I'm making a sandbox campaign using 5e to run a post apocalyptic fantasy Tokyo adventure, so each main location is known to the players and I can't just put in random encounters. Those locations need to have a strong connection to what is there today. The players will explore the world to pursue their goals while a mysterious villian observes from the darkness.  I want to use player background as a motivation and incentive for them to explore, and sometimes run into places they should have left alone. How do I use their backgrounds to help them decide which locations to explore so that I know which locations to prepare?  The sandbox is supposed to take them from lower heroic tier to lower epic, so I want to give plenty of space and time for them to develop and find clues, so I can't put all their motivation into one single location, and I don't want to transform every landmark into a generic encounter.  Here's an example of my map   I have all the marked locations named, but I don't know if I should map the dungeons yet because I don't know how often should I include something to aid the players find their goal and how often I should make them a deathly nest of aberrations and treasure.  You can see I have many locations, and it's overwhelming to prepare them all.  Where should I start?

Obviously you need to have some high level idea of what's going on in the world around the players, and where you are heading with the story, but in an ongoing game at some point players will be players and will head off in a different direction to what you planned.  How far ahead should you be planning to minimise or eliminate being caught off guard, but also try to minimise the amount of 'wasted content' you come up with but never gets used?


Let $p$ be an odd prime. For any integer $k$, define $S(k,p) = \sum^{p}_{x=1}(\frac{x(x+k)}{p})$.   (i) Show that S(0,$p$) = $p$-1  (ii) Show that if p does not divide k then $S(k,p) = S(1,p)$  (iii) Conclude that if p does not divide k then $S(k,p) = -1$  Been struggling with this question for a couple of days with no progress.

Let $p$ be an odd prime, and put $$s(a, p) =  \sum_{n=1}^{p} \left(\frac{n(n+a)}{p}\right) $$  Show that:  (i)  $s(0, p) = p − 1$  (ii)  $\sum_{a=1}^{p}s(a, p) = 0.$   (ii) If $(a, p) = 1$ then $ s(a, p) = s(1, p).$  (iii) Conclude that $s(a, p) = −1$ if $(a, p) = 1.$  Is it enough for me for ii) to say that if $n>0$ and $s>0$ then the $\sum(s)>0$ hence cannot be true   Im not sure what to do for the other ones


Conservation of energy and momentum governs Newton cradle. If $n$ balls were lifted, $n$ balls will bounce of on the other side. This happens if all balls have the same mass. Now, assume that you have a cradle with balls $a,b,c,d,e,f.$ All balls except $f$ has weight 1. Ball  $f$ has mass $n+0.5$ (1.5 or 2.5). We lift ball $f$ and bring it to motion. What will happen on the other side?  I would guess that n balls would fly to the original height and one more ball will fly half way.   =================================================     As far as I can tell physicists never tried this experiment fearing it will destroy the Universe. :-)  The so called duplicate is NOT a duplicate because it talks about integer mass ratios, whereas I ask about fractional mass ratios. Also, that answer provides a link to a single clip about a single case. that doesn't answer anything. Besides, even if that question was related, there is no way for me to revitaliate it.   =================================================

Using a "successive impact model" (as if each ball were seperated from the other ones), I produced the following animations:    You can see any combination of balls with masses of 1 or 2 (left) or 1 and 4 (right).  Unfortunately, I do not have any Newton cradle to make some experiments, and I'd like to compare my results with observations. I contacted the author of , which is the most instructive one I found about asymmetric Newton cradle. In particular, he writes that the "OoO" configuration behaves as the "ooo" one, which is not what I simulate. But the author is not sure whether who is wrong because he did the experiments a long time ago.  I am especially interested in asymmetric Newton cradle with simultaneous impacts: left and right balls collinding at the same time.   Please let me know if you have any idea on where to find such experimental data.  Edit Just of few general remarks to avoid extending the comments.    Energy and momentum are conserved. However, they are sufficient to ensure uniqueness of the post-impact velocities only when there are 2 balls. The successive impact model precisely consists in propagating the impact ball after ball, and therefore leads to a unique solution (which conserves momentum and energy globally). From the waves point of view, changing the mass of a ball can be done by increasing the diameter, or the density (or a combination of both). This simple model cannot account for such subtleties of course, but maybe it does not matter when the balls are "small enough". Even if I think it's quite basic, following WetSavannaAnimalakaRodVance's comment, I am ready to hand out my Mathematica code to anybody who wants it. I'll check for good ways to share it.


Please don't mark it duplicate. I have been through the rest of the posts and suggestions!  I am trying to dual boot Windows 7 with Ubuntu or Kali Linux but i am unable to do so.  I have backed up all my data to an external hard drive. So it is safe to work with partitioning.  I have a 500 GB hard drive and installed windows 7 onto a 150GB partition created with windows 7 installer partitioning tool.   I created Kali Linux bootable USB but when i proceed to the manual partitioning tool in the installer, it doesn't detect the Windows partition. It says the 500 GB space is free (unallocated).  I booted into the live kali linux form usb and tried gparted. It gives me the following error.  /dev/sda contains GPT signatures, indicating that it has a GPT table.  However, it does not have a valid fake msdos partition table, as it should.  Perhaps it was corrupted -- possibly by a program that doesn't understand GPT partition tables.  Or perhaps you deleted the GPT table, and are now using an msdos  partition table.  Is this a GPT partition table?   I tried the fdisk and its output is given below.  root@kali:~# fdisk -l  Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors  Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0xf17f14b8  Device Boot      Start         End      Blocks   Id  System /dev/sda1   *        2048      206847      102400    7  HPFS/NTFS/exFAT /dev/sda2          206848   115345407    57569280    6  FAT16 /dev/sda3       115345408   430327807   157491200    7  HPFS/NTFS/exFAT  Disk /dev/sdb: 7747 MB, 7747397632 bytes 255 heads, 63 sectors/track, 941 cylinders, total 15131636 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000b19d6  Device Boot      Start         End      Blocks   Id  System /dev/sdb1   *          63    15131635     7565786+   c  W95 FAT32 (LBA)   How should i fix this?

I have a 1TB drive and installed Windows 7 on a 128GB partition.  When I now try to install Ubuntu 11.04 it does not recognize the Windows partition but offers the complete 1TB drive to install Ubuntu on instead. It displays:    However, in the Ubuntu Disk Utility the Windows partitions are recognized.    What do I need to do in order for Ubuntu to recognize the Windows 7 partition and install Ubuntu as a dual boot?   Response to comments  The following commands were executed and the results are shown below:  fdisk -l  WARNING: GPT (GUID Partition Table) detected on '/dev/sda'! The util fdisk  doesn't support GPT. Use GNU Parted.  Disk /dev/sda: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x34a38165     Device Boot      Start         End      Blocks   Id  System /dev/sda1   *           1          13      102400    7  HPFS/NTFS Partition 1 does not end on cylinder boundary. /dev/sda2              13       16318   130969600    7  HPFS/NTFS  Disk /dev/sdb: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x14a714a6     Device Boot      Start         End      Blocks   Id  System /dev/sdb1               1       60801   488384001   83  Linux   parted -l  Warning: Unable to open /dev/sr0 read-write (Read-only file system).  /dev/sr0 has been opened read-only. Error: /dev/sr0: unrecognised disk label


I am thinking about visiting Cork for 5 days In September . I need a visa , and I'm worried about not meeting the sufficient funds requirement . I'm a university student and I'll be funding the trip by a money reward I won , It's not much , but it's enough for The activities I selected , tickets , accommodation . I also have a bank account,but I heard that I must have a bank account with at least 3000 euros,is showing the documents of paying enough?  Thanks for reading

The UK Visas and Immigration Directorate publishes  that provides helpful tips that can result in successful visa applications. Section 2 of this guidance opens is entitled "other documents you may want to provide" (emphasis mine).  Section 2: other documents you may want to provide – all visitors This section provides guidance on the types of documents that you may want to provide to help us consider your application against the Immigration Rules. Previous travel documents/passports, which show previous travel. Financial documents showing that you have sufficient funds available.  These must clearly show that you have access to the funds, such as:  bank statements building society book proof of earnings such as a letter from employer confirming employment details (start date of employment, salary, role, company contact details) where a third party (who is either in the UK or will be legally in the UK at the time of your visit) is providing financial support to you e.g. a business, a friend or a relative, documents to show that they have sufficient resources to support you in addition to themselves and any dependant family should be provided   The first item is "bank statements" and this ties in with the , which says...  evidence that you can support yourself during your trip, eg bank statements or payslips from the last 6 months  (Note 'eg' is a Latin abbreviation meaning "for example"; this appears to be optional rather than a fixed requirement.) Question: How should someone interpret this such that the chances of success are maximized? How many statements should I submit? What are they looking for and what do my bank statements tell about me?


I have a mail server which has a domain pointer with a .ca and .com (ie. mail.example.com and mail.example.ca).  Is it possible to have an SSL certificate for each for that mail server?  I am running Qmail with an Apache Web server front.  I tried to put the SSL pointer for the secondary extension in it, but that did not work.  So, currently it is only running for the .com extension (for SSL).

I know that a dedicated IP is needed for setting up SSL. What happens if we add SSL for  domains sharing an IP ? (Namevirtualhost)


How to change the following class to a class that uses ArrayList and LinkedList? I have to change all of the code in this class.  I am confused about ArrayList and LinkedList  import java.util.ArrayList;  public class ArrayStack {     private int maxsize;     private int top;     private int[] items;      public ArrayStack(int maxsize) {         if (maxsize <= 0)             throw new ArrayStackException("Stack size must be positive");         items = new int[maxsize];         this.maxsize = maxsize;         top = 0;     }      public void push(int item) {         if (top == items.length)             throw new ArrayStackException("Overflow Error");         items[top]=item;         top++;     }      public int pop() {         if (isEmpty())              throw new ArrayStackException("Underflow Error");         return items[--top];     }      public boolean isEmpty() {         return (top==0);      }      public static class ArrayStackException extends RuntimeException {         /**          *           */         private static final long serialVersionUID = 1L;          public ArrayStackException(String message) {             super(message);         }     }      public static void main (String[] a) {         ArrayStack stack = new ArrayStack(3);         stack.push(1);         stack.push(2);         stack.push(3);          // srtack.push(4); //over flow error          System.out.println(stack.pop());         System.out.println(stack.pop());         System.out.println(stack.pop());     } }   give me some explanations on this problems.

I've always been one to simply use:  List<String> names = new ArrayList<>();   I use the interface as the type name for portability, so that when I ask questions such as these I can rework my code.    When should  be used over  and vice-versa?


How to make the object follow another object's vertex?

I just created a plane and added a wave modifier to it, to simply make it look like something fluid. Now, I have an Object that I want to place on the surface of this fluid plane. But how do I do that?  I thought of adding a driver to my Objects location, but I have no clue how to get the location of a certain vertex in runtime.


