphabet is different, the vocabulary has very few similarities to English, the grammar is all different.... If you really find Korean easy, you're a language genius!
For English speakers, I think Korean is very tough compared to learning, say, French or Spanish, which have a lot of similarities in vocabulary with English.
Having said that, the Hangul alphabet is easy to learn, and (as emz says) is an obvious starting point. And if you know English and Hangul, you already know words like 주스 and 비타민.
Also, you say in your bio that you are learning Japanese - and there is a lot of Sino-Korean (Chinese-derived vocabulary) vocabulary that has similar equivalents in Japanese. An example is 만화 - see https://en.wikipedia.org/wiki/Manhwa#History_of_the_term.
I think you'll be disappointed if you expect Learning Korean to be easy, but it is probably something that will go well with learning Japanese. This article on medium goes into some more ideas as to why.


What is difference between two Thread Forming Taps?

Question: What is difference between Thread Forming Taps: 1/4-20 UNC GH6  and  1/4-20 UNC-2B HSS Right Hand Taps?
Answer: The GH number tells you the fit of the threads. I don't know what 2B is but I imagine it is something similar.
So you can have a looser fit, or a very tight, precise fit, or you might be expecting dimensional changes after heat treatment or plating operations so the threads need to be cut oversized or undersized beforehand to compensate (same with your tap drill size).
Basically your tap drill size determines the minor diameter of the threaded hole while the tap determines the major diameter of the threaded. At least with cut threads. With formed threads the tap drill size and the tap fit need to go hand-in-hand for proper thread formation.


Cosmological Redshift Data

Question: Is there somewhere on the internet I can find cosmological redshift data.  In particular, I would like to know the redshift around the time when the acceleration of the Universe began to accelerate.
Comment: Have you looked at the supernova cosmology project papers?
Comment: @RobJeffries, I did look at the supernova cosmology project and I was able to get data for distance modulus, but I'm looking for redshift data as a function of time.
Comment: @ChrisL. If you want that, in particular, you're going to have to do some work to convert things that get measured into a quantity you want. Since that conversion is dependent on the cosmological model, you'll have to figure out how to calculate those quantities using the models you want to test.
Answer: One of the main places where data about galaxies gets aggregated is the NASA Extragalactic Database (NED). For example, here's the information page for M101 with the default cosmology in their search form. In particularly you want to look at the redshift-independent distances, and the redshift data points. Using the 'Metric Distance' you can calculate the cosmological redshift it would have if it weren't moving (for a given cosmology) by numerically inverting equation 15 from Hogg's cosmology calculations summary paper (probably have to numerically integrate, too).
Note that the peculiar velocity (velocity relative to Hubble flow) is usually around hundreds of kilometers per second. So, for any redshift greater than about $0.01$ (equivalent to a radial velocity of about $3,000\operatorname{km}\operatorname{s}^{-1}$) is almost certainly entirely dominated by the cosmological redshift of the object. There are a lot of databases replete with redshifts of galaxies that stretch back to round $z=1$ for ordinary galaxies, and much further carefully selected galaxies and active galactic nuclei/quasars. For example: Sloan Digital Sky Survey (SDSS), DEEP2, the AGN and Galaxy Evolution Survey (AGES), and Galaxy and Mass Assembly (GAMA). This list is nowhere near complete, of course.
Answer: Redshift of the time when the universe started to accelerate:
From Friedmann's equations:
$$\dot{a}=aH=H_0\sqrt{\Omega_{m0}/a+a^2\Omega_{\Lambda 0}}$$
required is:
$\ddot{a}>0$.
Calculation gets you
$$a=\left(\frac{\Omega_{m0}}{2\Omega_{\Lambda 0}}\right)^{1/3} \approx 0.6$$
$\rightarrow z=1/a-1 = 0.67$

Cosmological Redshift Data


Shortest path with a start vertex that touches all nodes at least once with repeats allowed

