Why was this meta answer deleted?

Question:
It was an honest question, and I know Bernardo takes the issue very seriously.
Comment: I fail to see why the question should not have been deleted. It is not worded such that a constructive answer can be given.
Comment: I dare you to 'correctly phrase a consistent rule' of what is offensive. Context, connotation, denotation, and intent are all a part of using language, and all conspire to make it impossible to make a uniquely deterministic rule of what is offensive. Heck, look on StackOverflow to see deep discussions of how a compiler _should_ behave in certain cases - and computer languages have (nominally) none of the complexities of real human languages.
Comment: @JonCuster "I dare you" is hostile.
Comment: I'd be interested in seeing the answer to this question as well.
Comment: @JonCuster It is something that I would like to see discussed at Bernardo's AMA, which I cannot attend because I was suspended.
Comment: And I don't understand the hostility from you, I don't even know you.
Comment: No, the 'dare' is a challenge based on things like Goedel's completeness theorem to uniquely and precisely delimit the use of human language. It cannot be done. You asked for the impossible in your comment to your deleted question.
Comment: @ocelouvskypoulo7 I just wanted to point out something regarding [this](https://chat.stackexchange.com/transcript/71?m=37495214#37495214). Yeah, it is true that "it" is not a "living thing". But the second part of your statement is false. You can't be disrespectful against (or atleast show your disrespect publicly) because that "thing" is intricately associated with the lives of many people. It is similar to saying things along the lines of "Your car is garbage". Insults don't always have to directed at a person for it to be offensive. Overall, I feel the ban/deletion was justified.
Comment: @JonCuster Moderators from other sites should not invade foreign chats and put language bans in place. Beyond that, I have no interest in deciding what is "offensive" or not. (The term in question did not violate the Be Nice policy.)
Comment: True, you don't. Yet you jumped to 'hostility' for pointing out issues with your deleted question and comments (the one asking for a policy on offensive) that you set out to the whole Physics SE community. Interesting...
Answer: Such hyperbolic language, i.e. "censorship, political correctness, and moderator brutality", isn't appropriate on this site. If someone used that type of language directed at a non-moderator, it'd probably lead to an immediate suspension for violation of the "be nice" policy, on at least points 1 and 2, if not also 3. (This is rude and belittling [point 1], doesn't assume good intentions [point 2], and arguably counts as being a jerk [point 3], though I could see that last one being debatable.)
We usually go a little easier on these things when they're directed at moderators in their official capacity, so e.g. we might hold off on the immediate suspension, but that doesn't make it perfectly okay. Given the inappropriateness of the content, the post doesn't belong here. You should take that as an implicit warning not to post that sort of thing.
If you really do believe that there is censorship, political correctness, and moderator brutality happening in the chat... well, generally speaking, if conditions in a community are that bad, I'd say the thing to do is leave. But if you would rather try to resolve the issue and continue to participate, there are ways of doing that too. What you need to do is have a constructive discussion with the people who you have your complaint with, i.e. the moderators and possibly SE staff. Just as with asking questions on the site, you have to come with the attitude of wanting to understand why things are happening the way they are, rather than wanting to lash out at other people. It's also possible to effect change this way, but you have to come with clear suggestions, and be open to the possibility that there might be reasons your suggestions can't be implemented.
Answer: This is really a comment, but it got a bit long for the comment box.
The going in point that everyone needs to understand is that the chat rooms are not a bastion of free speech and you have absolutely no rights there. The chat rooms are provided (for free) by the Stack Exchange, and what they say goes. If you are suspended by a community moderator then you have no recourse because, well, it's their playground and their word is final. You may consider that an intolerable restriction, and if so don't use the SE chat system. It is as simple as that.
The SE have also made it perfectly clear that when it comes to the chat rooms the moderators (all the moderators) act as their lieutenants and with their authority. So if a moderator asks you to stop doing something then you stop - with no arguments. If the moderator is willing to discuss the matter then you can certainly discuss it with them, but the going in point is that you do what the moderators say. Again, if you don't like this then once again don't use the SE chat system.
As for exactly why your answer was deleted, well I'm not a moderator and I'm not privy to the moderator discussion areas. However it seems fairly obvious you are attempting to derail the discussion away from physics/maths/technology to the chat room policy. Since, as explained above, that policy is dictated from on high all this could possibly do is result in a round of futile spleen venting.
If you take a step back and look at it the Stack Exchange policy is understandable. They are a commercial organisation and they need to make money from the site. For this they want lots of activity on the main sites to impress the advertisers, and it's only worth investing in the chat if it furthers this goal. If their view is that the chat system is attracting disruptive elements who don't contribute to the main site than they'll remove anyone they deem to be a disruptive element, or in extreme cases permanently close the chat room (as happened to the SF chat room).
A quick footnote:
I see this answer has attracted a downvote, but I'm not expressing an opinion here. I'm just stating the facts. I don't see how you can disagree, and therefore downvote, unless you think my statement of the facts is wrong, and in that case please add a comment explaining where I'm wrong and why.
You may not like this answer but the SE make the rules and they didn't consult me, or indeed our moderators, before making those rules.
Comment: @tpg2114 I think [this](https://meta.stackexchange.com/a/76352) answer sums it up well. I agree.
Comment: I've always been curious about where people get the idea that any Stack Exchange site is a free-speech filled democracy. Any time there are issues regarding moderation or policies or even features, people seem to feel like they have more rights and influence than they actually do. I wonder if there are ways to make it more clear how it really works, or if part of the appeal is the perception and it's better left unsaid until somebody bumps against the edges of what is okay. Anyway, your answer is spot on, whether people like it or not.
Comment: @blue That's an interesting read and mirrors what John said here -- with which I agree also. But the fact that post is from 2011 and we still, repeatedly, have conversations about "democracy" and "freedom" of the community means that message isn't being communicated effectively. It would be interesting to try and track down *why* people think the site is different from reality, and whether clearly stating reality helps or hurts participation. On the other hand, I'm sleep deprived so maybe it isn't that interesting of a topic after all!
Comment: The reason folks keep discussing it is that [there *is* a great deal of, uh, "collective autonomy" on these sites](https://meta.stackexchange.com/questions/124911/individual-community-preferences-vs-se-network-policy-who-wins/124915#124915), @tpg2114. Y'all decide what questions you want, which answers are allowed, who gets to wear the moderator hat, etc. - if there was an overwhelming consensus here that homework questions would only be allowed on Tuesdays when containing green-colored formulas, you could make that happen. Problem is, some folks forget where that autonomy ends.
Comment: Read to the end of that answer, @tpg2114. We're here to do Q&A. Anything that *hurts* doing Q&A is a problem. We're *not* here to run chat services - chat's just here to facilitate the people keeping Q&A going. So for example, if you're spamming your question in chat instead of asking it on main, that's a problem. If you're driving away folks from Q&A with your behavior in chat, that's a problem. Chat - like comments, review, meta, and everything else that isn't a useful answer to a practical question - are ultimately expendable. Practical questions & useful answers are the "absolutely must".
Comment: @Shog9 I feel like that post just muddies the waters. The bit about not viewing policies as edicts from on high (granted, it does say not *all* policies) makes it really unclear about what is or is not okay for local communities to change. It sounds like some people think chat room policies can be localized and then get upset when people outside come and enforce the "edict on high." But maybe chat can't be localized? Be nice seems to always be a rule that can't be overridden, but some sites go further than others so it is still localized a bit. Is there a list of absolute musts somewhere?
Comment: @Shog9 Great point, I didn't read all the way though the first time because I was reading while LaTeX was compiling...

Why was this meta answer deleted?


A reply to the Chinese room argument

Question: All replies to the Chinese Room Argument (CRA) that I've seen assume the computer science concept (explanation, "definition" as Searle says) of the electronic digital computer. But what of other conceptions? If there are alternative understandings that are true to the hardware and also could allow the acquisition of an internal semantics, would this rebut the CRA? Even if it is not clear that an alternative conception allows inner semantic content, does the fact that (a) such an alternative exists, and (b) that the CRA has not addressed it, rebut the CRA? For wouldn't the CRA's conclusion then merely be that the computer science concept (i.e., Turing's concept) of the machine could never think whereas other conceptions that are true to the hardware, might?
Comment: CRA is specifically directed at the "computer science conception" (so-called "strong AI") not being able to explain "understanding", as Searle sees it, not at the generic idea of "thinking hardware". So all alternative conceptions of it are moot to his argument. Searle himself allows that we may well be able to build thinking machines one day, he just thinks that it takes material with special causal properties (like organic matter) for these machines to attain "understanding", see [Biological naturalism](https://en.wikipedia.org/wiki/Biological_naturalism).
Comment: @Conifold And Searle says humans are thinking machines. Suppose there's an alternative concept of the computer that is accurate, and there are reasons to suppose this other conception allows an internal semantics, would this be a rebuttal of the CRA? If not, and if there is such other conception then supporters of the CRA would still have their argument, and AI would still have its machine. AI would need the better concept of the machine but that's a much better outcome than the machine being forever a prisoner in a universe of mere syntax. Does this idea, sort of a win-win solution, stack up?
Comment: No, it would not be. Arguments have limited scope, they can not rule out vaguely anticipated somethings that may one day emerge, such as conception of a machine which is we know not what. It is possible that CRA can be modified to argue against such conceptions as well, but we'd have to see what those conceptions are first. Arguably, even artificial neural networks are sufficiently different from the von Neumann computers Searle was caricaturing to raise doubts about intuitive persuasiveness of CRA against them, upon which he relies. Syntax is Semantics is the motto of Rapaport's programme.
Answer: John Searle takes the Chinese Room Argument beyond the Turing machine model in the "brain simulator reply" in section III in Minds, Brains and Programs:

The problem with the brain simulator is that it is simulating the wrong things about the brain. As long as it simulates only the formal structure of the sequence of neuron firings at the synapses, it won't have simulated what matters about the brain, namely its causal properties, its ability to produce intentional states.

