I am mounting an ISO file, and looking at . They use the command:  $ mount -o loop disk1.iso /mnt/disk   I'm trying to understand the use of -o loop. I have two questions:   When I look at the long man page for mount, it takes time to find that -o option. If I do man mount | grep "-o" I get an error, and when I look in the file I do not find any info that "loop" is a command text for option -o. Where is that documented? Also, what is the "loop device" concept for mounting?


Is my induction on euler's formula sufficient?

$n-m+l=2$, where n=#vertices, m=#edges, l=#faces. I've been asked to demonstrate an intuitive, inductive proof (whatever the hell that means). Anyway so I've shown it's true for a tree, where necessarily $m \leq n-1$, and also for when $m=n$. Am I done, or do I need to show it also for when $m \geq n+1$?


Wireless not working on Kubuntu 14.04 Qualcomm Atheros AR9485

I'm a newbie on Linux stuff and maybe the solution to my problem is obvious, but I need your help.  I decided to install Kubuntu 14.04 on my laptop (HP pavilion g6-2330sf) and the installation worked perfectly, but even if my Ethernet connection works, the wireless network refuses to be enabled.   So I spent a couple of hours trying to install drivers, NetworkManager etc... but nothing works, or should I say I can't make it work.  When typing the following command in the console $ sudo lshw -C network I get the following output:  *-network     description: Ethernet interface     product: RTL8101E/RTL8102E PCI Express Fast Ethernet controller     vendor: Realtek Semiconductor Co., Ltd.     physical id: 0     bus info: pci@0000:06:00.0     logical name: eth0     version: 05     serial: 74:46:a0:85:dd:93     size: 100Mbits/s     capacity: 100Mbits/s     width: 64 bits     clock: 33MHz     capabilities: pm msi pciexpress msix vpd bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd autonegotiation     configuration: autonegotiation=on broadcast=yes driver=r8169 driverversion=2.3LK-NAPI duplex=full firmware=rtl_nic/rtl8105e-1.fw ip=************** (knowingly hidden) latency=0 link=yes multicast=yes port=MII speed=100Mbits/s     resources: irq:46 ioport:2000(size=256) memory:f0204000_f0204fff memory:f0200000-f0203fff  *-network UNCLAIMED     description: Network controller     product: AR9485 Wireless Network Adapter     vendor: Qualcomm Atheros     physical id: 0     bus info: pci@0000:07:00.0     version: 01     width:64 bits     clock: 33MHz     capabilities: pm msi pciexpress bus_master cap_list     configuration: latency=0     resources: memory: f0100000-f017ffff memory:f0500000-f050ffff   Furthermore when using the command nmcli nm I get the following output:  RUNNING               STATE                 WIFI-HARDWARE   WIFI        WWAN-HARDWARE   WWAN running               connected             enabled         disabled    enabled         disabled   I already read the following Questions:        Could someone help me activate the Wireless network?


do...while scoping issue when initializing variables inside of body

Was having some fun with prompt, parseInt and do...while and just stumbled upon the following:  do {     let length = prompt('Enter a number between 8 and 128 (inclusive) for your length.');     length = parseInt(length, 10); } while (length < 8 || length > 128);   Every time I would use the Chrome Developer tools to inspect the value of length during the while execution, I would see a value of 0. I thought there was something up with the radix I had chosen for parseInt but that was not the case.  I noticed that VS Code was complaining that the let length was not being used anywhere. That was odd. Once I removed the variables outside of the loop and declared as separate string and number fields instead, (i.e., let lengthPrompt and let length), everything worked out:  let lengthPrompt; let length;  do {   lengthPrompt = prompt('Length?');   length = parseInt(lengthPrompt, 10); } while (length < 8 || length > 128);   Is this an issue with scope or some other weird JS specific thing I am unaware of.


Is there a version of Windows OS that will allow a bootable disc beyond 2 TB capacity?

I have a shiny new 5TB WD Black and was hoping to use it as the OS System disc and for a fair number of audio production programs, Workstations, samplers, synthesizers and such. Moving from a 2TB. The new drive loses nearly 3 TB as "unallocated space" if run direct from the Win7 program disc. I reset the drive, initialized it in GPT, got back all 5 TB but can't put the OS there. Do any newer versions allow this or do I go backwards to a 4 year old 2 TB that's in the habit of crashing to bluescreen at least daily and use the new one for all programs but windows? (I'm backing the old drive up using Acronis in total as I type, (tired of rebooting ). Win 10 upgrades are free right now...will this change allow me to increase the storage on my system while using a new drive for the system? Old format has 2TB OS + programs, 3TB full of samples, 2 x 3TB as RAID backup system, too many usb drives to list when I need to empty stuff out......Thank in advance!


When the root URL of a domain doesn't have a specific site, how should visitors be directed to language folders?

My question is not technical (how to do it using X technology), it's about choosing proper approach that is good for SEO.  Description  Let's say I have a website example.com. It's a multilingual site, but there is no default language at root level. Instead of that I'd like to redirect to proper subdirectory based on http_accept_language (or any other condition, whatever) to keep things consistent. Condition is unimportant right now, but let's make it easier with example:  example.com     # redirects to … example.com/es  # … /es if spanish is accepted language example.com/da  # … /es if danish is accepted language example.com/en  # … /en otherwise   They're actually the same websites, with translated content so if example.com/en/items/1 exists, also /es/items/1 and /da/items/1 exist. Of course all pages have alternate hreflang links etc.  Question  Is it good design? Can you tell me why if not? And how should it be done?


Commenting on locked questions requires 1 reputation?

On locked questions and answers (), the "add comment" button is disabled. Makes sense, since commenting is disabled on locked posts. However, it indicates a requirement of 1 reputation to be able to comment:      Since 1 reputation does not allow you to comment a locked post, can this be removed?


Why does this date parsing javascript return an array with NaN?

I am parsing a string for use in a Date object, and I have this following code that doesn't perform how I expected: const dob = "10-10-2010"   dob.split("-").map(parseInt)  What I expected was a return value of [10, 10, 2010] but instead I get an array with [10, NaN, NaN] What am I doing wrong? Am I using .map incorrectly, or parseInt? Why is one of the numbers correct, but not the other two?


Why can't I put children in my Falkreath house?

I got my Falkreath house, but it says I own no homes in my game stats. Also, I can't adopt a child. Do I need both child's beds and chest before I can adopt one? What's up with this?


Son: Dad, where do Transformers come from?   Me: The planet of Cybertron.   Son: Who made the Transformers?   Me: Transformers make each other. Remember how Wheeljack and Ratchet made the Dinobots?   Son: But who made the first Transformer?   Me: ...


Proof $X\backslash\bigcap \limits_{i\in\Lambda} A_i = \bigcup\limits_{i\in\Lambda} (X\backslash A_i)$

Let $X$ be a universe. Let $\{A_i\}_{i\in\Lambda}$ be a family of sets in $X$, where $\Lambda$ is a set of index.  I want to prove:  $$X\backslash\bigcap \limits_{i\in\Lambda} A_i = \bigcup\limits_{i\in\Lambda} (X\backslash A_i)$$    How do I prove this? It looks like a generalised de-morgans laws, but I don't understand how I can work with these without operators in and out of the iterated intersection/unions.


$m,n>1$ are relatively prime integers , then are there at-least four idempotent (w.r.t. multiplication) elements in $\mathbb Z_{mn}$ ?

If $m,n>1$ are integers such that $g.c.d.(m,n)=1$ then is it true that there are at-least four elements in $\mathbb Z_{mn}$ such that $x^2=x$ ( i.e. idempotent ) ?


Resources to understand why dependence is a problem

For many statistical procedures, it seems the observations must be independent. For example the observations within each group in a two-sample t-test must be independent for the standard error/P-value to be accurately computed. Likewise, the observations of an independent variable in linear regression must also be independent. But I cannot understand why dependence will cause incorrect standard error/P-values.  and unfortunately didn't understand the answer. This time round I'm hoping someone can point me in the direction of resources that clearly explain why dependence a problem and that also demonstrate it being a problem. Are there any books/videos/PDFs/blog posts out there that achieve this? I'm particularly interested in resources that visualise why dependence a problem.


Is there an algorithm to decide if a symlink loops?

Unix systems usually just error out if they are confronted with a path that contains a symlink loop or just too many symlinks, because they have a limit to the number of symlinks they will traverse in one path lookup. But is there a way to actually decide if a given path resolves to something or contains a loop, even if it contains more links than a unix is willing to follow? Or is this a formally undecidable problem? And if it can be decided, can it be decided in a reasonable amount of time/memory (e.g. without having to visit all files on a filesystem)?  Some examples:  a/b/c/d where a/b is a symlink to ../e and e is a symlink to f and f is a symlink to a/b  a/b/c/d where a/b/c is a symlink to ../c  a/b/c/d where a/b/c is a symlink to ../c/d  a/b/c/d where a/b/c is a symlink to /a/b/e where a/b/e is a symlink to /a/b/f where a/b/f is a symlink to /a/b/g   Edit:  To clarify, I am not asking about finding loops in the file system, I am asking about a decision algorithm that decides of a given path whether it resolves to a definite file/directory or whether it does not resolve at all. For example in the following system, there is a loop, but the given path still resolves fine:  / -- a -- b where b is a symlink to /a   This directory tree clearly has a cycle, but the path a/b/b/b/b/b still resolves fine to /a.


So I have this class and struct: class ISDFParams { public:     virtual ~ISDFParams() = default;     Vector3 point; };  struct SDFSphereParams : public ISDFParams { public:     float radius; };  I use it later like this SDFSphereParams p; p.radius = 4;  GetDensityData(p);  In GetDensityData(ISDFParams sdfParams) I do SDFSphereParams* _params = (SDFSphereParams*)&params;  The problem is when I print _params->radius its anything else but 4. What am I doing wrong? P.S. I know the example is a bit pointless, but the original code is rather long so I cut down it my problem.


Well I have a simple 2D game where all positions are defined by and X and Y coordinate.  There are objects moving at a constant velocity. And a turret fires a bullet at the X and Y coordinates of the object. By the time the bullet goes to the desired area, the object has already moved.  So i need to adjust the X and Y target positions for the turret to shoot at taking into account the bullet speed and object speed.  Here's an image showing the problem.


resume: Present Perfect or Past Perfect?

I'm creating my resume, and I have to write about my education.  from 2007 until 2012 - I was a student (I'm not any more). Now I have to write that in sentence that has meaning.  1.  I had been studying economics from 2007 until 2012.  2.  I have been studying economics from 2007 until 2012.  Also, I want to stress this, that's why I'd like to use 'Continuous', but which one?


How to move, resize or remove KDE widgets since Plasma 5.5.5 (xenial)

Until Plasma 5.4.2 (wily) widgets could be unlocked and showed a side menu when hovering over them with the mouse. The side menu allowed moving, resizing and removing the widget. With Plasma 5.5.5 (xenial) the side menu does not appear anymore.


