Is there a layer of hell associated with forging or constructs?

Question: I have an idea for a campaign where a particular villain makes a deal with a an archduke of one of hell's layer and that archduke supplies/assists them with evil constructs or helps them build them/supplies the resources (was thinking of Dispater and Dis for this) are there any layers associated with evil constructs?
Comment: Are you interested in layers as described in this particular adventure, or is lore from 5e Forgotten Realms ok? Or lore from earlier editions?
Answer: The Second Hell: Dis and its Iron City
The second layer of Baator is Dis, named for Dispater, its ruler since the beginning.¹ It is an endless, arid, barren wasteland around a single megacity, also named Dis—because it dominates the layer, to the point that many will tell you it is the entire layer. The Iron City might be the only place in Hell that is even remotely welcoming to travelers, and one of the greatest trading hubs in the Multiverse.²
Dis's epithet is very literal. All streets, buildings, and amenities in the Iron City are made of iron—and that iron is all red-hot. (Fire resistance is necessary for all visitors.) It is constantly remodeled by devils and their slaves to curry favor with Dispater, and it churns out metalwork of all kinds at all times. The city is near-literally a forge itself, and contains within it an endless array of forges.
On the other hand, Dis does not have any strong association with constructs. Hell doesn't tend to care for them—when devils want endless labor, they get the souls of the damned to do it. An unfeeling construct that never tires of its post and never bemoans its lot is a wasted opportunity in a place where suffering is power. The Iron City probably manufactures a fairly-large number of iron³ golems, just because it makes a lot of everything iron,³ but it isn't something the City is known for in particular.
That said, particularly for a scheme in which actual devils are undesirable, manufacturing constructs does seem very in keeping with Dis. Mechanus, the plane of Law, manufactures inevitables, robots made from alloys of pure law, to enforce certain laws—Hell could do something similar.⁴ They are, after a fashion, just as lawful as Mechanus.
Or just corrupt some actual inevitables. If anyplace can do it, it's Dis—the other thing that Dis manufactures is corruption, in the prison of Mentiri, where those who break Hell's laws are tortured until they really embrace Hell's evil work. A secret cell buried in the depths of Mentiri is the perfect place to work on corrupting the supposedly-incorruptible.
The best sources for information on the Iron City of Dis are 3rd edition supplements, Manual of the Planes⁵ and Fiendish Codex II: Tyrants of the Nine Hells. The 2nd edition supplement Guide to Hell is also useful. I don't believe anything in 5e has covered Dis in any significant detail, but the Nine Hells are still nine, so Dis still exists.

Of the baatezu occupation of Hell, that is. Which will be "the beginning" as far as you're concerned, at least while in Hell, if you know what's good for ya. Bringing up any dark about a time before that is asking for trouble.

Comparable to the City of Brass, which between them are tied for second to Sigil, the City of Doors.

And other metals, and non-metals too, for that matter—Dis manufactures a lot of everything. Iron is just something of a specialty.

The exact process of manufacturing inevitables is a closely-guarded secret, so Hell wouldn't be able to easily replicate it exactly, but the general idea, perhaps somewhat less refined, should be well within their capability.

Note that D&D has used the title "Manual of the Planes" several times for separate publications in different editions. So far as I know, the 3e one is the only one with significant information about Dis.

Not Mechanus, but...
The Clockwork Nirvana is not a great answer to this question, because while modrons can be corrupted, when they are, they no longer fit into the great machine that is Mechanus. Mechanus doesn't have a place or the time for evil—and it doesn't accept things that aren't in their proper time and place. There's a reason why Acererak's pet pentadrone was in his tomb: it didn't really have anywhere else to go.
Even corrupting some chunk of Mechanus itself is a poor answer, because:

That's never happened, and that's despite the Primus being killed and temporarily replaced by a being of supreme Evil and Chaos (Tenebrous, the god-slaying god that the Demon Prince Orcus became when he had the Last Word).

Even if it somehow did, that corrupted chunk would cease to be a part of Mechanus. Mechanus is Lawful Neutral—whatever is not, is not Mechanus. Pieces of planes can and do shift from one plane to another when things get too far out of whack—a third of Arcadia, the layer of Menausus, slid off and became part of Mechanus because the Harmonium, which headquartered there, was so adamantly non-good. If a cog of Mechanus becomes evil, it would also drop out of Mechanus.

Which itself might not be a bad idea. It wouldn't—likely, or at least at first—go to Hell, because Acheron is in between, and frankly Baator wouldn't have a place for it anyway—the Nine Hells will remain Nine. But Acheron could take it—one weird cog floating among the cubes is plausible. You might even miss it; Mechanus has a lot of cogs, and while the modrons would definitely notice, they wouldn't go advertising it. And no can ever really be confident about what is or isn't to be found in Acheron, being the way it is.
I still like Dis better, though. The Mechanus-cog-corrupted-into-Acheron approach is for if you really want to make up something wholesale; Dis is for if you want to fit this into existing lore.
About Acheron
If Mechanus is too much machine for evil, and Baator is too evil for machines, the plane in between them might seem plausible. And certainly, such a plane could well fit in the lawful-by-lawful-evil slot in the Great Wheel. But that plane isn't Acheron.
Acheron is, instead, an endless, pointless, battlefield. There are no goals, nothing to protect, nothing to win, and no victories to be had. Souls there fight for nothing more than their own survival—not surviving for anything, but just because they aren't willing to give up. (Until they do.) In many ways, Acheron is a mockery of chaos: there isn't any particular order to the plane. There is no rhyme or reason to who lives or who dies. It may, in that sense, seem very chaotic. But all that randomness comes out in the wash, because none of it means anything. Nothing ever changes in Acheron because all these random events have no effect whatsoever on any grander destiny. The whole point of the plane is that without some kind of order giving things purpose, even absolute chaos becomes uniform, sterile, and ordered. (Chaos has its own mockery of law in the form of Carceri.)
So Acheron isn't really associated with forges or constructs. It's only by importing a corrupted Mechanus cog that you might introduce some of those elements. That, or a divine realm.
Comment: I think Dis is absolutely the right call... but I think the correct way to go about it is probably for OP to lower their ambitions for the bargaining partner in the equation. As you've noted, Dispater has never shown any particular interest in using constructs to maintain and expand the iron city... but that sounds _exactly_ like the sort of idea that an ambitious and creative Rakhasa or other devil in his service might pursue. Maybe he's developing a new process to bind the souls of the damned imprisoned in Dis into an Iron Golem, in hopes of currying favor with the Duke...
Comment: @LessPop_MoreFizz I don't think Dispater would have a _problem_ using constructs for the right job; remodeling Dis just isn't the right job. On the other hand, I agree that Dispater is an awkward choice for this role. Dispater is the most paranoid devil in Baator—and _that's_ saying something!—on a **good** day. The odds of him trusting foreign agents with anything seems rather low, at a guess. I would have to do more research to make that better than a guess, though. (Also, rakshasas aren't devils; they are lawful fiends, but native to the Material, not Hell.)
Answer: Mechanus, the Clockwork Nirvana.
There is no layer of Hell that really fits what you're looking for. However, the outer plane of Mechanus seems to be right on theme; quoting from chapter 2 of the DMG (p. 66):

On Mechanus, law is reflected in a realm of clockwork gears, all interlocked and turning according to their measure. The cogs seem to be engaged in a calculation so vast that no deity can fathom its purpose. Mechanus embodies absolute order, and its influence can be felt on those who spend time here.
Modrons are the primary inhabitants of Mechanus. The plane is also home to the creator of the modrons: a godlike being called Primus.

While it is not an evil plane, rather, Lawful Neutral, its inhabitants are not incorruptible. In Tomb of Annihilation (p. 177), we learn that the archlich Acererak used modrons from Mechanus to bring Mechanus chains into the tomb and drive his machines:

To drive his infernal machinery, Acererak contaminated a workforce of modrons from the plane of Mechanus. Under the stewardship of a corrupt pentadrone, the modrons rerouted one of their great chains into the tomb. The sections of the shaft above and below the balconies exist outside of normal space, preventing the shaft from intersecting with the tomb's other levels.

So while Mechanus does not generally feature evil constructs, it has the constructs you need, and they can be corrupted.
Comment: I think the reason why there is no layer of hell crammed with devilish machines is likely because the hell in the game is modeled after Dante's Divine Comedy, and when that was written, there was no steam power or other advanced automation in existence, so his hell lacked it. Considering that there are Hellfire Engines, and there is a layer full of ore and metal, it would be useful to have one that has more evil machinery, but I am also not aware this has been docuemented anywhere, at least not for 5e.
Answer: While Dis is probably the best answer, weapons and armor for the Blood War are forged in Avernus. The forge, which also serves as Bel's fortress, is carved out of a volcano.
Source: Descent into Avernus, Ch. 3 (p. 113)


Formation of oximes by ketones and aldehydes

Question: Why do symmetric ketones form a single oxime and asymmetric aldehydes and ketones can form two isomeric oximes?
Comment: Because geometric isomerism.
Answer: An oxime is formed by the reaction of hydroxylamine (NH2OH) with either an aldehyde or ketone. The oxime nitrogen has a double bond (sigma and pi) to the oxime carbon, a lone pair and a single (sigma) bond to the hydroxyl oxygen. If we use valence shell electron pair repulsion (VSEPR) theory to deal with the problem.
Then the oxime nitrogen will be trigonal planar.
If the two groups on a ketone are identical then the molecule will be the same which ever way around we put the lone pair and the hydroxyl. But if the two carbon groups are different then we can have two isomers.
Consider for a moment the 2-hydroxyoximes used as LIX extraction agents for copper. There is a paper from the 1970s on the separation of the isomers of LIX 63 (T.T.Tammi, Hydrometallurgy, 1977, Volume 2, Issue 4 (October), Pages 371-380) which you migh want to read.
To make it more clear we have diagrams here of the two isomers of LIX63.
Comment: Good answer and +1 from me.  Might be worth noting that hydroxylamine_s_ react as a class -- the reaction happens w/ more than just $\ce{NH2OH}$.  O-methyl hydroxylamine gives O-substituted oximes, etc.


In what ways the letters of the word "PUZZLE" can be arranged to form the different new words so that the vowels always come together?