Later he remarks that "formal properties are not by themselves constitutive of intentionality". These formal properties are not restricted to Turing machines.

Searle, J. R. (1980). Mind, brains and programs. A debate on artificial intelligence. The Behavioral and Brain Science, 3, 128-135.
Comment: I don't really understand Searle's response. He talks about water in pipes simulating neural pulse propagation. Why not dispense with water molecules and replicate the brain organic molecule for molecule? Would he still say there is no intentionality? I take the Church-Turing idea of simulation where a system is quite accurately described and the description run through a computer (as the program). Then the output of the program describes what would have been the output of the system, had it received as input what is described by the input to the program. I'm just confused.
Comment: @Roddus What he is suggesting with the water pipes is that if one simulates understanding by some other means than a Turing machine, he could still put in a human to simulate the formal structure of the simulator and that human would still not understand. The water pipes is just an example of another kind of simulation of neural activity. What has to be done is not simulate the formal structure but somehow reproduce the causal properties of understanding. What makes the problem difficult is that it is unclear what those causal properties are.

A reply to the Chinese room argument


What is it called when someone acts one way then acts another way in front of someone else and gets you in trouble?

Question: My sister has made me mad so many times by not saying or doing something alone with me but then goes and says it to me in front of my parents, and I have been getting in trouble for it.
Answer: One word that might be suitable is fickle:

It shall be fickle, false and full of fraud,
  Bud and be blasted in a breathing-while;
  The bottom poison, and the top o'erstraw'd
  With sweets that shall the truest sight beguile:
  The strongest body shall it make most weak,
  Strike the wise dumb and teach the fool to speak.
Answer: hypocrite might be the word you are looking for.
Please have a look at the definition here


When to use Community Wiki option?

Question: When should this community wiki button be ticked while answering or edit?
Answer: See https://physics.stackexchange.com/privileges/community-wiki

When should I make my answers Community Wiki?

When you want to enhance the "wiki" aspect of your post, so that it can be a continually evolving source of good information through
repeated editing.

When you feel your post would benefit from less concern about voting affecting the reputation of those participating in it.

Basically, when you want the post to be a collaborative one. Creating a CW post basically invites radical changes and additions -- unlike normal posts, where the wiki aspect is more in grammar/formatting/small tweaks.
Answer: The CW scheme is just when you want other users to help in revision of your post. Not for formatting,etc. which is already done by the fellow users - but, for improving (additional information) of your post which shouldn't be normally done by fellow users. They can edit the post for clarification. But, they can't change the post by adding additional info. There's also this historical lock (which a mod can put on a post) for the prevention of edit wars...
The influences: When a post goes beyond 10 edits, it's automatically reverted to a CW. When the post is marked by CW, additional (+) or (-) votes doesn't influence your precious reputation. Be sure to check out the -1'd user..! Well, he's the -1 in every site. He owns the CWs...

If you've got some time, consider reading What are "Community Wiki" posts? and When to mark the 'community wiki' checkbox on a new question? which are themselves CWs...
Comment: Doesn;t really "own" them (try voting your own CW post down/up.)

When to use Community Wiki option?


Is it illegal for my landlord to endanger the life of my emotional support animal?

Question: My landlord came and did a carpet cleaning, but did not notify me in advance. Luckily I was there to remove my dog, an emotional support animal, from the premises in order to ensure she wouldn't get hurt by the chemicals. I have done research and learned that many chemicals present in carpet cleaner are deadly to dogs. If I had not been there to remove my dog from the premises, my dog could have died, especially considering her small size which makes her more vulnerable to the chemicals. Is it illegal for my landlord to endanger the life of my emotional support animal?
If so, please point me to the law that says the landlord must provide a safe environment for my dog.
I live in Utah.
Comment: What does your lease say? Normally landlords have the right to clean and inspect their property, but I would assume there should be advance notice.
Answer: There is probably not a law in Utah that prohibits the use of cleaning chemicals that are harmful to dogs without advanced notice. This would be particularly true if the landlord generally prohibits pets but your emotional support animal is an exception to that general rule.
If you let your landlord know that the chemicals are harmful to your dog and that you would like advanced notice in the future, you might have a negligence suit if the landlord failed to do so in the future and your dog was harmed. But, even then your landlord's duty of care would have to be balanced against your own duty to supervise your dog and keep it from harm.
As noted in another post, it also matters if the carpet is inside or outside your unit. If it is inside your unit, you are generally entitled to notice of the landlord's intent to enter, although the lease will usually provide for an exception in case of emergencies, which would not normally include carpet cleaning.
Answer: There aren't any special laws about landlords, dogs, or support animals. There is an animal cruelty statute which could have been relevant, had there been injury to the animal. And likewise, you could sue the person if they negligently harmed the animal, assuming that the harm was foreseeable. One can presume that a defendant would dispute the claim of causality (or that it was foreseeable). There are laws against reckless endangerment, but those require deliberately ignoring danger, and also pertain to danger to a person.
Of course, there is the matter of entering an apartment. Utah Code 57-22-4 states

Except as otherwise provided in the rental agreement, an owner shall
  provide the renter at least 24 hours prior notice of the owner's entry
  into the renter's residential rental unit.

so you should look at the lease for any statement about advance notice.


Why did it take 11(ish) years to make Deadpool?

Question: According to several stories regarding the just released Deadpool movie, it is stated Ryan Reynolds (who had played a previous version of Deadpool) had to wait 11 years to play the main character in the Deadpool film. Why did it take 11(ish) years after the release of X-Men Origins: Wolverine to make Deadpool?
Comment: Ryan Reynolds had to learn how to be funny.
Comment: Because they were making other films in the meantime.
Answer: Because it was in development hell.
To be precise, it was in development from 2000, making it 16 years. But there were various reason at various levels. Here are the bullet points of it from Wikipedia:-

May 2000, Artisan Entertainment announced a deal with Marvel Entertainment to coproduce, finance and distribute a film based on
Deadpool.

2004, New Line Cinema attempted to produce a Deadpool film with writer/director David S. Goyer working on the spin-off and actor Ryan
Reynolds.

By August, Goyer lost interest in favor of other projects.

In March 2005, after New Line put Deadpool in turnaround, 20th Century Fox became interested in moving forward on production for the
project.

Fox considered a Deadpool spin-off early in the development of X-Men Origins: Wolverine, with Reynolds cast in the role, and after the
opening weekend success of that film announced that it was lending
Deadpool out to writers, with Lauren Shuler Donner acting as a
producer. Donner wanted the film to reboot the character of Deadpool,
ignoring the version and giving more justice to comic version with
breaking the fourth wall.

Rhett Reese and Paul Wernick were hired to write the script in January 2010.

The script leaked in the February of 2010 and garnered a positive reaction by the fans, prompting Fox to grant a small budget for test
footage.

In July 2014, the visual effects test footage created for the film in 2012 and starring Reynolds through motion capture, was leaked
online. Blur Studio, the company that created the test footage,
subsequently released it officially.

In September 2014, Fox gave the film a release date of February 12, 2016

So in short, it was delayed because of Goyer's disinterest, studio change etc etc. But the leaks were too much responsible to there greenlight of the project.
Comment: I read somewhere that the poor reception of *Green Lantern* in 2011 made the studio a bit wary of putting out a superhero movie with Ryan Reynolds as the leading man. Could be nonsense, but hopefully *Deadpool* has put paid to that kind of nonsense.
Comment: Ryan Reynolds also just did an interview where he states that he was blackmailed to play the horrible version of Deadpool in Wolverine Origins if he ever hoped to have an independent film. He told them their version was bad, and it wasn't upon pilot testing the film and everyone hating the character that the urgently flew Ryan from Canada back to the studio to film the post credit scene with Deadpool's eyes open, a wink, and mouth not sewn shut. Because of the backlash they created, they were also hesitant. Thank "the person" that leaked the DP Test footage from ComicCon
Comment: @PaulD.Waite I have heard that too but got no proof for it yet, might dig it later.
Comment: I think that Reynolds "leaked" it
Comment: @user001 i did heard that somewhere, don't have proof fro now
Answer: Well, another reason that might not be so obvious to some people was the fact that Ryan Reynolds had to fondle a guy's balls who's name rhymed with "Pulverine"
In the movie, Deadpool clearly states that he can't tell you who he you who balls he had to fondle ,but he does include some clues as to who's he did,
First scene in this video,

Then Ryan Reynolds discusses this in this interview,

Q: Can you tell me what you imagine fondling Wolverine balls feels
  like, b/c that played on my mind?
A: Its like Santa's sack he is carrying around, that thing is is like
  a good 15 to 16 lbs a peice

So, although it is pretty encrypted, the message is that he had to fondle Wolverines balls, or more specifically Hugh Jackman's. Which in itself was one of the main reasons it took 13 years.
Comment: I can't tell if this classifies as an 'in-universe' answer or not.
Comment: @DaaaahWhoosh: exactly. It's all fun and games breaking the fourth wall, but then you realise you actually needed it intact.
Comment: @strictly in universe.
Comment: An out of universe DP answer is still an in universe DP answer. I read it in a book. ;)


Can ficus root growth be controlled trimming the tree?