To get a ^ (caret) character, I have to press the ^ key two times. The first time, nothing happens, the second time two ^ appearing. So I have to delete the second.  Same behaviour when I want to print a single ´ (apostrophe) or a single ` (backtick)

in Windows XP, when I type an apostrophe ', or  ", no character is displayed.  If I type another character, the apostrophe or dumb quote and the next character appear at the same time.  This happens with double quotes ", apostrophes ' and tilde ~ characters.  What could possibly be causing this?  This occurs in all applications I have tested - wordpad, firefox, ms word etc.


Can someone tell me why I dont have the coordinate slots? I have a screenshot of it.

When I press F3 to see the debug screen in I use Minecraft 1.8.1, some information is missing.   Most notably, there are no X, Y, Z coordinates.     What happened to my debug overlay?


I had Win 8 and Ubuntu 12.04 peacefully coexisting on a Toshiba Portege Z935.  EFI mode, Grub2, secure boot off, had to use "recommended repair" on Boot-Repair tool to get the boot working after original Ubuntu install.  All happy for about 10 months until....  I foolishly accepted MS's suggestion to update Windows to 8.1.  After the upgrade, each boot brought me to a "grub rescue>" prompt.  Was able to do a lengthy workaround to get back to grub menu on each boot, but wanted it fixed.  So, I started messing around with Boot-Repair, repeatedly, until the box wouldn't boot at all (just get blacks screen with "Insert disk with command files" or some such).  Tried reinstalling Win 8, upgrade to 8.1, then reinstalling Ubuntu.  Same result - wouldn't boot at all.  Tried reinstalling 8 without upgrade to 8.1, same result.  Tried installing JUST Ubuntu.  Same result.  Finally, set box from UEFI to CSM, installed Ubuntu again.  Now it boots!  So, I'm guessing the UEFI is somehow hosed in the "firmware" by one or more of the actions above.  How to fix?  I'm out of ideas, and I want EFI back.  THANKS!!!

I have an Ubuntu 13.10 and Windows 8 dual-boot working properly, and upgrading to Windows 8.1 breaks grub2 as expected. However, this time boot-repair was not able to bring grub back for me. My laptop jumps right into windows.  I double checked that Windows 8.1 re-enabled fast startup, so I've disabled it. And in my BIOS, UEIF is used for boot and secure-boot is disabled.  I have a 500GB GPT partition, in which, sda1 is the efi partion, sda2 is the /boot, sda3 is the / for ubuntu, and sda7 is the swap area. For Windows, sda4 is the msft reserve, sda5 is c://, and sda6 is Windows recovery. Those are (at least) my original setup.  Here's the boot info:   I also tried mount my hard drive from a live ubuntu session, then re-install grub on /dev/sda, which didn't work either.  Is there any other thing I could try to bring my Ubuntu back?


Let $f:[a,b]\Rightarrow \mathbb{R}$ , $f$ is continuous and nonnegative such that  $\int_{a}^{b}f(x)dx=0$. Prove that $f(x)=0$ on $[a,b]$    It is given that $f(x)$ is integrable (either because of the fact that $\int_{a}^{b}f(x)dx=0$ or because it is continuous in a closed interval and therefore continuous and bounded in a closed interval). Therefore, $0=\lim_{\lambda(x)\rightarrow0}\sum_{k=1}^{n}f(c_i)\Delta x_{i}=(b-a)\cdot \lim_{\lambda(x)\rightarrow0}\sum_{k=1}^{n}f(c_i)$ because $(b-a)$ is positive $\lim_{\lambda(x)\rightarrow0}\sum_{k=1}^{n}f(c_i)=0$ and because $f$ is continuous and nonnegative $f(c)=0$ and therefore $f(x)=0$ let us assume that $f(x)\neq0$ because $f$ is continuous and nonnegative $f(x)>0$; now $f$ is integrable on $[a,b]$ (either because of the fact that $\int_{a}^{b}f(x)dx=0$ or because it is continuous in a closed interval and therefore continuous and bounded in a closed interval).  So $$0=\int_{a}^{b}f(x)\leq \mid\int_{a}^{b}f(x)\mid\leq \int_{a}^{b}\mid f(x)\mid=0$$   Therefore $f(x)=0$ for all $x\in [a,b]$.  Are the proofs valid?

If $f$ is continuous, nonnegative on $[a, b]$, show that $\int_{a}^{b} f(x) dx = 0$ iff $f(x) = 0$  "$\Rightarrow$" Assume by contradiction that $f(x) \neq 0$ for some $x_0 \in [a, b]$. Without loss of generality, assume that $f(x_0) > 0$. Since $f$ is continuous, $\exists \delta > 0$ such that $f(x) > 0,  \forall x \in (x_0 - \delta, x_0 + \delta)$. Since $f$ is continuous on $[a, b]$, then it is Riemann integrable. Therefore $\int_{a}^{b} f(x) dx = \sup L(f, p)$ for some partition $p$. Now what I want to do is to show that the lower sum, $L(f, p) > 0$, in that case its supremum is $>0$, and that contradicts the condition that $\int_{a}^{b} f(x) dx = 0$. However, I don't know how to articulate it.  "$\Leftarrow$" If $f(x) = 0, \forall x \in [a, b]$, then $\int_{a}^{b} f(x) dx = \int_{a}^{b} 0 dx = 0$


I have one of these breakers in my panel? What is its purpose (vs a pair of two-pole breakers)? There are other  that deal with tandem breakers but not specifically dual tandem breakers.

I keep hearing about tandem breakers, and how they won't work with 240V loads and how they should never be used for a multi-wire branch circuit.  Aside from those issues...  What is a tandem breaker?     (note: they can be thrown independently).


I'm at my wit's end. I've searched up this problem a dozen times and found no good solutions. My drivers are up to date, and my GPU should still be plenty capable (Radeon RX 580). I've tried repairing my installation, and reinstalling, nothing. Flipping normals does nothing, switching between local and non-local user perspective does nothing, every element in the scene should be visible, not even the cube you get upon launch is visible, nothing I've found works. In object mode I can see only the outline of the mesh, in edit mode I see a translucent grid. Am I missing something really simple here? I started having the problem when I went looking online for some 3D mannequins to use as a drawing reference. Everything worked perfectly fine before then. Maybe one of the .blend files busted my settings, though, this wouldn't explain the persistence of the problem through reinstall. Still, I've put links to the models I tried using below. Also, I can't remember if the cube was invisible before or after I tried importing the files. I'm just looking to pose a 3D model as a reference for a drawing, nothing complicated. Model 1:  Model 2 (I'm using version 2.71):

I don't know why but now, when i go in material preview or rendered (in solid mode it works fine), my object is entirely gray, or invisible idk, because it has the same color of the background. I've been working for days on this project without having this issue, it suddenly showed up. I tried opening other old projects and suddenly they all do the same so i guess it is some blender program setting that applies for all the projects, but idk how it happened cuz i didn't change anything :/, anyone got any tips?


Would anything happen to my computer if I left it overnight to download something, such as my battery life going down or something similar happening?

I have an old HP dv7-7210sp laptop and I want to use it as a server. Is it safe to have it turned on 24/7? The server will be used with Nextcloud to backup my data.  Should I remove the battery from the laptop or keep it as a backup power source?  Also, is it safe to run HDD 24/7 or should I enable APM so it spins down after some time of inactivity?  Can the laptop burn if I leave it running?


how to type the fraction 3/2 with different height in Latex as show in the picute

I know I've seen somewhere how to typeset 1/2 as ½, but with arbitrary fractions (that is, a macro that takes two arguments and makes the first denominator and the second numerator...). Now I can't seem to find it.  How do I typeset an arbitrary fraction the same way as ½?


I created a TCP socket and tried to examine its file descriptor. I can list it without a problem:  [/proc/24846/fd]$ ls -al 11 lrwx------ 1 danb danb 64 10-Sep-19 22:58 11 -> 'socket:[38186892]'   But trying to cat or write to the file fails because the shell cannot find the file all of a sudden:  [/proc/24846/fd]$ echo 'hello' > 11 bash: no such device or address: 11 [/proc/24846/fd]$ cat 11 cat: 11: No such device or address   I don't expect those commands to do anything useful, but at least there should be consistency and the file should be found. So why is it that the shell fails to find the file when doing those particular operations?  To clarify, I'm not wondering how can I communicate with the socket via the VFS, but the reason why I cannot perform file operations on this file.

I’m running a Debian Squeeze web server. I’ve installed memcached on it, and configured memcached to listen on a Unix domain socket (at /tmp/memcached.sock), as it only needs to receive messages from the website, which lives on the same server.  It seems to be working fine, but I’d also like to communicate with memcached via the shell, to check that it’s doing what I think it’s doing.  memcached accepts messages via a simple ASCII protocol (if I understand correctly). If it was listening on TCP/IP, I could send messages to it via e.g. nc:  $ echo "stats settings" | nc localhost 11211   But I can’t figure out how to send that text to the domain socket instead.  On my laptop (which runs OS X Lion), both nc and telnet have options (-U and -u respectively) to use domain sockets. However, on my Debian Squeeze web server, these options aren’t present.


The target must succeed on a Wisdom saving throw or follow the command on its next turn.   If you were to cast Command as a reaction (e.g. readied action or war caster opportunity) on the turn of the spell's target, does the effect of the spell take place immediately or on the next round?  e.g. If I held the command spell and triggered it once an orc ran around the corner into view and told it to "grovel", would that end the orc's turn there, or would the orc complete it's turn unaffected, only being forced to grovel next round?     Grovel: The target falls prone and then ends its turn.

Several spells take effect on the target's next turn. Command is one example (PHB, p. 223):     You speak a one-word command to a creature you can see within range. The target must succeed on a Wisdom saving throw or follow the command on its next turn.   Compulsion has similar effects.  A spellcaster with the War Caster feat can cast these spells as a reaction (instead of a melee opportunity attack), during the target's turn. For example:     Harrek the Barbarian is within reach of Almira the War-Cleric. Harrek wants to go hit Almira's pet troll, so he moves away from her, figuring that he can shrug off any melee attack she might make. Almira casts command, with a command of "Halt". Harrek fails his Wisdom save.   When does Harrek "Halt"? Immediately, effectively ending his turn? Or on his next turn, after he has had a chance to move and attack the troll, and after Almira has had her turn and had a chance to cast another spell.    This point was raised in , but wasn't the main focus.


$$y=u\times v$$  How does one derive this formula, called the product rule?  $$y^{'}=uv^{'}+u^{'}v$$

How can I prove the product rule of derivatives using the first principle?  $$\frac{d (f(x) g(x))}{d x}    = \left( \frac{d f(x)}{d x} g(x) + \frac{d g(x)}{d x} f(x) \right)$$  Sorry if i used the wrong symbol for differential (I used \delta), as I was unable to find the straight "d" on the web.


