I have a list of packages on my system, that were installed and removed again, but not purged, i.e. there are still a lot of conffiles etc. laying around.  The output of dpkg --get-selections | grep deinstall lists about 85 different packages which I don't need and want to be purged entirely.  So my short question, which I decided to finally ask after experimenting around has lead to , is:  How do I completely purge previously installed packages that are already removed?  Reinstalling and then purging is not an option, of course.
I was doing a package removal with apt-get remove but then realized I should have done a --purge along with it to remove the configuration files.  Can I remove the packages configuration files easily or do I need to reinstall the package and then remove with a --purge?
Is an explanation of 'effect of Earth's rotation on $g$' possible from an inertial reference frame? Edit : Added a picture for better understanding of my querry. All the texts I have studied has used an non-inertial frame to explain the phenomenon. But every time I see something explained with pseudo forces, I try to realize in real forces.   But in this case I tried to explain it in a frame which is centered in Earth's center and not rotating. But I couldn't explain what happens to the tangential component (to the point on Earth's surface where $g$ to be measured) of centripetal acceleration in this scenario. It doesn't cancel out.   But then I thought the tangential component is so low that practically it would have no effect.  Is my explanation wrong? I just installed a new version of Ubuntu and I want to roll it back to the previous version.  How can I do that? Is that even possible? Sign of Work and potential energy in electrostatics Conceptual question:  Suppose we have a configuration of point charges. If the potential of the energy of the system is negative, this means work is positive.   I'm kind of rusty with my mechanics, does the fact that the work is positive mean that to arrange the configuration you have to do work against the electric field? I.e. supply energy via some external force?  In terms of electrostatics, is there a general way of interpreting the sign of potential energy and work? ls command operating differently depending on recipient cannot start Tomcat 7 server - java.net.BindException: Address already in use Plotting Complex Quantity Functions Applying for tourist visa for US in country other than your own Possible Duplicate:          Can British passport holders apply for a B2 USA visa from other countries, if they are living there? Or do they have to go back to Britain to apply for it? I would like to know how to make this effect of merged circle selection. Here are images to illustrate:     Basically I'm looking for this effect:    How the merge effect of the circles can be achieved ? I didn't found any explanation concerning this effect. I know that to project those texture I can develop a decal system but I don't know how to create the merging effect.  If possible, I'm looking for purely shaders solution. Product of binomial coefficient as a basis Fractional Laplacian on the torus Add existing ssh key for git I'm used to doing all my coding in one C file. However, I'm working on a project large enough that it becomes impractical to do so. I've been #including them together but I've run into cases where I'm #including some files multiple times, etc. I've heard of .h files, but I'm not sure what their function is (or why having 2 files is better than 1).  What strategies should I use for organizing my code? Is it possible to separate "public" functions from "private" ones for a particular file?   question precipitated my inquiry. The tea.h file makes no reference to the tea.c file. Does the compiler "know" that every .h file has a corresponding .c file? Object rotate in a strange way today i run into another problem. i dont know how i have done it (probably i clicked sth what i should not click) - anyway - since that moment my objects are behaving totally different when i try to rotate them. the objects are now rotating around the pivot point but they keep their alignment - not sure if i am clear. eg. if u would rotate a plane which is lies flat on the ground it makes the rotation but the faces of the plane would still be up and dont which shouldn't be the case with the "normal" rotation that i know. so i want to understand what i have done (because this kind of rotation could be also usefull sometimes for me) and how can i return it in the case it happens again. how to show only changed rows if want querying the following table :  EventDateTime (DateTime), Host (guid), Flag ( bit) 2013-04-01 05:00, {id-x}, 0 2013-04-01 05:01, {id-x}, 0 2013-04-01 05:02, {id-x}, 0 2013-04-01 05:03, {id-x}, 0 2013-04-01 05:04, {id-x}, 1 2013-04-01 05:05, {id-x}, 1 2013-04-01 05:06, {id-x}, 1 2013-04-01 05:07, {id-x}, 0 2013-04-01 05:08, {id-x}, 0 2013-04-01 05:09, {id-x}, 0 2013-04-01 05:10, {id-x}, 0 2013-04-01 05:11, {id-x}, 1 2013-04-01 05:12, {id-x}, 1 2013-04-01 05:13, {id-x}, 1 2013-04-01 05:14, {id-x}, 1 2013-04-01 05:15, {id-x}, 0   and the result should be:  2013-04-01 05:04, {id-x}, 1 2013-04-01 05:07, {id-x}, 0 2013-04-01 05:11, {id-x}, 1 2013-04-01 05:15, {id-x}, 0   i have try it with LAG,LEAD and OVER Clause. but no luck :( How can friction do no work in case of pure rolling? I have read various answers , on PSE and elsewhere , and most of them explain that the point of contact of the rolling object undergoes 0 instantaneous displacement in the direction of friction, I agree , but then there is a feeling that the friction does provide a torque , so how can it do 0 work . ( The pure rolling here is under a constant external force on the object so friction does act ). I'm looking for a class in java that has key-value association, but without using hashes.  Here is what I'm currently doing:   Add values to a Hashtable. Get an iterator for the Hashtable.entrySet(). Iterate through all values and:   Get a Map.Entry for the iterator. Create an object of type Module (a custom class) based on the value. Add the class to a JPanel.  Show the panel.   The problem with this is that I do not have control over the order that I get the values back, so I cannot display the values in the a given order (without hard-coding the order).  I would use an ArrayList or Vector for this, but later in the code I need to grab the Module object for a given Key, which I can't do with an ArrayList or Vector.  Does anyone know of a free/open-source Java class that will do this, or a way to get values out of a Hashtable based on when they were added?  Thanks! Finding Elevation Change, any method So, I think it'd be cool - for goal setting for example - if I could keep track of my elevation change.  The problem is, the local cyclocomputers I looked at seem to use barometric pressure to determine the change.  This is fine, unless some weather is moving in, which happens not infrequently in the Midwestern United States.  Or do some of them try to use an inclinometer, your speed, and some math you learn in Calculus II to keep track of your change?  That would seem more accurate!  I could try to use a GPS meter, but those things are expensive -  and based on back when I had service to my smart phone, not guaranteed to match my car's odometer for distance even - I've read from some other riders that the distance varies at least slightly from local measurement on a bike as well.   Alternatively, let's say that I ride along a known route.  Is there any good way of plotting that route for elevation change?  Thanks! I'm using Ubuntu Maverick and Virtual Box 3+. I have Windows 7 Ultimate. The problem is that it doesn't detect USB drives in Windows 7, but USB peripherals (mouse + keybord) are working.  I followed , but I can't find the user group vboxusers. How can I continue? I would also like to upgrade to the latest version without any risk (without losing my virtual hard disk drive). How to control RAM / swap usage Is there a way (application) to control RAM / swap usage policy at application level.  I have some applications that I use all the time and I want them to stay in RAM all the time and there are also application that I use quite seldom and they might be thrown to swap at demand. I know that default configured windows should give me best performance but I want to check whether I can get more :).  I use windows 7. Profile changes in Q&A are not pushed to Area 51 I just noticed that the info text on  is an older version of the text in .  I found  from April 2016 where Adam Lear says:     Area 51 is a separate codebase. It's also heavily outdated. Currently we can push a profile update from Q&amp;A to Area 51, but not the other way around   I think the pushing isn't working anymore. I just updated my text on SO again and it was changed in all my accounts, except Area 51.