Let $p$ be an odd prime and $\omega$ be a primitive $p$th root of unity. The question is to prove that:  $$(1-\omega)(1-\omega^2) \cdots (1-\omega^{p-1})=p$$    What I have done so far is:  I can see that this is true for $p=3$  $$(1-\omega)(1-\omega^2)=1-(\omega+\omega^2)+w^3=1-(-1)+1=3=p$$  I am not able to prove this in general....  $$(1-\omega)(1-\omega^2) \cdots (1-\omega^{p-1})=1-(\omega+\omega^2+\cdots+\omega^{p-1})+????+\omega^{\frac{p(p-1)}{2}}$$  I do not have any idea what that $????$ could be but all I can say is:   $(\omega+\omega^2+\cdots +\omega^{p-1})=-1$ $\omega^{\frac{p(p-1)}{2}}=1$   So, $(1-\omega)(1-\omega^2)\cdots (1-\omega^{p-1})=3+????$  I am not able to do more than this.  There could be some (hard) way of doing it by hand multiplying all those things but I am looking for a more theoretical idea.  Please help me to clear this up.


Realtek RTL8723BE wifi card not detected and no internet via Wifi or Wired connection

When I am installing Ubuntu I cannot connect to my wifi network. It keeps trying and finally fails.  After installation I am not able to use internet either via WLan or even if I directly attach the LAN cord of my router to my laptop.  What is going wrong and how do I fix it ?  dkms status output :  rtlwifi-new 0.10 4.4.0-21-generic, x86_x64: installed


No folder triangles on desktop only - OS Sierra

This just happened tonight.  Without warning and for no reason at all, the little triangle next to the folders on the desktop just disappeared.  So I cannot easily see the contents of the folders, I have to double click them.   But it's only on the desktop, all other folders have the triangles.   I only have one display.  I checked all the settings I could and did not see anything.  I don't even know what those triangles are called.


You can’t buy your kids clever. What’s more, if they’re merely above average, by sending them to some hideous Holland Park hothouse, you’re probably buying them miserable.  — Alex Proud,   ""   As far as I know, clever and miserable are both adjectives, not nouns. So why were they used with to buy? Is this an idiomatic way of saying You can't buy your kids intelligence and you're probably buying them (moral) misery? If so, what is the idiom used here? I'm not familiar with it.


I want to list tags of my current post  I am using below code  <?php $tax_tags = get_terms(array('post_tag'));    foreach($tax_tags as $tag){      ?>
      <?php echo ucfirst($tag->taxonomy).' : ' ?>          <a href="<?php echo get_term_link($tag); ?>"><?php echo $tag->name ?>
      <?php } ?>   The output is   Post_tag : 1024x768  Post_tag : pics  Post_tag : india  Post_tag : 1366x768  Post_tag : 1920x1080  Post_tag : 1920x1200  Post_tag : 2015  Post_tag : 3d  But it shows list of all tags and i want to list tags which is related with Post ID = 17


In the Harry Potter universe can a spell deflect or redirect to hit an unintended target and have the same effect?

If a person casts a spell and it's deflected can it hit an unintended target and work as intended?  For example, if a wizard casts a spell at someone to turn them into a dog, and it's deflected and hits another person, will that person turn into a dog?  I know there's the example of Ron's broken wand with the slugs and the charms spells, but I attribute that to the wand just having bad aim by being broken and just casting in the wrong direction.   Please account for Voldemort's casting of the Avada Kedavra spell at Harry and it killing the horcrux inside of Harry. Clearly that was not the intended target for the spell.


RSA PKCS#1 v.15 Signature verification computational complexity explanation?

I've been experimenting with MBEDTLS on an ARM-M4 (but this question is not platform-specific) and am confused/surprised regarding the computational complexity (execution time) of mbedtls_rsa_pkcs1_sign() versus mbedtls_rsa_pkcs1_verify(). Apparently the _sign is much more computationally complex than the _verify. I don't understand this and would expect the opposite to be true.  Observations:   mbedtls_rsa_pkcs1_decrypt() or  mbedtls_rsa_pkcs1_sign()    < 3 secs mbedtls_rsa_pkcs1_encrypt() or  mbedtls_rsa_pkcs1_verify()  < 100 millisecs (this is for RSA-2048 / SHA-256)   I would have assumed that the verify should be similar in complexity to the decrypt (because it requires decryption of the signature hash) and that the sign would be similar in complexity to encrypt (because it requires encryption of the hash). I understand that for the signature operations the Private and Public key use is reversed, but I'm not sure how/why that affects things.


Buffered Reader Not Reading Certain Lines

Here is my program          String thisSchool=buffer.readLine();         String thisLine;          while((thisLine = buffer.readLine()) != null){             if(thisLine=="*")             {                 thisSchool=buffer.readLine();             }             else             {                 School school = new School(thisSchool);                 Student student = new Student(thisLine, school);                 StudentList.add(student);             }        }   My text file reads like this:  School1 A B C * School2 D E * School3 F   The output of my driver class is:  A School1 B School1 C School1 * School1 School2 School1 D School1 E School1 * School1 School3 School1 F School1   This is what I WANT it to look like  A School1 B School1 C School1 D School2 E School2 F School3   Here's what the problem looks to be The "currentSchool" variable is never changing, and I don't know why! The " * " is treated as a student (I want to use it as a delimiter, i.e., the program will ignore it when it is encountered). Instead, the "if line= * " command is being ignored completely, and consequently, the school never changes, and the students are being written incorrectly


Best approach for precise Rational arithmetics in MySQL

As we all know some  have errors when represented as floating point as witnessed here :  SELECT SUM( TEST )  FROM (  SELECT @N := @N +1 AS rownumber, 1/3 AS TEST FROM INFORMATION_SCHEMA.COLUMNS, (  SELECT @N :=0 )dummyRowNums LIMIT 3000 ) AS test   I have extensive use of rational numbers arithmetics in my system and im looking for an approach to make it as precise as possible, is there any out of the box solution to this?  Its not a duplicate of  as I'm asking how to do rational arithmetic right on mysql, while there they discuss why rational arithmetic is broken.


How is weight distributed in a stack of boxes?

Consider the following stacks of 2D boxes with uniform density:        A                   B                        C  ___________          _________                _________ |           |        |         |              |         | |___________|     ___|_________|____     _____|_________|___ |   |   |   |    |        |   |     |   |        |     |     | |___|   |___|    |________|   |_____|   |________|     |_____|   How is the weight of the boxes on top distributed to the lower ones?  A) 50:50  B) Theoretically 100:0, since I can just get rid of the lower right box because the center of mass of the top box is just above the edge of the lower left one?  C) ?  Is there an equation or algorithm to calculate this?


Separate bibliography files for separate bibliographies

For a research project, I would like to create a literature list that organizes a relatively large number of references into different categories, using biblatex. I would like to do this by having multiple .bib files, and then be capable of printing all references in such a file with a single command, without having to cite them first.  Is there a way to do this?


I've got a weird question. Here is the sentence:     "Inky the shy Blue ghost, whom goes about in the room without a   precise purpose"   Is it correct to use "whom" in this context ? The fact that the "ghost" has a distinct name leads me to believe we can use it instead of "that". But my, the thought is staggering.


How do remove trailing numbers in python

I am working on a python project and get a problem.   I have a for loop that makes a list with numbers. The problem is when I print out the list to check if the numbers are correct.  Some of the more simpler calculations are: 2.6 * 3 and 1.3 * 9  If you check with a calculator you should get 7.8 and 11.7, but I get 7.800000000000001 and 11.700000000000001  Which is not a big problem, but I don't like how it looks. (First world problem, I know)  Is there any way to fix it?


Is someone misusing my email to post on SE?

I  just got these 10 e-mails 5 hours ago from do-not-reply@stackexchange.com:      Recently, you asked a question on [X] Stack Exchange, but you haven't verified your email address yet.      Click on the following link to verify your email and set a password so that you can log in.      Here, [X] refers to all of the following:    GameDevelopment.SE SharePoint.SE Unix.SE  Skeptics.SE Japaneese.SE HomeImprovement.SE SciFi.SE PersonalFinanceMoney.SE  DatabaseAdmins.SE  TeX.SE    I haven't posted on any of these except for TeX.SE, but that was not recently, and through my real account.   =   I asked about this , and was told that someone seems to be impersonating me by using my email. Is it possible for staff to stop this?   Also, I'm pretty surprised there is no measure to stop people from using emails to existing SE accounts (see for example, on wordpress.com, if you use an e-mail which has an existing account on wp.com, you are asked to log in.).    EDIT:  I just got 2 more emails an hour ago for SharePoint.SE, and for AmateurRadio.SE.


What the function of the pronoun"it" here, does it refer to the contractor because the author did not know precisely what the contractor's gender is?

To the extent that the Contractor believes it is entitled to additional payment (there can sometimes be a dispute as to what is meant by ‘additional’) then it is required to make a claim in accordance with sub-clause 20.1. What the function of the pronoun it here? Does it refer to the contractor because the author did not know what the contractor's gender is?


keypressed ENTER not initializing if else statement

For this problem, my enter key for JTextField is not initalizing the if-else statement inside the chat();   I tried putting the userinput.addKeyListener(this); inside public guitest(); as well but its not working.   How do I get it work so that I can initialize the if else statement to reply me an answer. The error given was:  Exception in thread "main" java.lang.NullPointerException     public class guitest extends JFrame implements KeyListener{ ArrayList questionarray = new ArrayList(); ArrayList answerarray = new ArrayList(); public JTextArea scriptarea = new JTextArea(); public JTextField userinput = new JTextField(); public String stringinput;  public ArrayList getquestionarray(){     return questionarray; } public ArrayList getanswerarray(){     return answerarray; } public guitest(){      //gui     this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);         this.setSize(600, 600);     this.setVisible(true);     this.setResizable(false);     this.setLayout(null);     this.setTitle("Minion AI");     setLocationRelativeTo(null);      //jtextfield location and field     userinput.setLocation(7, 530);     userinput.setSize(580, 30);      //jtextarea location and size     scriptarea.setLocation(15, 5);     scriptarea.setSize(560, 510);     scriptarea.setEditable(false);      //adding methods to frame     this.add(userinput);     this.add(scriptarea);     chat(); } @Override public void keyTyped(KeyEvent e) { }  @Override public void keyPressed(KeyEvent e) {     if(e.getKeyChar() == KeyEvent.VK_ENTER){         stringinput = userinput.getText();         scriptarea.append("[You] " + stringinput + "\n");         userinput.setText("");                 }     if(e.getKeyChar() == KeyEvent.VK_ESCAPE){         System.exit(0);     } } @Override public void keyReleased(KeyEvent e) { } public void chat(){     Random random = new Random();     ArrayList greetingarray = greetings();     ArrayList quotesarray = quotes();     scriptarea.append("[AI Minion] "+greetingarray.get(random.nextInt(greetingarray.size()))+"\n");     userinput.addKeyListener(this);         if(greetingarray.contains(stringinput)){             for(int i=0; i<1; i++){                 scriptarea.append("[AI Minion] "+greetingarray.get(random.nextInt(greetingarray.size()))+"\n");             }         }else if(questionarray.contains(stringinput)){             scriptarea.append("[AI Minion] "+answerarray.get(questionarray.indexOf(stringinput))+" \n");         }else if(stringinput.contains("who")){             scriptarea.append("[AI Minion] I am a creature created to assist you in your experience in talking to me. \n");         }else if(stringinput.contains("bye")||stringinput.contains("end")){             scriptarea.append("[AI Minion] Bye byee ♥‿♥ \n");         }else{             scriptarea.append("[AI Minion] Sorry, I dont understand your alien language. \n");         } } public static void main(String[] args){     new guitest(); }   }


How to calculate $\langle 1/r^2 \rangle$ for hydrogen using Hellmann-Feynmann Theorem? Wikipedia is wrong, isn't it?