Basically, not a techie at all, but trying to be. And I can follow directions well. Have a cheap old Lenovo laptop, and Ubuntu is too slow for me. I have 2GB of RAM and 1.6GHz.  Wanting to switch to Lubuntu, but have no idea how. I don't really know what it technically is called, but someone will ask...I don't insert a USB to boot, I just turn my computer on, and Ubuntu is first in the boot load.  I already installed lubuntu-desktop, but from what I understand, that just installs the desktop environment, but all of the Ubuntu processes that slow down older computers will still be running (and it certainly seems like it's still slow to me).  Are there any videos or step-by-step guides on how exactly to make the switch? I can re-install all of my apps, and re-login to all of my stuff, it's no problem. What might be the best way to do this? Factory reset, possibly? Not sure. Just trying to make the most out of my old laptop, so I can get rid of my MacBook finally.

I accidentally issued some commands I thought were safe in the terminal, and I ended up with no System Settings and lots of other missing functionality, but the OS still boots normally. I've decided I want to install Lubuntu instead of fixing Ubuntu for a fresh start and since my laptop is running on a 1GHz dual core AMD CPU.  I created a bootable USB as I usually do and placed Lubuntu 17.10 amd64 using Rufus 2.14.1086. I have GRUB that was installed with Ubuntu upon first install I still have Win8.1 which I still want to keep.  PS: I also tried creating a startup disk from Ubuntu  The question is: How can I boot from USB with GRUB2 so I can overwrite Ubuntu?


I want to make a new game on Let’s Go that only has Psychic Pokémon in my party. I already got my mew out from the pokeball plus though. Is it possible to put mew into Pokémon home, make a new game of Let’s Go on another Nintendo User account on my Switch and then move mew to that new game? I don’t want to buy another pokeball plus to get mew into the new game....

When Pokémon Let's Go! Pikachu/Eevee was released, a special edition included the Pokéball controller. This controller contained a Mew, which could be transferred to the game.  Once the Mew was transferred to a game, it was no longer in the controller and starting a new game meant losing the Mew.  Now that Pokémon Home has been released, does that still hold true? Or would it be possible to start a new game and keep the Mew by doing the below?   Transfer the Mew from Let's Go! to Home Start a new game on Let's Go! Transfer the Mew back into the new game of Let's Go!


I believe it was a standalone, but possibly 2 books. The main character was a female. The mages in the story exploded when they died unless they were completely drained of power first.  They could be drained by making a small cut and then the other mage touching the cut and draining them (to the extent it would kill them). A large portion of the book was main character's training to use magic at a school where thy would basically put up magical shields and duel each other. I believe I read it in late 90's to early 2000.

I read a young adult novel around the turn of the century. This story features a young female protagonist that is very naturally gifted in magic. She is attending a  to learn mastery and control over her gifts.  A lot of her school revolves around magic dueling. The participants are taught to extend their inner aura like a second magical skin, possibly referred to as creating a shield, or . The user can increase the strength of the shield by focusing harder on it, but doing so means you have less ability to be offensive. The amount of energy needed to create a shield was half the energy a foe would need to focus at you to break it.  Ex: Mage A and B are equally matched. Mage A focuses half his power into a shield. Mage B would then need to focus 100% of his power to break A’s shield.  Another aspect I remember is that when dueling, a school master would extend a personal shield on to one of the combatants as a sort of secondary shield that goes underneath the combatants. When one mage broke the others mages personal shield, the school masters shield protects the losers life from harm, and the breaker of the shield is declared the winner.  I distinctly remember one match in which the protagonist is having a duel with another strong student. She creates a wind storm around herself that picks up the sand from the arena floor and makes her impossible to see and thus makes it hard for her opponent to focus on her shield to break it. She then lashes out at her opponent with incredibly powerful strikes with the final strike being so hard it shatters the opponents shield and then breaks the school masters shield as well and stops just shy of killing her dueling partner.  Any assistance on this one? I think my daughter would love to read it.


Say I have several conhost processes that happen to be running already. Now I run a batch file, which starts a cmd process which, in turn, causes another conhost process to open up. From within the batch file    I know I can , but  I don't know how to get the PID of the associated conhost process.   My goal is to be able to close down all the other conhost processes that were running previously (or possibly after the batch file was run) and not close the conhost associated with the very batch file and cmd.exe doing all the closing. If that conhost gets closed, so will its cmd process and the batch file will end prematurely (I want it to do other things after that).  This is not a duplicate of the question asked in the link above. That question only dealt with getting the pid of the cmd, not the associated conhost PID.

I'm trying to find a way to get my own PID from a command prompt (for later use in bat scripts).  So far the only useful way I found was to use getpids.exe from here : , but I'm looking for a command that's "built in" to Windows.  I'm looking for a "bullet proof" way. No assumptions about my process being the only cmd.exe or anything.


I have problems in using Biblatex, when I compile when file,  the references are not shown and an error message of "empty bibliography" is shown.  Then I tried find a biblatex template provided by the overleaf platform. The following is the link of the template I found.  I open the file in overleaf, and everything works fine when I compile the file, I can see the references and citations correctly.  Then I tried to delete the contents of the .bib file, and then I compile, a message of "empty bibliography" is shown. This is also ok, because the .bib is blank.  However, when I put back the contents to the .bib file, and compile, the message of "empty bibliography" is shown again, and no referencing can be seen.  I tried the same procedure in two different computers (with the same overleaf account), and the same problem appears.  I would want to know how to fix the problem. Thank you in advance.

I am working on the  collaborative platform. I am facing the following error code :  ./main.lof:18:  Missing $ inserted.  <inserted text> $  l.18 ...some figure_name}}{23}{figure.17}   The thing is, even after correcting/deleting the figure that causes this error, the compilation will always stop on this.  From my understanding, I would need to erase the .lof file to avoid this error again but I do not know how to access it on the overleaf platform.  Do you think I undersand well the situation? Do you know how to access the .lof file?


We had a discussion the other day that needs settling. I am a medical student and in our "industry" we use a lot of three letter abbreviations such as: CPR (Cardiac Pulmonary Resuscitation), PUN (Patient Unmet Need), PEN (Practitioner Educational Need) etc. You get the message. Now, the other day our tutor wrote in a presentation: PENs, PUNs, CPRs and I argued (who am I to argue with the tutor?) that it should be PEN's, PUN's CPR's as we are pluralising an abbreviation. What is the rule (if any) about pluralising abbreviations? Dan

For example, if I wanted to write the equivalent of  There are many automated teller machines in this city.  Would it be  There are many ATMs in this city.  or  There are many ATM's in this city. (could get confused with possessive form or contraction).  or just  There are many ATM in this city. (assuming the final s is included in Machines represented by M).  Maybe something else?


Prove or disprove: Let $f$ be a function that is defined on a neighbourhood of $0$. Suppose that $\underset{x\rightarrow0}{\lim}\frac{f\left(x\right)}{\left|x\right|}=1$ , then $f$ is not differentiable at $0$ I somehow think its false but couldn't find a counter example. So I tried proving it and this is my prove of it being true: let us assume by contradiction, that $f$ is differentiable at $0$. thus: $\underset{x\rightarrow0}{\lim}\frac{f\left(x\right)-f\left(0\right)}{x}=f'\left(0\right)$ Which implies: $f'\left(0\right)=\underset{x\rightarrow0^+}{\lim}\frac{f\left(x\right)-f\left(0\right)}{x}=\underset{x\rightarrow0^+}{\lim}\underbrace{\left[\frac{f\left(x\right)}{\left|x\right|}-\frac{f\left(0\right)}{\left|x\right|}\right]}$ and: $f'\left(0\right)=\underset{x\rightarrow0^-}{\lim}\frac{f\left(x\right)-f\left(0\right)}{x}=\underset{x\rightarrow0^-}{\lim}{\left[\frac{f\left(x\right)}{-\left|x\right|}-\frac{f\left(0\right)}{-\left|x\right|}\right]}=\underset{x\rightarrow0^-}{\lim}-\left[\frac{f\left(x\right)}{\left|x\right|}-\frac{f\left(0\right)}{\left|x\right|}\right]=\underbrace{-\underset{x\rightarrow0^+}{\lim}{\left[\frac{f\left(x\right)}{\left|x\right|}-\frac{f\left(0\right)}{\left|x\right|}\right]}}$ They must be equal, thus: $\underset{x\rightarrow0}{\lim}{\left[\frac{f\left(x\right)}{\left|x\right|}-\frac{f\left(0\right)}{\left|x\right|}\right]}=0$ As we know $\underset{x\rightarrow0}{\lim}\frac{f\left(x\right)}{\left|x\right|}=1$, then: $\underset{x\rightarrow0}{\lim}\frac{f\left(0\right)}{\left|x\right|}=1$ which cant be, because if $f(0)=0$, then the limit is $0$, and if $f(0)\ne0$, the the lim is $\pm\infty$ Which in both cases, doesn't equal $1$, Contradiction. . . Was there a problem separating to $0\pm$ and change $x$ to $|x|$ without modifying $f(x)$? Or was there any other problem ? First post, be gentle. Thank you!

$$\lim_{x \to 0} \frac{f(x)}{|x|}=1$$ Then prove that $f$ is not differentiable at $0$. I was given this assignment and I'm not sure about my proof.. it feels like I'm assuming too much and not explaining with enough detail. Is there anything I need to add to make it sufficient? Assume toward contradiction that $f$ is differentiable at $0$. Then by definition we know that $f$ is continuous at $0$. Therefore $\lim _{x\to 0}f\left(x\right)=f\left(0\right)$ We know that $\lim _{x\to 0}\frac{\left(f\left(x\right)\right)}{\left|x\right|}=1$ Therefore we can conclude $\lim _{x\to 0}\frac{\left(f\left(x\right)\right)}{\left|x\right|}\cdot \left|x\right|=1\cdot 0=0$ But we can also rewrite this as $\lim _{x\to 0}\left(f\left(x\right)\right)\cdot \frac{\left|x\right|}{\left|x\right|}=f\left(0\right)\cdot 1=0$ Therefore $f(0) = 0$. Since $f$ is differentiable at $0$ we have $\lim _{x\to 0}\frac{\left(f\left(x\right)-f\left(0\right)\right)}{x-0}=\lim _{x\to 0}\frac{\left(f\left(x\right)-0\right)}{x}=\lim \:_{x\to \:0}\frac{\left(f\left(x\right)\right)}{x}\cdot \frac{\left|x\right|}{\left|x\right|}=\lim \:\:_{x\to 0}\frac{\left(f\left(x\right)\right)}{\left|x\right|}\cdot \:\frac{\left|x\right|}{x}$ Since the one sided limits of $\frac{f\left(x\right)}{\left|x\right|}$ exist, and are both equal to 1, we have $\lim \:_{x\to 0^+}\frac{\left(f\left(x\right)\right)}{\left|x\right|}\cdot \:\:\frac{\left|x\right|}{x}=\lim \:_{x\to \:0^+}\frac{\left(f\left(x\right)\right)}{x}\cdot \:\:\:\frac{x}{x}=1\cdot 1=1$ $\lim \:_{x\to 0^-}\frac{\left(f\left(x\right)\right)}{\left|x\right|}\cdot \:\:\frac{\left|x\right|}{x}=\lim \:_{x\to \:0^-}\frac{\left(f\left(x\right)\right)}{-x}\cdot \:\:\:\frac{-x}{x}=1\cdot -1=-1$ Since the limit doesn't exist, we have a contradiction to the fact $f$ is differentiable at $0$. Therefore $f$ is not differentiable at 0.