Question: I have very large ficus growing near a corner of a building. It is very overgrown. My gardener has suggested trimming the tree significantly and says that will significantly reduce the expansion of the root system, thereby protecting the building from further root growth. Is he correct?
Answer: The best thing you can do is water your tree. It will not have to go searching for water.  You should also dig a trench about 2 feet deep and cover your foundation on the side with your tree with galvanized metal, making sure you have air between the foundation and the metal.
Trimming the tree is fine for health but not for reducing root systems.  How silly.  In fact, too much pruning of the top growth will enhance root growth just because there is a large amount of energy the plant needs to put somewhere...why waste all that work making food if it can't be stored in the roots?


What did Mayor Wilkins hope to accomplish through his ascension?

Question: In his pre-ascension state, Mayor Wilkins is apparently invincible to Buffy, the Scoobies, or anyone else who crosses him. He attempted to have the volcanological research of Lester Worth squashed via Faith: he knows that in fully-ascended/Big Time Demon form he will be vulnerable to death, yet the acquisition of ultimate power is his main objective so invulnerability would definitely be an advantage. Why sacrifice these abilities in order to become a big combustible snake?
Why would Mayor Wilkins want to ascend?
Comment: My understanding was that the invincibility wore off after the hundred days. It was either become a powerful demon, or revert to a very mortal ..whatever he was before the 100 days.
Comment: Some people dream of being a rock star, some people dream of being a giant snake.
Comment: I attempted to find this answer via SE and Google search. The site I found on Google that seemed to address it has so many advertisements I couldn't even load the page.
Answer: He was a soulless servant to demons of the Hellmouth and was seeking to become more powerful than them
Mayor Wilkins had committed himself one hundred years prior to the events of Buffy to what is termed the Ascension. This backstory is revealed in scripts for Buffy: The Animated Series.  There, Wilkins was a human who originally arrived in California in the 19th Century, and founded Sunnydale on the site of Boca del Infierno shortly after a Vampire Slayer, Naayéé'neizgháni, had been killed there. Wilkins stumbled upon the Hellmouth and found it overrun with demons because of the death of the Slayer. He ended up making a pact to avoid being killed himself. He agreed to make Sunnydale a refuge for demons, free from outside interference, so that they could feed on the inhabitants unchecked. As part of the deal, he gave up his soul. In 1899, he began planning his 100-year Ascension into the form of a pure demon — this is what you see happening in Season 3 of Buffy.
So his choice was to remain a soulless human maintaining a feeding ground for demons, or ascend to become a powerful pure demon, not under the control of other lesser demons.
Finally, note that his invulnerability was never stated to be permanent, but rather a temporary power that kicks in for the 100 days leading up to the Ascension.  So (a) he became invulnerable because he was on the way to Ascension (these are not independent things), and (b) the invulnerability was not a permanent transformation.
Comment: @1252748 : With the power he was amassing, yes.  You're only seeing him in the 100 days leading up to the Ascension, where he is invulnerable.  But he didn't start that way.  Also, his back story is based on *The Animated Series* (not the books, as far as I am aware).  Like I said, he only survived his discovery of the Hellmouth by selling his soul and agreeing to maintain Sunnydale as a feeding ground.
Comment: As far as I can tell, Buffy: The Animated Series never made it to production and only a 4 minute clip has ever been released, of which I don't believe any of it involved the mayor.  So either you're confusing it with the comic book, or you're coming to us from a parallel universe.  On the off chance it's the latter, please, how do I get there?
Comment: I haven't read any of the books, but in the TV series he sure didn't seem like he was "under the control of lesser demons". He seemed like he was the big cheese shot caller.
Comment: I didn't even know there was an animated series. Is it good?
Comment: Excellent answer **_and_** a new show recommendation. Can't beat that. Thanks!
Comment: @1252748 : Thanks --- glad to be of help!
Comment: @starpilotsix : I based my answer on the scripts for it.  I'd seen the clip and thought it looked okay, but not worth investing time in.  Didn't realize that's all there is and it wasn't just a trailer.  But the scripts are out there and Whedon-endorsed, as far as I can tell.


¿Cuál es la diferencia entre honor y honra?

Question: Hace poco me di cuenta de que existen dos palabras en español que equivalen a la palabra "honor" en inglés: honor y honra. ¿Cuál es la diferencia entre estas dos palabras? ¿Cuál es más común?
Answer: IMHO, the distinction is very slim (in fact, some times can be exchanged) but...
Honor would be something that dignifies your position in the society for doing something "honorable" not only for you, but for said society itself (a heroic sacrifice in an act of war, for instance) whereas Honra would be a bit more personal (you live your own life with virtue)
If you search both terms in the dictionary of the RAE, the fist two entries for Honor mention that is something you get when fulfilling obligations with oneself but also (here's the important part) with your fellow men. On the other hand, the definitions of Honra are exclusively related to the individual.
To me, honor sounds "bigger" (more important or solemn) than honra.
It's a pretty tricky distinction, though.
And about which one is more common... I would say "honor" is used more often but that's just (once again) my opinion.
Comment: Also, when used as a verb "to honor someone" in Spanish is "honrar a alguien"
Comment: "honor" is used more often than "honra" and it's not an opinion, have a look at this graph: https://books.google.com/ngrams/graph?content=honor%2Chonra&year_start=1800&year_end=2000&corpus=21&smoothing=3&share=&direct_url=t1%3B%2Chonor%3B%2Cc0%3B.t1%3B%2Chonra%3B%2Cc0


Concepts in topology successfully transferred to graph theory and combinatorics with non-trivial applications?

Question: What are some of the difficult concepts in topology that have been transferred to graph theory and combinatorics where a certain new application has been found.
A good example is Lovász's proof of Kneser's conjecture.
Comment: Not clear yet if this is successful, but Kronheimer and Mrowka have an ambitious program to understand graph colorings (in particular, the four-color theorem) in terms of a certain instanton Floer homology for graphs: see https://arxiv.org/abs/1508.07205, https://arxiv.org/abs/1508.07207, https://arxiv.org/abs/1710.05002.
Answer: The question asks for concepts, not applications, so in a sense the example given in the OP isn't one.
Here are five quick examples:
(0) One could argue that girth is a transferral of the concept systole from metric-topology, though this is an ahistorical argumentation: the two concepts arose independently in their respective fields.
(1) The concept of associated abstract polyhedral/simplicial complexes. This is the central concept in both Lovász's proof of Kneser's conjecture, and in the proof in [Babson--Kozlov, Proof of the Lovász conjecture, Annals of Mathematics (20 165 (2007) 965-1007]
(2) The concept of topological connectivity (i.e. (1+) smallest dimension such that there exists a non-nullhomotopic continuous map from a correspondingly-dimensional sphere to the geometric realization of the complex (this is strongly related to what the opening poster already mentioned, yet it was not explicitly mentioned yet.
(3) The similar concepts of Whitney complex and barycentric subdivision (see recent work of Oliver Knill).
(4) The concept of Freudenthal-compactification (see 'ends of graphs'), an important tool to enlarge the language with which to speak about infinite graphs.
Comment: I agree on your point. But it is clear I meant the mechanism of the proof.
Comment: I am interested in where those concepts made a meaningful impact.
Answer: Discrete Morse theory has been developed into a thriving subject by Robin Forman and others.
Answer: There has been very interesting work on defining curvature on a discrete graph.
For example:

Knill, Oliver. "A graph theoretical Gauss-Bonnet-Chern theorem."  arXiv:1111.5395 (2011). (Abstract.)

