Better Techniques/Equipment for BGA Soldering

I've recently been soldering ball-grid-array parts to boards. This is relatively new to me, and there has been a few mishaps with my technique. I was just wondering how does the community perform BGA soldering? What techniques/equipment do you use to make this process more efficient and less error prone?  My technique involves using a Hakko FR-830 Preheater to do the work. I use an old board holder to hold my board in place, and then I apply some solder to the board using a syringe (ChipQuik SMD291AX). My part is a 6x6 BGA array, with the pads 1mm apart from each other in a square grid. Once I place the solder onto the pads, I slowly put the part onto the pads, aligned as close as possible. Then, once it's ready, I turn on the preheater through its temperatures from 150-300 degrees Celcius at 50 degree intervals for about a minute and a half at each temperature. The apparatus is not enclosed, so I put a piece of metal over my board holder so that the top of my PCB board is not exposed to open air.   My process is not exactly ideal, but thus far, it works alright. However, I noticed that the solder doesn't seem like it really 'melted'. I think that this might be because of my methods, and running a hot air gun on the sides doesn't really help much. Any tips or suggestions? This is all done in-house, and I have to do this by myself, so learning how to do it better would be helpful.


If $ g\left(x\right)\geq f\left(x\right) $ and $ \intop_{a}^{b}g=\intop_{a}^{b}f $ then $ f=g $?

Let $ g:[a,b]\to\mathbb{R} $ and $ f:[a,b]\to\mathbb{R} $ be continuous functions, such that $ f\left(x\right)\leq g\left(x\right) $ for any $ x\in[a,b] $. Assume $ \intop_{a}^{\boldsymbol{b}}g\left(x\right)dx=\intop_{a}^{\boldsymbol{b}}f\left(x\right)dx $. Is it true that $ f=g $? I think that its true. I'll explain why: we know that $ g\left(x\right)\geq f\left(x\right) $ and thus $ \intop_{a}^{\boldsymbol{b}}g\left(x\right)dx\geq\intop_{a}^{\boldsymbol{b}}f\left(x\right)dx $ so $ \intop_{a}^{\boldsymbol{b}}(g\left(x\right)-f\left(x\right))dx\geq0 $ If we will assume by contradiction that $ g\neq f $ then we could find  $ x_{0}\in[a,b] $ such that $ g\left(x_{0}\right)-f\left(x_{0}\right)>0 $. But $ f $ and $ g $ are continuous, and thus $ g-f $ is continuous, and we found $ x_0 $ such that $ (g-f)(x_0 $ is positive, thus the integral $ \intop_{a}^{b}\left(g-f\right) $ should also be positive. So that's why it seems correct to me, but I wanted to make sure because that's a strong assumption to make. Thanks in advance.


keep getting null pointer exception in linked list

I am trying to delete a particular string from the linked list, but i keep getting null pointer exception error! Any help fellas?  public void delete(String deleteName) {          LinkedListNode current = head;         if(head==null){             System.out.println("Nothing to delete from the list! Insert data.");         }         // for head         else if(current.getName()==deleteName){             head=current.getNext();         }         // for tail         else if(findTail().getName() == deleteName){             while(current.getNext().getNext()!=null ){                 current = current.getNext();             }             current.setNext(null);         }         else{             while(current.getNext().getName()!=deleteName){                 current=current.getNext();             }             current.setNext(current.getNext().getNext());         }         System.out.println("");         System.out.println(deleteName +" has been deleted from the list.");      }


Recommendations on a single dedicated app GUI for Debian

I have a project that requires a Debian device to run one simple custom app on a touchscreen from boot to death. It shouldn't be possible to exit the app.  I've looked into Gnome, KDE, XFCE, and Tcl/Tk, but it's hard to tell which are the best for a single app rather than an entire desktop. What are the best options out there?  Bonus points if the solution is in any way easy to program and/or better than average on security.


Since Kirk found Khan much later in the series, how did he get revived early in the movie?

We all have seen Kirk reviving Khan in TOS But in the latest movie set years before this event we see Khan revived, how is that? Second part of the question is if he was again sent into space in the capsule?  [Edit]  The other questions set as the original of this duplicate is related to the topic, but is a different question, is this not obvious?


Are gravitational waves produced only when a mass accelerates?

Why? They are not a form of EMR, are they. Or are the rapidly changing ones the only ones we can detect?


Is there an easy way to show which spheres can be Lie groups?

I heard that using some relatively basic differential geometry, you can show that the only spheres which are Lie groups are $S^0$, $S^1$, and $S^3$.  My friend who told me this thought that it involved de Rham cohomology, but I don't really know anything about the cohomology of Lie groups so this doesn't help me much.  Presumably there are some pretty strict conditions we can get from talking about invariant differential forms -- if you can tell me anything about this it will be a much-appreciated bonus :)  (A necessary condition for a manifold to be a Lie group is that is must be parallelizable, since any Lie group is parallelized (?) by the left-invariant vector fields generated by a basis of the Lie algebra.  Which happens to mean, by some pretty fancy tricks, that the only spheres that even have a chance are the ones listed above plus $S^7$.  The usual parallelization of this last one comes from viewing it as the set of unit octonions, which don't form a group since their multiplication isn't associative; of course this doesn't immediately preclude $S^7$ from admitting the structure of a Lie group.  Whatever.  I'd like to avoid having to appeal to this whole parallelizability business, if possible.)


When you indent an image in a list, it overhangs

As you can see, the image is overhanging the edge of the box. This is also easy to see in editing and creating:    Here you can see that the dotted lines are blocked by the image going over it.


can i install perl module in my hosting provider machine

My hosting service provider has not installed HTML::Template perl module, and he is not ready to install it giving some security concerns.   Is there any way, i can install it in my root directory or any other place and can use it.  If yes then how and how can i use it?  is there any other option except change the host provider?  Please provide your comments.  Thanks, Devesh


I have a question regarding the interpretation of the whiskers of a boxplot. I have read the following: "On the top and bottom of the rectangle, the “whiskers” show the range of 1.5 times the distance between the 0.25- and 0.75-quantiles", but do not entirely understand what is meant by "distance".  It can't be that the probability mass is meant, since between the 0.25 and 0.75 quantile we obviously always have the same percentage of data. What then is the idea?


I’m a Sprint customer and I changed my network to T-Mobile at the T-Mobile store.  Since then my voicemail is not available. I setup my voicemail at the store and when I try to retrieve my voicemail it asks me to set a password and greeting?


1 hour ago though it is already about 110 minutes

I tried a small experiment. I posted a post on Facebook at exactly: 21:01 and waited to see how many hours ago it will say. When it was 22:50 it still said that my post was posted 1 hour ago.  Though some days back on this forum some people told me that when something started at 21:01 and it is 22:50 that I should say it started 2 hours ago.  So whom should I trust now?  All social networks like Facebook, Instagram and YouTube etc. use the system where it would say 1 hour ago even if it was 119 minutes already, so meaning they will never say it was 2 hours ago unless at least 120 minutes passed.  This was the way I used to express 1 hour ago as well. However, since I heard the answers from many other people I feel unsure about it right now...  I am talking about casual speech with friends etc. In such scenario. What would you say? 1 or 2 hours ago? Is Facebook/YouTube/Instagram wrong or?   if we decide to agree on the theory that if it is more than 1 hour and 40 minutes it is a good idea to round to 2 hours ago.   So what time span would you imagine if something happened let say 10:10, now it is 11:50.  If somebody said to me that something happened 2 hours ago and I looked on time saying 11:50 I would image that it happened some time between. (9:30-9:50)  That is why it feels so weird for me to say 2 hours ago thought it has not been more two hours yet.   I dont know why but more logical for me it feels to say 1 hour ago though it can already be more than 100 minutes  and still just say that it happened an hour ago when talking with friends, teachers, whoever in casual speech unless it is something super important i would say exactly hours and minutes.  How do you say it in your life? How do you express time in such situations? Do you express time the same way as Facebook or?   I know that some of you may think this is some kind of joke, unfortunately it is not and I am going crazy and depressed without knowing system for this... It has been already 2 months and I still feel overwhelmed with this ideas and questions... I cannot help myself, please help me, please.  Thanks for your help.


PhD university ranking when going for post doc/ jobs

I have completed my bachelors and masters in engineering from a top UK uni and I am currently working towards my PhD at a low ranked uni (50th in the UK) mainly because it was one of the very few project in my field and with partial funding for non-EU students. My question is how negatively will the ranking of my new university affect me when applying for research jobs / post docs in the future?


Given $E[Y]=1$ , $E[Y^2]=2$ and $E[Y^3]=5$, Y non negative integer random variable, find min of $P[Y=0]$

If $Y$ is a non negative integer-valued random variable with $E[Y]=1$, $E[Y^2]=2$ and $E[Y^3]=5$ ,where  $E$ is the average value of $Y$. Find the minimum value of the possibility $P[Y=0]$. I know that $E[Y]=\sum^{n}_{i=1}y_{i}p(y_{i})$ and $E[Y]=\sum_{y:p(y)>0}yp(y)$. I know that Markov's inequality is : $P[Y\geq a] \leq\frac{E[Y]}{a}$ I know that  Chebyshev's inequality is : $P(|Y-E[Y]|\geq k)\leq \frac{Var(Y)}{k^2}$ The book I'm studying is the : A first course in probability 8th edition , Sheldon Ross


What kind of "mathematical object" are limits?

When learning mathematics I tend to try to reduce all the concepts I come across to some matter of interaction between sets and functions (or if necessary the more general Relation) on them. Possibly with some extra axioms thrown in here and there if needed, but the fundamental idea is that of adding additional structure on sets and relations between them.  I've recently tried applying this view to calculus and have been running into some confusions. Most importantly I'm not sure how to interpret Limits. I've considered viewing them as a function that takes 3 arguments, a function, the function's domain and some value (the "approaches value") then outputs a single value.  However this "limit function" view requires defining the limit function over something other then the Reals or Complexes due to the notion of certain inputs and outputs being "infinity". This makes me uncomfortable and question whether my current approach to mathematics is really as elegant as I'd thought. Is this a reasonable approach to answering the question of what limits actually "are" in a general mathematical sense? How do mathematicians tend to categorize limits with the rest of mathematics?


As a thought experiment, I was trying to find a way to constantly dilate time while keeping an object effectively in place. I quickly decided that moving forwards and backwards wouldn't work—the speed would be zero at the turning points.  My next idea was to use circular motion—an object could move at a great speed in circles while staying in the same location.  Would time still dilate for such an object?  EDIT: One of my problems with this concept is that a rotating radius would have different speeds along its length, possibly therefore leading to different degrees of time dilation along its length.