Question: I tried this way:
Taking 'UE' together and remaining 'PZZL'.
So, as 'Z' is repeating, I divide it by $2!$.
My answer: $(5!/2!)\cdot 2! = 120$.
Is it right?
And why do we divide by its factorial if some letters are repeating?
Comment: We divide by $k!$ if a letter appears $k$ times because the factorial at the numerator assumes that all letters are distinguishable, which they are not.
Answer:
Take 'UE' together and 'PZZLE' is remaining

The $E$ should be together with $UE$, so in fact you have something like $(UE)PZZL$ or $(EU)PZZL$.

So, as 'Z' is repeating I divide it by 2!

That's correct. If we call the two letters $Z_1$ and $Z_2$, there are $2!$ ways to arrange the $Z$'s, but there is only one distinguishable combination: you cannot tell $Z_1$ and $Z_2$ apart.

My answer :- (5!/2!)*2! = 120. Is it right?

Yes. There are $5!$ ways to arrange the $5$ objects $UE$, $P$, $Z$, $Z$ and $L$. $U$ and $E$ are interchangeable so we can multiply by $2!$, but as earlier said the two $Z$'s are not, so we divide by $2!$.


Apple Watch face blank

Question: I mistakenly unpaired my Apple Watch from my iPhone. Now the voice over on my watch is on, screen curtain is on, but my screen is blank. I don't know which button to press and I have been trying to pair it back. Since my screen is blank, how do I do this?
Answer: Try restarting it by holding down the Digital Crown and side button together until you see the Apple logo appear. When that doesn't work, set it on charge for 15 minutes and repeat. After an hour and no life, you might need a hardware repair or service technician to diagnose it from the service port.

Apple Watch face blank


sums and differences in consecutive grid

Question: Fill in each square of the grid with a number from $1$ to $16$,
using each number exactly once. Numbers at the left or top give
the largest sum of two numbers in that row or column. Numbers
at the right or bottom give the largest difference of two numbers in
that row or column.
Comment: This is another USAMTS past puzzle that you have not declared as such in the post - it comes from the Round 3 problem set from 2016-17. *You must provide attribution for puzzles created by others or sourced from elsewhere.*
Answer: Very nice puzzle!

@WeatherVane beat me to the answer but thought I'd post with some logical deductions:

Logic on how to solve:

Initial deductions about combinations

Firstly, there are two 28 sums which can only be made by $12+16$ and $13+15$, so one pair must be in each of the two sums' row/column. It also means the $14$ is not in either of these rows/columns, as then the maximum sum would be more than 28.

There are also two 13 sums, each with a max difference of 7. There are also only two ways to each achieve these, but this time we know nearly the entire row: $[9,4,3,2]$ or $[8,5,?,1]$ with $? = 4, 3$ or $2$.

The two sums overlap in the first cell, and the $?$ must be in this cell, although we don't know which digit it is yet.

Now consider the 23 sums. One has a difference of 8, and there are 3 ways this could happen, with $[14,9,?,6]$, $[13,10,?,5]$ or $[12,11,?,4]$ where the $?$ is always between the second and last number. Similarly the 23 with a 12 difference has 4 ways.

Now finally consider the 25 sum. There are 4 ways to make it $[16,9,?,4]$, $[15,10,?,3]$, $[14,11,?,2]$ and $[13,12,?,1]$. But it can't be the $16$ or $13$ option as the $9/4$ and $13/12$ are required in the 13 and 28 sums.

It also cannot be the $15$ option, as the $15$ would have to go in the overlap with 28, and then $13$ can only go on the right to complete the 28 but then both the 25 and 23 column both need a $10$. So the 25 must be $[14,11,?,2]$ and numbers can start to be placed.

Placing numbers

The $2$ must overlap with the 13 sum so goes at the top. That leaves a $4$ or $3$ top left, and we also know which way round the 13 sums go, and the $9$ must be at the top.

Now the $14$ can't overlap with the 28 sum so is in the bottom two rows. But if it is in the 23 sum, a $9$ is required, but that is already required at the top, so it must be second bottom.

If the $11$ now goes on the bottom row, the $12$ must go next to it to complete the 23 but overlap with 28, but then that leaves no place for the $13/15$ pair for the other 28. So the $11$ must be on the second row.

The $14$ cannot have a difference of greater than 8, so no other cell in that row can be below $6$. This means in the first column there must be an $8$ for the 13 sum. The $1$ then has to be on the second row, as if it is on the bottom row then the 23 cannot be made, and hence the $5$ is on the second row.

There is only two places left for the $12/16$ pair to complete the 28 in row 2, and the only number in the pairs for the 28 that can overlap both 28s is the $12$, as it doesn't affect $13+15$, so that goes in the second column, and $16$ in the last.

The 23 sum in the 4th column needs a $4$ for a difference of 12 and this must go in the first row for the 13 sum. This completes the sum and a $9$ can be put in the second column, and a $3$ in the top left.

 The 23 sum at the bottom now is from $13+10$, so the $15/13$ pair to complete the remaining 28 pair must have the $13$ at the bottom.

There are $6$, $7$ and $10$ remaining to be placed. The $15$ in the 3rd row now means the remaining cell on the right cannot be below $7$, so the $6$ must be in the bottom row , as does the $10$ for the 23 sum, and the $7$ goes in the 3rd row.

Finally, the $10$ can't go in the final column, otherwise it would make a sum of 26, so it goes in the 3rd column, and we're done!
Comment: Nice logical approach – it seems we verified each other's solution.
Comment: @WeatherVane upvoted as thats harsh, maybe add a bit about what the algorithm works would help?
Comment: Thanks to you :)
Comment: *It also means the 14 is not in either of these rows/columns* - Why?
Comment: @BadHorsie if 14 was in the same row/column of either of those pairs, you'd be able to create a sum more than 28, so it has to be elsewhere. E.g. if it was the same row as 12+16, the new maximum sum would be 14+16 which isn't 28
Answer: My solution:

 Method: programmed recursion in C –
 Permute the 16 numbers on the bottom row.
 For each arrangement, check the maximum sum and difference tally.
 If so, mark those numbers as used and move to the next row up.
 Repeat using the available numbers until the top row is solved.
 Finally verify that the maxima for each column is correct.
 One solution only was found.
  3  9  2  4
  1 12 11 16
  8 15 14  7
  5 13 10  6


Setting custom x/y bed bounds for Anet A8/marlin

Question: I have an Anet A8 that I just flashed with the latest Marlin firmware (1.1.9). I'm sending prints to my printer with Ultimaker Cura via OctoPrint.
I have affixed a PEI surface to my bed that's about 10 mm smaller in each direction than the full size of the bed (that is, I lose about 5 mm on each side of the bed). This hasn't been a huge problem as usually I account for this myself and just make sure there's lots of room on each side of a print, but having upgraded my firmware, I'd like to take advantage of Marlin's bi-linear bed-levelling. Unfortunately, several of the points it chooses are outside the bounds of my PEI surface and so it's impossible to get a decent setting for those points.
What's the "correct" way to configure Marlin to know that my bed size is actually smaller than it thinks it is? Do I need to additionally adjust settings in Ultimaker Cura and/or OctoPrint?
Comment: The answer to the question can be found in [How to center my prints on the build platform? (Re-calibrate homing offset)](/q/6375). You need to set correct bed size dimensions and offsets from end stops. This question is a possible duplicate.
Answer: As you just flashed your own Marlin, you probably have the marlin.ino and its associated files in the Arduino IDE set for your Processor and board and know how to work with them to some degree. This is just the short version where to find what you need to change the bed size, if the marlin.ino is based on the marlinfw-release.
Changing "home"
In Configuration.h there should be a set of lines that reads akin to this:
// Travel limits (mm) after homing, corresponding to endstop positions.
#define X_MIN_POS 0
#define Y_MIN_POS 0
#define Z_MIN_POS 0
#define X_MAX_POS X_BED_SIZE
#define Y_MAX_POS Y_BED_SIZE
#define Z_MAX_POS 200

Usually it is faster to use Ctrl+F and then typing in X_MIN_POS and adding the hook in front of Search all Sketch Tabs and then moving through all the finds till the right one pops up. This not only brings you right to the lines you want to alter, but also covers up the bases in case the distribution you work with did put the movement limits into a different location like Configruration_adv.h.
Changing Bed Size
Alter these minimum positions and make sure that the Maximum positions (usually just after them) to fit the maximum of the bed.
If you reduced your bed size, you also might need to change X_BED_SIZE and Y_BED_SIZE, which (in the marlin.ino) is in the same Configuration.h - I found it to preceede the Travel limits:
// The size of the print bed
#define X_BED_SIZE 200
#define Y_BED_SIZE 200

Adjust these as needed to fit the new sizing.
Hint: Getting the Values for Adjusting
For finding the adjusted values, I have had good experiences using Repetier Host on Manual Control to move the nozzle (lifted 1mm to prevent any accidents) into the correct XY-position and taking this position as adjustments for the minimum positions. Finding your personal settings is a bit of a trial and error still, so take your time.
Finishing up
Now, recompile the marlin.ino (the checkmark in the top left) to check for errors and flash the new firmware it.
Comment: Thanks! The starting (x,y,z) values in my config were (-33, -12, 0) and it took me a bit of experimentation to figure out that to adjust the bounds of the bed 12mm right and 5mm back I needed to go to (-45,-17,0), but having sorted that out (and adjusted the max positions accordingly) everything seems to be working the way I'd expect.
Comment: @AwesomeTown remember to adjust the ?_BED_SIZE correctly - I forgot to include their lines in the old version, fixed that.


