Why not use the third derivative for numerical optimization?

Question: If Hessians are so good for optimization (see e.g. Newton's method), why stop there? Let's use the third, fourth, fifth, and sixth derivatives? Why not?
Comment: You haven't made a scientific breakthrough. Halley beat you by about 3 1/4 centuries. Halley, E., 1694, "A new, exact, and easy method of finding the roots of any equations generally, and that without any previous reduction" Philos. Trans. Roy. Soc. London,18, 136–145.  3rd derivative methods for optimization have existed and been studied for many years, but have not achieved great popularity. If implemented well, their greatest advantage can be an increase in robustness vs. a well-implemented Newton's method. This can be of advantage for the nastiest problems.
Comment: Once you find the optimum, why look further?  Indeed, what are you really trying to ask?  What is your statistical question?
Comment: I'm voting to close this question as off-topic because it's not about statistics. It's about numerical optimization
Comment: If you can do something, does not mean you *should* do it. Higher order derivatives are increasingly susceptible to noise.
Comment: I voted to reopen as optimization is important in machine learning, which is on-topic on this website.
Comment: In many cases, the limiting distribution of estimates that solve optimal estimating equations or minimize objective functions are jointly normal, so they can be characterized entirely by their first and second moments.
Answer: I am interpreting the question as being "Why does Newton's method only use first and second derivatives, not third or higher derivatives?"
Actually, in many cases, going to the third derivative does help; I've done it with custom stuff before.  However, in general, going to higher derivatives adds computational complexity - you have to find and calculate all those derivatives, and for multivariate problems, there are a lot more third derivatives than there are first derivatives! - that far outweighs the savings in step count you get, if any.  For example, if I have a 3-dimensional problem, I have 3 first derivatives, 6 second derivatives, and 10 third derivatives, so going to a third-order version more than doubles the number of evaluations I have to do (from 9 to 19), not to mention increased complexity of calculating the step direction / size once I've done those evaluations, but will almost certainly not cut the number of steps I have to take in half.
Now, in the general case with $k$ variables, the collection of $n^{th}$ partial derivatives will number${k+n-1} \choose {k-1}$, so for a problem with five variables, the total number of third, fourth, and fifth partial derivatives will equal 231, a more than 10-fold increase over the number of first and second partial derivatives (20).  You would have to have a problem that is very, very close to a fifth-order polynomial in the variables to see a large enough reduction in iteration counts to make up for that extra computational burden.
Comment: No, it's not - it's a little deeper comment than it may first appear.  The point is twofold - most ideas that appear good at first, aren't, for reasons that may not be at all obvious, and the real key to a breakthough may not be the idea itself but something that overcomes or works around the flaw in the idea.  This reasoning, in effect, points that out, and tells you to look for weaknesses in the idea.  It's not about giving up, it's about thinking things through, and with a critical eye at that.
Comment: As one of my professors - a very successful consultant as well - said to us once, "Whenever you think you've figured out how to build a better mousetrap, try to figure out why the 1,000 people who came up with that exact same idea before you haven't put it on the market."  The whole point of using Newton is to save computation - otherwise, we'd just do exhaustive search.  I assure you, adding a third derivative to a 3 dimensional problem will very, very rarely pay for the doubling of computation at each step with greatly reduced iterations unless the function is ~ a cubic.
Comment: @whuber What the OP is referring to, extremely unclearly I have to admit, is Newton's method in optimization.  The question really is "Why does Newton's method only use first and second derivatives, not third or higher derivatives?".  It's off-topic as well as being unclear what he/she's asking, but I thought I'd just give an answer rather than vote to close for one reason or another.
Comment: +1 I think this is a good answer, but it could be improved by showing what you're up to based on the taylor expansion.
Comment: Could you explain just *how* you are making use of higher derivatives?
Comment: @MatthewDrury - thanks!  Good point about the example, that would clarify things considerably.  I'll do that.
Comment: I'm not convinced that this is a good reason not to use higher order derivatives. I think I have a scientific breakthrough here
Comment: It's reasoning along that line that ruins scientific breakthroughs
Answer: I don't really see what the statistical aspect of this question is, so I'll answer the optimization part.
There are 2 parts to convergence: iteration cost & iteration count
Pretty much every answer here is focusing on just the iteration cost and ignoring the iteration count. But both of them matter. An method that iterates in 1 nanosecond but that takes $10^{20}$ iterations to converge won't do you any good. And a method that blows up won't help either, no matter how cheap its iteration cost.
Let's figure out what's going on.
So: Why not use >2nd-order derivatives?
Partly because (and this is true for 2nd-order too, but more on that in a bit):
Higher-order methods generally only converge faster when near the optimum.
On the other hand, they blow up more easily when they are farther from the optimum!
(Of course, this isn't always true; e.g. a quadratic will converge in 1 step with Newton's method. But for arbitrary functions in the real world that don't have nice properties, this is generally true.)
This means that when you are farther away from the optimum, you generally want a low-order (read: first-order) method. Only when you are close do you want to increase the order of the method.
So why stop at 2nd order when you are near the root?
Because "quadratic" convergence behavior really is "good enough"!
To see why, you first have to understand what "quadratic convergence" means.
Mathematically, quadratic convergence means that, if $\epsilon_k$ is your error at iteration $k$, then the following eventually holds true for some constant $c$:
$$\lvert\epsilon_{k+1}\rvert \leq c\ \lvert\epsilon_{k}\rvert^2$$
In plain English, this means that, once you are near the optimum (important!), every extra step doubles the number of digits of accuracy.
Why? It's easy to see with an example: for $c = 1$ and $\lvert\epsilon_1\rvert = 0.1$, you have $\lvert\epsilon_2\rvert \leq 0.01$, $\lvert\epsilon_3\rvert \leq 0.0001$, etc. which is ridiculously fast. (It's super-exponential!)
Why not stop at 1st order rather than 2nd-order?
Actually, people often do this when second-order derivatives become too expensive. But linear convergence can be very slow. e.g. if you got $\epsilon_k = 0.9999999$ then you'd need maybe 10,000,000 iterations with linear convergence to get $\lvert\epsilon\rvert < 0.5$, but only 23 iterations with quadratic convergence. So you can see why there's a drastic difference between linear and quadratic convergence. This is not true for 2nd and 3rd-order convergence, for example (see next paragraph).
At this point, if you know any computer science, you understand that with 2nd-order convergence, the problem is already solved. If you don't see why, here's why: there is nothing practical to gain from tripling the number of digits every iteration instead of doubling it—what's it going to buy you? After all, in a computer, even a double-precision number has 52 bits of precision, which is around 16 decimal digits.
Maybe it will decrease the number of steps you require from 16 to 3... which sounds great, until you realize it comes at the price of having to compute third derivatives at each iteration, which is where the curse of dimensionality hits you hard. For a $6$-dimensional problem, you just paid a factor of $6$ to gain a factor of $\approx 5$, which is dumb. And in the real world problems have at least hundreds of dimensions (or even thousands or even millions), not merely $6$! So you gain a factor of maybe 20 by paying a factor of, say, 20,000... hardly a wise trade-off.
But again: remember the curse of dimensionality is half the story.
The other half is that you generally get worse behavior when you're far from the optimum, which generally adversely affects the number of iterations you have to do.
Conclusion
In a general setting, higher-order methods than 2 are a bad idea. Of course, if you can bring additional helpful assumptions to the table (e.g. perhaps your data does resemble a high-degree polynomial, or you have ways of bounding the location of the optimum, etc.), then maybe you can find that they are a good idea—but that will be a problem-specific decision, and not a general rule of thumb to live by.
Comment: Great answer, but I think the Abel-Ruffini theorem is a red herring. First of all, we are speaking about multivariate problems, so computing zeros of univariate polynomials is at most an easy subproblem of limited interest. And, more importantly, it doesn't matter if there is a closed formula for the solution or not: in practice, as far as I know, people don't use closed formulas even for degree-4 polynomials. They're just too long and complicated and unstable. Zeros of polynomials are computed numerically, in practice (using QR on the companion matrix).
Comment: @FedericoPoloni: Yeah, the same thoughts came to my mind when I was deciding to put it in. I didn't have it in originally... I thought maybe I should put it in as just another example of why higher degrees can have unexpected problems. But I guess I'll take it out again if it's unhelpful, thanks for the comment.
Comment: @FedericoPoloni: P.S. while we're on the topic of numerical computation, you might find Sturm functions interesting (if you haven't heard of them already).
Comment: Why do you get worse behavior? Can you explain this? It just seems like with a third order model you have a more accurate model of what the function looks like locally. So it should be be better. The other reason, i.e. the possibly  high computational cost rules rule out higher order methods in some cases but definitely not in all. For example I have a case where computing the derivatives (to any O(1) order) is orders of magnitude cheaper than computing one additional function value.
Comment: ... So if any algorithm can reduce the number of function calls can be even slightly at the cost of requiring higher derivative information I am very interested in that algorithm.
Answer: Even calculating Hessians is quite a bit of work:
$$H = \begin{bmatrix}
  \dfrac{\partial^2 f}{\partial x_1^2} & \dfrac{\partial^2 f}{\partial x_1\,\partial x_2} & \cdots & \dfrac{\partial^2 f}{\partial x_1\,\partial x_n} \\[2.2ex]
  \dfrac{\partial^2 f}{\partial x_2\,\partial x_1} & \dfrac{\partial^2 f}{\partial x_2^2} & \cdots & \dfrac{\partial^2 f}{\partial x_2\,\partial x_n} \\[2.2ex]
  \vdots & \vdots & \ddots & \vdots \\[2.2ex]
  \dfrac{\partial^2 f}{\partial x_n\,\partial x_1} & \dfrac{\partial^2 f}{\partial x_n\,\partial x_2} & \cdots & \dfrac{\partial^2 f}{\partial x_n^2}
\end{bmatrix}.$$
Now see how the third derivative looks like:
$$\partial H/\partial x=\begin{bmatrix}
  \dfrac{\partial H}{\partial x_1}\\
  \dfrac{\partial H}{\partial x_2}\\
  \vdots\\
  \dfrac{\partial H}{\partial x_n}
\end{bmatrix}$$
This is a three dimensional matrix. Here's how its elements look like:
$$(\partial H/\partial x)_{ijk}=\dfrac{\partial^3 f}{\partial x_i\partial x_j\partial x_k}$$
Sixth's derivative will be six dimensional matrix:
$$\dfrac{\partial^6 f}{\partial x_i\partial x_j\partial x_k\partial x_l\partial x_m\partial x_n}$$
Usually, the trade-off is not favorable for going after higher than Hessian. I mean the trade-off between potential gain in speed through using higher order approximations vs. the noise amplification. You always have noise in inputs because we're talking about statistical applications. This noise will be amplified by the derivatives.
If you play golf then the analogy in optimization is to first swing trying to get to the green, not worry to much about a hole. Once, on the green, we'll putt aiming a hole.
Answer: Typically, when you analyze the effectiveness of such algorithms, you'll find results such as one step of a fourth order algorithm having roughly the same effectiveness as two steps of a second order algorithm.
So the choice of which algorithm to use is relatively simple: if one step of the fourth order algorithm takes twice as much work or more than one step of the second order algorithm, you should use the latter instead.
That is the typical situation for these sorts of methods: the classical algorithm has the optimal work-to-effectiveness ratio for general problems. While there are occasional problems where a higher order approach is unusually easy to compute and can outperform the classical variant, they are relatively uncommon.
Answer: You can think of the order of derivatives as the order of a polynomial approximation to the function. Most optimization routines rely on convexity. A quadratic polynomial will be convex/concave everywhere whereas a 3rd order or higher polynomial will not be convex everywhere. Most optimization routines rely on successive approximations of convex functions with quadratics for this reason. A quadratic approximation that is convex requires a positive definiteness condition to be imposed in order for the quadratic to be convex.
Comment: No, quadratics are not necessarily convex or concave (think of $x^2-y^2$).
Comment: It's a quadratic function but neither convex nor concave.
Comment: @Dirk $x^2-y^2$ equal to what?
Comment: @Dirk yes you are right, I should've added a positive semi-definite caveat. I will add that to my answer.
Answer: Let me be the only one here defending 3rd order methods for SGD convergence, but definitely not in the entire space what would need $\approx dim^3/6$ coefficients, but e.g. in just a single direction, which needs only a single additional coefficient if already having 2nd order model in this direction.
Why single direction 3rd order model can be beneficial? For example because close to zero second derivative in this direction basically means two alternative scenarios: plateau or inflection point - only the former requires larger step size, and 3rd derivative allows to distinguish them.
I believe we will go toward hybrid multi-order methods: 2nd order method in a low dimensional subspace e.g. from PCA of recent gradients, what still allows for free 1st order simultaneous gradient descent toward part of gradient orthogonal to this subspace ... and additionally I would add e.g. 3rd order model for a single most relevant direction.