I recently had ants find and then swarm to a food container that I put down on a desk. I'm curious as to whether an ant would have needed to get lucky (i.e., discovering the food after crawling up the desk) or ants have the ability to sense food from a distance.  I'm skeptical of believing that ants simply scout around until finding food; I'll use this case as an example:   My room has had no food or drink in it for weeks, so the area wouldn't be a "hotspot" for ants to be interested in. I put the mostly empty food container down on my clean desk and turned my lamp off to work on the computer. No more than 2 hours later did I turn my light back on to discover a trail of ants swarming to the container I put down. It happened pretty quickly. The desk is high, standing on four thin legs. I find it difficult to believe that an ant would crawl up the desk as often as a 2 hour time frame to scout for food, for the message to be passed to the colony so quickly.    I've been curious about this scenario for a long time. So my question:  Can ants sense food from a long distance? If so, how does it work? If not, how is the phenomena (ants locating food quickly in unlikely places) explained?


Identifying a creature that appears to be a worm wrapped in a cocoon

This creature was found on a bed. At first, I thought it was a piece of lint, but then it suddenly moved. I picked it up in a paper towel and put it in an eye cream containers, which it is currently in. I believe this means that it is pretty strong, since it appeared to have pulled itself all the way up from the floor, to the top of the bed, then across to the other side of a King-sized mattress.   It appears to be a worm wrapped in a cocoon. It is pretty short, being small enough to fit inside an eye cream container.  The creature is a pale yellow-white/cream, with brownish-red tips on each end (unless it can somehow turn around without exiting its casing). It looks from the side as if it has a rather flat face, one that comes to a slight bump at the bottom, but is pretty much flat. The casing is light grey, with some small portions that appear to be almost the same color as the organism, just slightly darker. There is an opening at each end of the casing, which the organism uses to slide slightly out. It has never fully come out of the casing. The edges of the openings at each end are white. The casing seems to either be made out of or covered in dust.  It can create a substance that is sticky and strong enough to support its weight. I cannot tell if the substance is created by the 'worm', or the 'cocoon'. A thread at each end of the casing is connected to the side of the container by the substance. When I accidentally detached one end of the casing, the entire thing began to shake violently when held so that one end was hanging. It wouldn't stop until I had turned it so that both ends were touching the side of the container. Within minutes, though, it had reattached the broken end. Minutes. Not hours, but one minute.  The holes at each end of the cocoon can either grow or shrink closed. I believe this allows us to tell which opening is in use. If it is nearly shut, it will come out the other end.  It appears to be nocturnal, since it doesn't move during the day, but it is very active at night. It also appears to react to light. If some is put on it, it will poke out to look around.    It has survived for four days straight without food, as far as we know. We put a small piece of lettuce in with it. However, there are two small, brownish things on the bottom of the container. This may be its excrement.  The creature moves by reaching out with its 'tentacle/worm', grabbing onto something (including the ground), and pulling itself forward.  I cannot tell if the creature is attaching to the container's side to climb, or because it is morphing. If that is the case, then the outer shell may be a cocoon. It did detach itself from the side of the container, and first hid under a ledge of lettuce, but now has wrapped itself in lettuce.  To summarize: can someone please help me identify this creature?


USA - Can I write off time spent using this metric

Situation  Let's say my organization does pro bono work for company X - a non profit  I pay 3 employees Y amount and can write that off to the Federal Government  Question  I'm in a pass-through LLC, will I still be able to pay myself? Assume that all employees including myself get equal pay.


Should I answer beginners' questions or simply downvote and flag them as duplicates?

Every day, I see a lot of questions on the same topics, for example:   How to perform an Ajax call / how to regularly update data from a database on a page How to use dates in PHP or in MySQL How to reformat a PHP array   These kind of questions are asked many times, everyday, often from new users, who say right away that they are beginners in JavaScript, jQuery, PHP, etc.  Should I answer these questions? Or downvote them, and flag as duplicates?


I have been using AMPscript for a while and I know that there is no way to create custom functions. I was wondering if anybody has come up with an alternative for this?  thanks


I'm facing an issue with comparing two Objects.  I'm comparing an incoming Object, with an Object Array, to see if the Object is already in the array.  I tried two methods:  (betTemps is the Array of Objects, tempBet is the current object which should be compared.)  var duplicate = false; for (let bet of this.betTemps) { console.log(tempBet);   console.log(bet);   if(bet === tempBet) {     console.log("reached");     duplicate = true;     break;   } }   The if afterwards:  .. else if(duplicate){   alert("The Bet is already in the List"); } ...   Console Output after adding an Object which is already in the Array:  Console Output Screenshot    As you can see, they are equal, still the other Object is added to the array.  I tried using this method too with indexOf:  if(this.betTemps.indexOf(tempBet) > -1){   alert("The Bet is already in the List"); }   Console Output after adding an Object which is already in the Array:  Console Output Screenshot    PS:  The code before the comparison:    addBet(bet, index){ var tempBet = Object.assign({}, bet); var select = (document.getElementById('select'+index)) as HTMLSelectElement; select = select.options as HTMLSelectElement; let count = 0;  tempBet.category = []; for(let i = 0; i < 3; i++) {     if (select[i].selected) {       tempBet.category.push(select[i].value):       count++;     } }   The code after the comparison:  if (count == 0) {   alert("There has to be at least one Category choosen!"); } else if(duplicate     <- This part changes individually which method you use ->){   alert("The Bet is already in the List"); } else {   this.betTemps.push(tempBet); }


How to make a pickaxe that can break only certain blocks?

How can you make a pickaxe that can break only certain blocks in mcpe? What is the command for that?


Can I hang a 60 lbs TV on 1 inch drywall?

Can I use drywall screws with plastic contraption 3/8" diameter to put a TV on the drywall?  What is the load limit for 1 inch drywall and how many screws and how close apart they can be put to carry 60..65 lbs TV ?


Variable doesn't get updated after function processes

I'm building this calculator app with two textviews (one for the formula and one for the result). Now the result after calculations is stored in a variable called result which is left empty by default. But when I run it, after the function executes, everything works but the result variable still remains an empty string. Please help me.  ScientificCalculator.java   int prevAnswer = 0; TextView formulascreen; TextView resultscreen; String formuladisplay = ""; String resultdisplay = ""; String result = ""; String operator;  public void onClickEquals(View view) {      Toast toast = Toast.makeText(getContext(), "Equals to: " + String.valueOf(result), Toast.LENGTH_SHORT);     toast.show();      if (operator == "+" || operator == "-" || operator == "x" || operator == "÷") {          getResult();         updateresultdisplay();      }  }  private boolean getResult() {      if (operator == "") return false;      String[] operation = formuladisplay.split(Pattern.quote(operator));      if (operation.length < 2) return false;      result = String.valueOf(res.format(simpleOp(operation[0], operation[1], operator)));      return true;  }  public double simpleOp(String a, String b, String op) {      switch (op) {          case "+":             return Double.valueOf(a) + Double.valueOf(b);          case "-":             return Double.valueOf(a) - Double.valueOf(b);          case "x":             return Double.valueOf(a) * Double.valueOf(b);          case "÷":             return Double.valueOf(a) / Double.valueOf(b);          default:             return -1;      }  }


$I=1/2\pi i\int_C |1+z+z^2|^2dz$ where C denotes the unit circle centered at zero and integral is taken anticlockwise.  I saw that as application of Cauchy Goursat theorem as it seems analytic to me everywhere. So the integral should be zero?


I have a minor issue that I think might get solved without much ado. Although currently I can't find a link, quite a sizeable number of people tend to ask questions asking for software recommendations on SO. Even though the FAQ clearly states that that shouldn't be done.  Some questions are still off-topic, even if they fit into one of the categories listed above: .....Questions asking us to recommend or find a tool, library or favorite off-site resource are off-topic for Stack Overflow as they tend to attract opinionated answers and spam. Instead, describe the problem and what has been done so far to solve it.  Some new users might think that they can probably get away with a couple of questions along those lines even though the FAQ requests that it shouldn't be done. I was wondering if only we could add a link in the FAQ, something along these lines:  Although if you must ask for recommendations check out another wonderful site on the StackExchange network,   Would that help in controlling the problem? This isn't a major feature request per se and nothing hard to do, and anyway there's no reason I can think of that this shouldn't be done. Also on a related but tangential topic, I am aware that individual questions can be flagged to be "migrated" to other StackExchange sites if that seems appropriate. I recently came across a question that was well formulated but not fit for SO, it was asking us to review the code. I decided that it would be very well, by definition, suited to . I proceeded to flag it as such, but was presented with this.  There wasn't any option for codereview. What's the deal with this? Is this a bug? Or is it a matter of reputation, allowing only flags to certain sites. The specific question at hand itself is no longer a problem, I simply flagged it as 'needs moderator attention' with the description 'should be migrated to codereview.se' and that was taken care of. Not that the option not being there created any hassles, I am just curious as to why I didn't get codereview in this list. Note that the sites listed are not the one's I have accounts on, for instance I have accounts on math.se and physics.se, and I don't have accounts on tex,dba and sharepoint.


How to get the accurate relativistic momentum form for photons?

I have studied from Griffiths, the relativistic form of momentum is $$p = \frac{1}{\sqrt{1-\frac{v^2}{c^2}}} m_0v$$   Now when I evaluate the momentum for photon, I just insert $v=c$ and $m_0=0$ and I get $p= 0/0$. How does it make sense?   Can you tell me that where I am wrong?


How to add an external jar file to the classpath dynamically at runtime?

I want to add a JAR file to my project's classpath dynamically using Java code. If it is possible, I want to use external jar files and load their classes, and then execute them as beans later (Spring Framework).