I was taking a read at the  on wikipedia. Basically, the theorem claims:     Theorem: If $\hat H_\lambda$ is the Hamiltonian operator dependent on a continuous parameter $\lambda$, and $E_\lambda$ is the eigenvalue of the eigenstate $\psi_\lambda$, both of them depending on continuous parameter $\lambda$, then:    $$ \frac{dE_\lambda}{d\lambda} =  \bigg\langle\frac{d \hat H_\lambda}{d\lambda}\bigg\rangle =  \bigg\langle \psi_\lambda \bigg| \frac{d \hat H_\lambda}{d \lambda} \bigg| \psi_\lambda \bigg\rangle $$   Wikipedia also . So far so good. But then, wikipedia seems to think one can use the theorem to compute $\langle 1/r^2 \rangle$ on the hydrogen atom. . I disagree on his proof. Here is a copy paste of all relevant points in wiki's proof:     $$ \hat{H}_{l}=-\frac{\hbar^{2}}{2\mu r^2}\left(\frac{\mathrm{d}}{\mathrm{d}r}\left(r^{2}\frac{\mathrm{d}}{\mathrm{d}r}\right)-l(l+1)\right) -\frac{Ze^{2}}{r} \quad\implies\quad \frac{\partial \hat{H}_{l}}{\partial l} = \frac{\hbar^{2}}{2\mu r^{2}}(2l+1) $$    Then:   $$ \begin{align} \bigg\langle\psi_{nl}\bigg|\frac{1}{r^{2}}\bigg|\psi_{nl}\bigg\rangle &= \frac{2\mu}{\hbar^{2}}\frac{1}{2l+1}\bigg\langle\psi_{nl}\bigg|\frac{\partial \hat{H}_{l}}{\partial l}\bigg|\psi_{nl}\bigg\rangle \\ &=\frac{2\mu}{\hbar^{2}}\frac{1}{2l+1}\frac{\partial E_{n}}{\partial l} \\ &=\frac{2\mu}{\hbar^{2}}\frac{1}{2l+1}\frac{\partial E_{n}}{\partial n}\frac{\partial n}{\partial l} \\ &=\frac{2\mu}{\hbar^{2}}\frac{1}{2l+1}\frac{Z^{2}\mu e^{4}}{\hbar^{2}n^{3}} \\ &=\frac{Z^{2}\mu^{2}e^{4}}{\hbar^{4}n^{3}(l+1/2)}. \end{align} $$   Wiki chooses the angular quantum number $l$ as $\lambda = l$. First of all, $l$ is not a continuous parameter, its discrete. Though, we can all pretend its continuous. Second of all, eigenvalues of the eigenstates $E_n$ does not depend on $l$. Third of all, in the middle of the proof Wikipedia does: $$ \frac{\partial E_n}{\partial l} =  \frac{\partial E_n}{\partial n}\frac{\partial n}{\partial l} \neq 0 $$  What just happened there? How can $dn/dl$ be non-null, if both $n$ and $l$ are independent?  What I am asking is: is this proof correct? Ie, the wiki calculation of $\langle 1/r^2 \rangle$.   If yes: why? Why is it correct in those three points? If no: Can one calculate $\langle 1/r^2 \rangle$ for hydrogen using the Hellmann-Feynmann Theorem? How?


Share the clipboard between bash and X11

In  the top answer shows how to copy text that has been previously selected with the mouse on a gnome-terminal, to the clipboard in X11.  My question is: Say I copy a piece of text from the terminal using bash set-mark and copy keyboard shortcuts (i.e. set-mark + M-w). Is it possible to share this clipboard with X11?   EDIT: In the original question, I talked about sharing the clipboard with GNOME, but as Gilles points out below, GNOME doesn't specifically have a clipboard (it's general to X), so I have updated the question.


I am trying to understand the definition of differentiation, I am working on some problems and ran across this one:     If f+g is differentiable at x = a and f is differentiable at x = a,   then g is differentiable at x = a   I think this is true because the addition operation shouldn't change it, but I find it difficult to use the definition to actually prove this. Like it seems like this should just work by properties but I am not sure.


How do I get a string representation from a nullable type?

Say I have something like  var T = Type.GetType("System.Nullable`1[[System.DateTime, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]");   which is a nullable datetime.   T.FullName gives me:   "System.Nullable`1[[System.DateTime, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]"   How can I extract DateTime? or Nullable<DateTime> as a string representation from the Type?


Middle aged man travels through portal to a Greek speaking world?

Trying to find the name of this book I've read 25-30 years ago.  I think it was a Roger Zelazny book, but could be well off the mark as I wasn't able to find a description that tallies with my recollection of the plot.  It starts with a middle aged man who through some emergency ends up going through a portal - this world seems to speak an ancient Greek dialect (which he just so happens to have been an expert in on Earth, having taught Greek). This man has had amnesia and only recalls stuff from around his twenties onwards.  In this world, which is built in layers - like a pyramid, he becomes young and healthy (back to his mid twenties form) and starts climbing up towards the palace of the (missing) ruler of this universe.


What is launchpad in apt-get error messages?

when I do sudo apt-get update I get these errors,  Err http://ppa.launchpad.net trusty/main amd64 Packages 404  Not Found Err http://ppa.launchpad.net trusty/main i386 Packages  404  Not Found W: Failed to fetch http://ppa.launchpad.net/adilson/experimental/ubuntu/dists/trusty/main/binary-amd64/Packages  404  Not Found W: Failed to fetch http://ppa.launchpad.net/adilson/experimental/ubuntu/dists/trusty/main/binary-i386/Packages  404  Not Found E: Some index files failed to download. They have been ignored, or old ones used instead.   I have no idea what launchpad is. what this error is? what this error points to?  How can I remove this error?  Thanks.


Is the general equation for a straight line not considered a linear function in linear algebra?

Is the general equation for a straight line, which we called a linear function in highschool, i.e.  $$f(x)=mx+c \tag{1}$$  not considered to be a linear function according to the linear algebra definition that it need to satisfy  $$f(\alpha x_{1} + \beta x_{2}) = \alpha f(x_{1}) + \beta f(x_{2}) \tag{2}$$  since the two sides of equation $(2)$ would differ by the constant term if using equation $(1)$ as the definition of $f$? As far as I understand the first equation I posted would be considered an affine function but not a linear function in linear algebra (right?).  Are there just (annoyingly) two completely different definitions of what a linear function is or is there a reason that these two definitions have the same name (i.e. are the concepts related)?


What does “” exactly mean in “echo  temp.txt”?

Non existing file  $ ls file_not_exists.txt ls: cannot access file_not_exists.txt: No such file or directory $ echo <> file_not_exists.txt  $ ls file_not_exists.txt  file_not_exists.txt $ cat file_not_exists.txt $   File with content  $ cat temp.txt  asdf $ echo temp.txt  temp.txt $ echo <> temp.txt   $ cat temp.txt  asdf    If the file does not exist, echo <> file_not_exists.txt will create a new file. So I think > works (redirecting the empty output into a newly created file). But if there is something in the file (like temp.txt), why it is not emptied by echo <> temp.txt?


Let $f(x)$ be a quadratic expression which is positive for all real values of $x.$ If $g(x)=f(x)+f'(x)+f''(x)$

Let $f(x)$ be a quadratic expression which is positive for all real values of $x$. If $g(x)=f(x)+f'(x)+f''(x)$, then for any real $x$,   $$(A)\, g(x)<0,\quad (B)\,g(x)>0,\quad (C)\, g(x)=0,\quad (D)\;g(x)\ge 0.$$   My work so far.  Let $f(x)=ax^2+bx+c$ be the quadratic polynomial. Then $b^2-4ac<0$ and $$g(x)=ax^2+x(b+2a)+(c+b+2a).$$ Now I am stuck. I am not able to pick the right answer.


I recently posted a version of the twin paradox with a twist but here I'd like to propose a new thought experiment all together. Take two clocks, A & B, and place A 1 AU away from B. Once the clocks are separated and stationary relative to each other sync them up again; to do so send a light pulse from A to B, and when the pulse reaches B the clock will start ticking while A waits the exact amount of time it takes light to reach B to start ticking. The idea is to have two clocks that are in sync but separated by a large distance, and I imagine there are multiple ways to do this. Now take a third clock, clock C, which is also synced with A and B and have it travel the distance between A and B at .866c so that time runs at 1/2 the rate for clock C. However to Clock C, A & B would be running at half speed. When it arrived at B though we'd be able to compare the elapsed times and say for sure whether C or A & B had in fact been running slower, even though special relativity dictates both viewed each other as running slower and both are correct. The only decent explanation I can think of is that for C, simultaneity between A & B is broken rendering B's readings inaccurate, but that still leaves us in a very bizarre place as ultimately to C, B should read half the time and to B, C should read half the time.  *Note: Please don't try and use acceleration to explain the disparity, it is a common misconception that acceleration resolves the twin paradox when its actually that acceleration is used to confirm the change in reference frames. To avoid that conundrum all together you can imagine that clock C was already up to speed when it passed A and synced itself up with A as it passed C. Furthermore we can imagine C never actually slowed down when it passed B, rather it just took the reading from B to compare. This way C is in one inertial frame for the entire duration of the experiment.


Reporting, figures: good practice to cut y-axes or not?

Figure 1 is easier for identifying the difference. However, sometimes the practice of cutting y-axes is not recommended. Which one to report?


