What is the difference between "dentry" and "inode table" in Linux FS? Are dentries and inode table same thing? If not what is the purpose of each and where are they stored? How does the filesystem exactly work specifically "ext4" or "xfs"?
What is a Superblock, Inode, Dentry and a File? From the article  by M. Tim Jones, I read that Linux views all the file systems from the perspective of a common set of objects and these objects are superblock, inode, dentry and file. Even though the rest of the paragraph explains the above, I was not that comfortable with that explanation. Could somebody explain to me these terms?
How to escape text for regular expression in Java Does Java have a built-in way to escape arbitrary text so that it can be included in a regular expression? For example, if my users enter "$5", I'd like to match that exactly rather than a "5" after the end of input. Combined flair is showing hidden accounts The combined flair started to display in this week site icons from hidden accounts. For example, this is my current flair:  The freehand red circle shows a hidden community that you can't see in my . This issue looks to me as a privacy issue. Being associated with a SciFi community or Arqade is not a bad thing for my serious work-only profile, but it could be indeed an issue for people trying to hide association with a religious community due to the dark times that we are living on. I know that this question is similar to , but I'm posting this as  of Adam Lear Now that I'm looking into home automation, I'm thinking about automatically cutting off the fridge power from 3am ~ 5am. Given that modern refrigerators are well insulated, it should be able to withstand 2 hours of non powered cooling.  If I proceed with this project, will I see a big reduction in my monthly electrical bill? Note: I cannot specificly tell which version of which of the two conflicting packages fixed the issue, but as of 2016 mathpec and polyglossia no longer show the issue.   Basically, I have encountered the same error as  and the workaround suggested by Andrey Vihrov reenables me to compile the document. The problem now is, that any shorthand defined by the ngerman-package (most notably the non-breaking hypen "~) has now been disabled, and I see combinations of american style closing quotes followed by a non-break space where a non-breaking hyphen should be.  Is there any way possible of keeping the shorthand definition, or redefining it to something else (something like \nbhy pops up to mind)?  I am using XeLaTeX as supplied by TeXLive. Finding joint density of dependent variables I've got two random variables, $x$ and $y$, where $x=u(y)$ and $y=v(x)$. How do I find the joint density of the two variables?   The eventual purpose is to find the integral  $\int^a\int^b f(x,y) dydx$,  where $f(.)$ is said joint density function.  This question is related () but I'm still a bit confused by the answer. I am indeed effectively looking for $Prob(x \leq a, y \leq b)$ but don't understand how I can get there without knowing the PDF first.  Any advice is much appreciated. Thanks a lot in advance! is $\sqrt{x}$ always positive? One asks “how does x taste,” implying that they’d like an adverb describing the way it tastes. But one answers with an adjective, “it tastes good” instead of “it tastes well,” which would imply that x is tasting something else. What’s the reason for this discrepancy? Are $(x^3)^{1/3} $ and $\sqrt{x^2}$ monomials?    In mathematics, a  is, roughly speaking, a polynomial which has only one term. Two different definitions of a monomial may be encountered:  For the first definition, a monomial, also called power product, is a product of powers of variables with nonnegative integer exponents, or, in other words, a product of variables, possibly with repetitions.   For the second definition, a monomial is a monomial in the first sense multiplied by a nonzero constant, called the coefficient of the monomial. Identification of fuzzy insect in Pennsylvania I live in south eastern Pennsylvania, USA. About a month ago I came across this very peculiar insect. Its body was about an inch long, it was fuzzy, and it had a long proboscis(?) and long orange legs.  I've been wondering about it ever since. Can anyone identify it? 1.  Why is the wave function complex? I've collected some layman explanations but they are incomplete and unsatisfactory. However in the book by Merzbacher in the initial few pages he provides an explanation that I need some help with: that the de Broglie wavelength and the wavelength of an elastic wave do not show similar properties under a Galilean transformation. He basically says that both are equivalent under a gauge transform and also, separately by Lorentz transforms. This, accompanied with the observation that $\psi$ is not observable, so there is no "reason for it being real". Can someone give me an intuitive prelude by what is a gauge transform and why does it give the same result as a Lorentz tranformation in a non-relativistic setting? And eventually how in this "grand scheme" the complex nature of the wave function becomes evident.. in a way that a dummy like me can understand.  2.   A wavefunction can be thought of as a scalar field (has a scalar value in every point ($r,t$) given by $\psi:\mathbb{R^3}\times \mathbb{R}\rightarrow \mathbb{C}$ and also as a ray in Hilbert space (a vector). How are these two perspectives the same (this is possibly something elementary that I am missing out, or getting confused by definitions and terminology, if that is the case I am desperate for help ;)   3.   