Edit Icons for MacOs Startup Manager (Windows, Linux & Macos)

After successfully installed Linux and Windows along with macOS High Sierra on my Macbook Pro 2013 13" with help from Mr. David Anderson (a great contributor here). Now I wonder how to change the icons for my Windows (installed on a separate internal SSD) and give MacOs Partition Icon of MacOs so that the startup manager will be beautifully labeled and easy to see. Thank you for the help in advance!  Current startup manager conditions:   My diskutil list:  /dev/disk0 (internal, physical):    #:                       TYPE NAME                    SIZE       IDENTIFIER    0:      GUID_partition_scheme                        *250.1 GB   disk0    1:       Microsoft Basic Data BOOTCAMP                250.1 GB   disk0s1  /dev/disk1 (internal, physical):    #:                       TYPE NAME                    SIZE       IDENTIFIER    0:      GUID_partition_scheme                        *240.1 GB   disk1    1:                        EFI EFI                     209.7 MB   disk1s1    2:                 Apple_APFS Container disk2         151.8 GB   disk1s2    3:       Microsoft Basic Data                         7.9 GB     disk1s3    4:       Microsoft Basic Data                         79.9 GB    disk1s4  /dev/disk2 (synthesized):    #:                       TYPE NAME                    SIZE       IDENTIFIER    0:      APFS Container Scheme -                      +151.8 GB   disk2                                  Physical Store disk1s2    1:                APFS Volume MacOsX                  14.6 GB    disk2s1    2:                APFS Volume Preboot                 24.5 MB    disk2s2    3:                APFS Volume Recovery                512.1 MB   disk2s3    4:                APFS Volume VM                      4.3 GB     disk2s4


C++ : Undefined reference in Map::insert

Somewhere in a .h file:  namespace gpBenchAPI {  struct AbstractConsts {   public:     static const uint8_t STATUS_TAG_NOT_FOUND = 2;  }; //AbstractConsts }   Somewhere in another .h file:  class MyClass{ private:      void method();      QMap<uint8_t, QString> errorCodes; };   Somewhere in a .cpp file:     void MyClass::method(){        using namespace gpBenchAPI;        errorCodes.insert(AbstractConsts::STATUS_TAG_NOT_FOUND, "A-1");    }   This code is rising a linking error:    undefined reference to `gpBenchAPI::AbstractConsts::STATUS_TAG_NOT_FOUND'   but this code compiles and links:   switch (status) {     case AbstractConsts::STATUS_TAG_HUNTING:         return 0;   }   If I do :    errorCodes.insert(2, "A-1");   no problem. Why?  Added:  If, like in the suggested dupplicated question's answer, I initialize the const in a cpp file like this:  const uint8_t AbstractConsts::STATUS_TAG_NOT_FOUND = 2;   and remove the initialization from the .h file, the "switch" does not compile anymore:  The value of 'gpBenchAPI::AbstractConsts::STATUS_TAG_NOT_FOUND' is not usable in a constant expression      case AbstractConsts::STATUS_TAG_NOT_FOUND:                           ^


Why is this plus sign in a yellow circle appearing on the selected face?

I am new to blender (about a week working after work). And I face this problem that I have this plus sign in yellow circle. And I am not sure how to get rid of it. I have no idea what is the name of it (if I would know name I probably would google it). This happens in edit mode.


Why did Tony Stark leave his armor to explore the castle in Sokovia?

In Avengers: Age Of Ultron, Tony Stark is the first member of the Avengers to get inside Baron von Strucker's castle, where he takes down a room full of soldiers before stepping out of his suit and travelling down a secret passage.  Why does he take off his suit in the middle of an enemy base when it might have protected him against Scarlet Witch's magic, or at the very least helped him better search the passageway with Jarvis' HUD?


Find $ \int_0^\infty \frac{x}{x^3 +1} dx$ What cantor should I choose?


How to convert date to milliseconds by javascript?

I have multiple date's for example(25-12-2017) i need them to be converted to milliseconds by javascript


Three prisoners are informed by their jailer that one of them has been chosen at random to be executed and the other two are to be freed. Prisoner A asks the jailer to tell him privately which of his fellow prisoners will be set free, claiming that there would be no harm in divulging this information because he already knows that at least one of the two will go free. The jailer refuses to answer the question, pointing out that if A knew which of his fellow prisoners were to be set free, then his own probability of being executed would rise from 1 3 to 1 2 because he would then be one of two prisoners. What do you think of the jailer’s reasoning?  If the jailer refuses to say anything, then the probability that prisoner $A$ is excecuted is $\frac{1}{3}$. If the jailer says to prisoner $A$ that prisoner $B$ will walk free, then $2$ prisoners remain to be considered, $A$ and $C$. One dies, one does not. Heads or tails essentially. $\frac{1}{2}$ ought to be the conditional probability that $A$ dies given that $B$ walks free no? Apparently not though, allegedly the correct answer is still $\frac{1}{3}$. Even my attempt to calculate the correct answer yielded the result $\frac{1}{2}$.   Let $A_D$ and $C_D$ respectively denote the event of $A$ and $C$ dying. Let $B_F$ denote the event that $B$ walks free. Assume that the jailer tells prisoner $A$ that prisoner $B$ will walk free.   Here's my attempt.  $$P(A_D\mid B_F)=\frac{P(A_D\cap B_F)}{P(B_F)}=\frac{P(A_D\cap B_F)}{P((B_F\cap A_D)\cup (B_F\cap C_D))}=\frac{P(A_D)P(B_F\mid A_D)}{P(A_D)P(B_F\mid A_D)+P(C_D)P(B_F\mid C_D)}=\frac{\frac{1}{3}\times 1}{\frac{1}{3}\times 1+\frac{1}{3}\times 1}=\frac{1}{2}$$  What am I doing wrong?  Edit 1: Intuitively I am still troubled but I understand now that $B_F$ may occur even though the jailer does not necessarally say $B$.   Edit 2: I suppose that it makes some sense if the faiths of the prisoners had already been decided before prisoner $A$ asked the jailer the question. If the jailer decides to reveal one of the others who will walk free then that must've been the case.


How much of a myth was Tom Riddle? And did the Death Eaters know he was a Half Blood, not a Pure Blood?

Additional duplicate:   In Harry Potter and the Chamber of Secrets, we first hear the name Tom Riddle. Until the end of the book, Tom appears to be good, although mysterious. In the school, there is even a trophy with his name on it which he won for special services to the school. Then when Harry goes to the Chamber of Secrets, we find out Tom is actually Lord Voldemort.   Now, why would the trophy for Tom Riddle still be up in the school if it was well known that Tom was Voldemort? But at the same time, it wasn't a secret. Dumbledore knew who Tom was. Slughorn knew who he was. Helena Ravenclaw did too as did a few Death Eaters who went to school with him (and probably a few more.) In fact, Lucius Malfoy knew the diary he had which he sneaked into Ginny's bucket belonged to Voldemort, and it had the name Tom Marvolo Riddle on it. So he must have knew his true name. So how many people knew? There must have been stories written about him after he was presumed dead following the murder of the Potters. Surely one newspaper then tried to find out more about who he was and where he came from.   But even after Harry knew, and he presumbly told a few friends, we never hear anyone other than Harry and Dumbledore call him Tom. I understand that Voldemort was his name then, so it made more sense. But how many people really knew the truth about Tom?  For that matter, if the Death Eaters knew he was Tom Riddle, then they must have known he wasn't Pure Blood. There were probably Half Blood Death Eaters too, but wasn't it a bit strange to Pure Blood Death Eaters that they were being led by someone who wasn't? It couldn't have been too big secret, since Dumbledore said he went after Harry and not Neville because Harry was a Half Blood. But was it just Dumbledore who thought of that? Did the Death Eaters know this is why he choose to go after Harry? And again, Lucius had the diary. At the least, he knew his true name. Didn't he ever do any digging? Or was Tom being a descendent of Slytherin himself enough to ignore his Muggle family?  So basically, was it well known that Tom Riddle was Voldemort and did the Death Eaters know he was a Half Blood?


How to check architecture needs before installing Ubuntu?

I am planning on installing Ubuntu on my computer that already has windows on it. I have a x64 based processor and windows is also in 64 bit operating system.  By using the uname -mcommand in the Ubuntu OS I get that it is x86_64 which I am guessing means that the Ubuntu I want to install also is a 64 bit operating system.  I have created an additional 20GB partition so all that is done too.  Is there anything else I should check before I install it or should it be fine to go ahead?


Prove that: $$\lim_{n \to \infty} n^{-1/(p+1)} (1^{1^p}2^{2^p} \cdots n^{n^p})^{1 /n^{p+1}} = e^{\frac{-1}{(p+1)^2}}$$  I really have no clue how to go about this. I try converting it into summation form by taking logarthims and then trying to approximate each term but to no avail. Can anyone please help me?


Possible to extend constructor in partial class?

I'm using an MS Access database (I know...), so to capture the auto-generated primary key, I'm extending the table adapter class. I took me a while to figure this part out, so if that's your problem, future reader, right-click on your dataset file (*.xsd) and select View Code. This will create a partial class. The GetLastID() method is just a query with SELECT @@IDENTITY. The trick is that it has to be done when the row is updated, without closing and opening a new connection, so the RowUpdated event needs to be handled. Here's the code for that: namespace TimeTrack.TimeTrackDataSetTableAdapters {     public partial class TimeSlipsTableAdapter     {         public void CustomSetup()         {             Adapter.RowUpdated += Adapter_RowUpdated;         }          private void Adapter_RowUpdated(object sender, OleDbRowUpdatedEventArgs e)         {             if (e.StatementType == StatementType.Insert && e.Errors == null)             {                 int lastID = (int)GetLastID();                 e.Row["ID"] = lastID;                 e.Status = UpdateStatus.SkipCurrentRow;             }         }     } }  My question is: Is there are way to avoid having to call the CustomSetup() method? I would like for somehow to include the event handler assignment in the construction of the table adapter without having to make an additional call. Is there a way?


Algorithms for computing multiplicative order modulo $n$

If I take the $k \in \mathbb{N}$ power of 10 and mod it by a large prime, I notice that the remainders repeat at some point.  For instance $10^k mod~7$ seems to repeat every $8$th value of $k$.  Given $k$ (the power of ten), and a large prime number $p$, how can I compute the size of the cycle?  I tried writing a python script that computes the first instance of a repeat. However, I don't know if this works since a single instance of a repeat may not necessarily mean a full cycle.


Story with a supercomputer with a God complex

I can't remember the title or author in which a new super computer is built and it answers the question...     Is there a god?   (omninously) with      There is now.


When reviewing reopen votes, when you click "Leave closed", it will prompt you with "Nominate this question for reopening?", causing a bit of confusion.


Performance difference of constraint placement in SQL join-on

Is there any difference in prepared query structure and thence performance, between  select *  from employee e join division d     on e.eid = d.eid     and e.div = d.div     and e.level > 5     and e.startDate > sysdate - interval '60' month ;   and:  select *  from employee e join division d     on e.eid = d.eid     and e.div = d.div where      e.level > 5     and e.startDate > sysdate - interval '60' month ;


How to get back a declined Outlook invitation

I accidentally clicked "decline" on an Outlook invitation and now I can't reverse it -- the event has completely disappeared from my calendar!  How can I get back the event invitation and change my "Decline" to "Accept" or "tentative"?


I installed Ubuntu in my Laptop today and i accidentally deleted all the partitions and data along with it. Now my Computer is blank af. Is there any way i can recover my data?? Pleasee


There's a lot of discussion going around about the new lightsaber in Star Wars VII. One criticism I've heard is that the cross-guard on the lightsaber doesn't look like it's going to do anything. One function of a cross guard is to stop your opponents blade from sliding down your own and lopping off all of your fingers. As you can see in the image below, there's a little nub of an emitter at the base of the cross-guard. Wouldn't an opponents lightsaber just lop the cross-guard right off as it slid down the blade?  With that in mind, what prevented people from losing fingers in the first place? Can lightsaber blades even slide against each other?  seems to suggest that they can.