Updating ubuntu 13.10 Problem on Dell E6410

When ever I try to update, I get this message:  W:Failed to fetch cdrom://Ubuntu-GNOME 13.10 _Saucy Salamander_ - Release amd64 (20131017)/dists/saucy/main/binary-amd64/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs W:Failed to fetch cdrom://Ubuntu-GNOME 13.10 _Saucy Salamander_ - Release amd64 (20131017)/dists/saucy/multiverse/binary-amd64/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs W:Failed to fetch cdrom://Ubuntu-GNOME 13.10 _Saucy Salamander_ - Release amd64 (20131017)/dists/saucy/restricted/binary-amd64/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs W:Failed to fetch cdrom://Ubuntu-GNOME 13.10 _Saucy Salamander_ - Release amd64 (20131017)/dists/saucy/universe/binary-amd64/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs W:Failed to fetch cdrom://Ubuntu-GNOME 13.10 _Saucy Salamander_ - Release amd64 (20131017)/dists/saucy/main/binary-i386/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs W:Failed to fetch cdrom://Ubuntu-GNOME 13.10 _Saucy Salamander_ - Release amd64 (20131017)/dists/saucy/multiverse/binary-i386/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs W:Failed to fetch cdrom://Ubuntu-GNOME 13.10 _Saucy Salamander_ - Release amd64 (20131017)/dists/saucy/restricted/binary-i386/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs W:Failed to fetch cdrom://Ubuntu-GNOME 13.10 _Saucy Salamander_ - Release amd64 (20131017)/dists/saucy/universe/binary-i386/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs W:Failed to fetch http://ppa.launchpad.net/tualatrix/ppa/ubuntu/dists/trusty/main/binary-amd64/Packages  404  Not Found W:Failed to fetch http://ppa.launchpad.net/tualatrix/ppa/ubuntu/dists/trusty/main/binary-i386/Packages  404  Not Found E:Some index files failed to download. They have been ignored, or old ones used instead.   Though i have internet connection. What would be the problem?


I'm trying to insert a number into my vector "heapvect." I keep changing from references and pointers and it still won't allow me to pass in num into the vector. I have made this without template and making a dynamic array (constructor/destructor), I'm unsure if having a vector and template made me think differently of the whole heap sort.  I tried having pointers for heapvect and getheapvect.  //main.cpp #include"heap.h" #include<iostream> #include<vector> using namespace std; int main() {     int size;     int num;     cout << "USER:" << endl;     cout << "Enter size for heap: " << endl;     cin >> size;     heap<class T> yeet;      cout << "Enter in " << size << " of items:" << endl;     for (int i = 0; i < size; i++) {         cin >> num;         yeet.getheapvect().push_back(num);     }     system("pause");     return 0; }    //heap.cpp #include "heap.h" template<class T> heap<T>::heap() { } template<class T> heap<T>::heap(int size) {     getheapvect().resize(size*2); } template<class T> heap<T>::~heap() { } template<class T> void heap<T>::insertin(const T item) {     getheapvect().push_back(item);     int index = distance(getheapvect().begin(), item);     while (index != 0 && getheapvect()[parent(index)] > getheapvect()[index]) {         swap(getheapvect[index], getheapvect()[parent(index)]);         index = parent(index);     } } template<class T> void heap<T>::minheap(int size, int index) {     int large = index;     int left = (2 * index) + 1;     int right = (2 * index) + 2;      if (left < size && getheapvect()[left]>getheapvect()[large])         large = left;     if (right < size && getheapvect()[right]>getheapvect()[large])         large = right;     if (large != index) {         swap(getheapvect()[index], getheapvect()[large]);         makeheap(size, large);     } } template<class T> void heap<T>::heapsort(int size) {     for (int i = (size / 2) - 1; i >= 0; i--)         makeheap(size, i);     for (int i = size - 1; i >= 0; i--) {         swap(getheapvect()[0], getheapvect()[i]);         makeheap(i, 0);     } } template<class T> void heap<T>::print(int size) {     for (int i = 0; i < size; i++)         cout << getheapvect()[i] << ' ';     cout << endl; } template<class T> void heap<T>::PRINT() {     print(getheapvect().size()); } template<class T> void heap<T>::swap(T  a, T  b) {     T temp = a;     a = b;     b = temp; }    //heap.h #ifndef HEAP_H #define HEAP_H #include<iostream> #include<vector> using namespace std;  template<class T> class heap { private:     vector<T> heapvect;     void print(int size); public:     heap();     heap(int size);     ~heap();     void insertin(const T item);     void minheap(int size, int index);     void heapsort(int size);     void PRINT();     void swap(T a, T b);     int parent(int i) { return ((i - 1) / 2); };     int leftchild(int i) { return ((2 * i) + 1); };     int rightchild(int i) { return ((2 * i) + 2); };     vector<T>& getheapvect(){ return heapvect; }; }; #endif    Output is supposed to bring out a sorted vector in ascending order.


Microphone volume at maximum yet too quiet

I have got a reasonbly basic desktop microphone, however for reasons that I don't understand it is extremley quiet. I dual boot, both systems run Windows 7, one system is working just fine although the other system, after I restarted the computer a couple of weeks ago, the microphone is now far too quiet.  I've been through the Sound control panel. The correct microphone is selected as the default communication device. The microphone level is set to 100. The microphone is plugged into a sound card, so I uninstalled the audio card (an Asus D1) driver and reinstalled it which made no difference. If I tap the microphone, it does register 5 or 6 green bars in the recording volume monitor. So, does anybody have any suggestions on where to look next?


Downloading Google Earth images in universal map downloader

How can I download Google Earth images in  in 2015 and 2020? There isn't any specific option for select year.


reverse a sequence by recurse method in python

I am attempting to write a reverse function by recursive method, somehow it returns none. Can anyone help? Thanks a lot.  def reverse(S, start, stop):      if start>=stop:         return False      elif start<stop-1:         S[start], S[stop-1]=S[stop-1], S[start]         reverse(S, start+1, stop-1) # test the code        myList=[2, 3, 4, 5, 51, 66, 88, 234, 444] print "input sequence is : "+str(myList) print reverse(myList, 0, len(myList))


How to check if a conference is "indexed" or "fake"?

I submitted my paper to a conference. Based on a previous accepted submission, the conference response seems suspicious, not to mention that gmail marked their email as "suspicious mail". Instead of getting the reviewer's comments, I got "your paper acceptance rate". According to IEEE, the previous book series of that conference appears in their digital library. But as far as I know, not all conferences in digital libraries are indexed. Is it done through ISBN search or how to can I figure out if a conference is being indexed?  According to a related asked question  The publisher or the sponser is known. The point is I have already participated in a conference (MIUCC) that was neither indexed nor scopus, however, the conference proceeding book was inserted on ieee digital library. So being in ieee digital library does not confirm being an indexed confenrence.


QGIS: Waypoint name (symbol label) in two rows

I have couple of longer waypoints names that I would like to put in two rows with center formatting but I just don't know how? I tried to put  tag but it doesn't help...  For example I have the waypoint with name 'one two three five six seven' and I want to make it like this:   one two  three five six seven


I am new to programming and would appreciate some help. The slightest bit of insight would be highly appreciated.  I have an issue with the following code. The program emulates a calculator but currently my main focus is on if and else if statements. The issue is that no matter what the user selects, the program will always add the two numbers i.e. 'number1' and 'number2' in the code  import java.util.*; public class Input {     private Scanner input;      public Input()     {          input = new Scanner(System.in);      }      public void calculation()     {         double number1, number2, answer;         String A, B, C, D, E;         String option;         A = "A"; B = "B"; C = "C"; D = "D"; E = "E"; //initialising the strings           System.out.println("add - option A \t (if your option is A, insert 'A')");         System.out.println("multiply - option B");         System.out.println("subtract - option C");         System.out.println("divide - option D");         System.out.println("power - option E (1st number - 'X' & 2nd number - 'n' following X^n)");         System.out.println("Remember Java is case sensitive, therefore, inserting 'a' as 'A' won't work");         System.out.println();         System.out.println("Insert your first number: ");         number1 = input.nextDouble();         System.out.println("Insert your second number: ");         number2 = input.nextDouble();         System.out.println("Choosing option: ");         option = input.next();          if(A == A)         {             answer = number1 + number2;             System.out.println("Your answer is: " + answer);         }          else if(B == B)         {             answer = number1 * number2;             System.out.println("Your answer is: " + answer);          }else if(C == C)         {             answer = number1 - number2;             System.out.println("Your answer is: " + answer);          }else if(D == D)         {             answer = number1 / number2;             System.out.println("Your answer is: " + answer);          }else if(E == E)         {             answer = Math.pow(number1, number2);             System.out.println("Your answer is: " + answer);          }else         {             System.out.println("Choose a suitable option");          }         } }


Generating unique random numbers and check duplicates

I would like to generate a 3*6 digits, that can form an array of 3rows*6cols. but I don't want a duplicated to be found in any column. They can be anywhere, in the same row, but in each column, there shouldn't be any duplicate of the same number. Is there an algorithm for generating that ?


Parse XML Webservice response to appropriate type c#

I've got a ASMX webservice that returns the following XML, which is a string array. How can I deserialize into the correct type?  <ArrayOfString xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://tempuri.org/">     <string>0 Item(s)</string>     <string>0</string> </ArrayOfString>   In JQuery this is easy, but I'm looking for a way to do it in C#.


How to create a copy of a file immediately when it's created?

I have an Android app that will create a file in /data/ and immediately delete it. I want to know how can I catch this file or create a copy or even disable user permissions to delete a file? I have root access to the device.


Transfer free upgrade Windows 10 to different laptop

Can i transfer my free upgrade win10 to different laptop? I'm going to buy a new laptop so i need to transfer the windows (retail iirc) from the old one. I search about this topic and found that you can do that for pc after you change hardware(motherboard), can i do the same with laptop? I already use digital license and my current laptop is registered when i check my account in Microsoft.  Thanks in advance.


Can I view a specific chapter in a manual?  I tried man socket(2) in WSL Ubuntu 16.04 (Xenial).  This is after I got a recommendation to see chapter 2 in a man of the socket utility.


I am new to DB. We have galera cluster on Test environment where mariaDB is replicated in 3 servers. Now customer want us to work with only 1 server. they cant provide 3.  Can we do replication on single physical server? Is it good idea? How can we achieve that?  Thanks in advance.


Failed to fetch jessie backports repository

I'm using a docker image as a base for my own development that adds the jessie backports repository in its Dockerfile and uses that to install a dependency. This image uses the following command to add the repository:  echo "deb http://ftp.debian.org/debian jessie-backports main" >> /etc/apt/sources.list   The problem is that fetching packages from the backports repository now  fails with the following error (this used to work previously):  W: Failed to fetch http://ftp.debian.org/debian/dists/jessie-backports/main/binary-amd64/Packages 404  Not Found  W: Failed to fetch http://deb.debian.org/debian/dists/jessie-updates/main/binary-amd64/Packages  404  Not Found   I looked on that server, and those paths are indeed not present there.  I tried to figure out on the Debian backports site whether this particular repository should still be available, and I didn't find any indication that this was deprecated or something like that.  Is this a temporary issue with the repository, or is the jessie-backports repository not available anymore? And if this is not a temporary issue, what options do I have to use this or an equivalent repository without upgrading to the newer Debian stable version?