Problems with playing dynamics on a yamaha psr e463

Question: I recently (about 5 months ago) have taken up the hobby of playing piano. I'm following the Alfred Basic Adult Level One book. Really loving it so far but I keep messing up when it comes to one aspect of playing it. As you read in the title, I recently purchased the yamaha psr e463 (was using a friend's keyboard before) to practice the piano. I find it very difficult to play dynamics on it. As you might know, the keys aren't weighted and are super easy to press. However the loudness does vary depending on how hard I strike the key. But still, it's hard for me to get a nice smooth rhythm to any of the pieces that I'm practicing. Is this just a problem with the type of keyboard I've purchased or is there a particular technique that I'm not able to get a handle on? And yes, I'm a completely beginner and am teaching it to myself. I was going to a teacher, but that all stopped cause, you know, pandemic and that.
Comment: Recently, something I noticed about digital piano (at least for me) is that the way you press the keys is highly affected by how strong/low the sound output is set. A few weeks ago, my right arm was getting terribly tired from some practice. I only realised that, because I had set the sound too low, I was reflectively pressing very strong on the weighted keys. It's pretty difficult to find a perfect middle between "too loud" and "too soft" for the sound output.
Comment: Otherwise, this is just an hypothesis, but maybe if the keys were weighted and "resisted" to being pressed, then it would be easier to press more softly. Or maybe there's also the way you press the keys. I noticed some pianists seem to move their arms like water waves when they play softly or something.
Comment: As @Clockwork says, synth-action keyboards do make it hard to control dynamics — the difference in force between 'hard' and 'soft' is so much less than for weighted keyboards.  And because of that reduced force, I don't think they're as good at training your finger muscles, either.  Certainly far better than nothing!  But you'll probably have to make allowances.
Comment: not answering the question, but I thought it may be of interest: there are many cheap keyboard that use pressure strips to determine how hard you strike the key; a whole keyboard may have 7-8 of them. They do not line up with octaves. It means that all keys mapped to one strip will end up with the same pressure. When you play multiple notes in one hand, sometimes all notes fall under one strip, sometimes they fall across two strips. Dynamics are horrible on these keyboards.
Answer: Spring action keyboards can be difficult for getting a good feel and dynamics. I looked at an online manual for your keyboard and found something that might help you. On page 52 of the manual there is a section called "Changing the touch response of the keyboard". There are 4 settings but "fixed" is useless unless you want all the notes to be the same volume. Try 1-3 and see which you like best. You should be able to find one that works best for you.
In case you don't have your owners manual here is a link to an online manual: https://usa.yamaha.com/files/download/other_assets/9/1170809/psre463_ew410_en_om_a0.pdf
One other thing to mention with this type of setting, sometimes the setting is saved when the keyboard is turned off but it's possible it may default to the factory setting and you have to set it each time you turn the keyboard on. You'll know when you try it.
Answer: I think you have more than one problem here.
The first problem is that non-weighted keys are not designed to be played in any way except fully-on or fully-off.  It's a design that comes from church organs and has followed on through other organ designs.  You can try to train your fingers to do this, but it's not going to be as successful.
The second problem is that having trained your fingers to do this, you're going to have real trouble transferring to a "proper" piano.  Much of what you've learnt as muscle memory, you're going to have to unlearn in order to play a normal piano.
The third problem on muscle memory, looking at the specs for your Yamaha, is that I don't believe it uses full-size keys.  This is really going to screw you over if you transfer to a proper piano, because you'll need your fingers that bit further apart.
And the fourth problem is that your Yamaha is a 61-key keyboard.  Of course the "dusty ends" of the keyboard aren't used that often, especially as a beginner, but you run into limitations surprisingly quickly on a smaller keyboard.  Certainly by next year, if you keep playing, I'd be amazed if you weren't seeing a couple of pieces you couldn't play the top or bottom notes of.
For sure it has a lot of bells and whistles.  USB recording, rhythm stuff, all those kind of gimmicks.  And you don't need any of them!  What you need is precisely one thing, and that's an 88-key keyboard with weighted action.  In short, you probably need to stop trying to do something with your Yamaha which basically isn't going to work; and buy something else which will work.
The very cheapest weighted-action electric piano keyboard will be much better.  Looking online, Gear4Music in the UK have an own-brand weighted-action keyboard which is actually cheaper than your Yamaha; equivalents probably exist wherever you live.  It might not be the best weighted-action keyboard, but any weighted-action keyboard is going to be better than what you've got now.
Comment: Can I not work with this at all? Is it a complete doom and gloom situation?
Comment: @AyushRoy If you're just kind of playing around a bit, then no worries. But if your aim is to be able to play piano, IMO this isn't the tool for the job. It's a bit like if you want to play guitar and you've bought a ukelele - you can still play tunes on it, but it's not going to work the same.


word similar to obfuscation, used for comedy

Question: there is a word, or perhaps a type of comedy, where simple things are described using terms that are correct but needlessly complicated or absurd for various effects. I am reminded by comics from nathanwpyle on Reddit and twitter examples:
example one
example two
other example sources are welcome
Edit: possibly tangentially related to observational comedy
Answer: If you are looking for a noun to describe such a way to speak or write, there is
circumlocution
noun

a roundabout or indirect way of speaking; the use of more words than necessary to express an idea.
a roundabout expression.

(Dictionary.com)
An example:
"The driveway was not unlike that military training device known as an obstacle course" is a circumlocution for "The driveway resembled an obstacle course.
Comment: Either circumlocution is not necessarily funny, or you chose a particularly weak example. I guess *funny* can't be defined, anyhow. Although, Is it intended to rhyme on *electrocution*? A memorable example in my mind is abuse of technical terminology: *dihydrogen monoxide exfiltrated from a civic resident aquifier*, or *tap water* for short.


Is there a standard way to identify if a mobile application is native or hybrid by looking at the apk file?

Question: I'm a beginner learning mobile appsec. I just wanted to know if there is a standard way to identify if a mobile application is native or hybrid by looking at the apk file?
Answer: If it uses native code, then it should have references to System.load() or System.loadLibrary(). But ...
It could also just execute something native with Runtime or ProcessBuilder, or use DexClassLoader to load a dex/jar which then performs this. But ...
Unfortunately, this could also be worked around, since Java could use reflection to hide any of the mentioned class/method names from static analysis.
Comment: I think there's a misunderstanding about the meaning of "native" here. If I interpret the OP's intent correctly, it's about an app written in "native" Java/Kotlin vs hybrid framework such as React Native, Ionic, Mobile Angular UI, jQuery Mobile, PhoneGap (which are JavaScript-based, hence some of them need WebView to work), but also Flutter and Xamarin,
Comment: Thanks domen.. I remember googling about this, where I read, if the application code contains 'webView' keyword then it could be a Hybrid application?? I don't know if its really that way.. Your inputs pls...
Comment: I don't understand the question. You read that apps containing WebView load native code? There's no obvious relation. Of course if you dig deep enough, you eventually come to native code, but that holds for many things (anything with system calls at least).


How can I configure a fax server?

Question: I would like to use an Ubuntu 11.10 workstation as a fax server.  What would be the best application to use?  How do I configure it to act as both a fax server and fax client?  I've tried efax-gtk, but keep running into issues.  It mostly seems that the program cannot communicate with the modem.  I've tried 3 different internal modems.  Do I have to use an external modem via a serial port/com port?
Answer: HylaFAX is in the repos and they also have a hardware compatibility list which might be a good start.
There are also a couple of tools that were created to provide a GUI for HylaFAX:

http://www.downv.com/Linux/download-Hylafax-Panel-10003413.htm
http://www.downv.com/Linux/download-gnu-hylafax-10001617.htm

Source: Faxserver with GUI or web based interface
"WinModems" are unlikely to give you any real joy so if you can find a "real" modem (as listed) that should work. Finding one of those might solve your problems with efax.
Edit: Or throw the modems away and use an email->fax service instead.
Comment: +1 for the edit comment. When someone asks me to fax something I usually ask if I can send it by telegraph or telegram instead. They usually get the point.

How can I configure a fax server?


Adding a very minor part of GPL3 code to a BSD-licensed project

Question: I am porting a library that somebody else released under BSD-3 license from Fortran to C++. In order to make it run easily under C++, I am using an interface that is only a very minor and almost irrelevant part of the entire library. This interface, however, is part of another code (of which I am the copyright owner) that is released under GPL3. Since the part is minor, is it allowed to include my C++ port with the original project without changing its license?
Comment: The fact that it is a "very minor part" hardly matters at all here. The fact that you are the author of that code matters almost entirely, here. If you had not been the author of that "very minor part", then the answer would be different.
Answer: Since you are the copyright holder of the interface, there is no issue whatsoever. The fact that you have previously included your interface in a GPL-licensed work does not prevent you from including that same interface in a BSD-licensed work. You may offer any number of licenses simultaneously on your own copyrighted work.
If you were not the author of the GPL-licensed work, the situation would be slightly different. The GPL would allow you distribute the interface within another work only if that whole larger work were licensed under the GPL.1 Failure to license the larger work in this way would expose you to legal action from the copyright holder of the interface. However, since the BSD license on the other work is GPL-compatible, it would be completely possible to license the combination in this required way.

The only possible way around this would be to take the legal gamble that the interface is too simple or mechanical to merit copyright protection, so any copyright license -- such as the GPL -- on it would be void. I would strongly discourage anyone from trying that before talking about your specific case with a legal professional experienced in copyright law.
Answer: To address the general issue (and so assuming that you aren't the copyright holder of the GPLv3 code):  Why are you using that interface?  Is it out of convenience, or because you need it to communicate with other software?
If it's out of convenience, don't.  If it's trivial enough to avoid copyright infringement, you should have no difficulty rewriting it.
If it's to communicate with other existing software, you can do that.  Although APIs and the like can be copyrighted in the US, it's legal to use them to make compatible software.  Copyright is not intended to make it impossible to do something, but to protect creativity.  At least in the US, if you can only write compatible software by copying an interface, that isn't a copyright violation.
(In Google vs. Oracle, Oracle claimed that Google hadn't used the Java API to write compatible software, as Oracle claimed conventional Java and Android Java software would be incompatible.  Therefore, since Google could use another API, one that Oracle hadn't copyrighted, it was a copyright violation.)
Comment: Can you clarify the part about "rewriting it"? If I want to use a GPL3 code, can I just rewrite it instead and I escape from GPL3?
Comment: If you take the functionality and write it yourself, you avoid all license complications.  If that's too much work, you're taking too much to disregard the license.
Comment: But wouldn't rewriting it, even if the code is different, be a plagiarism of the idea itself? Is that ok?