Question: I tried looking this problem up for quite a bit now, but can't seem to find a whole lot of discussion about this. At first it sounded like the TSP to me, but I don't think so (it's much harder to do I believe). Maybe I am over thinking this though? I'm not looking for the fastest solution, but I fear a brute-force algorithm may take an extremely long time to perform this on a undirected graph with say 30 nodes. I'm personally trying to figure out on a video game the fastest way to traverse through every spawn point of a monster on a given zone (with a start point of course) so I can find him faster. I've already constructed a graph and figured out the distances assuming a complete graph. I guess on my part, one way to reduce the run time of such an algorithm is to remove realistically what edges wouldn't and probably wouldn't be included in a optimal path. I assume adding lots of constraints could help too. Might anyone know if there's a specific name for this problem, or if there is a simpler approach aside from just the standard brute-force? Thank you!
Comment: Can you clarify whether the path should go back to the start vertex? Are you interested in approximation algorithm?
Comment: From your description it is not clear why this is not a TSP problem.
Comment: Sorry I should've said it explicitly. We don't want to go back to the start vertex, we just want to touch everything once!
Answer: Your problem is just a TSP in disguise.
1. Dealing with "visit each node at least once"
First, compute a modified distance matrix $D(i,j)$, $i,j=1,...,n$ using an all-pairs shortest path algorithm, such as the Floyd-Warshall algorithm. That is, you want $D(i,j)$ to be the shortest path length from node $i$ to node $j$. Using Floyd-Warshall you also compute a matrix $S(i,j)$ that gives the successor of $i$ on the shortest path from $i$ to $j$.
Now apply a TSP algorithm to the distance matrix $D$. This will give you a tour $T$ that goes through each node exactly once. You now expand each step of $T$ into a shortest path (you can do this using the matrix $S$). That is, if some step of $T$ goes from $i$ to $j$, you expand it into the shortest path from $i$ to $j$. Concatenating all these paths gives a tour $T'$ that visits each node at least once, with possible repeats. If $T$ is optimal for $D$, then $T'$ must be optimal for the original graph.
2. Dealing with "the tour does not need to return to the starting node"
Preprocess your graph as follows. Add a dummy node, node 0, such that the distance from 0 to the starting node $s$ is 0 and the distance from node 0 to any other node is $M := n \cdot \max_{i,j} D(i,j)$.
Now find a TSP tour on the modified graph using your TSP algorithm of choice.
Because the value of $M$ is so large, any optimal TSP tour will be of the form
$$ 0, s, \pi(1), ..., \pi(n-1), 0$$
where $\pi$ is some permutation of the nodes excluding the start node and node 0. Then the sequence $s, \pi(1), \ldots, \pi(n-1)$ represents your solution.
3. Exact vs heuristic
You can use any algorithm for the symmetric TSP problem. If $n$ is about 30, you will probably not be able to apply an exact (= optimal) TSP algorithm such as the Held-Karp dynamic programming algorithm. A very simple yet reasonable  heuristic you might want to try is 2-OPT, which is straightforward to program. A branch-and-bound approach might also work well in practice.
Comment: I guess a question then to ask is, what's the last step to not return to the start node?
Comment: Thank you for the amazing details :) I wish I could upvote your answer, but I don't have enough reputation!


Having to press submit button a few times in java web application

Question: I have a java web application and I am submitting some data in one of the forms using a submit button. I use servlets. However, I am having to press the submit button a few times before I reach the next step. I would have uploaded the code or provided some more information but I'm not sure which part to upload and I've no idea what this issue is about. Can someone advise me as to how to approach this issue?
Answer: The first thing I'd do is open up FireBug if you're using Firefox, or press F12 for IE. From there you'll be able to see the requests being sent to the server and the response. Keep an eye on those as you click the button.
Answer: There is a very useful tool for working with requests:
https://addons.mozilla.org/en-US/firefox/addon/tamper-data/
It is a FireFox add on, but monitors all the requests and lets you change them before they are sent.


How to export GMap configurations?

Question: I have a View block which renders a map through GMap formatter and includes two fields - Company Name and Address. When I export it through features and try to render it on another system, the map doesn't show up.
I've given custom height and width and some other configurations in GMap under Configurations > Web Services > GMap. I think the problem is that the configuration settings for GMap are not being exported with the feature. Is it possible? If so, how to export them?
Here's an image of the View
Answer: I found from my seniors that these configurations (in this case GMap configurations) are stored in variables and Strongarm module can be utilised to export them. After enabling Strongarm module, these variables will be available for exporting under Strongarm Feature Component in Features UI. The other system/environment on which these variables need to be imported will also need to have Strongarm module enabled.
Though these configurations were exported from my system and imported on the other system properly, the map still didn't show up on the other system, the reason being that the devel generate module which we were using to generate content of Contact content-type was unable to generate dummy latitude and longitude for the Location field (enabled through Location module). I entered those latitude and longitude values manually, saved the changes and vola! the map was rendered.
Note: In my case, I wasn't using a Google Maps API key so that wasn't a problem.

How to export GMap configurations?


How far off the ground would an android have to hover to not cause damage with their ionic thruster(s)?