C++ - Call Child Method Overwrites in List of Parents

Here's a sample program for what I'm talking about:  #include <iostream> #include <list>  using namespace std;  class Thing {     public:         virtual void jump() { cout << "Called from Thing class" << endl; } };  class Car: public Thing {     public:         virtual void jump() { cout << "Vroom vroom; imma car biotch" << endl; } };  int main(int argc, char* argv[]) {      Car myCar;      list<Thing> myList;      myList.push_back(myCar);      std::list<Thing>::iterator iterator;     for (iterator = myList.begin(); iterator != myList.end(); ++iterator) {         iterator->jump();     }      return 0; }     Output:  Called from Thing class     What I want to do is make a list of "Things". I want to be able to add instances of the child class from the Thing class; then I want to be able to call their overwritten function from an iterator.   The only issue is, even while using the "virtual" keyword, the iterator uses the Thing::jump function as opposed to the Car::jump function.  What can I do to make it not only work with Car, but all potential child classes from Thing, Car, etc. that overwrite the "jump" function?


Logistic Regression - Error Term and its Distribution

On whether an error term exists in logistic regression (and its assumed distribution), I have read in various places that:   no error term exists the error term has a binomial distribution (in accordance with the distribution of the response variable) the error term has a logistic distribution   Can someone please clarify?


Is it all right to answer own question with a summary of a discussion from the comments in case no other answers are posted?

I've asked a  on .   My question has received no direct answers (yet), but a very interesting discussion took place in the comments. I believe that reading through it pretty much helped me understand and formulate the answer. I would like to answer my own question with a summary of that discussion, listing every participant and quoting them. The discussion itself was overburdened by a couple of discrepancies in terminology, which might be interesting, yet it clearly is not related to the question itself.   Is this a decent thing to do?


I am going through the book  and I'm finding it extremely terse. I have a background in probability but not statistics so perhaps that is why. Anyway, in Chapter 3, section 3.2 (p.47), they discuss the unbiased estimator of the variance of the $y_i$. They write,      Typically one estimates the variance $\sigma^2$ by   $$ \hat{\sigma}^2 = \frac{1}{N − p − 1} \sum_{i = 1}^N ( y_i − \hat{y}_i)^2.$$   The $N − p − 1$ rather than $N$ in the denominator makes $\hat{\sigma}^2$ an unbiased estimate of $\sigma^2$.   Here the $y_i$ are the observations which we assume are distributed like  $ x_i^T \beta + \zeta_i$, where $x_i$ are the inputs, $\zeta_i$ are independent of everything, mean zero, variance $\sigma^2$, and $\beta$ is fixed. $\hat{y}_i$ are the estimated output from the linear regression we have constructed. Ie., $\hat{y}_i = x_i^T \hat{\beta}$ with $\hat{\beta}$ the linear multiplier, $\hat{\beta} = (X^T X)^{-1}X^T y$.  They make this comment without any explanation. Can someone explain why this is true. And even better, why this should be obvious.   Edit: Thanks to @gung for the link but I found that calculation still unclear and missing details. I'm putting down my calculation here just for completeness.  Some notation: Let $X$ be the $N \times (p+1)$ matrix of samples by characteristics (the extra $1$ is for the column of all ones!). Let $y = (y_1,...,y_N)$ and $\hat{y} = (\hat{y}_1,...,\hat{y}_N)$.   Under these conditions, $\hat{y} = X \hat{\beta}$ and $y = X \beta + \zeta$ where $\zeta$ is an $n\times 1$ vector of independent Gaussians with common variance $\sigma^2$. Using our formula for $\hat{\beta}$ above this gives $$ \begin{align} \hat{\beta} = (X^TX)^{-1}X^T y = \beta + (X^TX)^{-1}X^T \zeta \\ \end{align} $$ And so,  $$ \begin{align} y - \hat{y} & = X\beta + \zeta - (X\beta + X(X^TX)^{-1}X^T \zeta) \\ & = (I_N - X(X^TX)^{-1}X^T) \zeta \\ & := (I_N - B) \zeta, \end{align} $$ with $B:= X(X^TX)^{-1}X^T$. Therefore, $$ \begin{align} \sum_{i=1}^N \mathbb{E} (y_i - \hat{y}_i)^2 & = \mathbb{E} \left[(y-\hat{y})^T(y-\hat{y}) \right] \\ & =\mathbb{E} \left[ \zeta^T (I_N-B)^T (I_N-B) \zeta \right] \\ & = \sigma^2 Tr((I_N-B)^T(I_N- B)) . \end{align} $$ The last equality follows because the $\zeta$ are independent with common variance $\sigma^2$.  Finally, $$ \begin{align} (I_N-B)^T(I_N-B) &= I_N - X(X^TX)^{-1}X^T. \\ \end{align} $$ Therefore, $$ \begin{align} Tr((I_N-B)^T(I_N-B)) & = Tr(I_N) - Tr(X(X^TX)^{-1}X^T) \\ & = Tr(I_N) - Tr(I_{p+1}) \\ & =N-p-1 \end{align} $$


Show set of affine transformations is a group

I am tasked to show that the set of affine transformations of ,    Where S is an invertible linear transformation and b is a vector, forms a group under the composition of maps.   It was easy to show that   Now I need to show that there is an identity element, and that all elements are invertible such that   Im a little unsure what to do at this point....Can anyone help me on this? Thanks!


I'm stuck on a planet with no wood trees and no resources that are easy to exploit, and I want to get off of it as quickly as possible.  What do I need to do to get my spaceship enough fuel to go to another planet?


How to preserve ownership and permissions in Dropbox?

I have two machines, a Mac and a PC running Linux, that I am trying to keep a certain file synced between using Dropbox.  One of the files that I am syncing needs to be writable by another user (different UID on the same machine, not referring to another dropbox user) besides myself.  To be more specific, this other UID is actually a daemon.  So, either the file needs to be owned by that other user, or else write permission is needed for "group" and/or "other".  Initially I have set it up this way on both machines.  In addition, the directory containing the file is already owned (chmod 777) by the user that needs to have write access to the file.   However, whenever the file gets synced from one box to another, it appears that Dropbox completely ignores both sets of permissions, and changes the permissions on the newly updated file to be owned by me with permissions 0644 (rw for me, r for everyone else).  If the file isn't owned by me it even changes ownership back to myself! As a result, the other user no longer has write permissions until I manually go in and re-chmod the file.  Additional things I have tried that have not worked:   made sure the user account (for the "other user") on both machines has the same UID.  Not sure why this would be necessary, since my primary account doesn't have the same UID on both machines. chmod u+s <dir> and chmod g+s <dir> where  is the directory containing the file in question. changing ownership of the file to the other user and placing it outside the Dropbox directory, and creating a symlink to the file in the Dropbox directory.  Dropbox actually deletes the symlink, leaves the original file (outside the Dropbox directory) unchanged, and creates a new copy of the file where the symlink used to be!   How can I set things up so that my permissions and/or ownership are preserved?


I have heard about vote fraud.  What is it?  By which criteria is a vote declared as fraud?  How we can find out about these sorts of activity?  What are the consequences of it?  Edit  What if I am visiting a user's profile and listing his questions and answers and I decide to upvote many of his answers because I find them useful?  Will this also be considered as abnormal?


How can I replace 2-prong receptacles in a code compliant way?

I have some 2-prong non-grounding type receptacles, and I'd like to replace them with 3-prong grounding type receptacles.  According to National Electrical Code, what are my options?


What GUI (no command line) software or websites can I use to verify a PGP signature?  If I have a message like this  -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1  Because anyone can claim to be me. There's no validation of the user name or email address when someone posts a comment. While I do try to remove imposters, some may slip through. By signing my comments using this technique, anyone can independently verify that I was the author of the message by validating the signature. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (MingW32)  iD8DBQFFxqRFCMEe9B/8oqERAqA2AJ91Tx4RziVzY4eR4Ms4MFsKAMqOoQCgg7y6 e5AJIRuLUIUikjNWQIW63QE= =aAhr -----END PGP SIGNATURE-----   How can I verify the message against the public key to get the same signature back?  This  does not allow me to do that.


How to expose the visual force page with out using the portals and Communities

I need access a visual force page with out using salesforce credentials.


How do wizards distinguish between magical creatures and "mundane" animals?

The simple answer to this question would be that magical creatures are capable of using magic as an evolutionary advantage. Magical abilities are often considered to be "wondrous" and "special", but as we know, there are plenty of non-magical animals with unique characteristics like the changing of colours (the chameleon) or biological immortality (). In other cases, both magical and non-magical animals share the same ability; for example, the lotus leaf and augurey feathers are able to repel water but only one has a magical origin.  I appreciate that this question can lead to a discussion about how wizards do generally distinguish between "physical" and "magical" phenomena but since wizards don't use scientific methods like non-magical scientists, it strikes me that they would struggle to detect whether a phenomenon is "physical" or "magical" in its nature.   How can they distinguish between creatures that are magical and those that are mundane?


What is the right way to say a car driver to increase Aircon temperature?

Like should i say reduce the aircon or increase the aircon or any other easier way to say this?   Use case: i get into a Uber car and its chilling cold. I want the driver to increase the temperature to make it comfortable.   The confusion for me is reducing the speed of aircon increases the temperature and vice versa.


Using REST Assured library for testing SOAP webservices

Is there a possibility of using REST Assured library for testing SOAP webservices? I have a bunch of Test Suites in SOAP UI and I need to check if there is possibility of using REST Assured. Can anyone suggest if this is possible? Many thanks for any comments.


Why append an extra character in `test`/`[` string comparison in POSIX sh?

After reading Debian's /usr/bin/startx, there was something I found peculiar: mcookie=`/usr/bin/mcookie`  if test x"$mcookie" = x; then     echo "Couldn't create cookie"     exit 1 fi  I don't understand why the extra x is necessary - wouldn't it be equivalent to write the following? mcookie=`/usr/bin/mcookie`  if test "$mcookie" = ""; then     echo "Couldn't create cookie"     exit 1 fi  I initially thought that very early versions of sh might have printed some error if the mkcookie variable happened to be unset (this wasn't the only instance; these types of comparisons were scattered liberally throughout the script). But then it didn't make much sense after further thought because the variable was being quoted and the shell would expand it to an empty string. I perused the Dash, --posix section of the Bash man page and checked POSIX itself. It said nothing about it under : s1 =  s2 True if the strings s1 and s2 are identical; otherwise, false. I assume the people that wrote the script knew what they were doing - so can someone shed some light on this? Thankies, Edwin


Incompatibility between etextools and etoolbox command \dolistloop (\forlistloop)?

The following code uses the etoolbox package to convert a list a,b,c into an internal list (called \mylist) and then typesets that with colons: a:b:c:.  However, when I load the etextools package (by uncommenting the second line), I get no list output.   \documentclass{minimal} \usepackage{etoolbox} %\usepackage{etextools} \begin{document} A list: \def\mylist{} \forcsvlist{\listadd\mylist}{a,b,c} \def\do#1{#1:} \dolistloop{\mylist} \end{document}   I suspect it is is a bug since etextools claims to depend on etoolbox.  Is this a bug or am I doing something wrong?  In either case, how can I use \dolistloop with  etextools (which I want for goodies like \expandnext)?  Notes   \show\mylist produces the same output a|b|c| in both cases, so the problem is with \dolistloop which expands to \forlistloop\do The \forlistloop command becomes substantially more complicated when etextools is used.  might be relevant (but not obviously).