Multinomial Coefficient Estimate

Question: Let $\alpha = (\alpha_{1},\dots, \alpha_{n}) \text{ and } \beta = (\beta_{1},\dots, \beta_{n}) \in \mathbb{N}^{n}$ be two vectors of positive integers, and assume that $\beta_{i} \le \alpha_{i}$ for all $1\le i \le n$.
As usual, let $\alpha ! = (\alpha_{1} !) \cdots (\alpha_{n}!)$
and $$\binom{\alpha}{\beta} = \frac{\alpha!}{\beta! (\alpha-\beta)!}.$$
We set $\vert \alpha \vert = \alpha_{1} + \dots + \alpha_{n} $.
My question: Is it true that
$$ \binom{\alpha}{\beta} \le \binom{\vert \alpha \vert }{\vert \beta \vert} $$
Answer: The inequality is true, and in fact it's rather simple to proof it.
Observe that $\binom{\alpha}{\beta} = \prod_{i=1}^{n} \binom{\alpha_{i}}{\beta_{i}}$. The binomial coefficient $\binom{\alpha_{i}}{\beta_{i}}$ is the coefficient of $x^{\beta_{i}}$ in $(1+ x)^{\alpha_{i}}$, while $\binom{\vert \alpha \vert }{\vert\beta \vert}$ is the coefficient of $x^{\vert\beta\vert}$ in $(1+x)^{\vert \alpha \vert}$. The coefficient $\binom{\vert \alpha \vert }{\vert \beta \vert}$ of $x^{\vert \beta \vert }$ in $\prod_{i=1}^{n} (1+x)^{\alpha_{i}}$ is the sum of different products of monomial coefficients which contains $\prod_{i=1}^{n} \binom{\alpha_{i}}{\beta_{i}}$ as summand, and hence the desired inequality follows.
Comment: Is this Q/A thing done just to get a badge?
Comment: No, I just did not see the trivial answer yesterday.

Multinomial Coefficient Estimate


What causes an electric shock - Current or Voltage?

Question: Though voltage and current are two interdependent physical quantity, I would like to know what gives more "shock" to a person - Voltage or Current? In simple words, will it cause more "electric - shock" when the voltage is high or Current is more?
Comment: Related: https://physics.stackexchange.com/a/33613/2451
Comment: Lots of very good informed answers in that related question
Comment: Any one-word (or even one-sentence answer) will be dangerously misleading. You must *understand* electricity and the interaction with parts of the body to have a real chance and know where the danger lies.
Comment: Related: https://skeptics.stackexchange.com/q/1664/
Answer: You'd have to define 'shock', but what kills you is enough current during enough time, not voltage. Of course you need enough voltage to keep the current going over your body's resistance, but it definitely plays a secondary role.
In a former professional life I worked developing Residual Current Circuit Breakers, and 30 mA is the usual rating for devices aiming at protecting lives. In wet environments, such as bathrooms or swimming pools, sometimes 10 mA is recommended.
According to wikipedia's RCCB article, 25-40 ms of 30 mA is enough to send your heart into fibrillation, which probably qualifies as a pretty strong shock. That would require your heart being in the path of the current, though. This link has more information on what to expect depending, again, on the current, not the voltage.
Comment: @annav, this problem is in the context of a circuit which implies a closed path for a current to exist.  While I appreciate the point you've made, I believe it is actually out of context as there is no circuit in your example.
Comment: I suggest this is self evident. You can have a high voltage between two metal plates and put your hand through safely as long as you do not touch them. Otherwise nobody would be able to repair fuses so close to live wires. If there is no current there is no damage, it is the current we feel as "shock".
Comment: "it definitely plays a secondary role." Since voltage and current are proportional, I fail to see how you can assert that one is more important than the other.
Comment: They are proportional in a constant resistance setting. A relatively low voltage can give you a big shock if your hands are e.g. wet, since current will be higher then. Conversely, a not that low voltage may go unnoticed if it prices no current, e.g. because you are wearing non conductive shoes.
Comment: I know it depends but a between being the live wire(series connection) and providing an alternate path for current flow(parallel connection) to an appliance, the former is deadlier? Also a shock from step-down transformer secondary coil would be more dangerous than one from that of step-up transformer?
Answer: If we model the path for the current through the human body as a resistor, then by Ohm's law, the current and voltage are proportional.
That is, a greater current through the body will be associated with a greater voltage across the body.
Having said that, let's consider the source of the shock.  It is the case that sources may produce a large voltage but are not capable or sourcing significant current.  These sources are said to have high internal resistance.
The point is that a high-voltage source with high internal resistance may not give you much of a shock at all while a lower voltage source with low internal resistance may kill you.
So, there really isn't a simple answer to your question other than "it depends".
Answer: You see, current in one direction indicates the flow of free electrons in the other direction. Hence, current flows. But voltage does not flow. It's actually the work done per unit charge. (Joule/Coulomb). In other words, it's an energy or simply the potential difference between two points. Sometimes, a bird does not get a shock while resting on a carrier wire (Not all time the bird sits on the same wire). Whereas By touching the live wire and ground, we create a potential difference (a path which is sufficient enough for current to flow) with live wire relative to earth. Hence, we get a shock.
Electric shock is the sufficient amount of current flowing through human body which the person could feel. But, this doesn't mean that shock is not caused by Voltage. Of course, it depends upon voltage which is given by Ohm's law.
$$I=\frac{V}{R}$$
The shock your body feels, depends upon the applied voltage and resistance of your body. If your body has a resistance of about 10,000 $\Omega$, and the voltage is 230 V, then $$I=\frac{230}{10000}=23 mA$$
You would get a shock, but seriously. (You can't let go off this current.)
Hence, you cannot differentiate a shock based on voltage or current. It depends on both voltage and resistance of your body (which implies current).
Here's a page which shows current paths and another one which provides comparison info.
Comment: "You see, current in one direction indicates the flow of free electrons in the other direction." No, conventional current indicates a flow of positive *charge*.  In metals, this consists of a flow of electrons in the opposite direction.  In your body, it consists of positive and negative ions flowing in opposite directions at the same time. http://amasci.com/amateur/elecdir.html
Answer: The shock is the product of the current and the voltage, so in principle you need both. A friction spark from your shoe is high voltage by low ampage, but a shock from a power main is high ampage and comparatively low voltage.
The type of current, whether it is alternating or steady, is also important, as an alternating current will interfere with biological processes more than a steady current. But the energy deposited is the product of the two, so it is not meaningful to separate them out.
Comment: @Tabish: For the first thing, by voltage, one always means "voltage difference", the bird has no voltage difference between it's feet, so there is no effect. The product is the energy delivered by the shock, so it's how much you heat up, how much burning you get at the skin and flesh, but it isn't the severity of stopping your heart, which is a different thing, related to the electrical flows that regulate the heartbeat. Also, in terms of feeling the shock, setting up nerve impulses is not by power, but by the change in intermembrane voltages, but power is good rough guide to the effect.
Comment: "A friction spark from your shoe is high voltage by low ampage"  No, it's several amps.  It's harmless because of the short duration.
Comment: @RonMaimon: Usually when people say "static electrical discharges are low current", they actually believe that they are low current, and that that is what makes it harmless.  This leads to sayings like "it's the current that kills, not the voltage".  Static discharges are harmless because the current is short-lived, not because it is low.  http://skeptics.stackexchange.com/a/2588/155
Comment: Thanks for your quick response Ron but I would like to understand two more points on this :
1. When a bird sits on high voltage wire, nothing happens - of course the conductivity is not there so in spite of high voltage there is no "electric-shock".. Doesn't that suggest "Voltage" has no role in the intensity of the "shock" ?
Comment: 2. When you say "shock is the product of the current and the voltage", do you say this is how we can quantify the intensity of "shock" ? Is this the actual formula ?
Comment: Thanks Qmechanic, It helped.
Thanks Ron for taking time to address this.
Comment: @endolith: You know what I meant, I meant "charge delivered", so you get the energy out when you multiply.
Comment: @endolith: You are completely right of course, I wasn't thinking about nuances, I just wanted to explain the energetics is the product of the charge times voltage difference, and I used P=IV. I don't want to bump this, but if you feel strongly, edit the answer as you like.
Answer: It cannot be just voltage as you can demonstrate with a comb!
After a comb has been passed through dry hair it acquires a charge which can be shown by the comb picking up small pieces of paper which are close to it.
The potential of part of the comb relative to the holder of the comb is actually very large and can be thousands of volts.
This can be shown by using a (gold) leaf electroscope as a voltmeter which deflects if the applied voltage is greater than hundreds of volts.
Bringing the charge comb close to the electroscope will give a sizeable deflection.
If the holder of the comb touches the charged end then he/she will not feel a shock the reason being that although the voltage is high the charge on the comb is so small that when transferred to the holder the resulting current is very small.
A small electrostatic generator called an electrophorus when charged and touch can produce a tingling sensation and also sometimes a small spark, in the act of the electrophorus being touched, which can be hear and seen in a darkened room.
Still a high voltage but with more charge transfer, ie a larger current, results in a greater response by the human body.
So it is the current, the result of the applied voltage and the resistance of the human body, (and the time of contact) which determines how the human body reacts.
This table shows the relationship between effect and current although the quoted currents are approximate values.

The variability of data is shown by the fact that humans have been electrocuted with a voltage as low as $40\,\rm V$ and at the other extreme a man survived with making an electrical circuit touching a $340\,000 \,\rm V$ transmission line.
The Wikipedia article Electrical Injury gives more information about such matters as does the article The Fatal Current.
Answer: Technically, I would say that it's both. Voltage is basically the energy required to create current. So you would not have current without voltage.
In order for you to get hurt, you need enough current, but to get enough current, you need enough voltage.
Here's a possible analogy: If I shoot you with a gun, did I kill you, or did the bullet kill you?
Got this from a youtube video (I think the guy does an excellent job of explaining)
https://www.youtube.com/watch?v=XDf2nhfxVzg&list=TLPQMDQwMzIwMjGyA4boIQfH7w&index=10
Answer: Higher voltage causes more shock at the same wattage.
Low-voltage high-current exposure will be felt as warming up not as a shock.
Answer: the current generates the heat.....but the voltage (potential difference) generates shock...so i think shock is generat due to high voltage!!


