Nullable bool logical "AND" operator behaves differently with true and false

Using bool? variables, can somebody explain why true & null results in null and false & null results in false?  void Main() {         bool? a = null;     bool? b = true;     bool? c = a & b;      Console.WriteLine($"{b} & NULL => " + c);      b = false;     c = a & b;     Console.WriteLine($"{b} & NULL => " + c); }   Output:     True & NULL =>    False & NULL => False   I would also be happy about the duplicate, because I did not find it, yet.


What's the correct relative path to a local image?

I've created a topbar for my website that's displayed the whole time and added an image to it with  <img src="sites/default/files/MYFOLDER/IMAGE.png">   It looks great on the homepage, but when I for example visit a node, the image isn't found anymore. I guess this problem is caused by a wrong path, but I don't know how to fix it.  What's the correct relative path?


How to access Hard Drives in Ubuntu 15.10?

I'm new to Ubuntu. I don't know how to access my hard disks in Ubuntu. I  used to access Local disk F in Windows that contained all my music, photos etc. How can I access that Hard drive in  Ubuntu ?


I am a 12th grade student, and I am afraid that in realistic terms this question might not even make sense because of the infinities that have to be dealt with. However, in my attempt to calculate it's derivative, I did the following:  $$y=x^{x^{x^{.^{.^.}}}}$$  $$\ln(y)=\ln(x)x^{x^{x^{.^{.^.}}}}$$  $$\ln(y)=y\ln(x)$$  after taking derivative with respect to x on both sides, I obtained the following:  $$\frac{\mathrm dy}{\mathrm dx}=\frac{y^2}{x(1-\ln(y))}$$  I am fairly certain that the calculations up to this point are valid. However, to further continue, I analyzed the nature of y in different domains and obtained the values, by observation(that is, by observing how $x$, $x^x$, $x^{x^x}$, $x^{x^{x^x}}$, and so on would behave to draw a conclusion):   for $x<1,$ $y$ becomes 0 for $x=1,$ $y$ becomes 1 for $x>1,$ $y$ becomes infinite   These 3 points is where the first problem lies. Are these true? If so, how do we reach to the conclusion?  Secondly, considering this to be true, I get the derivative at:   $x<1$ to be 0. $x=1$ to be 1. for $x>1$, I took $x=2.$ then the derivative $\frac{\mathrm dy}{\mathrm dx} = y^2/[2(1-ln(y))]$ (replacing $x$ by $2$). Now, I applied L hospital's rule to get the value of the expression to be negative infinity.   This is the second problem. I have used L Hospital's rule, but limits were not concerned. Is this method valid? If not, how would we calculate it?


How do I move a Minecraft saved world from my desktop to my server?

I've been working a lot on my world on my computer in single player mode. My dad got me a server and so I want to transfer my world onto my server.  How is this possible?  I noticed that in %appdata%\roaming\.minecraft\saves, the directories in there look a lot like the world directory on my server. Can I simply transfer my saves directory to my server?


How to make a pattern follow a stroke, path or line?

Here is my MS Paint job on a real bad attempt at what I'm trying to achieve:    I have access to Photoshop and Illustrator CS6, and I want to be able to draw a thick line (that is not straight) and have a pattern within the line show arrowheads within the line to indicate the direction of the line.


SQL Server stored procedure to insert in multiple tables a

I have 2 tables, custlogin and custinfo:  custlogin:  custid int primary key auto notnull custusename varchar(25) custpassword varchar(50)   custinfo:  custid foriegnkey custlogin.custid ondelete set NULL custfirstname varchar(25) custlastname  varchar(25) custaddress   varchar(100)   I want to write a stored procedure which will insert into both tables  More precisely, insert into custlogin with custusername custpassword, which would return custid for use as foreign key for custinfo.  I have searched much but I didn't find any solution.


I didn't see anything different whether or not to permallink to a question.


Add something at the end of every typed command

Is there a possibility to add some text at the end of every command i type in the terminal? For example i type "ps" and after pressing enter, it becomes "ps -a", I type "ls" and it's "ls -a"


How to show \listoffigures and \listoftables on one page and in the ToC?

Is it possible to put the list of figures and tables onto one page? I only have two tables in my thesis, so having it on an extra page looks quite bad.  I've read about the tocloft package and tried to use it. It moved both lists onto one page, but they're no longer shown in the table of contents.  So is there a way to get \listoffigures and \listoftables on the same page while preserving the ToC entry for them?


Is there any regex to get the alt attribute? Example: <img src="http://static.adzerk.net/Advertisers/a61df59863ed44e59446d0b9bb805c56.jpg" title="" alt="blahblah" border="0" height="90" width="728">   I want to get the "blahblah" from above image tag.


How to solve following normal distribution problem?

If $$X \sim \mathscr N(\mu_1,\sigma_1^2)$$  $$Y \sim \mathscr N(\mu_2,\sigma_2^2)$$ $X$ and $Y$ are independent, how to show that  $$X+Y\sim \mathscr N(\mu_1+\mu_2,\sigma_1^2+\sigma_2^2)$$  Hint: $$\frac{1}{\sqrt{2\pi}} \int_{-\infty}^\infty e^{-\frac{x^2}{2}}dx=1 $$


What does the link symbol mean in the Wi-Fi network list on iOS?

What does the "link" () mean in the Wi-Fi network list on iOS?  Example (see red rectangle):


I have defined the following simple environment:  \newenvironment{renumerate}{\begin{enumerate}\raggedright}{\end{enumerate}}   I wonder how the above can be modified to use with, say, the following:  \begin{renumerate}[label=\color{blue}10.\theenumi] \item blah \item blah \end{renumerate}   The options given in [] are not known in advance.


If $f(x) = 1/\sqrt{x}$, find $f^{\prime}(x)$. Please show the answer by using   $$\lim_{h\to{0}}\frac{f(x+h)-f(x)}{h}.$$  I know the answer by using the shortcut, but my teacher wants me to get the answer using that equation. I am stuck and I got to: $-\sqrt{x}/2x^2$ by using the $\frac{f(x+h)-f(x)}{h}$.


What are the security effects of reusing a public RSA key to encrypt large data by blocks?

I'm trying to figure out a way to do public key encryption on a very large piece of data.  For this, I of course want one side to do the encrypting but is unable to decrypt the data, and the other side to be able to decrypt data.  But for RSA encryption, there's a limit to the reasonable size-performance on how big it can encrypt.   I haven't really figured out a good solution to this problem, but the simplest one that comes to mind is to just reuse the public key to encrypt the data in blocks. Of course, this would create some sort of security problems, but as of right now I still don't exactly know what kind of security problems it would cause.   Could someone explain to me what problems this simple method would cause and perhaps also tell me of a way to achieve my goal of being able to do public key encryption on a large piece of data?


I just bought a motherboard that says it supports Dual-Channel RAM. The RAM I'm looking at says it's a "Quad-Channel Kit" . Will it work with my motherboard?  EDIT: Thanks all for the replies. Here is some more info:    Here is the RAM I'm looking at:    It all looks compatible to me, I just was curious about the four channel thing.


What is the font used in Hartshorne's Algebraic Geometry book for sheaves? I originaly thought it was \mathscr as $\mathscr F$ looks very much like the symbol for a sheaf F there. But that can not be, because $\mathscr O$ looks just so different from the symbol for the structure sheaf in the cited book. There it looks closer to $\mathcal O$, though it is not quite that either.


I'm stuck on the following problem (Source: Real Analysis for Graduate Students; Exercise 2.6; ):     Suppose $\mathcal A$ is a $\sigma$-algebra with the property that whenever $A \in \mathcal A$, there exists $B, C \in \mathcal A$ with $B \cap C = \emptyset$, $B \cup C = A$, and neither $B$ nor $C$ is empty. Prove that $\mathcal A$ is uncountable.   I think there is the added assumption that this is only true for $A \in \mathcal A$ having at least two elements, so it doesn't hold for singletons and the emptyset?  I tried to show this by way of contradiction and say that $\mathcal A = \{A_k\}$ is countable, but I didn't see how this could get me to a contradiction.  The other approach I tried was to look at $X = B_1 \cup C_1$ where $B_1 \cap C_1 = \emptyset$, then look at $B_1 = B_2 \cup C_2$ where $B_2 \cap C_2 = \emptyset$ and so on. If I look at the $C_k$'s they are pairwise disjoint and I either have a finite number of them or an infinite number of them in which case I've created a countable sequence of pairwise disjoint nonempty elements of $\mathcal A$. This path looked promising, but I couldn't see what to do next. Any ideas?  As a secondary question: I think this result is supposed to be used to show that if $\mathcal A$ is a $\sigma$-algebra with infinitely many elements, then it's uncountable, but I wasn't able to show that the property mentioned above (the one I'm trying to show) was satisfied in this case.


How long does it take for a dead body to disappear?

I accidentally killed a load of people. I didn't have enough cash to revive them all, and was forced to leave a few of the corpses around the place. However, after a while, the corpses disappeared entirely, and I couldn't revive them!  How long does it take for corpses to disappear?


I have matrices for my syllabus but I don't know where they find their use. I even asked my teacher but she also has no answer. Can anyone please tell me where they are used? And please also give me an example of how they are used?


EDIT: Plenty of info out there I'll get to it before I bother anyone for more answers.


After login as a particular user, how do I login as another user?

Such a basic thing I can't find anywhere in google. I just need to re login as another user, without having to annoyingly logout. Logout closes my putty terminal, and I have to relaunch and reconnect again


can someone help me to convert the following PL SQL code into it's MSSQL equivalent? Thanks in advance.  return to_date(l_date_time, 'rrrrdddhh24miss');


I'm building a physics simulator for a graphics course, and so far I have it implementing gravitational and Coulomb forces. I want to add collisions next, but I'm not exactly sure how to go about doing it.   A quick summary of how this is working so far is: All objects are spheres of a set radius, mass and charge. The mass's and charges of the spheres are treated as point charge/mass for the calculation. Every step in time (about 1/50th of a second) the forces acting on each object are calculated in a nice big nested for loop that figures out the coloumb and gravitational force between 2 objects, for every set of 2 objects, and then they are summed together. I use this net force to determine the acceleration, and the rest is fairly obvious from there.   What I want to add in is collisions. I can deteremine pretty easily if a collision is happening (if the distance between them <= radius of one + radius of other), what I am not so certain of is how I should add in the collision force (and would need to do it component wise). I want elastic collisions, though for now I'd just be happy with getting conservation of momentum  The information I have easily available are: the velocity of each object (and I mean velocity, speed and direction), the position of each object, the mass/charge (charge obviously not needed here) and the Net force calculated so far for each object for the next step in time. I dont need exact formulas (would prefer if they arent exact), just need a nudge in the right direction.


Like Darth Vader, Asajj Ventress was often seen choking people, many times Jedi like Anakin and Obi-Wan.  Is it possible for Force-users or non-Force-users to counter or defend against a Force choke without distracting the attacker or using ysalamiri?