I am not professional photographer and own a Nikon Coolpix B700.  I am trying to achieve background blur aka bokeh with my clicks with same camera. I have done google and played around Manual setting as suggested yet I am unable to achieve that. People have accomplished this with same camera. Only difference I observed is uses of tripod. Do I must have tripod to have bokeh with B700? Can't I have such without uses of tripod? Suggestion please!  I am keen to learn basic of photography jargon and how to use it with B700. Would be great if someone can suggest a tutorial or guide.  Thanks


I have a requirement that an application I am working on prevent the user from being able to easily capture the contents of the screen.  I have communicated that there is no feasible way to completely prevent this from happening, but I'm looking for methods to introduce some hurdles to the process.  I'm using C#/.NET 2.0 and WinForms


Connecting 2 External Monitors to a Laptop in 2013?

I know about the 2009 question:   It's 2013 now and I want to know if anything has changed.  I want a laptop with two external displays, to make three in total with the laptop screen.  Or even three external displays with the laptop screen disabled.  Is this possible? If so, what should I look for when choosing a laptop?


functions satisfying $f(x - y) = f(x) f(y) - f(a - x) f(a + y)$ and $f(0)=1$

A real valued function $f$ satisfies the functional equation $$f(x - y) = f(x) f(y) - f(a - x) f(a + y) \tag 1 \label 1$$ Where $a$ is a given constant and $f(0) = 1$. Prove that $f(2a - x) = -f(x)$, and find all functions which satisfy the given functional equation. My Try: Put $x=y=0$ in equation \eqref{1}. $\implies f(0)=f(0)^2-f(a)\cdot f(a)\implies f(a)^2=0\implies f(a)=0$. Now Put $x=a$ and $y=x-a$. $\implies f(2a-x)=f(a)\cdot f(x-a)-f(0)\cdot f(x) = -f(x)$. My question is how can I find all function which satisfy the given functional equation. Help me. Thanks.


Correlation between a categorical and a numerical variable

I have a general statistical question. I have a categorical variable and a numerical variable; is it okay to use the pearson correlation coefficient to determine the relationship between the both? Regards


How to find the largest attribute value in a XML file?

I am trying to create a small program that is able to print out the largest value of a attribute in an XML file. I have wrote the following code:  public class GetMaxLog {     public static void main(String[] args) throws Exception {      DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();     factory.setNamespaceAware(true);      DocumentBuilder builder = factory.newDocumentBuilder();     Document doc = (Document)builder.parse("FILE");      XPathFactory xpathfactory = XPathFactory.newInstance();     XPath xpath = xpathfactory.newXPath();      XPathExpression expr = xpath.compile("//PasswordVault/User[@id = 1]//Log[not(@LOG < ../Log/@LOG)]/LOG/text()");      Object result = expr.evaluate(doc, XPathConstants.NODESET);     NodeList nodes = (NodeList) result;         //returns the element at tag value 0 thus only the first set of data         System.out.println(nodes.item(0).getNodeValue());  }   }  And the XML file looks like this.  <?xml version="1.0" encoding="UTF-8"?> <PasswordVault>   <User id="1">     <Log LOG="1">       <AccountType>afsdgsd</AccountType>       <Username>asdas</Username>       <Password>dsgsdg</Password>       <E-mail>aadfaf</E-mail>     </Log>     <Log LOG="10">       <AccountType>afsdgsd</AccountType>       <Username>asdas</Username>       <Password>dsgsdg</Password>       <E-mail>aadfaf</E-mail>     </Log>   </User> </PasswordVault>   There is a NullPointerException error when i run the program. I am trying to find the largest LOG value and then print it out.I think that my query within Xpath is incorrect .Could anyone help me fix this query and the NullPointerException error also.


I want to include some figures from Simulink (pdf file) in my thesis. However, the size of the images are usually too large and I have some extra white spaces that are quite ugly in the document. I don't have acces to acrobat to resize the pdf, and I would like to know if there is any possibility to reduce the height of the figure.  Thanks for your time!


Include errors with hierarchical inheritance

I have a class structure like this:  Entity Creatures and Tiles are Entities Players and Enemies are Creatures    My problem comes in a header file that includes both enemy.h and tiles.h. I'm not really sure what the problem is, but it will only compile properly if I don't include one of the headers. This is a stripped down version of what I have.  #include "enemy.h" #include "tiles.h"  class foo {   public:     list<Entity>* GetTiles();     list<Entity>* GetEnemies();   private:     list<Entity>* tilesList();     list<Entity>* enemiesList(); }   Before I threw in enemy.h and the enemy functions, it compiled properly. enemy.h includes creature.h which includes entity.h. tiles.h includes entity.h  I'm really not all that familiar on how #include really works, but it's obvious that it's the problem. How can I fix this?


Cannot install phpmyadmin on ubuntu 14.04 LTS

I have installed ubuntu along side with window 10 (dual boot). I have set up apache2 server, mysql and install PHP 7, and then I want to install phpmyadmin I cannot install it. I have try many time, but still have the same problem. And here is the error that I get:      Reading package lists... Done Building dependency tree        Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation:  The following packages have unmet dependencies:  phpmyadmin : Depends: libapache2-mod-php5 but it is not going to be installed or                        libapache2-mod-php5filter but it is not going to be installed or                        php5-cgi but it is not going to be installed or                        php5-fpm but it is not going to be installed or                        php5 but it is not going to be installed               Depends: php5-mysql but it is not going to be installed or                        php5-mysqli but it is not installable or                        php5-mysqlnd but it is not going to be installed               Depends: php5-mcrypt but it is not going to be installed               Depends: php5-json but it is not going to be installed               Depends: php-gettext but it is not going to be installed               Recommends: php5-gd but it is not going to be installed E: Unable to correct problems, you have held broken packages.   It says I have broken packages, and I really don't know how to fix this. Please help!   Many thanks in advance.


Mojave - How can I lower the lowest volume?

Currently I'm at 1/4 volume (option+shift+volume) but it is still loud.  All of the systemic solutions are out of date or about limiting maximum volume.  Is there a way to permanently lower the lowest volume?


How to compute the sum of random variables of geometric distribution

Let $X_{i}$, $i=1,2,\dots, n$, be independent random variables of geometric distribution, that is, $P(X_{i}=m)=p(1-p)^{m-1}$. How to compute the PDF of their sum $\sum_{i=1}^{n}X_{i}$?  I know intuitively it's a negative binomial distribution $$P\left(\sum_{i=1}^{n}X_{i}=m\right)=\binom{m-1}{n-1}p^{n}(1-p)^{m-n}$$ but how to do this deduction?


prove the following results for the eigenvalues of an $n \times n$ matrix $A$

Prove the following results for the eigenvalues of an $n \times  n$ matrix $A$:   (a) $0$ is an eigenvalue for $A$ if and only if $A$ is not invertible.  (b) $A$ and $A^T$ have the same eigenvalues.


Understanding the differential $dx$ when doing $u$-substitution

I just finished taking my first year of calculus in college and I passed with an A.  I don't think, however, that I ever really understood the entire $\frac{dy}{dx}$ notation (so I just focused on using $u'$), and now that I'm going to be starting calculus 2 and learning newer integration techniques, I feel that understanding the differential in an integral is important. Take this problem for an example: $$ \int 2x (x^2+4)^{100}dx $$ So solving this... $$u = x^2 + 4 \implies du = 2x dx \longleftarrow \text{why $dx$ here?}$$ And so now I'd have: $\displaystyle \int (u)^{100}du$ which is $\displaystyle \frac{u^{101}}{101} + C$ and then I'd just substitute back in my $u$. I'm so confused by all of this.  I know how to do it from practice, but I don't understand what is really happening here.  What happens to the $du$ between rewriting the integral and taking the anti-derivative?  Why is writing the $dx$ so important?  How should I be viewing this in when seeing an integral?


Run A Script Every X Minutes for Y Minutes

Good morning !  I am trying to run the following script every X minutes for Y minutes. Basically, this script outputs a logcat for 5 minutes and checks for files older than 30 minutes to remove them. So far, I haven't found a way to loop this script every 5 minutes beside using watch -n 300 Script.sh    timeout 5m adb shell logcat > ~/ADB/"$(date +%F_%H-%M-%S)".txt    find ~/ADB/ -type f -name '*.txt' -mtime +30m -exec rm {} \;   So far, I have tried with a while loop but it stacks the script every second. The only way it works is using a watch -n 300 Script.sh in a terminal. It lets the script run every 5 minutes for 5 minutes (Then check for files older than 30 minutes to remove them) but I would like to have the whole thing in a single script I can run at bootup.  Edit :  while true; do timeout 5m adb shell logcat > ~/ADB/"$(date +%F_%H-%M-%S)".txt find ~/ADB/ -type f -name '*.txt' -mtime +30m -exec rm {} \; done


Should two laser pointers always shine a point on the screen with same intensity?

Lasers are coherent beams so they can be totaly cancelled out if applied a source out of phase of 180 degrees. So the question is simple... do two different coherent lasers of same luminosity when pointed at a point sometimes produce a more destructive and sometimes a more constructive interference depending just on timing when they are switched on in that way that the light beams sometimes start its journey out of phase or in phase to each other? Important:the distances to the point on the screen are equal.


I have a ddos protection proxy in place to deal with SYN floods and such. But http floods are still getting through. For some reason their ddos proxy is not blocking any of the flood. So there are about 500 ips connecting to the box as many times as possible and max out at about 20k connections. This is causing php to spawn 1k processes overloading the box. How can I mitigate this http flood? I thought setting up an htaccess file which required a cookie to access the site would work but rewritecond seems to be invoking php which causes the box to overload.  How can I mitigate this?


Prove Operator Norm is a Norm on linear space

Prove that the operator norm defined by $$\left \| A \right \| = \left \| A \right \|_{V\rightarrow W} = \sup_{0\neq v\in V} \frac{\left \| Av \right \|_{W}}{\left \| v \right \|_{V}}$$ (Given norms $\left \| \cdot  \right \|_{V}$ and $\left \| \cdot  \right \|_{W}$ on vector spaces $V$ and $W$, and an operator $A:V\rightarrow W$)  is a norm on the linear space of operators from $V$ to $W$.  That question () about operator norms but in no way answers my question


Has any previously unknown result been proven by an automated theorem prover?

The  states:     Despite these theoretical limits, in practice, theorem provers can solve many hard problems...   However it is not clear whether these 'hard problems' are new. Do computer-generated proofs contribute anything to 'human-generated' mathematics?  I am aware of the four-color theorem but as mentioned on the Wikipedia page, perhaps it is more an example of proof-verification than automated reasoning. But maybe this is still the best example?


What's a simplistic recipe to connect my PC to my WLAN through my laptop?  I have one wireless network, one desktop that (for practical reasons) has no connection to the WLAN, and one laptop with wireless and an ethernet port.  I would like to run a cable from my desktop to my laptop, connect my laptop to my WLAN and forward the network to my desktop.   Is there a solution?