Another discrete curvature is the Ollivier-Ricci curvature:

Bauer, Frank, Jürgen Jost, and Shiping Liu. "Ollivier-Ricci curvature and the spectrum of the normalized graph Laplace operator." arXiv:1105.3803 (2011).
  (Abstract.)
Comment: @Turbo: I believe Knill's definition works for any graph.  I am less familiar with the Ollivier-Ricci discrete curvature.
Comment: Does the definition work for bipartites too?
Answer: You maybe interested in my work with Terrence Bisson, we have studied closed models in various categories of graphs in particular in the category of directed graphs in which we have defined a closed model for which two finite graphs are homotopic equivalent if and only if they are isospectral.
We have defined another closed model in the category of directed graphs related to dynamic systems which characterizes the topology conjugacy class of some walkable finite graphs.
In a paper, I have defined a closed model structure which characterize strongly connected component. I have also studied closed models in the category of undirected graphs and shown that there does not exist a closed model which characterize the Ihara zeta function.
You maybe also interested in the work of Deborah Vicinsky who has constructed spectra for the model that I have defined with Bisson which characterizes isospectral graphs.
Symbolic dynamics and the category of graphs
T Bisson, A Tsemo - Theory and Applications of Categories, 2011
Homotopy equivalence of isospectral graphs
T Bisson, A Tsemo - New York J. Math, 2011
Closed models, strongly connected components and Euler graphs
T Aristide - Proyecciones (Antofagasta), 2016
Tsemo Aristide
Applications of closed models defined by counting to graph theory and topology
Algebra Letters, Vol 2017 (2017), Article ID 2
Vicinsky Deborah
The homotopy calculus of categories and graphs.
https://scholarsbank.uoregon.edu/xmlui/bitstream/handle/1794/19283/Vicinsky_oregon_0171A_11298.pdf?sequence=1
Answer: Riemann-Roch theorem for graphs is a good example of topological concepts in algebraic geometry transferred to graph theory. More references may be found here.
Answer: Infinite graphs have been used as a "discrete version" of topological spaces, for instance infinite Cayley graphs as a discretisation of homogeneous spaces). Gromov constructed homogeneous spaces out of limits of infinite Caley graphs
to prove his theorem on homogeneous spaces. Homogeneous spaces and Cayley graphs share the property that you can transfer any point (vertex) to any other by an auto-homeomorphism (isomorphism).
Answer: Last year I co-authored a paper whose title speaks for itself:
Comparative Genomics Meets Topology: a Novel View on Genome Median and Halving Problems
The introduced topological framework allowed to advance analysis of some hard combinatorial problems in comparative genomics, and further obtain a closed form answer for an open problem.
Answer: Here is a closed model defined in the category of undirected graphs, which maybe answer the question that you raised in your comment to my previous answer: I believe you want to define an homotopy theory which characterizes perfect matchings. The model here characterizes maximum matchings.
Homotopy theory in category theory have been defined by Quillen to generalize classical homotopy theory defined in the category of topological spaces to various settings.
In general, the notion of path does not exist in every category, but, it is possible to define a notion of weak equivalence, fibration, cofibration between two objects. It is on this purpose that Quillen has defined the notion of closed model:
${\it Definitions.}$
Let $C$ be a category, and $W$ a subclass of the class of morphisms of $C$, we say that $W$ verifies the $2$-$3$ property if and only if for every morphisms $f:X\rightarrow Y$ and $g:Y\rightarrow Z$, if two morphisms of the triple $(f,g,g\circ f)$ are in $W$, so is the third.
Let $C$ be a category complete and cocomplete; we say that $C$ is endowed with a closed  model  if and only if there exist three classes of morphisms $(Fib,Cof,W)$ such that:

$W$ satisfies the $2$-$3$ property,
Let $Fib'=W\cap Fib$,  $(Cof,Fib')$ is a weak factorization system
Let $Cof' = W\cap Cof$, $(Cof',Fib)$ is a weak  factorization system.

See the reference for the definitions, the class $W$ is called the class of weak equivalences the class $Fib$ is called the class of fibrations, the class $Fib'$ the class of weak fibrations, the class $Cof$ the class of cofibrations, the class $Cof'$ the class of weak cofibration.
In th reference, I have described a method to generate closed models in a category: closed models defined by counting:
Let $C$ be a category complete and cocomplete whose initial object is denoted by $\phi$.
 For every objects $X$ and $Y$ of $C$, we denote by $X+Y$ the sum of $X$ and $Y$.
 Let $(X_i)_{i\in I}$ be a family of objects of
$C$ and $l_i: \phi\rightarrow X_i$ the canonical morphism.
There exist morphisms $j^i_1:X_i\rightarrow X_i+X_i$ and $j^i_2:X_i\rightarrow X_i+X_i$ such that for every
morphisms $f:X_i\rightarrow Z$ and $g:X_i\rightarrow Z$, there exists a unique morphism $m(f,g):X_i+X_i\rightarrow Z$
such that $m(f,g)\circ j^i_1 = f$ and $m(f,g)\circ j^i_2 = g$. We set $m_i = m(Id_{X_i},Id_{X_i})$.
Such a morphism is often called a folding morphism. We suppose that the class of morphisms $l_i,m_i\in I$ admits the small element argument.
We denote by $W_I$ the class of morphisms which are right orthogonal to every  morphisms $l_i$ and $m_i, i\in I$.
\medskip
{\it Proposition.}
There exists a closed model $(Hom(C),cell(I),W_I)$ defined on $C$ where $Hom(C)$ is the class of morphisms of $C$ and  $cell(I)$ be the class of morphisms of $C$ which are  retracts of  transfinite compositions of pushouts of $l_i,m_i,i\in I$.
\medskip
Remark that a morphism $f:X\rightarrow Y $ of $C$ is an element of $W_I$ if and only if for every $i\in I$, the map $c^i_f:Hom_C(X_i,X)\rightarrow Hom_C(X_i,Y)$
defined by $c^i_f(h) = f\circ h$ is bijective.
\medskip
This model can be apply to the category of undirected graphs: Let $C_U$ be the category which has two objects that we denote by $0$ and $1$. We suppose
that $Hom_{C_U}(0,1)$ contains two elements $s,t$, $Hom_{C_U}(0,0)$ contains one element,
 $Hom_{C_U}(1,1)$ contains the identity and an involution $i$ such that $i\circ s =t$, and $Hom_{C_U}(1,0)$ is empty. An undirected graph is a presheaf on $C_U$. We denote by $UGph$ the category of undirected graphs, its a complete and cocomplete category since it is a Grothendieck topos.
Particular examples of undirected graphs are the undirected arc graph $A_U$ is the graph defined by $A_U(0)=\{u_1,u_2\}$, $A_U(1)=\{a_1,a_2\}$ such that $A_U(i)(a_1)=a_2$, $A_U(s)(a_1)=u_1$
and $A_U(t)(a_1)=u_2$.
The graph $V_U$ is the graph defined by $V_U(0)=\{v_1,v_2,v_3\}$, $V_U(1)=\{b_1,b_2,c_1,c_2\}$ such that $V_U(s)(b_1)=V_U(s)(c_1)=v_1$,
$V_U(t)(b_1) = v_2, V_U(t)(c_1)=v_3$, $V_U(i)(b_1)=b_2$ and $V_U(i)(c_1) = c_2$.
\medskip
We consider the closed model $(Fib,Cof,W)$ defined by counting the object $V_U$ of $UGph$.
\medskip
{\bf Theorem.}
{\it Let $X$ and $Y$ be finite graphs, a weak equivalence $f:X\rightarrow Y$   for the closed model defined by counting  $V_U$  induces a bijection between the maximum  matchings of $X$ and $Y$. Conversely, if the cardinal of the set of arcs of $X$ and $Y$ are equal, then a morphism $f:X\rightarrow Y$ which induces a bijection between the maximal matchings of $X$ and $Y$ is a weak equivalence.}
\medskip
{\bf Proof.}
A maximum matching of $X$ can be defined by $p_Y:\sum_JA_U^j\rightarrow Y$ where $A_U^j$ is a graph isomorphic to $A_U$ such that: $p$ is injective on arcs, $p_Y(A_U^{j_1})\cap p_Y(A_U^{j_2})$ is empty and every arc of $Y$ shares a vertex with an arc of $p_Y(\sum_J A_U^j)$.
Let $p_X:\sum_JA_U^j\rightarrow X$ be a maximum matching let's show that $p_Y=f\circ p_X$ is a maximum matching. Consider $b$ an arc of $Y$, there exists an unique arc $a$ of $X$ such that $f(a)=b$ since $f$ induces a bijection on arcs. If $a$ is not in the image of $p_X$, $a$ shares a vertex with $p_X(A_U^j)$ for an element $j\in I$, this implies that $b=f(a)$ shares a vertex with the image of $f\circ p_X$. Suppose that $f(p_X(A_U^{j_1}))$ shares a vertex with $f(p_X(A_U^{j_2}))$, you can define a morphism $m:V_U\rightarrow Y$ whose image is the subgraph of $Y$ whose arcs are $f(p_X(A_U^{j_1}))$ and $f(p_X(A_U^{j_2}))$. Since $f$ is defined by counting $A_U$ and $V_U$, there exists a unique morphism $n:V_U\rightarrow X$ such that $m=f\circ n$,  but the arcs of $n$ are $p_X(A_U^{j_1})$ and $p_X(A_U^{j_2})$, contradiction, since they do not share a vertex.
Now we show that $f$ induces a surjection between the sets of maximum matchings of $X$ and $Y$. Let $p_Y:\sum_JA_U^j\rightarrow Y$ be a perfect matching. Since $f$ is defined by counting  $V_U$, it induces a bijection between the sets $Ar(X)$ and $Arc(Y)$ of arcs of $X$ and $Y$. We can define the morphism $p_X:\sum_J A_U^j\rightarrow X$ such that the restriction $p_X^j$ of $p_X$ to $A_U^j$ is the unique morphism $p^j_X:A_U^j\rightarrow X$ such that $p_Y^j=f\circ p_X^j$, $p_X$ is a maximum matching:
Consider an arc $a$ of $X$ which is not in the image of $p_X$, $f(a)$ is not in the  image of $p_Y$, this implies that there exists $j\in J$ such that $f(A_U^j)$ shares a vertex with $f(a)$,  we can define a morphism $g:V_U\rightarrow Y$ whose image is the subgraph of $Y$ which arcs are $f(a)$ and $p_Y(A_U^j)$. Since $f$ is defined by counting $A_U$ and $V_U$, there exists a morphism $h:V_U\rightarrow X$ such that $g=h\circ f$, the image of $h$ is $a$ and $p_X(A_U^j)$.
Remark that $p_X(A_U^{j_1})\cap p_X(A_U^{j_2})$ is empty since $p_Y(A_U^{j_1})\cap p_Y(A_U^{j_2})$ is empty. We deduce that $p_X$ is a maximum matching. We deduce that $f$ induces a surjective map on maximum matchings.
Suppose that $X$ and $Y$ are finite undirected graphs such that the set of arcs of $X$ and $Y$ have the same cardinal and $f$ is a weak equivalence: firstly we remark that $f$ induces a bijection between the sets of arcs of $X$ and $Y$. Let $b$ be an arc of $Y$, there exists a maximum matching $p\sum_JA_U^J\rightarrow Y$ whose image contains $b$, we can lift $p$ to $q:\sum_JA_U^j\rightarrow X$ such that $p=f\circ q$, this implies that there exists an arc $a$ of $X$ such that $f(a)=b$. Since $f$ is surjective on arcs and the cardinals of the set of arcs of $X$ and $Y$ are equal, we conclude that $f$ induces a bijection between the sets of arcs of $X$ and $Y$. Let $g:V_U\rightarrow Y$, there exists arcs $a,a'$ of $X$ such that the image of $(a,a')$ the subgraph of $X$ which is the union of $a$ and $a'$ by $f$ is $g(V_U)$, suppose that $a,a'$ do not have a common vertex, there exists a maximal matching $p\sum_JA_U^j\rightarrow X$ whose image contains $(a,a')$, but $f\circ p$ is not a matching: contradiction, since we have supposed that $f$ induces a map well defifined on maximal matchings. This implies that $g$ can be lifted to $X$ and $Hom(V_U,X)\rightarrow Hom(V_U,Y)$ induced by $f$ is surjective. This map is also injective since $f$ is induces a bijection on arcs.
\medskip
If one supposes that $X$ and $Y$ do not have isolated vertices, similar arguments show that a week equivalence between $X$ and $Y$ induces a bijection between their respective set of perfect matchings.
\medskip
This closed model is not trivial, consider the graph $X$ which is the undirected path of length $2$  (or $V_U$), it is obtained by identifying one vertex of two copies of $A_U$, and $Y$ which is the concatenation of $A_U$ and a circle. You can define $f:X\rightarrow Y$ obtained by identifying the middle vertex of $X$ with a vertex at its end. It is a weak equivalence.
Tsemo Aristide
Applications of closed models defined by counting to graph theory and topology
Algebra Letters, Vol 2017 (2017), Article ID 2