Syntax highlighting of single line comments ending with backslash broken

C:  #include <stdio.h>  int main(){     printf("Path to typical Windows directory: ");     // We need to escape backslashes: \     printf("C:\\Windows\\\n");     printf("Can you see it?\n");     return 0; }   C++:  #include <iostream>  int main(){     std::cout << "Path to typical Windows directory: ";     // We need to escape backslashes: \     std::cout << "C:\\Windows\\" << std::endl;     std::cout << "Can you see it?" << std::endl;     return 0; }   The syntax highlighting of single line comments of C/C++ ending with a backslash (\) is broken.  Comments ending with a backslash should continue to the following line, but as you can see it is incorrectly highlighted.  The problem is discovered from an answer to a question on . Link:


What is "the URL" that restricts the Host header?

The following quote from  assumes "the URL" comes from somewhere and uses it to restrict the Host header. Where does "the URL" come from? Is it from the first line of a HTTP request (e.g. after GET), or from the input to a web client (e.g. an argument to curl, or the input in the address bar of a web browser)? Thanks.     The Host header specifies the Internet host and port number for the   resource being requested, as obtained from the original URL:  Host = "Host" ":" host [ ":" port ]       In particular:      • If the Host header does not contain a port, the default port for the   scheme is assumed.      • If the URL contains an IP address, the Host header should contain   the same address.      • If the URL contains a hostname, the Host header must contain the   same name.      • If the URL contains a hostname, the Host header should not contain   the IP address equivalent to the URL’s hostname, because this will   break virtually hosted servers, which layer multiple virtual sites   over a single IP address.      • If the URL contains a hostname, the Host header should not contain   another alias for this hostname, because this also will break   virtually hosted servers.


Conservation of Mass during Electron - Positron Annihilation

An electron has a mass of $m_e = \; 9.1094 × 10^{-31} kg$. A positron has the same mass. So during electron positron low-energy annihilation, won't the law of conservation of mass be violated?  Note: I am a high school student interested in physics and read about electron positron annihilation in a book. So if there is a flaw in a concept behind the question, please do point it out.


How to launch program on lock and close it on unlock

Have siblings who like to "play" with my laptop by waking it from suspension and then typing random keys on the keyboard into the password field. Afterwards, they always deny it. I plan to install motion and only have it run while the computer is locked. After the computer is unlocked, the process should be killed. How would I go about launching motion when CTRL + ALT + L is pressed and kill motion when the correct password is entered?


Show that every irrational number in $\mathbb{R}$ is the limit of a   sequence of rational numbers. Every rational number in $\mathbb{R}$ is   the limit of a sequence of irrational numbers.   How can I prove this?


I remember reading a story once where we had all interbred such that there were no longer any blacks, whites, Asians, etc.  We were all 'brown'.  Somehow they 'found' 5 children that were purebred 'races', and I don't remember much else.


Music video that looks like "Where the Wild Things Are" (film)

I'm searching for a music video that has a scene exactly the same as the  film, with the boy and the monster.   It's not a song from the soundtrack!  It's just an underrated song with an awesome video.


multithreaded logging for high performance application

I have an application (server application) that needs an extensive amount of logging implemented and shouldn't be too affected performance wise by enabling logging.  The application has a thread pool of worker threads performing the work.  Originally I was going to just log on these thread pool threads, but then I'd need to lock practically the whole thread and so there goes my 'multithreaded' app.    I have been looking at better ways to log from multiple threads and I've found using a Queue or ring buffer could be an idea.  Can anybody suggest (perhaps from experience) any good ways to implement effective logging (to a file mostly) for a multithreaded application that also should stay somewhat performant?  I would like to use the Boost Logging Library.


Joint distribution function of max and min of independent, identically distributed random variables

Suppose we have independent random variables $X_1,\ldots,X_n$ with the same distribution. Let $F(\cdot)$ be the cumulative distribution of $X_i$ for all i We are interested in the cumulative distribution of (Max,Min) where $\text{Max}=\max\{X_1,\ldots,X_n\}$ and similarly for min. This is what I've worked out for far;  Let $G(x,y)$ the cumulative distribution of (Max,Min)  \begin{align} G(x,y) & = P(\text{Max}\leq x, \text{Min} \leq y) \\[8pt] & = P(\text{Max}\leq x) - P(\text{Max} \leq x, \text{Min} \gt y ) \\[8pt] & = P(X_1 \leq x,\ldots,X_N \leq x) + P(y \lt X_1 \leq x) \\[8pt] & = F^n(x) - [F(x) - F[y]]^n \end{align}  Is this correct? Thanks


Load Windows 7 OS to RAM from USB Pendrive

Look for tips on how to load the Windows 7 operating system into RAM. In a word of introduction, I will describe what I want to achieve. I would like to have a built computer without a hard drive in which the motherboard, processor and adequate amount of RAM will be installed. Components such as a keyboard, touchscreen and router will be attached to the computer. It seems that the computer will recover from the power cut. To be precise, I would like to connect the pendrive with the system to the computer, run it, wait for the system loading, and then disconnect the pendrive and get the computer working with a fully functional operating system in the RAM memory. How can I create (what programs do I need) a self-image of the system that will self-load into RAM?


Evaluate $ \int_{-\pi/2}^{\pi/2} \frac{\cos(x)}{1+e^x} dx$

$$ \int_{-\pi/2}^{\pi/2} \frac{\cos(x)}{1+e^x} dx$$  Using integration by parts   $$\int u v  = u \int v - \int u' \int v$$  with $u(x) = \cos(x)$ and $v(x) =  \frac{1}{1+e^x}$,   $$ u \int_{-\pi/2}^{\pi/2} v dx  = \left[ \cos(x) \int_{-\pi/2}^{\pi/2} \frac{1}{1+e^x} dx \right]_{-\pi/2}^{\pi/2} = \left[ \cos(x) ( x - log(1+e^x) \right]_{-\pi/2}^{\pi/2} $$  $$ \int_{-\pi/2}^{\pi/2} u' \left( \int_{-\pi/2}^{\pi/2} v dx \right) dx = \int_{-\pi/2}^{\pi/2} -\sin(x) \int_{-\pi/2}^{\pi/2} \frac{1}{1+e^x} dx $$  $$ = \int_{-\pi/2}^{\pi/2} -\sin(x) \left[ ( x - log(1+e^x) \right]_{-\pi/2}^{\pi/2} $$  Short of continuing ad nauseam, is there a better way to determine the answer (given as $1$) ?


How can I prove that $|A| + |B| = |A\cup B| + |A\cap B|$?

If $A$ and $B$ are sets then $|A| + |B| = |A\cup B| + |A\cap B|$.


Kworker, what is it and why is it hogging so much CPU?

I recently upgraded to the Kubuntu Natty Beta 1 and I've been having a lot of issues with the process kworker. At moments it uses almost half my CPU. Also, strangely enough it seems to affect my USB ports; whenever I plug in an USB drive, the process kworker goes into hyperdrive, leaving me unable to work.  I have thought about filing a bug but since I haven't even found any reasonable explanation on what kworker is I figured I should find out first.


Just because I can't find where this has been asked before, could someone explain the always-friday-in-iceland meme?


How do I replace all characters in a string for other characters?

I'll explain a bit of my project so you can get a notion of what I'm trying to accomplish. I'm making a "translator" of an invented language to english and vice versa. It consists on replacing all letters for new ones, for example:  English string: Hello world. Invented language string: Ajuuq lqyue.  I've tried a lot of options in order to get my task done, but nothing seems to work at all, and I haven't found a proper solution to my problem. I'll leave in here the options that I've already used.  string = string.replace("l", "u")   This one only worked with one case, and I've thought of assigning a different variable for each letter in order to get it, but I think it won't really work.  I used for, a dictionary but nothing seems to do what I really want.  Thanks beforehand.


Changing system partition to another hard drive

I recently bought a new 1TB hard drive (labelled D:) and cloned it with my 160GB main system hard drive (labelled C:). Now I want to replace my old 160GB hard drive (C:) with my new 1TB hard drive (D:), and then format (C:) into a regular hard drive like my 500GB (E:) drive. How can I do that?  Basically I want (D:) to replace (C:) and then format (C:). (D: is cloned with contents of C:)


Delayed eraser experiment (Kim experiment)

Will I receive an interference pattern on D0 detector   if D1, D2, D3, D4 exist in the set up of the experiment, but they are thousands of light years far? Simply, to set up the experiment so that I detect all of the signal photons on D0 before I detect any of idler photons!


I've ripped music files from my CD but they were in .wma format and cannot play on my Android phone. So that I need to re-rip them into .mp3 files.  But the ripped button is disabled in Windows Media Player and the status of the file reads Ripped tolibrary  How can I force a re-rip/rip again?


How can I disable the UITableView selection?

When you tap a row in a UITableView, the row is highlighted and selected. Is it possible to disable this so tapping a row does nothing?


SMB for FTP for file access over the internet

I am using an old computer running Ubuntu Server 18.04 as an all around server. It is hosting a Plex server, a small website and is used as a home NAS. I am using SMB shares when using it as a home NAS. If I want to access them files from outside the network what is better/more secure, do I port forward the SMB shares or do I use something like FTP or is there a better option that I don't know about. Thanks


Breaking the speed of light relative to a moving object

You can't go faster than light, and light can't be additive (if you shine a light from a spaceship, the light is not going $c$+"speed of spaceship", it's just going  like it always does).  But what happens when two spaceships, each going 75% the speed of light, are traveling directly towards each other?  Aren't the two spaceships now traveling, in reference to each other, at 150% the speed of light?


A function which is continuous in one variable and measurable in other is jointly measurable

Please help me to prove the following;  Let $ \ f:[0,1]^2\longrightarrow\mathbb{R}$ be such that: (i) $\ f(x,\cdot)$ is measurable for each fixed $x\in[0,1]$; (ii) $\ f(\cdot,y)$ is continuous for each fixed $y\in[0,1]$. Show that $\ f$ is measurable.


Difference between Mutable objects and Immutable objects

Any one please give the diff between Mutable objects and Immutable objects with example.


Where can I ask for algorithm recommendations?

I recently asked this .  Where can I ask about algorithm recommendations? Because there are two algorithms for what I'm trying to do, and both have a very high error rate, at least for my case. It seems that Stack Overflow is not the right place for algorithm recommendations.


How much work is done when pushing against a brick wall?

So this is one of the questions on my physics assessment and I would like to know how to calculate how much work is done when pushing against a brick wall.  My teacher has told me the calculation is: weight(kg)x10 (this gives me the force)x distance.   But what is the weight of and the distance of? As when you push against a brick wall the wall doesn't move and you can stop yourself from moving.  Please answer as soon as possible, also I'm kind of younger so could you explain clearly(sorry)   Emsee


I have a quick question. I am a Canadian born citizen travelling (with my Canadian passport) and I have been traveling back and forth from Canada to the US to visit my boyfriend with my longest stay in the US this year being for 34 days. My question is I am reaching the 180 day mark for the year and was wondering if the visits were counted by calendar year (January - December) or from the date of entry. I’d still like to go in November (which would use up my last 12 days) as well as in December but only for 3 weeks per time. However the December trip will put me over the 180 days for the year.  Also, is it possible if you go over the 180 day mark for a year to be barred from returning to Canada (do they care how long you were gone for)? I apologize if this seems a bit off for a question but it is something I am worried about and would like to comply with the requirements.   I do return to Canada for longer than what I was away for and have never been pulled into secondary. I have the funds to support my trips.   Whenever asked I always say the purpose of my trips is to go to Disney, since he lives in Orlando.