I have an issue with the if/else function in my Java code (Android / Eclipse).  When I'm in debug mode, checkGender is equal to "M", but goes directly to "else" instruction and considers that 'checkGender' is not equal to "M". I don't understand why? For information, searcher.getString("Gender") takes information from MySQL.  String checkGender = "";  checkGender = searcher.getString("Gender");  if(checkGender == "M") {     bGenderM.setChecked(true); } else {     bGenderF.setChecked(true); }   Debug info : checkGender = "M" (id=8300460...) value[0] = M  If I replace "searcher.getString("Gender");" by a simple "M", it works.  Thanks for your help.  Tom


Prove $(\ker T)^\bot = \operatorname{Im}(T^*)$

If $T$ is a linear operator.  Prove the following:  $$ (\ker T)^\bot = \operatorname{Im}(T^*) $$  where $T^*$ is the adjoint operator of the $T$.


There are cases that the accepted anwser is not relevant anymore.  I encounter this situation often lately, particular at stackoverflow.  For example, this question:   Early versions of Docker made it diffulult to do what the user asks. I guess the accepted answer was correct at 2013 but not anymore. Later versions allow this functionality out of the box (you can check my answer at the page)  People usually take the aswers they find for granted, so a wrong accepted answer with many upvotes is very misleading.  I think a mechanism to dispute the accepted anwser would work nicely in this case.  Another solution would be to mark the question or answer as deprecated.   Update  The answers at question  do not address the problem, because this is from the perspective of the person asking the question.   My question is from the community perspective: What to do when we see an accepted answer with many upvotes that is wrong. How to inform the users that the accepted & upvoted answer may not be valid any longer.


Questions on parametric and non-parametric bootstrap

I am reading the chapter on Frequent Statistics from Kevin Murphy's book "Machine Learning - A Probabilistic Perspective". The section on bootstrap reads:     The bootstrap is a simple Monte Carlo technique to approximate the   sampling distribution. This is particularly useful in cases where the   estimator is a complex function of the true parameters.       The idea is simple. If we knew the true parameters $θ^∗$ , we could   generate many (say $S$) fake datasets, each of size $N$, from the true   distribution, $x_i^s \sim p (·| θ^∗ )$, for $s = 1 : S, i = 1 : N$.    We could then compute our estimator from each sample,   $\hat{\theta^s}=f (x^s_{1:N})$ and use the empirical distribution of   the resulting samples as our estimate of the sampling distribution.   Since $\theta$ is unknown, the idea of the parametric bootstrap is to   generate the samples using $\hat{\theta}(D)$ instead.       An alternative, called the non-parametric bootstrap, is to sample the   $x^s_i$ (with replacement) from the original data $D$ , and then   compute the induced distribution as before. Some methods for speeding   up the bootstrap when applied to massive data sets are discussed in   (Kleiner et al. 2011).    1. The text says:       If we knew the true parameters $\theta^*$ ... we could compute our   estimator from each sample, $\hat{\theta^s}$...             but why would I use the estimator of each sample if I already know the  true parameters $\theta^*$?    2. Also, what is the difference here between the empirical distribution and the sampling distribution? 3. Finally, I don't quite understand the difference between parametric and non-parametric bootstrap from this text. They both infer $\theta$ from the set of observations $D$, but what is exactly the difference?


Is the second "t" silent in the word "twenty"?

I have always pronounced the word "twenty" as "twen·tee" and taught my daughter accordingly. But she told me that her pre-kindergarten teacher pronounced it as "twen·nee", making the second "t" silent. Which pronunciation is correct? Do we ever have a silent "t" in similar situations?


Upgrade to 14.04 Serious errors were found while checking the disk drive for /

I recently upgraded to Ubuntu 14.04 LTS from 13.10. I had installed the earlier version using WUBI. I am receiving the following error on booting Ubuntu with the latest kernel 3.14  Serious error while checking for the  disk drive for /  The follow up says either to ignore, skip mounting or the manual recovery. I can boot into Ubuntu 14.04 using the previous kernel version 3.11 in the advanced options specified in the boot options of Ubuntu. I have run the fsck on the root.disk and it says the disk is clean.


I have a CPT called "products" so in the menu on the left there is "products" and "add new", I want to have "product categories" within the menu too so that the user can add as many product categories as they like, and then when they "add new product" they can assign it to a product category.  Here is how I have registered my CPT:      register_post_type( 'products', // CPT Options     array(         'labels' => array(             'name' => __( 'Products' ),             'singular_name' => __( 'product' )         ),         'public' => true,         'has_archive' => true,         'taxonomies' => array( 'Product-categories' ),         'hierarchical' => true,         'rewrite' => array('slug' => 'products'),     ) );   How do I get a "product categories" taxonomy menu within "products" on the left please?  Thanks


Evaluate ${k \choose 0} + {k \choose 2} + {k \choose 4}+ {k \choose 6} +...+ {k \choose k}$ for even $k$

I want to evaluate ${k \choose 0} + {k \choose 2} + {k \choose 4}+ {k \choose 6} + ... +{k \choose k}$ for even $k$ in closed form, using methods of counting. How could this be done?


What kind of clause or phrase is used in the first part of the following sentence (Frail and seemingly disoriented at times)? Would you elaborate on its structure.     Frail and seemingly disoriented at times, he is looking vulnerable.


Let us be more creative with our hat placement

So, safe to say, I am fairly addicted to the hats. They are a lot of fun and their silliness is addictive.  In the spirit of the winterbash, I am hoping we can be allowed to have more control of hat positioning. After asking for a downvote in chat so I could get that babe mullet, I wondered if I could give myself a mullet-beard but it won't allow 360 degree rotation.   Just think of all the absurd things we are missing out on!    Sweet ass soccer necklace    Mulletbeard™    Crab face googly eyes    iPhone Plus Plus  Now sure, some nay sayers will say "but they're hats!"... If you're concerned with keeping them as hats, it's too late! I am already  it up. Furthermore, when I get tired of my stache, I switch out to crab eyes so, resistance is futile!


I use Ubuntu 18.04 with Gnome Shell and gdm3.  When I press Ctrl + Alt + F1 I see gdm3 home screen. My current desktop session is on the second "screen" Ctrl + Alt + F2.  Is it a bug?  I had a random bug and I don't know if it's related to the duplicate gdm3 instances: when I logged back after locking my screen, I was unable to reopen with session and I had to reboot the computer by pressing Ctrl + Alt + Del on another screen, like Ctrl + Alt + F3.  I removed gdm3 with sudo apt remove --purge gdm3 and reinstalled it and there are still 2 instances.  Update: once my screen is locked, sometimes I can't log in again as my password is rejected, but if I switch to the first "screen" with Ctrl + Alt + F1 I can log in again.


Is $\sqrt[3]{24+\sqrt[3]{24+\sqrt[3]{24+\cdots}}}$ even? prime? composite? an even prime?

I am not being able to solve this question.  It is basically a high school level question and chapter I think is basic fundamentals of maths.  The value of $$\sqrt[3]{24+\sqrt[3]{24+\sqrt[3]{24+\cdots}}}$$ is equal to ...  an even number a prime number a composite number an even prime number


After switching from windows 7 to Ubuntu 18.04, the number of partitions in my hard drive reduced from three to one and all my data got lost. Now, I want to recover all of my data.


Cylinder rolling on an incline with offset center of gravity

Consider a hollow cylinder with a dense 1kg weight affixed to one point on the inside.  If placed on an inclined plane, the cylinder will not roll down if there is sufficient friction.  If we gradually reduce the density of the weight toward the volume of the cylinder (edit: alternately, if we advance the cylinder's rotation), there will reach a point where it will begin to roll.  What factors determine this point?  I presume it has to do with the center of gravity with respect to the rotating axis?  Edit: This is not homework.  I'm a high school dropout.  I am considering the construction of a robot that is essentially a heavy box hung between parallel bike wheels on a single axle.  I am considering the rollover condition, i.e.: how far can the box tilt before rolling over given a known center of gravity.  The box would lean forward if climbing a slope.  If the climb is too great, the box would turn too much and roll over.  I would limit the tilt with software to prevent a rollover if I knew the limit.  Edit 2: My question is essentially this one, which has been answered:   Thanks to commenter below who gave me the correct search terms.


The sun is shining and a spherical snowball of volume 340 ft$^3$ is melting at a rate of $10$ cubic feet per hour. As it melts, it remains spherical. At what rate is the radius changing after $2.5$ hours?   And this answer is wrong? please help $10\times 2.5 =25$ $340 - 25 = 315$ so $r^3 = \dfrac{315\times 3 }{ 4\pi}$ $r= 4.2$ ft


Please tell me the Difference between 18 and 30 GB wubi installation. Do I get all packages installed in 30gb wubi installation?


Is Sigma 150-600mm f 5-6.3 contemporary "F4-5.6" on Crop Sensor?

I bought Sigma 150-600mm f5-6.3 Contemporary DG OS HSM Lens for my Crop Sensor Canon 1300D.  What I've noticed is that it gives me max aperture of f5.6 at 600MM instead of f6.3 and f4.5 at 150mm on my Canon 1300D.   Please provide your views. Here's the link to the pic with Metadata–


Is our company logo too similar to this established brand?

I designed our company logo by incorporating the two first letters of our name (W and M) and then put a circle around it.  We chose a teal color that was pulled directly from the color of a lake we visited. It was by chance that the W and M happened to be reminiscent of mountains.    It's been brought to our attention that Marmot's logo may be too similar and that we should consider changing ours before it turns into a lawsuit at some point.  It doesn't look similar to me, but then again I am very attached to our logo and have no clue where we would go from here.  I'm looking for objective opinions.   Our company manufactures yoga apparel (specifically leggings) with crossover appeal amongst many sports (outdoors included).  Marmot manufactures mainly technical outdoor gear like outerwear and sleeping bags so not exactly the same market but similar.    TIA!  Our logo by itself:   Marmot's logo:


How to start an official email to a professor

I want to send an email to a professor to inform him that I want to accept the offer of PhD admission and Research assistantship. But I do not know how to start email. Is the following good? if not, would you please recommend better phrase.     Dear Professor,      I hope you are keeping well ....


Internationalized domain name silently dropped

If you try to enter a internationalized domain name as your "website" in your profile, it will be silently stripped of any non-English characters.  Ex: My webiste is  but when I try to enter that it saves it as http://linus.unnebck.se/ when it actually should display linus.unnebäck.se and link to http://linus.xn--unnebck-9wa.se/ (or just link with the ä, don't now what is the right thing to do).  As I wrote this post I also noticed that the markup ends the link at the first non-English character aswell, look at the example above.


What are the names of these variations on the transpose of a matrix and symmetric matrices?