Allow users to edit their own content and admin-generated content

Question: On Drupal 6, how can I let registered users edit their own content and also allow them to edit an already existing admin content (just one content type) and then when saved, the user takes ownership of that node?
Answer: You can give the 'Authenticated user' role permission to 'Edit any <content type> content'. If you configure that content type to create a new revision by default, the user will be registered as the author of that revision (and if you don't give them the 'Administer nodes' permission, they can't uncheck the option to make a new revision). The original author of the node will however still be listed. I can't think of an easy way to change that automatically. But the users can already edit all nodes of that type anyway, so it would only be relevant if you use the node author for some listing or so - in that case, you can probably use Rules to do assign latest revision author as node author.
Edit: OK, so in that case this doesn't help. You can investigate if something along these lines works (I haven't done something like this so I'm not sure it's possible without coding):

Setup a condition for Rules with Context Rules, something like 'Node author is "admin"'.
Create a Rules action using Content Access to set 'Per node access control' if that Context condition is triggered.
Comment: SO i created a rule which checks if the user is visiting the node editing page, and check if he is the owner of the node or if its an admin-authored content. Rules will allow access to the page if the above conditions are met otherwise redirect to the previous page if the node is not his own.
Comment: I think its possible to program / alter the authorship of the node upon saving. Either rules or custom code.

My only problem now is that with "Edit any  content" , the users can edit other user's content.
Comment: Hm, in that case this doesn't help. Maybe someting like in above edit is possible (not sure if you need to code something to trigger this though).
Comment: I think I will probably grant the 'Edit any ' permission but I will perform additional checks (via Rule) to see if the user owns the content or an admin generated it. This is also to restrict them from editing other user's content.
Comment: Let us know what you end up using :)


What is the mechanism of formation of Grignard's Reagent?

Question: What is the mechanism of formation of Grignard reagents? I couldn't find much in my book or on the Internet. This page says something which I am unable to understand. Why are the $2$ electrons in the $\ce{Mg}$ separated? Shouldn't they be together?
Comment: So why would the university website say that? Don't most things in organic chemistry have a probable mechanism rather than an actual one?
Comment: It is not entirely known.
Comment: It is rather simplest version, certain simplification for students, but if you have problem even with that... Actually pure griniards aren't monomers and have multicenter bonds so...
Answer: Looking at the mechanism:

We see that these are not double headed arrows, but single headed arrows. This indicates the movement of single electrons, rather than electron pairs as is common in most mechanisms.
Mechanisms that involve movements of single electrons tend to form free-radicals.
The lewis structure of Mg has the electrons seperated in order to make it clearer to read.
In step 1, the shared electron pair in $\ce{R-X}$ has been split to form two radicals: $\ce{R}{\small{•}}$ and $\ce{X}{\small{•}}$. However the $\ce{X}{\small{•}}$ radical is further attacked by an electron, this time coming from the $\ce{Mg}$. Thus forming a free-radical magnesium halide: $\ce{X^-Mg^+}{\small{•}}$.
After this, the two free-radicals undergo a termination step to form the Grignard reagent.


Signal boosting capability of Windows Phone 8.0

Question: I found an interesting app in Windows Phone Store to boost the signal strength of the phone and help to increase network bandwidth too. Does the windows phone has the capability of boosting signal?
Comment: possible duplicate http://windowsphone.stackexchange.com/q/2930/3389
Comment: I highly doubt apps get such low-level functionality.
Comment: Those apps are fraudulent. It's not technically possible to do that and never will be.
Comment: @Neil - if the apps are suspected to be fraudulent, then should they be reported to Microsoft in an effort to protect consumers (we are all consumers)?
Comment: @jww yes, of course. But a lot of people must report and app for Microsoft to take notice.
Answer: As of today Windows Phone 8 SDK does not expose any API you can manage the way signal is used by the device.
You can find more about what can be done in apps in What's new in Windows Phone SDK 8.0
Answer: Firs thing - Windows phone applications dont have access to Hardware level . They are sandboxed and they cant access much of the hardware component unless they are exposed .
There are methods to get the signal strength because that API is exposed but there is no way to boost the signal strength !!


Dataset of Home Appliance Usage

Question: I'm interested in obtaining a dataset that includes the electricity usage of individual home appliances measured at hourly intervals. An example of such a dataset is the IRISE Project from REMODECE. Unfortunately the data provided on their website contains daily averages and I need the data for each day. Does anyone have any idea of datasets that contain this information, or how to obtain the full IRISE dataset?
Comment: Can you clarify what you mean "individual home appliances". A hair dryer listed at 1.8 kW will consume exactly that. Do you mean "hourly household consumption data"?
Answer:
The Almanac of Minutely Power dataset Version 2 captures three major types of energy consumption, namely electricity, water, and gas. It includes data from many individual home appliances such as clothes dryer, clothes washer, dishwasher, heat pump, fridge, TV, wall oven, etc.
The data were captured in a Canadian residential house over a 2-year period (1 minute intervals). Also, it has been beautifully cleaned and ready to be analyzed.
DRED (Dutch Residential Energy Dataset) contains energy consumption data of a residential house in the Netherlands over 6 months (1 minute intervals). It also has data of individual appliance.
Comment: Unfortunately the link for the DRED dataset is not active anymore, so I can't download the dataset. Does anybody know an alternative download link or has downloaded the data in the past and can hand them over to me? Thanks :)
Answer: I think you might be able to look at the REFIT project for such datasets:
REFIT: Electrical Load Measurements (Cleaned)

The REFIT Electrical Load Measurements dataset includes cleaned electrical consumption data in Watts for 20 households at aggregate and appliance level, timestamped and sampled at 8 second intervals.

Dataset of Home Appliance Usage


TBB upgrade: What happened to my bookmarks?

Question: I have just upgraded to the Tor Browser Bundle version 3.5.  I overwrote my old Tor directory, which normally preserved my bookmarks.  With this upgrade, all of my bookmarks are gone. Is there anyway to restore them?
Comment: most easy for me was export bookmarks from old version to html. open new bundle and import from html. all bookmarks were there again.
Comment: I have the same problem with the most recent upgrade of the Tor browser - unfortunatley all my bookmarks were overridden (disappeared) with the new upgrade. I really need those bookmarks, one in particular! I am a relative newbie when it come to computer navigation - can you walk me through the steps of how to restore my previous version of Tor so I can get my bookmarks back?
Answer: The folder-structure between version 2.X and 3.X has changed. While the bookmarks were stored in
\Tor Browser2.X\FirefoxPortable\Data\profile
they are now stored in
\Tor Browser3.5\Data\Browser\profile.default.
You better create a new folder for the new TorBrowserBundle and then copy the bookmarks over.
It is recommended to export the bookmarks, unpack the new bundle to a different or new folder, import the bookmarks and then remove the old bundle.