I made an overworld portal (Portal A) at [x:-21, z:233]. This took me to a new portal in the nether (Portal C) which as at [x:-4, z:41].  I then went to another location in the overworld and created Portal B at [x:-613, z:-373]. This is a total of around 1200 blocks away so I thought it was a safe distance. However, when I stepped through, I arrived at Portal C again.  So, I tore down Portal C and used a  to tell me where Portal B's match in the Nether should be. The calculator gave me [x:-77, z:-46], so I went there and constructed Portal D.  When I stepped through Portal D, I ended up at portal B, as I expected. So I ran back to Portal A, and stepped through it again.. only to end up at portal D in the Nether. When I stepped back through portal D, I ended up at portal B.  What's happening is this:  A -> D <-> B  Whereas what I want to happen is this:  A <-> C and B <-> D  How can I achieve this? I don't mind tearing down portals, but I'd rather avoid that as it's quite time consuming.


Best Resource to learn about internal working of ML algorithms for an absolute beginner?

My previous question was about looking for pseudocodes for Boosting algorithms like XGB, Random Forests and LGBM.  I figured it would be better if i had some resources to refer to, which would detail the internal working of such algorithms.   I feel it would help out a beginner like me in understand the 'under-the-hood' stuff.  If anyone is aware of any relevant resources, especially those which are beginner-friendly, please kindly cite them in your answers.  The answers would be helpful to other beginners too, in the future


How do I display all the characters between two specific strings?

I want to display all the characters in a file between strings "xxx" and "yyy" (the quotes are not part of the delimiters). How can I do that ? For example, if i have input "Hello world xxx this is a file yyy", the output should be " this is a file "


Can a Sorcerer protect their friend from Web by using Careful Spell?

With the metamagic "Careful Spell" does the caster protect his friend from a Web spell for its full duration or just for the first save? If the friend stays in the area or re-enters the area does he continue to automatically save against the restraining effect?


Where can I rent a decent mountain bike in Zürich?

I am going for a 4 day trip in Zürich and I would like to bike quite a lot. Though biking is quite advertised, I failed to find a decent bike rental shop in the city. Would highly appreciate some tips!


I'm trying to find two compact, nonhomeomorphic subsets of the plane, say $X$ and $Y$, such that $X \times [0,1]$ is homeomorphic to $Y \times [0,1]$. I can not think of how a homeomorphism arises when you product with the interval.


Pronoun usage - subjective /objective/possessive

The fact that John was a good student resulted in his/him having many offers for the job.   Which one should be used and why?


Show that a complex polynomial of degree $n$ doesn't have zeros in a unit ball

Let $n>1$ and $c_0>c_1>c_2>\dots >c_n>0$ and $f(z)=c_0+c_1 z+\dots + c_n z^n$. Show that this polynomial doesnt have zeros in a unit ball $B(0,1)$.  Can you give me some feedback?


When will Ubuntu GNOME 16.04 be released?

Please tell the date of release for the stable version of the GNOME flavor.


Finding the last two digits of $3^{400}$

I'm having some trouble with the following exercise:  Find the last two digits of the decimal representation of $3^{400}$.  This exercise Is under the Euler's theorem and Fermat's little theorem section of the worksheet so I think that we are supposed to use those to solve this. My problem is that this is the first time I'm seeing an exercise of this kind and I don't know how to proceed. Can someone give me a tip on how to do this or show me how it's done?


youtube-dl - Download playlists into corresponding directory, and number the videos in the playlist

I want to download two series of playlists from this channel:   The channel has a "Biology" series of playlists and a "Biochemistry (by chapters)" series of playlists. Essentially, I want to make two directories "Biology" and "Biochemistry" that contain subdirectories that bear the name of the playlists in the series with the corresponding name on the channel. Additionally, I would like for the videos to be in order, so each video in a playlist has its index before the title and URL section of the file name. How can I accomplish this?  Thanks in advance.


Evaluate $\int_0^{\infty} \frac{\log(x)dx}{x^2+a^2}$ using contour integration

This question is Exercise 10 of Chapter 3 of Stein and Shakarchi's Complex Analysis.  Show that if $a>0$, then $$\int_0^{\infty}  \frac{\log(x)dx}{x^2+a^2}=\frac{\pi \log(a)}{2a}.$$  The hint is to integrate over the boundary of the domain $\{z: \epsilon<|z|<R, \Im(z)>0\}.$ I'm not sure what to do with the integral over the outer arc.


Why does Android require porting to each device, unlike Windows? Or rather, why isn't there a way to simply download a setup program for pure AOSP and install it in any device?  I already read , and it says that Android requires specific porting to each device configuration (hardware setup) to even work at all. But my question is, why was Android designed in such a way that requires modification of its base source to suit the device hardware (adding drivers, etc)? Why doesn't it support installation of original AOSP from Google with basic drivers on any hardware, which can then be enhanced to work better with device-specific drivers from the manufacturer?  In contrast, Windows has been designed such that the same setup program can install it on any variant of a hardware configuration. You can come up with a configuration that no one has ever come up with before, and Windows will most likely install and run on it just fine. The chances of a complete failure to run Windows on a particular configuration are extremely low and likely only because of niche hardware.  Even if the correct drivers can't be found for a device, Windows will attempt to find the closest match for the device and attempt to run the device in a basic mode anyway - and the user can then upgrade to the correct driver after Windows installation is complete. And the chances of certain devices failing completely may be higher but still very low, and such failures can usually be resolved by installing the missing drivers.  By contrast, Android doesn't even have a concept of "driver installation", but drivers are added at the source level in a process called porting, which leads to many different ROM variants, including stock ROMs from device manufacturers, and vanilla ports like CyanogenMod, MUIU, etc. This brings the problem that if no one is porting Android for your device, you don't have a ROM to install on it (except the stock ROM it came with) - unless you build one yourself.  I understand that Android is fundamentally very different from Windows and even Linux (which it's based on), and I don't mean to compare apples with oranges. I merely want to understand why such a paradigm shift in device support was necessary for Android.


Track Windows Login/Logoff events in Java

I want to fetch WIndows Login/Logoff events through Java  System name Username Timestamp Login/Logoff/Lock/Unlock   I already got the below event codes that windows genearte  4608  STARTUP 4609  SHUTDOWN 4624  LOGON 4634  LOGOFF 4800  WORKSTATION_LOCKED  4801  WORKSTATION_UNLOCKED   WHich library should I use in order to track all these?


I've encountered the phrases "lying through his teeth" and "lying". Both have been used in similar contexts to (at least what I understand) as similar definitions. What is the meaning of the idiom of "to lie through one's teeth" and how is this different from just regular lying? Does lying through your teeth mean you lie while smiling?   , but not a duplicate. The answer there only tells the difference between "lying through his teeth vs lying in his teeth". My question is unique because I am asking about the difference in the usage of lying through his teeth vs lying in similar context, while the related question only addresses the origin of the phrase.


How to make a series of step-by-step figures has a fixed position on every beamer frame?

Some frames have texts describing steps on the associated figure. I want to make the figures still fixed in position no matter there is a description text.  \documentclass{beamer} \setbeamertemplate{navigation symbols}{}  \usepackage{pst-eucl} \psset{PointName=none,PointSymbol=none} \newpsstyle{helper}{linewidth=.5\pslinewidth,linecolor=red,arcsep=-1}  \begin{document} \begin{frame}{Problem No. 2} \only<1>{Draw the $x$ axis.} \only<2>{Draw a line at angle $45^\circ$.} \only<3>{Draw an arc of radius 2 intersecting both lines.} \begin{pspicture}[showgrid=false](-5,-1)(7,5)     \pnodes(0,0){O}(5,0){X}(4;30){A'}     % x-axis     \only<1->     {         \psline(X)         \uput[-135](O){$O$}         \uput[-45](X){$X$}     }     % vector A     \only<2-4>{\psline[style=helper](A')}     \pstInterLC[Radius=\pstDistVal{2}]{O}{X}{O}{}{I1}{I2}     \pstInterLC[Radius=\pstDistVal{2}]{O}{A'}{O}{}{J1}{J2}     \only<3-4>{\pstArcOAB[style=helper]{O}{I2}{J2}}     \only<4-5>{\psline{->}(O)(J2)}     \only<5->{\uput[90](J2){$A$}} \end{pspicture} \end{frame} \end{document}   As you can see from the following animation, the current result shows the figures move up and down. How to fix it?


How to redirect the output of a command to an already existing file without deleting its contents?

I am making a backup of some files and am creating a checksum file, checksums.txt, to later check the integrity of my data. However pasting each checksum manually into the file is inconvenient since my backup consists of hundreds of files, so asking around I got the suggestion to simplify the process by redirecting the output to the checksum file:  $ md5sum file > checksums.txt   or  $ sha512sum file > checksums.txt   However doing this replaces the contents of the checksums.txt file with the checksum of, in this example, the file file; I would like, instead, to append the checksum of file to checksums.txt without deleting its contents. So my question is: how do I do this?  Just one more thing. Since I am a basic user, try (only if possible) to make easy-to-follow suggestions.


If bacterial plasmid DNA is methylated then how do we digest it using restriction enzyme in cloning experiments?

So, I was reading about how bacteria protects its own DNA by methylation against restriction enzyme. But if the plasmid DNA is also methylated then we can't cut plasmid using restriction enzyme for doing cloning. And if we are isolating this plasmid from Methylase deficient strain so that the plasmid is not methylated, won't it would be digested by the bacterial restriction enzyme. Do we isolate these plasmid from a strain that is also unable to produce restriction enzyme ?


Uniformly continuous functions on the interval

Let $f:[1,\infty)\to\mathbb R$ be uniformly continuous.   Prove $\exists$ $M > 0$ s.t $$\frac{\big|f(x)\big|}{x} \leq M, \hspace{11pt} \forall x\in[1,\infty)$$


I have got a SharePoint 2010 website with a WebPart-page and a few WebParts on it.  One of the WebParts displays a list/a view of a list.  The views of that list have been updated due to business needs - but the view in the WebPart on the WebPart-page is not updated.    If I edit "Modify Shared Web Part" (the one with the list / list view),  the "Selected view" is set to "<Current view>".  My question is now: Which view of the list is the "<Current view>"? Is it any view of the list at all - or has the WebPart some kind of its own view to that list?