Question: If a humanoid robot or other similar weight and sized robots used ionic thrusters on their feet/base of their body to fly and hover along the ground, how far would they need to hover from the ground or near things to make sure the thrusters don't cause any damage to surfaces or things?
Comment: The world most powerful ion engine can produce a whopping 290mN of force... my apologies you'd better stick to jumping that's over 9000000mN!
Comment: There are ion engines which throw ions behind them at great speed, and ion engines which use charged particles to entrain air and make wind.  What are your robots using?
Comment: Throwing heavy ions at immense speeds will be very tough on the surroundings.   That is particle radiation.  You would be able to tell where Iron Man had landed because all the vegetation there would die of radiation poisoning.   That method works fine in space where you are limited in what you can take with and there is nothing around to kill.  But in the atmosphere probably safer to throw large volumes of charged gas around at slower speeds.
Comment: I was sure what method they should use to hover, rotary blades or jets might be the most effective but they don't seem advanced enough for an advanced civilization.
Comment: @willk from your previous suggestion some of my small drones will use that method as well as an earlier flapping method, for these human sized robots one idea is iron man style feet and hands another is hovering life forms or robots, I don't know which engine is best for the task of lifting a mass of 50kg-200kgfor flight and hovering with precision movements?
Comment: @Willk Great thanks.
Answer: "Ionic thrusters" ...
If you talk about ion drives, in the real world these are low-thrust, high-$I_{sp}$ designs. Good to move a space probe, but unable to hover in any serious gravity field.
Real ion drives have been tested in chambers like these, which gives you an upper limit on the safety distance -- less than the length of the chamber.
Comment: They also function only in vacuum (which is why they need to be tested in chambers like those). There's also "lifters" which work by partially ionizing and propelling air, but those are bulky, fragile, and hopelessly inefficient...I'm not sure if one's been built yet that can lift its power supply. In the real world, you'd only use ion thrusters to "hover" on small asteroids, and it'd be more like stationkeeping next to the asteroid.


Changing the backgound of a lot of images in GIMP of Pixelmator

Question: How do I bulk change the background of the images to White. I have 400 Images of jewelry in which I want to batch edit them to change their background.
Answer: You'll probably need to use a batch script to accomplish that.
How difficult this is depends on the individual images.
If they all have, for example, black cloth backgrounds it won't be easy. but not impossible. If all the backgrounds are different,it will be significantly harder


Why it is said to recite any mantra 108 times?

Question: In order to complete any prayer or sadhana, it is said to repeat any mantra for at least 108 times ? What is the significance and importance of that ?
Answer: It is taken from here.

1.There are 9 planets in the solar system and 12 zodiac sign which are moving on 9 planets. So 9 X 12=108.This is simple says that one should
  chant no 108 for respecting the solar system .
2.In Sanatan Dharma there are 27 stars and each star has four Pada or Padas. So 27 X 4=108.So 108 has long been considered a sacred number
  in Hinduism and yoga.
3.Diameter of the Sun is 864327 miles and the Diameter of the moon is 2159 miles. If you multiply the diameter of Sun and Moon with 108 then
  you will find the distance of Sun and moon from the earth.
4.The number 108 represent the ultimate reality of the universes. The number 1 denotes that one thing and 0 denotes that nothing and 8
  denotes everything or infinity.
5.There are 54 letters in Sanskrit alphabet.Each has masculine and feminine,Shiva is the masculine and Sakti is the feminine. So it 54 X
  2=108.In some other arguments that Atman of human beings goes through
  108 stages on its journey. There are 108 upanishads for which it is
  beneficial to chant 108 times


Accelerating a Magnetic dipole through a uniform magnetic field

Question: If an (uncharged) magnetic dipole travels through a uniform magnetic field with uniform velocity perpendicular to the direction of the B field (lines) it experiences no force. But if I somehow ACCELERATE the magnetic dipole through the same uniform B field will it experience in its frame a magnetic field gradient and therefore experience a force? IOW, under acceleration does it see a spatial gradient dB/dr...and thus experience a force in the direction of the neg. gradient.
And if so, can someone derive or supply the equation of motion please. Thanks.
Answer: I could give you an answer only for such elementary particles like neutron and electron.
Lorentz force for electrons
From yor question it seems clear that you are familiar with this phenomenon. To go over to the neutrons behaviour first I have to explain to you what is the mechanism behind this deflection.
Perhaps you know that electrons have an intrinsic magnetic dipole moment and a parallel to this moment itrinsic spin. If an electron is under the influence of an external magnetic field the electrons magnetic dipole moment gets aligned.
If this happens with a moving (no parallel to the external field) electron the gyroscopic effect takes place and the electron gets deflected sideways. But any deflection is in physics an acceleration and since we observed many times, an acceleration is accompanied with the emission of photons. Photons have momentum and the emission from the electron dissalign the electrons magnetic dipole moment again. The game starts again until the electron came in rest to the external magnetic field.
Force on a neutron from an external magnetic field
What is the difference between a neutron and an electron? The neutron has no electrical charge and the values of the intrinsic spin and the magnetic dipole moment are different (but existing!). To make a experiment with neutrons is more difficult due to their production and their high velocity as well as their approx. 1000 times - in comparison to the electron - mass. But due to the neutrons intrinsic properties and kinetic energy it will be deflected in an external magnetic field.
So your statement