How to use Astropy to edit a keyword (not value) in batches of FITS file headers to be used in AstroimageJ (AIJ)? (summer undergrad research project)

Question: I would be so grateful if someone could help me. I am stuck for over a week now trying to find some way to use Astropy to write some small code to edit one keyword in batches of FITS file headers so that they can be used in AstroimageJ(AIJ) for a summer undergrad research project. Thank you so much for any help. AstroimageJ wants DATE-OBS (for example) but my files say DATE-BEG, which is not an accepted KEYWORD for the start of exposure date/time.   Thank you so much for any help. It's very appreciated. I've been stuck for a week now. Above is a screenshot of the AIJ documentation. Followed by a screenshot of one my .FITS file headers that I accessed just by renaming it as a .TXT file, and then I can edit it by hand. But I have thousands of files to edit. Thank you!
Comment: OK thank you for the "heads" up. Pun intended.
Comment: *Welcome to Stack Exchange!* Usually use of screenshots of text is discouraged, and text capture is recommended, but in this particular case that's going to be pretty difficult. I think the title of your question alone may be good enough for an answer, but by explaining so much more others may be able to provide a better or at least different solution as well.
Comment: Wow, thank you so much! Everyone. Including the very last post! Still not 100% sure what to do about the EXPTIME not being picked up by AIJ, it's telling me that at the end. The answers question guidelines say to "share your research" so here goes: This is a Hot Jupiter orbital decay project! I'm guessing the WASP-12b object name in the header file gave that away already! Thanks again! This may not be the last I post on this and I am so appreciative.
Comment: Thank you everyone so much! I ran this bit of code, on the science, flat and bias and it did work.. AIJ accepted it.                                                                                #science, bias, and flats
from astropy.io import fits
import glob
files = glob.glob('/file_path/*.fits')
for ifile in files:
    data,header = fits.getdata(ifile,header=True)
    datebeg = header['DATE-BEG']
    header['DATE-OBS'] = datebeg
    fits.writeto(ifile,data,header,overwrite=True)
    #header.remove('DATE-BEG')
Answer: This code snippet should do what you want for an individual fits file. It searches for the HDU containing 'DATE-BEG' and then writes a header 'DATE-OBS' containing the value of 'DATE-BEG'. You can use glob to search to get a list of all your fits files and run this code on all of them.
<code>from astropy.io import fits

file = 'insert path of fits file'
hdul = fits.open(file)
image_hdu_number = 0
for i in range(len(hdul)):
    if 'DATE-BEG' in hdul[i].header:
        image_hdu_number = i

date_beg = fits.getval(file, 'DATE-BEG', ext=image_hdu_number)
fits.setval(file, 'DATE-OBS', value=date_beg, ext=image_hdu_number)
</code>
Comment: if the batch is all in the same folder then`files = glob.glob('d*.txt')` and `for file in files:` could work, with a `try` and `except` to avoid fatal crashing for simple errors.
Comment: Can't tell from the above example header (a `hdul = fits.open(fits_file) ; print(hdul[0].header)` would get you a more readable version) but you should check whether there is an `EXPTIME` or `EXPOSURE` in the header as well when converting `DATE-BEG` to `DATE-OBS` so AstroImageJ can correct the time to the midpoint of the exposure (which is what you really want). Otherwise you will want to modify the above answer's code to insert this also.
Comment: Wow thanks, folks, Astro snapper, and Uhoh you were all right on with that. I solved it. ...but...although my header already contains an EXPTIME ...AIJ is still throwing me an error at the end saying it "can't calculate exposure time and beginning of the exposure."    I'll post my interim solution. and go from there. Not 100% sure how to do that.  I'll post two.


NHibernate and generic list in abstract base class

Question: This is kind of a complicated question and I've tried so many angle I can't remember what I have and haven't tried yet. But basically, my project consist of some base classes for a football league. I have the following classes:
League - abstract base class for a league in my library
Team - abstract base class for a team in my library
FootballLeague - derived from League (could be any other type of league though e.g. BaseballLeague, SoccerLeague, etc.)
FootballTeam - derived from Team (same as above)
Basically what I'd like to do is have a list of teams in the League class so I can have more general methods in that class that can operate on just Team objects. And then in my FootballLeague be able to reference that same list except get back the FootballTeam objects (which the list really contains).
Here is my implementation so far at a very basic level:
public abstract class League
{
   protected IList mTeams;
}

public abstract class Team
{
   public virtual League League
   {
       get;
       protected set;
   }
}

public class FootballLeague : League
{
        public virtual IList<FootballTeam> Teams
        {
            get { return this.mTeams.Cast<FootballTeam>().ToList(); }
            protected set { this.mTeams = value.ToList(); }
        }

        public FootballLeague() : base()
        {
            this.mTeams = new List<FootballTeam>();
            this.mConferences = new List<FootballConference>();
        }
}

This works pretty much exactly how I want except for an NHibernate problem.
1) When I load a FootballLeague object, it loads all the FootballTeam objects as well. If I remove the mTeams declaration in the base class and just use an auto get/set for the IList in the FootballLeague object lazy loading works and my teams don't load until actually access the collection. So basically having that member variable that the list accesses in the base class, causes NHiberate to bypass lazy loading.
Is this implementation the way you would handle this type of library. Whereas you have abstract base classes that should have functionality on lists, but the derived classes should also be able to access more specialized versions of the list as well? If not, how should I implement that so it works with NHibernate?
Answer: public abstract class League<T> where T : Team
{
    protected IList<T> mTeams;

    public League()
    {
        mTeams = new List<T>();
    }
}

public class FootballLeague : League
{
}

and map mTeams as IList and hasmanyToAny to avoid casting errors
Does this work for you?


Any way to include file in a email sent to user?

Question: We are implementing a Coupon page on a client's website. Basically just a page that displays the coupon JPG. I have a channel setup with a field to upload an image. The client wants the user to be able to input their email address into a form field and submit in order to get the coupon JPG emailed to them. Any ideas how this can be accomplished? The Coupon JPG will update occasionally. Thanks for any info!
Comment: I know SolSpace Freeform can attach file uploads from a Freeform form file upload field. But there won't be a file upload field, so is there a way to pass the url to the JPG in a hidden field so that it would be attached in the email?
Answer: You cannot attach a file to a notification email unless the file is uploaded along with the form being filled (I recommend submitting this as a Feature Request here: http://support.solspace.com/support/discussions). Usually the best you can do is have a link in your notification email template pointing to your file which users can then download.
With an image file, however, you might have one more option. You will need to enable HTML for your notification email template in Freeform.
Since Freeform 4.x, EE tags can be used in the notification email template body, which means you should be able to retrieve your coupon data from your entry channel. Along with HTML enabled for the entry, you could create an  tag in your email body, which should display your coupon to the email recipient.
Here's an example. I'll assume, for demonstration purposes, that your channel is called "coupons" and that your entry_id containing the coupon is "123". The coupon File custom field would be called {cf_coupon_image} in this example. In your email notification template body, you could do this:
{exp:channel:entries channel="coupons" entry_id="123" dynamic="no"}

{/exp:channel:entries}

If HTML is enabled, and your recipient can view HTML emails, the email body should contain an image of your coupon :)
Only catch: the image is still coming from your site. If you change that image in your entry and the filename does not change, this will change the image for the recipient of the email as well.
Comment: It's not 100% want i was hoping, but i think this should appease the client. Thanks for your help!
Comment: Added a small edit about the bottom note: the image would change in the recipient's email if the image in your entry changes **and** the filename remains the same. Assuming the filename changes and the old image file is still on your server, the recipient of the email should still see the old coupon file.


Is there any way to play Left 4 Dead on a LAN?

Question: It seems the only option for playing Left 4 Dead with my friends is to have all computers online, even though I bought the 4 pack from Valve. Is there anyway to plan a LAN game on Left 4 Dead 1?
Answer: It is possible. If you use srcds to set up a dedicated server and note the LAN IP of the computer hosting it, you can enable the developer console in-game (under Keyboard settings then advanced) press the ~ key (on foreign keyboards, it is usually whichever key is next to the 1 key) to open it and enter the command connect <LAN IP of server> into it. You'll then be dropped into the game. Make sure to edit the key of the server so that random people don't start joining. Consider setting it to LAN-only.
If you're using a non-QWERTY keyboard, sometimes binding the developer console may not work. If so, you can edit the launch options and add --console. Then, whenever you launch the game, you'll have console open.
Comment: @Bora Nope. You can run Steam in offline mode, and play it on a LAN. I've done it before.
Comment: @Bora Also not true. If you reboot your computer without a working internet connection, Steam offers you the option to switch to offline, assuming you have logged in some time before that.
Comment: All clients have to be connected to the internet throughout, though. Steam DRM still applies.
Comment: Ok, scratch the throughout part. You have to connect to Steam once to switch to offline, at least.
Comment: I was referring to the "some time before that" part, which might render the whole process inconvenient, just for the sake of getting around the DRM process.
Comment: @Bora In that sense you are correct. Most people have Steam set-up to auto-login, but I do realise that this is not the case for everyone. Sorry for the confusion.


Buddhist claim of the concept "Atman" or true self being egoistic?

Question: Is Anatma (or no true self as discussed in Buddhist doctrines), an antithesis of Advaita Vedanta? And is the concept of atman "egoistic"?
Comment: Sanatana dharma recognizes that there is a difference between ahamkara (false ego) and atma (soul), the latter being our true identity. Throwing away our false ego and aiming for self-realization is quite the opposite of egotism, depending on what you believe to be the nature of atma.
Comment: Buddhism also uses a version of neti-neti, but doesn't stop at consciousness like Advaita does.
Comment: Sanatana dharma uses the term atman. But problem here is we think Atma is "something " - this is what Buddhist deny and they are true. Atman is not something.  Atman cannot be described. The state of indescribable existence which buddhists call as nirvana is what vedantis call atman. The one which is beyond anything.
Comment: No. Nirvana is the realisation of shunyata (emptiness) and nothing to do with Atman or Brahman or Advaita.
Answer: Advaita Vedanta differentiates the True Self from the false self (egotism).
What is the false self according to Advaita?

Therefore give up the identification with this lump of flesh, the
gross body, as well as with the ego or the subtle body, which are both
imagined by the Buddhi. Realising thy own Self, which is Knowledge
Absolute and not to be denied in the past, present or future, attain
to Peace.  Cease to identify thyself with the family, lineage, name,
form and the order of life, which pertain to the body that is like a
rotten corpse (to a man of realisation). Similarly, giving up ideas of
agency and so forth, which are attributes of the subtle body, be the
Essence of Bliss Absolute.
Vivekachudamani 296 - 297

Identification with the gross body, subtle body, family, lineage, name, form, order of life etc. is associated with the false self.
This is not so different in Buddhism, as found in the Bhara Sutta in which the false self is referred to, as the "carrier of the burden".
What is the True Self according to Advaita?