Changing projection for field calculator

Question: I've just succeeded in getting the area of a polygon using field calculator.  The polygon was drawn on a Google hybrid aerial photo. There are no units given in the calculation and I assume the area figure is based on latitude / longitude.  How do I go about changing the projection in order to get an area figure in hectares?
Comment: what software are you using?
Comment: QGIS - sorry for omission!
Answer: You have to look up what CRS is used for the polygon layer with Rightclick -> Set CRS for layer.
If it is in EPSG:3857 (the same as for openlayers plugin background), it has no real unit. Google mercator units (although called "metres") fit only at the equator to real metres.
To get a real metres layer, choose the UTM projection for your part of the world, and

reproject your layer into it with Rightclick -> Save as ...
create a new layer in that CRS and draw the polygon again.

Note that simply changing the CRS with Set CRS for layer does not reproject your data to the desired CRS.
Comment: why someone need to redraw a polygon when it is possible just to reproject the layer? O_o
Comment: @SS_Rebelious: For a beginner, it might be quicker to redraw than to reproject ;-)
Comment: I sincerely doubt that reprojection is slower for the beginner and that such approach is valid in general. See, this question and answer have a huge chance to pop up on top of google search for a relevant query, so it will be better at least to mention reprojection possibility.
Comment: [UTM is not a great choice](http://gis.stackexchange.com/questions/31701) for area calculations and will be invalid for any regions with considerable longitudinal extent.  [*Any* equal-area projection](http://gis.stackexchange.com/questions/20054) that covers the region of interest would do fine.  Note, too, that the area in the end has to be converted from square meters to hectares (divide the value by 100^2=10,000).
Comment: Writing as a beginner, I did find it easier to re-draw the polygon than to re-project the layer.  Agree that UTM did not help for area calculations - I was wanting to work with British Ordnance Survey backdrop and found out that the appropriate CRS for that is OSGB 1936 - British National Grid.


Troublesome tags that need cleaning up

Question: We've got a ton of incoming questions and I've realized some tags really do need some love, so I'm going to make a list of the worst ones:
Answer:
broadcom - specifically questions having to do with BCM4311 need de duping.
boot - IMO our worst tag, these are hard because they're "my computer won't boot"
software-center - A bunch of these seem like bug reports.
upgrade - Probably a bunch of too localized bug reports.
nvidia-optimus - these are really troublesome in linux and we need a way to point everyone to one canonical question that makes sense for a bunch of people.
Comment: @Luis No, the tags are appropriate, it's just they might contain a bunch of dupes and need a once over, for example today we had like 5 bcm4311 questions that could have been merged, things like that.
Comment: Basically go through a whole bunch of questions and reading them to see if the tag is appropriate? Yes?
Comment: Got it Bot. Will do, after all, robot will take over the world. Better start respecting them already.

Troublesome tags that need cleaning up


How much did Didius Julianus pay to become emperor of Rome?

Question: According to Wikipedia, Didius Julianus was proclaimed Roman Emperor in AD 193 by the Praetorian Guard after offering them 25,000 sesterces per soldier (outbidding Sulpicianus's offer of 20,000 sesterces each).  But "25,000 sesterces" is just a number.  How much money would that have been, compared to the yearly pay of a typical soldier (or a typical Praetorian)?
Answer: Short Answer
Didius Julianus (ruled 28 March to 1 June 193 AD) promised a total of around 200 million sesterces to the Praetorians but apparently did not have sufficient funds to meet this commitment. For context, a legionary foot soldier was paid (annually, before significant deductions) around 2,400 sesterces following the pay rise in 197 AD, and a praetorian an estimated 6,000 to 8,000 sesterces.

Details
In answer to the main question, How much did Didius Julianus pay to become emperor?
There were an estimated 8,000 praetorians at this time so:
8,000 x 25,000 sesterces = 200,000,000 sesterces in total (or 50,000,000 denarii), though officers may have been offered more.
Didius Julianus, a former consul, was one of the richest men in Rome but, according to Herodian (c. 170 to c. 240 AD) in (Roman History 2.7),

It was quickly discovered, however, that he had lied to the
praetorians and deceived them, as he was unable to fulfill his
promises.
The truth is that he did not have as much money in his personal
possession as he had pretended to have, and no money was available in
the public treasures;...

The lack of public funds (which Julianus might otherwise have used to make up for the lack of his own) seems to be supported by Cassius Dio who, when commenting on Julianus' immediate predecessor, Pertinax (emperor Jan-March 193 AD), noted that:

At this time, then, there was such a dearth of funds in the imperial
treasury that only a million sesterces could be found.

The answer to How much money would that have been, compared to the yearly pay of a typical soldier (or a typical Praetorian)? is rather more difficult as documentary evidence is limited for this period.
The basic annual pay of a legionary foot soldier in AD 197, during the time of Didius Julianus' (AD 193) successor Septimus Severus (AD 193 - 211), is estimated to have been 2,400 sesterces. As there was a pay rise in AD 197, the figure for 193 AD would have been less than this, and there were also substantial deductions made for food, clothing, boots etc., but soldiering was nonetheless a well-paid occupation.
Praetorians were paid more: 6,000 to 8,000 sesterces in AD 197 under Septimius Severus.