Somebody use Rode NTG-8 ?

Question: Somebody use RODE NTG-8 ? I think new model.
Answer: Never noticed they had something like that. While off-topic, I really wish Rode made a M-S shotgun/field mic.
Comment: this! M/S from Rode would be great.
Answer: Hi, are you sure you don't mean the NTG-3 (may look like an 8, i guess).  If so, I use this mic often and it sounds fantastic for outdoor booming.  It was a toss up between this mic and the Sennheiser MKH416 and I found that the MKH416 sounded a bit thinner and not as warm as the NTG-3.  A little side note, they used the NTG-3 on "Lost", so booyah to that.
Comment: You might want to look at their website again haha, I was surprised myself when I saw this new mic.
Comment: 8. site says 8 too ;

Somebody use Rode NTG-8 ?


How To Install Ubuntu 14.04 on HP Dynamic Smart Array b120i logical drive

Question: I've got some problems when trying to install ubuntu on hp proliant dl 160 gen8. I've got 3 logical drives in dynamic smart array controller, and on installation screen I see only physical drives. How to install it on logical volume? I am using Ubuntu 14.04
Answer: Unfortunately the b120i does not have stables drivers under Ubuntu/Debian yet - this issue is discussed at https://answers.launchpad.net/ubuntu-certification/+question/214703.
There is a PPA by HP (note these are not fully tested nor certified): https://launchpad.net/~hp-iss-team/+archive/ubuntu/hp-storage?field.series_filter=trusty
If you need something suitable for production (as we did), then you are going to have to install a raid controller that is supported such as a P4xx controller.
You can also not use the onboard controller in raid mode - use Sata and configure software RAID within Ubuntu - https://help.ubuntu.com/14.04/serverguide/advanced-installation.html#software-raid
Answer: Apparently, HP has some of the software (the Management Component Pack fpr ProLiant, MCP) ready, as it is now offered at http://downloads.linux.hp.com/SDR.
Having some of it installed on Ubuntu 14.04.2 LTS (Kernel 3.16.0-45-generic #60~14.04.1-Ubuntu SMP), I can confirm that at least hplog and hpasmcli provide usable output.


Black hole Creation

Question: I just had an idea not sure if this would work but if we dropped something into very deep water like the marina trench could the pressure crush it small enough to create a black hole?
Comment: Why stop at bottom of marina trench, why not all the way to the center of the Earth.
Comment: Welcome to the astronomy SE btw.  Earn another badge by taking the tour! http://astronomy.stackexchange.com/tour
Comment: There is already stuff down there like water and likely dead flora and fauna. Those aren't being crushed into black holes are they?
Answer: There already is something at the bottom of Mariana Trench. Rocks and stuff. Luckily they haven't been turned into black holes. So empirically, we can say that the answer is no. If it had, it would have attracted its surroundings, and eventually the rest of Earth would fall into it.
To create a black hole, you need to compress a certain mass to within a certain radius. But solids and liquids are really hard to compress. Although the pressure at the bottom of the Mariana Trench is over 1000 atmospheres, water is compressed only by 5%. And solids like rocks and metals are virtually incompressible$^\dagger$.
Even at the center of the Sun, where the pressure is 250 billion atm, the density is only 150 times that of water (under 1 atm). That is, 1 kg of water placed at the center of the Sun would fill not one liter, but $0.7\,\mathrm{cl}$.
But to turn a mass $M$ into a black hole, you'd have to compress it to within it so-called Schwarzschild radius, which is given by
$
r_\mathrm{S} = 2GM/c^2,
$
where $G$ and $c$ are constants. For $M = 1\,\mathrm{kg}$, this equates to $10^{-25}\,\mathrm{cm}$, much smaller than the radius of an atom.
Such conditions arise only in extreme events, such as the core of a dying star collapsing, and even then only the most massive stars. So unfortunately, you won't be able to create a black hole.

$^\dagger$Solids are not entirely incompressible, since otherwise sounds wouldn't be able to propagate through them.
Answer: No, for a black hole to form the core of a star much larger than our sun must collapse into itself, forming a singularity.  This happens after a star has expended it's fuel no longer being able to offset the inward force of gravity. The result is a rapid release of its outer layers in a supernova. The resulting core then collapses into the singularity. The mass is so great that this singularity is an infinite bend in space time.
Of note, if we took your object and were able to squeeze it down so small that it's radius reached the Schwarzschild radius, it could become a black hole. The Mariana Trench could not provide enough pressure to this.
There exists little fish and organisms near the bottom of the Mariana Trench. Dropping something like a penny would just cause it be distorted by the pressure above it.
Comment: @nataliaeire: Under the standard model, you'd need 1e17 times the energy of the LHC to create BHs from colliding particles. If string theory is correct, you could perhaps create one, but it would evaporate immediately. Even if Hawking radiation is a lie, it would grow too slowly to engulf Earth in billions of years (if there is ≥7 dimensions) or have observable effects in the Universe (if there are 5-6 dimensions). This is not my field of expertise, though, but Earth is hit ~1e5 times per second by cosmic particles with energies ≥ the LCH energy and we're still here, so I think it doesn't work
Comment: @nataliaeire: I apologize, I put more into your comment than you deserved. It's just that a couple of years ago, there was quite a lot of criticism from some people who thought that the LHC were able to create BHs, that would then engulf Earth. Your point is absolutely valid.
Comment: While we are mostly used to black holes forming from stars, that's not a criterium for something to be a black hole. The LHC at CERN is potentially creating black holes, and they are definitely not dealing with core collapse stars over there. Anything can become a black hole, if it becomes dense enough!
Comment: @nataliaeire aye, but I didn't want to confuse this person. I didn't want the follow up of, "Yeah it would crush it so small that a black hole would form." Although, my answer is isn't as complete as pela's. However, I'll try and edit my answer to be more complete.
Comment: @pela Yes, though, I don't see why you would bring up engulfing the Earth, seeing how that, too, is not a criterium for being a black hole. And that is my point; that to get a black hole you "simply" need to compress something within a certain radius for any given mass. In other words, I thought your answer was more complete.
Answer: Theoretically any object with a mass great enough that its own gravity is able to overcome its molecular movement and provided there is no forces to counteract that force such as atomic fission or fusion can in deed implode to a singularity, however the pressures from the sea are far to weak even at the center of the earth to initiate such a reaction it takes a mass of over 3 times that of our sun to even come close.
   On the other hand it may be possible hypothetically to compress an Eisenstein Condensate kept at temperatures near 0K (say 1k) at extreme pressure might be able to form a mini hole. But the heat caused by that pressure would disrupt the process and even if successful it would evaporate in pico seconds

Black hole Creation


Restricting Office 365 Users from sharing folders to external users

Question: From the Admin Portal, how can one restrict Office 365 users from sharing specific folders on Team Sites to external users.
Comment: Do you want the ability to share to external users on other folders/items?  If not, simply disable the feature in the SharePoint Admin center.  Otherwise you'll need to provide some more information.  Are these folders all on the same site?  Do you want users to be able to share anything else on that site to external users?
Comment: You could use permissions to restrict access to a folder. However if the information in the folder/library should not be available to the public you should probably review the permissions settings for the site and not allow anonymous access.
Comment: So you cannot make permissions to the folders not to be shared externally?
Comment: I don't know what you have done so far. but by default unauthenticated users do not have access to anything. For the Authenticated users you should use groups, for a more granular access to specific resources on the site. i think you should read up on SharePoint permission model and how to manage it, here is a link fo ryou to get started. http://office.microsoft.com/en-001/help/permissions-in-office-365-HA104043996.aspx
Comment: If that's the case, then I will just have to create a site that I can make the folders be public. Thanks @wjervis
Answer: It's not possible to restrict external sharing of folders, since this is controlled on the site collection level in the SharePoint Admin Center. Either you allow external sharing on the entire site collection, or you don't.
Reference: Restricting Office 365 Users from sharing folders to external users
Comment: If that's the case, then I will just have to create a site that I can make the folders be public. Thanks @Benny-Skogberg


What's the difference between a FL-D filter and an ND filter?

Question: What's the difference between a FL-D filter and an ND filter? I see that FL-D is to improve light, but so is ND. What exactly is the difference?
Comment: See also: [Are there reasons to use colour filters with digital cameras?](https://photo.stackexchange.com/questions/586/)
Comment: Related: [Is a fluorescent filter worth using, and how and when?](https://photo.stackexchange.com/questions/22936/is-a-fluorescent-filter-worth-using-and-how-and-when)
Comment: To improve light? Where do you see this?
Comment: @osullic  Sales literature stops marginally short of outright lying.  "improve light" in their secret code means "the photo will look more like the lighting was what you want it to be"
Answer: An FL-D filter is a color correcting filter to make fluorescent lighting appear more daylight-ish to your film/sensor. An ND (neutral density) is for reducing the amount of light seen by your film/sensor with no (ideally) color modification, which is why it's termed neutral. Most FL-D filters I've seen have a noticeable color tint to them, while an ND filter is just gray.
Answer: FL-D (and other color correction) filters are not used as much in digital photography as they were in film days. Furthermore, there many different types (and hence color casts) of fluorescent lighting today than were available thirty years ago. Unless a fluorescent color correction filter is matched to the color of the fluorescent light, it can have a different color cast result than intended. It's so much easier to control white balance in camera (or in post, if shooting raw images) than it is to deal with filters, in general.
That's not to say that color correction filters are useless. I'm generally an advocate of getting the shot as correct as possible in camera, to reduce what needs to be done in post. There are plenty of situations where it might make sense to use color correction filters. See also: Are there reasons to use colour filters with digital cameras?
ND filters just reduce the amount of light coming into the lens, with (ideally) no color cast. Say you are shooting outdoors on a bright day, and want to capture an image with shallow depth of field. That requires you to shoot your lens with a wide aperture. But that means there's a lot of light coming through a wide aperture. You can't get your ISO usefully much lower than 100, so your only means to control exposure to use a fast shutter speed. But if your shutter isn't fast enough (or for some reason you want a slow shutter, such as trying to create some blur), then you need a way to reduce your exposure. That's where ND filters come in. Think of ND filters as the real-world exposure control slider in Photoshop.