SO i got regex to make first letter capital but i need now a regex to make the last letter caps, ive tried google searches and came up with nothing  Example of what im talking about  razor123  james333  firefire32923932  laser   Need them to turn into   razoR123  jameS333  firefirE32923932  laseR


Question whether we need transit visas for stopover in Istanbul with no exit from airport

I am a Cameroonian national with the UN Laissez-Passer traveling with my family of 4 (wife and 3 kids with Cameroon passports) from Phnom Penh, Cambodia, to my final destination, Yaounde, Cameroon and transitting through Istanbul on a Turkish Airlines flight. Do we need transit visas?  Best regards,


In many situations (problems as well as solutions) I encounter the complex number $i$ which many times is defined as $i^2=-1$ instead of $i=\sqrt{-1}$, since it is "more preferred". Does anyone know why? Is it because there are two solutions to the equation $x^2+a=0, \ \ a>0$?


How do I upgrade my Ubuntu 10.04 LTS to 12.04 LTS? My update manager tells me my Ubuntu release is not supported anymore.   I did pressed Alt+F2 and typed update-manager-d but still had no luck. I could really use some help with this issue. Thanks in advance!


I need to animate sliding gate following the path in two points where the wheels touch the rail. The rail is not straight.


Can I roast peanuts in convection microwave?

I found a small bag of raw un-roasted peanuts, around 200 grams, in my cupboard. Any idea how can I roast these peanuts in my convection microwave oven? Would appreciate if some one can add suggestions :-)


I have ruby and homebrew running for a while and I'm starting to play with Bash. I have encountered a problem with my PATH variable as echo'd:  /opt/local/bin:/opt/local/sbin:/opt/local/bin:/opt/local/sbin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/X11/bin??n’export   As you can see, there is both redundancy and junk at the end int he form of illegal characters (causing a host of other issues). I can change the PATH with   export PATH="/opt/local/bin:/opt/local/sbin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/X11/bin"   which does indeed return the desired PATH when echo'd:  /opt/local/bin:/opt/local/sbin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/X11/bin   But I can't figure out for the life of me how to save the PATH so that it doesn't reset on reopening. I don't need to add paths. I just want to make this the new value of that variable. Please, how can I make this change permanent?


What is the difference in the meaning of following sentences?        If Tom were to do my homework, I would watch a film.   If Tom did my homework, I would watch a film.      I know that both of these questions express unlikely or imagined condition. I'm not sure but I think. There's is difference in the meaning between two sentences. Here is my opinion:   In the first sentence, the speaker thinks that  it's impossible for Tom to do his homework or Tom isn't able to do his homework or Tom is a baby. So, the speaker is  imagining a impossible thing. In the second sentence, the speaker thinks it's a bit possible for Tom to do his homework.Tom is the speaker's friend and Tom is able to his homework but he isn't willing to do. So, the speaker is expressing his imagination and saying "If Tom did my homework I'd watch a film".   For more clearification of my openion i would say: I'm not sure but I'm just guessing the possible meaning of those sentences like this:  both sentences are all about imagination but first sentence indicates impossible imagination and second expresses unlikely but expected imagination. AM i correct?  Am I correct in my opinion ? If not, what is the correct meaning?    Please explain it in details.


Can't install package bcmwl-kernel-source package

Need to get my wireless network adapter working on Ubuntu 14.1, but when trying to install the required package bcmwl-kernel-source, the "apt-get install bcmwl-kernel-source" installation command hangs on asking repetitively for a Ubuntu cdrom installation disk mount even after one is provided. Here is the exact terminal output that I am receiving:  $ sudo apt-get install bcmwl-kernel-source Reading package lists... Done Building dependency tree        Reading state information... Done The following NEW packages will be installed:   bcmwl-kernel-source dkms 0 upgraded, 2 newly installed, 0 to remove and 12 not upgraded. Need to get 0 B/1,576 kB of archives. After this operation, 8,386 kB of additional disk space will be used. Do you want to continue? [Y/n] y Media change: please insert the disc labeled  'Ubuntu 14.10 _Utopic Unicorn_ - Release amd64 (20141022.1)' in the drive '/media/cdrom/' and press enter  Media change: please insert the disc labeled  'Ubuntu 14.10 _Utopic Unicorn_ - Release amd64 (20141022.1)' in the drive '/media/cdrom/' and press enter   I tried mounting my installation cdrom as requested, but after pressing enter it seems that the installation unmounts the cdrom and loops back to request that I mount it again. Can't get out of this loop. Why does the installation of this package reqest an installation cd? Other packages install fine without requesting this.


If $f'$ is increasing and $f(0)=0$, then $f(x)/x$ is increasing

Let $a>0$ and $f:[0,a] \to \mathbb{R}$ continuous function that is twice differentiable on $(0,a).$ Also $f(0)=0$ and $f'$ is strictly increasing function on $(0,a).$   I have to show that the function $g$ defined as $$g(x) = \frac{f(x)}{x}$$ is strictly increasing on $(0,a].$    Progress: I computed $g'$ and got $g'(x) = \frac{f'(x)x-f(x)}{x^2}.$ I have to show that $g'(x)>0 \ \ \forall x \in (0,a].$  Since $x^2$ is always positive for $x \in (0,a]$ I have to show that $f'(x)x-f(x) >0 \ \ \forall x \in (0,a].$ I know both terms are positive, but I don't know how to show that $f'(x)x>f(x) \ \ \forall x \in (0,a].$


Keeping GUIs responsive during long-running tasks

Keeping the GUI responsive while the application does some CPU-heavy processing is one of the challenges of effective GUI programming.   of how to do this in wxPython. To summarize, there are 3 ways:   Use threads Use wxYield Chunk the work and do it in the IDLE event handler   Which method have you found to be the most effective ? Techniques from other frameworks (like Qt, GTK or Windows API) are also welcome.


How do I create all permutations with three lists? Python


I want to Parse DateTime that contains time zone EST, PST etc

I have searched on internet but unable to find this answer for this specific question.  This question is different from others because we don't know whether parsing string contains EST, PST at compile time. I am parsing RSS Feed's for a lot of sites and expecting pub date of some RSS in this format I want to parse this kind of format  Wed, 02 Oct 2002 08:00:00 EST   The problem is that i can not parse EST, PST etc when they come on run time.  The only solution left is to use a switch  like this  so when PST comes at the end of string, i use forexample   string TimeZone="";  string LastThreeChar=raw.substring(raw.length-4,3);  switch(LastTHreeChar)   {      case 'PST':      TimeZone= "Pacific Standard Time";      break;    }   TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById(TimeZone);   Kindly help me.


I would like to encrypt my hard drive so that it requires a password to access it. However features like BitLocker in Windows will only work under Windows, and cannot be accessed from another OS such as  Ubuntu or Mac OS X.  How can I create a cross-platform encrypted file system?


Upgrading straight handlebars to drop handlebars

I have a two-and-a-half year old  (with a road-bike-like frame and thin tires; it's somewhere in the loosely-defined "hybrid" range) that I use to commute to work, twenty-five miles round-trip, once or twice a week. The bike has straight handlebars, and having gotten used to the idea of commuting via bike, I'm interested in upgrading to drop handlebars. It looks like I'd need new break/shift levers to go with the handlebars; the whole upgrade looks like it'd run a couple hundred dollars. This is a sizable fraction of the original cost of the bike, which leads me to wonder if I'm better off saving my money for a new bike that's a little better adapted to my use.  Is upgrading my bike's handlebars a reasonable investment?


Why the second references author name become '-' when the author having 2 books but different title?

@article{1testing,   title={Title 1},   author={Zanthony1, Anthony2 and Anthony3},   journal={Journal 1},   volume={24},   number={2},   pages={258--300},   year={1992},   publisher={Springer} }  @article{2testing,   title={Title 2},   author={Zanthony1, Anthony2 and Anthony3},   journal={Journal 2},   volume={24},   number={2},   pages={200--264},   year={1992},   publisher={Springer} }   Both books by same author but different title of the book.    using:  \usepackage[backend=biber, style=authoryear, citestyle=authoryear]{biblatex}     \cite{1testing}          \cite{2testing}


Font for the normal sheaf N_D of a divisor D

What kind of package / font should I use to get the following version of the capital N in math mode?    This is the standard notation for the normal sheaf associated to the divisor D.


C++ - Undefined reference to all the methods of all the classes

i'm getting "undefined reference to ... " errors. Though, i can't find any error in the code.     main.cpp:11: undefined reference to `Grid::Grid(int, int)'   This happens for all the methods of the 2 classes, so i'm going to write here just one class, feel free to ask for the other one too (The other one is a pretty long code).  main.cpp:  #include <iostream> #include "Grid.h"  using namespace std;  int main() {     Grid<int> a(5, 5);      return 0; }   Grid.h:  #ifndef GRID_H #define GRID_H  #include <vector>  using namespace std;  template <class T> class Grid{ private:     int W, H;     vector<vector<T>> grid;     Grid(); public:     Grid(int w, int h);      bool SetContent(int x, int y, T content);     T GetContent(int x, int y); };  #endif /* GRID_H */   Grid.cpp:  #include "Grid.h" #include <vector>  using namespace std;  template <class T>  Grid<T>::Grid(){}  template <class T> Grid<T>::Grid(int w, int h){     W = w;     H = h;     grid.resize(h);     for(int y = 0; y < h; y++)         grid[y].resize(w); }  template <class T> bool Grid<T>::SetContent(int x, int y, T content){     if(x > 0 && x < W && y > 0 && y < H){         grid[x][y] = content;         return true;     }     return false; }  template <class T> T Grid<T>::GetContent(int x, int y){     if(x > 0 && x < W && y > 0 && y < H){         return grid[x][y];     }     return grid[x][y]; }   This is the compiler command, if necessary (I guess it's a compiling error):     g++ -o dist/Debug/MinGW-Windows/pacman build/Debug/MinGW-Windows/Grid.o build/Debug/MinGW-Windows/Vector2.o build/Debug/MinGW-Windows/WinAPI_Console.o build/Debug/MinGW-Windows/main.o  -static-libgcc -static-libstdc++   If you need more informations, just ask, i'll wait for replies here.


We are facing an issue with iPhone due to activation lock.  The device was used by an ex-employee of the company.  The email address that was used for this device no longer exists because it looks like 'employeename@company.com'. So we can't use the forgot password or reset password options.  Is there any solution to use this device?


How could Sauron physically acquire the ring?

In The Lord of the Rings Sauron is essentially a spirit which has taken the form of the great eye. If the fellowship had failed, how would the forces of Mordor actually give the ring to him? In the books things are a little different, but in the films Saruman claims "He cannot yet take physical form". How would the forces of evil have given him the ring?


Is backlinking to yourself in violation of Google's guidelines?

Many people say that setting up your own backlinks is not good. Is this true?  Nobody can expect backlinks to be built by other sites naturally unless they are social networking sites or some good topic. Even the top news sources won't have backlinks naturally.  Google doesn't know these, so can we build backlinks ourself?


Is ';;' a chaining operator in Unix? How does it work?

My teacher lists the following chaining operators:  & && ( ) ; ;; | || new line   How is ;; a chaining operator and what does it do?