Main source:
Michael Speidel, 'Roman Army Pay Scales'. In The Journal of Roman Studies (Nov. 1992)
Comment: *The basic annual pay of a legionary foot soldier in AD 197...2,400 sesterces.* If one denarius were equivalent to four sesterces, that means they were getting paid the equivalent of 600 denarii per year.  At least as of about two centuries prior (early 1st century), one denarius was the baseline pay for a day's labor.  Maybe it changed by 197, but in early 1st century terms, that would mean the rank-and-file soldiers were basically getting paid about 1.5 - 2 times the baseline pay for a day laborer.  (365/366 days a year, but it depends on how many of those days a day laborer really worked.)
Comment: @Nzall You are comparing a highly developed 21st century country to a pre-industrial society. If we compare the GDP per capita of the modern USA and the (estimated) GDP per capita of the Roman empire according to Wikipeda, the difference is around 100x. In other words, the Roman empire was much closer to some of the poorer counties in Africa today. So a reasonable estimate would be to say that the average Roman made about a dollar a day, making 1 Denarius roughly equivalent to 1 USD.
Comment: So if 1 Denarius is a day's worth of labor, and Romans worked a 6 hours day, 1 Denarius would be roughly equivalent to 90 USD of modern money. So those 50,000,000 Denarii would be around 4.5 Billion dollars in today's money (or 6 billions if you go by the more modern 8 hour work day).
Comment: @Nzall, currency conversions over such a long time period are essentially meaningless, which is why I asked for a comparison in contemporary terms.
Comment: @Mark I was trying to make a comparison based on modern pay for a day's labor, which is around 15 USD an hour according to the source I found. I also didn't make a comparison based on GDP. I wanted to make an analogy for "what if this happened today in the most powerful country in the world with the same ratio between base wages and the bribe used?" Something to make a rough example for how much this would cost a modern dictator, i.e. bribing 8000 elite soldiers with thousands of times the payment for a regular civilian.


Large ibdata file in MySQL

Question: I am having MySQL database with all my tables as InnoDB with file_per_table config on. But Still I m seeing huge ibdata file ( ~50GB). All tables are having .ibd file as well. This is a machine I have created by taking dump and loading. What is a reason for this.
Comment: Probably there is one or more transactions that modifies or inserts a large amount of data. Check for undo log or change buffer that are hosted into ibdata tablespace. This article may help you: http://www.percona.com/blog/2013/08/20/why-is-the-ibdata1-file-continuously-growing-in-mysql/. Or wait for Rolando answer  :-)
Answer: You probably have lots of large transactions or one really big transaction.
Take a look at Vadim Tkachenko's Pictorial Representation of InnoDB

If you look inside the system table (ibdata1), you see rollback segments and undo logs.
When a rollback segment rolls back a transaction, it has to use the MVCC information it stockpiled in the undo space. That's where most of the growth occurs. Percona mentioned this back on Jun 10, 2010 (Reasons for run-away main Innodb Tablespace)
I have discussed this before

Apr 23, 2013 : How can Innodb ibdata1 file grows by 5X even with innodb_file_per_table set?
Mar 31, 2014 : mysql directory grow to 246G after one query, which failed due to table is full
Jun 16, 2014 : MySQL Index creation failing on table is full

UPDATE 2015-03-22 15:00 EDT
If you are convinced the data dictionary is the cause, there is only one sure way you can verify this.

STEP 01) Get another DB Server (Dev or Test)
STEP 02) Install MySQL on it
STEP 03) mysqldump the schema-only (using --no-data)
STEP 04) load the schema-only dump into the empty database
STEP 05) run ls -l /var/lib/mysql/ibdata1 | awk '{print $5}'

The number that comes out will be the size will be the size of ibdata1 with just data dictionary entries for the current list of tables, but with no data in them.
In your last comment, you said

So open transaction doesnot seem to be right reason. We use to create some 200-300 table on daily basis (by our ETL tool) and drop them after some processing periodically ( drop some 2k-5k tables once in 2-3weeks), could this attribute to the big file ?

You could be right for same reason: Just like rollback segments and the undo space have no provision for reclaiming unused diskspace for the OS, dropping tables and creating new ones would likewise have no provision for reclaiming unused diskspace for the OS.
To prove that, you would have to use that new server with all tables but no data. Then, perform the same dropping and creating of tables every week. If the ibdata1 grows just for doing that, then you have proven undeniably that dropping and creating tables alone can grow ibdata1 with innodb_file_per_table enabled.
If you want to cleanup ibdata1, please see my posts

Sep 26, 2012 : How do I shrink the innodb file ibdata1 without dumping all databases?
(on why you have to dump all data, remove ibdatat1, and create a new ibdata1)
Oct 29, 2010 : Howto: Clean a mysql InnoDB storage engine? (on how to actually do this)

GIVE IT A TRY!!!
Comment: I suspect the data dictionary. We have thousands of tables with 200 to 400 QPS, mostly ran with auto-commit on. I think, we separating some databases to a different machine (and setting new machines ) would help.
Comment: The data dictionary has absolutely nothing to do with ibdata1 growth. I have worked with a client that 800 databases (168 tables / database) with innodb_file_per_table. That's 134,400 tables. The ibdata1 file never surpassed 1G. If no more tables were added and you enable innodb_read_only (http://dev.mysql.com/doc/refman/5.6/en/innodb-parameters.html#sysvar_innodb_read_only), ibdata1 would never grow because the rollback segments and undo space would never be used. Therefore, the data dictionary has never been, or ever will be, an issue when it comes to file size growth.
Comment: The similar ibdata size is present in all the slaves as well. So open transaction doesnot seem to be right reason. We use to create some 200-300 table on daily basis (by our ETL tool) and drop them after some processing periodically ( drop some 2k-5k tables once in 2-3weeks), could this attribute to the big file ?
Comment: Here is an experiment you really need to do: 1) Get another DB Server (Dev or Test), 2) Install MySQL on it, 3) mysqldump the schema and load the schema-only dump into it (no data). 4) run `ls -l /var/lib/mysql/ibdata1 | awk '{print $5}'`. If the number is near 53687091200 (50G), then you can suspect the data dictionary. I would then be incredibly shocked.
Comment: i would try it and will let you know  thw result. Thanks for you valuable inputs
Answer: I wish add something to the answer of Rolando. From Mysql 5.6 it is possible to put out undo logs away from ib_data1. I have tried the following experiment.
On a fresh installation I have put undo log out of system tablespace (ibdata1) and created a lot of tables to check how ibdata1 grows.
Then I created a big table and opened a transaction in one session. Into another session I raised an update, so I checked how undo tablespace grows in this case.
Creating a lot of tables
The manual page is Storing InnoDB Undo Logs in Separate Tablespaces.
First I added to .cnf the following lines:
innodb-undo-tablespaces=2

Recreated the datadir and checked the size of system and undo tablespaces:
$ mysql_instal_db --basedir=... --datadir --defaults-file=...
$ cd data
$ du -h undo00* ib*
10M  undo001
10M  undo002
12M  ibdata1
48M  ib_logfile0
48M  ib_logfile1

Fresh ibdata1 (with my configuration) is around 12M. I launched a simple script to create 200000 tables like this:
create table t_<xxx> (i int unsigned auto_increment, c char, d datetime, primary key(i) ) engine=innodb;

After the tables creation the tablespaces sizes are:
$ du -h undo00* ib*
10M  undo001
10M  undo002
141M ibdata1
48M  ib_logfile0
48M  ib_logfile1

The 200000 tables occupy less than 129M. Next I dropped tables and recreate them. No difference to the size of ibdata1.
Playing with the undo tablespaces
To continue my experiment I created a table sbtest1 with 4000000 rows using sysbench:
$ sysbench --test=<path>/update_index.lua --mysql-host=... --mysql-port=... --mysql-user=... --mysql-password=... --oltp-table-size=4000000 prepare

$ du -h sbtest1.ibd
957M sbtest1.ibd

I started a transaction in session 1:
session1> start transaction
...
session1> select * from sbtest limit 1;

select * from sbtest1 limit 1;
+----+---------+-----------------------+----------------------------+
| id | k       | c                     | pad                        |
+----+---------+-----------------------+----------------------------+
|  1 | 2006885 | 08566691963-88624.... | 63188288836-92351140030... |
+----+---------+-----------------------+----------------------------+
1 row in set (0.00 sec)

Sizes don't changed:
$ du -h ibdata1 undo00* ib_logfile*
141M    ibdata1
49M undo001
10M undo002
48M ib_logfile0
48M ib_logfile1

I started another session:
session2> use information_schema;
...
session2> select trx_id, trx_rows_locked, trx_isolation_level from INNODB_TRX;
+---------+-----------------+---------------------+
| trx_id  | trx_rows_locked | trx_isolation_level |
+---------+-----------------+---------------------+
| 3714243 |               0 | REPEATABLE READ     |
+---------+-----------------+---------------------+
1 row in set (0.00 sec)

session2> use sbtest;
...
session2> update sbtest1 set k = k + 1;
Query OK, 4000000 rows affected (3 min 40.75 sec)
Rows matched: 4000000  Changed: 4000000  Warnings: 0

If I check size of ibdata1:
$ du -h ibdata1 undo00* ib_logfile*
141M    ibdata1
209M    undo001
10M undo002
48M ib_logfile0
48M ib_logfile1

If I commit transaction on session1, undo001 doesn't shrink.
Conclusion
A open transaction could grow the ibdata1 file more than 200000 tables.
I know that it is a very simple test and it can be very different by a production workload.
Interesting into mysql 5.7 there is the possibilitliy to truncate undo tablespace, see manual: Truncating Undo Logs That Reside in Undo Tablespaces
Hope it help.
Comment: @cjg: I don't know if you identified the  source of your issue. I could try to use a thread to purge the undo log. Here the [manual page](http://dev.mysql.com/doc/refman/5.5/en/innodb-improved-purge-scheduling.html)
Comment: +1 for a course of action around undo log growth
Comment: I would certainly try out. Unfortunately, my production servers are running on 5.5.38 and got upgraded few month back. :(

Large ibdata file in MySQL


Is there any way to tell which questions a deleted user effected?