Can I leave the airport if I am traveling though the US from the UK?

Question: I'm staying over in New York for 4 hours before my next flight that lands again in America. If I do my immigration at New York, can I leave the airport for example to get food, and then just come back 3 hours later and wait for my next flight? Or do I need to wait in the airport until my final flight?
Comment: Possible duplicate of [Is it possible to get out from the L.A airport during a connection?](https://travel.stackexchange.com/questions/8676/is-it-possible-to-get-out-from-the-l-a-airport-during-a-connection)
Answer: Yes, you will pass through immigration and customs at your first point of entry when your plane lands in New York. At that point, you have entered the US and you may go wherever you like.
You will probably find, however, that 4 hours isn't that long for a domestic connection. The New York airports are always busy, and you may be waiting for some time to pass through the border checkpoint. Then getting anywhere from the airport takes time, no matter how you choose to travel. You will definitely not have 3 hours spare to wander around.
There are plenty of options for food inside the airport for people in exactly the same situation as you.
Comment: I've been in this situation (in NY) and done both things: a) left to look around, and b) just stayed in arrivals/departures and chilled.  a) ended up being not very interesting and a bit stressful (I can't go through security without getting stressed, they're kind of designed that way).  b) was relaxing.  Just stay in there.
Comment: Walking around NYC in 3 hours is like counting the gravel near the tracks of a bullet train while at full speed.  Plus I've seen domestic security take 2 hours or more...even in smaller cities.  I'd just stay inside.
Comment: Unless you have like 8 hours or more of a wait, don't bother leaving the airport.
Comment: FWIW, every time I've been through Newark Liberty Intl (almost NY!), four hours was _more_ than enough and I did indeed have 3 (long, tedious) hours spare to wander around. However, I believe I was in part lucky and your advice is good in general.
Comment: @LightnessRacesinOrbit In my experience, Newark does not usually suffer from the same ground traffic congestion as JFK, allowing planes to get to the gate more quickly to unload.  Immigration and baggage claim also seem to take less time on average, sometimes significantly less.  So your "free time" might easily begin 45 or 60 minutes after a landing in Newark, while it would be unexceptional to take twice as long at JFK.
Comment: @phoog: Fair enough.
Comment: Re "plenty of options for food": in JFK yes, in LGA not so much.  But then OP is international so won't be subjected to that horror show.
Comment: @cbmeeks If I had an extra hour in JFK, I'd take the train to Jamaica, buy a daily news, and get a slice of pizza and enjoy NYC for a bit. It is was too early in the morning for a slice, I'd get an egg sandwich on a hard roll. A great hour, that would be.
Comment: There is also to take into account that they will have four hours after a long flight. So clear immigration, freshen yourself up in the bathroom, all while being sluggish, stiff and inexplicably tired although you slept most of the flight. Poof, you have one more hour to grab some food at the airport and find your departure gate.
Answer: In theory, yes, though you may not have enough time.

if I do my immigration at New York

You have no choice about that; you will do immigration there.  You'll also need to claim your checked bags, if any, clear customs, and recheck the bags, after which you'll need to pass through TSA security before reaching your gate.
All of this could easily take a couple of hours.  It's unlikely to take much less than one.  Even reaching the gate to get off the plane can take 30 or 45 minutes at JFK; such times are not at all unusual, and if something exceptional is happening then it can be longer.
Once you've rechecked your bag, nothing keeps you from leaving the airport, but do check the security line to see how long it is before you make any decisions.  It takes an hour or more to get to Manhattan, so that's almost certain to be out of the question.  If you're arriving at JFK, you might take the A train to the Rockaways and have a stroll on the beach.  If you're arriving at Newark, there's not much to do as far as I'm aware.
Comment: Nope you'll struggle to do anything outside of Newark Liberty without onward (and return) travel - I advise staying in the airport.
Comment: The only exception is if OP flies through a preclearance airport.
Comment: @JonathanReez the question specifies "from the UK," where there are no preclearance airports, but the point is well taken for others who might be traveling from a preclearance airport.
Comment: I'd take the airtrain to Jamaica before going to the Rockaways.
Comment: Ireland has a couple of airports that can do pre-clearance
Comment: @axsvl77 what would you do in Jamaica? I'm not aware of anything touristy to do there unless one is interested in watching trains in the station.
Comment: @PaulG indeed, the only preclearance airports in Europe.  They are not in the UK, however.
Answer: You will be able to leave and return again, but bear in mind, you will need to clear security again. You will not however, need to clear customs and immigration. You do that at your first port of entry.
Answer: As the other answers say, you must go through immigration at your point of entry and you can leave the airport in principle. However, there's nowhere to go that's close enough to the airport that you could get there, do something, and get back to the airport in time to catch your connecting flight.
Comment: Jamaica isn't that far by air train. Can get a slice of pizza and walk around a little. For those of us who miss New York, that would be a great hour.
Answer: You can leave the airport, but four hours is not that much time, especially as you will need to go through immigration and security (for your connecting flight) in that time. Also, bear in mind that you will need to obtain a visa before flying to New York, unless you qualify for a wavier (I don't know the conditions on this, but all my colleagues from the UK here need to have a visa just to pass through the US between the UK and Mexico).
Comment: Strange, Isn't pretty much everyone with a British passport, that describers the holders nationality as "British Citizen", eligible to the visa waiver programme? Unless of course they have visited the restricted countries, or have criminal convictions.
Comment: @dlatikay they won't be able to abandon the clearance process in any case. All passengers must clear passport control and customs, even those who are connecting to a flight to another country.
Comment: I assume this refers to travel authorization from the [Electronic System for Travel Authorization](https://esta.cbp.dhs.gov/esta/), which the U.S. maintains is technically different from a visa. Travel authorization has been required for entry through the Visa Waiver Program since 2009.
Comment: @MichaelHoffman It would be a very unusual mistake to confuse ESTA and a visa. Almost everybody thinks that "ESTA" means "visa-free entry to the USA" (i.e., what is actually the VWP).
Comment: returning ESTAs are much faster. if OP is coming in by first-time ESTA to JFK, his mileage may vary between 30 minutes and 4+ hours from debarking to clearance completed. And I'm afraid once they entered the "Non U.S." queue they may not be able to simply abandon the clearance process when they realize its going to take too long to catch their connecting flight. but stopover with final destination in US will require full clearance in JFK anyway...
Comment: It's not an unusual mistake, in my experience. Especially among people who rarely have to get real visas.
Comment: @dlatikay U.S. airports don't have international transit zones. Transiting a U.S. airport requires admission to the U.S., even for international-to-international connections. This allows domestic and international flights to depart from the same gates. It generally makes life easier for domestic-to-international connections (and airport operations,) but more difficult for international-to-international connections.


What is the relationship between the end of season one and the short season two?

Question: Season one ended with the main characters leaving for some unexplained adventure.  But in season two, they're still hanging around the capital.  Does season two take place before the end of season one?
Answer: Actually, there is no season 2. Those 4 episodes were more like an OVA that Netflix mislabelled as season 2. Season 2 is coming, nobody actually knows the date when it's going to be aired.
Comment: You're basically right, but it isn't actually an OVA. The 4 episodes aired on TV. The closest description is probably "TV special" though they aren't that common.
Answer: What Netflix labeled as "Season 2" isn't exactly a new season, but rather special episodes from the Manga that aired on TV in Japan.
Answer: It seems like a continuity issue, to me. You are correct that at the end of Seaon 1, Elizabeth jumps on the Giant Boar and they all ride off, presumably to find Escanor the Lion's Sin of Pride.


Where can I ask questions about web hosting control panels?