Javascript function with methods via prototype

What I would like to have is something like this:  var fnc = new constructor(); // --> function()... fnc(); // --> Running main function fnc.method(); // --> Running method   So that one could create new fnc instances, while having the methods in the constructors prototype. However, I don't seem to be able to have result of the constructor as a function, as regardless of the return clause, it seems to become a object, resulting to ..  Uncaught TypeError: Property 'fnc' of object [object Object] is not a function    :(  Edit: Added example code. So what I'm thinking is along these lines.  var constructor = function() { return function() { console.log('Running main function.') }; }; constructor.prototype.method = function() { console.log('Running method.'); }  var fnc = new constructor();  console.log('constructor: ', constructor); console.log('fnc:         ', fnc); console.log('fnc.method:  ', typeof $.method); console.log(''); fnc(); fnc.method();   In this case, one gets the...   Uncaught TypeError: Object function () { console.log('Running main function.') } has no method 'method'    ...error as the function provided by the constructor is different than the constructor itself, on which prototype chain is tacked on. Just can't seem to wrap my head around this. Did one version with jQuery like initialization, which did the trick alright but I later on found out that it ended up doing it through the empty function prototype, meaning every function got the methods.


Prove that the set $\left\{ x, Ax, \dots, A^{k-1} x \right\}$ is linearly independent

Problem: Let $A\in M_{n\times n}(\mathbb R)\,$ be a matrix and suppose that a positive number $k\,$ exists such that $A^k = 0\,$ and $A^{k-1} \neq 0$. Suppose that $x=\left[ \begin{matrix} x_1 \\ \vdots \\ x_n \end{matrix} \right]$ is a vector in $\mathbb{R^n}$ such that $A^{k-1} x \neq 0$. Prove that the $k\,$ vectors $\,x,Ax,\dots,A^{k-1}x\,$  are linearly independent.     My attempt: Suppose $x + Ax + \dots + A^{k-1}x = 0$. Multiply both sides with $A^{k-1}$. Then we have $A^{k-1}x + A^k (x + Ax + \dots + A^{k-2}x) = 0 \Leftrightarrow A^{k-1}x = 0 \Leftrightarrow x = 0$   which implies $x + Ax + \dots + A^{k-1}x\,$ is linear independent.    This problem looks quite easy but I want my proof to be checked. Is it correct?


Puzzle: Find largest rectangle (maximal rectangle problem)

What's the most efficient algorithm to find the rectangle with the largest area which will fit in the empty space?  Let's say the screen looks like this ('#' represents filled area):  .................... ..............###### ##.................. .................### .................### #####............... #####............... #####...............   A probable solution is:  .................... ..............###### ##...++++++++++++... .....++++++++++++### .....++++++++++++### #####++++++++++++... #####++++++++++++... #####++++++++++++...   Normally I'd enjoy figuring out a solution. Although this time I'd like to avoid wasting time fumbling around on my own since this has a practical use for a project I'm working on. Is there a well-known solution?  Shog9 wrote:     Is your input an array (as implied by the other responses), or a list of occlusions in the form of arbitrarily sized, positioned rectangles (as might be the case in a windowing system when dealing with window positions)?   Yes, I have a structure which keeps track of a set of windows placed on the screen. I also have a grid which keeps track of all the areas between each edge, whether they are empty or filled, and the pixel position of their left or top edge. I think there is some modified form which would take advantage of this property. Do you know of any?


How do I get Photoshop to support RAWs from FZ2000?

I previously thought that RAW format is just a one format and any Ps version works with it. But now I know that different RAW formats from newer cameras are not supported by the Ps version that exists at the time the cameras is released. Anyway, I found a  which what ACR and LR versions support this specific camera's RW2 files are mentioned. (It says ACR 9.8 & LR 6.8 support RW2s from the FZ2000, right?) So, how can I know about what Photoshop version that supports FZ2000's RW2s? And, is the ACR (in this case, version 9.8) integrated in it?; do I need to get the ACR (9.8) separately?..


Hi. I've compiled a Persian language beamer file by both luapersian and persian babel package using LuaLaTex, and in both I've the same problem in pdf bookmark as shown in the figure (some strange characters are shown instead of correct characters).


I did a Ph.D. in the area of engineering mathematics. The thesis used some of the concepts from Mathematics, such as basic probability and statistics (Bachelor/Master level), calculus (Bachelor/Master level), optimization (Bachelor/Master level), etc. Mostly, the works applied the existing mathematical tools to some physical problems instead of developing methods. However, it was possible to publish some of the works in good applied mathematics/mechanics journals. All my undergraduate and graduate degrees were obtained from the mathematics department of a reputed institution in India. Being a student of Mathematics background, I now want to learn and work in the area of applied numerical analysis/scientific computation. I am currently working as a postdoc researcher in a reputed university in the USA, but that also in the area of engineering mathematics. Is it possible to get a postdoc opportunity in the area of applied numerical analysis/scientific computation or other related areas where mathematical techniques are developed rather than using it? In that case, how to convince the supervisor that I am capable of learning the research topic and work on it when I have no such publication record yet? Please give your suggestion on how to proceed.


How to disable screensaver in Ubuntu 16.04

The All Setting Brightness & lock do not stop the screensaver


If a,b and c are positive real numbers then find the minimum value of $\frac{a}{b}+\frac{b}{c}+\frac{c}{a}$   Logically,a=b=c=1 but mathematically, I have tried to use some AM-GM, GM-HM inequalities but I am unable to solve this.


Ubuntu Software (Software Center) Crash - Ubuntu 16.04

Ubuntu Software instantly crashes as I try to open it. Tried to access from terminal and gives the following error:  (ubuntu-software:5523): Gs-WARNING **: failed to open plugin /usr/lib/gs-plugins-9/libgs_plugin_xdg_app_reviews.so: /usr/lib/gs-plugins-9/libgs_plugin_xdg_app_reviews.so: cannot open shared object file: No such file or directory


I have Ubuntu on my MacBook 2007 with a Spanish keyboard, on MacOS the @-sign was typed using Alt (Option) + 2, but on Ubuntu I have no idea. I have to copy and paste it every time. How do I type an at sign?


If a polynomial $f(X,Y)$ vanishes on all $(x,y)$, can we conclude $f(X,Y)=0$?

Let $k$ be an infinite field and $f(X,Y) \in k[X,Y]$ be a polynomial with two variables. If $f(X,Y)$ vanishes on all points $(x,y) \in k^2$, i.e.,  $$f(x,y) = 0, \forall (x,y) \in k^2$$ can we conclude that $f(X,Y) = 0$?  Put another way, let $k$ be an infinite field, and let $$k[X,Y]^* := \{f : k^2 \longrightarrow k, (x,y) \mapsto f(x,y) \mid f(X,Y) \in k[X,Y]\}$$ denote the ring of polynomial functions. Then do we have $k[X,Y] \cong k[X,Y]^*$?


Ubuntu: "Booting in insecure mode" with SecureBoot enabled

I have just installed Ubuntu 15.10, after having been with 16.04 LTS for some time to try it out. While I was using 16.04, I tried to install Nvidia Drivers and got told that I needed to disable SecureBoot for that, so I provided a password and on the next reboot some software asked for it. However, my BIOS settings still showed SecureBoot to be enabled, and I could still see how if I tried to boot from anything that wasn't signed, it would refuse to do so.  However, when I reinstalled Ubuntu 15.10 (completely deleting everything related to 16.04, including grub in the EFI partition), every time I boot I get a Booting in insecure mode message.  I have checked everything, and both: Windows and the BIOS setting report SecureBoot to be enabled


Prove that if $a+b+c$ divides $abc$, then $a+b+c$ must be composite.

I have seen another post for this same question but it never got an answer. Since I am fairly new, I can't comment on other's posts, therefore I am creating a new one. The question states:  If a, b, and c are positive integers, prove that if $(a + b + c) | (a*b*c)$, then $a+b+c$ is composite.  I do not really know how to approach this.  The link to the post with the same question is:


Show if/when the answer was seen by the author of the question

The following seems very useful to me:  A visual marking that tells when (or just if) an answer was seen by the author of the question.  Arguments:   People that land on an unanswered question but with all present answers seen knows he can still contribute It nicely replaces eventual comments like Could you please detail your answer?, letting the author of the answer know he waits for more.   Edit: Concrete example I asked something. Someone gave a brief answer with the exact solution. I can't figure it out right away, so I go document some more, making sure that I did my best to understand on my own, without poking the guy on each one of my lacunas. It seems fair to me that the author of the question to do his part of the work. Meanwhile, though, the author of the answer knows that I seen his answer but I didn't yet accepted it, so he might choose to detail his answer a little more.  Edit2: The fact that it's implicit (as opposed to comments - that are explicit) silently brings some additional info you may opt to use.


Time not sync in Ubuntu and Windows 10 dual boot

I have setup my computer to have a dual boot for Ubuntu 20.04 and Windows 10. My time in Ubuntu is OK ,but when I go to Windows it changes. How can I fix my clock in Windows?


Prove the triangle inequality on the sphere $S^2$ in $\mathbb{R}^3$.

Let $S^2 = \{x=(x_1,x_2,x_3) \in \mathbb{R}^3: x_1^2+x_2^2+x_3^2=1\}$ be the unit sphere in $\mathbb{R}^3$ and $d_i(x,y) = \cos^{-1}(x\cdot y)$, where $x\cdot y$ is the usual dot product of vectors in $\mathbb{R}^3$, be the intrinsic metric on $S^2$ (the length of the great circle arc joining $x$ and $y$). Prove that $d_i$ satisfies the triangle inequality, $d_i(x,z) \le d_i(x,y)+d_i(y,z)$.  It has been suggested that I use the Gram Matrix $$A=\left( \begin{array}{ccccc} x\cdot x &\ & x\cdot y &\ & x\cdot z \\ y\cdot x &\ & y\cdot y &\ & y\cdot z \\ z\cdot x &\ & z\cdot y &\ & z\cdot z  \end{array} \right)$$ and the fact that $det(A) \ge 0$ and somehow reduce the desired inequality, $\cos^{-1}(x\cdot z) \le \cos^{-1}(x\cdot y)+\cos^{-1}(y\cdot z)$, to $det(A)\ge 0$.   I'm just missing out on how to do that. Thank you.


How could one find $$\sum_{n=0}^{\infty}{\frac{\cos(nx)}{n!}}\,?$$   I tried to use Fourier series and integrals depending on a parameter to reduce the problem to a differential equation, but that didn't work.


Intuition behind expected value formula?

I just learned the expected value formula for a positive random variable: $E[X] = \int_0^\infty P(X>x)dx$.  I can follow the proof but I'm a little unclear as to what the intuition behind this formula is. Can someone formulate it in a more intuitive manner?


Fixing "This branch is X commits behind Y." through the GitHub web interface

After forking a GitHub repo, some commits were pushed to the forked repo, and as a result GitHub indicates that  "This branch is X commits behind Y.":    How can I fix it through the GitHub web interface?     I know how to do it through git: :  git remote add upstream https://github/upstream/repo.git git pull --rebase upstream master git push --force-with-lease origin master


Android Canvas 2D Game: Supporting multiple screen sizes/resolutions

I'm planning to develop a 2D game for android devices by using simple Canvas Surfaces (I know that OpenGL might be more efficient - but Canvas should definitely be enough for my type of game).   I'm currently researching on how I should handle different screen sizes/resolutions/ratios of the different android devices. I don't think it's a big deal to scale a bitmap if the screen size is just 920x512 instead of 1920x1024 (for example) - but what about completely different ratios? Like 1200x800px screens? I would have to stretch these bitmaps, or just make more objects visible from my game, which would normally be hidden in shorter screens.   I didn't really find anything useful on my research (mainly some discussions about Canvas VS OpenGL...) - so I'm giving it a try here. What's the best/most common used technique to adjust a game to different screen sizes? Other than just putting black borders along my game, if the width/height is too large.


