Proofs of Determinants of Block matrices

I know that there are three important results when taking the Determinants of Block matrices  $$\begin{align}\det \begin{bmatrix} A & B \\ 0 & D  \end{bmatrix} &= \det(A) \cdot \det(D) \ \ \ \ & (1) \\ \\ \det \begin{bmatrix} A & B \\ C & D  \end{bmatrix} &\neq AD - CB & (2) \\ \\ \det \begin{bmatrix} A & B \\ C & D  \end{bmatrix} &= \det \begin{bmatrix} A & B \\ 0 & D - CA^{-1}B \end{bmatrix} \\ \\ &= \underbrace{\det(A)\cdot \det\left(D-CA^{-1}B\right)}_\text{if $A^{-1}$ exists} \\ \\ &= \underbrace{\det\left(AD-CB\right)}_\text{if $AC=CA$} & (3) \end{align}$$  Now I understand in result $(3)$, that all that row operations are being performed to bring it into the form we see in $(1)$, but I can't seem to convince myself that result $(1)$ is true in the first place.  Furthermore in result $(3)$, I understand that,  $\det(A)\cdot \det\left(D-CA^{-1}B\right) = \det\left(A(D-CA^{-1}B)\right)= \det(AD-CB)$, via the product rule for determinants I also understand that we need $A^{-1}$ to exist, for the initial row operation to reduce the matrix into an upper triangular form $U$, and I understand that we require $AC = CA$, to allow commutativity when we multiply $ACA^{-1}B$ to reduce it to $CB$.  Can someone provide proofs for results $(1)$ and $(2)$, as I can't seem to find proofs for them in any of the textbooks I have at my disposal


We all know that light has no mass at all. Yet we say that the gravitational pull of a Blackhole within Schwarzschild radius doesn't let light to pass. If the light has no mass, how can it experience the force? Secondly, does this phenomena suggest the particle nature of light?


No wireless connection detected HP Pavilion DV6 1220 with a Broadcom BCM 4312

I just installed Ubuntu 11.10 on my HP Pavilion DV6 1220 ek and the Laptop doesn't detect any wireless connection. Two hours before that, Windows 7 was running on my machine and the WiFi functioned perfectly.   Does anyone have an idea? I've been trying for several hours to fix it without success.   Output of lspci -nnk | grep -i net -A2:                                           02:00.0 Network controller [0280]: Broadcom Corporation BCM4312 802.11b/g LP-PHY [14e4:4315] (rev 01)     Subsystem: Hewlett-Packard Company Device [103c:1508]     Kernel driver in use: b43-pci-bridge -- 03:00.0 Ethernet controller [0200]: Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller [10ec:8168] (rev 02)     Subsystem: Hewlett-Packard Company Device [103c:3628]     Kernel driver in use: r8169   Output of sudo ifconfig wlan0 up;iwconfig:                                                 SIOCSIFFLAGS: No such file or directory lo        no wireless extensions.  eth0      no wireless extensions.  wlan0     IEEE 802.11bg  ESSID:off/any             Mode:Managed  Access Point: Not-Associated   Tx-Power=0 dBm              Retry  long limit:7   RTS thr:off   Fragment thr:off           Power Management:on


Ubuntu can't find an executable file in ~/.local/bin

after installation with  pip3 install --user steem-piston you will get a new executable piston installed in ~/.local/bin   I installed the tool using pip install, but I cannot find the executable file.  I'm not quite sure I understand what this directory is: ~/.local/bin.  Is it just root/local/bin?


I am running the following script in Platypus but the MAC address does not change:  #!/bin/zsh  IF=en7  mac=`ifconfig $IF | awk '/ether/{print $2}'` echo "$IF mac before change=$mac" randmac=`openssl rand -hex 6 | sed 's/\(..\)/\1:/g; s/.$//'` sudo ifconfig $IF ether $randmac mac=`ifconfig $IF | awk '/ether/{print $2}'` echo "$IF mac after change=$mac"   Not receiving errors anymore.  However, the MAC address is not changed by the script.  Commands work individually pasted into Terminal, but not executed as an application by Platypus.  Platypus screenshot:


When a question gets to  you can hover it to see how many hotness points it has.    (Note this doesn't occur for the HNQ list in the bottom right of most pages, it's just for the central HNQ page.)  Is there any way to get that information for any other questions that aren't there?


What stops me from reformatting a DVD+R?

It just interest me how, no matter what computer I put it in, whether it be running Windows, Mac or Linux, I can't seem to format it (I know that they're made to be write-once only). I'm guessing it's a hardware thing. But even so, what stops a computer from ignoring the rules and formatting the disc anyway?


How can I encode or encrypt a PHP source code?   I've tried this one , the problem is that it is easy to decrypt for someone who knows it. For a stronger encryption I use this one , but if I encrypt some PHP code my page doesn't work.   Which is the best method? I don't want to use Ioncube or Loaders.


Is this circuit for Piezo Transducer sufficient?

I want to drive this Piezo Transducer () directly from a pin on my STM32F0 microcontroller. I don't want to use a BJT transistor because the max current consumption of the transducer is so low (5mA). Right now I have the following schematic.          – Schematic created using   The pin on the STM32F0 can source a max of 3.3V (peak-to-peak). Since the max current consumption of the transducer is 5mA, I want to limit the current going into it to 2.5mA to be on the safe side. Using Ohm's Law, I get a resistance value of R = \$\frac{V}{I}\$ = \$\frac{3.3V}{0.0025A}\$ = 1320\$\Omega\$  Is this circuit correct or am I missing something fundamentally?


Are the humans in the Star Wars Galaxy really humans?

Related:   This is a subtly different question because I'm not asking whether there's a historical relationship between the two lineages.  I am asking this question because answers to these questions:      are making assumptions about the appearance of Padme while pregnant, the period of gestation, and appearance of newborn babies.  All of these presuppose that the "humans" of the Star Wars Galaxy are 100% biologically equivalent to us.   In fact, as far as I know, we don't actually know any of those facts from canon.   (Do we?)   All we know is that "human" children and adults look like us.  So, do we have any canon or out-of-universe commentary that tells us that Star Wars humans and Earth humans are biologically equivalent?  Another way to put this would be  If presented with a Star Wars human and a Milky Way human, would the best doctors or the best medical droids be able to distinguish them?


let G be a group of order pq,where p and q are primes. Show that any non-trivial subgroup of G is cyclic  how do we exactly go about doing this question


How to deal with months that have 31 days vs those that only have 30?

I am trying to create an errand reminder. The idea is the user can create a reminder, and they can set the frequency of the reminder. They can choose to be reminded daily, weekly or monthly. Now if they choose weekly, I only need to know the day of week they want to be reminded and all is well. The issue however is monthly. What if the user wants to be reminded every 31st of the month? Some months obviously don't have that, and being that the reminder goes out every month, I have no reason to keep track of the month itself.   I am really not sure how to about this. If it matters, this is a node.js app.


Is there any consistent way to detect if a user is System Admin via Apex?

I am currently developing a managed app where I have a Visualforce Page that should that should be used only by the System Admins.   I wanted to know if there is any consistent way of figuring out if the current user is an Administrator or not, other than checking by the Profile with a hardcoded value like 'System Admin'.  The workaround that I've thought so far is:  After installation notify all users that the app/package was installed, and if you're a System Admin, you should go to the custom settings and define a hardcoded value for the Profile of the System Admin that you are using. If there are 2 system admins(even though I wouldn't understand why would it be the case to have more than one), one of them will do the work.   After that, I can succesfully detect if the user is a System Admin and I can let him do some "administrative" stuff relevant to the functioning of my app.  Is there any other workaround that is more consistent and avoids this round trip of configurations?


Strategies to find the set of functions $f:\mathbb R\to\mathbb R$ satisfing the functional equation: $f(x^3)+f(y^3)=(x+y)(f(x^2)+f(y^2)-f(xy))$

My question is as follows: What methods can be used to find the set of functions $f:\mathbb{R}\to\mathbb{R}$ satisfying a certain functional equation. An example of a case where this applies is the following:  Find all functions $f:\mathbb{R}\to\mathbb{R}$ which satisfy the following equation: $$f\big(x^3\big)+f\big(y^3\big)=(x+y)\Big(f\big(x^2\big)+f\big(y^2\big)-f(xy)\Big):\forall x, y\in\mathbb R$$  I'm curious as to whether there are general methods (or strategies) for solving this type of question, or whether questions like these should just be handled on a case-by-case basis. Thanks in advance.


If $F[x]$ is a principal domain does $F$ have to be necessarily a field?

If $F$ is a field, then $F[x]$ is a principal ideal domain.  Conversely, if $F[x]$ is a principal domain does $F$ have to be necessarily a field?  My Thoughts: Suppose instead of $F$, we take the set of polynomials $R[x]$ over a commutative ring $R$ with unity. Then, suppose $I$ is an ideal of $R[x]$. Let $g(x) \in I$ such that $g(x)$ is the polynomial of the lowest degree in $I$. Then: $ \langle g(x) \rangle \subseteq I .......... (1)$ Let $f(x) \in I$. Then $f(x) = p(x)g(x) + r(x)~~|~~p(x),r(x) \in R[x], \deg r(x) < \deg g(x)$ Since, $I$ is an ideal $\implies f(x) - p(x)g(x) = r(x) \in I$ But, $g(x)$ is of the lowest degree in $I \implies r(x) = 0 \implies f(x) \in \langle g(x)  \rangle \implies I \subseteq \langle g(x)  \rangle ......(2)$ Then from $(1),(2) : I = \langle g(x) \rangle$ Does the Presence of zero divisors in $R[x]$ really make a difference? The only advantage I see is that if there are no zero divisors in $R[x]$ then $I=\{0\} \implies I= \langle 0  \rangle$. But, every ideal contains the zero element. Why is there the condition of a field specifically given in textbooks for $F[x]$ to be a principal ideal domain? Thank you for your help.


Hide page for user logged and redirect for profile?

I have a page on wordpress, that after you enter is redirected to your profile page. So far so good.  However, after the user logged in would have had no more access to the homepage. I've hid the "HOME" menu, but if for some reason it access the home page, I would like him to be redirected to their profile page.  Is this possible?


BFS method show nullpointerexception repeatly

in my homework i must embody Bfs and Edge method in BFS method  i must use queue to memory visited edge in Edge method i must store arraymatrix if i input , it shows nullpointerexception void Bfs(int v) {      Queue<Integer> q = new LinkedList<>();          q.add(v);     for(int i=0;i<numofnodes;i++) {         visited[i]=false;     }     visited[v] = true;           while(!q.isEmpty()){             int temp = q.poll();             System.out.print(temp + " ");                          for(int j = 0; j <numofnodes; j++){                 if(AdjMatrix[temp][j] == 1 && visited[j]==false){                                        q.add(j);                                            visited[j]= true;                                 }                 }                            } }     void Edge(int n1, int n2) {      AdjMatrix[n1][n2]=1;     AdjMatrix[n2][n1]=1; }  java.lang.NullPointerException  i 5 e 0 1 e 0 3 e 1 2 e 1 4 e 2 3 e 3 4 bfs 0 0 1 3 2 4


Whenever I log into the Steam website or into the Steam client on my work computer (or other computer that I do not normally use), Steam Guard prompts me to check my email for a code before I am able to log in - as per below;    Is it possible to disable this for both the Steam client and the Steam website? If so - how?


