Experiments are done to see if a process is symmetric (or asymmetric) with respect to the reversal of time. So if a process happens if the particles move in one direction, but not the other way round if you reverse the velocities of the particles participating in the process (after the process) the other way around it is asymmetric with respect to time reversal. Does this mean that time is reversed locally by giving the velocities of the particles after the process an opposite direction, while the velocities of all the other particles in the Universe stay the same (the clock in the lab runs forward)? Is time (locally or globally) reversed if you give all the particles velocities the opposite direction (disregarding for the moment the collapse or development of the wave functions or the expansion of the Universe? Would the locally changed velocities of the above-described process will still be asymmetric in time if you give all particles an opposite velocity?

First, how i got to the question.  I was randomly looking at this page:   describing some sort of cellular automaton.  Here is the path of this automaton after more then 10000 steps:    You can clearly see that after some time ant gets stuck in the loop (actually its a highway) and will be going on it forever.  Here comes the problem with many faces:  If we turn back time and start ant from one of the loop(highway) points we will never get to the original messy part, so obviously this computation is not time reversible since there is no way out of the loop! :) (But there should be ! :D)  Another thing is that information is also not time reversible - since if at some point in computation operation DELETE is used to erase all the previous data there is no way to get that data back.  Ok. So far so good. Lets take this question one step further. How is that so? They always told us laws of physics are time reversible and so on.  My intuitive answer is following.  We can say that in the universe there are so called LAWS (physics and so on) and OPERATIONS. What is the difference?   LAWS do not change the objects on which they are operating and hence probably are time reversible.  OPERATIONS on the other hand can change objects, their number in the system and hence  are not time reversible (if I delete some files there is no algorithm how to restore them again)  I understand its very close to the idea and interpretation of information.  So when they show us movie backwards and we think time got reversed its actually false! Yes you can reverse the motion of the people and objects, but you can not reverse speach for example since there is no logical connection between phrases being said. Here we can see how the content of the movie (life) is actually twofold - time revesible part (geometry in the poorest sense) and informational part (speech, computations and so on).  From all above it seems that the universe overall is NOT time reversible, and there is no way to go back in time! :) Or is there?


Suppose we have $n$ keys. We try each key at random to open a door. If   we $\bf discard$ the ones that don't work, what is the probability   that we open the door in the kth try? What if we dont discard the   previously tried keys?   $$\bf \underline{Attempt \; to \; the \; solution}$$  We can call $E_i$ to be event that the ith key opens the door. Clearly, since we have $n$ keys $P(E_i) = \frac{1}{n}$. Here is where I am having trouble trying to express our outcome in terms of events $E_i$. I feel like the answer is just $P(E_k) = \frac{1}{n}$ but perhaps the phrasing of the problem is confusing.  Now, if we dont discard. Suppose we put first key into door. there are $n-1$ possible ways that it wont work cause $1$ of them is the one that works.same holds for the second and third and so forth until we get to the $k-1$th case. The next case the one that opens the door can be done in 1 way of course. Thus,  $$ P = \frac{(n-1)^{k-1} }{n} $$  Is this a correct approach?

A woman has $n$ keys, one of which will open a door. a)If she tries the keys at random, discarding those that do not work, what is the probability that she will open the door on her $k^{\mathrm{th}}$ try?  Attempt: On her first try, she will have the correct key with probability $\frac1n$. If this does not work, she will throw it away and on her second attempt, she will have the correct key with probability $\frac1{(n-1)}$. So on her $k^{\mathrm{th}}$ try, the probability is $\frac1{(n-(k-1))}$ This does not agree with my solutions.   b)The same as above but this time she does not discard the keys if they do not work.  Attempt: We want the probability on her $k^{\mathrm{th}}$ try. So we want to consider the probability that she must fail on her $k-1$ attempts. Since she keeps all her keys, the correct one is chosen with probability $\frac1n$ for each trial. So the desired probability is $(1-\frac{1}{n})^{k-1} (\frac1n)^k$. Again, does not agree with solutions.  I can't really see any mistake in my logic. Can anyone offer any advice? Many thanks


This isn't a duplicate, but I couldn't respond here:    Someone said "space isn't that kind of vacuum" and "it doesn't suck".   If that is so, why not?  How can this essentially pure vacuum possibly not be strong enough to overcome gravity and suck off the atmosphere?

People said outside earth is a vacuum.  But the air does not get sucked from the  Earth's surface. Some said it is due to gravity and some said the speed of air molecules are not high enough to escape.  We know vacuum will suck air like your vacuum cleaner and it has nothing to do with gravity. If outer space is really a vacuum, what prevents air escape the earth?