How can I download the Unreal 4 mannequin into Blender with materials?

I found this model over here  But the model is imported without its materials. How can I import it into Blender with its proper materials so it looks as it does in UE4?


Typesetting a function defined by case analysis

Can any one suggess me the code to write this equation in LaTeX.


I am making a dropper mini game on my Minecraft server and I am using a button to give a player the diamond. I need a command block that sees if they have a diamond already so they don't get two diamonds.


alias to take a parameter and exit after execution

In my ~/.bashrc, I have an alias called yy as follows  alias yy="youtube-dl -f 'bestvideo[ext=mp4]+bestaudio[ext=m4a]'"   But I often run it this way  yy <url list> && exit   I would like to make it simpler and convert it to a simple alias called yye.  yye <url list>   Would anyone please advise how to carry out this alias definition?


Canceled Mac OS Big Sur update still takes 8 GB of space

I recently downloaded the installer for Mac OS Big Sur, to update my MBP from Catalina. After the download finished, and before I clicked "Install", I had about 35 GB of space left on my machine. However, a little after clicking continue, I clicked cancel (the round "X" button). And now the installer will not accept clicking install again, saying it required 8 more GB's. I checked my storage again, and it shows about 26 GB left. So over 8 GB taken like this! I assume these are temp install files for Big Sur, and if so, how can I remove them and resume installation of Big Sur?


I’m thinking about taking a 70-year old math professor as my PhD advisor, in a US school. I like his teaching and research. If I don’t choose him, I would probably have to switch fields, which I can do with some pain, since I have not specialized deeply yet. My main concerns are:   As he is far more likely than a young supervisor to pass away suddenly due to his age, how should I best plan for this scenario? What will happen to me if it happens? He is also far more likely to retire than a young supervisor – could his retirement (in the unspecified future) cause problems for my future career in academia, with respect to references and networking?   Related:


Does the function level influence the region of memory allocation of a variable from main

I want to create a function that allocates space for a pointer (from main) to point at. If having the memory allocated in a function, will this memory still be available and safe to use after the that function returns? Here is an example of code:  int foo(int **number) {     *number = (int*)malloc(sizeof(int)); }  int main() {     int *myVar;     foo(&myVar); }   So we see that the memory is allocated in the process of execution of the foo() function.   Will the memory for the myVar variable be allocated in "space" of the foo() function, or in "space" of the main()?   After finishing the execution of the foo(), its memory is being cleared. Will myVar point to the same "space"? Will it be safe to use?   Could it be overwritten by other function, or variable declarations?


Which experiment can differentiate a statistical mixture from a superposition state?

I am in trouble with polarization and entanglement. Let's consider three cases : Case 1) : Statistical mixture of $|H\rangle$ and $|V\rangle$ polarized photons Case 2) : Photons in a superposition state $1/\sqrt{2}(|H\rangle+|V\rangle)$ Case 3) : Photons which are entangled with twin ones in $1/\sqrt{2}(|H,H\rangle+|V,V\rangle)$ state Which experiments can be conducted to differentiate the case  statistical mixture from the case  superposition state ?   Which experiments can be conducted to differentiate the case  statistical mixture from the case  entangled photons in superposition state ?   Using a $45^\circ$ polarizer I think you can differentiate case 1/case 2 but not case 1/case 3 I don't know how to differentiate case 1/case 3 except maybe using quantic tomography and Wigner function. Is it true ? Is there any other simpler way ? Thanks a lot for your answer and sorry for this maybe dummy question...


Is there anything that is totally random?

When I say totally random, I mean absolutely random, not pseudorandom. If I want to say "totally random" numbers such as 1,26,17,4,1 and 27, although I see them to be totally random, they aren't. These are numbers that I think are influenced by my childhood, ideology and everything that I've seen. So, what do you think? Is there anything completely random?


Array operations: -X[array_name] result?

#include <iostream> int main() {   using namespace std;   int arr[] = {1,2,3,4,5}; //initialization    cout << -3[arr]; //line A   return 0; }   How is the output of line A -4? Thanks in advance.


Color custom list items based on Status using OOTB

I want to change color of the list item row based on the field value without any code.  For Example : I do have custom list with fields Title, Status(Pending,Running,Completed). I want to color list items based on color like If Status is    Pending than row color should be yellow Running than row color should be light green  Completed than row color should be dark green.   Can somebody please let me know the easy step to do that without code using just SharePoint designer or any other out of the box solution?  Thanks in advance


BLUE SCREEN after logging on a freshly installed bone 16.04

I reinstalled UBUNTU 16.04 via the official iso burned to DVD on my Lenovo laptop (I am not simple boot) The installation ends as planned, I launch ubuntu, until then by problem, I make 5 updates via Ubuntu softawre. I restart the computer, I enter password to access my Ubuntu session and there: bulk pixels, then BLUE screen! My mouse disappears, appears, in short, I can not acceder my session and the terminal does not work.  I run the trial version of Ubuntu in live cd to have access to BOOT REPAIR as indicated in this forum:   I install it as expected, I restart the computer and I see that the Grub is displayed, so far no. But at the level of the blue screen it is the same ... I can not access my Ubuntu session.  Also, I tried to reinstalled 16.04 a second time. during the installation I got this message:  The microcode of this system has started the installer in UEFI mode but there seem to be other operating systems that use the BIOS compatibility mode. If you continue the installation in UEFI mode, it may be difficult to restart these operating systems at a later time. If you want to retain the ability to restart other installed systems; you should NOT (in uppercase in the text) force the installation into UEFI mode.   Anyone know more?  LAM


How to determine where a non-linear PDE is elliptic, hyperbolic, or parabolic?

I'm trying to understand the classification of PDEs into the categories elliptic, hyperbolic, and parabolic. Frustratingly, most of the discussions I've found are "definition by examples.''   I think I more or less understand this classification in the case of quasi-linear second-order PDE, which is what's described on Wikipedia. I want to understand what makes a non-linear second-order PDE elliptic, parabolic, hyperbolic. MathWorld says something vague about this: "A non-linear PDE is elliptic at a solution u if its linearization is elliptic at u"   (). What is meant by "linearization" here?   To be concrete, I want to be able to answer a question like the following: where (in the $x-y$ plane) is the non-linear second-order PDE   $$ a \partial_x^2 u +  b \partial_x \partial_y u + c \partial_y^2 u +  d (\partial_x u)^2 + e \partial_y u = 0$$  elliptic, hyperbolic, or parabolic (here all coefficients depend on $x,y,$ and $u$)? This doesn't really fit the form of any discussions I've found, so I'm not sure how to make sense of it.   EDIT: I am aware of the question at , but I believe that the answer there really only addresses linear PDE.   Several people have marked this question as already being answered at that link, but I don't see how. I would be much obliged if you could sketch a procedure for classifying the qualitative behavior for a non-linear example operator of the form I describe.


"UnboundLocalError: local variable 'x' referenced before assignment" But it's a global variable

I am making a Python Discord bot with discord.py. I am relatively new to Python but have about eight years of experience with other languages. My problem is that I get the UnboundLocalError: local variable 'prefix' referenced before assignment even though I have defined prefix as a global variable. (I am using Python 3.6.8)  I have tried defining the variables outside the on_ready function, but I get the same result.  import discord;  client = discord.Client();  @client.event async def on_ready():   print('Loading complete!')   ...   global prefix   prefix = 'hello world'  @client.event async def on_message(message):    if message.author == client.user:     return    messageContents = message.content.lower()   splitMessage = messageContents.split()   try:     splitMessage[0] = splitMessage[0].upper()lower()   except:     return   if splitMessage[0]==prefix:     ...     (later in that if statement and a few nested ones)     prefix = newPref  client.run('token')   I expected the output would be that it runs the code within the if statement, but instead I get the error UnboundLocalError: local variable 'prefix' referenced before assignment and no code is run.  The only thing I can think of being the problem is prefix = newpref. I tried:  global prefix prefix = newpref   But then I got the error: SyntaxError: name 'prefix' is used prior to global declaration and the bot didn't start at all. What should I do?


Whats the size limit of a person to be able to fly on a specific flight?

My mother is flying with United Airlines, and she is about 400 pounds, but looks maybe 350 or so. She will be taking flights:  Airbus A320: seat 7C Canadair Regional jet 700: seat 18B Bombardier Q400: seat 7b Boeing 737-900: seat 8D  I haven't flown for awhile and I just want to make sure my mother isn't embarrassed if she was to go to the airport, and they told her she needed to buy a second seat, because in reality I wouldn't want anyone to go through that because well its embarrassing. So I guess my big question is: Do you think she would fit fine, maybe not comfortable but fine, or do you think she might have some issues?


How to resolve "Attempt to invoke OnclickListener() on a null object listener" in android?

I am getting this error - java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at com.example.meetup.HomeActivity.onOptionsItemSelected(HomeActivity.java:100)   @Override public boolean onOptionsItemSelected(@NonNull MenuItem item) {     switch (item.getItemId()) {         case R.id.Settings_btn:             return true;         case R.id.Logout_btn:             Dialog dialog = new Dialog(HomeActivity.this, R.style.Dialog);              dialog.setContentView(R.layout.dialog_layout);             Button yes, no;             yes = findViewById(R.id.yesBtn);             no = findViewById(R.id.noBtn);              yes.setOnClickListener(new View.OnClickListener() {           //**ERROR**                 @Override                 public void onClick(View v) {                     FirebaseAuth.getInstance().signOut();                     startActivity(new Intent(HomeActivity.this, LoginActivity.class));                 }             });             no.setOnClickListener(new View.OnClickListener() {                 @Override                 public void onClick(View v) {                     dialog.dismiss();                 }             });             dialog.show();             return true;     }     return super.onOptionsItemSelected(item); }


I'm not yet 18, but I have been studying business for quite a while, paper trading, investments, etc. at this point, I'd like to try my hand at building some credit and making some money, but I am still a minor, which makes this quite difficult. My parents have bad credit, and though it hasn't influenced my own business education, it means I can't loan on their names, and I can't back loans on their assets.  While I am also interested in what trading and investment options exist for minors, first things first, how can I take out a loan or line of credit as a minor without being weighed down by my parents' credit history?


Get SQL parent key column name and table name of a child

So I know what the all the child foreign keys are by looking   SELECT *  FROM INFORMATION_SCHEMA.STATISTICS;   However I now need to get what the parents of the foreign keys are called and what tables they are stored in. So I need the SQL to return a table which stores the following data:  | Child Table | Child Column | Parent Table     | Parent Column | ================================================================= | #_article   | category     | #_category_store | id            |   I have tried using this:  SELECT * FROM information_schema.REFERENTIAL_CONSTRAINTS;   However that only gives me the child table and parent table. I cant then find the parent column.