This world, though an object of our daily experience and serving all
practical purposes, is, like the dream world, of the nature of
non-existence, inasmuch as it is contradicted the next moment. The
dream (experience) is unreal in waking, whereas the waking
(experience) is absent in dream. Both, however, are non-existent in
deep sleep which, again, is not experienced in either. Thus all the
three states are unreal inasmuch as they are the creation of the three
Gunas; but their witness (the reality behind them) is, beyond all
Gunas, eternal, one, and is Consciousness itself.
Aparokshanubhuti 56 - 58

If the universe be true, let it then be perceived in the state of deep
sleep also. As it is not at all perceived, it must be unreal and
false, like dreams.
Vivekachudamani 234

The waking world doesn't exist in the dream world. The dream world doesn't exist in the waking world. And both don't exist in deep sleep, which is neither experienced in the waking world nor the dream world. However, the True Self, the Atman, the Eternal Witness is in all of them and is Consciousness itself.
The waking world (the physical universe), the dream world and deep sleep are unreal. Only Atman, the True Self, the Consciousness, is real.
Furthermore, despite the illusion of there being many people, there's only one Consciousness.

The Supreme (Purusha) known as "I" (ego) is but one, whereas the gross
bodies are many. So how can this body be Purusha? The immutable Atman, the
substratum of the ego, is thus different from these two bodies, and is the
Purusha, the Ishwara (the Lord of all), the Self of all; It is present in
every form and yet transcends them all.
Aparokshanubhuti 31 - 32

So, while the false self is identification with limited impermanent identities like name, form, gross body, subtle body, family etc., the True Self (Atman), the real "I", is the Pure Consciousness that is the Witness of everything and is the same True Self in all. It is also the Supreme Purusha, Ishwara and Brahman.
More about this can be found in the Vivekachudamani and Aparokshanubhuti, both authored by Adi Shankaracharya.
How is this different from Buddhism?
The Buddha taught "all phenomena is not self" (Dhp 279). He did not say there's no self at all (Attakari Sutta). Just that if you break down phenomena into its constituent parts, you find that none of it is self.
He used the analogy of the lute or vina in the Vina Sutta. The lute produces beautiful music, but if it's broken down into its constituent parts, music cannot be found in them. Music is simply an emergent phenomena that arises when different parts of the lute work together.
Similarly, when you carefully examine form (body), feeling (sensation), perception, mental formations and consciousness, you cannot find the self anywhere in them. This is because the self is an emergent phenomena according to the Buddha, a mental idea (Tuvataka Sutta), that arises when form, feeling, perception, mental formations and consciousness work together, according to a mechanism known as dependent origination, that he taught.
And what about consciousness? Why isn't consciousness the self in Buddhism?
In the Mahatanhasankhaya Sutta, the Buddha taught that there are six types of consciousness that arises from moment to moment, dependent on the six types of sense media and their sense objects - eyes and forms, ears and sounds, nose and smells, tongue and taste, body and tactile sensations, and mind and thoughts. He called them eye-consciousness, ear-consciousness, mind-consciousness etc. Consciousness is therefore impermanent, and dependently originated.
The Buddha taught that "all conditioned things are impermanent" (Dhp 277), and consciousness is conditioned by the six sense media and their sense objects. He also called the six sense media and their sense objects "The All" (Sabba Sutta), meaning you cannot find any other reality outside of them. Also, please see Bahiya Sutta.
Of course, the physical world is also conditioned and impermanent. Buddhism is not concerned with whether the physical world is real or unreal. It simply holds that it is conditioned and impermanent.
Dreams are mental formations or mental fabrications in Buddhism, and thus also conditioned and impermanent.
What about Nirvana? Is it not the self in Buddhism?
Nirvana is simply peace and bliss experienced by the mind when it is free of defilements, in Buddhism. It's not a state of Super Consciousness.

OP: And is the concept of atman "egoistic"?

According to Advaita, Atman is not the same as the false self (associated with identities like name, body, family, lineage etc.). Atman is the eternal True Self, the Consciousness that is the Eternal Witness.
However, according to Buddhism, both the false self (associated with identities) and consciousness without association with identities, are both conditioned and impermanent.

OP: Is Anatma (or no true self as discussed in Buddhist doctrines), an antithesis of Advaita Vedanta?

Yes. They definitely contradict each other, as explained above.
Comment: Yes, with the Buddhist view, consciousness is also anatman. That's the pivotal difference from Advaita, which takes consciousness as Atma.


How did the Weeping Angels get the TARDIS key?

Question: How did the Weeping Angels in the Doctor Who episode "Blink" get the key to the TARDIS in the first place?
Comment: Pretty obvious that they stole it when no one was looking
Comment: The *first* place? I assume you missed the bit where everyone's able to whip around time like a bunch of mad things.
Answer: tl;dr: We don't know, because it happens off-screen, but it most likely came from The Doctor himself.

The key thing to understand about Blink is that entire episode is cyclical. From Sally Sparrow's perspective, the episode happens as we see it. But from the perspective of The Doctor and Martha, the end of the episode happens before the beginning.
At some point after/before the episode, The Doctor encountered some Weeping Angels in the abandoned property. The Angels wanted to use his TARDIS to feed themselves back up to full strength. The Angels managed to send The Doctor and Martha into the past. We are left making the assumption that they also stole a TARDIS key at the same time.
Unfortunately for the angels, the police department found and moved the TARDIS before the Angels could get to it. They can't exactly search through the city for it, so they were a bit stuck. Then Sally came along and took the key, as well, and the rest of the episode happen.
Comment: Ehhhh... I got the impression they didn't know where it was.  Once Sally found it (and they were following Sally, 'cause they wanted the key back), they got it out easily
Comment: that's probably true; they may not have known where the police took it, and it's not like they can wander aimlessly around the city.


Water sample preservation

Question: I am taking my students to collect water samples from different bodies of water. These bodies of water include the local river, a park pond, and water accumulation from recent rain. Once we gather the samples students will be analyzing the samples under standard light microscopes. I was wondering what is the best way to preserve any life that may be found in the samples in case there is no immediate opportunity to analyze the samples under the microscopes? Is there a specific time frame to analyze the samples before they have to be replaced? Also if they are kept in a bottle/jar does the container have to be unsealed or with perforations to allow air flow? Thank you.
Comment: What sort of timeframe? Collect in the morning & analyze in the afternoon would be good. Next day? Next week? Next month?
Comment: The samples will be analyzed within a week. Collection will take place Monday and the analysis of samples no later than the Friday of the same week they were collected.
Comment: Things start changing in minutes in sea water: I picked this up from some book on salt water aquariums when I had them.. I can tell you delicate inverts start dying in one day when power failure shuts down the circulation pumps although battery powered air pumps are running.  The main reason I gave up on salt after about 15 years.
Answer: Depending on what you are trying to look at, for zooplankton you can take water samples and filter them through a 100-200um mesh and store them in glass or plastic bottles. For my research we used mason jars that were cleaned thoroughly. After filtering just submerge the biomass in 70-90% ethanol and they can be stored in a fridge for quite some time.
If you want to look at phytoplankton, you can look into using Lugols Solution for preserving your samples. The nice thing about using lugols is that it will stain the phytoplankton as well. Your best bet for these is to store in amber bottles and keep in cool dark place. Here is a decent guide on how to collect the samples and prep the solution.

Water sample preservation


SocketException in Mongo

Question: I just set up a replica set in Mongo (prod environment).  I'm now getting a lot of exceptions like below (clipped).
I went into mongo and ran a serverStatus command on my primary mongo node and only have about 300 connections going, so it's hardly working.
Below are my connection option settings in my server code:
auto_connect_retry = false
connections_per_host = 10
threads_multiplier = 10
max_wait_time = 120000
connect_timeout = 10000
socket_timeout = 0

Do I have something mis-configured?
Sep 9, 2013 8:31:26 PM com.mongodb.DBPortPool gotError
WARNING: emptying DBPortPool to /10.0.8.10:27017 b/c of error
java.net.SocketException: Connection timed out
    at java.net.SocketInputStream.socketRead0(Native Method)
    at java.net.SocketInputStream.read(SocketInputStream.java:146)
    at java.io.BufferedInputStream.fill(BufferedInputStream.java:235)
    at java.io.BufferedInputStream.read1(BufferedInputStream.java:275)
    at java.io.BufferedInputStream.read(BufferedInputStream.java:334)
    at org.bson.io.Bits.readFully(Bits.java:46)
    at org.bson.io.Bits.readFully(Bits.java:33)
    at org.bson.io.Bits.readFully(Bits.java:28)
    at com.mongodb.Response.<init>(Response.java:40)
    at com.mongodb.DBPort.go(DBPort.java:142)
    at com.mongodb.DBPort.call(DBPort.java:92)
    at com.mongodb.DBTCPConnector.innerCall(DBTCPConnector.java:244)
    at com.mongodb.DBTCPConnector.call(DBTCPConnector.java:216)
    at com.mongodb.DBApiLayer$MyCollection.__find(DBApiLayer.java:288)
    at com.mongodb.DBApiLayer$MyCollection.__find(DBApiLayer.java:273)
    at com.mongodb.DBCollection.findOne(DBCollection.java:347)
    at com.mongodb.DBCollection.findOne(DBCollection.java:332)
    at com.mongodb.casbah.MongoCollectionBase$class.findOneByID(MongoCollection.scala:232)
    at com.mongodb.casbah.MongoCollection.findOneByID(MongoCollection.scala:866)
    at com.novus.salat.dao.SalatDAO.findOneById(SalatDAO.scala:353)
    at com.novus.salat.dao.ModelCompanion$class.findOneById(ModelCompanion.scala:173)

Comment: Could you attach the logs for the primary node?
Comment: Also, please tell us how you connect the replica set by showing the relevant code or configuration.
Answer: Generally a connection timeout occurs from one of the following in a replica set

1) All members are not able to communicate with each other
2) A program is connecting to replica for update and it is unable to send it to primary due to overload or 1st as well
3) All relicas are not in sync and one is lagging behind too much
4) Leader election is going on but not completed due to some reason

Please check if your relica set is consistent and all nodes are working by issuing rs.status() on primary node , also as earlier suggested check primary logs for more information

SocketException in Mongo


Empty field value showing in webform email content

Question: I have a file attach field in my webform. When i have submit my webform without this field,in my email content showing like "ATTACHED FILE: [webform_submission:values:attach_file]".
I have checked "Exclude empty elements" in my email handler.This is working for all other fields in my form except this "File attach" field.How can i solve this issue?
Answer: Similar question was recently answered by the Webform module developer at drupal.org:
"You might just need to append the :clear prefix.
[webform_submission:values:element_value] => [webform_submission:values:element_value:clear]"
https://www.drupal.org/project/webform/issues/2982562
So, in your case use replacement pattern: [webform_submission:values:attach_file:clear]
Comment: Thank you..its working.But now the link (if i have attached file) is missing and link  to file is  showing as plain text.Can i solve this?