"Due to" vs. "As a result of " in this sentence

I wrote :     English language learners (ELL) are likely to experience more difficulties as a result of problems in auditory discrimination of speech sounds.   But I feel it may sound better with     English language learners (ELL) are likely to experience more difficulties due to problems in auditory discrimination of speech sounds.   Am I right? As I found in this question  due to could be traditionally used as adjective, and here it may play the adjective role of difficulties. Is there any difference here?


Customise Touch Bar for a specific application

So I've been using the MacBook Pro with Touch bar for a week and the Touch Bar seems pretty convenient. However, I haven't found an option to customize the Touch Bar for a specific app.  For example, whenever I code via , I'm used to having the F[0-12] Buttons (which aren't displayed in the keyboard anymore in favor of the Touch Bar). I know that if I'm holding the fn button, I'll be able to see the F[0-12] Buttons. But I want them to be displayed by default without the need to hold the fn button.  Is there a way I can achieve this?


Does the Symmetric difference operator define a group on the powerset of a set?

$G$ is the set of all subsets of a set $A$, under the operation of $\triangle\;$: Symmetric Difference of sets.  $A$ has at least two different elements.  I need to check if this is a group, and if it does to show if the group is abelian and/or finite.  Associativity - easy from Symmetric Difference. Identity element - empty group. Inverse element - each element is inverse to itself. Am I right?  abelian? finite?


Why does $\mathbb{C}$ have transcendence degree $\mathfrak{c}$ over $\mathbb{Q}$?

It's pretty well known that $\text{trdeg}(\mathbb{C}/\mathbb{Q})=\mathfrak{c}=|\mathbb{C}|$.  As a subset of $\mathbb{C}$, of course the degree cannot be any greater than $\mathfrak{c}$. I'm trying to understand the justification why it cannot be any smaller. The explanation in my book says that if $\mathbb{C}$ has an at most countable (i.e. finite or countable) transcendence basis $z_1,z_2,\dots$ over $\mathbb{Q}$, then $\mathbb{C}$ is algebraic over $\mathbb{Q}(z_1,z_2,\dots)$. Since a polynomial over $\mathbb{Q}$ can be identified as a finite sequence of rationals, it follows that $|\mathbb{C}|=|\mathbb{Q}|$, a contradiction.   I don't see why the polynomial part comes in? I'm know things like a countable unions/products of countable sets is countable, but could someone please explain in more detail this part about the polynomial approach? Since $\mathbb{C}$ is algebraic over $\mathbb{Q}(z_1,z_2,\dots)$, does that just mean that any complex number can be written as a polynomial in the $z_i$ with coefficients in $\mathbb{Q}$? For example, $$ \alpha=q_1z_1^3z_4z_6^5+q_2z_{11}+q_3z^{12}_{19}+\cdots+q_nz_6z_8z^4_{51}? $$  Is the point just that the set of all such polynomials are countable?  Thanks,


I am creating a pdf document using C# code in my process. I need to protect the docuemnt  with some standard password like "123456" or some account number. I need to do this without  any reference dlls like pdf writer.  I am generating the PDF file using SQL Reporting services reports.  Is there are easiest way.


error when installing gnome-control-center on Ubuntu 20.04.1 LTS

when I try to install gnome-control-center on Ubuntu 20.04.1 LTS I get the following error. gnome-control-center : Depends: colord (>= 0.1.30) E: Unable to correct problems, you have held broken packages. Any advice?


The magnetic part of the Lorentz force acts perpendicular to the charge's velocity, and consequently does zero work on it. Can we extrapolate this statement to say that such a nature of the force essentially makes its corresponding work independent of the choice of path, and hence that the magnetic force is conservative?


Toshiba satellite c640-x4014.Is ubuntu compatible with my laptop? so please help me with this,or any other Linux OS available for the system


At System → Administration → Language support →  Text. I can only choose standard locales, but I would like to fine-tune. For example in Windows I could customise things like time and date format, measure units, decimal separator, currency, etc manually - how can I do this in Ubuntu?


A short story, genre fantasy, read during the 1960s in English, I think in an anthology instead of a magazine.  A human and a devil interacted, possibly the human sold his soul but I don't remember.  The devil mentioned he was preparing for the coming elections in Hell. The human was surprised by the idea of elections in Hell, but the devil explained it by saying that Hell was a totalitarian state and all totalitarian states have elections.


how do I exit the purple command screen?

I switch my laptop on then it's intro is normal then suddenly it appears for me somestuff written and at the end written failed Then after 1 minute/lesser a list of commands or operating text appears for me then they want me to type some commands I tried holding shift or lshift and no grub menu appeared  Please help me


What is the most efficient way to make money?

What are some of the most efficient ways to make money?   Based on:    time initial investment required progress (in the game) special equipment/gear


Can data generated by generative models be used for training unsupervised learning models?

I'm working on a signal denoising problem. Because of not having enough data for training I'm considering using one of the generative models like VAE or GAN to generate data similar to real data for training. I didn't find any relevant precedents with regard to my use case for generative models. Is it because generative models don't work for my purpose or am I missing something?


Should I stress highlighted articles in my CV

Part of my research attracted some attention like:   Nature research highlights Monthly DOE (Department of Energy, USA) highlights Institute newsletter (Is also read by other labs) Editors suggestions on paper (like PRL)   My question is should I mention those in my CV or publications list or not at all, since the former three are not written by me but only about my work and as such not my work to claim.  Background: I'm drafting my CV for a young investigator grant. My overall resume is solid but nothing that keeps you awake at night. Especially empty are the two sections: received grants and won scientific awards.


Why should I use a subdomain structure over a directory structure?

I want to do blog.mysite.com but i know it will negatively impact my PR with Google. When is it preferable to structure your site like that vs mysite.com/blog? Is it only for the benefit of PR?


I want to know the formula for the below  if 40% of A1 is less than 15000 then A2 =15000 else A2 should be equal to 40% of A1.  What i want is A2 should not be less than 15000.  Thanks much in advance!!


What is Iron Man's flight range and max air speed?

In the Iron Man movie Tony flies the Iron Man armour from Miami to Afghanistan, roughly 7800 miles.    What is the maximum range of the Iron Man armour?   What sort of speed does the armour cruise at?  How long would the flight from Miami to Afghanistan have taken?   Could Iron Man circumnavigate the globe without stopping, and how long might this journey take him?   EDIT: Just found this (funny) image, New York to Washington in under an hour?!? :)


eclipse.desktop on launcher being replaced on reboot

I've finally gotten eclipse installed on my 14.04 machine so that it launches from a new terminal with an eclipse.desktop file. I can drag it onto the launcher and when I click it everything works!  Except when I close eclipse later, shut down, boot back up, and the eclipse.desktop file is no longer on the launcher. Instead is an icon from a previous installation of eclipse that leads nowhere.  So there are two issues here, how to get rid of the icon from the previous installation, and how to get the .desktop file to stay on the launcher.


Is there a way to password protect individual apps?

Is it possible to password protect a specific Mac application?  For example, I am interested in protecting Mail because even if you cannot retrieve new emails, you still can read all the already received emails.  This is not a question about security. It's about sharing a device within a family. I don't have crucial information. I just want to avoid my girl or son to send accidentally emails from my account or prevent them to read some of them.


Remove particularly tricky items from context menu

I've found various sources of info about removing these annoying things which I never use... but I haven't succeeded in getting rid of the following.    (Avira-related:) - Scan selected files with Avira  (I believe all this is M$ crapware... I presume it's all been lovingly crafted so they're all impossible to remove. You never know, though: some super-uber-uber-geek might just have found a way) - Restore previous versions  - Cut - Copy - Delete  - Rename


Best way to start investing, for a young person just starting their career?

I am young, just started my career, and looking to begin investing so I can make my money work for me. I'm still living like I did in college (occasional purchase on myself, but most of it goes into savings) and I would like to take the extra money and invest it.   What would you suggest are the best options for me to begin? I was considering getting a personal investor [a financial advisor] for perhaps a year or so, but I've heard that they really are not worth the money. I wanted to get the input of the great minds here.


java.lang.NullPointerException: Attempt to invoke virtual method on ViewPager

I have an error with my app. I want to put viewPager in fragment. But there are some problem when do the setCurrentItem on viewPager.  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setCurrentItem(int)' on a null object reference   this is error message  public void clickBottomToolbar(View view) {     viewPager viewPager=new viewPager();     int position=0;     switch (view.getId()) {         case R.id.map:             position=0;             break;         case R.id.customerList:             position=1;             break;         case R.id.captureNameCard:             position=2;             break;         case R.id.captureDocument:             position=3;             break;         case R.id.documentList:             position=4;             break;     }     viewPager.setPosition(position);     FragmentTransaction fragmentTransaction=fm.beginTransaction();     fragmentTransaction.replace(R.id.fragment,viewPager);     fragmentTransaction.addToBackStack(null);     fragmentTransaction.commit(); }   Upper is code in main_activitiy.java and Lower is viewPager.java  public class viewPager extends Fragment {     ViewPager viewPager;      @Nullable     @Override     public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {         View view=inflater.inflate(R.layout.viewpager,container,false);         viewPager=(ViewPager)view.findViewById(R.id.viewPager);         viewPager.setAdapter(new viewPagerAdapter(view.getContext()));         return view;     }     public void setPosition(int position){         viewPager.setCurrentItem(position);         return;     } }   This is viewpager.xml  <RelativeLayout     android:layout_height="match_parent"     android:layout_width="match_parent"     xmlns:android="http://schemas.android.com/apk/res/android">     <android.support.v4.view.ViewPager         android:id="@+id/viewPager"         android:layout_width="match_parent"         android:layout_height="match_parent"         xmlns:android="http://schemas.android.com/apk/res/android">     </android.support.v4.view.ViewPager> </RelativeLayout>


If $f$ is holomorphic on the unit disk and $f(0)=0$, then $\lvert f(z) + f(-z) \rvert \le 2 \lvert z \rvert^2$

Let $f$ be a complex valued function holomorphic on the unit disk with $f(0) = 0$. Then $\lvert f(z) + f(-z) \rvert \le 2 \lvert z \rvert^2$.   I was looking at this  but I still unsure about certain steps.  $\textbf{proof attempt.}$  Define $g(z) = \frac{f(z) + f(-z)}{2}$ (which is also holomorphic). Then $g(0) = 0$ and if I could show $\lvert g(z) \rvert \le 1$, then by Schwarz's lemma $\lvert g(z) \rvert \le \lvert z \rvert$. Now define $h(z) = \frac{g(z)}{z}$, and by Riemann removable singularity theorem we can define $h(z)$ on all of $D(0,1)$ since $h$ is bounded at $z=0$ since $\lim_{z\to0} \frac{g(z)}{z} = g'(0) = 0$. Thus $h(0) = 0$ and $\lvert h(z) \rvert = \lvert \frac{g(z)}{z} \rvert \le 1$ finally applying Schwarz's lemma to $h$ we obtain $\lvert \frac{g(z)}{z} \rvert \le \lvert z \rvert$ which is the desired result.  //  How do I show $\lvert g(z) \rvert \le 1$?