Why does this URL have "?as=1" at the end of it?

Recently a URL was posted on Ask Different that looked like this:   Why does it have the "?as=1" at the end of it? I understand that it is part of the workings of the website, but what is its purpose?


What's more correct "is my hair" or "are my hair" when I'm referring to all my head hair? ("do my hair look bad" or "does my hair look bad" for example)   Thank you


Can "X is enough." be used when X is plural?

I was writing a  on another site where saying "Done." was a sufficient post. In order to meet the character limit, I typed the sentence:     Sometimes five characters is really enough.   After looking at it, I changed it to:     Sometimes five characters are really enough.   Somehow, as a native speaker, the first one still feels better to me, although I can't figure out why that is or if my feeling is misleading me.  Is my initial pass on the sentence grammatically correct? Does it mean something different than the second take?


Two load icons simultaneously appearing in Android app

This  confirms that the Android app is using two different loaders since last year, but just today I've noted that, at the questions page, it is using them simultaneously. I've never noted this, so I believe this bug was recently created.  I hope the following gif is clear enough to show the issue. Also, note that the bigger loader is "freezing".    SE Android App Version: 1.0.60 My Android OS Version: 5.0.2  Still observed in version 1.0.89


Create a '.desktop' shortcut for 'Show Applications' on Ubuntu 18.04

I need to create a .desktop shortcut for 'Show Applications', so that I can pin it to the Plank dock to view all applications and search.


In accessing array elements I have long been using syntax like arrayname[index]. However I saw this syntax 'index[array name]' in a program. It does compiles, giving output '3'. But is it a right or wrong syntax? int arr[5] = {1,2,3,4,5}; cout << 2[arr] << '\n';  I can't find explanation of such thing in previous posts or elsewhere so I open up this post. Thank you.


How do I change my profile picture on main user, Area 51?

How do I change my profile picture on my main user on Area 51? I successfully changed it on my discuss user (hovered over my profile picture, clicked link "change picture"), but the "change user" link does not appear on my main user profile page.  Thanks!


I'm aware of $.extend, which does almost what I need, but it also seems to 'unwrap' the prototype, by copying over all the methods as members of the new object. Is there any way to tell it to skip inherited members, or do I have to roll my own copy function?  Here's what I currently have, but I'm not sure if it can be improved upon:  function Foo() {   this.x = 3;   this.y = {a: 4}; } Foo.prototype.z = 5; Foo.prototype.clone = function() {   var res = new Foo();   for (var key in this) {     if (this.hasOwnProperty(key)) {       // assuming that all members are plain values or objects/arrays       if (this[key] instanceof Array) {         res[key] = $.extend(true, [], this[key]);       } else if (this[key] instanceof Object) {         res[key] = $.extend(true, {}, this[key]);       } else {         res[key] = this[key];       }     }   }   return res; };  var foo = new Foo(); var bar1 = $.extend(true, {}, foo); // {x: 3, y: {a: 4}, z: 5, clone: function} var bar2 = foo.clone(); // {x: 3, y: {a: 4}}   Update: looking at $.extend implementation, it seems very similar to what I have, except for hasOwnProperty check, so perhaps this is the best way to do it after all?


How to get inheritance working with an Array of objects?

for education I have to write a programme involving different objects and inheritance. The project is about different Locks with Transponders to open them. Let me explain with a simplification of my programm: class Lock { public :      Lock(int ID, int Transponder1, int Transponder2);     void OpenLock(int Transponder); protected:     int _ID = 0, _Transponder = 0; }; class SafetyLock : public Lock { public:     SafetyLock(int ID, int Transponder1, int Transponder2);     void OpenLock(int Transponder1, int Transponder2); protected: };  There are Normal Locks and safetylocks. The Safetylocks are inherited from the normal Locks. Normal Locks need only one Transponder to open, thus OpenLockhas only 1 parameter. The SafetyLock needs two Transponders to open, its OpenLockhas two Parameters. class Managment { public:     void StartSimulation(); protected:     Lock allLocks[2] =     {         Lock(1,10,20),     //"A normal Lock can be opened by either Transponder 10 or 20"         SafetyLock(4,40,10)//"A safety Lock with needs BOTH 40 and 10 to open"     }; };  Managment handles everything, this is why I listed all Locks there are(in my simplification only 2) in a List of type Lock. void Managment::StartSimulation() {     allLocks[0].OpenLock(10);                                                                          allLocks[1].OpenLock(40, 10); //Here the problem occurs since OpenLock only has one parameter in                                   //Lock   }  When I know try to open both Locks with their respective transponders all goes well for the Normal one but for the Second one, it tells me that I have too many arguments even though I declared a different OpenLock for the type SafetyLock. I can only guess that my problem is that I have an Array of type Lock but I tried to google my problem and don't know how to proceed now. Send help. Whole Test Code I wrote: #include <iostream> using std::cout; using std::cin; class Lock { public :      Lock(int ID, int Transponder1, int Transponder2);     virtual void OpenLock(int Transponder); protected:     int _ID = 0, _Transponder = 0;  };      class SafetyLock : public Lock { public:     SafetyLock(int ID, int Transponder1, int Transponder2);     virtual void OpenLock(int Transponder1, int Transponder2);  protected:    };  class Managment { public:     void StartSimulation(); protected:       Lock allLocks[2] =     {         Lock(1,10,20),     //"A normal Lock can be opened by either Transponder 10 or 20"         SafetyLock(4,40,10)//"A safety Lock with needs BOTH 40 and 10 to open"     }; }; void Lock::OpenLock(int Transponder) {     if (Transponder == 10 || Transponder == 20)     {         cout << "succes!";     }      } void SafetyLock::OpenLock(int Transponder1, int Transponder2) {     if (Transponder1 == 40 && Transponder2 == 10)     {         cout << "succes!";     } } void Managment::StartSimulation() {     allLocks[0].OpenLock(10);     allLocks[1].OpenLock(40, 10); //Here the problem occurs since OpenLock only has one parameter in                                                                  //Lock }    int main() {     Managment A;     A.StartSimulation(); }


Is it possible for a function to be in $L^p$ for only one $p$?

I'm wondering if it's possible for a function to be an $L^p$ space for only one value of $p \in [1,\infty)$ (on either a bounded domain or an unbounded domain).  One can use interpolation to show that if a function is in two $L^p$ spaces, (e.g. $p_1$ and $p_2$,with $p_1 \leq p_2$ then it is in all $p_1\leq p \leq p_2$).   Moreover, if we're on a bounded domain, we also have the relatively standard result that if $f \in L^{p_1}$ for some $p_1 \in [1,\infty)$, then it is in $L^p$ for every $p\leq p_1$ (which can be shown using Hölder's inequality).  Thus, I think that the question can be reduced to unbounded domains if we consider the question for any $p>1$.   Intuitively, a function on an unbounded domain is inside an $L^p$ space if it decrease quickly enough toward infinity. This makes it seem like we might be able to multiply the function by a slightly larger exponent. At the same time, doing this might cause the function to blow up near zero. That's not precise/rigorous at all though.     So I'm wondering if it is possible to either construct an example or prove that this can't be true.


Enable wysiwyg on textarea summary field

Anyone know how I can enable the WYSIWYG editor for the textarea summary field in D8? I have a "body" field on my news content type set to "Text (formatted, long, with summary)" but only the main textarea gets the WYSIWYG editor while the summary field is just a standard textarea.    The summary field does support rich text, presumably using the same text format as the main textarea, but it's not clear since CKEditor is not there.  Note there's a similar question asked but it's from 2011:


Why do I get a NullPointerException when I read the input of a scanner into an ArrayList?

I want to read the input from my scanner into an arraylist. I already tried it but I always got a NullPointerException. Can somebody tell me why?  private static ArrayList<String> allWords; private static int numberOfWords;  public static void main (String[] args) {         Scanner sc = new Scanner(System.in);         while (sc.hasNext())         {             String s = sc.next();             allWords.add(s);             numberOfWords++;         }         sc.close(); }


How to restore default sharing extension under Yosemite

OS X Yosemite introduce few extensions like sharing extensions. With some defaults one like share with Apple Mail, iMessage, ... but today thoses extensions are missing for me. Is there's any knowed way, even with CLI to restaure them ?


Is it possible to duplicate `div` in css?

Is it possible to duplicate div in css? for example I have div look like that:    And I need to duplicate extactly like that without using javascript (for).  Somehting like background-repeat just "div-repeat" or something else that make it work.


Command not found when adding third parameters to a shell script

Being on Ubuntu Server I am trying to write an automation script.  Here is what I have:  #!/bin/bash  while [ "$1" != "" ]; do     case $1 in         -p | --port )           shift                                 PORT=$1                                 ;;         -d | --domain )         shift                                 DOMAIN+=("$1")                                 ;;         -l | --location )       shift                                 PATH=$1                                 ;;         * )                     exit 1     esac     shift done  echo "Parsing finished. List of domain is: " for val in "${DOMAIN[@]}"; do     echo " - $val" done  echo "Generating -d domain list..." for val in "${DOMAIN[@]}"; do     domains="$domains -d $val" done  echo "-d list is: $domains"  echo "Port is: $PORT."  echo "Location to save is: $PATH"  certbot certonly --standalone --standalone-supported-challenges http-01 --http-01-port $PORT $domains --cert-path $PATH   When ran with just two parameters, it works correctly. When I specify the third parameter -l or --location, it gives:  cert-ggm.sh: line 35: certbot: command not found   I tried to rename the -l parameter to capital P, got the same result. The test echoes return correct value parse. What's the deal with the location parameter casting certbot command uncallable? Thank you in advance.


Why is my method changing the value of my original variable?