Question: My question was closed as off-topic because it is "about a web hosting control panel". But I still need help. Where can I ask my question?
Answer: Unfortunately Server Fault is unable to support web hosting control panels for a variety of reasons. But you may still be able to get help at:
Your Service Provider
If you are using a web hosting resource (e.g. shared hosting or VPS) provided by someone else and need help with the control panels to manage it, first contact your service provider. If the service provider is unable or unwilling to help, continue on:
Vendor Support
Generally you should first seek support from the vendor of your control panel. They know their products best and will be able to give you the most appropriate help. The support pages of the most popular control panels are available:
cPanel/WHM
DirectAdmin
ISPConfig
Kloxo/HyperVM
Plesk
Sentora
ServerPilot
VestaCP
Virtualmin
ZPanel
Stack Exchange
Some Stack Exchange sites may also be able to help you with your question.
Webmasters may be able to help you with questions about running your website.
Unix & Linux may be able to help with questions about Linux and Linux applications.
Web Hosting Industry
There may be other forums and community resources you can visit. A small sampling of these follows:
Digital Point Forums has a Site & Server Administration section.
Web Hosting Talk has a Hosting Software and Control Panels section.
Comment: Before you ask: Webmin is _not_ a web hosting control panel, so it is not included here. Its extension Virtualmin, however, _is_.
Comment: Why webmin it's not a control panel? Because it's opensource? The objective of webmin is the same as that of a control panel. It is to provide a web interface to the administrator. And also has its own forum.
Comment: @abkrim Webmin (alone) is not designed for _hosting web sites_. That's Virtualmin.
Comment: @abkrim So we should also ban questions about Webmin, then?
Comment: Different cases are and should be threaten very differently. Say: bind9 issue on ISPConfig. It's not an ISPConfig related issue, as it just produces raw bind9 files in the etc directory, if the asker provides full bind9 confs, there's no need to threat it as an ISPConfig related issue. Just cause the asker wrote "ISPConfig" in the question. If he didn't, then the same question would be threaten differently. That's stupid. https://serverfault.com/questions/807050/bind9-will-not-serve-txt-records-for-some-domains-and-will-serve-it-for-others
Comment: that it's your opinion. Webmin its perfect for hosting. If you know system Webmin it's perfect. On a scale of 0 to 10 on usability for hosting panel, webmin would be a Virtualmin 1 and 3. Both panels are very poor facilities, but suficinetes for the same purpose.
Comment: For purists if. Now, of all panels on the list in tens of thousands of questions and hundreds of thousands of responses. It's curious.
Comment: I know nothing about cpanel, exept that I used a cpanel host in my young time, but a quicksearch on webhostingtalk.com (a reference for me for webhosting) return a lot of query about webmin used as plesk or cpanel. It can be a good discussion to have if we add that tool to the list.
Comment: @yagmoth555 My understanding is that Webmin just does general system administration (via a web interface), and that web hosting is done by its addon Virtualmin (which you don't have to use). I could be wrong about this, or people could be trying to do web hosting with Webmin alone (which strikes me as doubly insane)...
Comment: ah ok! thanks for the clarification about the addon. I now suspect then the post I seen told webmin term, but would use virtualmin in the final, would make more sense.
Answer: What is the use of StackExchange forum or site, when we have to go to vendors or service providers to resolve our issues? If system admins or the vendors themselves want to ask a question about system admin, it means this site is useless for them?
It is a really stupid decision.
Comment: Sometimes, going to the vendor is the correct thing to do. This is true of the WHM/cPanel support questions.
Comment: cpanel is a special case. as we support what lies underneath, not the tool that customize the whole system over the other tools. not to forget that usually we would help cpanel user, not the server admin, as usually the admin got a support contract and would just reformat the box in case of a trouble. so as iain told, in must cpanel issue it would end up in cpanel support anyhow, as a customized tool, giving advice for the beneath tool could make more damage than anything.
Comment: Seems like for Every technology, we should always contact the vendors, or the product developers. so whats the use of serverfault? (stackexchange) i think it kills the purpose of building such websites where  ppl can get help, when they cannot get help from anyone else.. also when they ask complicated questions, other people benefit from them as well.
If everyone solve their issues by Vendors, then would there be Any use of stackexchange? i think no. so its better to shut this site down for good
@Hanginoninquietdesperation
Comment: @Farhan [I want to say these should be left open, but these panels muck about so much with the system that, unless one is a frequent cPanel user (which none of the SF "Answerers" are), it's impossible to know what exactly cPanel is managing and what it's leaving alone.](http://meta.serverfault.com/a/8056/218888)
Comment: @yagmoth555 : how is anyone suppose to make sure that every question that comes,its Precisely only related to cPanel? it could be any other issue, just because its based on cPanel,it means no one should touch any question related to it ? how does it makes any sense?
Comment: @Farhan What I'm saying is that unless you are very proficient in troubleshooting cPanel, the issue is likely clouded by the fact that cPanel changes so much about the core system. As such it is usually / nearly always much faster to contact cPanel support. And if you are a professional sysadmin with a licensed cPanel instance, you should have access to their support.
Comment: i agree, but there are hundreds of )probably thousands) of cases, where it Not the cPanel or any WHM... so you mean to say if that is the case, serverfault should be banned to be used for those issues? or such issues should be denied that they dont exist?
Comment: @Farhan to put it in context, when cpanel question got called offtopic, a lot, lot of cpanel question was unanswered. As Reace mention it, it scramble the system and it's really hard to answer in SE style (question/direct answer). The best option if someday you want cpanel question back would be to have like cpanel's support watch the cpanel's tag to help out. (as like Microsoft do with the internet-explorer tag on SO)
Comment: @Farhan `Spiceworks` for the win
Comment: @lain: you are right, you said "sometimes" not Always good.
so Sometime we should go and ask from other sources too. venders are not always reliable and provide all solutions


How can I create a custom assignment field, like Finish Variance, to display in Resource Usage?

Question: I'm trying to create a finish variance field on assignments in the Resource Usage view, but I keep getting "#ERROR".  Both the Finish and Baseline Finish fields are available on Resources and Assignments, but not Finish Variance.  If I try to define the field Finish1 in the Resource Custom Fields with "=[Finish]-[Baseline Finish]", it accepts the formula, but when I insert this column in the table, it doesn't populate.  I have also tried checking/unchecking "Roll down unless manually entered" for assignment rows with no success.  Any help is appreciated, thanks.
Answer: Subtracting one date from another date produces a number, not another date. So instead of Finish1, use a number field, such asNumber1 or a duration field, such as Duration1.
Comment: Thanks, but it's the number that I'm looking for.  The difference in dates would be the number of days of variance (i.e. # days earlier/later than planned).
Comment: Edit: The error is different with a number field, such as Number1 or Duration1, but the problem still exists.
Answer: The simple answer is no, you can't, at least not using a formula.  Formulas don't get applied to assignments.  The "roll down unless manually entered" is exactly that - all the resource assignments for a given resource inherit the custom field value that is computed for the resource using the formula.  Though I haven't tried it, I think you could populate a custom resource variance field at the assignment level using vba (i.e. "manually entered").  While straightforward, the effort wouldn't be trivial for anyone who's not accustomed to vba in Project.


Coffee and milk for the lactose intolerant

Question: I am lactose intolerant. How can I prepare a good cup of coffee with milk? I don't like the taste of black coffee. I usually use soy-milk, but it is nowhere near original milk in taste.
Comment: Almost all coffee "creamers" in the grocery store (Coffemate, International Delight) are actually non-dairy.
Answer: Best option is lactose-free milk. I assume you live in India and it may be hard to find in India as lactose intolerance is not common among Indians. In that case, you may try goat milk which has naturally less lactose than cow milk. But I'm not sure if this will be enough (personally) for you.
Comment: Hey thanks, we do have lactose free milk available easily from online groceries like big basket and grofers. Amazon too offers it.
Answer: Try frothing the soy milk with a hand-held frother, even if you just slightly froth it.
According to this Milk Frothing Guide

Incorporating air into the milk improves and sweetens the taste. Milk that has not been foamed at all tends to taste flat and dull by comparison.

Also consider experimenting with other kinds of milk substitutes: almond milk, almond-cashew milk, coconut milk, hazelnut milk, hemp milk, oat milk, and rice milk.
Update: I've found that I like oat milk the best. It should be feasible to make oat milk, but I haven't tried that yet.
Comment: Also try different varieties / brands of soya milk. There can be a lot of variation between them. eg sweetened or not, or some brands can have a strange taste or texture.
Answer: Personally I love almond milk in hot drinks. Though I usually use soy milk with coffee, I love to have almond milk chai. That's a tea drink, but maybe it will do it for you in coffee. I recommend it because it's usually touted as a good cow's milk alternative
I would also recommend trying different "alternative" milks to find what you like. In the way you might not like soy milk, I don't like coconut milk in drinks, but other people swear by it. Rice and oat milk are pretty good in my opinion, however.
I'll say this, though: If you go a while without consuming dairy (say a year), your taste palate will change. This is a commonly reported phenomenon among vegans and lactose intolerant people who stop consuming dairy. I can testify personally that I can no longer stand the taste of milk or cheese, and I'm five years "plant based".
Answer: I don't like the taste of soy and almond milk, but I grew accustomed to oat-milk. The barista variety of a certain Swedish brand foams really well and makes good cappuccino's.


yum to install fails on default empty server

Question: I used to download Fedora from site X, for example, but lately the site has not updated itself with new packages, therefore commands used to install any of those packages report back with errors as the packages required are not found on the specified server. I would like to learn how to change the default mirror URL inside my install Linux so that it can search freely anywhere the particular packages are available ? Is this possible ? Thank you for any help.
Comment: Can you give the repo you are using?
Answer: The mirror used is stored in one of the files in /etc/yum.repos.d .  The exact file is going to depend on which repository you are actually using.  You can find a list of up to date Fedora mirrors at http://mirrors.fedoraproject.org/publiclist/