Movement speed of electricity in cable, is same as speed of light in space? In other words, electricity  moves in usual electro cable  aproximatelly  300 000 km/second ?

How is it possible to calculate the speed of an electron in a circuit? What factors does it depend on?


I need to run some script when user click the content div and another script when user click the container div.  But when I click content div it run content script and container div.  How to make it only run content script when the content div is clicked.  Thanks

Consider the following:
   something inside the header
   How can I make it so that when the user clicks the span, it does not fire the div's click event?


I am trying to connect Access database with QGIS like I would in ArcView but I get this problem.     Data source name not found and no default driver specified QODBC3: Unable to connect  Hoping someone can help.

So I followed the instruction here:  for adding a .mdb into QGIS. There are great instructions about 1/3 of the way down. But I still can't get it to open. I on Windows 7 with QGIS 2.4  I restarted QGIS and my computer. I am still getting the error: "Invalid Data Source: ODBC:co2014ProdSumm (btw this is the .mdb) is not a valid or recognized data source. "  These are not vector layers nor is this a ESRI personal geodatabase. This is an Access database with 2 tables I need out of it.   I also found a few other posts    and this one might be the answer but I don't know what it's talking about:   Is there any way to add a .mdb into QGIS? Also I do not have Access on my computer.   Edit 1:I hope this clarifies my issue.  Each time I get Invalid Data Source: C:...Co 2014 Annual Production Summary-xp.mdb is not a valid or recognized data source. Here is where I added the access connection    Trying to add as a vector file   Trying to add a database, I also tried local:host 3000 The error in the pic is the same no matter the source, name etc... I've tried changing all fields around.


Could someone give me a hint to this problem please? Here is what I do: $2003n+2002=100(20n+2)+3n+1802$ then I'm stuck at $20n+2|3n+1802$ Please help

The only solution that I have been able to come up with is $d=1$, but because $d>2$, I can't seem to figure out how to find a solution.


Say we have a random variable $Y$ which is positive, and a binary variable $X$, i.e. takes values 0 and 1 only.  I have seen (in various places) that:  $$Cov(X,Y) = E[Y | X = 1| - E[Y | X = 0|$$  How do you prove this?  I tried attacking it using the definition:  $$Cov(X,Y) = E[XY| - E[X]E[Y]$$  but it led nowhere.

Suppose $y$ is a continuous random variable and $d$ is a binary random variable that takes the value $1$ with probability $p$ and $0$ with probability $1-p$.   How do I show that $\text{Cov}(y,d)=(E[y|d=1]-E[y|d=0])p(1-p)$?


How do I find a right flash not to get red eyes? I did try all options.

Although tools exist to remove red-eye in post-production, what's the best way to avoid it while creating the photograph in the field?


I cannot upgrade to MOJAVE.  After spending a lot of time searching through Apple's download site, I contacted Apple support and they told me that I cannot download Mojave 10.14.0.  That version has been removed from their download files.  Other later versions are still available.  However, I CANNOT INSTALL 10.14.4 OR 10.14.6 without first installing 10.14.0.  Are there any non Apple sites that make that 10.14.0 download available?????

Sometimes it's hard to search for older versions of macOS & OS X  on the App Store.  This is an attempt to provide the canonical QA for this issue, as per the Meta QA -  I expect it to be modified over time to hopefully become a complete information resource.  How can I get any older version of a Mac OS to be able to run as a VM, or to reinstall on my Mac?


Question in Title. Why does $\det(A^2)=\det(A)^2$? Old quiz answers gave this as a proof of why if matrix $A=A^2$, then $A=0$ or $1$.

Given two square matrices $A$ and $B$, how do you show that $$\det(AB) = \det(A)\det(B)$$ where $\det(\cdot)$ is the determinant of the matrix?


Like in subject. I got null pointer, how it is possible ?       java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference    public class MainActivity extends AppCompatActivity {     Button button, button2;     TextView textView, textView2;     String abc;     public List list = new ArrayList<>();     int size;      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);          list.add("abc");         abc = (String) list.get(0);          button.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View view) {                 textView.setText(abc);             }         });          button2.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View view) {                   size = list.size();                 textView2.setText(size);             }         });     } }

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


I have to prove that a group of even order must contain a odd number of elements of order 2 and I know that if i take all the elements with order $>2$ that that subgroup has a even number of elements. But where do i go from here?

I am working on the following problem from group theory:     If $G$ is a group of order $2n$, show that the number of elements of $G$ of order $2$ is odd.   That is, for some integer $k$, there are $2k+1$ elements $a$ such that $a \in G,\;\; a*a = e$, where $e$ is the identity element of $G$.