I have created a method that takes a List as an input, brewMethod.getmMethodBrewPours() and depending on the users preference, the method returns those variables as they are or multiplied by a number. I store the returned value as a new variable, brewPours. The issue is, not only is this method returning new values to be stored, but it's also changing the values of the original variable. Why is this being changed, and what should I do to prevent it?  Code that calls method:  // Custom class storing sets of data         brewMethod = i.getParcelableExtra("brew_method");          //logs original packaged values         for (int j = 0; j < brewMethod.getmMethodBrewPours().size(); j++) {             Log.v("Original pour value #: " + j + ": ", brewMethod.getmMethodBrewPours() .get(j).toString());         }          //changes values based on users preference         brewPours = replacePours(brewMethod.getmMethodBrewPours());          //report the values again of the original packed values, but they are changed for some reason         for (int k = 0; k < brewMethod.getmMethodBrewPours().size(); k++) {             Log.v("New value on Original pour value #: " + k + ": ", brewMethod.getmMethodBrewPours() .get(k).toString());         }          //log the values of the new variable brewPours         for (int l = 0; l < brewPours.size(); l++) {             Log.v("Value for new variable brewPours pour # " + l + ": ", brewPours.get(l).toString());         }   Code of the method:      public List<Integer> replacePours(List<Integer> waterPours) {      SharedPreferences pref = getSharedPreferences("preferences", MODE_PRIVATE);      Integer newServingSize = pref.getInt("pref_key_serving_size", 1);      if (newServingSize == 2) {         for (int i = 0; i < waterPours.size(); i++) {             newPour = waterPours.get(i) * 2;             waterPours.set(i, newPour);         }     }      return waterPours; }   Output:  06-19 16:50:34.474 30159-30159/com.brewguide.android.coffeebrewguide V/Original pour value #: 0:: 60 06-19 16:50:34.474 30159-30159/com.brewguide.android.coffeebrewguide V/Original pour value #: 1:: 200 06-19 16:50:34.474 30159-30159/com.brewguide.android.coffeebrewguide V/Original pour value #: 2:: 300 06-19 16:50:34.474 30159-30159/com.brewguide.android.coffeebrewguide V/Original pour value #: 3:: 380 06-19 16:50:34.475 30159-30159/com.brewguide.android.coffeebrewguide V/New value on Original pour value #: 0:: 120 06-19 16:50:34.475 30159-30159/com.brewguide.android.coffeebrewguide V/New value on Original pour value #: 1:: 400 06-19 16:50:34.475 30159-30159/com.brewguide.android.coffeebrewguide V/New value on Original pour value #: 2:: 600 06-19 16:50:34.475 30159-30159/com.brewguide.android.coffeebrewguide V/New value on Original pour value #: 3:: 760 06-19 16:50:34.475 30159-30159/com.brewguide.android.coffeebrewguide V/Value for new variable brewPours pour # 0:: 120 06-19 16:50:34.475 30159-30159/com.brewguide.android.coffeebrewguide V/Value for new variable brewPours pour # 1:: 400 06-19 16:50:34.475 30159-30159/com.brewguide.android.coffeebrewguide V/Value for new variable brewPours pour # 2:: 600 06-19 16:50:34.475 30159-30159/com.brewguide.android.coffeebrewguide V/Value for new variable brewPours pour # 3:: 760     Edit: I adjusted the method's code following the advice from @Vampire and got the results I was looking for. Below is my adjusted code, thanks!  public List<Integer> replacePours(List<Integer> waterPours) {      List<Integer> returnedPours = new ArrayList<>();     SharedPreferences pref = getSharedPreferences("preferences", MODE_PRIVATE);      Integer newServingSize = pref.getInt("pref_key_serving_size", 1);      if (newServingSize == 2) {         for (int i = 0; i < waterPours.size(); i++) {             int newPour = waterPours.get(i) * 2;             returnedPours.add(newPour);         }     }     return returnedPours; }


Algorithm for procedureral 2D map with connected paths

Problem to solve: Generate a random 2D dungeon map for a tile-based game where all rooms are connected.  I am looking for better solutions than what I currently have.  My current solution is that I run two algorithms. The first generates the dungeon with its rooms. The second make sure that all rooms are connected. I am curious what other soltions may exist. Faster and / or easier etc. Speed is not really a concern, but if speed can be gained at no real cost, well, that is a good thing. More important is that I, and others that read, may learn different ways to approach and solve the problem.  Below are my current implementation. Rooms currently have no exits or exits in any 2, 3 or 4 directions.  Generating the dungeon rooms  Setup: Set the current room to the top left room.   Get a valid room type for the room (where valid room type is a type with no exits out of the dungeon and that have exits that matches the exits of the room above and the room to the left. Only need to check above and to the left due to step 2 below). Put down the room and advance the x-coordinate one step. If the x-coordinate exceeds the dungeon width, set the x-coordinate to 0 and advance the y-coordinate one step. If the y-coordinate exceeds the dungeon height, we are done. Repeat from #1.   I then check to see if all rooms are connected If they are not all connected I run a second algorithm that, in a non-sexy but definately good enough way in terms of dungeon layout, goes through the rooms and change them so that all end up being connected.  Checking to see if all rooms are connected  Setup: Create a 2D map of integers representing paths and initialize the entries to a "unprocessed" (not yet traversed) value, -1. Set a start path index integer that keeps track of the current path to 1. Set the current room to the top left room by adding it to a stack of rooms to check.    If the stack contains rooms to check, pop it set the path index of the room to the current path index. If the stack does not contain any rooms, increase the path index and try to get a room by advancing column by column, row by row, until we get a room that has not been processed yet. If no room can be found, we are done. Check to see if the room has an exit to the left. If it has add the left room to the stack if it is not already on there. Repeat step 2 for down, right and top directions (since we are using a stack that means the rooms are traversed in clockwise order, starting with the top direction). Repeat from step 1. If the path indices count is greater than one, there are disconnected rooms.   If there are disconnected rooms I then group the rooms by their path index, get the index of the biggest path and connect all other rooms to those rooms. This is a work in progress, but my (current, "brutish") plan is to go through each room in a room group (except the first) check to see if there is a horizontal or vertical path to the biggeset room group, and if so, create a horizontal / vertical path there by injecting / updating the rooms inbetween. Rinse and repeat. Ugly, yes, but it is something that will not be noticable in terms of visual pattern so it works in that sense.


Accidentally removed myself as administrator on Facebook business page, now can't edit it

I accidentally removed myself as administrator on my Facebook business page and now I can't edit it.   The pages, at "golfbookie", now has no administrator and is inaccessible by me, its creator.   How do I fix it so I can edit it, or at least reinstate myself as the admin?  I've had no response from Facebook.


minecraft - Always active repeating command block doesn't bypass given command

When I enter the following command in a Repeating Command Block (always active), nothing happens.  execute if block ~ ~1 ~ minecraft:dropper{Items:[{Slot:0,id:"minecraft:redstone",Count:1},{Slot:1,id:"minecraft:redstone",Count:1},{Slot:2,id:"minecraft:redstone",Count:1},{Slot:3,id:"minecraft:redstone",Count:1},{Slot:4,id:"minecraft:iron_axe",Count:1},{Slot:5,id:"minecraft:redstone",Count:1},{Slot:6,id:"minecraft:redstone",Count:1},{Slot:7,id:"minecraft:redstone",Count:1},{Slot:8,id:"minecraft:redstone",Count:1}]} run setblock ~ ~1 ~ minecraft:dropper{Items:[{Slot:4,id:"minecraft:iron_axe",Count:1,tag:{Unbreakable:1,display:{Name:"{\"text\":\"UnbreakableAxe\",\"italic\":\"false\",\"bold\":\"true\",\"color\":\"gold\"}"}}}]} replace   All following requirements of the command are fulfilled:   A dropper on top of the command block (fulfills relative coordinate ~ ~1 ~) Dropper contains redstones on slot 1,2,3,4,6,7,8,9 and an iron axe on slot 5. (subtract 1 for each slot for the command)   Am I doing something wrong? I'm assuming there is something wrong in the command, though, I still don't know.


Gimp: how to remove background noise/artifacts and enhance handwritten text

I have a lots of scanned handwritten lecture notes (PDFormat) and I want to improve their readability (I have uploaded an example). In particular I'd like to remove the "squares" on the back. I would appreciate any advice you may have. Thanks in advance.


Prove $\frac{1}{1 \cdot 3} + \frac{1}{3 \cdot 5} + \frac{1}{5 \cdot 7} + \cdots$ converges to $\frac 1 2 $

Show that $$\frac{1}{1 \cdot 3} + \frac{1}{3 \cdot 5} + \frac{1}{5 \cdot 7} + \cdots = \frac{1}{2}.$$  I'm not exactly sure what to do here, it seems awfully similar to Zeno's paradox. If the series continues infinitely then each term is just going to get smaller and smaller.  Is this an example where I should be making a Riemann sum and then taking the limit which would end up being $1/2$?


Why Wikipedia does not have duplicate content issues with search engines?

I discovered that the following 2 URLs are serving exactly same content. Why is this not impacting Wikipedia's SEO? I've heard having same content across 2 URLs has negative impact on SEO.      Disclaimer: I'm a developer, not in SEO or marketing so don't know much about SEO.


Two manifolds $X$ and $Y$ with two bijective continuous functions from $X$ to $Y$ and $Y$ to $X$, but not homeomorphic

I happen to found  about finding two metric spaces $X$ and $Y$ such that there exists bijective continuous functions $f:X\to Y$ and $g:Y\to X$, and $X$ and $Y$ are not homeomorphic. I could not produce my own example, and I think the reason is that I am thinking of manifolds only.  Suppose we have two second-countable Hausdorff metrisable manifolds $X$ and $Y$ such that there exists bijective continuous functions $f:X\to Y$ and $g:Y\to X$. Can we show that the two manifolds are homeomorphic? Or is there still a counterexample?  Please note that I have taken only one course on metric space and topology, and I don't have much experience with manifolds. So please explain answers in details or post references to the details.  Edit: In case of any ambiguity, I would like to state that I do not restrict attention to manifolds without boundary, i.e. the manifolds may have boundary, if such a counterexample exists.


My 1yr 3month old daughter crying every night

Don't know what could it be but my daughter keeps on crying every night. She's sleeping and suddenly she starts crying. Hungry ? (She drinks her last bottle of milk around 8pm.) Maybe teething? (every night, don't think so) Miss being in mommy's and daddy's bed? (she cries even if she's in our bed) I'm out of ideas, and we are kind of exhausted! Any ideas what might be the reason for her to cry every night?


How do I delete my wifi driver or something else to permanently disable wifi?  I do not want to blacklist, or use security I want it deleted. I want to KEEP my wired networking.  Thanks  THIS IS NOT A DUPLICATE AS I WANT TO DELETE NOT DISABLE


Can I request the code behind a research paper from the author?

I am in the field of computer science. It is often the case when I am reading a paper I start to wonder, "Wow stunning results, however, I would like to prove that." or "How exactly did he get these amazing results? He/she just wrote a rough overview of the real methodology used in this paper.". As you can see, a lot of times the small things have a huge impact on the overall performance of the underlying methodology. Often they are not part of the paper or not revealed at all.  My idea would be to contact the paper writer, to ask for his research programs to recreate them and understand them. Can/should I do that?   I personally think that there are probably not a lot of researchers, who would let somebody else "look at their cards". What's your experience with that?