I have been going through String class in Java in depth.         String in Java is backed by character array.  To create strings that have initial values, we call the constructor as:       /* String creation */          String s = new String("example");   The constructor code in the String class is:          public String(String original) {             this.value = original.value;         }   Can some one please explain me the logic of "original.value". From the source code, I understand it returns character array. But how java generates it?

In Java, are there clear rules on when to use each of access modifiers, namely the default (package private), public, protected and private, while making class and interface and dealing with inheritance?


I have a string like  String[] toppings = {"1234", "56789", "123456"};  for each element of toppings I need to check the length, and if it is less than 9, I need to add zeros at the end.  for example consider first element of the array, it is 1234. Its length is 4, so I need to add 5 zeros at the end which looks like "123400000".  similarly I need to do it for all the elements present in toppings.  And finally at the end I need to concat all the vales present in toppings to one string. Means my output must look like String x = "123400000567890000123456000".  Any suggestions?  Thanks,

How do you left pad an int with zeros when converting to a String in java?  I'm basically looking to pad out integers up to 9999 with leading zeros (e.g. 1 = 0001).


Why don't dictionaries include what is, in my opinion, the most common meaning of the word "punt", which is to "(strategically) give up"      They punted on the hard problem.   Neither Oxford's, nor M-W list this meaning. In fact, M-W lists ten different meanings, many of which I never encountered.

Somewhere, I picked up the use of “to punt something” (or “to punt on something”) to mean “choosing not to do something” or “choosing not to do something now”. Examples:     The weather looks bad, let’s punt (on) the bike ride.   But I am having doubt that this is a correct use of the term, and I can find hardly any related references, so I am seeking clarification.  Also, is it to put something or to punt on something, or both?  Some of the possibly related references I found are:      Let’s extend all the tax cuts and punt again. ()   says:        Informal To cease doing something; give up: Let's punt on this and try something else.     Multiple slang dictionarlies ( and ), which maybe indicates that this used in computer jargon, but not in general English. According to , it is also business jargon.


Does anyone know how I can get the coordinate value displayed at the buttom of the qgis window? I have been searching through the qgis api but am not able to find anything suitable..

I am trying to get coordinates from a mouse click in QGIS 3 and python 3 using the plugin builder.  I have tried using the response , and i can manage to get the coordinates printed to the python console in QGIS but at the same time i get the message that "'TypeError: 'QgsMapToolEmitPoint' object is not iterable" or "'QgsMapToolEmitPoint' object does not support indexing"   I can't remember i ever seen a python program causing an error but still manage to compute and output the wanted result. The "not iterable" error traces back to the line with the for loop "for point in ... " the "does not support indexing" error is caused if i do e.g. x = pointTool[0]  Here is a version of the code:  from qgis.gui import QgsMapToolEmitPoint   def display_point(pointTool):     #print(pointTool)     cood = []     for point in pointTool:         cood.append(point)     print(cood)  # a reference to our map canvas canvas = iface.mapCanvas()  # this QGIS tool emits as QgsPoint after each click on the map canvas pointTool = QgsMapToolEmitPoint(canvas)  pointTool.canvasClicked.connect(display_point)  canvas.setMapTool(pointTool)  display_point(pointTool)


I want to know how groups work in Linux. In windows users that belong to admin group can have access to everything. So I want to know how to create a user and add that user in Root group or whichever group has access to everything in Linux.

I want to create a user with administrative privileges and all the regular setups like home directory.   Is there a adduser parameter to give the user sudo powers automatically? What are the default settings for adduser? Will it automatically create home directories and all the other things without extra parameters? (i.e. is adduser <username> enough?)


I'm trying to match a pattern and then print out two lines after it. I'm successfully able to do it with the following code.  awk '/'202404'/{c=3}c&&c--' consolelog.log > testing.txt   I'm trying to replace the 202404 with something I can enter in the terminal. So far I have tried   echo "Enter peak value" read peak awk '/${peak}/{c=3}c&&c--' consolelog.log > testing.txt   But it does not work.   I don't necessarily need to use awk, grep or sed or anything will do. I just need to match a user inputted pattern and print 2 lines after it.   ***UPDATE***** I was playing around with it and I got it to work. It was something I totally missed. Here's what I did.  awk 'c&&!--c;/'$peak'/{c=2}' consolelog.log > testing.txt

Having the following in one of my shell functions:  function _process () {   awk -v l="$line" '   BEGIN {p=0}   /'"$1"'/ {p=1}   END{ if(p) print l >> "outfile.txt" }   ' }   , so when called as _process $arg, $arg gets passed as $1, and used as a search pattern. It works this way, because shell expands $1 in place of awk pattern! Also l can be used inside awk program, being declared with -v l="$line". All fine.  Is it possible in same manner give pattern to search as a variable?  Following will not work,  awk -v l="$line" -v search="$pattern" '   BEGIN {p=0}   /search/ {p=1}   END{ if(p) print l >> "outfile.txt" }   '   ,as awk will not interpret /search/ as a variable, but instead literally.


I am trying to render the layer in QGIS as a map using python console.  I am using QgsComposerLegend() for drawing the legend in the map.  Is it possible to make the layer name hidden in the map legend using python console?

Is there a way to hide a layer name in the composer legend using pyqgis as we do from the legend properties (see picture)?    The only way I've found so far is by changing the layer name in the composer legend but it will also change it in the Layers list and I don't want that.   This is the code I used:          itemLlegend = composition.getComposerItemById('Legend')         modelindex=itemLlegend.modelV2().index(0, 0)         itemLlegend.modelV2().setFlag(QgsLayerTreeModel.AllowNodeRename)         itemLlegend.modelV2().setData(modelindex,'')         itemLlegend.updateLegend()   Any idea?


I am reading an example that gives a sequence and show how two topologies on the vector space containing the sequence will give different limits of the sequence. They conclude without proof: "the two norms cannot be equivalent" (equivalent in the sense $C_1 \|\cdot\|_1 \leq \|\cdot\|_2 \leq C_2 \|\cdot\|_1$). I don't see why differing limits give in-equivalent topologies.  Note: Open Mapping Theorem has not been introduced yet (which I've read can be helpful here -- but am not sure), so I suspect there's some more elementary/topological argument.

Suppose we have two equivalent norms, $\|\cdot \| \sim \left\vert\!\left\vert\!\left\vert \cdot\right\vert\!\right\vert\!\right\vert$. We assume that $x_n \rightarrow x $ in $(X,\|\cdot \|)$. Show that $x_n \rightarrow x $ in $(X,\left\vert\!\left\vert\!\left\vert \cdot\right\vert\!\right\vert\!\right\vert)$  We observe since the norms are equivalent, there exits constants $\alpha, \beta$, such that $\alpha \|\cdot \| \leq \left\vert\!\left\vert\!\left\vert \cdot\right\vert\!\right\vert\!\right\vert \leq \beta \|\cdot \|$, with $0 \lt \alpha \leq \beta$  Since, $x_n \rightarrow x$ in $(X,\|\cdot \|$) we know that for all $\epsilon>0, \exists K(\epsilon)$ such that for n>$K(\epsilon),$ we have $\|x_n -x\| \leq \epsilon$  Since, we know $\beta \gt 0$ , then $ \beta \|x_n -x\| \leq \beta \epsilon$, Thus we see that $\left\vert\!\left\vert\!\left\vert x_n-x\right\vert\!\right\vert\!\right\vert\leq \beta \epsilon$.  This is how far I've gotten, our goal to is to find a a $J(\epsilon)$ such that for all $\epsilon>0, \exists J(\epsilon)$ such that for n>$J(\epsilon),$ we have $\left\vert\!\left\vert\!\left\vert x_n-x \right\vert\!\right\vert\!\right\vert \leq \epsilon$  My candidate for $J(\epsilon$) is $J(\epsilon) = \frac{K(\epsilon)}{\beta}$ from my above argument, but I'm not exactly sure how to validate this. If someone could help me on the proof, it would be very appreciated. I believe I'm pretty close, just missing something small.


How can I open a file with another program than the default one with a command line in the terminal?  For example I want to open a PDF. To open it with the default PDF viewer I just write xdg-open theFile.pdf, but if I want to open it with "okular" for example, what command should I write?

I often see things like     read man xyz   For more information read xyz's man page.   see info xyz    so I wonder:   How can I get help on terminal commands generally? What exactly are these man and info pages?   How can I find and view them?


I am using Samsung Note 3. My friend's profile picture has suddenly disappeared! Is this a known problem? Is there anyway I can get the pictures to show again ?  Thanks

It's been a few days now since my friends contact images started to disappear on my Samsung Galaxy Sii. Whatsapp up to date. Android is 4.1.2.  I've already tried:   Turn off/on the phone; Add/remove the contact from the address book of the phone (my contacts are on the gmail account); Clear the phone cache (under App Management). Just the cache. I don't want to loose conversations; Checked whatsapp space usage (under App Managent). It's like 23MBytes total. Some apps use much more;   Some facts:   Some friends (few of them) are still showing the profile images. They are from the same source (Gmail Addr Book); If I delete/recreate those friends with profile images, their image is re-downloaded correctly. I also deleted the profile image in the "Profile Pictures" folder and whatsapp downloads it again;   My guess: Users that are changing their profile image recently are being set as "no profile photo" (in the server). This propagates to everyone else who refreshes their address book for any reason.  Can somebody check my findings?


Ubuntu 16.04 16GB RAM.  How can i increase swap memory in my case? And how many GB i have to add?

I'm going to install 64 bit 14.04 on a new machine with something like 1 to maybe 128GB RAM and even more RAM later. How much space should I allocate to the swap partition?   And especially: WHY those recommendations for these numbers?    (None of the existing answers  and  explain any of the why and are a bit dated if we look at 1GB or RAM and up)


I am running the Wine PPA (VErsion 1.4rc2 right now) and was going to test it with World of warcraft and Skyrim. But in the WoW video configuration it appears as tho it is not detecting the Shader Model 3.0. Basically it says there is none. I am running the game with and without the -opengl parameter with no luck.  How can I activate the SM3.0 in Wine since I am using the proprietary Nvidia drivers (290.xx) and have an Nvidia GT440 with 1GB Ram.  Additionally today I went to the winecfg and the options for Vertex and Pixel Shading are gone. It only shows the virtual desktop and a couple of other options but no Video configurations.

I am looking for a step by step instruction to guide me in the ways of installing, configuring and debugging many of the issues new users have when dealing with Wine in Ubuntu.  What is the recommended way of installing Wine, some of the key issues that it has and how to solve them?  If I have a specific problem with an App in Wine, how do I go about solving it? What are the recommended steps to ensure that I can fix a problem related to an app I wish to use?