If an (uncharged) magnetic dipole travels through a uniform magnetic field with uniform velocity perpendicular to the direction of the B field (lines) it experiences no force.

makes somehow sense only for macroscopic bodies. But here are some phenomena observable too. It will happens a separation of electrons in some directions of the body. The magnetic dipole will be aligned and this is a force. Some RM radiation takes place, this will slow up the body.
So could you be more specific what you want to find out with your question?
Comment: Fiedler   ...  So you think the trajectory of an UNCHARGED particle with a magnetic dipole  traveling perpendicular to UNIFORM Magnetic field lines will deflect ??
Comment: Gary, if this particle is a neutron, yes, it will be deflected. But this is difficult to prove in an experiment and it is as I know not performed until now and so it is a prediction.
Comment: @Fiedler   ... prediction based on what?
Comment: Prediction based on the fact that since neutron has an intrinsic spin and a corresponding magnetic dipole moment the behaviour in an external magnetic field will be similar to the behaviour of protons, electrons as well as of the antiparticles.
Comment: Ok; but I was under the assumption that it was the CHARGE of a particle that caused the deflection in the trajectory...not the dipole moment  Doesn't standard physics say a magnetic field alters only the alignment of the spin moment (not the trajectory) in a uniform field??
Comment: About what says standard physics you are right. Otherwise did Ampere and Lorentz - you name it - know anything about intrinsic spin? Only since the Einstein-De Haas- experiment it is proofed that spin is the reason for deflection, similar to the gyroscopic effect.


What is Dark Souls' frame rate on PS3 and Xbox 360?

Question: I'm musing about possibly getting the remaster on Switch, running at   30fps and I'm curious about the original frame rate on the Xbox 360 and PS3.
Comment: Hopefully I didn't edit the post too heavily. The title is now more SEO-optimal as well.
Comment: Depends, in Blight Town or outside of Blight Town?
Answer: I don't know about Xbox 360 but on PS3 it has 30 fps at 720p.
Comment: The original Dark Souls game was locked at 30 FPS for all platforms, but on PC you were able to unlock it by using DSFix.
Answer: Locked at 30fps according to Digital Foundry (performance analysis video):

[...] at a locked 30 frames per second, just as with the PS3 and 360 entries.


How to best inform users that a monthly process includes today

Question: I have a dropdown where a user can select a date they want they want to auto pay their bills every month. For example, if they choose the 12th, every 12th day of the month they will be charged for the balance on their account. How do I best inform users that if they choose the 11th and today is 11th that their account will be charged today?
Comment: You can not hide today as an option to select?
Comment: @Danielillo Welcome to UX.SE! Allowing the user to set up automatic billing for the current day is a valuable feature, and requires only a bit of extra work to make it unambiguous to the user. I don't think we should take it away to avoid that bit of work.
Answer: Consider replacing the dropdown – which is simple to implement but less intuitive for date data – with a more natural calendar widget that pops up the current month, wherein the current day is distinguished visually (both color and marker for visual accessibility).
Try prototyping that solution.
Then, if it proves to not feel right in your case, use the prototype as a reference point and increment the dropdown 'towards' that solution. The calendar widget will expand your thinking and will suggest new ideas.
Perhaps the dropdown list items can be given more structure. Possibilities include: the current day can be separated by non-selectable delineations, given a css color, amended with the label of "today" with a typographic variance.
Once a selection is made, generate a plain language summation with special case:
Your bill will be paid on the 11th of every month.
(!) Your first payment will occur immediately today.

Comment: Welcome to UX.SE! I agree. I think regardless of whether the date is selected with the calendar widget or the original dropdown, the main issue is resolved by "Once a selection is made, generate a plain language summation..." to clarify any ambiguity.
Answer: Next to your drop down, add the date of the first payment and the number of days from now.
For example:
Day of month: [ 11 ]
First payment: May 11, 2018 (today)

Day of month: [ 12 ]
First payment: May 12, 2018 (tomorrow)

Day of month: [ 10 ]
First payment: June 10, 2018 (in 30 days)

If one of the choices will cause the user to pay separately for the current cycle in order to avoid being late, prefer a default value that isn't one of these choices, and consider alerting the user if they make one of these choices, for example:
Day of month: [ 10 ]
First payment: June 10, 2018 (in 30 days)
Warning: your account will be past due by then.
[Start today instead]


What exactly is an electric hook up?

Question: An ENG-GER dictionary (there seem to be no entries in monolingual dictionaries) tells me that it is a power connection, but search results from Google and Google Images let me assume that the term is used only for outdoor purposes, and especially for camping sites. Is this correct or what else would be an appropriate meaning?
Comment: Can you add the German word or phrase? I think you are right though, in that it refers to connecting some usage point to an electric supply.
Comment: The German word given for this is "Stromanschluss", which means a power connection in general. The translation was taken over from a picture dictionary, which also shows a camping site.
Answer: According to Cambridge online dictionary, hook-up means:

a connection to an electricity supply, a telephone network, the internet, etc.

