I can't use MongoDB so I need to uninstall, but when I try to reinstall it, the program shows me a lot of errors in MongoDB, MySQL and also in dpkg. sudo apt-get purge mongodb-org* Reading package lists... Done Building the dependency tree        Reading status information... Done Note : selection of mongodb-org-unstable-tools for the regular expression &quot;mongodb-org*&quot;. Note : sélection de mongodb-org-mongos pour l'expression rationnelle « mongodb-org* » Note : sélection de mongodb-org-tools pour l'expression rationnelle « mongodb-org* » Note : sélection de mongodb-org-unstable-database-tools-extra pour l'expression rationnelle « mongodb-org* » Note : sélection de mongodb-org-unstable-server pour l'expression rationnelle « mongodb-org* » Note : sélection de mongodb-org-unstable-shell pour l'expression rationnelle « mongodb-org* » Note : sélection de mongodb-org-shell pour l'expression rationnelle « mongodb-org* » Note : sélection de mongodb-org-unstable-mongos pour l'expression rationnelle « mongodb-org* » Note : sélection de mongodb-org-database-tools-extra pour l'expression rationnelle « mongodb-org* » Note : sélection de mongodb-org-unstable pour l'expression rationnelle « mongodb-org* » Note : sélection de mongodb-org-tools-unstable pour l'expression rationnelle « mongodb-org* » Note : sélection de mongodb-org pour l'expression rationnelle « mongodb-org* » Note : sélection de mongodb-org-server pour l'expression rationnelle « mongodb-org* » Le paquet « mongodb-org-unstable » n'est pas installé, et ne peut donc être supprimé Le paquet « mongodb-org-unstable-mongos » n'est pas installé, et ne peut donc être supprimé Le paquet « mongodb-org-unstable-server » n'est pas installé, et ne peut donc être supprimé Le paquet « mongodb-org-unstable-shell » n'est pas installé, et ne peut donc être supprimé Le paquet « mongodb-org-unstable-tools » n'est pas installé, et ne peut donc être supprimé Le paquet « mongodb-org-unstable-database-tools-extra » n'est pas installé, et ne peut donc être supprimé Le paquet « mongodb-org-tools-unstable » n'est pas installé, et ne peut donc être supprimé Please use &quot;sudo apt autoremove&quot; to remove it. The following packages will be REMOVED :   mongodb-org* mongodb-org-database-tools-extra* mongodb-org-server* mongodb-org-shell* mongodb-org-tools* The following selected packages will be changed:   mongodb-org-shell mongodb-org-tools 0 updated, 0 newly installed, 5 to remove and 0 not updated. 4 partially installed or removed. After this operation, 53.5 MB of disk space will be freed. Would you like to continue? Y/n] Y E: The dpkg --set-selections sub-process returned an error code E: Couldn't clean the currently selected dpkg states
OS: Ubuntu 12.04  Accidentally deleted dpkg. Now, packages can't be installed. So, needs an dpkg installer which installs packages.