Here is my code:      public boolean isBST() {         return isBST(this.root);     }      private boolean isBST(BinaryNode<T> rootNode) {         if (rootNode == null) {             return false;         }         if (rootNode.isLeaf()) {             return true;         }         T left = null;         T right = null;          if (rootNode.hasLeftChild()) {             left = rootNode.getLeftChild().getData();             if (left.compareTo(rootNode.getData()) < 0) {                 return this.isBST(rootNode.getLeftChild());             }             else {                 return false;             }         }         if (rootNode.hasRightChild()) {             right = rootNode.getRightChild().getData();             if (right.compareTo(rootNode.getData()) > 0) {                 return this.isBST(rootNode.getRightChild());             }             else {                 return false;             }         }         return true;     }   This code works for simple binary trees, but it doesn't work for other ones. Such as if I have a tree like so:           5        /   \       3     6      /\     1  2   It won't mark it false even thought it should since 2 is smaller than 3 and is in the wrong place. My code just checks the left child's left children, and the checks the right child's right children and not the inner children. What can I do to make this code work in the way that I wrote it? How can I modify it?

In Java, arrays don't override toString(), so if you try to print one directly, you get the className + '@' + the hex of the  of the array, as defined by Object.toString():  int[] intArray = new int[] {1, 2, 3, 4, 5}; System.out.println(intArray);     // prints something like '[I@3343c8b3'   But usually, we'd actually want something more like [1, 2, 3, 4, 5]. What's the simplest way of doing that? Here are some example inputs and outputs:  // Array of primitives: int[] intArray = new int[] {1, 2, 3, 4, 5}; //output: [1, 2, 3, 4, 5]  // Array of object references: String[] strArray = new String[] {"John", "Mary", "Bob"}; //output: [John, Mary, Bob]


$ sudo add-apt-repository ppa:bitcoin/bitcoin  error: NOT MAINTAINED. The OS-library linking packages here had a series of issues.  PLEASE DOWNLOAD DIRECTLY FROM bitcoincore.org (and verify the signatures of said files).  IF YOU WANT AUTO-UPDATES, please see the officially-maintained snap package - https://github.com/bitcoin-core/packaging/tree/master/snap  More info: https://launchpad.net/~bitcoin/+archive/ubuntu/bitcoin Press [ENTER] to continue or Ctrl-c to cancel adding it.  Hit:1 http://in.archive.ubuntu.com/ubuntu focal InRelease Get:2 http://in.archive.ubuntu.com/ubuntu focal-updates InRelease [111 kB]     Get:3 http://in.archive.ubuntu.com/ubuntu focal-backports InRelease [98.3 kB]  Ign:4 http://ppa.launchpad.net/bitcoin/bitcoin/ubuntu focal InRelease          Get:5 http://security.ubuntu.com/ubuntu focal-security InRelease [107 kB]      Err:6 http://ppa.launchpad.net/bitcoin/bitcoin/ubuntu focal Release              404  Not Found [IP: 91.189.95.83 80] Reading package lists... Done E: The repository 'http://ppa.launchpad.net/bitcoin/bitcoin/ubuntu focal Release' does not have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details.

When updating, I get the following error message:   W: The repository 'http://ppa.launchpad.net/mc3man/trusty-media/ubuntu xenial Release' does not have a Release file.   Here, I find another statement on this error:   This recommends removing certain PPAs; and, I'm not sure if I should do that since it might mean not getting the updates that I need.    Is this what I should do?


Let $(G,*)$ be group and $H_{1}, H_{2}$ subgroups of $G$. If $H_{3}$ is subgroup of $G$ that satisfies   $H_3 \subseteq H_1 \cup H_2$ and $H_3 \not\subset H_2$, then $H_3 \subseteq H_1$. Prove or give counterexample.   I really don't know how to solve this ,any help would be appreciated.

"Let $G$ be a group, and suppose $G=H \cup K$, where $H$ and $K$ are subgroups.  Show that either $H=G$ or $K=G$."  Let $h \in H$ and $k \in K$.  Then $hk \in H$ or $hk \in K$ (since every element of $G$ is in either $H$ or $K$).  If $hk=h'$ for some $h' \in H$, then $k=h^{-1}h'$, so $k \in H$.  If $hk=k'$ for some $k' \in K$, then $h=k'k^{-1}$ so that $h \in K$.  If for all $h \in H$ we have $h \in K$, or if for all $k \in K$ we have $k \in H$, then $H \subseteq K$ or $K \subseteq H$.  Then since $G=H \cup K$, we must have either $H=G$ or $K=G$.  I'm not sure if the first paragraph of my 'proof' implies the second.  I've shown that for arbitrary $h \in H$, $h \in H$ and possibly $h \in K$, and similar for $k \in K$.  I don't know how to wrap it up (or perhaps this route won't lead anywhere at all).  If this way won't work, I'd just like a hint on a new direction to take.  Thanks.


I am trying to formally learn electrodynamics on my own (I only took an introductory course). I have come across the differential form of Gauss's Law.   $$ \nabla \cdot \mathbf E = \frac {\rho}{\epsilon_0}.$$  That's fine and all, but I run into what I believe to be a conceptual misunderstanding when evaluating this for a point charge.   I know the math looks better in spherical coordinates, but I will be using Cartesian.   So when I calculate the divergence I obtain:  $$ \nabla \cdot \mathbf E = \nabla \cdot kQ\langle\frac{x}{(x^2+y^2+z^2)^{\frac{3}{2}}},\frac{y}{(x^2+y^2+z^2)^{\frac{3}{2}}},\frac{z}{(x^2+y^2+z^2)^{\frac{3}{2}}}\rangle = \frac{-3(x^2+y^2+z^2)}{(x^2+y^2+z^2)^{\frac{5}{2}}}+\frac{3}{(x^2+y^2+z^2)^{\frac{3}{2}}}.$$  This can further be simplified:  $$\frac{-3(x^2+y^2+z^2)}{(x^2+y^2+z^2)^{\frac{5}{2}}}+\frac{3}{(x^2+y^2+z^2)^{\frac{3}{2}}} = \frac{3}{(x^2+y^2+z^2)^{\frac{3}{2}}}-\frac{3}{(x^2+y^2+z^2)^{\frac{3}{2}}} = \frac{3-3}{(x^2+y^2+z^2)^{\frac{3}{2}}}.$$   Now instinctively I would say that 3-3 is zero and then the while thing is zero everywhere. I am confused as to why (purely mathematically) this expression is not equal to zero at the origin. I completely understand why it physically has to be that way. And I also understand that it is modeled with the delta dirac function. But what (again, mathematically) is stopping me from saying that equation is just zero even at the origin?

I just started in Griffith's Introduction to electrodynamics and I stumbled upon the divergence of $\frac{ \hat r}{r^2} \equiv \frac{{\bf r}}{r^3}$, now from the book, Griffiths says:  Now what is the paradox, exactly? Ignoring any physical intuition behind this (point charge at the origin) how are we supposed to believe that the source of $\vec v$ is concentrated at the origin mathematically? Or are we forced to believe that because there was a contradiction with the divergence theorem? Also how would the situation differ if $\vec v$ was the same vector function but not for a point charge? Or is it impossible?


Hex Warrior specifies you can use Charisma for attack and damage with any non two-handed property weapon, which would eliminate longbows.  But would taking Improved Pact Weapon allow for longbow?

Hex Warrior says:     you can touch one weapon with which you are proficient and that lacks the two-handed quality. When you attack with that weapon you can use your Charisma for attack and damage rolls.   later the ability says:     This benefit extends to every weapon conjured with the Pact of Blades feature, no matter the type.   (emphasis mine)  Does this allow me to use my charisma with 2 handed weapons(provided it is my Pact Weapon and my Hex Warrior Blade)?  This question is not the same as . That one is asking how many weapons, I'm asking if type means 2 handed or something else(Slashing or Ranged for examples).


I used to be able to do so, but something as simple as this fails now:  gksudo gedit   and this also fails:  sudo gedit   I receive the error:  Cannot open display.   I haved checked this:   .Xauthority and .ICEauthority have my user as owner and also read/write permissions As both files are binary, I cannot understand them and check if they are corrupted   Probably, I have some misconfiguration. I have read this  and many other guides before asking.  I'm using Ubuntu Precise 12.04 64-bit.

I've read  and am interested in this line:     You should never use normal sudo to start graphical applications as Root.   Why? What is the difference? Please provide a simple explanation, as I'm just a normal desktop user.


I have learned Python for about 4 months, I thought I know every basics now. But currently I accidently tried a simple python expression, and the result is out of my expectation. for example: test = [1,2,3,4]  test[0:-1:-1]  and the result is an empty list([]). However, my expected result is [3,2,1] for "test[::-1]" will output "[4,3,2,1]". Can anyone tell me why?

I need a good explanation (references are a plus) on Python's slice notation.   To me, this notation needs a bit of picking up.   It looks extremely powerful, but I haven't quite got my head around it.


Are all groups of order $2\cdot p$ abelian?   I would like to prove that Dihedral group $D(p)$ is the only non-abelian group of that order. $p$ is any prime $>2$.  Thanks for advice.

I'm looking for a simple proof that up to isomorphism every group of order 2p (p prime) is either $\mathbb{Z}_{2p}$ or $D_{p}$ (The Dihedral group of order 2p).  I should note that by simple I mean short and elegant and not necessarily elementary. So feel free to use tools like Sylow Theorems, Cauchy Theorem and similar stuff.  Thanks a lot!


Does divergence of $\sum a_k$ imply divergence of $\sum \frac{a_k}{1+a_k}$?  Note: $a_k > 0 $  I understand that looking at the contrapositive statement, we can say that the convergence of the latter sum implies  $\frac{a_k}{1+a_k}\rightarrow 0$ but from here is it possible to deduce that $a_k\rightarrow 0$ because it is not completely straightforward. If we assume $a_k$ to be convergent, this trivially follows but it could diverge in which case this is nontrivial to me.

Prove that if $a_n\gt 0$ and $\sum a_n$ diverges, then $\sum \frac{a_n}{1+a_n}$ diverges.     This is the solution to this problem, but I'm having a hard time understanding it. Why does $a_k/(1+a_k)$ not converge to $0$ if $a_k$ doesn't converge to $0$?   I'd appreciate it if anyone could answer this question for me.


I want to find positions of zeros in a list. mylist = [0, 1 ,False,2, 0.0, 'a', 0]  all_items=[i for i in enumerate(mylist)] # all_items=  [(0, 0), (1, 1), (2, False), (3, 2), (4, 0.0), (5, 'a'), (6, 0)]          res1=[] for i in enumerate(mylist):     if i[1] is 0 or i[1] is 0.0:         res1.extend([i])  # res1 =[(0, 0), (4, 0.0), (6, 0)]   res2=[i for i in enumerate(mylist) if i[1] is 0 or i[1] is 0.0]  #res2=[(0, 0), (6, 0)]    I supposed res1 and res2 to be equivalent, but they differs. Why 0.0 is not in res2?