When I create the pdf all I obtain is a frame with the name of the image instead of the image itself. Here’s the code I’m using :   \documentclass[11pt,a4paper,draft]{article}   %Packages importants>>>>>>>>> \usepackage[utf8]{inputenc}                  \usepackage[francais]{babel}                 \usepackage{amsmath}                         \usepackage{amsfonts}                        \usepackage{amssymb} \usepackage{mathtools} \usepackage{lipsum}                          \usepackage[pdftex]{graphicx}                        \graphicspath{{C:/Users/dad/Desktop/projet_recherche}} \begin{document}     \lipsum[1]     \includegraphics[scale=0.25]{car}\\     \lipsum[2] \end{document}     Is there something I should omit or add?

I'm using IEEEtran to format an article, and I wanted to include an image. I included the graphicx and hyperref packages, and used the following code, like normal, to include an image.  \begin{figure}[!t] \centering \includegraphics[width=3in]{fetch} \caption{Pipeline: Fetch Instruction} \label{fig:fetch} \end{figure}   What appears, however, is this:    Fetch.png is a file in the directory, and if I remove it, pdflatex errors instead of producing an output. I'm using MiKTeX 2.9 on Windows 7. Any ideas?


I'm new to this game. I'm mining in 12th and 13th layers by making 2x2 tunnels, and have made several 50-60 block long tunnels. The problem is so far I'm only able to find iron, redstone, coal, lapis lazuli, but no diamonds and only a little gold. So, my question is why am I not able to find reasonable amount of gold and diamond. Is the problem my technique of mining or am I searching in wrong layers? What is the best way to mine gold and diamond in Minecraft? What am I doing wrong?

The durability of iron tools is really starting to annoy me, but in all my hours of playing I've only stumbled across one deposit of diamond ore that provided around 7 Diamonds. What's the best way to locate more in Survival mode? Where is it most commonly found?


Imagine you were on a spherical spacecraft that had equal mass all the way around and you were deep in space, away from the gravitational pull of any planetary bodies or stars. If you released a marble at arm's length, would it be gravitationally pulled toward your body? If you flicked it in one direction, would it begin to orbit you? (If a marble is too big, then maybe a grain of sand?)

Since humans are not large in mass, do we exert enough gravitational force for a small object to orbit around us? (Assuming that the only gravitational force acting on the object is from the human). Using Newton's law of gravity and using myself as the human mass, I exert a 10^-8 force on a 1 kg object .5 meter away, but I am not sure if even this small of a force will be acceptable. What is the baseline "force" between two objects for 1 to orbit another?  Edit: I am not sure if this is a SpaceExchange question.


I'm a senior high school student. I want to learn particle physics as a hobby. I did some research about it ,and I learned that I should learn Quantum Field Theory for entering Particle Physics. QFT needs some high degree math. How can be a possible learning path in math/physics for me?

I am currently in the process of teaching myself QFT.  It is not an easy task.  I have armed myself with many of the standard textbooks.  However, I am slow learner.   I get stuck on a thousand different terms which I don't understand, and a style of 'mathematics speak'  which loses me 95% of the time.   There are so many gaps in my knowledge that if I were a ship I would be at the bottom of the ocean.  What I really need is a book called 'QFT for Morons'. That's a bit harsh but 'QFT for dummies' doesn't quite express it clearly enough and besides there isn't such a book as far as I can find.  Any suggestions of resources or books that might help?   What I am really looking for is the one that explains QFT like you were talking to a five year old.  Perhaps I am asking the impossible.  I will add a bit more of a specific question here.    I have learnt that there are groups and non-abelian Lie groups like SU(2) etc., and then there a lagrangians, as well as a few other things like operators and states.   So a really dumb question is how are the lagrangians derived?  Are they determined by the group?  I am also confused because I understand some of the groups like SU(3) are used for different things in QFT.   I feel compelled to appologize for my ignorance but I am determined to make so more progress with this.   The problem when one is teaching oneself is you don't know which is the most fruitful path to follow.


Early on it surprised me that questions marked as duplicate seem to still function normally. They can be answered, voted on, and commented on.  So what does happen when a question is marked as duplicate?  Clearly the 'duplicate' banner and a comment with a link to the duplicate are added.  Does anything else happen?

When a question has pending close votes, the system now adds a banner indicating that the question might be a duplicate:    But the first user to vote still generates a possible duplicate comment:    Those comments were always a hack, just like editing the link into the top of the post. The banner eliminated the need for the latter; can we stop generating those comments too?


user's details or user details, which one is the correct form when referring to the details of a user in a database?  Regards

I’ve been looking over what has been posted regarding the use of ’s.   I used to be a Technical Writer (years ago). The title of one of our training documents was Users’ Guide.  Once, a coworker said every time he saw that title he expected users to start coming.    Never made any sense to me, but I have to admit that the majority of us didn't understand the use of s’ in place of ’s.  What is the difference?