Convert Xml hexadecimal values to integer in c#

I have the following xml:  <RootLevel>   <Level1 type="Integer" value="0x53494553"/>   <Level1 type="Float" value="0x07"/>   <Level1 type="Short" value="0x0002"/>   <Level1 type="Short" value="0x0000"/> <RootLevel>   Respect to this xml, i get the Type value and cast them with no problem. But when i try to parse the hexadecimal values with   Convert.ToInt32(node.Attributes["value"].Value) or Convert.ToInt32(node.Attributes["value"].Value,NumberStyles.HexNumber) or int.Parse(node.Attributes["value"].Value) or int.Parse(node.Attributes["value"].Value, NumberStyles.HexNumber)   It gives the following error:  Input string was not in a correct format.  In case i am trying to parse into integer but for every dataType it will be similar. Parsing for integer help is enough.  What am i missing here?


Do both superiority dice from Superior Technique and Martial Adept only increase die size when a character reaches 10th level Battlemaster?

Also, does that mean that dice gained from either of these features never become d8's?


How do I duplicate a server's packages and configuration to another machine?

I have a production server running Ubuntu. I would like to setup similar configuration installed on my local machine. I'd like to have same packages installed.  Since bandwidth is a constraint the traditional disk cloning methods won't work for me. Having same packages installed and same users with same passwords created would be wonderful; I'll tweak the rest of the things manually.  Is there a good solution for my requirements?


Point of Diffie-Hellman key exchange when public keys are known

Since the basic version of Diffie-Hellman key exchange protocol is vulnerable to Man In The Middle Attack, some sort of authentication is needed. It was mentioned that RSA digital signature can be used to handle this case. However, I don't understand that if the public keys of the two parties are known to each other, what would be the point of using DH at all? One of them can just propose a shared key k, compute its hash value and send the (k, h(k)) encrypted with the other one's public key. I appreciate if anyone can clarify the benefit of using DH in case of known public keys.


I'm experiencing a strange behavior with USB ports on my Ubuntu. Part of the time they work fine, but sometimes they randomly disconnect/reconnect or significantly slow down. This is OK for mouse and keyboard, but this is a problem for other devices: flash drives, wifi adapter, printers.  Below are some details that may help.  $ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description:    Ubuntu 16.04.3 LTS Release:    16.04 Codename:   xenial  $ uname -r 4.10.0-37-generic   My motherboard is B350 PC MATE.  Also I have a dual boot on the computer with Windows 10 as another system, and on Windows there are no problems with USB.


isomorphic planar graph with its complement

I need to demonstrate that there is a finite set of planar graphs with the property that the graph G is isomorphic with its complement graph.Can you give me some suggestions or hints ?Thank you


Rotating screen breaks "Post" button for comments in Android app

How to reproduce bug:   Start typing a comment. Rotate the screen orientation of your device. Try clicking the "POST" button. Nothing will happen.   I've reproduced using the the latest version (1.0.85) of the app on Samsung I9305 running Android 4.4.4   And Asus ZE551ML (5.0).   @IlmariKaronen  on Samsung XCover 3 (5.1.1).  @JonasCz has reproduced this on Cyanogenmod (4.4).  @meatball has reproduced this on Nexus 5 (6.0.1).


Does Stack Exchange use caching and if so, how?

Recently, I read this  about how they have some of their infrastructure laid out. I was curious to know, does Stack Exchange use caching (both at the application layer and/or database layer) and if so, how?


Can anyone explain why we use the definite article the for the following:     The upper classes often go fox hunting.   but     People in High society often go fox hunting.


No units in quotient ring equivalent to no units in original ring?

Definition: Let $R$ be a ring with $1$. $r\in R$ is a unit if and only if $r \neq 1$ and there exists $s\in R, s \neq 1$ such that $rs=1=sr$.  Let $R$ be a ring with $1$ and let $I$ be a proper ideal of $R$.      $R/I$ has no units $\Rightarrow$ $R$ has no units?   What about the converse,      $R$ has no units $\Rightarrow$ $R/I$ has no units?


What do the numbers on the Winter Bash leaderboard mean?

I thought that they represented the rank of the person by the number of hats they have collected. The numbers "jump" however, they do not follow an unbroken order:  There are also really big gaps:  What do these number mean? Are they supposed to be like this?


I am using XeTeX and love it very much. When I use helatex, I have no problems at all.  But I want to try do it «True Way»: plainTex. XeTeX takes all annoyance with unicode from me, but sample like this  \font\foo=bar \foo {\bf Привет, мир!}   {Jellios} \bye   fails, because font have not cyrillic symbols.  So, my question is example of font(with tfm file), that have cyrillic symbols.  My system is Arch GNU/Linux.


How do I understand the meaning of the phrase "up to~" in mathematics?

I am reading a book that explains elementary number theory: Number Theory: A Lively Introduction with Proofs, Applications, and Stories by James Pommersheim, Tim Marks and Erica Flapan.  The authors say,      "We express this idea in the statement of the Fundamental of Arithmetic by saying that prime factorization are unique up to order.  ... for example, 40 and -40 are equal up to sign, the functions $12x^2$ and $x^2$ are equal up to a constant factor, and so forth."   Because I am not an English native speaker, the phrase "up to" is ambiguous for me a little bit. I would like to figure out the meaning of the phrase and use it properly. How do I do?


How to flash a BIOS when only a Windows binary is provided?

I want to update the BIOS on Toshiba QOSMIO-G30. The exe file that I downloaded from the manufacturer web site is supposed to be Operating System independent! Yet using Wine I could not execute the file to FLASH System BIOS. Is there any way to update the BIOS in Ubuntu?


I'm using foundation 5 framework (not sure if that matters). I will be passing all information to another page, so it's very important that each CELL is an individual distinguishable item/value when I do pass it, but I'm not sure on how to start on this problem. It should add another row every time add is hit. Same goes for Delete.  Can anyone guide me on how to approach this? Here is what my mark up looks:  Add line Delete line

                 Status	                 Campaign Name	                 URL Link	                 Product	                 Dates (Start to End)	                 Total Budget	                 Daily Budget	                 Pricing Model	                 Bid	                 Targeting Info	                 Total Units

                 df	                 dfd	                 fdsd	                 fdsfd	                 dsf	                 dd	                 dd	                 dd	                 dd	                 dd	                 dd


Plants and animals have the following distinct properties:    Plants live from solar energy by , they use solar energy to make sugar and oxygen out of carbon dioxide, which gives them energy. Animals live from the sugar and oxygen plants created and produce carbon dioxide for their energy. Animals can move across the planet while plants are tied to the ground.   Clearly, animals have a harder time to survive with no plants within their reach than plants have without animals coming close. This is logical because solar energy is always there while plants are not.  So my question is: Are there animals that can do photosynthesis? It's obvious that an animal with plant-like stateliness would be non-beneficial since it relies on eating other plants for it's energy and there may not always be plants within reach from it's spot.  But animals using the sun and carbon dioxide for energy production does not sound so stupid.   Night animals could also gather energy in their sleep. Much easier than plants, animals could make sure nothing blocks their sunlight. Many animals go through periods of hunger because food is scarce, for some of them this period is paired with high sunlight levels. (the dry season f.e.) (EDIT: This is just an idea, of course photosynthesis requires water, which is absent in the dry season. But still, in warm period with enough water, there's sometimes too much animals to feed from the available vegeation.)   Some things I already took into consideration:   I know that plants, because they are small in mass (compared to the area with which they can collect sunlight) and static, don't need nearly as much energy as animals do. Is this the main reason? I know that f.e. reptiles, but in fact all cold-blooded animals, already use the sun's energy. But they only use the heat from the sun to warm their bodies, they don't photosynthesize.


Are there any ferries from Europe to Egypt?

Are there any ferries to Egypt from Italy, Turkey, Greece or any country from south Europe?


I am on a Raspberry Pi, and I am using a program called fswebcam, which allows you to take pictures with a webcam.  ~$ fswebcam image.jpg   That command if entered in terminal takes a picture and saves it to your computer, however I want to build a simple python program that can access the terminal and execute that same command as I have listed above.  I have tried to import os and use os.system('fswebcam image.jpg') But it isn't working for me.   How can I have python execute terminal commands?


Which is stronger, a rope without knots or a rope with knots?

Suppose I have two identical ropes, one of which I manually tie some knots in. If I use them to hang clothes, which one is more durable?      Personally I think that rope with knots will be more durable, but I can't come up with a satisfactory reason.


calculate the given sum (related to Newton's binomial formula)

i was given the following question:  given n is a positve integer, calculate the given sum: $$ {n \choose 1} -2{n \choose 2} +3{n \choose 3}+ \ldots +(-1)^{n-1}\cdot n {n \choose n} $$  I looked at the expression and it reminds me of Newton's binom.. but i have no idea where to begin.. can someone help me understand how should i approach this?  thank you


I am trying to solve this limit :  $$\lim_{n\to \infty}\frac{(1)(2)(3)\cdots (n)}{(n+1)(n+2)(n+3)\cdots(2n)}.$$ Any direction ? I think i should i use the Sandwich theorem or something else.


Is it safe to use the EPEL repository on CentOS systems?

I recently submitted a Puppet patch which would have enabled the EPEL repository on a number of our CentOS 7 systems (I need this in order to install Python 3).  One of the sysadmins rejected the patch, claiming that EPEL is not safe, and can conflict with the base repository packages. I was told that EPEL can make determining "which package will be available on which node somewhat unpredictable."  I am a software developer now, but I was a full-time sysadmin from 1995 to 2013. I have never heard about this kind of conflict before, and asking a few friends about it, none of them have either.  So my question is: can EPEL conflict with the stock/base CentOS 7 repositories? Is there any documentation out there of this happening? I didn't find anything when searching online, except a couple of statements indicating exactly the opposite.


Prove or disprove the uniform continuity of $f: \mathbb{C} \to \mathbb{C}, z \mapsto f(z)=\frac{z^2}{1+|z|}$

I tried using the definition of the continuity to try and find a $\delta$ but I got stuck here $$ |f(w) - f(z)| = |\frac{w^2 \cdot (1+|z|) - z^2 \cdot (1+|w|)}{(1+|w|)\cdot(1+|z|)}|$$ What can I do to find a suitable $\delta$ that would end my proof?


For $x_1, x_2 > 0$, let $$f(x_1,x_2) := \frac{1}{x_1^3x_2}$$ Is function $f$ convex?  I think it is because Hessian matrix is $$\begin{pmatrix} \frac{12}{x_1^5x_2} & \frac{3}{x_1^4x_2^2} \\ \frac{3}{x_1^4x_2^2} & \frac{2}{x_1^3x_2^3}\end{pmatrix}$$ And I think the matrix is positive because each value is positive (is it true?) Thanks!


set of permutations of set $\lbrace 1,2,..,n \rbrace$

Prove the following lemma for set of permutations of $\lbrace 1,2,\dots,n \rbrace$ $(n\geq2)$ and a fixed number $k\neq1$:  $\textbf{lemma: }$The number of permutations where 1 and $k$ are in the same cycle, and the number of permutations where 1 and $k$ are in different cycles, are the same.  I don't understand this task. Do you have any hint?