Are there tools to measure traffic to social media sites from a LAN

Question: We are looking for a tool which can monitor traffic to social medsia sites from within an enterprise or a LAN environment. Are there any tools which let you monitor this, since we could infer such traffic at the network level (say HTTP) or by snooping for the API calls which are exposed by these social media platforms.
Answer: Yes, you can.
Since there are so many options how to do this and to what level of detail, the question is not really easy to answer in detail.
There is hardware that lets you monitor this, depending on the size of your network and your requirements. Normally the access will be logged on an IP basis. So for example if you want to track per-user access that might be using the same IP address, things get more complicated.
You can have a simple logfile where you then will have to find yourself which URL is a social media and which is not (facebook for example uses several different top level domains). Or on the other extreme, you can subscribe to a service that will automatically classify also newly created websites of certain types as "social networks". This is specially used for companies that want to block certain types of websites from being used.
For your specific personal usage, you will have to give more information as to how many users you have, what kind of information you want (access, data transferred, time spent per site, per user, per IP etc) and what kind of money you want to spend for that.
more information on URL logging and the meaning of a log entry
Getting URL logs: Depending on what hardware you have, you might have already or can easily setup URL request logging. If you can tell what router and/or firewall you are using, this might give the answers already. You can setup network URL logging yourself with any router with this trick, but this might slow down your network traffic. So depending on your network traffic, it might be worthwhile to get a proper solution. One option might be also to use a linux based system with two network cards that simply sits in the middle between your LAN and WAN and runs the analysis there. That is a bit more manual, but the cost is as small as a simple cheap PC. You can also install software on every user's computer to monitor what they are doing.
Interpreting the logfile:
A standard logfile will normally show you something like this:
[IP 1] [Time 1] [URL 1]
[IP 1] [Time 2] [URL 2]
This means that the a computer (that has the IP "1") accessed the URL 1 (Let's say "facebook.com" at time 1 (let's say 12:00).
The same computer (same IP "1") accessed at time "2" (Let's say 20 minutes later) another URL, let's say a different facebook URL, such as a user profile.
What does this tell you? At the minimum, it tells you that from the same computer, someone opened facebook and then, went to copy something, work or do whatever, and then came back to the browser 20 minutes later and clicked on a link on the facebook page. Nothing else.
It however also could be that the user wrote a message on facebook for 20 minutes (without clicking a link though or other requests), and then he read one the next page for 2 more hours after the second click. It is in this case impossible to say.
However: In the end you will realize that such a log entry is highly unlikely. People who work, will maybe open facebook once, check some messages and that is it. It will result in some clicks over 15 minutes, and then stop. People who do not work, will spend many more clicks and time on facebook, reddit, etc etc. If you would filter the lines of business relevant websites out of the logfile and see that a user opened 2000 other links within his working day, you have an issue.
In the end, what you have to take care about is that no logfile and more so no money spent to get that logfile will help you unless you analyze it properly and then look at the data, too - and then take consequences.
I made the experience in a larger company (6k+ computer users) where the decision was done against such a log analysis software because people realized that nobody will take the time and really look at it on a per-user basis to take action against users for browsing too much. The only thing that was done was to monitor the data throughput of each service (youtube for example) since the data transferred caused the network to be slow. So Youtube and other video services was blocked. There was also a block for certain types of website (gambling, porn etc) - since there are more serious issues at hand if a user watches porn in the office as opposed to be simply lazy. Facebook was not blocked because the opinion was that it is not possible to make people more productive by blocking facebook - or anything else. People have been lazy before facebook too. IF you block facebook, they will be unhappy and will find other ways to spend their time instead of working. Nobody would win. Instead it is more important to make sure people are managed and motivated properly so they do not spend all their time on facebook.
Btw here is another short article on network analysis.
Comment: I would like to identify user id handles (e.g. facebook id or twitter id) of the users who are using on a periodical bais.
Comment: We are more interested in monitoring what messages they are posting in Facebook, Twitter. We will be able to isolate once we have their id(s)
Comment: @Samuel actually I think this is a different question. I would first layout your network infrastructure in a question a bit more so people can understand if you talk about 10 or 1000 users. I would then ask the concrete question how you can catch FB and twitter messages from these users. What I can tell you right away however that this is a completely different scale than just knowing which URL they connect to. You will have to read every packet. On top of that, FB uses encryption (SSL) which makes it impossible. You will also face some criticism regarding privacy and likely legal issues.
Comment: @Samuel your current question "How to measure" would be right if you wanted to know how only much time people spend on certain websites. If you really want to know the content of messages, you need much, much more advanced hardware and software.
Comment: Ok assuming I wouldn't know who it was. Is there a way to know how much time a certain IP spent on a social media site (say Facebook or Twitter).
Comment: Example, UserA tweets a message at 10 AM, 10.01 AM, 10.05 AM, 11AM, 11.30AM. Does that mean he spent 90 mins or he spent 10 mins just averaging out the nuances. What tool is available to do this
Comment: @Samuel Let me add that above...
Answer: There are numerous products that offer the monitoring functionality you request e.g. Netnanny, OpenDNS, Netintelligence, ...
See also: alternativeTo


How is MIDI used with a keyboard?

Question: How is MIDI used with a keyboard? I have a roland d-20, and I've heard that it connects with MIDI through USB. But what exactly is MIDI? How does it differ from a microphone input?
Comment: Are you asking how to get more sounds via MIDI, or just how to use MIDI in general?
Comment: See my answer for your [other question](http://audio.stackexchange.com/questions/1259/how-can-i-get-more-sounds-for-my-roland-d20/1261#1261) about the sounds for help with that.  I have edited this question to better reflect how to use MIDI.
Answer: You will need some sort of MIDI connection on your computer.  I'm not sure which MIDI interfaces are available for the Mac, but For the PC most every sound card has a MIDI connection.  Usually the joystick port doubles as a MIDI interface and requires an adapter cable.
You will then need to plug one MIDI cable from the MIDI Out on your keyboard to the MIDI In on your computer, and another from the MIDI In on your keyboard to the MIDI Out on your computer.
Now that your computer is hooked up to the keyboard, you need software on your computer to talk to the keyboard via MIDI.  On the Mac you can use Garage Band.  Reaper is an inexpensive program which works on Mac or PC.
Using the software, you will be able to record and play back music from the keyboard.  The software also should allow you to send information to the keyboard including sounds and other system data (see the D-20 manual volume 2 chapter 5).
Answer: Friend of George answered perfectly, and this will probably be the most useful application of MIDI for you in the long run.
But there are many other things you can do with MIDI prior to hooking it up to a computer.
First off, let's face it, the D-20's sound engine leaves much to be desired. It's pretty bad. But the keyboard and on board controls are fine. You can find countless used sound modules at music stores and on Craigslist. If you are just starting out, look for a module that has a good complement of sounds you may enjoy and are appropriate for your style of music. Then it's just a simple matter of hooking up the MIDI out of the D20 into the MIDI in of the module. Be sure to hook up the audio outs of the module as well...MIDI doesn't transmit any audio whatsoever...think of it as the D20's keys telling the module what notes to play. If you also hook up the audio outs of the D20 into a mixer with the module, you now have a very versatile synth that has several layers utilizing several different methods of synthesis. Now the brash attack of what the D20 laughlingly calls a piano sound becomes a really evocative attack for a warm analog pad from the module. This USED to be the way things were done prior to powerful computers, and I would argue that, even with cheap synths, it creates a sound that is hard to get from any single software synth no matter how powerful.
You can also use MIDI to sync up a drum machine with the built in sequencer on the D20. I don't know that I would have the patience to program full songs into the UI nightmare that is the circa 1990 Roland on board sequencer, but it's perfect for patterns, and it's great for hooking up to a drum machine to lock them in time with each other. If you are a guitarist, it provides a nice canvas on which to try ideas and motifs. You can hook up the MIDI ports in either direction depending on which device is assuming tempo and meter control. If you do decide to do this, there is ample documentation out there on the Net.
Eventually, you are going to want to hook up to a computer, but in the meanwhile, there are many other live applications that you should play with to get a comprehensive overview of MIDI.
Comment: Is it completely devoid of patches (sounds) right now? The D20 had some ROM sounds that could not be erased from memory. Are those not there?
Comment: Kurzweil has great piano sounds.  You can still pick up their [Micro Piano sound module on Ebay](http://shop.ebay.com/?_from=R40&_trksid=p5197.m570.l1313&_nkw=kurzweil+micro+piano&_sacat=See-All-Categories) for under $100.  Then all you need is a MIDI cable plugged in from the MIDI out of your keyboard to the MIDI in of the sound module, and you have a great sounding piano.
Comment: That's not exactly true. You still need audio outs from the Micropiano. Then, if you want both the D20 sounds and the Micropiano sounds, you'll need a mixer.
Comment: Dude, what you need is a bit more concept knowledge. But first, why don't you tell us exactly what you want to use it for first. Are you going to use it for live performance? Are you in a band? Are you going to only use it with a computer to compose pieces? Are you just messing around to see if you want to learn how to play keyboards? This site is really geared towards specific questions and answers, so with specific questions, you will get much mor ehelpful advice. Cool?

How is MIDI used with a keyboard?


How can I recognize what formation a soccer/association football team is in?

Question: When watching soccer on TV I often hear the commentators say stuff like, "They've come out in a 3-5-2, not their usual 4-4-2 in the hopes of ..." or "they've got so-and-so acting as  'false 9' today." How could I recognize these strategies myself?
Answer: The easiest way is to watch the pregame show. Usually about 5-10 minutes before kickoff they will show the two teams and their formation on the field. This can also be a good way to familiarize yourself with different players.
If you miss the pregame show and are just watching the run of play, it can be tougher, but still possible. Formations are always described defense-to-offense (excepting the goalkeeper). So a 4-4-2 means 4 defensive players, 4 midfielders and 2 attackers.
The number of defenders and the number of attackers are usually the easiest to identify. Look for the defense to hold an offside line and see how many there are to get an estimate of the defensive line. When the ball is back in the defensive half, see how many players are staying up near the midfield line to get the number of attackers. Subtract those two from 10 and you'll get the number of midfielders.
This is not completely accurate, as people will play where needed during the normal run of play, but it will at least get you an idea.
Secondarily, you should also pay attention to the style of play and who's passing to who. If a team has a lot of possession, you can usually tell who is playing in the same line by where the passes are going. If player A and B send a lot of passes laterally to each other, and sometimes backwards to player C, then A and B are probably midfielders and C is probably a defender. Again, not 100% accurate, but can give you an idea.
The last thing to do is familiarize yourself with some common formations and how they are different from one another. For example, a 4-5-1 can look very similar to a 4-3-3 but the style of play is much more on the attack in a 4-3-3 and more on the counterattack in a 4-5-1.
Here's a good site that lists a bunch of formations (some common, some not so common) and how they're typically used:
Bleacher Report Article on Formations
Comment: As you point out, when the ball's in play, the players will move out of formation, sometimes significantly so (e.g. a fullback overlapping their winger). At a goal kick there's an opportunity for everyone to regroup towards where they're "supposed" to be, so that's probably the best time to look.
Answer: For me every formation can be traced back to one of the two basic formations: 4-3-3 and 4-4-2. All the other formations are just another interpretation of player roles here, or just another way of setting the players (for instance, playing with a defensive midfielder instead of a attacking midfielder).
This in my opinion makes a lot more sense since a team always has to react on situations during the match. An example: Real Madrid mostly plays a almost classis 4-3-3 formation, with Marcelo as their left full-back. In the Primera Division, Real is almost always the better team, resulting in a lot of possesion, so Marcelo can stand much deeper (almost playing as a midfielder or even a winger). But when Real is playing against Barcelona, we mostly see Barca in possesion, so Marcelo has to think defensively more and thus will stand less deep than when having much possesion. You see that in this case, the formation in possesion can almost be described as being a 3-4-3 formation, while not being in possesion yields a 4-3-3 formation.
The main difference between 4-3-3 and 4-2-2 is the number of strikers. Where 4-3-3 in most cases uses one striker and two wingers (nowadays mostly cutting inside), 4-2-2 uses 2 strikers.
I will give an example using the 4-4-2 formation and transform it to a 3-5-2:

Here we see the standard 4-4-2 formation. We see that the midfielders are all close to the center of the field, so only the Wing Backs occupy the wings. This formation is useful for 2 different tactics:

A tactic where short passing is the main cause. Especially useful for teams without tall strikers.
A tactic where the long ball is played to very tall strikers. This tactic is played a lot by the more fysical teams. This is why this tactic is quite popular in the English Premier League.

Now, if we want to transform this 4-4-2 to a standard 3-5-2 we only have to move some players. First, and most important, one of the Center Backs is re-positioned as a Defensive Midfielder. This causes a big gap in the center of the field, which is catched by moving your Full-Backs closer to the center (they're actually becomming normal backs now). The last problem that has to be catched now is the center midfield, which is to heavily occupied. We catch this by moving the 2 Central Midfielders to the wings. Now our standard 3-5-2 is created:

This is just an example. You could for instance also transform a classic 4-3-3 into a 4-2-3-1 formation. (e.g. moving your wingers back a bit, and play with a attacking midfielder).
So, in the end we can actually state that a real formation doesn't exist, it all is about the overall tactics and players that are used in the tactics. The only way to really learn how a team plays is watch it often.


Can knowledge about argumentation be sufficient for philosophical logic without too symbolic or mathematical concepts?

Question: The most important element for expression of truth is trough an argument, with premises and conclusion. Argumentation requires to avoid fallacies and adhere to the truth. However logic if treated as a subject itself and not a part of something else grows bigger and deeper, that it leads to symbols which I find unnecessary for philosophical usage of asserting an existential claim or in other words it turns to mathematical than philosophical, take for example the concepts of propositional and other forms of modern logic with terms and functions to obscure to be used for philosophical assertions. So can the basic knowledge about argumentation, fallacies, and adherence to truth be sufficient for philosophical logic or philosophical purposes without too symbolic or mathematical concepts?
Comment: Am I mistaken, or is this question really about your own personal taste?  You say that formal and symbolic logic is "too obscure" and you find it "unnecessary for philosophical usage", and then ask us if it is possible for philosophical logic be done without it being "too" symbolic.  But how are we to judge what is "too obscure" or "too symbolic" in this context? Clearly, there are varying degrees of formalization found in various philosophical texts; what criteria would you like us to use to assess these?
Comment: Plenty of philosophers don't use or even study any formal logic beyond basic undergraduate logic courses. So if the question is whether we can do good philosophy without symbolic logic, the answer is "of course we can." In fact, artificially formalizing arguments when you need not introduce formalisms is frowned upon in academic philosophy and can easily get papers rejected from publication.
Answer: I assume by "basic knowledge" you mean "Aristotelian logic", namely syllogisms.
The answer is no, this is not sufficient. Inductive logic cannot be expressed in this manner, and (more damningly) Frege's introduction of quantifiers and variables showed that there were a large number of sentences which can't be expressed in standard Aristotelian form.
However, there are an infinite number of ways of writing logic (more formally, an infinite number of Universal Turing Machines which enumerate theorems), and so any particular encoding is arbitrary. If you don't like the current symbols, then by all means substitute your own. (Or if you prefer writing "for all" to the upside-down A, etc.)
Some examples where "complicated" logic is useful in Philosophy:

Fitelson and Zalta's Steps to a Computational Metaphysics
Lokhorst's Towards the Metaethical Robot
Lucas and Penrose have both advanced theories of mind related to Godel's second theorem. You can find an overview of their thoughts here.
Comment: @ThomasKlimpel - Waving your hands about creativity is waving your hands.  Do you have any theoretical basis for assuming that one cannot compute creativity?  Or that various unproven alternatives cannot be explored in depth by an algorithm?  (Chess programs already do the latter.)  Does having the last word make one's truth-statements any more true?
Comment: While I agree with most of your points (+1), I feel compelled to point out that we have _no evidence that humans are better theorem-solvers than Turing machines_.  We have come up with clever ways to solve _individual_ problems (and classes thereof) that would naively be out of reach of a Turing machine, but there is no proof that a Turing machine could not implement the same clever approaches that we use, nor can we demonstrate that we are universal solvers (though it's tempting to assume we are!).
Comment: @RexKerr There are good reasons to believe that all (present, past and future) human minds together (including the tools they will invent) are better problem solvers than any given Turing machine using sound reasoning, at least with respect to their creativity. They won't use only sound reasoning, and they have the "game theoretic" privilege to always have the last word.
Comment: Rex: I do not mean to agree with Lucas or Penrose (I don't), I just wanted to point out that an understanding of their argument requires a fairly deep understanding of logic.
Answer: Both traditional (e.g., syllogistic or dialectical reasoning) and modern symbolic logic are based on equivalent rules of formal inference. What is essential to either case is not the content expressed in the premises or conclusions of the arguments, but the mediation of the premises according to certain abstract laws of thought, which can be expressed either formally or informally.
In a categorical syllogism, for example, the major premise "All men are mortal," and minor premise "Socrates is a man" is what supplies the content rather than the form of the argument. In this case, the inference rule is categorical since it coordinates the middle term (man) with the major term (mortal) and minor term (Socrates) to yield the conclusion that "Socrates is mortal." In other words, a categorical syllogism is a formal pattern of reasoning that certifies the inference from universal to particular.
The very same rule can also be expressed in predicate logic using, for instance, the law of universal instantiation, as in the following: ∀xP(x); ∴ P(c). Stated in natural language, this argument would be rendered as: all (∀ = the universal quantifier) mortals (x = the subject or variable) are men (P = the predicate); therefore (∴ = the logical consequence or entailment) Socrates is mortal, as Socrates is an instance (c = an element of the domain) of men (P): or more economically ∀xP(x); ∴ P(Socrates).
The point here is that there are always formal laws of logic operative in philosophy. Whether these are expressed implicitly in a natural language, or explicitly using artificial formalisms is more a matter of taste and the particular kinds of problems one has to deal with. A complex empirical theory, for example, might require the precision and mathematical grip made possible by the latter, whereas a more creative or synthetic account may depend on the fluid or rhetorical properties of speech made possible by the former. With either approach, though, you are still accountable to the same logical laws; that is, the distinction is closer to vocabulary or mode of presentation, than of logical rigour or expressive power.


How is data encrypted and decrypted in onion routing?

Question: I read that onion proxy adds a layer of abstraction for each onion router in a route,and each onion router just removes a layer of encryption then does onion proxy knows about all onion routers in the route? and does onion routers just decrypts the data and not encrypt them?
Answer: directory server periodically uploads the list of nodes that are available for relaying data. client selects three nodes from this list and gets their public key using which it encrypt data multiple times and sends data to first node of the circuit. each node in the circuit decrypts one layer using their private key. and exit node send data to the destination.
Comment: can client select more than 3 nodes?what tor proxy does?
Comment: in tor there client is restricted to select 3 nodes. but onion routing can have other implementations where this number can change.
Comment: tor and onion routing is different?tor directory uploads the list of nodes...what tor proxy does then?
Comment: onion routing is a technique of achieving anonymity. But tor is one of its implementations. Tor proxy is actually a bridge between client and the anonymous path.
Comment: read about bridge in tor documentation, you will get clear picture of how connection is established using bridge or without bridge..... if you are satisfied with answer please up vote my answer.
Answer: Let's imagine you want to reach a website. Your tor client gets 3 relays out of list of available ones. After that it shares different decryption/encryption keys with each relay. Then it encrypts the packets 3 times and sends them. Each relay decrypts one layer and exit one can see all data going to the website decrypted as plain text. When your data reaches the website the website sends data back to the exit node again in plain text. Then RELAYS share encryption/decryption keys with you. Exit node encrypts the first time, middle second and entry third time. Then you get the data and you decrypt each layer.
So yeah... relays encrypt and decrypt data. Also when the website sends data back to exit node it has some way to link it to middle and middle to entry and entry to you. I don't know how but I hope none of them knows the whole path.


Can I download my own voice greeting in Google Voice?