In North American English variants, hook-up typically means the connection to any utility, irrespective of where. The meaning is very generic. Your house might get a new telephone hook-up, or Rogers might be hooking up your new Internet.

I wish my home Internet hook-up was as fast as the power at our campsite: took them half an hour!
Answer: "electric(al) hook-up" often refers to the hook-up cable (basically a wire) with which you can connect your unit to a bollard (power bollard or electrical distribution bollard) or a utility post. Either end of the connection is called a hook-up point. Sometimes "electric(al) hook-up" refers to the action, like in, "I've established an electrical hook-up to my computer". (Camping and caravanning club)
Comment: Hookup does not refer to the cable, it refers to the provision of the electrical source.  By hooking up you are able to maintain the leisure battery.  The cable you show has the European standard outdoor electrical connections.  While it is used for hookups, it is not specific to them.

What exactly is an electric hook up?


How to understand rational functions?

Question: I know that if we divide a number by a tiny decimal we get a very large number, and that we can't have zeroes in a fraction or in the denominator, so that the asymptotes defines the functions limits regarding this? But I have a hard time understanding why a rational function looks like it does. The graphs are going in all directions, how can anyone see the connections here? Like in this example.
Comment: It will have asymptotes where the denominator vanishes.
Comment: Thank you. Yes, I can see this, but if you look at my example where I have found the three x if the function equals 2x+4. The line goes through (excuse me my Norwegian/English math) one zero point, one bottom point and 0.5. And in different "quadrants"(are there six?). I don't understand this at all. How can the graph be all connected and come in from all directions.. Maybe the wrong question to ask, I appreciate any help
Comment: The graph goes crazy at only two places. One near x = -1 and another near x = 1. Everywhere else does the graph look normal to you ?
Answer:
and that we can't have zeroes in a fraction or in the denominator

It's no problem to have zeroes in the numerator. Even the denominator can have zeroes, but the function won't be defined there; i.e. if the denominator becomes zero, the fraction becomes meaningless (you can't divide by $0$...!).
To understand how the function behaves, I think it might help to see how the numerator and denominator behave, separately. Since these are both polynomials, their behavior is simpler and easier to understand.
If you then fix a certain point on the $x$-axis, you can look at the values of the numerator and denominator and consider that the actual rational function will be the quotient of these values. The behavior of the rational function then follows from how fractions work:

if the numerator has a zero and the denominator doesn't, the fraction is $0$ so the function will pass through the $x$-axis;
if the denominator tends to zero (becomes smaller and smaller in magnitude) and the numerator doesn't, then the fraction becomes arbitrarily large (in magnitude);
if the numerator and denominator have the same sign (both positive or both negative), the function will be positive; it will be negative when the numerator and denominator have different signs;
...

With the graphing software you used to plot the rational function, plot the functions $x^2-4$, $x^2-1$ and $\tfrac{x^2-4}{x^2-1}$ and experiment a bit: you combine the (simple) behavior of two polynomials with how fractions work.
Answer: In this answer I will use "large" and "small" to mean "far away from $0$" and "close to $0$" respectively. This is not the standard meaning of those words (especially not for negative numbers), but it will suit my answer very well, and therefore I will use it like that this time.
Along the left side of the left asymptote, you're dividing a negative number which is not very small ($x^2-4$ is negative close to the asymptote, and its value is close to $-3$) by a very small positive number ($x^2 - 1$ is positive and small close to the left side of the asymptote). The result is a very large negative number, which means that the graph of the function appears far below the $x$-axis.
On the right side of the first asymptote, on the other hand, both the numerator and the denominator of the fraction are negative, so the answer is positive. Also, the numerator is still not very small (still has a value close to $-3$) while the denominator is very small. Thus the value of the fraction will be large and positive, so the graph of the function will appear far above the $x$-axis.
For the right asymptote, you get an exact mirror image of this entire process.
Also, note that zeroes in the numerator aren't a problem at all. Your numerator has value $0$ when $x = 2$ or $x = -2$, and you can see that your graph intersects the $x$-axis at those points, so the rational function is also $0$ there. Things get interesting when both the numerator and the denominator have a $0$ for the same value of $x$, since for $x$-values close to that value the fraction will then be two small numbers divided by one another, and the exact behaviour of the function and the graph depends on whether they are about equally small, or if one of them is a lot smaller than the other.
Answer: $$f(x) = \frac{x^2-4}{x^2-1}$$
Let's do some calculation on this function with tools that you know from school.
First of all the function can be written as:
$$f(x) = \frac{(x+2)(x-2)}{(x+1)(x-1)}=:\frac{E(x)}{D(x)}.$$
Here I simply used the third binomial theorem $(a+b)(a-b) = a² +b²$. The notation with $E$ for enumerator and $D$ for denominator are simply for easier writing.
Domain:
The domain of this function is given by $ℝ\setminus\{-1,1\}$. These two points are the roots of $D$, and additionally it is $E(\pm1)\neq0$.
Points that fulfil this condition ($D(x_0)=0, E(x_0)\neq0$) are called poles. And since the English wikipedia article is pretty bad, here is the general definition:

Let $g=\frac{A(x)}{B(x)}$. Let $x_0$ be a root of $B$ of order² $k$. Then

If $A(x_0)\neq0$, then $x_0$ is a pole of order $k$.
If $x_0$ is also a root of $A$ - with order $j$, then:

$j<k$ ⇒  $x_0$ is pole of order $k-j$.
$j≥k$ ⇒  $x_0$ is a discontinuity¹.

¹I am not sure if that is the correct English term. Basically it means, that the function will not tend to infinity, and is simply not defined at that point. E.g. take the function $f(x) = \frac{\sqrt{x}-1}{x-1}$ on $ℝ_{≥0}\setminus\{1\}$. As you can see here, this function does not tend to $\pm ∞$ at $x_0=1$.
²Root of order $k$ means, that you can write $B(x) = (x-x_0)^kR(x)$ with remainder $R$.

In our example we have the case that $x_0=\pm1$ are poles of order $1$. So you already know that $f$ must tend to $∞$ or $-∞$ for $x→\pm1$.
Roots:
The roots are defined by $f(x)=0$. Since $E(\pm2)=0$ and $D(\pm2)\neq0$ we already found our roots with $\pm2$.
Intersection with y-axis:
This is pretty simple:  $$y_0= f(0) = \frac{0-4}{0-1} = 4.$$
At this point we already have a pretty good understanding of the functions. But what is still missing is the asymptotic behaviour at $x→\pm∞$ and at the poles.
Asymptotes (horizontal):
We can rewrite $f$ to:
$$f(x) = \frac{x^2-4}{x^2-1} = \frac{1-\frac{4}{x^2}}{1-\frac{1}{x^2}}$$
Hence we get:
\begin{align*} f(x) &→ \frac{1-0}{1-0}=1, \qquad x→∞ \\
 f(x) &→ \frac{1-0}{1-0}=1, \qquad x→-∞
\end{align*}
Which means, the horizontal asymptotes are at $y=1$ for both $x→∞$ and $x→-∞$.
Asymptotes (vertical/poles):
We know that the roots are $\pm2$ and the poles are at $\pm1$. Also we know that $f(0)=4>0$. Therefore $f$ can't pass the x-axis in the interval $(-1,0]$ and $[0,1]$. It follows:
\begin{align*} f(x) &→ ∞, \qquad x→-1,\qquad  \text{ with }x>-1 \\
 f(x) &→ ∞, \qquad x→1,\qquad  \text{ with } x<1
\end{align*}
If you have trouble following this argument, then have a look at the graph of your function. Assume that $f(x) → -∞$ at $x=-1$ coming from the right. Now if you move from $4=f(0)$ to $x-1$ you would need to cross the x-axis to reach $-∞$. And that is not possible - as the argument above tells you.
This is the behaviour of $f$ at the pole $x=-1$ "coming from the right", and at $x=1$ "coming from the left.
The same works for the other side of the poles. We know, that $f(x)>0$ for $x<-2$, as $x=-2$ is a root, and $f(x)→0$ for $x→-∞$, and there are no other roots in $(-∞,-2)$. As $x=-2$ is a simple root (=root of order 1) we know that the sign of $f$ will change. [At multiple roots, e.g. $x=0$ of $g(x)=x^2$, the graph might "bounce" off of the x-axis.]
Therefore, it follows that $f(x)<0$ in $(-2,-1)$. And since there are no additional roots in $(-2,-1)$ we follow:
\begin{align*} f(x) &→ -∞, \qquad x→-1,\qquad  \text{ with }x<-1 \\
\end{align*}
Using the same argument for the positive pole we get:
\begin{align*} f(x) &→ -∞, \qquad x→1,\qquad  \text{ with }x>1 \\
\end{align*}

Conclusion:
At this point we have all necessary information to draw the behaviour of this function:

$f(0)=4$
Roots at $-2$ and $2$.
Poles at $-1$ of "type $-∞/∞$" and $1$ of "type $∞/-∞$.
$f→1$ for $x→-∞$ and $f→1$ for $x→∞$

Note that to really draw this function exactly, you would also need to compute the derivatives, to see that e.g. $x=0$ is a local minima and not a turning point.

How to understand rational functions?


