How does Bash parameter expansion work?
Usage of :- (colon dash) in bash
Index of the center of a group in the group is not a prime number The question is to prove index of $Z(G)$ in $G$ is not a prime number.    We know that $|G:Z(G)|=|G:C_G (x)||C_G (x):Z(G)|$ where $C_G (x)$ means centralizer of $x \in G$  I want to mention that we do not want to use $G⁄Z(G)$ theorem.   We may assume that $|G:Z(G)|=p$ where $p$ is a prime. Proof that a sequence of continuous functions $(f_n)$ cannot converge pointwise to $1_\mathbb{Q}$ on $[0,1]$ Heartbleed: What is it and what are options to mitigate it? This is a  about understanding and remediating the Heartbleed security issue.   What exactly is CVE-2014-0160 AKA "Heartbleed"? What is the cause, what OSs and versions of OpenSSL are vulnerable, what are the symptoms, are there any methods to detect a successful exploit?   How can I check to see if my system is affected? How can this vulnerability be mitigated? Should I be concerned that my keys or other private data have been compromised? What other side effects should I be concerned about? I wanna create a new partition from the existing root partition.My root partition is about 250GB.I wanna create a new partition say 150 GB taking space from this root partition.Can anyone help me with the procedure on doing this?  output: fdisk -l  karthick@karthick:~$ sudo fdisk -l [sudo] password for karthick:   Disk /dev/sda: 250.0 GB, 250000000000 bytes 255 heads, 63 sectors/track, 30394 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: 0x28219744  Device Boot      Start         End      Blocks   Id  System /dev/sda1   *           1          61      487424   83  Linux Partition 1 does not end on cylinder boundary. /dev/sda2              61       30395   243650561    5  Extended /dev/sda5              61         124      498688   82  Linux swap / Solaris /dev/sda6             124         186      498688   82  Linux swap / Solaris /dev/sda7             186       30395   242651136   83  Linux How can you tell if if a meal is thawed? I am planning to place a meal (salmon + rice) in a refrigerator after having frozen it. How can I tell when it's thawed? How can I sound proof bathroom walls? I'm trying to figure out the best, least intrusive way of sound proofing the walls of a bathroom. The bathroom shares a wall with my bedroom, and my 3 yea old's bedroom. The main problem is the sound of water running (plus every bump on the counter and everything) echos loud and clear through the wall into my sons room.  I found  and it seems like a good choice. Another option is adding another layer fo drywall with something like  between them. But all the walls and ceilings in the house are textured. So replacing just one or two walls in a room is just not possible.   This is the layout of the two rooms. I've added red box around the wall with the most noise.   Is there anything else I'm missing here that I could do to dampen the noise short of tearing the bathroom apart? Usage of "as if" as interjection My question concerns the usage of "as if" as an idiomatic interjection. The references I have consulted (etymonline, online dictionaries, etc.) seem to agree that "as if" is used in this context to convey incredulity or doubt. This is how I have always thought of it.  The other day, I was with friends who used "as if" to express their surprise and joy about a wedding proposal. They weren't being sarcastic or incredulous; they were genuinely happy about the proposal. Here is a loosely paraphrased version of what they said:  "As if they're getting married!"  Is my friends' usage of "as if" standard? Is it a primarily regional distinction? (I am in Ontario, Canada right now.) The closest example we could come up with is someone says "I can't believe that you won first prize!" Of course, the person can and does believe it, so their words ought not to be taken literally. Is it the same idea with "as if"? How to get the filename without the extension from a path in Python? How to get the filename without the extension from a path in Python? For instance, if I had &quot;/path/to/some/file.txt&quot;, I would want &quot;file&quot;. I want to collect the most common mistakes, misconceptions, pitfalls, etc that (La)TeX and Friends users make. Please one answer for each mistake, misconception, pitfall, etc.  I am only interested in more technical, objective cases rather than psychological, social, subjective cases.  From this complete infinite list of technical and objective cases, we can have a reference how  to teach newbies much better directly or indirectly via writing a good book.  The technical and object cases are, for example, as follows.   Beginners sometimes use $\huge E=mc^2$ with the hope they will get a huge formula. It actually does not produce the expected result. The correct way is \huge $E=mc^2$. Beginner sometimes use longtable inside table because they assume longtable is the longer version of tabular which is able to be sandwiched in table. etc. I see a lot of questions comparing full frame (e.g EF for Canon, FX for Nikon) and crop lenses (e.g. EF-S for Canon, DX for Nikon) but I can't find the answer to what would be the differences between the photos taken with say a 50mm f/1.4 EF and EF-S lenses both used with   same APS-C sensor sized camera same ISO same f/1.4 f-stop same focal length same shutter speed   What would be the resulting differences in the photos? Which one would   be brighter than the other due the EF-S lens concentrating the light more? no that's wrong. Both put the same amount of light from the same FoV on the sensor. have greater depth-of-field? neither less problems towards the edges? generally the full frame more lens flare? generally the full frame lens unless there is, or you provide more shading anything else? not really, unless you start down the road of which one is typically of better build quality.   Edit: Added the answers from what seems to be the general consensus from the multiple answers and comments.  Results: My desire to buy a fast medium-high quality lens compatible with both full frame and crop camera's doesn't have to be hampered by the APS-C sensor size of my current camera.  This means I'm willing to part with more money to get a higher performance/quality lens as the performance/quality will be useful now and when I upgrade my camera.  