I'm reading  and I'm trying to understand the proof under "Degeneracy in One Dimension".  Here's what it says:     Considering a one-dimensional quantum system in a potential $V(x)$ with degenerate states $|\psi_1\rangle$ and $|\psi_2\rangle$ corresponding to the same energy eigenvalue $E$, writing the time-independent Schrödinger equation for the system:       $$-\frac{\hbar^2}{2m}\frac{ \partial^2\psi_1}{ \partial x^2} + V\psi_1 =E\psi_1$$       $$-\frac{\hbar^2}{2m}\frac{ \partial^2\psi_2}{ \partial x^2} + V\psi_2 =E\psi_2$$   Multiplying the first equation by $\psi_2$ and the second by $\psi_1$ and subtracting one from the other, we get:       $$\psi_1\frac{d^2}{d x^2}\psi_2-\psi_2\frac{d^2}{d x^2}\psi_1=0$$   Integrating both sides       $$\psi_1\frac{\partial \psi_2}{\partial x}-\psi_2\frac{\partial \psi_1}{\partial x}=constant$$   In case of well-defined and normalizable wave functions, the above constant vanishes, provided both the wave functions vanish at at least one point, and we find: $\psi_1(x)=c\psi_2(x)$ where $c$ is, in general, a complex constant. So, the two degenerate wave functions are not linearly independent. For bound state eigenfunctions, the wave function approaches zero in the limit $x\to\infty$ or $x\to-\infty$, so that the above constant is zero and we have no degeneracy.   Here are the parts I don't understand:   How does integrating $\psi_1\frac{d^2}{d x^2}\psi_2-\psi_2\frac{d^2}{d x^2}\psi_1=0$ yield $\psi_1\frac{\partial \psi_2}{\partial x}-\psi_2\frac{\partial \psi_1}{\partial x}=constant$.  Without having explicit formulas for $\psi_1(x)$ and $\psi_2(x)$, how do we just apparently pull them both out of the integral? I don't understand how the constant in the last equation vanishes just because $\psi_1$ and $\psi_2$ vanish at infinity. Even if it does vanish, how does that imply $\psi_1=c\psi_2$? I am trying to use Stack Exchange Andoid App to use my accounts in Stack Overflow &amp; Area 51.   For the Area 51, there is only Area 51 Discussion. Even Area 51 Discussion isn't working in the App!   VERSION 1.0.51  When adding this site, it's showing the correct full name as in this screen-shot:     However, when I pin this site to my fav sites in Stack Exchange, it is showing: Unknown Site. When clicking it, it shows black screen then just quit the App!  Here is the screen-shot:       Is the site not yet capable with Android? or is it a bug in the App itself?  PS: this question isn't duplicate:   In the previous versions of the App, the site was opening but with Unknown Site name. However, in this version, it quits the app when pressing the area site! It isn't opening at all! This question is also to track this bug in the App. As it's about the site name issue &amp; the content as well. I have a professor at my university who uses content from an un-cited textbook that he has never referenced anywhere, including his green sheet (syllabus), as an additional resource. At least some slides he has used include parts of content that have been re-worded and others that are 100% the same. I noticed this by Googling for textbooks on the material we're studying in class and found that examples given in one that I found were exactly the same as what he has provided.  Would this technically be plagiarism? Should he be given the benefit of the doubt in this situation? What is the difference between "getting robbed" and "getting mugged"? I can't seem to find the difference on the internet between "getting robbed" and "getting mugged". I would appreciate it if you could explain it to me. How do you kill a java.lang.Thread in Java? I want to update ubuntu 11.04 throught apt-get. So I added the following lines in apt.conf  export http_proxy=http://username:password@proxyserver.net:port/ export ftp_proxy=http://username:password@proxyserver.netport/  export http_proxy=http://deepak:Deepak@123@12.1.1.1:3128   My question is: how do I insert special characters to a username or password?  For instance: my password for proxy is Deepak@123 and it is getting an error. ConcurrentModificationException Woes How do I convert materials from Blender Internal to Cycles? I know this may be a tough or confusing question, but I have numerous existing materials I created and reuse for a project, which were all prepared for Blender Internal.  Now, I want to start the transition to Cycles, but I've hit a roadblock. How can I transition my materials without completely starting over? Or should I just forget it and start with fresh materials? Time Dilation When In Orbit Imagine a space ship orbiting the sun at near relativistic speeds, when compared to Earth (say from the reference frame of the sun) there would be x amount of time dilation.  This would mean people on the ship could live for 100's of Earth years.  My question is what would happen if a second ship flew directly away from the Sun and back (ignoring acceleration) at the same speed the orbiting ship is travelling, would the time dilation for the ship that travels in a straight line be the same as that moving in a circle?  The reason I ask is that I was imagining a scenario where intergalactic travel is possible as time dilation means even a journey of light years only ages the crew a fraction of that time, with space stations orbiting certain star systems at similar speeds so that people that don't work on ships can live a similar length of time. I understand that time dilation is all linked to a certain reference frame but working with a reference frame of the sun what would the time dilation be for the different objects taking different paths but at the same speed relative to the sun? If the ship docked back with the space station would they both say the same amount of time had passed? LaTeX baffled by BOM---Unicode's byte order mark. Unicode applies the convention of using a  as signature at the beginning of a text stream, identifying the encoding used within it. The following three bytes at the beginning of a file: EF BB BF, identifies this file as a UTF8 file. Vi and most text editors gracefully ignore this signature. Open office does that as well, but it adds this signature at the beginning.  