Prove metric space $X$ is connected iff $\forall A\subset X,$ $\partial A\neq\emptyset$.   Attempt at a proof: $\rightarrow$ $X$ connected $\implies$ $\forall A\subset X$, $A$ is connected. Then, intuitively there should be no "space" between the sets because if there were, $X$ would not be connected. Not sure how to formalize it, though.  $\leftarrow$ If the boundary is nonempty $\forall A\subset X$, then suppose there exist $U, V$ open in $X$ such that $U,V$ disconnect $X$. Then, (1) $U\cap X\neq\emptyset$ and $V\cap X\neq\emptyset$, while (2) $(U\cap X)\cap (V\cap X)=\emptyset$ and (3) $(U\cap X)\cup (V\cap X)=X$. Then, let $U\cap X= A$. Clearly $A\subset X$ but by (2) $\partial A\cap A^c=\emptyset$. This is a contradiction. .


It looks like other people have had similar issues and I tried to do what people were advising, but it didn't work.    Edit: sudo ppa-purge ppa:mc3man/trusty-media returns sudo: ppa-purge: command not found


Solve the initial value problem: $\frac{dy}{dx} = e^{x+y}$, given $y(0)=0$.

I have attempted the question several times so far, and I have always reached the same answer that differs from the solution, any advice would help greatly! My attempt $$\frac{dy}{e^y} = e^x dx$$ Taking the integral, I got $$-e^{-y} = e^x + C.$$ Solving for $y$, I got $$y=-\ln(C-e^x).$$ After subbing in $y(0)=0$, I got $$0=-\ln(C-1)$$ and solving for $C$, I got $$C=2.$$ Thus, I got $$y=-\ln(2-e^x).$$ However, the solutions have $y=-\ln(1-e^x)$ as the answer. Have I done something wrong? Thanks in advance!


what does this mean " I got 70 + application forms"

Today I saw, someone has written      I got 70+ application forms   What is the purpose of the plus sign in that statement?


Looking for a short story where a guy travels through time in the London underground

I read this story around 10-12 years ago but was probably written in the 1990s or earlier.  Here's what I recall: There's a guy (I want to say his name's John, but not too sure about that) who goes into the London underground and ends up visiting a platform he's never seen before. It turns out that he has somehow travelled to the past (19th century, I believe). He sees that all the people there are wearing Victorian clothes. One phrase from the story that's stuck with me all these years is brass spittoon since that's the first time (and probably the last time) I've seen that phrase being used.


What is "veiling glare"? How does it affect my photos, and how can I avoid it?

Someone mentioned that "veiling glare" or "veiling flare" was to blame for reduced contrast in a photo. What does this mean exactly?  What causes veiling glare, and how can it be avoided? How does it relate to those floating polygonal lens flares one often sees in movies?


"You can only post once every 40 minutes" on different sites

This morning I posted a question on a SE site. Then realized a different SE site would be more appropriate.   I proceeded to delete the question on the first site and copied it to the second, but I got the dreaded "You can only post once every 40 minutes.", even if the question was deleted from a different SE site.   I have only the affiliation reputation on both of those sites. Now I'm sitting here waiting for the 40 minutes to pass.  Paradoxically, as a trusted user in SO, I'm more likely to come to other SE sites to ask a few things about topics that are new to me (as opossed to answering in SO), yet I feel more limited.   Maybe trusted users from other sites should have slightly lower restrictions than <125 on the fellow communities? In particular in order to ask a couple of questions.


we have linux machine with 32G  we capture the mem  as the follwing  mem=` cat /proc/meminfo | grep MemTotal | awk '{print $2}' ` echo $mem 32767184   and now we convert it to GIGA  mem_in_giga=`  echo $(( $mem / 1024 / 1024)) ` echo $mem_in_giga 31   but from results we get 31 and not 32G  the same story with free command  free -g               total        used        free      shared  buff/cache   available Mem:             31           9          17           0           4          20 Swap:             7           0           7   so how to get the 32G by any command solution?


Raising and lowering indices: is it a convention?

We can raise and lower indices of any tensor with a non-zero rank by applying the metric tensor with indices properly located. My question is: why is the metric tensor the tool we use for such operations? If we use another tensor we would perform the same raising or lowering operations but obviously with different numerical results. In different words, if I have a covariant vector $\tilde T=T_\nu\mathbf e^\nu$, why do I get its contravariant version $\vec T=T^\mu\mathbf e_\mu$ just through the metric tensor?


I used select in if for example :    select IF (LEAVETYPE = 1 , (select test1,test2 from TableName),(select test3,test4 from TableName where id = 2)  FROM TableName     I Wanne Used Select in IF


C(0, 1) has infinitely many prime ideals not of the form Mp

I know $\mathcal C([0, 1])$ has all maximal ideals of the form $M_p=\{f\in \mathcal C([0, 1]) : f(p) =0,\  p\in [0, 1] \}$. My question is little bit different.  If I replace $[0, 1]$ by $(0, 1)$  then how can I show that this ring has infinitely many prime ideals not of the form $M_p$ ?


Prove that for any cardinal numer $a,b,c$ that $a^b a^c = a^{b+c}$.  Start with three non-empty sets $A,B$ and $C$ such that $A∩B=\emptyset$,and show that $|A|^{|B|} \dot |A|^{|C|} = A^{|B| + |C|}$  Workings:  This would be done by establishing a bijection between $A^B \times A^C$ and $A^{B \cup C}$   But I'm not sure what the bijection could possible be.  Any help will be appreciated.  Note: I know of this .  But that uses notation and concepts I am not familiar with.


What verb do I use when 'y(ies)' is used together in a sentence

For example, should it state: The beneficiary(ies) on your account were updated? OR The beneficiary(ies) on your account was updated? I'm thinking the first, but want to be sure.


Using the "flag" loophole to pass every review audit

My question pertains to the review audits that occasionally appear when using the "review" feature on Stack Overflow. I know that . This was implemented () because:     A lot of people are blindly upvoting everything in the queue without even reading the posts, just so that they can get the badges. So, some posts in the review queue are designed to catch such users...   However, I think there is a loophole in this system. A user can conceivably pass every audit without reading the post by using the following method:   Immediately select "flag" or "Recommend Deletion" without reading the post. If the question/answer being reviewed was an audit, then the results will automatically appear when the user flags the post. Since (as far as I know) the audits are always negative tests; i.e. they are posts that should be flagged or deleted and not posts that should be approved, if the audit results do not automatically appear, it means the post is not an audit. After determining if the post is an audit, the user can ultimately choose not to flag/recommend the post for deletion by Xing out the screen that asks for the reason the user wants to flag/recommend for deletion. They can then approve the post without reading it and without running the risk of failing an audit.   Especially since posts can be flagged within the ~3 seconds during which the system does not allow the user to click "No Action Necessary," this is a simple method to pass every audit while wasting no time in moving through review posts. Hence users can continue to blindly allow posts or edits that should be flagged/deleted/undone to earn badges, to the detriment of the Stack Overflow community.  My question: Wouldn't it be better to force the person to confirm the flag or deletion recommendation before displaying the audit results?


Elegant ways to support equivalence ("equality") in Python classes

When writing custom classes it is often important to allow equivalence by means of the == and != operators. In Python, this is made possible by implementing the __eq__ and __ne__ special methods, respectively. The easiest way I've found to do this is the following method:  class Foo:     def __init__(self, item):         self.item = item      def __eq__(self, other):         if isinstance(other, self.__class__):             return self.__dict__ == other.__dict__         else:             return False      def __ne__(self, other):         return not self.__eq__(other)   Do you know of more elegant means of doing this? Do you know of any particular disadvantages to using the above method of comparing __dict__s?  Note: A bit of clarification--when __eq__ and __ne__ are undefined, you'll find this behavior:  >>> a = Foo(1) >>> b = Foo(1) >>> a is b False >>> a == b False   That is, a == b evaluates to False because it really runs a is b, a test of identity (i.e., "Is a the same object as b?").  When __eq__ and __ne__ are defined, you'll find this behavior (which is the one we're after):  >>> a = Foo(1) >>> b = Foo(1) >>> a is b False >>> a == b True


Whenever I attempt to install aircrack-ng in terminal I get the following error:  Package aircrack-ng is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source However the following packages replace it:   iw  E: Package 'aircrack-ng' has no installation candidate"   I'm new to Ubuntu and so have no idea what to do.


NASA's "Impossible" Space Engine, Take Two

This question seems to be a close parallel of , but it's about a different design by a different author.  I read a  about a "helical engine" design by NASA engineer David Burns. The design allegedly exploits relativistic effects to seemingly violate conservation of momentum (as in the earlier question). It involves an oscillating mass which travels faster in one direction than the other, thus having higher relativistic mass on one side and imparting unbalanced momentum to its container.     But, Burns asks, what if the ring’s mass is much greater when it slides in one direction than the other? Then it would give the box a greater kick at one end than the other. Action would exceed reaction and the box would accelerate forwards (see video below).   Read more:   Now, I'm not a physicist, but I'm just smart enough to have gotten the sense that this is almost certainly nonsense. As soon as I read "may violate the laws of physics" in the headline, in fact. Is it nonsense, and if so, what is unaccounted for in this model that would balance the momentum transfer at each side of each oscillation? How does the math play out?


What language should I speak to my daughter?

I am a Greek, born, living and working in France, married to an Albanian woman, working all day in English.  I have a 2,5 year old daughter, who lived from:    September 2014 to April 2015 and February 2014 to April 2014   in Albania (11 months, approx. 36% of her lifespan), where people only talked albanian to her.  I speak only French with my child, BUT I only speak Greek with my wife, because she refuses to speak French with me, because she is insecure in French. Yet, my wife speaks Albanian to my child.  These facts lead to the circumstance, that the language development of my child seems a bit delayed, because she doesn't yet make three word sentences.  Though I am a little worried about her language development, I want to know, if there is a problem if I also start speaking English to her on a regular basis, since I heard that children are capable growing up learning different languages.  Is there something like a burnout/depression danger in children? Since I can see it in her eyes that she wants to communicate but is not able to and I can see it bothering her a lot.  Should I cut my communication with my daughter down to only French? Should I cut it down to speaking Greek with her, since this is the language I speak with her mother every day? Or should I just continue mixing everything up? Or can I even start speaking English with her?  I don't want her to struggle to the point of extreme frustration, but if this means that in the end, her language development will catch up to normal kids, I am inclined to let her struggle a bit. So are there any longterm deficits for her, if I introduce English?  Please advice.  George


I did a kmeans cluster plot to identify how my plants cluster based on  4 morphological traits of them. It gave me 3 clusters as shown in the figure. I'm not sure how to interpret these dimensions though. Do the 1st and the 2nd top dimensions explain 61% and 18% variation in my data set respectively? If so I want to know what are these two top dimensions? It's not mentioned anywhere in my out put.   Can someone  help?  Thanks]


I own a [Lenovo Z410][1] laptop, and its battery is not removable.  Lenovo published an ['energy management' driver for Windows][2] that let you to use ac power instead of battery when the battery power is between 55% and 60%. How may I do this in Ubuntu?  I notic that if i turn on this option in windows and restart to ubuntu whitout unpluging charger, battery doesn't charging and device use ac power.  [1]: cpu: core i7 4702MQ  [2]: you're right. It's a driver. But when you install it, an app named "power manager" appear in app menu.