RDS MSSQL in-place upgrade how to update master db compatibility level when rdsa account is db owner

Background  My workplace infrastructure team ran a typical in-place upgrade of an RDS MSSQL instance to update the version from 2012 to 2017. After the upgrade, while logged in as the "master user", I was able to update all user and system databases to 2017 compatibility level except for master and rdsadmin. (I'm not worried about the latter.) Keeping the master database at 2012 compatibility level concerns me.  Is it recommended that I also update the compatibility level of the master database to 2017? I presume that leaving it at the 2012 level means that I'd be sacrificing some functionality. (I opened a github issue with  for clarification.) () If that is a yes, here is my problem I cannot change the compatibility level of master. The "master user" assigned to this RDS instance is not the db owner for the master database. The db owner of the master database is rdsa, which as you're probably aware, is a disabled AWS sysadmin user that I cannot utilize. Troubleshooting  I tried running  ALTER DATABASE master SET COMPATIBILITY_LEVEL = 140;  But I got this error User does not have permission to alter database 'master', the database does not exist, or the database is not in a state that allows access checks.   This makes sense. The "master user" that I am logged in as is not the db_owner of the master database.  Next, I asked the infrastructure team to reset the Master User password. According to these links, resetting the password should reset anything wrong with the db_owner role:       Unfortunately, this didn't change the db_owner of master. It was still rdsa. I rebooted the instance just in case and got the same results.  Then I tried adding the "master user" account as dbo in the master database.  USE [master] GO  CREATE USER [mymasteruser] FOR LOGIN [mymasteruser] GO  USE [master] GO  ALTER ROLE [db_owner] ADD MEMBER [mymasteruser] GO  That didn't work either, as expected. User does not have permission to perform this action.  Help Are there other steps on the configuration side that I can try? That side of things is a bit of a black box for me so any insight is appreciated. My next step is to contact AWS support.


I am new to this forum. I want to get started with graphic design. I have a linux OS , what software and books do i require to get started? Also i would like to start with pixel art . Hope you can guide me.


Identify a book with a social engineering theme

I originally read this book in the mid- to late '70s.   The premise was a bureaucracy whose job it was to manipulate events in human history by making the smallest possible change that would effect the desired outcome. Not time cops in the sense of going after law breakers.  The intent was to maintain a policy of non-interference as much as possible but when interference was warranted then to make the least possible change and to do so invisibly.  For example, they might take someone's keys off the dresser and put them just out of sight underneath the dresser where they plausibly might have fallen.  The subject would never know of the manipulation but would then be delayed getting out of the house and the ripples grew from there to avert a war or otherwise affect events on a large scale.  After reading that, whenever I would lose something - especially in an improbable way such as dropping a screw at my feet and then finding it on the other side of the room half an hour later - I would take some consolation in the thought that I had just averted some global catastrophe.  I was pretty scatterbrained as a kid (we call that ADHD nowadays) so I experienced this a lot.  Given that I've spent so much time pondering the ideas from the book, I'd love to re-read it.


Can I automate saving different combinations of layers?

I have a source file for an icon. It has a base layer which is the icon background, and a number of layer folders, each of which contains layers for each individual icon. There are 20 or so of these folders. To save the icon set, I need to:   Make the base layer visible, and hide all other layers Show the folder of the icon I want to save Save the file, with an appropriate name (the name of the folder) Hide that folder. Repeat steps 2-4 for every folder   I've played around with the scripting in Photoshop but haven't been able to make something that does this automatically (it's an annoyingly time-consuming operation). Is it possible?


Polygon and Vertices count for Blender 2.9?

How can I find the polygon and vertices count for all the objects in the scene in Blender 2.9? It used to be on the bottom right corner, but in blender 2.9, its not there. Here is a screenshot. The top screenshot is Blender 2.83, and the bottom one is Blender 2.9. Thanks


Using two different font sizes in math mode

Please see the below code:  \begin{small} \[\begin{array}{l} Some math that should be displayed in small font  \begin{tiny} some math that should be displayed in tiny font \end{tiny}  some more math in small font  \begin{tiny} some more math that should be displayed in tiny font \end{tiny}  \end{array}\]  \end{small}   My code only shows the math code in small. Your help is appreciated.


Why does Zemo want to know what happened in December 1991?

At the end of Captain America: Civil War, Zemo reveals that       he trapped Bucky to make the Avengers fight each others.   But around the middle of the film, he      interrogates Bucky    in order to learn what happened on 16 December 1991.  It doesn't seem to be an essential part of the plan, and everything has already happened when all is revealed. Actually to me it looks more like a matter of luck if he has something he could use it      to make Iron Man fight Cap and Bucky    after      they all made a truce... Which happened because Tony knows that all is Zemo's fault.   So why does he want so much to know that?


Can a linear regression model's r-squared value exceed the sum of the r-squared values of its input variables?

Suppose the $R^2$ value of $x_1$ with $y$ is equal to $0.15$. The $R^2$ value of $x_2$ with $y$ is equal to $0.35$. Can there exist constants $a,b$ such that the variable $X=ax_1+bx_2$ has an $R^2>0.5$ with $y$? I'm thinking no, but I can't find anything on the subject online to verify this. I know in some cases this obviously wouldn't be possible (such as if the sum of the r-squared values of the input variables exceed 1). But can it ever be true? Is there a rule related to this subject?


I am from India and studying for a master's in France. I am working as an intern in France on a programming language and I got an invitation letter from a UK university for an international conference. The conference is all related to my internship and I want to attend it.  Is it possible to apply for a visitor's visa from Paris because I am a student at Paris Saclay University? Could you please tell me if it is possible to apply on the basis of an invitation letter?


If $(1+\cos A)(1+\cos B)(1+\cos C)=(1-\cos A)(1-\cos B)(1-\cos C)$ then prove that each side $=\pm \sin A\sin B\sin C$  I didn't get any idea even to start the first step.


How this where generic type constraint work?

I'm studying generic where constraint and I bumped into this and get stuck. I've tried replicating the code by my own classes but I get "Inconsistent inaccessibility".  //this is the reference study class public class MainView<T> : System.Windows.Window where T : INotifyPropertyChanged, new(){}  //my own interface ITest{}  class B : ITest {     public B()     {      } }  public class MyClass<T> : B where T : ITest, new() {  }   I couldn't figure this out. What is there in the reference study class? How can I do the same signature with my own defined classes and interface?


What is the best way to roll-back a change set using Subversion?

I've been using various source control systems for a while, but when it comes to reverting changes I'm not yet an expert. Can someone help given this scenario:  Scenario   Given a bug was introduced in revision #5 And 3 files were changed in revision #5 And changes in 2 files were responsible for the bug When the customer discovers the bug in a release of revision #9 (HEAD) Then 2 of the files causing the bug from revision #5 must be reverted to revision #4 And changes from revision #6 to HEAD must be applied to the two files   I expect there must be a way to compare revisions #4 and #5 of the two files and generate a patch that undoes the changes in revision #5, which can then be applied to the HEAD revision to roll-back the defect.


When is a gerund supposed to be preceded by a possessive adjective/determiner?

I assume that the following sentences are grammatically correct:   He resents your being more popular than he is. Most of the members paid their dues without my asking them. They objected to the youngest girl's being given the command position. What do you think about his buying such an expensive car? We were all sorry about Jane's losing her parents like that.   I'm still getting used to this possessive gerund structure. It sounded so weird to me at first. Is the structure used in both formal and informal contexts? Are there any alternative structures that result in the same meaning and are more frequently used? (Examples taken from )


Unit testing c++. How to test private members?

I would like to make unit tests for my C++ application.  What is the correct form to test private members of a class? Make a friend class which will test the private members, use a derived class, or some other trick?  Which technique does the testing APIs use?


I read a text about kernel stable and I updated my kernel to 3.6.1. And I solved problems like WIFI and resolution but I cant solve kvm disabled by BIOS. Before update I didn't see this KVM : Disabled by bios Thanks for helps


How to get a toddler to let you know when he needs to go to the toilet

my son turned 3 on january 28th. We have started to toilet train for the last 5 days. I dont use the potty and placed him straight onto the toilet. He had a small toilet seat to fit on top but as he is quite capable we dont even need to use this anymore and sit straight onto the toilet.  I have recently had another child on february 26th, and i have previously tried twice unsuccesfully to toilet train before my second child was born.  Both times before i gave up as he would completely refuse to use the toilet and i had to literally pick him up and take him and it was turning into a power struggle and even when he sat he would not do anything no matter how long we sat there so i thought he was probably not ready and gave up both times after a few days.  This time however we have been succesful in getting him to the toilet and actually weeing. However, he will not go on his own accord or let me know. I have to take him every 20-30 mimutes and if i get distracted he has an accident on the floor. He knows he has done something wrong because he will freeze in his place and tell me.   Also because i know he is having alot of accidents i part use pull ups and part try to keep him just in knickers (I use pull ups when i need to cook or i know i will be busy and cant take him every so often, also for naps, going out or to sleep in). I have read alot that pull ups confuse him but i cant afford for him to have an accident all the time when i am busy with something else.  Any suggestions of where i might be able to improve the situation and any advice on how to get him to let me know he needs the toilet instead of having to take him myself all the time.   I know its early days but its really such a strain i just feel so tense all the time because if i forget or get too busy then we have an accident to deal with.  One final thing he has been holding in his bowel movements, and im worried he is going to cause himself some harm with constipation.


Can I safely prepare these dishes ahead of time?

I'm making some dishes for an event. Due to constraints in my schedule I'm thinking of making them ahead of time.   The first is a Buffalo Chicken Dip, it is mainly a bought cooked rotisserie chicken and cream cheese. The second is Kimchi-ppang which contains pork, kimchi and dough.  I'd like to assemble it to the point of a final bake (the dip is mixed, the pork is cooked and the dough unbaked) for both and then store it in the fridge for about 3 days. Will this be safe to do? I may be able to make it fresh on the day, but I'd have to rush a lot.


Disable automatic driver update for only one device in Windows 10

Is there a way we can disable automatic driver update for a specific device in Windows 10? The updated driver for that device (Intel Management Engine Interface 11.x in particular) causes problems on some laptops during. The version 9.x works perfect.  I don't want to disable automatic driver installation for all devices.


Is every additive monofunctor between abelian categories left exact?