One way I have thought about the above question is that the wave function can be equivalently written in $\psi:\mathbb{R^3}\times \mathbb{R}\rightarrow \mathbb{R}^2 $ i.e, Since a wave function is complex, the Schroedinger equation could in principle be written equivalently as coupled differential equations in two real functions which staisfy the Cauchy-Riemann conditions. ie, if $$\psi(x,t) = u(x,t) + i v(x,t)$$ and $u_x=v_t$ ; $u_t = -v_x$ and we get $$\hbar \partial_t u  = -\frac{\hbar^2}{2m} \partial_x^2v + V v$$ $$\hbar \partial_t v  = \frac{\hbar^2}{2m} \partial_x^2u - V u$$ (..in 1-D) If this is correct what are the interpretations of the $u,v$.. and why isn't it useful. (I am assuming that physical problems always have an analytic $\psi(r,t)$). "Authoring" versus "Writing" Problems with character input using scanf() Suppose $f$ is an isometric (i.e., distance preserving) function on $\mathbb{E}^2$ such that $f(0,0) = (0,0)$.  Then I want to show that $f$ is necessarily linear.  Now $f$ is linear iff $f$ is both additive and homogenous.  The following is an attempted proof for the homogeneity of f (missing the last step); still more, I have no idea how to argue for the additivity of $f$.  Any ideas?  Let $x \in \mathbb{E}^2$ and $\alpha \in \mathbb{R}$   We know that $\forall x \in \mathbb{E}^2$, $\Vert x - 0 \Vert = \Vert f(x) - f(0)\Vert = \Vert f(x) - 0 \Vert$ so that $\Vert x\Vert = \Vert f(x)\Vert$.  From this we immediately have the following facts:  $\Vert x \Vert = \Vert f(x) \Vert$  $\Vert \alpha x \Vert = \Vert f(\alpha x) \Vert$  We can then argue that since $\Vert \alpha x\Vert = |\alpha| \Vert x \Vert = |\alpha| \Vert f(x) \Vert = \Vert \alpha f(x) \Vert$, we also have that $\Vert f(\alpha x) \Vert = \Vert \alpha f(x)\Vert$.  Finally, we have that  $\Vert \alpha x - x \Vert = \Vert \alpha f(x) - f(x) \Vert$   iff $ \Vert (\alpha - 1)x \Vert = \Vert (\alpha - 1) f(x) \Vert$   iff $|\alpha - 1| \Vert x \Vert = |\alpha - 1| \Vert f(x) \Vert$  Since the last of these statements is in fact true, we now have $\Vert \alpha x - x \Vert = \Vert \alpha f(x) - f(x) \Vert$ as desired.  Now at this point it seems like I have all of the facts required to assert that $f(\alpha x) = \alpha f(x)$, but I can't figure out how to formally state why without illegally appealing to visual intuition.  Any ideas? Can I share my usb keyboard between two computers I love my Filco keyboard, I use it as primary keyboard for my Lenovo thinkpad all time. Now Im moving into the mac world and wonder:  is it possible to split my USB keyboard between two USB ports, ie one at my lenovo and one at my new iMac.   I was thinking that maybe there exists some kind of box with a switch to decide which port should receive the input, or preferable it would be possible to switch between the two via a keyboard shortcut. Calculate total sum of all numbers in c:forEach loop Problem with glossary I am copying the very first piece of code from  in order to create a glossary. While I get no problem in the compilation I do not get the "glossary part" that appears in the example. I literally copy paste.  Also, I want to create a document that only consists of a glossary of various terms. That is to put everything in alphabetical order (with the possibility to include references as well). How could I possibly do this? I tried some itemize options with alphabetical order but does not look that good. Is there a software utility to adjust screen gamma/brightness/contrast? I use to work at night and it is eye-hurting to watch at lightbulb-bright screens (I've got two - laptop's built-in panel and an external 18-inch CRT) in a dark environment. So I adjust my screens to be darker.  Can I do this a software way instead of pressing monitors' buttons that many times every time? Kinetic energy conservation in collision.  In any type of collision type of collision if we take the system to comprised of both bodies then the net external force is zero. So the work done by external force is also zero. By the relation $W=K_f-K_i$ as $W$ is zero hence kinetic energy is conserved. But this not the case.   Can you tell me what is the flaw in my argument? Some people say that the argument has neglected the fact that some kinetic energy is transformed into heat. But heat is created due to the interactions between bodies during collision which is thus an internal force and thus shouldn't affect kinetic energy. Do I need to pay in full for hostel reservation to show proof of accommodation for a Schengen visa? I am applying for a Schengen visa to travel to Germany and one of the requirements is showing proof of accommodation. I booked all my hostels via hostelworld.com, but only paid the non-refundable deposit (a couple of dollars for each place) instead of the entire amount. I intend to pay the rest of it on arrival at the hostel (or cancel it and go CouchSurfing, thus saving money).  But for the visa application, will the non-refundable deposit be enough to show proof of accommodation?  The reason I ask is, I emailed one of the hostels requesting a document showing my name and accommodation confirmation, and they replied saying they could only give me such a document once I pay in FULL.  Is this how I'm supposed to book for all places?  Have I been doing it wrong all this while (by only paying the tiny non-refundable deposit instead of full hostel fare)? What is a simple example of a limit in the real world?