My  has failed me.  In Python, are the following two tests for equality equivalent?  n = 5 # Test one. if n == 5:     print 'Yay!'  # Test two. if n is 5:     print 'Yay!'   Does this hold true for objects where you would be comparing instances (a list say)?  Okay, so this kind of answers my question:  L = [] L.append(1) if L == [1]:     print 'Yay!' # Holds true, but...  if L is [1]:     print 'Yay!' # Doesn't.   So == tests value where is tests to see if they are the same object?


This equation is directly given in my book and I am don't know anything about its proof.I tried L'Hospital rule by differentiating the both numerator as well as denominator(division rule), but the result is still coming in indeterminate forms.I am a beginner , and haven't practiced limits that much. This formula is really confusing me.


I know atoms undergoing alpha decay emit alpha particles, but I was wondering why specifically helium nuclei? If these atoms wanted to emit the smallest unit of matter (I'm talking about hadrons here, not subatomic) they could just emit hydrogen nuclei, or if they wanted to emit the smallest unit of protons/neutrons attached together they could just emit deuterium. Yet for some reason, they choose to emit helium nuclei. Any thoughts?

It is said in many textbooks that alpha decay involves emitting alpha particles, which are very stable. Indeed, the binding energy () is higher than for $Z$-neighboring stable isotopes. But the binding energy is lower than, for example, ${}^9\mathrm{Be}$ (). My question is why aren't other nuclear compounds ejected from heavy nuclei, e.g. ${}^9\mathrm{Be}$?  The   $$e^{-\frac{4\pi}{\hbar}\frac{Ze^2}{4\pi\epsilon_0}\frac{1}{v_\alpha}}$$ decreases exponentially in $Z$, so it explains intuitively why lower-$Z$ particles would tunnel more often. Specifically, it would explain why we would see ${}^9\mathrm{Be}$ emission ${e^{-2}}\simeq 0.14$ times as often compared to ${}^4\mathrm{He}$ emission. Also, the particles need to form in the nucleus prior emissions; but with a similar binding energy per nucleon (~7.08 MeV for ${}^4\mathrm{He}$ vs. 6.47 MeV for ${}^9\mathrm{Be}$) and higher total binding energy for the ${}^9\mathrm{Be}$ nucleus, I would expect that its formation in the same order of prevalence as the alpha particle (according to Ohanian, between 0.1 and 1 alpha particles are in existence at any moment in time).  Can anyone explain this? A reference to an article/textbook would be preferable.  EDIT Same goes for ${}^{16}\mathrm{O}$ which is also a double magic isotope, as 'anna v' pointed out. For it, the Gamow factor is smaller by $e^{-4}\simeq 0.02$, and emission should still be viable.


Take for example the two sentences:   "I was at the park and I was wondering about the future."  "I was at the park and was wondering about the future."  I hear the two being used interchangeably in spoken English all the time. However, are they both grammatically correct?

I was wondering how linguists analyze sentences like "She hugged and kissed her mother" or "Will you have that with or without syrup?" or "Four and five are the square roots of sixteen and twenty-five, respectively"?  My previous understanding was that all sentences can be , with each word being part of the "argument" of exactly one other word.  So in the sentence "Will you have that with syrup", will have is the verb that the entire sentence hangs from, with you being the subject, that the object, and with syrup a prepositional phrase in which syrup depends on with. (Please correct me if my understanding is incorrect.) But how would you ever draw a tree for "with or without syrup"? Specifically, whose child is syrup?  My first thought was that with or without forms a sort of super-preposition. But then what about "She rescued and provided shelter for the cat", in which the cat is simultaneously the object of a verb and a prepositional phrase?


When you do , it correctly displays as:     results found containing   mail   on the right.  However, if you were to do , it displays as:     results found not containing   and not containing   Can this be fixed?

I've been retagging posts matching [special] -character -[character] is:question  The sidebar gives this helpful description of my query:     results found not containing   and not containing   tagged with       not       search options   questions only   It looks like there are some words missing there...


These examples are very confusing to me and I still can't understand the difference between 's and of. For some sentences, it is grammatically wrong but for some sentences it is correct. Please help me out. Thank you in advance! :)

I gave a quick answer to part of  which had not been covered by previous answers, trying to clarify the reason you would say time of decoding but not decoding’s time. I said it was ’s usually indicates possession, but of course there were several counterexamples that would have occurred to me after a moment’s consideration, and these where helpfully supplied:   Britain’s climate two days’ time  a day’s work  the sun’s rays   I am still of a mind to say that possession of some sort is what allows the ’s. Even though the sun does not have title to its rays, they do belong to the sun. Now, at the risk of duplicating the original question and/or being pigheaded, I am curious as to why time of decoding but not decoding’s time is correct, if not for the reason I gave.


i have a string value '4578,6978,6578,987', now my requirement all comma's in the string should not come in resultset and should display like 4578 6978 6578 987

Using SQL Server, how do I split a string so I can access item x?  Take a string "Hello John Smith". How can I split the string by space and access the item at index 1 which should return "John"?


This is a very minor problem, but if we go to a user's bounty page (e.g. ), there is a misalignment between questions with 1 answer and questions with multiple answers.  I don't think this is intentional; it's inconsistent with the main page where 1-answer and non-1-answer questions are aligned.  I just thought I'd mention it. Firefox for Linux Mint 81.0 (64-bit):    Chromium Version 85.0.4183.121 (Official Build) Built on Ubuntu, running on LinuxMint 19.1 (64-bit):

There's something wrong with the vertical alignment on the :   (click to enlarge)  On the , which uses a similar list but without the Favorite column, the vertical alignment is correct.  (Tested in the latest Firefox, Safari and Chrome on macOS Catalina.)


$\displaystyle{\sum_{n=1}^{\infty} \left[\left( 1 + {1 \over n}\right)^{n} - {\rm e}\right]}$  I tried both root and ratio tests  (for the root test, the expression became way too complex to handle) but both didn't really work out.  Would there be an easy way of showing that this diverges?

How can we find the exact value of the infinite sum  $$ \displaystyle\sum_{n=1}^\infty \left\{\mathrm{e}-\Big(1+\frac1n\Big)^n\right\}? $$  This problem appears in:  , p.114.


I am trying to animate rolling dice and i dont want them to go out of bounds in relation to my camera so, I put a transparent fence around them but the problem is when i try to render it there are black parts of the transparent mesh showing. PLease Help thank you.

Using v2.73, cycles and a very simple scene: an array of cubes, no big deal.   If I set the shader's material to transparent, the cubes in the foreground do become transparent but those far away in the back do not disappear completely and this strange dark things appear (visible in rendered mode and in final renders)    I've played with the clipping distance on the viewport and camera, but I can't figure out how to make those ghosts go away...


I know that this is probably a very basic question but I can't seem to find an answer through Google searches.   I would like to create a field in an attribute table (in ArcMap 10.2) for a Number Label (i.e.. 1, 2, 3, 4, ... etc.) is there a way to calculate this field with the field calculator rather than typing in each individual number?

So I'm relatively new to ArcGIS and ArcCatalog.  I have created a field name of PROJECTID in a feature class in a Personal Geodatabase.  The data type is TEXT.  This will be a ten digit ID.  The first five characters will be a acronym.  The sixth character will be a digit that represents the type of feature.  It will be a number.  The last four characters will be numbers that should be incremented starting at 0001.    Example:     WATER-1-0001  Screen shot of the field:   So my question is how can I do this in ArcCatalog.  I've seen some Python code that will autoincrement like the following:  rec=[OBJECTID] def autoIncrement(a):   global rec   return "water" + str(a) + "-" +  format(rec, '04d')   Again I'm a newbie when it comes to ArcGIS . Now I am getting an error NameError name 'OBJECTID' is not defined.


Is there a tally somewhere of the exact number shown to be lost over the entire series, and (where possible) the episodes in which they were lost (or when the audience learned they were lost, if appropriate)?  Possibly complicated by the "Year of Hell" storyline and other cases where there were time resets; please note where a shuttle destroyed in an episode would have (logically, at least) been restored due to a time reset, to get an accurate count of the shuttles destroyed in the final timeline.

In the episode , at the start of the episode when Voyager is in the process of a major maintenance overhaul there are at least 3 shuttles that can be seen. I have lost track of the number of times a shuttle has been destroyed. How many shuttles does Voyager have, not including The Delta Flyer?


You know those jokes where someone has need for a number like for a WiFi password then they're given an integral so they'd just give up? People like sending me those cause I love math. But today I got a unique one.  $$\int_{-2}^2 \left(x^3\cos \frac{x}{2}\right)\sqrt{4-x^2} \, dx$$  Why is it different? Cause I evaluated it on Desmos and it's equal to $\pi$!  How is that possible? I'm trying to work around it and it's proving tricky. The much I know is if I can separate the square root term as an integral then it'll be the area of a semicircle with radius 2.

I saw this today, I checked in Mathematica and the integral comes out to $\pi$, but I have no idea how to solve it.     FREE Wi-Fi: The Wi-Fi password is the first $10$ digits of the answer.   $$\int_{-2}^2\left(x^3\cos\frac x2+\frac12\right)\sqrt{4-x^2}\ dx$$


Is it possible to bind a table name?  I want to make a class to read the columns from a tables and, depending on field type, generate the form inputs for me. When I do $form = new form("users");, the constructor is supposed to start with getting the field names from the table with the following code:  class form{      public function __construct($table, $skip = array("id")){         $pdo = new PDO('mysql:host=localhost;dbname=site;',USER,PASS);          $query = $pdo->prepare("DESCRIBE :table");          $query->bindValue(':table', $table, PDO::PARAM_STR, strlen($table));          $query->execute();          while($field = $query->fetch(PDO::FETCH_NUM)){             var_dump($field);             echo "

";         }          unset($pdo);     } }   This works just fine when I specify "users" instead of ":table" in the prepare statement, but the bind it's working, and I'm pretty sure it's because it's trying to bind a table name. Also, this needs to be binded because I'd like to have the ability to pass my table names through $_GET and the such.

Why can't I pass the table name to a prepared PDO statement?  $stmt = $dbh->prepare('SELECT * FROM :table WHERE 1'); if ($stmt->execute(array(':table' => 'users'))) {     var_dump($stmt->fetchAll()); }   Is there another safe way to insert a table name into a SQL query? With safe, I mean that I don't want to do  $sql = "SELECT * FROM $table WHERE 1"


I noticed that when I right click manually on an index and choose "Rebuild" or "Reorganize", its not giving any indication that its doing so, then I click on properties again for the same index, I see the fragmentation level is still at the same percentage even after refreshing!  Am I missing something?  I'm using the SQL Server 2008 R2 Standard edition  Thanks in advance

I have used ALTER INDEX REBUILD to remove index fragmentation. In some cases REBUILD does not seem to remove this fragmentation. What are the reasons why REBUILD does not remove fragmentation? It seems that this happens especially with small indices.