Problems with taking the first difference of a stationary series

Question: Suppose you have sufficient observations for running a time-series regression, but you do not have sufficient observations to accurately test for the stationarity of the residuals. If you do take the first difference (as a conservative approach), you have the possibility of have taken the first difference in a model in which the residuals might be stationary, although you do not have the data to confidently test for that. What are the problems that you are risking to meet with this approach?
Comment: You may search for "overdifferencing" online to find some relevant sources.
Comment: Also, there a quite a few good posts if you search for ["differencing"](http://stats.stackexchange.com/search?q=differencing). Just dig into them, and you will find a lot of relevant information.
Answer: Lets say your time series $x_t$ is stationary, as you say. You didn't say what type of stationarity so I'll assume each $x_t$ represents an iid observation from some distribution.
What can happen, then, if you form a series $d_t=x_{t+1}-x_t$? Right off the bat, its highly likely that your resulting distribution will change (unless they are normally distributed), but worse, you run the risk of inducing an artificial autocorrelation structure in your time series: Large differences tend to be followed by equally large differences in the opposite direction (so as to preserve the stationarity of the undifferenced time series). Finally, the variance of the time series will actually increase: $\operatorname{Var}(x_{t+1}-x_t)=2\operatorname{Var}(x_{t+1})$, since the $x_i$ are iid. Had your observations actually been positively correlated, then it's likely this would decrease for strong correlations.
However, you should be able to check the correlogram of your time series to identify any autocorrelation and/or trend. At least check the autocorrelation statistics before and after differencing to see.
Comment: Saying *I'll assume a strong form of stationarity: each $x_t$ represents an iid observation from some distribution* may be misleading as there is an established time series notion of strict stationarity / strong stationary which is **not** that $x_t$s are all i.i.d.
Comment: @RichardHardy ah..ok, that would be misleading...I'll just say we'll assume iid and leave it at that.
Comment: The thing about this situationis that you cannot test accurately test if the variables do have a unit-root or don't  -- because of the low potency of tests such as the augmented dickey fuller for a relatively small number of observations. But then again, is there a heuristics here? For instance, if there is no evidence for autocorrelation for the estimation of the series without differencing them, the residuals are tested to be stationary (this might not be true, as it was explained) and appear to be normally distributed, one could proceed without conservatively taking the first difference?


Dynamic routing algorithm

Question: In static routing where the network parameters dont change, we can use Djikstra's or Bellman-Ford's algorithm to find the shortest path to send data from source to destination.However in dynamic routing how do we do that?
Answer: $DVR($uses Bellman-Ford algorithm to reach the next hop e.g., $RIPv_1)$ and Link state$($uses Dijkstra algorithm for finding the shortest path to keep the knowledge of entire topology e. g. $OSPF)$ is the example of dynamic routing protocol.
In dynamic routing routers exchanges the routes (routing database) periodically with neighbors (for $DVR$) or with whole entire topology(for $OSPF$) to confirm that "is there any change has made in route"? For example if there is any broken has happen in route then router will  find alternative route to reach any other router.

Dynamic routing algorithm


How can I describe a square in OpenGL ES 2.0?

Question: I need to draw a Tic-Tac-Toe board in Xcode using OpenGL ES 2.0. I am new to graphics programming and can't find good information on drawing a square in opengl es in iOS. I looked at Ray's tutorials, which are good, however he covers drawing a rotating cube. All I want is a square; how can I describe a square for OpenGL?
Answer: This tutorial from Ray covers preparation of the OpenGL render pipeline and the setup required to describe a square. It's about halfway down.
Specifically, to draw a square you'll want to draw two triangles. Ray's code organizes them like this:

That's four vertices and six indices (two sets of three):
Vector2 vertices[] = {
  Vector2(1, -1), Vector2(1, 1), Vector2(-1, 1), Vector2(-1, -1)
};

short indices[] = {
  0, 1, 2,
  2, 3, 0
};

(Ray's tutorial uses 3D positions and also provides color information, which I'm excluding for brevity.)
Store this data into the appropriate buffers using glBufferData (assuming you've previously created both buffers):
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, 4 * sizeof(Vector2), vertices, GL_STATIC_DRAW);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, 6 * sizeof(short), indices, GL_STATIC_DRAW);

Then use glDrawElements to submit the draw command to the card.
Note that you'll likely need to adjust the coordinates of the vertices depending on your current projection matrix (et cetera); the provided coordinates will fill the screen when the transformation pipeline is configured with a series of identity matrices, but is only really suitable for initially bootstrapping rendering.