Now, if I open a TeX file with OpenOffic.org, and I do that quite a lot (for mixed directionality editing), the signature is added, and baffles LaTeX, which produces an error message such as:   ! LaTeX Error: Missing \begin{document}.   See the LaTeX manual or LaTeX Companion for explanation.  Type  H &lt;return&gt;  for immediate help.  ...                                                l.1   ��\documentclass{article}   whereas a simple dump of the file does not show the problem. Is there a way to eliminate this problem, while staying in the realm of latex? How to stop the find command after second match? How to make find command, that will show only first two matches and then end, something similiar to  just version for two records. File changed listener in Java How to see python symbolic names of objects on cursor hover of menu items in Blender 2.8 in Blender 2.79 one could hover over a UI element and see the symbolic python name of said element. How would one accomplish the same with Blender >= 2.8? I just ran the following command in a directory with several files, some owned by root, some by a normal user. I got a strange message:  $ sudo chmod -rwx * chmod: example-file: new permissions are ----w----, not ---------   Why the heck does chmod refuse to clear all permissions, if a file had group write rights? What is the thought behind this behaviour?  And is there a way to force removing all permissions in one step, without having to execute sudo chmod g-w * afterwards? My printer does not print light magenta. (Canon MP220 - CL-38) I have a Canon MP 220, with new cartridges. Prints fine everything, but it won't print light magenta. I cleaned it and deep cleaned it many times. I have no idea what could be the problem. Cartridge models: CL-38 and PG-37.  Any ideas ?  LE: Now it won't print magenta at all! For every generation of Excel I can remember (including 2010, which I'm using now), Excel's "Auto Size Row" features sometimes fails to actually auto size a row when the cell contains wrapped text. When it works properly, all the text is revealed and there is no additional space below the last line of text. When it fails, it adds extra space below the text. To make matters worse, what you see is not always what you get, i.e., text that appeared okay on screen gets cut off when it's printed. You also get different sizing depending on whether you are zoomed in/out or at actual size.  Simple test case:  Why is there a one-line gap after the text in cell A1 but not in A2?  (To reproduce: set width of column A to 17.14 (125 pixels), text wrap on, and cell alignment top.)  (I double-checked that I applied Auto Fit Row Height to both rows. Zoom level is 100%.)    Is there any known remedy for this without resorting to manually adjusting the row heights (which is not practical for more than a handful of rows)? This is a tricky one and I've always relied on techniques, such as permission-based emails (i.e. only sending to people you have permission to send to) and not using blatantly spamish terminology.  Of late, some of the emails I send out programmatically have started being shuffled into people's spam folder automatically and I'm wondering what I can do about it.  This is despite the fact that these particular emails are not ones that humans would mark as spam, specifically, they are emails that contain license keys that people have paid good money for, so I don't think they're going to consider them spam  I figure this is a big topic in which I am essentially an ignorant simpleton. Hey guys I found one or two papers which use ridge regression (for basketball data). I was always told to standardize my variables if I ran a ridge regression, but I was simply told to do this because ridge was scale variant (ridge regression wasn't really part of our course, so our lecturer skimmed through it).  These papers I read didn't standardize their variables, which I found a bit surprising. They also ended up with large values of lambda (around the 2000-4000 level) via cross-validation, and I was told that this is due to not standardizing the variables.  How exactly does leaving the variable(s) unstandardised lead to high lambda values and also, what are the consequences of not standardizing the variables in general? Is it really such a big deal?  Any help is much appreciated. How can I do traffic shaping in Linux by IP? We have a transparent proxy setup. I tried looking for traffic shaping in Linux, and all I could find online was to limit traffic by interface (eth0/eth1...).  I need to limit the bandwidth (never exceeding a specific limit) by IP address or IP ranges and I can't find a way to do that.  Is there any way to do that? du shows completely different folder size for * and folder name I'm trying to move some data over and to start with I'd like to make sure that the size is ok. I run into a problem however, if I check the folder with   du -sh  myfolder/ 780M    myfolder/   but   du -sh * .. 71M     myfolder ..   I thought it might be something to do with hidden files but this particular folder does not have any inside.  Am I missing something?