My questions concerns a chapter in Michael Spivak's math book Calculus. On page 81, Spivak talks about finding a coordinate axes for a plane P that intersects a cone. What I don't understand is the part where he talks about a point in that plane having a certain first coordinate with respect to the newly created axes; he labels this as x. This same point has αx+β its first coordinate relative to the standard axes with which we are familiar. I don't understand where he got the αx+β. I really hope someone clears this up for me. Here is a quote from that page dealing with conic sections: "Now we have to choose coordinate axes in the plane P. We can choose L as the first axis, measuring distances from the intersection Q with the horizontal plane (Figure 5); for the second axis we just choose the line through Q parallel to our original second axis. If the first coordinate of a point in P with respect to these axes is x, then the first coordinate of this point with respect to the original axes can be written in the form αx+β for some β. On the other hand, if the second coordinate of the point with respect to these axes is y, then y is also the second coordinate with respect to the original axes."

I have a question regarding the conics section of Spivak calculus and  the way he derives the final equation. I understand everything that he is doing up until:  Now we have to choose coordinate axes in the plane P. We can choose L as the first axis, measuring distances from the intersection Q with the horizontal plane (Figure 5); for the second axis we just choose the line through Q parallel to our original second axis. If the first coordinate of a point in P with respect to these axis is x, then the first coordinate of this point with respect to the original axes can be written in the form $$\alpha x+\beta$$ for some $\alpha$ and $\beta$  Now, I understand everything before that, and why he is changing coordinates from the 'standard' ones, xyz, to coordinates within the plane, so he can express the intersection of the cone and the plane in a equation. But the thing is how does he justify that there is some $\alpha$ and some $\beta$ that satisfy this condition for all x ? He just claims that such values exist, with no proof.  For anyone not familiarized with this chapter, i leave it down here so you can read it.   One of the simplest subsets of this three-dimensional space is the (infinite) cone illustrated in Figure 2; this cone may be produced by rotating a "generaling line," of slope C say, around the third axis.  For any given first two coordinates x and y, the point (x,y,0) in the horizontal plane has distance $$\sqrt{x^2+y^2}$$ from the origin, and thus $$\tag1 (x,y,z)\text{ is in the cone if and only if }z=\pm C\sqrt{x^2+y^2}$$. We can descend from these three-dimensional vistas to the more familiar two-dimnensional one by asking what happens when we intersect this cone with some plane P (Figure 3).  If the plane is parallel to the horizontal plane, there's certainly no mystery--the intersection is just a circle. Otherwise, the plane P intersects the horizontal plane in a straight line. We can make things a lot simpler for ourselves if we rotate everything so that this intersection line points straight out from the plane of the paper, while the first axis is in the usual position that we are familiar with. The plane P is thus viewed "straight on," so that all we see (Figure 4) is its intersection L with the plane of the first and third axes; from this view-point the cone itself simply appears as two straight lines.  In the plane of the first and third axes, the line L can be described as the collection of all points of the form $$(x,Mx+B)$$, where M is the slope of L. For an arbitrary point (x,y,z) it follows that $$\tag2 (x,y,z)\text{ is in the plane }P\text{ if and only if }z=Mx+B.$$ Combining (1) and (2), we see that (x,y,z) is in the intersection of the cone and the plane if and only if $$\tag{$*$} Mx+B=\pm C\sqrt{x^2+y^2}.$$ Now we have to choose coordinate axes in the plane P. We can choose L as the first axis, measuring distances from the intersection Q with the horizontal plane (Figure 5); for the second axis we just choose the line through Q parallel to our original second axis. If the first coordinate of a point in P with respect to these axis is x, then the first coordinate of this point with respect to the original axes can be written in the form $$\alpha x+\beta$$ for some $\alpha$ and $ \beta$. On the other hand, if the second coordinate of the point with respect to these axes is y, then y is also the second coordinate with respect to the original axes.  Consequently, (*) says that the point lies on the intersection of the plane and the cone if and only if $$M(\alpha x+\beta)+B=\pm C\sqrt{(\alpha x+\beta)^2+y^2}.$$ Although this looks fairly complicated, after squaring we can write this as $$\alpha^2C^2y^2+\alpha^2(M^2-A^2)x^2+Ex+F=0$$ for some E and F that we won't bother writing out. Dividing by $\alpha^2$ simplifies this to $$C^2y^2+(C^2-M^2)x^2+Gx+H=0.$$


Prove that $\mathbb{R}^n$ cannot be a finite union of its hyperplanes . I want a prove using linear algebra only and not functional analysis  i tried by contradiction  we know R^n is a vector space over R. let R^n = U Wi (i from 1-k) Wi's are hyperplanes so are proper subspaces, let x belongs to W1. and take y belongs to R^n-W1. so there are infinitely many x+ay for a belongs to R. x+ay doesnt belong to W1 as R^n=U Wi so x+ay belongs to some Wj, j not equal to 1. so Wj contains x and y. so W1 is a subset of U Wi (i from 2 to k) now applying induction we get R^n=Wk which is a contradiction as Wk is a proper subspace.  but my prof says there are gaps in the proof which i am not able to find.

If $U_1$, $U_2,\ldots,U_n$ are proper subspaces of a vector space $V$ over a field $F$, and $|F|\gt n-1$, why is $V$ not equal to the union of the subspaces $U_1$, $U_2,\ldots,U_n$?


I am planning on buying a Galaxy s7 and run ubuntu's mobile OS on it, is the phone able to run it stably?

With the announcement of the Ubuntu Phone OS I'd like to know what phone (and tablet) models are supported at this time.  Note from foss & Oli: We are making this the master question for all future "Will this work on <insert random tablet/phone/device here>?!" questions


I understand that we can say "walk on a hurt foot", but can we simply say "walk on foot" to mean go somewhere on foot? Isn't that a redundancy? For example, is this sentence correct despite the redundancy, or does the redundancy turn it into ungrammatical: "I walked on foot for a long time"?  Note: The scope of this question has nothing to do with which preposition to use in the phrase 'on foot'.

Which one is correct?         I go to school by foot.   I go to school on foot.       Are there instances when the expression by foot is preferred?    My last question is the following:   Why is the singular noun, foot, used?     If a person goes to school by bus/train/car they are using only one means of transport, they are travelling in one car not two. But people use both feet for walking, so why would the following expressions be ungrammatical?         I go to school by feet     I go to school on feet      I read the answers on this question  but they did not convince me.


I have read several texts that give a very technical description of what a topological space is, but I can't find any notes that really give an intuitive description of what it is and I'm really struggling to get my head around it. Is the idea behind a topology the notion that we wish to be able to have a notion of "nearness" of elements to one another in a set, without introducing a notion of "distance"? By "nearness" is it meant that two elements are within the same neighbourhood (i.e. they lie within the same open subset)? Given this, is the idea that two objects are topologically equivalent, e.g. a coffee cup and a doughnut, that the neighbourhoods that elements "reside" in are unaffected under a continuous deformation from one object to the other, such that "nearby" elements remain "nearby" (relative to one another)?  I would really appreciate it if someone is able to give me an intuitive notion of a topological space, and also a motivation for such a concept. Thanks.

I'm studying topology since a few months ago and I have never caught a good intuition of the topological spaces, but now I think that I did.  My intuition is the next; as many people point out the open sets capture a notion of nearness, (but I did never understand the exact way of this nearness intuition),the points in the open sets are near, and two points in distinct open sets are far, and then the axioms try to capture the behaviours of the opens.  To find a good intuition I have worked with two examples of spaces which I named A and B; A=[{a,b,c,d,e,f},({a,b,c,d,e,f},{},{a,b,c,e,f},{e,f},{a,b},{a,b,d,e,f},{a,b,e,f})], B=[{a,b,c,d,e,f},({a,b,c,d,e,f},{},{a,b,c,e,f},{a,b,d,e,f},{a,b,e,f})] and I obtained the next pictures (and here is my first question: are these  the correct spatial representaition of the spaces? A is in the right, B is the left, the black circles represent points):                                                                                And then the union axiom allows to establish different degrees of nearness, specifically the opens that aren't union of other opens  have near points, and the unions have points nearer than other points that aren't. Concretely in the space A; {e,f} and {a,b} are nearer than c and d, then the unions allow to speak of a "global " nearness.  The intersection axiom also talk about  different degrees of nearness, in the way that if we have near points and we have other near points that have common points, then than points are near, and in fact they are nearer, and so the intersection  talk of a "local" nearness.  And finally the axiom of the necessary membership of the space itself and the empty set, guarantees the fact that "there are nothing outside the space" or the totality of the space and in that sense all the points are near in the space.  Is this a good intuition? if not, please give me a good one.


My synaptic package manager in ubuntu is giving error:    Unable to get exclusive lock   This usually means that another package management application(like apt-get or     aptitude) is already running. Please close that application first.

I get this error when trying to use apt-get:  E: Could not get lock /var/lib/dpkg/lock - open (11 Resource temporarily unavailable) E: Unable to lock the administration directory (/var/lib/dpkg/) is another process using it?     How can I fix this?


The frequency of the following to happen, is quite high.    User asks a question. Somebody answers it correctly which solves the problem/issue. Instead of upvote or accept, the user edits the question and puts forth a new scenario/question that arose....after applying the answer, which is completely different from the original one.(And is not caused due to the answer)    Is there any other mechanism which can advise the user against such behaviour?    Is there any way to not let the user edit the question after getting the answer for the original question? Or should this be of no concern?    (or should i ask this question somewhere else, in some other way)

I'm not sure if there's already an existing term for this, so I'm inventing my own. (tl;dr: I call them "chameleon questions" because they change every time you submit or edit an answer.  If you're already intimately familiar with the phenomenon, please skip past the first set of bullet points to where I ask for recommendations.)  I think many of us have experienced this on occasion:  You open up a narrow-looking question, usually dealing with some specific error message.  The question probably contains a snippet of sloppy but not quite awful code; code indicating that the author, typically a new/low-rep user, possibly a , doesn't really know what they're doing.  I'm not trying to be condescending here, they're probably very intelligent and hardworking, but in this specific case, they're clearly in way over their head.  However, as a question, it's not really too bad.  The goal and problem are both clearly stated.  The code is formatted (sort of).  Mort was polite and checked their spelling.  The question looks answerable, although from a rep perspective* it's an obvious dead-end, it's had maybe 3 views in the past 30 minutes.  So you decide, you know what, this person took the time to write up the question properly, they deserve an answer, put on your good citizen hat and throw them a bone.  You slog through the ugly code, find the offending line, direct their attention to it and explain why it's wrong and how it needs to be fixed.  Later, they leave a comment saying that yes, that was indeed the problem and your answer helped them fix it (great!).  Oh, but, now there's another problem (uh-oh...). Something else is broken.  After letting out a long sigh, you read the comment and/or edited question, roll up your sleeves, and write up Take 2, hoping that's the end of it.  And of course it's not the end.  Now maybe the error is gone, but it's not doing what it's supposed to.  If you're anything like me, your patience is now starting to wear thin. It's lousy code and you didn't volunteer to help them rewrite their whole app.  And of course, the question still only has 12 views, and nobody has upvoted either the question or your answer, including the person you're helping, so this is turning out to be a genuinely thankless task in all respects.  Welcome to "Family Tech Support", Web 2.0 Edition.   * Which is of course just an arbitrary number that none of us care about. Not really, anyway. Not very much, at least.  So, here's where I get to my question.  At this point, do you:  Leave a comment, stating as politely as possible that you've done your best to help them answer the original question they asked, and if they have a new problem then they should start a new question?  (I did this once, and actually ended up with an accept, but I felt kind of guilty afterwards, I don't think anybody answered their 2nd question).  Bite the bullet and edit your answer a 3rd, 4th, 5th time, however many times it takes to resolve their issue, knowing full well that they may not even remember to accept the answer once you're done? (I may work for free on SO, but that doesn't mean my time is worthless.)  Just abandon the question, hoping that it will force Mort to start thinking for himself?  Something else?   I've tried all three of the above and none of them ever quite feel right. I do want to help, but at the same time there are a lot more "lucrative" questions I could be answering. And I don't mind spending a lot of time on an answer either, if the question is interesting or important to me, but debugging is dull work. I'd prefer not to reference specific questions here; I'm pretty sure that this is a shared experience, and my objective isn't to point fingers at "misbehaving" members.  I'm more looking for some practical advice on how to dig myself out of these pits of despair. Anybody have any other ideas?