As stated in the question, I want to know how to save an activity's state. My application has a list of products and allows the user to click on a product, starting the second activity that displays all the information about that product. On that second activity, the user can "Add the product to the shopping cart" by pressing a button.  When you press the button, the 3rd activity starts. It's a listview displaying the added product's name and price - as shown in the below code.  How do I save the data added so that if I go back and add another product, it adds it to the listview below the one already there?   I hope the question is clear, if not, please ask and i'll add whatever is needed.   Thanks in advance :)  package activity_app;  import java.util.ArrayList; import java.util.HashMap;  import android.app.ListActivity; import android.content.Intent; import android.os.Bundle; import android.widget.ListAdapter; import android.widget.ListView; import android.widget.SimpleAdapter;  public class shopping_cart extends ListActivity {   private ListView lv;  private Intent intent;  private String name;  private String price;  ArrayList<HashMap<String, String>> oslist;  private static final String PROD_PRICE ="price";  private static final String PROD_NAME = "name";  ListAdapter adapter;   @Override  protected void onCreate(Bundle savedInstanceState) {   super.onCreate(savedInstanceState);   setContentView(R.layout.shopping_cart_activity);   getActionBar().setTitle("Ordered Products");    intent = getIntent();   name = intent.getStringExtra("PROD_NAME");   price = intent.getStringExtra("PROD_PRICE");   oslist = new ArrayList<HashMap<String, String>>();    HashMap<String, String> map = new HashMap<String, String>();   map.put(PROD_NAME, name);   map.put(PROD_PRICE, price);   oslist.add(map);     adapter = new SimpleAdapter(shopping_cart.this, oslist,             R.layout.shoppingcart,             new String[] {PROD_NAME, PROD_PRICE}, new int[] {R.id.name, R.id.Price});     setListAdapter(adapter);


The question says, Which of the following statements apply?   And the answer says this one does but I'm not sure why.   The clauses {a,b},{a,-b},{-a} are unsatisfiable The clauses {a},{-a,b},{-b} are unsatisfiable   Also, why is it not possible to derive the empty clause from {x,y},{-x,-y}?


Do men and women have the same number of genes?

As far as I know, humans have 23 pairs of chromosomes, each one which contains a particular amount of genes. But in the "last" pair, men have a XY pair chromosome, and women have a XX pair chromosome. Does the missing "leg" of the XY pair make men to have fewer genes than women, and if so, how many genes do each sex have?


What causes a potential drop in a resistor or load?  Why a does wire with neglible resistance have the same potential across it?


I did my English homework and I searched this sentence. They said that it's "Elvis has died age 79"   Can I use "Elvis died at the age of 79" instead? Is it still correct? Can you explain? (I hope my grammar isn't wrong.)


Using srand(time(NULL)) seems overly deterministic. For example, when I run std::cout << rand() % 9000 I get 4275. When I run it again, I get 4311. It's too based on time.


Deciphering the following line of code: new (void*) custom_func_pointer(std::forward(function))

I am studying a game-engine codebase and trying to figure out what the last line of the following function does: template<typename FuncT>     static void Submit(FuncT&& func)     {         auto renderCmd = [](void* ptr) {             auto pFunc = (FuncT*)ptr;             (*pFunc)();              // NOTE: Instead of destroying we could try and enforce all items to be trivally destructible             // however some items like uniforms which contain std::strings still exist for now             // static_assert(std::is_trivially_destructible_v<FuncT>, "FuncT must be trivially destructible");             pFunc->~FuncT();         };         // storageBuffer here is a void* pointing to a memory location in a buffer         auto storageBuffer = GetRenderCommandQueue().Allocate(renderCmd, sizeof(func));         new (storageBuffer) FuncT(std::forward<FuncT>(func));     }  I have honestly never come across such a syntax in C++ so any help to decipher it would be appreciated. What I am really trying to figure out is the last line of code new (storageBuffer) FuncT(std::forward<FuncT>(func)); the syntax (i.e., new (void*) FuncT(std::forward<FuncT>(function))) of which is confusing. The Allocate function: void* RenderCommandQueue::Allocate(RenderCommandFn fn, uint32_t size) {     // TODO: alignment     *(RenderCommandFn*)m_CommandBufferPtr = fn;     m_CommandBufferPtr += sizeof(RenderCommandFn);      *(uint32_t*)m_CommandBufferPtr = size;     m_CommandBufferPtr += sizeof(uint32_t);      void* memory = m_CommandBufferPtr;     m_CommandBufferPtr += size;      m_CommandCount++;     return memory; }


Is there any max inventory and management in the wastes?

Sending dwellers into the wastes to explore, and I find they stop finding items after 13. Is there a maximum capacity for explorers, and any way to get them to drop low-value items while they are out there?


Why is my table appearing before my text?

Possible Duplicate:          I am trying to create a table after some text:  Some text. foobar foobar \\  \begin{table}[t] \centering \begin{tabular}{|c|c|c|c|c|c|} \hline  & a & c & & &  \\ \hline $\{X, X', Y\}$ & & b &  & &  \\ \hline \hline \end{tabular} \end{table}   However, the table is appearing before the text even though I type if after I type the text. Why?


When I cut a layer using marquee tool, I get blur edges to cut side. How do I get sharp edges after cut?

I am using rectangular marquee tool to cut a portion of the layer in photoshop cs5, but after cutting, the edges are not sharp, I get blur edges.      how can I get sharp edges?


I have a cheap wireless pool thermometer (AcuRite 617 ) and I'd like to intercept the temperature data at the receiver and use it with a computerized data-logging system.  Conveniently, inside the receiver is a small break-out board that is connected to the antenna and has digital "V", "G", "D", and "SH" pins:    Here is a segment of captured data from the "D" pin during a transmission (these happen once per minute). Before this segment, there is what appears to be much-higher-rate data, but I believe that might be noise -- this is the beginning of the 1.36kHz / 680Hz data.    I've googled a bit and can't find an encoding that looks quite like this, but if I were to guess what's going on, here's what I'm thinking:   the initial 4 cycles of 680 Hz are to synchronize the clocks but contain no data the 13 cycles of 1.36 kHz (2x the initial rate) that follow appear to have one of two forms: they either drop low before the midpoint of the cycle or after it -- i'd assume one form is a logical one and the other is a zero. after that, there appears to be a weird gap, but if you discount the part of the low that is part of the preceding "1", then the remaining gap is 735 µs, which is a (phase-correct!) continuation of the 680 Hz preamble.   Am I looking at this correctly? Is there a name for this encoding?  Some further notes on the break-out board:   the board is marked "RF211" and looks remarkably consistent with the MICRF211 "general purpose, 3V QwikRadio Receiver that operates at 433.92MHz" the MICRF211 data sheet has the following figure (with very little explanation), which looks tantalizingly like what i'm seeing except for the double-data-rate square wave as compared to my capture:    2016-02-14 Update: I've revisited this project and appear to be getting a clean 64-bit stream between a 4-cycle preamble and a 1-cycle "postamble", after which the display board shuts down the RF module by pulling ^SH low (top line):    According to Micrel's "33/66% PWM" scheme (which appears nowhere else on Google), that's  -_-_-_-_0000011110011000110000000000000000000000100011101000010010101010-_   So now I have to start manipulating the temperature to decode the bits. Here ("x") are the bits that seem to change without any apparent change in the display:  0000011110011000110000000000000000000000100011101000010010101010 ------------------------------------------------x----xxxx----xxx   I assume these are either least-significant bits or battery-level (which is only shown as "Low" when it drops significantly).  2016-02-15 Update: I'm taking the show on the road to give the new "Reverse Engineering" stackexchange a crack at determining meaning:


which predictive model should I use if column is having string values?

I want to create a predictive model to predict a categorical value (1,0) but the independent variables are also having few string columns (country, location, age) which I feel are important for the prediction and should be included.  Which model should I use, will Linear Regression work? till now I did regressions which only had continuous or discrete value, is there any norm to address values which has columns with string values ?  Below is the similar question been asked before, but unfortunately I didn't get much information    I am in an initial phase of learning and practicing machine learning please spare me if this question breaks the eligibility of valid question.  Please provide some insight, any source of help will be appreciated!!!  Edit: Added partial dataset below       Year     Location      Country 0  2016      chitwan      Nepal    1  2016      siberia      Russia    2  2016    Oba Hills      Nigeria    3  2016     Edumanom      Nigeria   4  2016        Kanha      India    Age                                Injury Survived Time     09                         attack on head     N    11h00   19                            Neck Injury     N    11h00   23                              lower leg     N    04h43   65                             leg injury     N    11h00   NaN                  attacked from behind     N    18h00


“Double use” of a4paper (geometry/KOMA)?

In my preamble, should I give the a4paper option just once or twice, i. e. once for the KOMA-script document class (scrartcl) and once for geometry? Is this redundant or does scrartcl need the option for the calculation of the type area (or something else)?  \documentclass[12pt,a4paper]{scrartcl} \usepackage[a4paper]{geometry}   Lately, I have just used  \documentclass[12pt]{scrartcl} \usepackage[a4paper]{geometry}   and I haven’t had any adverse effects. Still, it seems a little strange to me not to pass any “size options” to the document class. But is this the “right way” to go?  By the way, I am using XeLaTeX to typeset.


Downloaded Ubuntu64 SublimeText from   Double clicking opens Ubuntu Software, which seems to try to load endlessly  Opened terminal   cd Downloads ls sublime-text_build-3126_amd64.deb  exec sublime-text_build-3126_amd64.deb bash: exec: sublime-text_build-3126_amd64.deb: not found   I'm sure this is very simple.


Theorem A map $\phi$ maps a topological space $X$ to another $Y$, where $X$ is Hausdorff, $Y$ is compact and the graph of $\phi$ is closed. Then $\phi$ is continuous.   Is it reallly necessary to include the condition that $X$ is Hausdorff?  Since I see no reason, and I appear to have a proof without using the condition, I would like to know the answer.            A proof:     For any closed subspace $C$ of $Y$, the pre-image $D$ ought to be closed. For any element $a$ in the complement of $D$, we can use the compactness to show that there is a finite number of open sets in $Y$ such that the union of them covers the C, and then the corresponding open sets in $X$ is an open neighborhood of $a$ which has an empty intersection with $D$; so $D$ is closed.     P.S. in the proof, those open sets are obtained by the condition that the graph is closed and that $(a,c)$ is not in the graph for any $c$ in $C$.


What if the vesting period of a startup has not ended when it is acquired?

Suppose employee of a startup company has a vesting agreement, saying she can execute options for 1/4 of total package each year.  What if only one year have passed and startup was bought.   Which share an employee can convert into a money then?


how to get data from mysql in php page in proper way?