Why do we use 'did' with questions using the simple past tense?

Where did you go last night?   Where went you last night?   Is there a reason we say the first of the previous two sentences as opposed to the last one?   I know the second sentence is ungrammatical. I was just wondering if there was more of a rule than just "asking questions in the simple past needs 'did' + verb in the present tense."


Is a Weierstrass curve a topological manifold?

Obviously a Weierstrass curve is not a smooth manifold, but it seems like a Weierstrass curve should be a topological manifold (which I now see is a suspicion supported by  post), since it is a continuous image of the real line.  That said, I am a particularly concerned about the locally Euclidean requirement.  I know that a Weiestrass curve generally has a non-integer Hausdorff dimension (see )--does that impact this requirement?


Using the context of the 'this' keyword with jQuery

As a jQuery neophyte I am somewhat confused by the different contexts in which the this keyword is used.  Sometimes it refers to a DOM element e.g. this.id and sometimes it refers to a jQuery object e.g. $(this).val().   is helpful but I would like to know how you would explain the difference to a novice.  Is the difference strictly a jQuery issue or common to all Javascript?  Thanks for all the responses so far - great stuff, I will pick an answer tomorrow.  Here is another blog post I subsequently came across that was also helpful:  .


I have a HashMap HashMap<String, List<OtherModel>> - I need to sort by the field of the first List<OtherModel> element, have any ideas?) I have incorrect code for example:  public static HashMap<String, List<AsoInfoModel>> sortAsoByValue(HashMap<String, List<AsoInfoModel>> items) {         List<Map.Entry<String, List<AsoInfoModel>>> list = new LinkedList<>(items.entrySet());         list.stream().sorted(Comparator.comparing(Map.Entry::getValue::AsoInfoModel::position, Comparator.naturalOrder());          HashMap<String, List<AsoInfoModel>> temp = new LinkedHashMap<>();         for (Map.Entry<String, List<AsoInfoModel>> aa : list) {             temp.put(aa.getKey(), aa.getValue());         }         return temp;     }


Justify each step in the following proof of Proposition 3.9 (a). I like to know if I'm in the right track and I'm also missing a few of them

Proposition 3.9(a): If a ray r emanating from an exterior point of triangle ABC intersects side AB at a point between A and B, then r also intersects side AC or side BC.  proof. (a) Let r= array XD with X an exterior point of triangle ABC and D ∈ AB such that A ∗ D ∗ B (see first figure on next page).  (b) Line XD intersects either AC or BC. Without loss of generality, say line XD intersects AC at point E.  (c) Note E =/ A.  (d.5) Either E = C or A ∗ E ∗ C.  (f) Note C and E are on the same side of line AB  (g) Observe X and one vertex of the triangle must be on opposite sides of the line  through the other two vertices. Without loss of generality, say C and X are on  opposite sides of line AB.  (h) Exactly one of D ∗ E ∗ X, E ∗ D ∗ X, or D ∗ X ∗ E hold.  (i) Suppose E ∗ X ∗ D holds.  (j) Thus, E and X are on the same side of line AB  (K) Thus, C and X are on the same side of line AB  (l) This is a contradiction.  (m) So D ∗ E ∗ X or E ∗ D ∗ X hold.  (n) Therefore, r = ray XD intersects either AC or BC.  My solutions  (a) by Hypothesis  (b) Pasch’s theorem guarantees that the line containing the ray r (that is, the line XD in the picture) intersects either AC or BC.  Assume, for example, that it intersects AC at point E. We want to show that E is in the ray XD, that is, that ∼ E ∗ X ∗ D. Since every point between D and E is interior to ∆ABC but X is not, then, as we were hoping for, ∼ E ∗ X ∗ D.  (c) there exist a point E not on the line A, D, B (Proposition 2.3)  (d.5)  if E=C, then E lies on line AC   (f) by definition Line AB and C,E point not on line AB, C, E are on the same side of line AB if C=E or if CE  does not intersect line AB  (g) If C is on the same side of line AB as X, then C is on the opposite side from B, which means that line AB intersects BC and does not intersect AC; similarly if X is on the same side of AB as C, then  AB intersects XD and does not intersect AC (separation axiom).  (h)we know by betweenness axion 3 that exactly one of the relations Exactly one of  D ∗ E ∗ X, E ∗ D ∗ X, or D ∗ X ∗ E hold. (I) Suppose E ∗ X ∗ D holds RAA hypothesis  (j) by definition AB is a line and E, X points not on line AB. E, X are on the same side of line AB if E=X or if XE does not intersect line AB.  (k) by definition AB is a line and C, X points not on line AB. C, X are on the same side of line AB if C=X or if XC does not intersect line AB.  (l) This is a contradiction (no idea what to write)  (m) by B-3 given any 3 distinct collinear points D,E,X exactly one is between the other two. So D ∗ E ∗ X or E ∗ D ∗ X hold.  (n) I had no idea what to write


I am trying to center my chapters/sections/subsections.  I have used the following:  \newcommand{\cchapter}[1]{\chapter[#1]{\centering #1}} \newcommand{\ssection}[1]{\section[#1]{\centering #1}} \newcommand{\ssubsection}[1]{\subsection[#1]{\centering #1}}   This seems to work for chapter, but not for section and subsection. What is wrong?


What is the standard (or best supported) big number (arbitrary precision) library for Lua?

I'm working with large numbers that I can't have rounded off.  Using Lua's standard math library, there seem to be no convenient way to preserve precision past some internal limit.  I also see there are several libraries that can be loaded to work with big numbers:      (might be identical to #2)  (but I can't find any source)   Further, there are  in C that could be called from Lua, if the bindings where established.  Have you had any experience with one or more of these libraries?


Choosing the best model from among different "best" models

How do you choose a model from among different models chosen by different methods (e.g. backwards or forwards selection)?  Also what is a parsimonious model?


True or false? $(\mathbb{Z} \setminus \left\{0\right\}, \cdot)$ is a   group   I need to know this because it's from an old exam and it might be asked in my exam, or a task like that.  I'm not entirely sure but I would say that the statement is false. The associative property will work, there will be an identity element too. But we will fail when we are looking for inverse elements as these would require rational numbers.  (So even if we had something like $(\mathbb{Z}, \cdot)$, it wouldn't be a group still.)    I hope I did it alright?


How to find and move files between certain dates?

I have two repertories named 'test1' and 'test2' with multiples files with .jpg or .mp3 extensions. I want to find and move all files between 22-juin-2016 and 21-September-2018 to a new folder called 'data'. How would I be able to do this with one line of command ? Thank you very much for you help !


How to fix error, File ended while scanning use of \@cline error

hi I have this code   \begin{table}[h] \centering \caption{My caption} \label{my-label} \begin{tabular}{c|c|c|c|c|c|c|} \cline{2-7}  & Windows Forms & PDF & Windows Forms/GDI+ & Windows Media Player & Direct3D & \textbf{WPF} \\ \hline \multicolumn{1}{|c|}{Grafické rozhranie} & X &  &  &  &  & \textbf{X} \\ \hline \multicolumn{1}{|c|}{Dokumenty na obrazovke} & X &  &  &  &  & \textbf{X} \\ \hline \multicolumn{1}{|c|}{Dokumenty s pevným,formátom} &  & X &  &  &  & \textbf{X} \\ \hline \multicolumn{1}{|c|}{Obrázky} &  &  & X &  &  & \textbf{X} \\ \hline \multicolumn{1}{|c|}{Video a zvuk} &  &  &  & X &  & \textbf{X} \\ \hline \multicolumn{1}{|c|}{2D grafika} &  &  & X &  &  & \textbf{X} \\ \hline \multicolumn{1}{|c|}{3D grafika} &  &  &  &  & X & \textbf{X} \\ \hline \end{tabular} \end{table}`   and I have this error      File ended while scanning use of \@cline   Can you help me pls?


Definite and indefinite articles when referring to generic abstract objects

My classmate wrote a text about zoos in general, and the word "zoos" in plural form is mentioned many times in it. Later in the text he uses singular form "zoo" two times with indefinite articles, and both times he still refers to an abstract zoo, not to specific one. He wrote:  The place where animals can obtain shelter is a zoo. You can take the kids to a zoo.  I'm having trouble in figuring out whether it is correct or not. I think that he should have used a definite article the second time, because he already mentioned a singular abstract zoo, but he argues that he refers to "two different singular abstract zoos". So which article should be used in a second sentence?


Can anyone explain how the LIKE operator is implemented in current database systems (e.g. MySQL or Postgres)? or point me to some references that explain it?  The naive approach would be to inspect each record, executing a regular expression or partial string match on the field of interest, but I have a feeling (hope) that these systems do something smarter.


$$\sum_{k=0}^{\infty} \frac{(-1)^k(2k+1)}{(2k+1)^2 + 1} = \frac{\pi}{4}\mathrm{sech}(\frac{\pi}{2})$$ I tried to consider breaking up the alternating factor of the series by decomposing it into 2 separate series - one adding the even terms and the other subtracting the odd terms, but then I couldn’t figure out where to go. My attempt, letting $S$ be the sum of interest. $$S = \sum_{k=0}^{\infty} \frac{(2(2k)+1)}{(2(2k)+1)^2 + 1} -   \frac{(2(2k+1)+1)}{(2(2k+1)+1)^2 + 1}$$ Don’t know what else to do.


Bash script for loop which the last statement is first calculated

I wrote this bash script  x=64 y=1 ans=$((x-y)) z=`expr $ans` for i in {1..$z} do      echo $i done   Actually, I would like to print i values from 1 to 63, 63 which is first  obtained from the above addition. But it just prints {1..63}  Can someone please help me. Thanks in advance.


What is the word for accepting help from someone else, not by merit, but because they know you?

So, say that someone is about to start at a new school, and your sister says "Oh, I aced that class! Let me introduce you to the teacher; maybe he'll give you less homework/give you more opportunities."  For some reason the word "hedonism" is rattling around in my brain, though I know that's not it. Also maybe it's the opposite of "altruism"? I'm having an off day and can't for the life of me figure it out.


Is it unlikely to get the same number of heads/tails?

A question in probability by a non-mathematician:  A fair coin is tossed $2N$ times. Is it unlikely that we get exactly $N$ heads and $N$ tails?  From one side, this must be the most likely result! But intuitively, if someone reports to me that they threw 2,000,000 coins and got exactly 1,000,000 heads and 1,000,000 tails I would be a little suspicious.  If this really is suspicious, how does it compare to biased results? Obviously, 2,000,000 heads is a much more suspicious result. But, for what value of $K$ is $N+K$ heads and $N-K$ tails as suspicious as $N$ heads and $N$ tails?  Equations are very welcome, but please try to provide some aid in understanding them.  ADDED: Henning Makholm's answer helped me understand better what I want to ask: I always assume a fair coin and would like to compare the probability of the split N/N with the probability of getting either more than more than N+K or less than N-K heads. By ncmathsadist's answer , the probability for the N/N split goes like 1 over the square root of N.  What about the probability to get more than either more than N+K or less than N-K heads? For what value of K (approximately) does it equal to 1/sqrt(n pi)?  CLARIFICATION: If f(N) is the probability to get an N/N split in 2N tosses of a fair coin, and g(N,K) is the probability to get more that N+K heads or less than N-K heads in 2N tosses of a fair coin, then I am asking for a formula which, given N, approximates the values of K for each f(N) is closest to g(N,K). This is a formula that takes N and returns K so we can call it h(N)=K. Which kind of function is h? My guess from a little experementing with the online software in Brian M. Scott's answer is that the function h is apporximately the SQRT function, multiplied by some constant, or something like that.