Question: Recently a user got deleted and I would like to see which questions that has effected. When I delete my account does this also happen to other users?
Answer: Nope, and this is by design. Because it's possible that users may know which user had votes invalidated or an account removed, revealing which posts were voted on and how reveals their voting history, which is a big problem. As such, we can not show you this information.
Any time that a user deletes their account and has cast votes, those votes are generally removed upon deletion. For some users with large voting histories, we will review their account before deletion and sometimes retain those votes. This is handled on a case-by-case basis.
Comment: Were my votes casted reversed on the accounts I renewed recently?


Riddle of Kings at War

Question:
In a duel between naked kings
he who has a castle and steed shall prevail;
wrap the battlefield in and around itself, however,
and you'll find this is no longer the tale;
but before so doing, add a twist (actually, two!)
and you may find that as before,
our combatants no longer coexist.
Answer: I think this is about

 variants of the game of chess, played on boards where edges have been (as the mathematicians say) "identified".

In a duel between naked kings
he who has a castle and steed shall prevail;

 In ordinary chess, KRN v K is an easy win for the player with the rook and knight. (Not sure why "naked", exactly.)

wrap the battlefield in and around itself, however,
and you'll find this is no longer the tale;

 KRN v K is not a win in chess played on a torus, where the a and h files are "glued together" and so are the 1st and 8th ranks.

but before so doing, add a twist (actually, two!)
and you may find that as before,
our combatants no longer coexist.

 I take it this is talking about chess on a projective plane where the sides are glued together as above, but flipped, so that e.g. when you go "north" from a8..h8 you get not a1..h1 but h1..a1, and likewise for the join between a and h files. (Hence two twists.)

However,

 I haven't actually checked whether KRNvK is a win on a projective-plane board. It seems plausible that it might be because the R covers an awful lot more squares there than it does on a normal or torus board. (I did have a bit of a look on the internet to see if someone else has done the work, but didn't find anything conclusive.)

... Apparently I'm meant to prove this. OK then, let's have a go. The first thing is that

 on a projective plane, the rook is rather a monster -- it covers two whole ranks and two whole files.

Now

 suppose white has KRN against black's bare K. ("Bare" meaning "no other pieces", which doesn't seem to be the same as "naked" in the first line of the puzzle.) And suppose it's white's move with the BK not already in check.

First of all,

 save the WR and/or WN if attacked by the BK. [HOLE: I think this is always possible because the WR controls two ranks and two files at once, but maybe there are some awkward situations where the two are forked by the BK and you can't save both.]

Then

 get the WK protecting the WR, and then -- keeping it protected -- bring it to a corner (so that the BK is confined to the inner 6x6 region) and then gradually bring it inward, confining the BK to smaller and smaller areas, until the WR is on {c,f}{3,6} -- let's say c6 for definiteness -- and the BK is sitting in a 2x2 box.

Then

 bring the WN to f3, so it's protected by the WR on c6 and controls two of the squares in that 2x2 box. This means that B's moves are now completely determined and by choosing the parity of W's moves we can bring the WK to e2 just before the BK moves to e4.

And now

 Rc4 or Rc5 is mate.

Credit where due:

 I am a twit and somehow got mixed up and described how to mate with KQR v K instead of KRN v K. Feryll pointed this out in comments and sketched how the KRN v K mate works, and my comments above are an elaboration of that sketch.
Comment: Ah, yes, the full mystery revealed. Well done. But, before I give you the check mark, I should like a convincing argument that indeed, just as before, our combatants no longer coexist. That's right, this puzzle is a two-parter!
Comment: Uh, Gareth, you were meant to prove (rot13) XEA i X erfhygf va purpxzngr, abg XDA :c Ng fbzr cbvag lbh zhfg'ir tbggra zvkrq hc. Nygubhtu gur ebbx vf yrff zbafgebhfyl birecbjrerq ba gur cebwrpgvir purffobneq, gur nanylfvf bhtug gb or zber znantrnoyr—fvzcyl, jvgu fbzr unaqjnivat, pbeeny gur xvat vagb gur pragre sbhe fdhnerf, phg bss gjb bs gurz jvgu n xavtug, naq jvgu n fvzcyr gevnathyngvba, bccbfr gur xvat naq qryvire n "gjb-enax purpxzngr" jvgu bar ebbx. I'll go ahead and give you the check mark anyway, for your trouble.
Comment: Whoops, so I was. My apologies. I agree with your handwaving analysis and will make some appropriate comments in place of my handwaving analysis of something different.
Comment: (Done now. Sorry about that.)
Answer: This sounds

 like cutting a Mobius Strip with two twists along the center (of the battlefield, if you will), which will make two distinct, but interlocked loops (no longer coexisting).

you can

 make a Mobius Strip with two twists by cutting a regular Mobius strip down the middle.

Not sure what the other things reference, so maybe this is off.
Comment: On the right train of thought. But just to be clear: A "two-twist Mobius strip" is topologically indistinguishable from a simple cylinder :)

Riddle of Kings at War


How do I properly ground my subpanel that only has one neutral/ground bar?

Question: I am adding a sub panel in an unattached building. My sub panel has the  connection for the 2 hot wires coming from the source panel (a 40 amp double breaker) In addition it has one neutral/ground bar which has a green screw head for the ground and a row of places to connect neutrals. I am seeing advice on sites like yours to not connect the ground wire on the same bar as the neutral. So with only one bar I am not sure what to do with my ground wires. Do I need to install a second ground bar? I have the ground wire coming from the house that is well grounded through the house 200 amp service as well as a buried ground rods outside of the outbuilding. Do I use both and if so do I connect them both to the same ground bar?
Comment: Jay L's answer sounds good. The green head screw usually comes separately and is provided to bond the neutral bar to the panel and should not be used in a subpanel.
Answer: The neutral and ground MUST NOT be bonded at a sub-panel.  They should only be bonded at the main service panel.  If you bond them anywhere other than the main service, the neutral return current now has multiple paths, including though your ground wire.
You should be able to buy a second bar for the sub-panel if it really is meant to be used as a sub-panel.  The neutral bar will need to be isolated (it should have plastic insulator separating it from the case).  The ground bar should be bonded to the case.
The ground wire from the house must be connected to the sub-panel ground.  Since it is a detached building the ground rods are also required by code and should be tied to the sub-panel ground.  The ground to the service is the most important because it will provide the low resistance path back to the service in case of a fault.
Comment: 2008 NEC 250.32
Comment: "Grounding Electrode. Building(s) or structure(s) supplied by feeder(s) or branch circuits(s) shall have a
grounding electrode or grounding electrode system installed in accordance with Part III of Article 250."
Comment: `required by code`!? What code? Can you site the code section?  Can you quote the code?
Answer: The advice by Tim does not sound correct. For as long as I've been performing electrical service if you create a subpanel feed from your main service panel, the subpanel is supplied by 4 wires, two hot, one neutral and the other a ground. An insulated neutral must also be separate from the ground bar at the subpanel and if installed in a separate building must have it's own ground electrode with a solid #6 copper wire attached from electrode to the ground bar. The main service panel ground bar must be bonded and the subpanel unbonded.
Rule 10-208 allows for two options. Under first option, the neutral conductor running from the main service to a building supplied from this main service would function as a bonding conductor. In this case, no separate bonding conductor (between the main service and the service in any building supplied by the main single service) would be required, and the service in each building supplied from the main single service would have to be grounded in accordance with Rule 10-204(1)(b).Under the second option, each new service in the building supplied from the main single service would be considered as part of distribution system. In this case, no connection to ground would be made at each such building, as the only connection to ground would be allowed at the main single service. The neutral conductor which runs to each such building supplied from the single service, would be isolated from the service enclosure (it would be used only to carry a load current in a 2-wire circuit or an unbalanced current in a multi-wire circuit), and a separate bonding conductor would have to run from the main single service to each building supplied from this single service to bond the service equipment in each such building.
Answer: Changes to the Electrical Code now REQUIRE all unattached buildings with sub panels, to have the Neutral Bar Grounded with #6 wire to the panel box then to a grounding rod in the earth. (Rule 10-208)
You CANNOT use the ground included in say #10/3 wire as your sub panel ground anymore.
You are to treat the sub panel just as a service that is coming in from the meter, the only conductors that should be entering your sub panel now are your 2 Hot Feeds, and your Neutral. (no ground from the main panel.)
Now the confusing part, Rule 10-208 (b) states that you can ground any metal non current carrying components (outlet boxes) through a separate conductor back to the main panel if the building does not house livestock. However, since you must now have a bonded neutral in sub panels, this is more of a pain to attempt since you have a separate grounding circut right there already.
Comment: What rule is this you refer to? And just how do you know it applies to the OP? We don't know where either of you are from.
Comment: Tim's advice doesn't sound right to me. I've never heard of a neutral-ground bond in a sub-panel.  That's just inviting current on the grounding system.  I agree rules require a separate building to have a separate ground rod and tied to the ground in the sub-panel.  I wonder if this is confusion between NEC's weird phrases of  "ground*ed* conductor" for neutral, and "ground*ing* conductor" for ground.