My Mysql table contains one column Let's discuss together!! when when i get it into php page ? is displaying in place of ' means Let�s discuss together!!   . So how to to get data from mysql in php page in proper way


What does $ command 1>&2 do? As I understand it this runs the command but with the STDOUT redirected to the STDERR. But I'm not sure exactly how >& works.   I have seen it as $ command 1>&2 and $ command 2>&1.  I think the 1 and 2 are the file descriptors for STDOUT and STDERR, respectively, but I'm not really even sure what that means either.   I have found on SO and other resources that >& is some sort of redirection "thing (operator??)", I'm not sure exactly how it works. Is it a binary operator? Is it even an operator?   Can someone please explain in novice terms what this does.


What would be a formal way to prove the above statement?


What is the greatest number of free kick goals scored by a player in professional football?

Which player has the most goals from free kicks in professional football history?


How to make chapter number appear as a written number instead of an Arabic number?

I am using the memoir class. Is there any way to do this?


consequences of disabling 'The WinHTTP Web Proxy Auto-Discovery Service '

I am dba responsible for  several sql boxes running sql2008 standard on Windows 2008r2 datacentre Servers. Every now and again I see a spike in cpu which coincides with the event "The WinHTTP Web Proxy Auto-Discovery Service service entered the running state' and we see a brief degradation in performance, sometimes we briefly loose connectivity with the server. In order to disable this service what will I need to verify before doing so ? I am pretty sure we dont use proxys so is this an indication I can just disable it?


We have the factorization $561=3*11*17$. Because $\text{gcd}(a,561)=1$, there are integers $x,y$ such that $ax+561y=1$. So $ax=1\mod 561$. Since the gcd is $1$, we have $a\not \in 3\mathbb{Z}, 11\mathbb{Z}, 17\mathbb{Z}$. Therefore, $a^{560}\not \in 3\mathbb{Z}, 11\mathbb{Z}, 17\mathbb{Z}$. So $b^{560}=1\mod 561$. Is my reasoning correct? I have seen a problem that was similar to this that used Fermat's Little Theorem, but that can only be used when the number we  mod out by is prime.


In , it says that any epsilon number with the index that is countable is countable. How is it? Out of all those numbers, I especially want to know why $\epsilon_0$ is countable.  Thanks.


What was the nature of sorcery in Star Wars?

I am listening to the audiobook Darth Plagueis. In the book it mentions that there existed sorcery (at least in the past), and this sorcery had cross-over with the Sith but apparently was not the darkside itself.  This leaves me with some questions. The Force, from what I can tell, while an esoteric, celestial power with the Jedi and Sith pseudo-religous traditions surrounding it, was explicable by science. OTOH, I don't understand how sorcery could be -- was this part of the story a shift from Science Fiction to pure fantasy and magic?  Was the sorcery intertwined with the Force or truly separate? Was it stronger? Would only a Sith practice sorcery, or also Jedi? Could some examples of it be given?   I'm not making any distinction here between Disney and pre-Disney (I'm not even sure if this is a Disney era book), so feel free to draw from either.  This is VERY different than the question "does magic exist in Star Wars canon" wherein the answer is "no magic exists in the Disney version" because    I'm referencing a book that says it does exist and  I don't care about Disney vs. non-Disney   Also    I'm specifically asking about sorcery -- especially that which the Sith (and possibly Jedi) practiced; whether that is the same as "magic" or not is part of my question.


Can anyone explain to me with simple words the meaning of "PROTOTYPE" in JavaScript? I have seen one link but I am not clear about Prototype till now , Please let me know about this.


Add Wordpress Meta Box saved form input to Wordpress RSS feed

I'm teaching myself how to build Wordpress plugins. I found a great guide to creating a Wordpress Meta Box and saving the form input from it.    I want to send the entered and saved form input from the Meta Box that is in the Post edit view of Wordpress to the Wordpress RSS in its own tag. So when the user publishes the Post the Meta Box form data saves and adds the saved input to the post Wordpress RSS nested in its own tag.  This is the code that saves the form input:  function prfx_meta_save( $post_id ) {  // Checks save status $is_autosave = wp_is_post_autosave( $post_id ); $is_revision = wp_is_post_revision( $post_id ); $is_valid_nonce = ( isset( $_POST[ 'prfx_nonce' ] ) && wp_verify_nonce( $_POST[ 'prfx_nonce' ], basename( __FILE__ ) ) ) ? 'true' : 'false';  // Exits script depending on save status if ( $is_autosave || $is_revision || !$is_valid_nonce ) {     return; }  // Checks for input and sanitizes/saves if needed if( isset( $_POST[ 'meta-text' ] ) ) {     update_post_meta( $post_id, 'meta-text', sanitize_text_field( $_POST[ 'meta-text' ] ) ); }  } add_action( 'save_post', 'prfx_meta_save' );


How do I run a JAR file without installing Java?

My question may seem odd but this is indeed what I need to do. For the first in the last (maybe) 10 years I have to run a JAR file in my computer. But I don't want to install 'the Java' (and all those things it adds into your system). How can I run that JAR file?


Reference for scientific writing for an international journal in the micro-biology/micro-organism field

Could someone do me a favor for any guidance (link) for writing an article that is supposed to be submitted to an international journal in micro-biology/micro-organism field?  Could you please lead me to another source instead of ?


Can an attacker predict value of $d$ if attacker already used $n$ for encryption?

In RSA we have value of n and e which is known to sender. If the sender keep maintaining a database of possible n's he can easy calculate $\phi(n)$ because he already know $p$ and $q$ then. $d$ is $e^{-1} \mod \phi(n)$.  If we choose a large number which is product of two primes, can an attacker predict value of $d$?


I think I have understood properly the principle of , however the sensitivity is around  of accuracy of distortion. That looks pretty small... just starting with simpler phenomena, for example, thermal expansion. In order to avoid thermal expansion, the temperature needs to be control within a variation of $10^{-10}~\rm K$ or $10^{-11}~\rm K$ along the tubes.  I guess that the tubes do not need to be exactly $4~\rm{km}$ equal as the lasers can be synchronized although the distance is not exactly 4km within the range of $\left[10^{-18}~\rm m\right]$  How is the thermal noise avoided currently in LIGO, related to suspension and not complete vacuum?  It is already demonstrated that the frequency cut-off is low, but, how is that achieved? Which materials and isolation supported it?


Can we also Legendre transform the Lagrangian using $\frac{\partial L}{\partial q}$ instead of $\frac{\partial L}{\partial \dot q}$?

We calculate the Hamiltonian as the Legendre transform of the Lagrangian $$H(q,p,t) = p \dot q - L(q,\dot q,t), $$ where $p$ is the slope function $$p \equiv \frac{\partial L}{\partial \dot q} .$$  The general idea of the Legendre transform is that we replace our function $f(x)$, depending on some variable $x$, with a new function $F(s)$ that only depends on the slope $$s(x) = \frac{\partial f(x)}{\partial  x} $$ which, however, contains the same information.  For a function which depends on multiple variables $g(x,y,z,\ldots)$ we can do this for any of the variables and generate this way different Legendre transforms.  Therefore, I was wondering if it also makes sense to consider the alternative Legendre transform of the Lagrangian $$G(s,\dot q,t) = s  q - L(q,\dot q,t), $$ where $s$ is the slope function $$s \equiv \frac{\partial L}{\partial  q} .$$ If yes, what's the name of this alternative Legendre transform? And if not, why does it make sense to consider the Legendre transform with respect to $\dot q$ but not with respect to $q$?    PS: I found a related idea in this  but they consider Legendre transforms involving $ \dot p \equiv \frac{\partial H}{\partial  q} .$


Do I get the continent troops on every turn I have conquered the continent?

If I have conquered the entire continent do I get those bonus continent troops on each turn I play or just one turn after I have conquered it?


I have been working on a festival lantern for some hours and i had some different meshes in the blender project. Because i was going to use this in my unreal engine 4 project i had to join them together but after i selected every mesh and clicked on join, the mesh turned dark. In Unreal Engine its looking weird and the mesh is only rendering from one side.  Before i joined the meshes  After i joined the meshes.  In Unreal engine 4 (The part above the lantern is not correctly rendered.) Could somebody help me solving this problem?


Reply e-mail with 'Undelivered mail' message?

I was quite early with registering my Gmail account and I got a nice and clean baker@gmail.com address. Apparently all mails end up on my account when people make simple mistakes in typing the intended e-mail address. So I receive several legitimate mails each month from people that did not intend to mail me; people that I don't know and have no desire to know.  If it where snail mail, I'd write Undeliverable or Wrong address over the envelope and put it back in the outgoing mail box. Now I'm looking for a way to do the same for e-mail.   How can I show the sender of an e-mail that the e-mail address is wrong without revealing my identity?  Any solution involving a Gmail feature, third-party application, or manipulation of the SMTP protocol is acceptable (I can program it if it doesn't exist already), as long as it works from Windows.    I used to reply along the lines of: You sent this e-mail to the wrong address. You sent it to baker@gmail.com but you probably meant baker1@gmail.com. Kind regards, Marilyn Baker, revealing that my e-mail address is valid and who I was, and then they'd reply: Hey you have the same surname. You guys must surely be distantly related. Bla bla bla... John Baker is my husband, let's meet up... Bla bla. Anna Baker-Field  All names and e-mail addresses are fake.


Database accidentally deleted with a bash script

Edit: a follow-up question: .  My developer committed a huge mistake and we cannot find our Mongo database anywhere in the server.  He logged into the server, and saved the following shell under ~/crontab/mongod_back.sh:    #!/bin/sh DUMP=mongodump OUT_DIR=/data/backup/mongod/tmp  // 备份文件临时目录 TAR_DIR=/data/backup/mongod      // 备份文件正式目录 DATE=`date +%Y_%m_%d_%H_%M_%S`   // 备份文件将以备份对间保存 DB_USER=Guitang                  // 数库操作员 DB_PASS=qq■■■■■■■■■■■■■■■■■■■■■  // 数掘库操作员密码 DAYS=14                          // 保留最新14天的份 TARBAK="mongod_bak_$DATE.tar.gz" // 备份文件命名格式 cd $OUT_DIR                      // 创建文件夹 rm -rf $OUT_DIR/*                // 清空临时目录 mkdir -p $OUT_DIR/$DATE          // 创建本次备份文件夹 $DUMP -d wecard -u $DB_USER -p $DB_PASS -o $OUT_DIR/$DATE  // 执行备份命令 tar -zcvf $TAR_DIR/$TAR_BAK $OUT_DIR/$DATE       // 将份文件打包放入正式 find $TAR_DIR/ -mtime +$DAYS -delete             // 除14天前的旧备   And then he ran it and it outputted permission denied messages, so he pressed Ctrl+C. The server shut down automatically. He tried to restart it but got a grub error:    He contacted AliCloud, the engineer connected the disk to another working server so that he could check the disk. Looks like some folders are gone, including /data/ where the mongodb is!   We don't understand how the script could destroy the disk including /data/; And of course, is it possible to get the /data/ back?   PS: He did not take snapshot of the disk before.   PS2: As people mention "backups" a lot, we have lots of important users and data coming these 2 days, the purpose of this action was to backup them (for the first time), then they turned out to be entirely deleted.