Though reading reviews of some full frame lenses with short focal lengths, look out, as some are really only made to perform well on crop cameras even though they fit on a full frame camera and will give you a full frame picture, the edge quality is very bad. What does rate of change actually mean? If we have a function, say, $y=x^2$, then $dy/dx=2x$. Now $y=1,4,9,16...$ for $x=1,2,3,4...$ and $dy/dx=2,4,6,8...$ for $x=1,2,3,4...$ Now as $dy/dx$ represents rate of change of y w.r.t x but I can't understand how these particluar values of $dy/dx$ represent change ? I mean for x=3, the rate of change is 6. What does it mean ? I ran into an interesting behavior recently.  It seems that if I override .equals() to take a parameter other than Object, it doesn't get called.  Can anyone explain to me why this is happening?  It seems to violate my understanding of polymorphism in OOP, but maybe I'm missing something.  Here's much simpler code that shows what I'm seeing:  public class MyClass {   private int x;   public MyClass(int n) { x = n; }   public boolean equals(Object o) { return false; }   public boolean equals(MyClass mc) { return x == mc.x; }   public static void main(String[] args) {     List&lt;MyClass&gt; list = new ArrayList&lt;MyClass&gt;();     list.add(new MyClass(3));     System.out.println("Contains 3? " + list.contains(new MyClass(3)));   } }   When this is run, it prints "Contains 3? false".  It looks like the equals(Object) function is called, even though there is another that would work.  By contrast, if I write equals like this the code works as expected:  public boolean equals(Object o) {   if(!(o instanceof MyClass))     return false;   MyClass mc = (MyClass)o;   return x == mc.x; }   Why isn't it figuring out which version of the function to call based on the type of the parameter? SF Story about human adapting to alien environment Java. Splitting a multiple word string into two word strings every space How to rename objects with python? In the story I'm trying to recall, everybody on their thirteenth birthday (?) is assigned by some kind of brain analysis method a profession and given some kind of pill (?) that instantly (?) grants them the required knowledge and skills to start working immediately. Some professions are more sought after than others, especially in view of the olympic (?) games regularly held on a profession-by-profession basis.  The protagonist, however, is turned down from this system and dismissed with some general reason and has to work his way to adulthood the boring old way: studying from books. Eventually he rejects from his status as a "special" student and goes on the run, hiding from the teachers and envying the normal people.      Eventually, it turns out that the protagonist was actually smart enough that being spoonfed premade information was a waste. What he actually was assigned to was advancing the bundles of knowledge themselves, as well as being front line in the technological progress.  "Somebody has to write those textbooks! You can infuse knowledge about how to use today's technology, but you can't do that for tomorrow's - people that get assigned a profession become tied with their assigned technology and are only as relevant as that. If you want more, you must learn how things actually work, and there's no shortcut for that." (not an actual quote, but a specific passage as I remember it.)  The troubles the protagonists underwent were actually planned and necessary for him to acknowledge and accept his role in society.   This story was certainly longer than a couple pages, but it wasn't very long either. If it's a short story, it was probably written by Asimov, but I can't be sure. It rings me of Brave New World given the theme of government-issued population planning, but it certainly doesn't fit with anything else in the actual plot. Any idea? I run a guest ubuntu 12.04 on a host ubuntu 12.04, with VirtualBox, and the guest is much, much slower than the host (ALT+TAB takes 4-5 secs). I had a look around and I found contradicting opinions on VirtualBox versus VMware (free); so I thought to keep the former.   Both systems are updated, I installed the additions on the guest and I evenly split memory and video memory (64MB) between guest and host. I am running a Toshiba m200 laptop with 4GB ram and shared video memory. The host bios does not include a configuration option for machine virtualization. I have 2 cpus and I can't give them both to the virtual machine.  Is there anything I overlooked that could solve my problem?  Feel free to ask for more info, and thank you for any help.  EDIT Idling with the system monitor open the (single) guest cpu never gets below 55% and could rise to 80 - 90% just by moving the mouse around. Opening Firefox will cause the system monitor to show cpu usage 100% in the guest, while the host shows that both cpus are evenly working around 60%.  My cpu is Intel® Core™2 Duo CPU T5450 @ 1.66GHz × 2.  If this is not a configuration problem, does it mean my machine is too weak for virtualization? Can't install apps from App Store on iPhone with iOS 7 Benefits and Drawbacks of Swapping Associations of Positivity and Negativity of the Proton and Electron For historical reasons, I understand that a proton's charge was assigned the label of "positive", the electron's charge was assigned the label of negative, and, crucially, equations of current in E &amp; M are written with the notion that current is the flow of positive charge despite the rarity of actual flows of protons in real systems (which I understand are mostly biological systems).   If the possibility existed to instantaneously and at no cost, retcon these associations such that protons have a negative charge, electrons have a positive charge, and current remains the flow of positive charge, would there be any beneficial or detrimental outcomes?  For instance, would there be:   new interpretations of physical laws that would provide different or better insights into any relevant subfield of Physics significant simplifications to notation in any field of Physics or Engineering significant increases in understanding in the fields of electricity, electronics, electrical engineering, radiation/radiative transport, etc. a noticeably easier learning curve for any subfield of physics dealing with the concept of charge   Additionally, is there a permutation of positive charge, negative charge, and flow of current definition that would improve upon the one I suggested? What is the difference between update-grub and update-grub2? I'm making some changes on my grub file under /etc/default/grub. In some tutorials I have seen sudo update-grub and others sudo update-grub2. What is the difference?