Solspace Freeform 4+ submission per email address

Question: Possible to submit only one submission per email address?
I am trying to make the form gives an error if someone already has submitted and try submit again.
Thank you
Answer: If your users are filling in the form while logged in, you could look for Freeform entries authored by the currently logged in user and display the form only when no previous entries were found:
{exp:freeform:entries form_id="1" author_id="1"}
    {if freeform:no_results}
        {exp:freeform:form /* your other parameters */}
            // Your form...
        {/exp:freeform:form}
    {/if}

    {if freeform:count == 1}

You already submitted the form.

    {/if}
{/exp:freeform:entries}

(Note: You will need to adjust form_id and author_id values based on your setup. IDs of "1" above are just an example)

Unfortunately, for logged out users, the above won't work since there is no id for logged out users. In the case of logged out users, although a user could submit an email address in a Freeform field. The next time the form is filled out with the same email address, there is no way to stop the user from entering the same email address again. The validation would have to occur after submitting the form a second time.
You could build an extension using some of the available hooks for Freeform: http://www.solspace.com/docs/freeform/extension_hooks/
Alternatively, although you can't prevent entering the same email address in a field, you could give the impression that submitting the same email address again is not possible. Here's an example of what could be done. Assuming your have a Freeform field called email:

In {exp:freeform:form}, use return="template_group/template/%%entry_id%%" (provide your own template_group and template name, eg. form/thank_you
In your template_group/template template, retrieve the submitted form data using {exp:freeform:entries entry_id="{segment_3}"} (segment_3 will be the latest Freeform entry_id).
Pass the retrieved email in an embed which will check for pre-existing entries with the same email address:

template_group/template:
{exp:freeform:form entry_id="{segment_3}"}
     {embed="check/email" email_field="{freeform:field:email}"}
{/exp:freeform:form}

The embed:
{exp:freeform:entries search:email="{embed:email_field}"}
    {if freeform:no_results}Thank you for submitting{/if}
    {if count == 1}You already submitted the form with this email address{/if}
{/exp:freeform:entries}

Of course, within Freeform you will still see 2+ submissions with the same email (and even be notified more than once if you have email notifications set up), but the front-end user will see the "You already submitted the form with this email address" message the second time the form is submitted with the same email address. This is the illusion of a duplicate I mentioned earlier.
In the end, the better option would be creating an extension using the hooks.

UPDATE: There is an additional solution, using prevent_duplicate_on="". See: http://www.solspace.com/docs/freeform/form/#prevent_duplicate_on
This will allow you to detect duplicates based on email address (used with an email field). Perhaps the best approach.


What policies maximize incident detection (and compromise detection)?

Question: What are the equivalent digital parallels to the practice of offering bonuses to employees challenging persons in a secured area without a visible badge?
Comment: I like this question, but I'm finding it hard to see what kind of policy would maximize this... Looking forward to the answers
Comment: Hmm, now that I think about it - the question has a builtin contradiction. For a policy to "maximize detection", @Graham has a good answer... BUT if you're asking about "an equivalent parallel" to offering bonuses to employees, then @sdanelson's answer is spot on - and about as useless as the employee bonuses. To clarify, what I'm saying is **"the practice of offering bonuses to employees challenging persons in a secured area" does not maximize incident detection**.
Answer: The policy that improves incident detection is a policy to equip security staff with automated monitoring tools that save them from the tedious legwork of scouring log files and performing manual detection. By analogy: you don't improve physical security by asking your guard to walk faster, you give him CCTV monitors.
Answer: After thinking about this for a bit, and seeing the couple of (conflicting) answers that were offered, I realized - this is no different from your question on "What policies maximize employee buy-in to security?".

Awareness
Social norms (as per @Graham's answer there) - employees need to feel that they are expected to say something. Not quite "See something, say something" - more like "This is your office too, you'd say something if somebody walked into your home, wouldnt you?"
Getting them to care.
Priorities. Employees need to see that management cares about this too. Not by giving bonuses, but by actions. E.g. CEO goes over to a stranger... Or, contrarily, if an employee was late because he was questioning strangers or whatever, there shouldnt be repurcussions...
Appropriate tools, much as @Graham mentioned here. Moreover, automate detection as much as possible! Invest in good tools for the job at hand, and remove as much as possible reliance on the people.
Answer: I think the answer is a policy that rewards the reporting of unusual activity. IE software/hardware that is running abnormally slow, crashing unexpectedly, etc. The policy could also cover the discovery of bugs, misconfigured software/hardware, and poor practices.
In a healthy organization a lot of this activity should already be going on. IE users calling the help desk to report that their computer is running really slowly. The policy would just formalize the rewarding/recognition of employees who help discover incidents.
Comment: Re "policy that rewards the reporting of unusual activity", as Schneier says if you ask amateurs to do your security, don't be surprised when what you get is amateur security.
Comment: I agree with Schneier. For those interested the article that Graham quotes can be found at http://www.schneier.com/blog/archives/2007/11/the_war_on_the.html.
Comment: I accidentally hit enter on my last comment.

I don't think that the question or my answer opposes what Schneier argues. End users are not security experts, but end users are familiar with the software and hardware that they use on a daily basis. See Schneier's earlier article titled "Recognizing "Hinky" vs. Citizen Informants".
Comment: Another problem with this is that whatever you're rewarding for, will be gamed. You reward for reporting slow hardware? Expect everything to slow down. You give bonus for finding virus? All of a sudden every single virus appears in your network.  And so on...


which patents were prior to this patent D698,996

Question: Kindly ask you to help me with this issue.
I'm on 100% sure that SWIRLYDO™ coil/spiral hair ties has a prior rights than patent D698,996.
But i can't find it :(
Also pls help me to find other patent which has prior rights than patent D698,996
Thanks
Answer: Design patents cover the ornamental appearance of an item. The patent in question was issued a final rejection for not being novel in light of US5,003,993, Silver. The applicant pointed out that the spacing between the spirals were wider in '993 (relative to the width of the spirals than in the applicant's design.)  If you look up US5,003,993, you will see that its purpose is quite different that something for hair management!
I am also including a image of the Swirlydo.
It was not cited by the examiner. Possibly because their go-to resource is patents and possibly the SWIRLYDO was not yet made public before the filing date in 2012. IF it were prior art and cited, the applicant might have pointed out that the coils in the swirlydo are tighter and the relationship between the width of the coils and the radius of the overall circle was not the same.


Stack Overflow newsletter content based on favourite tags

Question: It would be awesome if Stack Overflow's weekly newsletter contained questions/answers from the set of tags I have chosen to follow, rather than receiving a newsletter that has content with languages that don't relate to my interest.
Answer: I agree this would be good, although I wouldn't want to lose the random news. Sometimes things I specifically don't follow on the site are still nice to read about in a newsletter, and often grabs my interest.
I think this is good for promoting content and possibly getting more users involved in areas they might not otherwise view.
So perhaps leave it as is, but with an addition of a new section "Your Favourite Tags" (rather than this be "instead of").


What is the best time/stage to ask Hosts/listers for phone verification?

Question: For holiday rental apps such as Airbnb, booking.com and likes. What is the best time/stage to ask Hosts/listers for phone verification? On signup or after they list the property? Keep in mind, they have to verify before the property is published!
Answer: I would force it on listing and soft-suggest on registering, that way, verification isn't a blocker to registration and there's value in the user going through the process on listing to secure a service.
Answer:
The earlier, the better but not too early that you lose the game even
  before it starts.

Phone verification makes sure that:

The user and his/her contact info is authentic
The user is genuinely interested in utilising the services
People can reach out to the user appropriately when needed

The trick is to ask the user for verification when he/she shows interest towards utilising the services but without annoying them, which could lead to user bounce back.


FullText Search

Question: We came across an issue using FullText Indexes and SQL 2008 R2, not sure if it's by design or I am missing something. When we search using a fulltext index, I noticed SQL appears to trim leading and trailing spaces for words, I also noticed it appears to do a start with. Meaning, if I am searching for last name that has ders, it won't return Anderson. But If I search for Ander, it will return Anderson. We have tried using CONTAINS and FREETEXT. Is there a way to for it to behave more like a like (%ders%) instead the way it is behaving? Thanks.
Comment: If you want `LIKE` functionality, why don't you use `LIKE`?
Comment: I thought to take advantage of the FullText index I had to use contains or freetext? We used like before and our wildcard searches took 30 seconds, when we enabled FullText index it went down to 5 seconds.
Answer: Like our expert ypercube mentioned, you can use LIKE if you know the phrase to be searched.
Otherwise you can also use something called CHARINDEX which I personally find a very useful command in SQL. I'll give you a small example. Suppose you have a keyword and you want to search that keyword in a column or a group of column, you can do it pretty easily.
DECLARE @keyword VARCHAR(20) = 'ders';
SELECT *
FROM YourTableName
WHERE CHARINDEX (@keyword, [LastName]) > -1;

This works on variables too very well. Let me know if this resolves your query.
Now if you had to apply the same search on multiple columns, you could write:
SELECT *
FROM YourTableName
WHERE CHARINDEX (@keyword, [LastName] + '|' + [FirstName] + '|' + [MiddleName]) > -1;

FullText Search