So everyone knows that when $ax^2+bx+c=0$,$$x = \dfrac{-b\pm\sqrt{b^2-4ac}}{2a}.$$ But why does it equal this? I learned this in maths not 2 weeks ago and it makes no sense to me


I am able to login in through the terminal without any problem but when I enter my password in the login box(GUI) it doesn't show any error, just that is prompts me again to enter my credentials. I tried to enter other passwords but it gives me error.  This issue started after I created another user account on my system. Any ideas how cant I sort it out?


How to install PYPY3 on Ubuntu, for newbies?

I want to install pypy3 in Ubuntu. I have read the answer for this question "How to install PyPy3 (2.1, beta) on Ubuntu?" and still have no idea what to do. Could some kind soul please explain it so that even I can understand it :)  Here's what I have done so far:  Went    Read that I had to go   Downloaded: pypy3-2.1-beta-linux_x86_64-portable.tar.bz2  Opened it with the Archive manager (because it seemed like a reasonable thing to do)  Extracted it to desktop/PYPY3  Then desperately tried all the shell commands I came across last night. I will not be able to give a clear account of what I tried and what errors came back, as it is kind of a blur to me at this point.  But I can tell you that I got the Tar thing unpacked at one point and that I have tried running the pypy executable from the command line from the folder containing it, but got this:   bash: /usr/bin/pypy: No such file or directory   Could someone please tell me what to do. (have read the readme, the install docs at pypy.org and lots of posts)


Anime with gems that can summon beasts to fight for the user, one is a purple turtle

What is the name of the anime TV show where a boy can summon beasts with crystals/gems. It was on SABC 2. There was also a boy that could summon a purple turtle . I think the gems were blue, green, and red.


I can't get the data to my Google Drive, see the code below:  var image = ee.Image(ee.ImageCollection("LANDSAT/LC08/C01/T1_SR") .filterBounds(roi) .filterDate('2018-05-01', '2018-05-30') .sort('CLOUD_COVER') .first()); Map.addLayer(image, {bands:['B3', 'B2', 'B1'], min:0, max: 3000}, 'True colour image');  var geometry = ee.Geometry. Rectangle(roi);   Export.image.toAsset({   image: image,   description: 'image_seoul',   scale: 30,   region: geometry,   maxPixels: 4020250081,   crs: 'EPSG:5186' });


Explaining halls effect and magnetic induction

Can someone explain to me in detail if halls effect is magnetic induction?


I have been asking a lot about optional back shifting. I understand that if what is said is still true at the time of reporting then back shifting of tense is optional. I just have one doubt. If what is said is no longer true, then colloquially and conversationally will it be acceptable to avoid back shifting of tense ?   P.S. -- I know while writing it would be wrong to not back shift the tense if what is said is no longer true.


sudo apt-get update error: Wrong sources.list entry or malformed file

I recently tried to install npm and nodejs and got some errors and was suggested to run sudo apt-get update.  After running sudo apt-get update I get the following error:   Failed to fetch http://archive.ubuntu.com/ubuntu/dists/trusty/Release  Unable to find expected entry 'universe/binary-amd64/Packages' in Release file (Wrong sources.list entry or malformed file)   E: Some index files failed to download. They have been ignored, or old ones used instead.   The output of cat /etc/apt/sources.list is :  deb http://archive.ubuntu.com/ubuntu trusty main universe restricted multiverse


I’m working on this limit I guess it had to do with the Riemann sums type of exercise so I am trying to compute it: $$\lim_{n\to\infty} \left(\frac{(2n)\,!}{n^n\,n \,!}\right)^{\frac{1}{2n}}$$  Here is what I have got so far:  $$\lim_{n\to\infty} e^{\frac{1}{2n}{\ln\left(\frac{(2n)\,!}{n^n\,n \,!}\right)}} $$ Now I try to reduce the factorial division: $\frac{(2n)\,!}{n \,!}=\frac{2n(2n-1)(2n-2) \cdots(2n-(n-1))(n)(n-1)\cdots2\cdot1}{(n)(n-1)\cdots2\cdot1}=2n(2n-1)(2n-2) \cdots(2n-(n-1))=\prod_{k=1}^{n-1}(2n-k)$  Therefore I can write the logarithm as : $\ln\left(\frac{\prod_{k=1}^{n-1}(2n-k)}{n^n}\right)=\ln \left(\prod_{k=1}^{n-1}(2n-k)\right)-n\ln(n)$   And I also transform the logarithm into a sum like that should looke like this: $\sum_{k=1}^{n-1}\ln(2n-k)$  So, in the end I got this: $$\lim_{n\to\infty} e^{\frac{1}{2n}{\sum_{k=1}^{n-1}\ln(2n-k)-n\ln(n)}}$$  Now what I can't figure out is how to continue, I want to get some kind of $k/n$ inside the sum and also the limits of the sum I got don't convince me... can someone help me out, or point out any mistakes I could have done?? Thanks in advance ;)


How to prove the lack of implicit order in a database?

Recently I was explaining to colleagues the importance of having a column by which to sort data in a database table if it is necessary to do so, for example for chronologically-ordered data. This proved somewhat difficult because they could simply re-run their query seemingly endlessly and it would always return the same set of rows in the same order.  I have noticed this before and all I could really do is insist that they trust me and not simply assume that a database table will behave like a traditional CSV or Excel file.  For example, executing the (PostgreSQL) query  create table mytable (     id INTEGER PRIMARY KEY,     data TEXT ); INSERT INTO mytable VALUES     (0, 'a'),     (1, 'b'),     (2, 'c'),     (3, 'd'),     (4, 'e'),     (5, 'f'),     (6, 'g'),     (7, 'h'),     (8, 'i'),     (9, 'j');   will create a table with a clear conceptual order. Selecting that same data in the simplest way would be:  SELECT * FROM mytable;   Always gives me the following results:   id | data  ----+------   0 | a   1 | b   2 | c   3 | d   4 | e   5 | f   6 | g   7 | h   8 | i   9 | j (10 rows)   I can do this over and over again and it will always return to me the same data in the same order. However I know that this implicit order can be broken, I have seen it before, particularly in large datasets, where some random value will get apparently thrown up into the "wrong" place when selected. But it has occurred to me that I don't know how this happens or how to reproduce it. I find it difficult to get results on Google because the search query tends to just return general help on sorting result sets.  So, my questions are essentially these:   How can I demonstrably and concretely prove that the return order of rows from a query without an ORDER BY statement is not reliable, preferably by causing and showing a breakdown of the implicit order even when the table in question is not updated or edited? Does it make any difference at all if the data is only inserted once en masse and then never updated again?   I would prefer a postgres-based answer since that is the one I am most familiar with but I'm more interested in the theory itself.


Confidence Intervals for Outputs of Regression?

Suppose I have some reasonably sized dataset and I do linear regression on it, so now I have a model, say $\hat{y}=Ax+b$, where $y$ is real (or perhaps a vector, but let's say real for now), $x$ (my data points) are vectors, and $A$ and $b$ are the parameters of my linear fit that I've found through whatever method.  Now I have a new datapoint (say $x_0$) and I run it through my model, which has a true "output" value of $y_0$ but a predicted value of $\hat{y}_0$.  The question is: how precise do I expect this prediction to be?  Better yet, can I construct a $95\%$ confidence interval (or whatever percentage) for $y_0$?  I'd be happy to have a link to any sources on this topic; I assume it's complicated enough that it's not a one-line answer.  It hasn't come up in the courses I've taken so far, so I wonder if it's even been done (it seems like it would have a lot of requirements, but one might hope the central limit theorem could help reduce the number of required hypotheses).  EDIT: I have, through the magic of tags, learned the word "prediction interval" and suspect it may be what I want.  But I do not know anything about them, or how to compute them, or what we assume about the data to make them meaningful.


Show that there is just one subgroup $H \subset S_4$ such that $[S_4:H] = 2$

I had to show that $S_4$ has one subgroup of index $2$. Below, you'll find what I tried to do so    Of course, $A_4$ is a subgroup index $2$. To show that there is not another subgroup with the same index, we search all the normal subgroups of $S_4$. To do so, we need to know the cylcetypes that we could encounter:   (1,1,1,1) (1,1,2) (2,2) (1,3) (4)   If $\sigma$ belongs to some normal subgroup $N$, every element of the same cycletype as $\sigma$ must belong to $N$, because of the identity  $\sigma (a_1, \cdots a_n) \sigma^{-1} \ = \ (\sigma(a_1), \cdots \sigma(a_n))$. Every cycle that can be written as a product of cycles of the same tape must be contained in $N$. Now we get the normal subgroups:   $\{e\}$ $S_n$ $\{(12)(34),(13)(24),(14)(23),e\}$ $A_n$ Maybe $A_n$ or else $S_n$.   For the last one I used that $(1234)(2134) = (143)$ That implies that this kind of cycles generates a normal subgroup that contains $A_4$. We see that the only normal subgroup containing $12$ elements is $A_4$, as we wanted to show.     Can you find flaws, or do you think this is a proof?


DuckDuckGo directed me to a rip-off site "stackovernet.com" in first page result

Here is an example the rip-off is apparently monetizing through add (sometime even pr0n). Is this site already known and under investigation? Rip-off :  Original:  PS: The site goes as far as duplicating a whole range of sub-sites and as one can see at top level site


Detect virtualized OS from an application?

I need to detect whether my application is running within a virtualized OS instance or not.  I've found an article with some useful information on the topic. The same article appears in multiple places, I'm unsure of the original source. VMware implements a particular invalid x86 instruction to return information about itself, while VirtualPC uses a magic number and I/O port with an IN instruction.  This is workable, but appears to be undocumented behavior in both cases. I suppose a future release of VMWare or VirtualPC might change the mechanism. Is there a better way? Is there a supported mechanism for either product?  Similarly, is there a way to detect Xen or VirtualBox?  I'm not concerned about cases where the platform is deliberately trying to hide itself. For example, honeypots use virtualization but sometimes obscure the mechanisms that malware would use to detect it. I don't care that my app would think it is not virtualized in these honeypots, I'm just looking for a "best effort" solution.  The application is mostly Java, though I'm expecting to use native code plus JNI for this particular function. Windows XP/Vista support is most important, though the mechanisms described in the referenced article are generic features of x86 and don't rely on any particular OS facility.


Why is Matthew Modine first in the credits of Stranger Things S02 EP09?

We see Matthew Modine (Dr Brenner) two times in Stranger Things S02 and he's first on the opening credits of the EP09.  My only theory is maybe he accept to join the casting only if he's first on the credits. Does anyone know why?


Loop through colors and plot sns.distplot()

Can someone spot the really quick fix to my problem? I'm trying to plot two distributions on the same figure using the Seaborn package. I'd like for one line to be red and the other blue. The way I have my for-loop set up now only produces blue lines. X and Y are 1-d arrays with data that I am plotting.  fig, ax = plt.subplots(1)  colors = ['r','b']  for a in [x, y]:     for i in range(2):         sns.distplot(a, bins=range(1, 25, 1), ax=ax,         kde=True, hist=False, color=colors[i])


Who’s fighting "whom" in Syria? Who's fighting "who" in Syria?

In the  of BBC News:     "Who’s fighting whom in Syria?"   Is it correct to use whom instead of who?   This is a specific example of the who/whom question that has been asked in a more general sense elsewhere. Every time somebody asks about who/whom does not mean it is a duplicate!