Lowest Gear Out of Whack

Question: Yesterday, I was having this problem.  Taking the advice, I messed with the barrel adjusters.  Now, every gear is working great except the highest gear and lowest gear.  I put my bike in the highest gear and I can still click the shifter once more, but nothing happens.  When it comes time to shift down gears, I have to click the shifter once before shifting has any effect.  In the lowest gear, the chain jumps.  I have to hold down the shifter to stay in gear there.
Comment: Are you sure you tightened the cable to fix the previous problem?  I.e., turning the adjuster anti-clockwise.  It sounds like the cable is even looser now which would explain the redundant click at the top end (smallest sprocket).
Comment: Yeah, you need to adjust the limit screws.  Since these don't normally go out of adjustment, if the bike was previously working well it may be that either the derailer has been bent, or somehow the wheel is not properly mounted in the dropouts (maybe a washer on the wrong side of a dropout, etc).
Comment: If you are having to click twice to get it to move, you probably have dirt in the cable housing. If the end of the cable is in good shape, you can clean it by putting a couple of drops of oil on the cable and drawing it through and back a couple of times.
Answer: Here's a video that explains how to adjust your rear derailleur. Since you didn't mention adjusting the high gear or low gear adjusting screws, this may be your problem area. Sometimes it's best to start with all adjustments in a "neutral" condition before you attempt to "fine tune" the derailleur. It would benefit you to tell us the brand and model of your deraileur syatem the next time you have a problem. Even different models from the same company, can have their little "quirks" ofetn learned by experience rather than instructions. Hope this will help you out! Good luck!
Comment: One thing not mentioned in this video is that you will often need to shift out of the highest or lowest (according to what limit screw you're trying to adjust) and back into that gear to see the result. This is especially true of older cables and housing because of the gunk that builds up in them over time.
Answer: Here are a couple of links that explain derailleur adjustment:
http://sheldonbrown.com/derailer-adjustment.html
http://www.parktool.com/blog/repair-help/rear-derailler-adjustments-derailleur
Comment: These are indeed both good reads but the answer would be better if you would summarize the sections that you think apply to the original poster's problem.
Comment: Good point - I should have said that I suspect that other replies already cover the most likely causes, but these might be useful if more information turns out to be needed.

Lowest Gear Out of Whack


SQL Server VSS Writer, Hyper-V and SQL Server 2008 backups

Question: I have a virtual server running SQL Server 2008 R2. On the server I have configured two maintenance plans, one that takes differential backups every day except Saturday and a job that takes full backups on Saturdays.
Now when I tried to restore a differential backup I didn't manage to do it because it complained that the diff backup was out of sync with the selected full backup.
After some investigation I noticed that because I run Windows Server Backup on my Hyper-V host machine (the one hosting the virtual server) Windows Server Backup makes snapshots of the databases on the virtual server. The differential backups starts to point to the snapshots instead of the full backups.
I now disabled the service SQL Server VSS Writer on my virtual server to prevent snapshots from being taken, but will Windows Server Backup now succeed in taking backup of the virtual server or does it need that specific service to lock the database files?
What is the correct way to have snapshots and "normal" backups running side-by-side? Can e.g. the snapshots be configured to be "copy-only" so that they don't mess up the normal backups?
Comment: I have run into this exact same issue using Symantec Backup Exec 12.5.  Backup Exec transaction log backups fail as soon as it performs a backup of the VM as a whole.  I am interested to know what solution, if any, you came up with.
Answer:
Can e.g. the snapshots be configured to be "copy-only" so that they
don't mess up the normal backups?

Yes, Windows Server Backup allows to choose between these two options:

VSS full backup
VSS copy backup

Choosing "VSS copy backup" should leave your SQL Server backups intact.
This tech community article explains the setting.
If you're using the configuration wizard for your Windows Server Backup, the setting is availabe during the step "Select items for Backup". Click the button "Advanced Settings" and then switch to the tab "VSS settings".
This blog entry has a few screenshots.
Answer: If you disable a VSS writer in the VM, the VM backups will not be coherent with respect to the database.  So you're much more likely to end up in a situation where you try to restore your VM backup and you find your database corrupt.  Since database repair can take a while, and since corruption can lead to data loss, I doubt that you should do that.
Comment: But how are you supposed to handle normal backups if the VSS writer is on? With the VSS writer I have to restore the whole server to a point in time instead of just a single database.
However I now first take normal backups of the database before running the Windows Server Backup on the Hyper-V supervisor server, so if the databases become corrupt I always have fresh database backups available.
Comment: That's really what "backing up a VM" means.  You can restore the whole server to a point in time.  If you want to back up a database, do that within the VM.  Many people would suggest that you might, now that you're using VMs, want to have a VM for each database.


Do universities keep your college application materials, if you are rejected?

Question: I guess I am just being curious, but I was wondering whether college applications are kept or saved (i.e common app) by the institutions you applied to?
I assume that if you are accepted they are pretty much kept until you graduate. But what happens to the application materials of people who have not being accepted? All those applications are kept for some period of time and then disposed?
Thanks!
Comment: @JonCuster: I can think of lots of reasons.  Audits to see if admission procedures were correctly followed.  Statistics on the applicant pool.  Analysis of factors related to applicant success.  Generic legal record-keeping requirements.  And, in the era of electronic records, the simple fact that deleting data requires more work than keeping it.
Comment: Why would they keep any of it?
Comment: And keeping all those records, likely with personally-identifiable information, is a huge risk as well. You run all the statistics you want, and then throw the records away. Frankly, the last thing the university wants to do is produce the last 10 years of applications in response to a law suit...
Comment: I don't know about unsuccessful undergraduate applications, but my (US public) university definitely retains *successful* application data for at least as long as the student is enrolled, and my department retains unsuccessful successful *graduate* application data for at least five years.
Answer: This would depend on many things, including the laws of the country in which the University is situated. I assume that in some places it is mandatory and others forbidden. In those places without such laws it probably is determined locally by the University itself.
I believe that in the US, many, if not most, college applications now are done electronically through an agency or organization with the applicant determining who can obtain the materials. For example, see https://www.commonapp.org. In such a case, the organization likely retains the materials, subject to the law, of course.
If you have a specific worry, about a specific University, you could ask them and get the correct answer, of course.


Inline JavaScript with RedDot CMS version 9

Question: I can not put in inline JavaScript in text area in reddot opentext cms version 9.  when saving code it automatically strips it out.  Does anyone know any hack or work around to solve this problem.  I do not want this fix to be done globally because we have other users in the cms which are not admins i want this done on a single or a certain page only.
Answer: Usually I wouldn't recommend puttin any inline javascript into a page.
If you have to do it, create a new template with a text element which is set to ASCII only and add your JS in this text element.
You can connect the instance to a container within the page any run your Javascript inline.


What does is really mean to say that a 3-body problem is not solvable?

Question: What does it really mean to say that a three-body problem (the Sun, the earth, and the moon) is not solvable? Why is it not possible to solve the differential equations on a computer with adequate initial conditions? What's the real issue here?
Comment: TLDR, "solve" means, "find a [_closed form expression_](https://en.wikipedia.org/wiki/Closed-form_expression) for the motion of the bodies." A [numerical simulation](https://en.wikipedia.org/wiki/Computer_simulation) of their motion doesn't count as a "solution."
Comment: Related: [Why does the three-body problem have no solution?](https://physics.stackexchange.com/q/510367/2451) More on [3-body problem](https://physics.stackexchange.com/questions/tagged/three-body-problem).
Answer: The three-body problem lacks a closed-form solution, which is a mathematical expression that uses a finite number of "standard" operations (addition, division, logarithm, etc.), usually expressed as a formula or equation. This means there is no equation for which you can plug in the initial positions, velocities, and masses, and solve for the exact positions and velocities at a later time. For most configurations of the three bodies, numerical methods are needed to iteratively compute the positions over time, although the chaotic behavior of the system means that even small numerical errors can propagate and result in large deviations over time.
Chaotic systems are very sensitive to their input parameters, so anything less than a perfect continuous estimation can result in wildly different results. Unlike a non-chaotic problem where a 1% error in velocity might result in a 1% error in position, a 1% error in velocity at some time step can result in arbitrarily large deviation at a later time. Even if your numerical approximation is very good, you may eventually find that your model predicts something entirely different from reality. You can run increasingly good approximations with decreasingly short time steps, but there is no numerical approach that is anything but an approximation, which simply may not be "good enough" in a chaotic system.
Of course, the three body problem does have a solution - it's whatever would actually happen when observing the three bodies in isolation. The physical reality is the solution to the problem. It's just that this solution cannot be expressed with common mathematical operations in "closed form".
See Why does the three-body problem have no solution?
Answer: Quoting from wikipedia

The three-body problem is a special case of the n-body problem. Unlike two-body problems, no general closed-form solution exists,[1] as the resulting dynamical system is chaotic for most initial conditions, and numerical methods are generally required.