I have seen many videos that make Ubuntu faster, but these methods only make desktop performance faster.  I am looking to make my computer boot faster. Is their anything I can do to make Ubuntu boot significantly faster?


Is there a formula for $1+\sqrt{2}+\sqrt{3}+\cdots+\sqrt{N}$?

Is there a known formula to the sum $$1+\sqrt{2}+\sqrt{3}+\cdots+\sqrt{N}$$ where $N$ is some natural number? Thanks


Unable to uninstall Universal Apps through PowerShell

I was in the process of uninstalling all the Universal Apps from a new Windows 10 installation when I hit a roadblock.  It's not the first time I do this and it always goes well. However, this time, whenever I write in PowerShell Get-AppxPackage -allusers | Remove-AppxPackage or something more specific like Get-AppxPackage -allusers *windowscalculator* | Remove-AppxPackage I get the following message:     Remove-AppxPackage : Deployment failed with HRESULT: 0x80073CFA, Removal failed. Please contact your software vendor. (Exception from HRESULT: 0x80073CFA)   error 0x80070032: AppX Deployment Remove operation on package Microsoft.WindowsCalculator_10.1605.1582.0_x64__8wekyb3d8bbwe from: C:\Program   Files\WindowsApps\Microsoft.WindowsCalculator_10.1605.1582.0_x64__8wekyb3d8bbwe failed.      This app is part of Windows and cannot be uninstalled on a per-user basis. An administrator can attempt   to remove the app from the computer using Turn Windows Features on or off. However, it may not be possible to uninstall the app.      NOTE: For additional information, look for [ActivityId] 75c5fc31-fb20-0001-77fd-c57520fbd101 in the Event Log or use the command line Get-AppxLog -ActivityID   75c5fc31-fb20-0001-77fd-c57520fbd101      At line:1 char:49      + Get-appxpackage -allusers *windowscalculator* | Remove-AppxPackage   +                                                ~~~~~~~~~~~~~~~~~~       + CategoryInfo          : WriteError: (Microsoft.Windo...__8wekyb3d8bbwe:String) [Remove-AppxPackage], IOException       + FullyQualifiedErrorId : DeploymentError,Microsoft.Windows.Appx.PackageManager.Commands.RemoveAppxPackageCommand   I'm getting this message for every single app I try to uninstall, including those I know are perfectly uninstallable like the calculator or image viewer, which has never happened before. Powershell is running elevated and everything else works and seems normal. Is there something I can do besides reinstalling Windows?


Read whole Strings from WebSocket Stream in C#

I am pretty new to C#.  In Java, we can read the whole String from an InputStream of a WebSocket.  For example:   dis = new DataInputStream(clientSocket.getInputStream()); String command = dis.readUTF();   and so on...  Is it possible to do the same thing in C#, because the only possible way I found so far is to read bytes?  Byte[] bytes = new Byte[client.Available]; stream.Read(bytes, 0, bytes.Length);   If there is no workaround, and we can only read single bytes in C#, how can I determine if the user have pressed the ENTER button (it would mean that the command is finished, and I can process it on the server-side)?


Python to regex to match ansible yaml in output

I'm trying to match this output from ansible ping module output:  srv1 | SUCCESS => {     "changed": false,     "ping": "pong" } srv2 | SUCCESS => {     "changed": false,     "ping": "pong" }   as well as this output from ansible setup module output:  srv1 | SUCCESS => { "ansible_facts": {     "ansible_all_ipv4_addresses": [         "192.168.50.100"     ],     "ansible_all_ipv6_addresses": [         "fe80::a00:27ff:fead:7504"     ],     "ansible_apparmor": {         "status": "disabled"     },     "ansible_architecture": "x86_64", ...a lot of lines } srv2 | SUCCESS => { "ansible_facts": {     "ansible_all_ipv4_addresses": [         "192.168.51.101"     ],     "ansible_all_ipv6_addresses": [         "fe80::a00:27ff:fe98:b137"     ],     "ansible_apparmor": {         "status": "disabled"     },     "ansible_architecture": "x86_64", ...a lot of lines }   I'd like to put everything between { .. } for specific host into matched variable, so later I can it using yaml.load.  I tried:  regex = r'(\w+)\s\|\s(\w+)\s=>\s(\{\n\s+"\w+":\s\w+,\n\s+"\w+":\s"\w+"\n\})' o = re.findall(regex,output,re.MULTILINE) for host in o:     yml = yaml.load(host[2])   This works for first output, but not for second. So I tried to generalize it:  regex = r'(\w+)\s\|\s(\w+)\s=>\s(\{.*\})' o = re.findall(regex,output,re.DOTALL) for host in o:     yml = yaml.load(host[2])   But this will match everything between starting { and last }.  What am I doing wrong?  Thanx for help


How can I circumvent regional restrictions in Google's Play Store?

I'm travelling to country X. I want to install an application which isn't available in my country, but is available in country X; but I prefer to download and install it in advance, while the data connection is still cheap.  Unfortunately, the Play Stores does not allow me to install this app. Is there any way to circumvent this limitation?


What's the deal with the 18ga wire in a light fixture?

I always read "rule #1: never use less than 14GA wire on a 15A breaker, and never use less than 12GA wire on a 20A breaker". The idea being that if the circuit gets to the max current allowed by the breaker, too small of wire can get too hot.  So recently I installed a direct-wire light fixture, and attached to the light and switch on the fixture where they wanted me to connect power were 18GA wires. So, excited about my new fixture, I connected my 14GA from the wall to the 18GA wires in the fixture, buttoned it all up, enjoyed my new light, but now am wondering "what was I supposed to do to not violate rule #1?".  It is "ok" for the wire to potentially get hot as long as it's in a metal fixture or something (vs in the drywall)? Or is it "ok" for the wire to get hot because it is onl 10" (presumably not?)? What gives??


Say I have a component and child as below:  Component  <aura:attribute name="acc" type="Account"/> <aura:handler name="change" value="{!v.acc}" action="{!c.valueChanged}" />  <c:myChild theAccount="{!v.acc}"/>   Component Controller  valueChanged: function(component, event,helper){      console.log('I have changed'); }   Child Component       <lightning:input aura:id="bAddress" name="bAddress" label="Address"     type="String" onchange="{!c.validateFields}" value="{!v.paymentProfile.Billing_Street__c}" required="true"/>   Child Controller  validateFields: function(component, event,helper){    //..Do something on input change... }  workAroundForChange: function(component, event,helper){     var updatedAcc = component.get("v.theAccount");     component.set("v.theAccount",updatedAcc); }   When data is entered in the field on the child component, the Account sObject is updated on the child and the value is captured. However the change event for the parent sObject attribute does not fire  A workaround is to explicitly call the workAroundForChange function when I am done with data entry then this fires the change on the parent   Is it expected that changes to fields on the attribute sObject will not fire the change event and the entire attribute needs to be updated in order to fire the change event?


Cannot vote to close immediately after edit

If I edit a question and then click the "close" link, it doesn't work. Nothing appears on the screen and I'm forced to reload the page before the link works.  A  covers similar ground (except my edit wasn't inline), however this was apparently fixed.  (I've tagged as  as this is the only site I have the reputation to reproduce the issue on.)


Will links to images be kept permanently when added to a comment and nothing else?

I assume, that Stack Exchange have some clean-up subsystem, which deletes all "abandoned" images (stored at i.stack.imgur.com), that is, all of them, that were initially uploaded, but no post is actually having link to them. Am I right?  If such subsystem is implemented and is doing its job on regular basis, then what about following scenario:   Start a new question or answer, anywhere. Hit button and upload an image. Copy generated image's URL  to clipboard. Close tab and drop editing post. Go to question on answer, you actually planned to reply. Post a comment to it and paste copied image's URL from clipboard to comment's body.   Will uploaded image, with URL pasted only to comment, be kept permanent? Does clean-up subsystem (if exitst) take care of checking for image's URLs in comments as well?


How to calculate $\int_0^\infty \frac{dx}{1+x^6}$

Whenever I tried to do, it failed. Is there anyone to help? $$\int_0^\infty \frac{dx}{1+x^6}$$


So let's say this is inside a .ini file:  [general] Something = 1 Somethingelse = 5  Inside the form are 3 things: 2 textboxes and one button. When i open the form it should load the ini file and make textbox1 to be equal to Something (1 in the example) and Textbox2 should be equal to Somethingelse (which is 5) And when i click the button it should save the changes (so if i changed Textbox1 to "2", it should change "something = 1" to "something = 2" inside the .ini file). I'm sorry for my bad english, Linuxfreak23


Possibility of sql injection using check boxes?

On a form that I made I check a lot of checkbooks and set values accordingly. For example, if checkbox1 is check I set $somevalue equal to Yes, else it is equal to No. I later than call $somevalue in an sql query.   Is this secure? I know you're never supposed to trust user input. I am parsing my input boxes with mysqli_escape_string and checking if drop down boxes contain values I expect. I'm just not positive if I have to do anything extra for my check boxes.


Why does this code throw an error when trying to create a Person account?

Code  trigger CreatePerson on Contact (before insert) {     RecordType personAccountRecordType =  [SELECT Id FROM RecordType WHERE Name = 'Person Account' and SObjectType = 'Account'];      Map<Contact, Account> accounts = new Map<Contact, Account>();    for(Contact record: Trigger.new) {        if(record.AccountId == null) {            Account newPersonAccount = new Account();            newPersonAccount.FirstName = record.FirstName;            newPersonAccount.LastName = record.LastName;            newPersonAccount.RecordType = personAccountRecordType;             accounts.put(record, newPersonAccount);        }    }     insert accounts.values();     for(Contact record: Trigger.new) {        if(record.AccountId == null) {            record.AccountId = accounts.get(record).Id;        }    } }   Error  Validation Errors While Saving Record(s) There were custom validation error(s) encountered while saving the affected record(s). The first validation error encountered was "Can not select a person account".   How can I associate the recently created Person account with the Contact?


If a superconductor has zero resistance, does it have infinite amperage?

If amps = volts / ohms, and ohms is 0, then what is x volts / 0 ohms?


Why won't you get electrocuted with a car battery unless you touch ground and positive?

First, if you have a better suggestion for title I'm really opened to suggestions, but it is the best I came up with.  If I touch an electric line and the earth, I will get electrocuted.  However, if I touch the positive of a car battery, people told me the same thing won't happen...why is it?  It seems I need to touch the battery positive and the battery ground.