On an old PC ~2007 running Windows XP I overwrote with my Windows 7 disk and then found out that I shouldn't do that. It's on my newer PC. There are no files on the HD and would like to wipe Windows 7 off, so I tried Ubuntu as an alternative OS, but I can't get a USB or DVD to boot. I downloaded Xubuntu 20.04 and created a live USB with Rufus (and Universal USB Installer) got into the BIOS (the first time for me) set First Boot Device to USB-FDD (there is also USB-ZIP and USB-CDROM) it just boots into Windows every time. I have tried every USB port, I burned a DVD and had CD-ROM as the first boot, but it still boots into Windows. I have tried 3 USB sticks. After Windows has loaded C: drive is 16.8GB free of 76.3GB and E: drive is showing Linux Mint 5.46GB of 7.44.  All I want is a basic PC that I can connect to the web / email, etc. I am obviously doing something really stupid, but I can't work out what.


how to use special letters in bib file properly?

Some author's name contains special characters like "ł" in Szałowski. The latex code for "ł" is \l.  But if I write the name in bib file as Sza\l owski, the the name contained in the output pdf's reference will be "Szał owski". That is to say, there will be a space in the name.  But if I write Sza\l owski in the main text of latex file, then the name will be ok without space.   So why there will be a space? How to deal special character in bib file?  and a related question: In the main text of LaTeX file, no matter how many space after \l, the output is the same. That is to say, the output of Sza\l owski is the same as that of Sza\l    owski, both output "Szałowski". Then what should I do if I want "Szał owski" in the main text.


Basics need to study quantum field theory after graduation?

What are the fundamental basics that i need to study quantum field theory? basics of Mathematics and physics??


The 0.9.5 update is out with a new block called the End Portal. But, I still can't figure out how to activate it and go to The End. Some videos in YouTube told me that I need ender eye, but I can't find it in the creative inventory.


How to access screen display’s DPI settings via javascript?

Is there a way to access the screen display's DPI settings in a Javascript function?  I am trying to position a HTML panel on the page and when the user's DPI is set to large (120), it throws the position off.  I need to be able to know what the DPI is so I can adjust the position accordingly.


ASUS X453M Freeze on Splash Screen on Booting or Restart / Shutdown

just fresh install on new notebook ASUS X453M  it's often to hang on boot or restart ubuntu,   its only respond to force shutdown button  i must forceshutdown and boot many times to can login to dekstop


I'm currently studying the basics of the substitution where the author goes:     To use substitution, we write $u$ as a convenient function of $x$   ideally one for which $du$ also appears in the function we want to   antidifferentiate.       For example, to antidifferentiate $x\sqrt{1+x^2}$,   $\color{red}{\text{we write }u = 1 + x^2 \text{, so that } du =  2xdx}$, which implies      $$f(x)dx = \sqrt{1 + x^2}x\ dx  = \frac{1}{2}\sqrt{u}\ du $$   So my main question is, where this   $$\tag{!}du = 2xdx$$ comes from?  I do understand that if $u = 1 + x^2$ then $\frac{du}{dx} = 2x$ but I don't get how we reach step $(!)$ from here.    I tried to make a wild guess by assuming that we can multiply both sides by $dx$, but seems like it would be invalid operation (or would it be?)


I just installed Ubuntu Restricted. How to use java?

I just installed the Ubuntu Restricted Extras. I want to code using java. How do I open the installed Extras and use java. When I type "java" in Dash home, I get many results.  Thank you.


Suppose we have $X_1, \cdots, X_n \overset{\textrm{i.i.d.}}{\sim} \mathcal{N}(0, 1)$ with $n > 50$, and let $X_{(1)}, \cdots, X_{(n)}$ be the associated order statistics. Are there any references pointing to formulas that specify (or estimate) the variance of the $k^{\textrm{th}}$ order statistic, i.e. $\textrm{Var}(X_{(k)})$, for $1 \leq k \leq n$? I am looking for formulas can be explicitly evaluated without resorting back to numerical integration.  I have seen this question: , which attracted a number of answers on approximate formula for the mean of the $k^{\textrm{th}}$ order statistic, e.g. Blom (1958) (and modifications based on work by Harter (1961) and Elfving (1947)). Searching on Google also yields a number of work on the variance / standard deviation for the $k^\textrm{th}$ order statistics for small $n$, all of them opting for a computation/tabulation route. They are: Godwin(1949), Teichroew (1956), and Parrish (1992). I have also attempted to derive something myself following the method sketched by @probabilityislogic in , along the lines of: $$\textrm{Var}(X_{(k)}) = \int_{-\infty}^{\infty} \left(x-\mathbb{E}(X)\right)^2 \frac{n!}{(k-1)!(n-k)!} f_X(x)[1-F_X(x)]^{n-k}[F_X(x)]^{k-1}\;\textrm{d}x,$$ with lower case $f$ denoting the PDF of a r.v. $X$, and upper case $F$ denoting the CDF. Noting $x = F^{-1}(F_X(x))$ and using the substitution $u = F_X(x)$ (with corresponding r.v. in upper case $U$), we have: $$\textrm{Var}(X_{(k)}) = \int_{0}^{1} \left(F_X^{-1}(u) - \mathbb{E}\left(F_X^{-1}(U)\right)\right)^2\,\mathcal{B}(u | k, n-k+1) \; \textrm{d}u,$$ where $\mathcal{B}$ denotes the PDF of a beta distribution (not the beta function). This can be rewritten as the variance based on the beta distribution: $$\textrm{Var}(X_{(k)}) = \textrm{Var}_{\mathcal{B}(u | k, n-k+1)}\left(F_X^{-1}(u)\right).$$ Approximating the RHS using (the variance bit of the) delta method, we get: $$\textrm{Var}_{\mathcal{B}(u | k, n-k+1)}\left(F_X^{-1}(u)\right) \approx \textrm{Var}_{\mathcal{B}(u | k, n-k+1)}(U) \cdot \left[(F_X^{-1})'\left(\mathbb{E}_{\mathcal{B}(u | k, n-k+1)}(U)\right)\right]^2,$$ where the prime denotes the derivative. The first term of the product is standard result. For the second part, given $(F^{-1})'(\cdot)=\frac{1}{f(F^{-1})(\cdot)}$ (see e.g. ), we then have: $$\textrm{Var}_{\mathcal{B}(u | k, n-k+1)}\left(F_X^{-1}(u)\right) \approx \frac{k(n-k+1)}{(n+1)^2(n+2)} \frac{1}{\left(f\left(F^{-1}\left(\frac{k}{n+1}\right)\right)\right)^2}.$$ Substituting in the standard normal distribution ($\phi$ for PDF, $\Phi$ for CDF) and scaling it to the desired variance $\sigma^2$ we arrive at: $$\textrm{Var}(X_{(k)}) \approx \frac{k(n-k+1)}{(n+1)^2(n+2)} \frac{1}{\left(\phi\left(\Phi^{-1}\left(\frac{k}{n+1}\right)\right)\right)^2},$$ which we can throw in a $\sigma^2$ term in front if it is not a standard normal. But surely someone must have derived that somewhere (again I am looking for some references), and there is a high chance that I have gone off track somewhere above.


Are there pronunciation patterns in English?

I know that English is not a phonetic language, but I think there may be general patterns to help pronounce English words.  Can native English speakers say the words without looking at phonetic symbols?


I have tried to log into Netflix today, I logged in without any problem and the 'watch instantly' page was displayed. When I click on a film I get transferred to a 'System compatibility' screen. I tried contacting their support and was told that they didn't support Linux. Can anybody help on this?


Is really a new Mersenne prime has been discovered for 2018 year?

I have read in  if it is true that $2^{282589933}-1$ is a new Mersenne prime which was discovered in 07 december 2018 , Really  I want to know how this was tested to be a prime number ?


What's the best way to parse a fixed position ascii file in c#

I have a fixed position ascii file that I need to parse.  The file gets passed in as a text document with hundreds or thousands of rows.  Each row is about 100 characters wide.  Each data element is varying length.  I really do not want to manually parse each data element.  I remember way, way back in the day when I coded in "C", that we could take some data, and overlay a struct, and then reference the data elements in the struct.  I have done some research, and I don't see any solid examples on how to do this in C#.  Any suggestions on how to parse this data?  This is an example of what the data could look like:  Mr John      Doe       123 Main St.        New York       NY11111 MrsMelissa   Schwartzen4444 Mississippi St.Philadelphia   PA11111   Title - Starts at column 0, has a lenth of 3. FirstName - Starts at column 3, has a length of 10. LastName - Starts at column 13, has a length of 10. Address - Starts at column 23, has a length of 20. City - Starts at column 43, has a length of 15. State - Starts at column 58, has a length of 2. Zip - Starts at column 60, has a length of 5.  The first thought to parse this data might be to iterate through each line in the file and get substrings for the Title, FirstName, LastName, Address, etc.   But there has to be a more elegant way to parse this data.  That is why I am asking if there is a way to use a pointer and overlay the data with a struct.  This is an unmanaged solution, but I can't think of any better ways to approach this.  Unless one of you smart and clever people can suggest something.


For each of the following, give an example of a sequence of functions $f_n$ that converges to f  A. uniformly but not in the mean square sense.  B. in the mean square sense but pointwise nowhere.  I know that for part A the domain of the function cannot be bounded but other then that I'm not sure how to go about the problem


A Noetherian domain $R$ is a UFD iff $I_{fg}=\{h\in R \mid hg\in(f)\}$ is principal for all $f,g\in R$.

Let $R$ be Noetherian domain. For $f,g \in R$, define the ideal $I_{fg}=\{h\in R \mid hg\in(f)\}$. Prove $R$ is UFD iff $I_{fg}$ is principal for all $f,g\in R$.   I'm stuck at this problem. The condition for a ring to be UFD on top of my head is Kaplansky's theorem. However I don't think I could make use of that theorem here since it involves considering all prime ideals. Also I don't really know how to make use of $R$ being noetherian. Any ideas to prove this?


Why is there more than one Stack Exchange site for one topic?

There is one Stack Exchange site, , where every question on any Unix-like operating system, including Linux, is welcome. So why a separate site, ?  Ubuntu is based on Linux and the questions there are on topic on Unix & Linux. Also there is another . But Android is also a Linux as well. So why these three sites? Questions on Ask Ubuntu and Android Enthusiasts are perfectly on topic for Unix & Linux. Shouldn't they be merged with the Unix & Linux Stack Exchange site?