Weird normals(I already Recalculate Normals,Remove doubles)

Question: So I am having a problem with my mesh I am not positive if it is normals I am a bit of a noob to blender probably been using it for 2 months  and I don't know something you may know
any help will be appreciated this is how it looks like
https://i.gyazo.com/21b0692adb4aafb5e089992e9361a344.mp4
ask any questions
and as I said
I already remove doubles and recalculated normals
Here is the file

Fixed
Comment: It's a bit hard to tell from the clip, any chance you could upload your .blend file? You can do it here - https://blend-exchange.giantcowfilms.com/
Comment: Yes give me one second
Comment: I have added the blend file
Comment: Hey. I think you uploaded your .blend1 instead of your .blend. Do you mind re-uploading? The file cannot be opened otherwise.
Comment: Sorry one second
Comment: Okay I done it it should work now
Answer: Ok, there are a couple of problems here.
The first and foremost is that you have many edges marked "sharp".

To fix this, simply enter edit mode, select the whole mesh (A), right-click and select "clear sharp"

However, as you can see, the mesh is still affected because of "ugly" topology. Blender favors the use of Quad based topology, and though sometimes tri's or n-gons are unavoidable, they are best kept on flat (non curved) surfaces. To reduce the chance of shading based artifacts, always try to keep your mesh as quad-based as possible.

To fix this for your project, you can either re-topologize it manually, or an easier approach would be to use a Remesh Modifier, either in it's own, or in conjunction with manual adjustments.

Once this is done, if you want your mesh "smooth" again, you could add a Subdivision Surface Modifier, and shade smooth. (NOTE - the smooth shading did not work properly for me until I applied the Remesh Modifier. I am currently using 2.9, so I'm not sure if it's unique to this version, but if it isn't shading smooth for you, try applying the modifier first)
Comment: Hey, no problem. The remesh modifier might not give the exact topology you want, but it should at least make it easier to adjust manually if necessary.
Comment: Aw man thank you so much this been a problem for the longest I'm pretty sure a bunch of other people will use this post in the future will use this as well!
Answer: I had strange-looking shapes that went back to typical appearance after I enter Edit Mode, select shapes and go to the menu Mesh > Normals > Reset Vectors


Second DNS forwarder not working

Question: I have DNS server in my network and two configured forwarders. DNS record that only have second DNS forwarder can not be resolved from my client computer. It is like DNS server only ask first DNS forwarder on the list, and never the second one. I have configured 3 seconds for query timeout.
Comment: Is the first forwarder responding at all? If it is then this is the expected behavior.
Comment: Yes, first forwarder is responding. So only if first forwarder is down for 3 seconds second forwarder will be asked for query? I tought that if first forwarder could not reslove the query than second forwarder will be asked?
Comment: No, that isn't how forwarders work. If the first forwarder responds then the second forwarder will not be used.
Answer: This is expected behavior: NXDOMAIN from one forwarder is a response, and no other forwarders are used unless the query was timed out. However, you may configure conditional forwarders i.e. tell that this domain should be resolved using another forwarder (or forwarders). This is possible with both Windows DNS and BIND:
zone "example.com" IN {
    type forward;
    forwarders {
        220.127.116.11;
    };
};

zone "example.net" IN {
    type forward;
    forwarders {
        18.104.22.168;
    };
};

Second DNS forwarder not working


Engine light turned on mid drive

Question: I was driving my Hyundai I25 2011.
And in mid drive the engine light turned on and the car feelt like it had a hard time to give a push and 3sec later it was fine.
Was it a one time thing or should I rush to the garage to have it check?
Comment: Is the engine light still on, or did it go away?
Comment: It went away and it was driving fine
Answer: That can happen when the engine detects a misfire. It can go into "limp mode," which limits power to keep the motor safe. That could be caused by bad fuel (or the wrong fuel grade, depending on the engine), spark plugs, ignition coils or any number of things.
Even if the light has gone off, the ECU will have stored whatever codes occurred when the light was set. Many auto parts stores will scan the codes for free, which would give you a better idea of what happened. (In the US, I know AutoZone does this.)
If it doesn't happen again, I wouldn't worry about it.

Engine light turned on mid drive


Is is possible to reuse Oracle native compiled shared libraries?

Question: Since Oracle can do a native C compilation for PL/SQL code (code is compiled with a C compiler like gcc into a shared object file on servers file system) I am wondering about this. Can I develop a piece of C code for extproc linking against the native compiled PL/SQL function? This would be a great thing, because all the difficult OCI stuff could be done in PL/SQL and all the logical or math stuff in C. Therefore I would need to know (at least, I think) the function names and parameters so that I can make a header file - right? Is there a way to reverse engineer the .so? Has anyone tried such a hack? Its more a "I want to learn and experiment" thing than solving an actual issue.
EDIT1:
What I have figured out: I can modify the $ORACLE_HOME/plsql/spnc_commands file and append a cp %(src) /tmp%(src) behind the linker command. So I can investigate the generated C code, but this is not a big help :-(
Answer: It seems that you looking for OCI Oracle Call Interface.