Of course, you can get a numerical solution for given initial conditions and masses. (Although, as Jon Custer points out, getting accurate numerical solutions is very difficult).
Comment: Now, whether you get the _correct_ solution is another question, particularly since numerical methods have limited precision, and slightly different initial conditions lead to that chaos thing...
Comment: @Solidification  I would think that the "yet" is in the realm of "impossible".
Comment: So the point is that numerical solutions exist, but no one has yet found an analytical solution?
Comment: @JonCuster Good point!
Comment: @Solidification Basically. Although (a) as Jon points out, the numerical solutions are very hard, and (b) it's not just that no one has found analytical solutions yet, it's that the solutions are known to have properties (chaos) that are *extremely hard* to represent analytically (like annav says, 'extremely hard' here probably means impossible to write a closed form expression in terms of simple functions).
Answer: There has been always discussion about what is called solvable in the community.
For example: Take the pendulum with a constant force acting on it (and not applying the small angle approximation, otherwise the solution is a simple sine function), which is given by
$$  {\ddot {x}} = -\sin(x) \,.$$
With the small angle approximation
$$ {\ddot {x}} = -x\,,$$
you can solve this directly with the well-known function
$$ x = \sin(t) + \phi_0\,.$$
However, you can solve the full (non-linear) equations of motion as a perturbation series.
One could take the ansatz of writing $x$ as
$$ x = \sum_{\nu=0}^N \alpha_\nu \frac{t^\nu}{\nu!}$$
To lowest order in time $t$ we would then have
$$ \alpha_2+ \alpha_3 t +\mathcal{O}(t^2) = -\sin(\alpha_0+\alpha_1 t + \mathcal{O}(t^2) ) $$
which gives with the Taylor expansion of the sine
$$ \alpha_2 +\mathcal{O}(t)  = -\alpha_0+\mathcal{O}(t)  $$
You can then solve this equation order by order for each $\alpha_\nu$.
This can be done up to any order you want. Some people would say that this is not an analytical solution, but keep in mind, that depending on your philosophy the sine function is just a name for some perturbation series that has a particular structure. Just because the perturbation series that solves the above differential equation does not have a name, does not make the solution any less important.
Now addressing the question: You can solve the differential equation describing the three body problem numerically, but people usually mean that there exists no well known function that describe the solution in easy terms. There is no 'sine' function for the three body problem. Note that this is different from the two body problem, where we know the solution of $r(\phi)$ to be quite simple.
Additionally, the three body problem is chaotic (as was pointed out by Andrew), so any small change in the initial conditions will lead to large deviations for predictions far in the future. Numerically, chaotic systems are not easy problems, since you do not want unphysical choices (like the time step you choose) to influence your final result, but this happens often in simulations of these systems.
Comment: @Solidification afaik, special functions like those are not generally considered "closed form", wikipedia actually has a nice table of what's included in each category https://en.wikipedia.org/wiki/Closed-form_expression#Comparison_of_different_classes_of_expressions
Comment: If I'm not wrong, the equation $\ddot{x}=-\sin x$ is exactly solvable (in terms of elliptic integrals).
Answer: It is Solvable...

Why is it not possible to solve the differential equations on a
computer with adequate initial conditions?

It is possible. But you will be hard-pressed to build a computer which can represent the "adequate initial conditions". We should say that a problem $P(x)$ is "solvable", if, for any input $x$, you give me a precise answer for $P$.
In the case of the sun-earth-moon system, that means that for arbitrary starting conditions and an arbitrary point in the future, you can tell me the positions of each body. For any system with precise dynamical equations, you can just plug in the initial conditions and iterate to the desired endpoint. What closed-form solutions give you is the ability to jump directly to the endpoint without performing any of the intermediate calculations. Obviously, this is very powerful. But it's more than that. It may be the only way to obtain a correct solution at all.
...In the Integers
The problem with a computer (all computers, including you) is that it can only compute with integers. IEEE 754 makes it look like you can compute with reals, but you are not. Floating-point numbers are just integers dressed up to look like reals, but actually doing a very poor job of it. You can perform exact symbolic operations on reals in the manner of Mathematica and friends, but the set of reals which can be handled in this manner is infinitely smaller than the full set of reals (due to the fact that all such reals must have a finite-length symbol attached to them, which just puts them in correspondence with the integers). Which means, the operations you can perform may quickly get exhausted while trying to obtain the answer you are looking for.
If your universe is quantized, and thus can be exactly described by integers, then, in principle, all 3-body problems should be exactly solvable. If time or space cannot be exactly represented by integers, then any computations you perform on them will contain errors. And any sequence of computations will accumulate growing errors.
Exponential Error
Some problems are sufficiently simple that the errors tend to cancel out, and one can feasibly obtain answers of arbitrary precision by performing computations of arbitrary precision (the precision of the result is proportional to the precision of the inputs). Simple harmonic motions, two-body problems, etc. fall into this category. When this happens, there is usually a closed-form solution which lets you jump straight to the desired endpoint.
When a physics problem is "not solvable", it generally means that despite an exactly precise dynamical description of the system (so far as we can tell, anyway), we cannot compute future states with arbitrary precision, because the accumulated error may grow without bound (i.e., "chaotic" systems). You can always increase the precision of the result by increasing the precision of the inputs and intermediate calculations; but if the error grows exponentially, then it quickly becomes infeasible to meaningfully improve the precision of the result by increasing the precision upstream of it. And this is what I mean by having trouble with "adequate initial conditions". If you want 64 bits of precision in your result, you might need something like 2^64 bits of precision in the initial conditions and intermediate calculations to achieve that. You can't build a computer big enough to get that answer.
That being said, some 3-body systems have "nice properties" which make their behavior not too chaotic. The bodies in the sun-moon-earth system are of masses and distances that we can compute useful ephemerides over most of the time periods of interest. Whereas, trying to determine which comets might collide with a planet in the next billion years might not be feasible at all, even given arbitrarily precise orbital elements.


How to identify if my site is vulnerable to DOS/DDOS attacks?

Question: I am hosting a site on a hosting server. How to identify whether my site is vulnerable to DOS/DDOS attacks?
Answer: Do you have a site?  If so, you're vulnerable.
A distributed denial of service attack (DDOS) consists of a number of computers throwing data at your site faster than it can handle it.  Unless you're operating on the scale of Google, you're vulnerable.  Your main defense is to not be a target worth the effort of attacking.
A conventional denial of service (DOS) attack consists of an attacker finding a way to make you do more work than him.  Unlike DDOS attacks, conventional DOS attacks can be mitigated through the design of the site (rate limiting, eliminating slow operations, preventing resource starvation using techniques such as SYN cookies) and stopped reactively, by blocking the attacker either at the firewall or with your upstream service provider.
Comment: DDOS attacks are effectively stopped by Prolexic, CloudFlare and similar services.
Comment: And even Google/Amazon/Microsoft can get knocked down briefly if a large enough attack occurs.
Answer: The likelihood is you are vulnerable. If you use a scale-able cloud application platform and have enough resource budget or you use a massive CDN (content delivery network - http://en.wikipedia.org/wiki/Content_delivery_network) you might not be. Likewise if your ISP is especially pro-active in mitigating such threats you may be ok.
So in terms of how you know:

Are you using a massively scaleable cloud architecture or CDN?
Ask your ISP what DOS/DDOS mitigation they provide for hosted servers
Answer: If you don't have any specific protection against DDOS you are probably vulnerable, those measures are usually quite expensive and many customer prefer to use services like cloudflare and others.
Here some tips which may apply or not depending on technology/language:

fingerprint your webserver version and openssl version and look for public known common issues such as memory consumption/allocation bugs.
monitor the memory profile of your web application using appropriate tools, you could simulate simultaneous users with a traffic generator and look at the difference in the memory profile to understand how much data get actually stored for every user.
look inside the code for issues like unhandled exceptions and memory corruptions.
always destroy sessions and deallocate resource or data after you don't need it anymore.


ASP.net Configuration Error- allowDefinition='MachineToApplication'

Question: I uploaded my webapplication using FTP to a space. I am getting this error. I have created the virtual directory and configured it in IIS.I am getting this error.
Configuration Error
Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.
Parser Error Message: It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level.  This error can be caused by a virtual directory not being configured as an application in IIS.
Source Error:
Line 52:             ASP.NET to identify an incoming user.
Line 53:         -->
Line 54:        <authentication mode="Windows"/>
Line 55:
Line 56:


Pushdown automaton with binary stack

Question: I have a problem where I'm asked to prove that if P is a pushdown automaton, then  there exists another pushdown automaton P' with only two symbols in its stack alphabet that accepts the same language as P.
I've tried to codify the stack alphabet of P in binary, using the same ammount of symbols for each representation so I know where the codification of one symbol starts and ends, but I don't know how to simulate P with P'.
Comment: What have you tried? Where did you get stuck? Please detail your attempts, and what you don't understand, and we'll help from there. This site does not accept homework dumps.
Answer: You're on a good path!  Keep at it.  Remember that a pushdown can have a finite-state control, and you can remember up to a finite amount of information in the finite-state control.  Also, it can have $\epsilon$-transitions (so the read head doesn't consume any of the input).  Those might be helpful.

Pushdown automaton with binary stack


Mapping redo in insert mode VIM

Question: How to remap a redo shortcut (Ctrl-R in normal) to Ctrl-Shift-Z in insert mode?
It would be helpful since I mapped undo to Ctrl-Z like this:
nnoremap <c-z> :u<CR>
vnoremap <c-z> :u<CR>
inoremap <c-z> <c-o>:u<CR>
vnoremap <c-z> <c-o>:u<CR>

So I want: undo - Ctrl-Z, redo - Ctrl-Shift-Z as in another text editors.
I found this answer, but it is just for normal mode change Ctrl-R to U. Not quite what I need.
Answer: inoremap <c-s-z> <c-o><c-r>

Mapping redo in insert mode VIM


Coded UI unexpected pop-up handling

Question: I'm doing a Coded UI test and I have a problem with unexpected pop-ups. In the function below after doing the first step "main.Open..." I get a unexpected pop-up (bug in the software which is normal).
My Assert still go through as "Pass" because it captures the control that is in the background (pop-up is in the foreground at this point), this is the first thing that I found strange...how come it captures the background process??
Second, it never do the main.RemoveNavigatorResultsLogoFilter() and this is not reported in the output.html and this test actually PASSES!! I'm fairly new to Coded UI.
My Playback setting is :
Playback.PlaybackSettings.LoggerOverrideState = HtmlLoggerState.AllActionSnapshot;

Code:
        main.OpenNavigatorResultsLogoFilterWindow().SelectElementInNavigatorResultsLogoFilterList(logoName).ApplyNavigatorResultsLogoFilter();
        Assert.IsTrue(String.Equals(logo.GetModifiedBy(), "VendorX"));
        main.RemoveNavigatorResultsLogoFilter();

Answer: EDITED: I ended up putting in the "main" a check to ensure that my main form is "Enabled before doing an action. In my case the Root (aka TopParent) is my main form and pop-up have there own Root.
if (MainForm.Enabled)
        return MainForm;

Coded UI unexpected pop-up handling