"error: invalid video mode specification 'text' . Booting in blind mode"

I'm running an Ubuntu 16.04 (ext4) and Windows 10 (ntfs) dual boot environment which worked perfectly until I seemed to have crashed it by switching temporarily from UEFI Only to Legacy Only in my bios to run hard drive diagnostic tools from USB.  Now the initial splash screen has changed and the grub menu (version 2.02~beta2-36ubuntu3.7) shows up in much lower resolution (640x480) then before.   This is not really a problem for me, but when I choose to start Ubuntu this message pops up for a second:  error: Invalid video mode specification 'text'. Booting in blind mode   Then two more message lines are shown:  [1.895670][drm: intel_set_pch_fifo_underrun_reporting [i915]] *ERROR* uncleared pch fifo underrun on pch transcoder A [1.895696][drm: intel_pch_fifo_underrun_irq_handler [i915]] *ERROR* PCH transcoder A FIFO underrun   After this, the Ubuntu loading screen appears in high resolution, but exits in emergency mode where I can login as root user.  When I type in glxinfo in Terminal I get Error: unable to open display.  It all seems to me that there is an issue with loading the Intel grahpics driver in Ubuntu (Windows starts without problems).  Has anybody experienced a similar issue before or better can help me to get my Ubuntu booting again? I've searched through the forums, but couldn't find a helpful solution yet. Would be great!  Update @rod-smith (see answer below) helped me already with UEFI/CMS/Legacy settings and got me back to the previous splash screen and the grub menu in high resolution. However, the main problem: error: Invalid video mode specification 'text'. Booting in blind mode still persists and I end up in emergency mode. Any more suggestions how to handle this?  If it helps, I'm running a Lenovo Thinkpad X1 Carbon from 2013.  Update 2 When I run journalctl -xb in emgergency mode, some red messages show up. Within them the messages fsck failed with error code 4 and Failed to Start File System Check on /dev/disk/by-uuid/..... Maybe this can help.  Update 3 The problem is solved. See my answer below.


Multiple citations as [1,2] with single \cite

At the moment I have something like this in my latex document: \cite{NgRussell:ICML2000,AbbeelNg:ICML2004}  However in the pdf this appears as [3], [5] while I would like to see [3,5].  The following lines in my preamble could be affecting this, but I have no idea which ones:  \usepackage[backend=biber,style=ieee,sorting=none,urldate=comp,dateabbrev=false]{biblatex} \addbibresource{references.bib} \DefineBibliographyStrings{english}{     urlseen = {Retrieved}, }


My 2 sons now have a ps4 each. Son number 2 started a Minecraft world on the original ps4. He now has a ps4 of his own. How do I move the world he has created from the old ps4 to the new ps4? He has the same 'account' and we've bought Minecraft again for this console and thought the world would be there when he signed in but it's not.


If $f(x)=g'(x),g(x)=-f'(x)$ for all real $x$ and $f(2)=4=f'(2)$ then value of $f^2(4)+g^2(4)$ is ? Now the above is true when we have a  constant function with constant $0$. But then that would not satisfy third condition ?what can this function be? Thanks !


java.lang.NullPointerException: Attempt to invoke virtual method 'int androidx.viewpager2.widget.ViewPager2.getCurrentItem()' on a null object rfernce

I'm creating a video application. There is no problem when the application is opened for the first time. However, when I close and open the application after logging in, I get this error. How can i solve this? Error Details: java.lang.NullPointerException: Attempt to invoke virtual method 'int androidx.viewpager2.widget.ViewPager2.getCurrentItem()' on a null object reference     at com.test.video.ActivitesFragment.Home_F.onPause(Home_F.java:266)     at androidx.fragment.app.Fragment.performPause(Fragment.java:2782)     at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:933)     at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)     at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:434)     at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2079)     at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1869)     at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824)     at androidx.fragment.app.FragmentManagerImpl.execSingleAction(FragmentManagerImpl.java:1696)     at androidx.fragment.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:299)     at androidx.fragment.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:235)     at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1244)     at androidx.viewpager.widget.ViewPager.setCurrentItemInternal(ViewPager.java:669)     at androidx.viewpager.widget.ViewPager.setCurrentItemInternal(ViewPager.java:631)     at androidx.viewpager.widget.ViewPager.setCurrentItem(ViewPager.java:612)     at com.google.android.material.tabs.TabLayout$ViewPagerOnTabSelectedListener.onTabSelected(TabLayout.java:3326)     at com.google.android.material.tabs.TabLayout.dispatchTabSelected(TabLayout.java:1767)     at com.google.android.material.tabs.TabLayout.selectTab(TabLayout.java:1760)     at com.google.android.material.tabs.TabLayout.selectTab(TabLayout.java:1720)     at com.google.android.material.tabs.TabLayout$Tab.select(TabLayout.java:2138)     at com.test.video.MainMenu.MainMenuFragment.lambda$setupTabIcons$2$MainMenuFragment(MainMenuFragment.java:298)     at com.test.video.MainMenu.-$$Lambda$MainMenuFragment$V-dggKmBsOwj0BA1tZlatjLuWxk.onClick(Unknown Source:2)     at android.view.View.performClick(View.java:7185)     at android.view.View.performClickInternal(View.java:7162)     at android.view.View.access$3500(View.java:819)     at android.view.View$PerformClick.run(View.java:27684)     at android.os.Handler.handleCallback(Handler.java:883)     at android.os.Handler.dispatchMessage(Handler.java:100)     at android.os.Looper.loop(Looper.java:224)     at android.app.ActivityThread.main(ActivityThread.java:7562)     at java.lang.reflect.Method.invoke(Native Method)     at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)  Home_F.java:266 @Override     public void onPause() {         super.onPause();         VideosList_F fragment = (VideosList_F) viewPager2Adapter.getFragment(menuPager.getCurrentItem());         fragment.mainMenuVisibility(false);     }


Getting GeoServer full datastore layer list by REST

I have installed GeoServer 2.6.1 with an Oracle datastore which has some of the tables of the database published - the others will be published in the near future.  The  says that It is possible to access to the published layers of the datastore by REST GeoServer service like following:   http://localhost:8080/geoserver/rest/workspaces/[WORKSPACE]/datastores/[DATASTORE].html  As far as I know, this REST method only lists all layers of the datastore which are published. I would like to know if could be possible to get all layers (published and non published yet) from a specific Geoserver's datastore.


I want to calculate the average time taken to call a method, but the results are very much dependent on the "numberOfTries" variable in the code below:       int averageExecutionTime = 0; int numberOfTries = someNumber;  for(int i=0 ; i<numberOfTries ; ++i){     long t = System.nanoTime();     CallSomeMethod();     averageExecutionTime += (System.nanoTime()-t); } averageExecutionTime /= numberOfTries; System.out.println(averageExecutionTime);   When I run my method for the first time, it takes about 6000 nanoseconds to call the method. However, when I call it again, the time taken reduces to about 50 nanoseconds. What is the cause of this reduction?


Invalid use of non-static member function when using cpp class

I have an callback function :  ARCONTROLLER_Device_SetVideoStreamCallbacks (deviceController, decoderConfigCallback, didReceiveFrameCallback, NULL , NULL);   Which decoderConfigCallback and didReceiveFrameCallback are function.  When myproject have only a main.h and a main.cpp and define (without any class declaration)      eARCONTROLLER_ERROR didReceiveFrameCallback (ARCONTROLLER_Frame_t *frame, void *customData);   eARCONTROLLER_ERROR decoderConfigCallback (ARCONTROLLER_Stream_Codec_t codec, void *customData);   In .h file . when I call the ARCONTROLLER_Device_SetVideoStreamCallbacks evry thing is ok . but when I'll use a cpp class and do these, I get this error:      invalid use of non-static member function


Mac's dictation is a easy audio-to-text tool. however to change the language one has to go to system preferences every time. is there anyway to change between languages quickly(i.e by shortcut)? E.g if one can change dictation language by terminal, then alfred or shell script can change it with keyboard shortcut.


Normalized vector of Gaussian variables is uniformly distributed on the sphere

I have seen in various places the following claim:  Let $X_1$, $X_2$, $\cdots$, $X_n \sim \mathcal{N}(0, 1)$ and be independent. Then, the vector $$ X = \left(\frac{X_1}{Z}, \frac{X_2}{Z}, \cdots, \frac{X_n}{Z}\right) $$ is a uniform random vector on $S^{n-1}$, where $Z = \sqrt{X_1^2 + \cdots + X_n^2}$.  Many sources claimed this fact follows easily from the orthogonal-invariance of the normal distribution, but somehow I couldn't construct a rigorous proof. (one such "sketch" can be found ).  How to prove this rigorously?  Edit:  It has been brought to my attention that this question was already asked before .  However, I find the answer there to be incomplete-it shows that $X$ is orthogonally-invariant, but does not explicitly explains why that implies it is uniform. Therefore I think there is value in keeping this copy as well, as I guess we cannot transfer the answer.  In my question, I explicitly asked for a complete rigorous proof-and I find the answer there to be incomplete.


Elizabeth's necklace changes to the opposite?

To be clear: this isn't a question about whether or not choosing one necklace or the other has an impact on gameplay, or a duplicate of , since (please read in full)...      refers to the scene where Booker enters the lighthouse and is drowned by the other Elizabeths (all without a necklace), implying that "his" Elizabeth hasn't entered with him at all (possibly to avoid the threat to her very existence should she enter since she would be killing her father before her own conception). The below refers to the scene in the rowboat before they enter the lighthouse where Elizabeth is seen with a different necklace (not the lack thereof)--this is therefore a different question with different implications (i.e. that the Elizabeth guiding Booker through the Sea of Doors to the drowning already is a different Elizabeth for some unknown reason).   I personally chose the bird for Elizabeth during a second play-through, and tried to pay attention to it the whole way through, now aware of its significance.   I noticed the following:     when I was rowing to the lighthouse with her and the Luteces for the third and last time before entering the lighthouse at the very end of the game, her pendant was briefly changed to the cage right up until Booker climbs the ladder of the dock (i.e. right after you cross the tear in the wall of your apartment of "20 years later" to join the Luteces waiting for you, they comment on the mark on your hand, and you board the rowboat for a third time).   The game gives you plenty of time to catch the switch during this scene:     as light reflects off the pendant multiple times while you're rowing to the dock and Elizabeth says "Booker wake up, this is where it started" to which he replies "I sold you... I sold you...", you can clearly see the pendant is now a cage when it should be a bird (in my case).   My question is: does this mean the Elizabeth that is with you during that very short segment is actually another Elizabeth? And, if so, what possible implications does it have?


Argument list too long when copying files

I just asked a  related to how I can count the files of particular extension. Now I want to cp these files to a new dir.  I am trying,  cp *.prj ../prjshp/   and   cp * | grep '\.prj$' ../prjshp/   but they are giving the same error,     bash: /bin/cp: Argument list too long   How do I copy them?


When does LASSO fail in terms of:   out of sample forecasting? selecting relevant variables?   (If there is a distinction between 1 and 2 to begin with.)  Also,   Under what conditions would one be better off using ridge regression or other techniques instead of LASSO?   I am looking for the most salient examples and conditions which should ring a bell for an applied modeller.


Ubuntu Software has multiple instances (snap and canonical updates) of software. Which are safest?

I reported a bug with LibreOffice (the 'official'  bionic-upgrade version) and LO support person suggested upgrading to a current version from their site.  They said I was using an old version.  I prefer to upgrade via 'Ubuntu Software' in an attempt to reduce risk (security and stability) so I looked there.  It caused me to wonder if the more up-to-date, snap version, which also appears in 'Ubuntu Software' alongside , is (more) trustworthy than the Canonical distributed one.  Basically, how much trust can be placed in snap of a provider?  This obviously requires comparing it to the trustworthiness of Canonical Corp...!  p.s. Please don't simply suggest to learn to read code and I won't suggest you learn DIY open heart surgery; humans specialise.