Is there an additive functor between abelian categories, which preserves monomorphisms, but is not left exact?


Why should I not initialize static variable in header?

So, let's say I have a header like this:  #ifndef BASECLASS_H #define BASECLASS_H  class BaseClass {     public:         static int getX(){return x;}     private:         static int x; };  int BaseClass::x = 10;  #endif   I have heard many times that I should not initialise static variables inside a header, but rather in cpp. But as there are guards, there should be only one copy of BaseClass::x. So I kinda do not understand why I should put   int BaseClass::x = 10;    in cpp.


Explain their differences if you like...  I wanted to ask when it is appropriate to use the conjunction 'that' in a sentence. For example:   The question I want to ask is...   Or  -The question that I want to ask is...  I can't think of more examples right now. But you get what I'm saying. Why do we sometimes use it and sometimes not use it? When is it correct to use??


Find the sum $\sum _{n=1}^{\infty} {1\over n^2}$ elementary!

Find the sum $$\sum _{n=1}^{\infty} {1\over n^2}$$ elementary! I know the result is $\pi^2/6$, but I wonder if there is an elementary approach i.e. with a high school knowledge to this sum.


Can I buy a prepaid mobile data plan while on route in France?

I will be driving through France soon and would like to have a local prepaid sim with data capabilities. I found a very interesting sollution in the , but I need a French delivery address. I don't have that on such a short notice, so I am looking for a plan that I could buy while on route (gas station, shopping malls, etc)


How to run an application with temporary root access from .desktop file?

Im new in Linux world, and i have a problem what is cant solve for like 17 hours.  Im using Ubuntu 18.04.3.  I would like to edit my files from the gui, because i don't want to use the nano, or mcedit every time i have to edit some config file.  So i downloaded Notepadqq (not the snap version!), and created a "shortcut" for it:  #!/usr/bin/env xdg-open  [Desktop Entry] Version=1.0 Type=Application Terminal=false Exec=/usr/local/bin/notepadqq Name[en_US]=Notepadqq Name=Notepadqq Icon=notepadqq   also in the /usr/local/bin i created a bash script named notepadqq, what contains:  #!/bin/bash /usr/bin/notepadqq --allow-root $* exit $? ###eof###   So this route (/usr/locl/bin) is the second in my $PATH, so this will run before the "real notepad" if i think it right.   I gave it my username with chown  chown myusername:myusername notepadqq   and set the read-write priviliges too  chmod 0755 notepadqq   So my plan was to run Notepadqq always as root.  But it dont works. The terminal script: 'sudo notepadqq' is works very well, but now what's the matter with --allow-root, if i have to 'sudo' to use the flag --allow-root? :D  i tried this:  [Desktop Entry] ... Exec=pkexec gedit /usr/local/bin/notepadqq   but it's not works. When i try this at the terminal (pkexec gedit notepadqq) i get this error:  Unable to init server: Could not connect: Connection refused   Now i shot all my thoughts, i dont know what to do.  Does anyone have any clues?


In the faq of meta sites you can read something like the following:     Voting here works a bit differently   from other Stack Exchange sites. On   Meta Stack Overflow, voting is used to   express agreement or disagreement, not   to point out a lack of quality or   helpfulness. Please don't be concerned   if you receive downvotes – members of   the community may simply disagree with   your bug, feature request, support   issue, or the nature of the   discussion.   My question is: If votes works differently on meta sites how does that of accepting answers work?  Take for instance a question on a meta site that is meant for the community to discuss some issue. What does it mean if the question is accepted? Accepting an answer is up to the author of the question so it cannot be a sign of what answer the community concludes from the discussion. It could mean that the discussion is over but that should be up to the community and not the author of the question. Is it so that accepting an answer for a discussion question on a meta site does not have a particular function?


Is it possible to download the SO Tags database?

Is there a way for me to download the full list of tags (and synonyms) used on Stack Overflow? My intent is to import these tags into an SQLite database as part of a process to convert all of my delicious bookmarks and tags to the ones used here on Stack Overflow.


I use ubuntu in dual boot with windows 10.  Besides the two partitions with the two operating systems, I have some unallocated space, I would like to use it to extend the ubuntu partition. I have tried with the 'Disks' tool, but I am only given the option to shrink the partition volume, not extend it.


Prove by mathematical induction that $1^3+2^3+...n^3=1/4(n^2(n+1)^2)$

In my attempt I arrived at $1/4(k^2(k+1)^2+4(k+1)^3)$ and don't know how to make any progress from there. I'm supposed to go from there to $(1/4(k+1)^2(k+2)^2)$ but have no idea how.


Trying to find a movie about a boy who finds a buried spaceship that then takes off

I'm looking for a movie that I saw some 20 or so years ago.  There's a boy who wanders about the countryside and falls into a hole to find himself in a corridor. He looks around, explores things...not sure if anything special happens in the mean time. The boy was youngish...around 10, maybe younger. From what I remember, it was generally very dark, the corridor might have been covered with dry bush branches. There might have been old screens / machines / computers overgrown with vegetation, but I remember things to be dark, brown, black, ...rather than green.  The corridor is actually a part of a spaceship that's burried there and seems to be dead. Anyway towards the end the boy triggers something that makes the spaceship come alive and start to take off. Not sure if the boy gets out or stays.  I'm not sure, but the ship may have started to talk to the boy...by voice or text on a screen...but I feel like I might be making that up :-)  Now that I think of it that's how it might have been. The boy visiting regularly, somehow communicating with the thing. In the end the ship then decided to take off. Until that moment I think it wasn't really obvious that it was a ship at all. Just an old dusty underground "house".   That's as much as I remember.


Why is the Carnot engine the most efficient?

It seems that the only condition used in proving that the Carnot engine is the most efficient is that it is reversible. More specifically, the Carnot engine can be run in reverse as a refrigerator. Furthermore, it is asserted that all reversible engines will have the same efficiency.   However, isn't any closed loop on a PV diagram reversible? The arrows can simply be drawn in the reverse way to create a refrigerator. If any closed loop is reversible then why does the specific Carnot engine (a specific loop) have the highest efficiency?


Firefox NoScript: How to block only one particular domain?

I started using the Firefox extension NoScript, but I'd like to allow all scripts by default, only one particular domain (google-analytics.com) should be blocked/blacklisted.   Is that possible? I could figure out only the other way around: It disables everything by default, but allows a few pages from a whitelist; but this behavior makes the web pretty unusable.


Gdal: how to get the max and min altitudes of my topographic raster?

Given a .tiff topographic raster image.   How to get the altitudes of the highest and lowest point/pixel ?


Regarding installing adobe flash player for ubuntu 14.04

I am using Ubuntu 14.04 . I wanted to install Adobe Flash Player. However the software centre shows that no such apt file is available. Upon checking online , the versions available are only up to 13.10 . What should I do?


Hats left floating when viewing "less" information in review queue

I was reviewing a question in the Reopen queue on Stackoverflow where someone who had edited the post had a hat on their profile picture:  At the time I had the "(more)" dialog open:  When I clicked (less) to hide the dialog, the hat of the user who edited the post remained where it was (as well as being redrawn in the new position):  I'm using Firefox 83.0 on Windows 10.


Perhaps I have misunderstood  so I ask another question.  In Bash desire to expand variables inside read without envsubst, arguments or heredocuments (and without any non shell-builtins) because I work in a shared hosting environment in which I don't have many common non shell-builtin utilities. The variable I want to expand is the environment variable HOME but I make this question variable-agnostic, i.e. I seek a way in which the user can expand inside read:  An environment variable A non environment variable Both types of variables   I have tried this which failed: IFS= read -r domain_dir     ${HOME}/example echo ${domain_dir}   Current output: ${HOME}/example Desired output: MY_HOME_DIRECTORY/example   How to expand variables inside read without envsubst, arguments or heredocuments (and without any non shell-builtins)? Edit to explain why I find marking this a duplicate is wrong According to the user terdon which marked this question duplicate, in this question I ask for something which is impossible. If terdon is correct in that regard than this question is not a duplicate and can be answered separately with an answer that explains if and why it is indeed impossible.


Cannot install tuxboot - repository does not have a Release file?

Trying to install tuxboot using Ubuntu PPA (Ubuntu 18.04), like so:   sudo apt-add-repository ppa:thomas.tsai/ubuntu-tuxboot   but I get   Err:8 http://ppa.launchpad.net/thomas.tsai/ubuntu-tuxboot/ubuntu bionic Release 404  Not Found [IP: 91.189.95.83 80] Reading package lists... Done                       E: The repository 'http://ppa.launchpad.net/thomas.tsai/ubuntu-tuxboot/ubuntu bionic Release' does not have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details.   I have read multiple accounts of users that successfully used the PPA to install tuxboot. What am I doing wrong?


My player died and if i clicked play in the main it will go to the last scene and say gameover

I am trying to make a gameover scene where in if the player is game over The game will go back to the main or start up then when I press play it will start new game however if i am game over and go back to main and pressed play it will only show me Game over and wont continue my code is..... Gameover code..  #pragma strict import UnityEngine.UI; private var StopGame: boolean=false; private var showGUI: boolean=false; var GUIstop: GameObject; var StopMenu; var respawn : Transform;    private var canvas : Canvas;  function Start() { canvas = GetComponent.<Canvas>(); canvas.enabled = false; }    function Update () {  if(HealthControl.LOVES==0){ Pause();    Application.LoadLevel (0);            }  } public function Pause() { canvas.enabled = !canvas.enabled; Time.timeScale = Time.timeScale == 0 ? 1 : 0; }  public function Quit() { #if UNITY_EDITOR  EditorApplication.isPlaying = false; #else  Application.Quit(); #endif }


How does the existence of a monopole affect the magnetic vector potential in gauss's law for magnetism?

Gauss's Law for magnetism is $$ \nabla \cdot B = 0 $$ This allows us to write the magentic field $B$ as the curl of another field the $\textbf{magnetic vector potential, } A$. $$ B=\nabla \times A $$ This adhers to $ \nabla \cdot (\nabla \times A)=0$ However, if a monopole does exist then we have $$ \nabla \cdot B= \rho_{m} $$ Where $\rho_{m}$ is some magnetic charge density however with a magentic vector potential this violates the equation, $ \nabla \cdot (\nabla \times A) \neq 0$. Does that mean if magnetic monopoles does exist, that the magnetic field can no longer be defined by a magnetic vector potential? In which case how was dirac able to still  define the magnetic field by a magnetic vector potentials?


Source:      There have been seven weeks of protests outside the site from which   "hundreds" of pupils were kept away on Monday.   Why does the sentence say “have been” not  simply “were”?  I think that indicates that the protesters are still protesting untill the moment of writing. Am I correct here?