Question: I'm trying to download my own voice message (my recorded greeting) from Google Voice. Is there an option to do it?
Answer: Yes, use the Google Takeout service to download your Google Voice data.
This is what the Google Voice archive will contain:

Your Voice billing history and conversations will be provided as HTML. Greetings and voicemail recordings will be provided as MPEG Audio (mp3). Your list of phones will be provided in the vCard format.
Comment: Unfortunately, you can't get _just_ the greetings. I don't have much data in my GV but it was well over a 60MB file. But my greetings were easily found as MP3s.
Answer: Note: You don't need to download it. Recording a new greeting doesn't delete your old one/s.
If you still want to download your greeting, here's a way to get just the greeting:

On Google Chrome, go to Google Voice - Settings
Play your active greeting
Refresh the page
Press ⌥⌘I to view Google Chrome's Developer Tools
Select the Network tab
Play your active greeting
Select the name of the request that appears with type media
Under Headers > General > Request URL, copy the text after base64,

Now, you have your Base64-encoded greeting copied to your clipboard.

Paste it into a file, eg: ~/Downloads/google-voice/greeting-base64.txt

On macOS, one way to decode it is by running the following commands in Terminal:
cd ~/Downloads/google-voice
base64 --decode --input=greeting-base64.txt --output=greeting.mp3

I'm not sure if this way gives you the same exact file you get by using Google Takeout, but I think it's the same exact file that plays when you play your greeting from Google Voice - Settings.


Can we have the two DSL language with same extension?

Question: I am developing a tool, and there are lots of Domain classes. I want to divide them in the different DSL's with same extension.
So it is possible to have multiple DSL projects with same extension?
And also after building the setup of all the dsl can we view all the Domain Classes of different DSL projects with same extension in Toolbar of one solution.
Answer: You might try the DSL forum on MSDN: http://social.msdn.microsoft.com/Forums/en-US/dslvsarchx/threads


2015 Toyota RAV4 service manual

Question: Can you buy a 2015 Toyota RAV4 service manual? The dealer has promised me one and it's been almost a month and no service manual.
Comment: I made the same deal with my Rav4. they even charged me 500 dollars. I got the "we owe you" slip. I waited the stated time and never got it. Had to chase the sales man down because he did not return any request for communication. Later , i did get my money back and found that service manuals are no longer made available . you have to pay for a level of access to their online service. while you can print the desired info, you cannot download the book. Corporations suck. They will never touch my car unless it absolutely cannot be avoided.
Answer: You can buy earlier ones from Best Brands Repair Manuals and Helm Inc, but not yet for the 2015.
I'm surprised the dealership has told you they'd give you the service manuals. Are you sure they aren't offering you the owner's manual? They don't usually hand out service manuals. Also, a lot of the newer service manuals for dealerships actually come via electronic means (online or CD), so won't be available that way either. I don't know if Toyota does it this way or not.
Comment: When I brought the car one of my stipulations was a service manual. I was told it was on a Cd but have not received it yet and am very frustrated. I do fix my own cars and I don't know if it's possible to get the manual from somewhere else. Thanks for answering, if you have any advice please help!
Comment: @Bob - If you are in the US, did you get anything in writing stating as such? It would be something called a ***we owe*** slip. If you didn't get it in writing, don't expect to get your service manual. If you have a we owe slip, you'll need to go in and talk to the General Manager (not the salesperson). The we owe is a binding document which the dealership has to fulfill. If they don't, you can take them to court (if it ever gets that far) and the court can enforce the document. Usually, the dealership will have you sign one which says "we owe you nothing" to cover their own butts.

2015 Toyota RAV4 service manual


Multiple next-hops for a destination

Question: I want to add a primary next-hop for a destination and then a secondary next-hope for the same destination, in case the first one fails. How can i do that? i couldn't find a straight answer on the Internet.
Thanks,
Alex
Comment: How do you define fails?  Are you expecting the to only detect if the next hop fails or are you expecting to find some method to know that the link is broken upstream?
Answer: Look up "metrics".
These are used to calculate the "cost" of a route, the lowest being the best, but as i understand it they aren't fully used with static routing, so you'll need a routing protocol to take advantage of it (rip, ospf, etc).

The last argument on the command line is the routing metric. The metric argument is not used when routes are deleted, but some older systems require it when a route is added; for Solaris 8, the metric is optional. Systems that require a metric value for the route command use it only to decide if this is a route through a directly attached interface or a route through an external gateway. If the metric is 0, the route is installed as a route through a local interface, and the G flag, which we saw in the netstat -i display, is not set. If the metric value is greater than 0, the route is installed with the G flag set, and the gateway address is assumed to be the address of an external gateway. Static routing makes no real use of the metric. Dynamic routing is required to make real use of varying metric values.
Info from this guide

Multiple next-hops for a destination


Views Search Returning Unexpected Results

Question: Problem:
Items are not grouping correctly.
The Setup:
I'm working in Views and trying to customize it to display items grouped by a taxonomy term field called 'Event Type'. Furthermore I'd like them to be grouped WITHIN each taxonomy term grouping by Category (in a specific order). Each resource has both an event type and category. There are three event types: timely event, quick study, and deep dive. There are 10 categories: webinar, conference, articles, etc. 3 of those categories are also in 'Timely Events'. 4 of them are in 'Quick study'. The other 3 are in 'deep dive'.
My categories are setup to be ordered. The category field is a field list and has key/value pairings to match what I want. So, for example:
1|Webinar
2|conference
3|Workshop
4|Articles
etc.

Note that webinar, conference, and workshop will the 3 under 'timely events' and that's why they're ordered that way. The next four starting with Articles are under 'Quick Study', etc.
So I have it structured the way I want it to appear in the view already. And I want the view to reflect this by displaying something like this:
Timely Events
All webinars listed
All workshops listed
All conferences listed

Quick Study
All Articles listed
All [other 3 categories in order as set in the key/value pair above]

Deep Dive
Same as the others

Then in the view itself I have set Format > Unformatted List > Settings (Grouping field Nr. 1: Content: All taxonomy terms).
In Fields I have 'all taxonomy terms' set as the first field, with the following settings: 'exclude from display' and 'limit terms by vocabulary' > set to 'event-type'.
Under 'Content: all taxonomy terms' in 'Fields' I'm displaying icon, price, title, event dates, and body.
My filter criteria is set to published, type=resource, search terms and other exposed filters.
My sort criteria is set to Category (asc), event-dates asc, content: title.
The Result:
    Timely Events (header)
    All webinars listed in the correct order.

    Deep Dive
    All certificates listed in the correct order.

    Timely Events (again - why?)
    All conferences listed in the correct order.

    Quick Study
    All articles listed in the correct order.

    Timely Events (yet again)
    All workshops listed in the correct order.

My Question for you:
How can I get my results to display so that the headers (event type) display ONLY ONCE followed by each of the categories in that header in the order in which I've set them in the key/value pairing in the field list?
It should be like this:
Timely events (header)
all webinars
all conferences
all workshops

Quick Study (header)
all articles
etc.

Deep Dive (header)
all certificates
etc.

And that's it.
Anyone have any idea how to correct my grouping here?
Answer: Of course. Since I have 10 sub-categories and I'm ranking them by 'key' number 10 is displaying AFTER number 1 and then 2, 3, 4, 5, 6, 7, 8, 9. That's why it's returning the incorrect results. 10 should be named something else like 99 so it comes after 9.


Are Restriction Enzymes obsolete with CRISPR?

Question: Are Restriction Enzymes obsolete with CRISPR?
Answer: No.
While CRISPR allows you cut a piece of DNA anywhere, you need to order a guide RNA to target your desired cut site. All standard plasmids still carry traditional restriction sites, and it's often convenient to use these. Using CRISPR as a restriction enzyme is probably more expensive and more complicated than using traditional restriction digest. Additionally, there are limitations about PAM sites with CRISPR. And you can always PCR a plasmid using whatever primers you want to produce a blunt end product that is "cut" where ever you want, and I'd bet the DNA oligos needed for PCR are cheaper than the guide RNA you need for CRISPR.


NCX TOC - Hide the external TOC in EPUB 2?

Question: Is there a way to completely remove or deactivate the external TOC?  Would the code be written in the NCX file or elsewhere?  If code could be provided that would be helpful as well.
Comment: The EPUB 2 specification doesn't refer to an "external TOC" in either of the OPS, OCF nor OPF specification.  Where is this external TOC defined? In specification or just in some software you are using?
Comment: I say external TOC to differentiate from the internal TOC which is literally inside the epub and is usually titled something along the lines of 'contents.html'  The NCX file functions as the 'external TOC' because it is what allows the reader to generate a sidebar TOC outside of the 'book' for quick navigational purposes.  I want to deactivate this functionality however, because I am working with a very simple children's book not requiring this functionality.
Comment: Is there a particular portion of the NCX contents that you would like to hide? Or would you just like for the reading system to ignore the NCX file entirely?
Comment: Ignore entirely
Answer: You cannot deactivate/remove the ncx file. As the epub will not validate without it. Why dont you just simply remove all the links from within it, that way, if a reader does open it up in a sidebar it will simply show a blank screen. Not really user friendly though. I would recommend you add atleast one entry, pointing to the start of your book or your "internal toc".
Taking the above into consideration your navmap inside your ncx file would look something like this:
<code><navMap>
    <navPoint id="navpoint1" playOrder="1">
        <navLabel>
            <text>Your book title</text>
        </navLabel>
        <content src="page1.xhtml" />
    </navPoint>
</navMap>
</code>
Comment: Okay, that's okay I guess - I'm working on a children's 10 page illustrated book where navigational means are obviously not necessary - I wanted to streamline the book without the NCX sidebar option because children will not really get what or why something is encroaching on their reading experience
Answer: @Morne's answer is correct; you cannot totally disable the NCX file but of course you don't have to put anything (or very much) in it.
However, another option might be to build an ePub 3 file - the NCX is optional in ePub 3, so you could just omit it.
That said, I do not know how existing readers render ePubs which do not contain an NCX.
Comment: epub3 is an option - that's true I might go that route - the guide in epub3 is necessary though but I don't remember how the guide manifests itself in the reader