Is there a name for the operator that reflects a matrix over the diagonal running from the top-right to the bottom-left? For the moment, define this reflection of a matrix $A$ as $A^*$. Is there a name for the family of matrices such that $A = A^*$? For example, let $$ A = \begin{bmatrix} 1 & -1 & -1 & 1\\ 0 & 1 & 0 & -1\\ 0 & 0 & 1 & -1\\ 0 & 0 & 0 & 1 \end{bmatrix}. $$


What is the expected number of boxes that remain empty?

10 balls are placed in 10 boxes independently at random. Assuming that all 10 boxes were initially empty, what is the expected number of boxes that remain empty? Here are the possible answers, but please explain the solution:  a)$\left(\frac{9}{10}\right)^9$  b)$\frac{9^9}{10^{10}}$  c)$\frac{9^{10}}{10^9}$  d)$\left(\frac{9}{10}\right)^{10}$  I guess that the answer is c) because the probability that box is empty is $(\frac{9}{10})^{10}$ and we should multiply it by 10 as there are 10 boxes.


What does the 'rc' in `.bashrc`, etc. mean?

Well, this is embarrassing. I feel like I just realised I don't know a loyal colleague's name after working with them for 10 years. "Hey, er... *cough!*, thanks for that great job you did on setting my aliases this morning..."  What do the letters rc signify in .bashrc, .kshrc, etc.?  If you know, please cite sources.  Even if you don't know, I'd also welcome unfounded assumptions, suggestions or alternatives if they're marked as such.


Generating a delayed pulse of 0,5sec with one 555 timer upon powering up the circuit

In the link below, this circuit I found is what I needed. Only the length of the pulse and the delay are not what I want.  When I want just 0.5sec before pin 3 is up and the pulse duration I want is also 0.5sec, can someone tell me how big my resistors and capacitors must be? Or can someone tell me how I can calculate this?  My source power is 16 Volts I have already found 555 timers that can operate with 16 Volts, so thats not the problem.  When someone has another idea with two 555-timers, or something else that does the same, it's also OK.  Thanks


Ever so often on Ubuntu 14.04 my desktop freezes. The mouse stops moving and nothing moves. However the sound keeps going and processes in the terminal keep going (although I can't see their progress).  To get my system working I have to go to ctrl alt f2 and then switch back using ctrl alt f7. This usually does the trick and everything resumes like nothing ever happened.  This has happened after a fresh install and continued since then. I expected it to go away after I performed all my updates- but it has not.  I'm on Ubuntu 14.04 with a nvidia graphics card. (I'm using Nvidia's drivers).  Note that this appears to be the same probalem as  but there has been no solution that works posted yet.  Has anyone ran into this issue- know of any solutions?


Problems with relative "axis cs:" coordinates in pgfplots

Please behold this MWE (compat is at 1.13, so by default the coordinates are in axis cs:):   \documentclass[border=10pt]{standalone} \usepackage{tikz} \usepackage{pgfplots}\pgfplotsset{compat=1.13} \begin{document}  \begin{tikzpicture}[     ]      \begin{axis}[         xmin=0, xmax=1500,            ymin=60, ymax=100,         axis y line* = right,         axis x line = none,         clip mode = individual,     ]         %\addplot [domain=0:1500] {97-x/150};         \addplot [domain=0:1500] {x/15};         \draw [green, <-] (600, 93) -- ++(0,-1.5);         \draw [red,  <-] (600, 93) -- (600, 93-1.5);     \end{axis} \end{tikzpicture} \end{document}   The two draw commands executes perfectly and they give the same arrow, so you really see just one:    If you now comment out the \addplot and use the previous one, i.e, like this:       \addplot [domain=0:1500] {97-x/150};     %\addplot [domain=0:1500] {x/15};   the relative coordinates \draw goes astray:     Where is my fault? Is that relative movements are not supposed to work in axis cs:? Why it depends on the previous plot?


Showing $\frac{x}{1+x}0$ using the mean value theorem

I want to show that $$\frac{x}{1+x}<\log(1+x)<x$$ for all $x>0$ using the mean value theorem. I tried to prove the two inequalities separately.  $$\frac{x}{1+x}<\log(1+x) \Leftrightarrow \frac{x}{1+x} -\log(1+x) <0$$  Let $$f(x) = \frac{x}{1+x} -\log(1+x).$$ Since $$f(0)=0$$ and $$f'(x)= \frac{1}{(1+x)^2}-\frac{1}{1+x}<0$$ for all $x > 0$,  $f(x)<0$ for all $x>0$.  Is this correct so far?  I go on with the second part: Let $f(x) = \log(x+1)$. Choose $a=0$ and $x>0$ so that there is, according to the mean value theorem, an $x_0$ between $a$ and $x$ with   $f'(x_0)=\frac{f(x)-f(a)}{x-a} \Leftrightarrow \frac{1}{x_0+1}=\frac{ \log(x+1)}{x}$.  Since $$x_0>0 \Rightarrow  \frac{1}{x_0+1}<1.$$ $$\Rightarrow 1 > \frac{1}{x_0+1}= \frac{ \log(x+1)}{x} \Rightarrow x> \log(x+1)$$


To familiarize myself with axiomatic set theory, I am reading Kenneth Kunen's  that presents ZF set theory. I haven't gotten really far since I am stuck at the axiom of Extensionality, stated as follows:  $$\forall x,y \; [\forall z(z \in x \leftrightarrow z \in y) \rightarrow x = y]$$  As far as I understood it, the purpose of this axiom is to state that every two sets that have exactly the same members are the same set. In terms of the above formula, when antecedent is true, the consequent needs to be true. What confuses me here is the case when the antecedent is false. Then, the consequent can be false or true, i.e., we can't say much about the consequent. But, don't we really want to say that in that case those two sets are not equal? More precisely, shouldn't we use equivalence instead of implication? If not, what is the reason?


How to set the image as a background using Url to Image formatter?

We have a need to set an element such as
 to have an image as a background. I am trying to figure out the way to get the image to display as a background but also with the image style that was used.  The image field (field_image) in question is used in multiple view modes with different image styles.   Example:   Basic page view mode: default, field_image with format = image and image style = large Basic page view mode: promoted, field_image with format = image and image style = small Basic page view mode: small tile, field_image with format=image and image style = medium   How can I accomplish the code below? Would the proposed solution work as I am not sure it is safe to use ['#markup']?

   Currently on View mode:   Field_image with Format = Image, Image Style = large   Current problem:   node.field_image.entity.uri.value returns the original images, not the one where the image style is applied.    Proposed solution:   set format = URL to image image style = large update the twig template to use node.field_image.0['#markup]


Why is homology invariant under deformation retraction/homotopy equivalence?

This is pretty basic, but I can't find any answers on this site on this already. I want to know why the homology of two spaces $X$ and $Y$ are the same when $X$ deformation retracts/is homotopy equivalent to $Y$. I would appreciate an intuitive explanation and a formal proof.  Specifically I'm working through Hatcher's Algebraic Topology (chapter 2.1) and by homology, I mean both simplicial and singular homology as defined in Hatcher.   I also assume this holds for relative and reduced homologies, but if you can explain why that would be great.


Freestyle of and through Transparent Material (with a caveat)

I'm trying to get blender to render freestyle contours on objects behind a transparent material (literally transparent, not glass) and I can adjust the QI Range to max at 1, and while this does draw the freestyle lines on the occluded objects, it also draws freestyle lines on parts of the opaque mesh that really should be hidden. My major problem is I still want freestyle lines around the transparent object, and I want freestyle lines around objects occluded by this, but I don't want freestyle lines on objects occluded by opaque objects. Is this even possible considering freestyle doesn't know anything about materials? Is there something I can do to the backfaces of the transparent object to make freestyle appear through it but not through the other (opaque) objects?


I need help with calculating probability

I need help with this question: Consider a loaded dice such that the probability to obtain an outcome of 1 is 2p/3, the probability of obtaining 2, 3, 4 or 5 is p each, and the probability of obtaining 6 is 3p/2.  (1) Compute the average outcome of throwing the above loaded dice. (2) Compute the variance in the outcome of throwing the above loaded dice  I have calculated p to be 6/37 and i've tried to do the other 2 questions but i don't know how to them


Lorentz transformation for timelike and spacelike points

On the page 28 of the book "An Introduction to Quantum Field Theory" by Michael E. Peskin and Daniel V. Schroeder in the last paragraph it says:     "When $(x-y)^2<0$  we can perform a Lorentz transformation taking $(x-y)\rightarrow -(x-y)$. Note that if  $(x-y)^2>0$  there is no continuous Lorentz transformation that takes  $(x-y)\rightarrow -(x-y)$"   Why is this happening?


When to use the present or the past perfect tense?

A few days back, I asked a question - why in reported speech is the present perfect tense sometimes not back shifted to the past perfect tense ? For example:     He said that he has painted the door.   Someone said - "if the situation is still relevant and the results of it can be seen, heard or felt then the present perfect tenses are not back shifted to past perfect tenses." And this was all about indirect speech, and I totally agree with what was said.  Now let's take a case which is not indirect speech. For example:     1) He noticed that he has finished painting the house.   My question is, is this sentence correct under the condition that finishing the painting has some present relevance ?     2) The president learned that the earthquake has caused havoc across   the country.   My question is, is this sentence correct under the condition that the earthquake has recently come and the effects of it can still be seen ?     3) I realized that he has left his wallet.      4) It was unclear that she has painted the door.   Are these 4 sentences correct or do I need to use 'had' in place of 'has' ?


Charge 19.5V laptop with 19V battery pack

I have a Dell Latitude E5450. On the original power supply it says output: 19.5V - 3.34A  Can I use a battery pack that provides 19V - 3A?  Hopefully somebody can explain this to me and what I need to be careful for. Is it OK to be below the numbers? Is it OK to be over? What is the range?


I've been having a problem with compiling.   I used the following test C code below and saved it as test.c in Home folder.  #include <stdio.h> int main() {   printf("Bruh!");   return 0; }   When I run in terminal the code   gcc test.c -o test   I get  nothing.  Thank you


How can I do this in python:  x = [1,2,3,4,5,6] for i in x:     if i == 4:        -restart the loop from beginning-     else:         print i   So here it will print till 4 then repeat the loop


When and why is the [featured] tag removed by the Community user?

I've found that the Meta (moderator only) tag  is automatically  by the  user. So, I want to know when and why is the tag  is removed by this user?  Is there any mechanism for this removal or is there simply a specified time period after which the  is automatically removed by the Community user?


Making Merge Tool run just once in ModelBuilder?

I have dozens of point shapefiles I want to merge. First I used the Feature Classes Iterator and declared the iteration output as input for the merge tool directly, the problem was that it merged the output files with themselves and the result was only the last shapefile from the folder.  What I did next, was to use the Model Builder's Collect Values tool, it did the job just fine, but took so much time because the model collects and the merges all the input feature classes once for each input file. (For example, I have 30 point shapefiles, the model collects all those 30, 30 times, and then merges 30 times).  My question is, how can I make the collect and/or the merge tool run just once? The model works fine but it'd be way better if it was more efficient. The solution may be conspicuous and simple but I can't seem to figure it out.