I have written the following code and got the output.  import java.util.ArrayList;  public class DuplicatesinArrayList {      public static void main(String[] args) {          ArrayList <String> al = new ArrayList<>();         al.add("Soumen");         al.add("Rahul");         al.add("Soumen");         al.add("Ram");         al.add("Rahul");         al.add("Rahul");         al.add("Rahul");         al.add("Ram");         al.add("Ram");         al.add("Ram");         al.add("Ram");          for (int i = 0; i < al.size(); i++) {               int ctr = 0;             for (int j = 0; j < al.size(); j++) {                 if(al.get(i).equals(al.get(j)))                     ctr++;             }             System.out.println(al.get(i)+" present " + ctr + " times");          }     } }   The result is as follows:  Soumen present 2 times Rahul present 4 times Soumen present 2 times Ram present 5 times Rahul present 4 times Rahul present 4 times Rahul present 4 times Ram present 5 times Ram present 5 times Ram present 5 times Ram present 5 times   I want for each word there should be one result. Can anyone help?

I have an ArrayList, a Collection class of Java, as follows:  ArrayList<String> animals = new ArrayList<String>(); animals.add("bat"); animals.add("owl"); animals.add("bat"); animals.add("bat");   As you can see, the animals ArrayList consists of 3 bat elements and one owl element. I was wondering if there is any API in the Collection framework that returns the number of bat occurrences or if there is another way to determine the number of occurrences.  I found that Google's Collection Multiset does have an API that returns the total number of occurrences of an element. But that is compatible only with JDK 1.5. Our product is currently in JDK 1.6, so I cannot use it.


Evalulate $\lim\limits_{x \to ∞} (x-x^2 \ln(1+1/x))$  I know the answer is 1/2 and we have to make use of the exponential function but i can't seem to simplify the expression to get the answer, please help

How do I determine this limit ?:  $$ \lim_{x \to \infty}\left[x - x^{2}\log\left(1 + {1 \over x}\right)\right] $$  I have tried to decompose the $\log$ function but I don't know how to proceed from there.


I am new to beamer. There are shortcuts for some of the commands like Ctrl+Shift+I for \item. Is there a shortcut for adding new frame in beamer? If no, can I add a new one? I am using TeXStudio.

This is not about new macros like \newcommand, \def and others. This is not about autocompletion like using .cwl (in TexStudio) This is also not about using shortcuts for predefined commands that are listed in the shortcuts sections.   It is more closely related to the 3. Though. I want to define shortcuts for commands that are not listed there.  e.g. When I type Ctrl + Shift + B, I want   \begin{bmatrix} \end{bmatrix}   to be inserted just like Ctrl+ Enter inserts \\.


Let $A ∈ \mathbb{R}^{n×n}$ be  a symmetric matrix. How can I demonstrate that A is positive definite iff the function $q(x) := x^TAx$ is coercive .  I know the eigenvalues of A have to be positive for a positive definite matrix. But I don't see how this relates to coerciveness.  Does't $x^TAx$ need to be greater than $0$ to be positive definite?

Let $M_{n\times n}(\Bbb{R}).$ We say that $A$ is positive if $\langle Ax, x \rangle>0$ for $x\neq 0.$  I want to prove that if $A$ is positive, then $\exists\;\alpha>0$ such that    $\langle Ax, x \rangle\geq \alpha|x|^2$ for $x\in\Bbb{R}^n.$  Please, I need help for this! Proofs and references will be highly regarded!


Covid-19 has shaken up the flight industry, and I noticed some flights to far off tourist destinations that seem like great deals, e.g. US to Italy for $1000 round trip. If they are so good, I'd like to take advantage while possible; though it would be preferred to wait until Covid-19 is gone to fly. To help with the decision-making process, is there any database of historical flight costs, so I can truly check if these are good prices, or just the usual?

How can I view the typical flight prices (ideally during a given date of the year) between two airports prior to the COVID-19 pandemic? Google Flights only show the future prices.


How do I display the word "AMS-LaTeX" properly in LaTeX like in the image below?  Is there a command for the "AMS" part similar to \LaTeX?

I'm looking after a macro to write the (La)TeX logo (with parentheses), i.e. something similar to \TeX, \LaTeX, but where the output includes ()'s.


i am using ubuntu 12.04lts i try to inslall php5 it create an error  "1.Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied)    2.Unable to lock the administration directory (/var/lib/dpkg/), are you root?"

I get this error whenever I try to install programs using the terminal:  home@ubuntu:~$ apt-get install myunity E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied) E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?   Also I'm unable to install updates using the terminal.


I want to construct a bash script which contains nested double quotes.    I've tried all of the usual tricks, in particular  rprint which everybody recommends. But nothing I've tried works.      In particular, rprint -v name "%q " lets me nest quotes but I then can't deal with the \'s it puts in front of the quotes.   Finally I settled on this extremely crude kludge:  shCommand=`echo !ssh -p $othPort!` execThis=`echo rsync -e $sshCommand etc etc | tr '!' '"'` eval $execThis   Thus execThis is what I want, i.e.,   rsync -e "ssh -p XXXX" etc etc   But there has to be a better way to do this since a) it's extremely crude and b) it won't work if I need the ! in following line --- there seems to be no special character that bash never uses.     Could somebody tell me what a real bash programmer would do in this instance?    Thanks very much for any advice

In my Bash environment I use variables containing spaces, and I use these variables within command substitution. What is the correct way to quote my variables? And how should I do it if these are nested? DIRNAME=$(dirname "$FILE")  or do I quote outside the substitution? DIRNAME="$(dirname $FILE)"  or both? DIRNAME="$(dirname "$FILE")"  or do I use back-ticks? DIRNAME=`dirname "$FILE"`  What is the right way to do this? And how can I easily check if the quotes are set right?


Practical question about usage of inheritance in php. I'm pretty new to this.  The project I'm working on encloses a.o. multiple charts which are all built up from data out of a database.  I've created multiple php classes. One class 'Filters' is inherited by all other classes. Filters connects to the DB and calculated and holds all arrays of selected filters and participants and the corresponding data.  2 classes, one class which creates the page Headers and one class which creates the Selectboxes, are used on each individual page (also inherits from Filters). And each individual page uses a class which creates a specific chart, which also inherits and uses a lot of variables from Filters. So each chart-page uses Filters + Header + Selectboxes + 'SpecificChart', the last 3 Classes inherit from Filters.  It all works perfectly. But because php does not support multiple inheritance, I created a function addFilters() to copy all necessary variables to use in the different classes, so I do not have to instantiate Filters multiple times..  I instantiate Filters and pass the object filters to the constructors of the other classes which call addFilters().  I was wondering if there's a better solution to this? Without the need to copy all the variables several times? I hope my explanation is clear..;)

I'm looking for a good, clean way to go around the fact that PHP5 still doesn't support multiple inheritance. Here's the class hierarchy:  Message   -- TextMessage     -------- InvitationTextMessage   -- EmailMessage     -------- InvitationEmailMessage    The two types of Invitation* classes have a lot in common; i'd love to have a common parent class, Invitation, that they both would inherit from. Unfortunately, they also have a lot in common with their current ancestors... TextMessage and EmailMessage. Classical desire for multiple inheritance here.   What's the most light-weight approach to solve the issue?   Thanks!


If i have 25 horses in one race you can tack 5 horse only, if you want find top 3 horse from this 25 horses than how many race you need for find top 3 horse from it?

There are $25$ horses. You can take $5$ horses at a time and race them. Each horse always finishes the race in the same amount of time, and there are no ties. The only information you get from each race is the order that the $5$ horses finished in. What is the smallest number of races you need to find the $3$ fastest horses, in order?   I found this problem on  and cannot figure out the best answer. Please help.


How can I prove that $\sqrt[n]{n} > \sqrt[n+1]{n+1}$ for $n \in \mathbb{N} \setminus  \{ 1,2 \}$ ?  My approach:  Step 1:  $n_0 := 3 \qquad \sqrt[3]{3} > \sqrt[4]{4}$  which is true.  Step 2:  $\sqrt[n]{n} > \sqrt[n+1]{n+1}$ is true for any $n \in \mathbb{N} \setminus  \{ 1,2 \}$  Step 3:  $A(n) \rightarrow A(n+1)$ for any $n \in \mathbb{N}_{>3}$  $\sqrt[n+1]{n+1} > ... > A(n+1)$  And here i don't know how to proceed.  Can someone give me a tip?

I am currently helping a friend of mine with his preperations for his next exam. A big topic of the exam will be induction, thus I told him he should practice this a lot. As at the beginning he had no idea how induction worked, I showed him some typical examples.  Now he showed me an exercise he was having trouble with, which states that one should prove $$n^{n+1} > (n+1)^n$$  for all $n \geq 3$. I have to admit that I too have trouble showing this inequality, as in all of my attempts, my lower bound is too low. Also, I have not yet figured out, how one gets the $(n+2)^{n+1}$, primarely the number $2$ is a problem. I think this might be solved using the binomial theorem, however, I don't think they have already seen the binomial theorem in school.  Is there an easy method to show this inequality by induction not using the binomial theorem? If no: How can one show it using the binomial theorem?  Thanks for answers in advance.


$\cos x$ and $\sin x$ can be defined by rotating $x$ units around a unit circle: $\cos x$ is the $x-$coordinate and $\sin x$ the $y$-coordinate. However, I am struggling to understand the analogous definition for $\sinh x$ and $\cosh x$. I understand that a hyperbola can be defined as the set of all points satisfying $(\cosh t,\sinh t)$. However, this still begs the question as to how one can work out what $\cosh t$ and $\sinh t$ are in the first place. I know that the hyperbolic functions can be defined using exponentials, but I think a geometric interpretation would be nice.

Ordinary trigonometric functions are defined independently of exponential function, and then shown to be related to it by Euler's formula.   Can one define hyperbolic cosine so that the formula $$\cosh{x}=\dfrac{e^x+e^{-x}}{2}$$ becomes something to be proven?