Let P be a prime ideal in a ring R (commutative with identity) and I be the ideal generated by the idempotents of R, contained in P. Show that R/I contain no idempotents other than 0 and 1.  An approach suggested is to show that for $x$ being one said idempotent in R/I, Then $x(x-1)$ belongs to I.If we then take X ∈ P , then one way suggested in the hint is to show that ∃ y ∈ I and y^2=y such that $yx(x-1)$=$x(x-1)$. I am unable to find this and then show (1-y)x is idempotent which implies x is idempotent

Let $R$ be a commutative ring with identity, $P$ be a prime ideal in $R$ and define $$X := \lbrace t \in P \mid t^2=t \rbrace. $$ Also let $J$ denote the smallest ideal of $R$ that contains $X$.  Prove that if $$a^2+J=a+J$$ in $R/J$, then $$a+J=J$$ or $$a+J=1+J$$  I am trying to solve this but I am new to algebra (aprox. 3 months), so I generally don't know how to start such questions. So any help is appreciated.


Unless I keep alt keyboard button pressed, the MacBook gets shutdown! After a few seconds of releasing the alt button, a message is popped up saying:     Are you sure you want to shut down your computer now?      Reopen windows when logging back in      Restart | Sleep | Cancel | Shut Down   This is a MacBook from 2009. Water poured on the top-right section of the keyboard. Afterwards, it gets shutdown unless the alt keyboard button is pressed continuously! Did anybody run into this issue before?    Also, when booting, the alt button needs to pressed. Otherwise, the MacBook gets shutdown while booting ...  Update  A colleague cracked open the MacBook, he did nothing, and put it together. Afterwards, surprisingly, the MacBook was working good for a couple of days! But got crazy again.  The behavior looks random. Sometimes it doesn't get shutdown for a couple of days and sometimes it shuts down frequently.

I have a a MacBook Air that works fine except popping up a shutdown dialog if left untouched for a couple of seconds (seems to be a consistent duration around 3 seconds or so). Hitting Cancel or Esc prevents the shutdown.  If I keep fidgeting around with the keyboard or trackpad, there's no shutdown attempt. I can even place something on the Fn key to keep the OS from shutting down.  It seems like some inactivity timeout etc. gone awry.  When taken to the Genius Bar for initial assessment, the guy there said it was probably the power button needing a replacement. But, I don't think this is the case, as the power button is functioning normally: I can still press it to explicitly initiate a sleep/shutdown.  There's a chance this was triggered by water damage. There was a recent water spill incident to which I acted quickly by turning off the machine + turning it upside down + not using it for a long while + keeping it in a box with rice to absorb any leftover humidity. But even if this is a water damage, I can't imagine a damage that manifests itself with this very narrow malfunction of wanting to shutdown on a short period of in activity. Absolutely nothing else seems to be wrong with the machine.  Any pointers? Any things I can try to (a) diagnose the root cause fix or workaround the problem?


As I've tried with the code below but it did not work. I would like to use Regular Expression for only whole numbers.  if (Regex.IsMatch(tbColumn.Text, @"^[0-9]") == true) {     MessageBox.Show("true"); } else {     MessageBox.Show("false"); }   With my code:  0 --> true 1 --> true 9 --> true 10 --> false (it must be true) 100 --> false (it must be true)   For example:  0 --> true 1 --> true 100 --> true 34343 --> true 0.5 --> false 1.42 --> false 1,2 --> false a1 --> false a --> false

I haven't used regular expressions at all, so I'm having difficulty troubleshooting. I want the regex to match only when the contained string is all numbers; but with the two examples below it is matching a string that contains all numbers plus an equals sign like "1234=4321". I'm sure there's a way to change this behavior, but as I said, I've never really done much with regular expressions.  string compare = "1234=4321"; Regex regex = new Regex(@"[\d]");  if (regex.IsMatch(compare)) {      //true }  regex = new Regex("[0-9]");  if (regex.IsMatch(compare)) {      //true }   In case it matters, I'm using C# and .NET2.0.


Are both Okay? I guess the problem is I could have made more than one error, but I could have made only one error

Which is correct?     There are no comments.  There is no comment.   Which would you use for a web application, i.e. what to display when a blog post or an article has no comment attached?    Actually, I am trying to fix an application that says: "There is no comments"! Would that ever be right?  More generally speaking, it feels wrong to have a plural after the negative no/none or with the preposition without (see my previous question ).  Those words imply zero, i.e. less than one, while plural is two or more. Yet, I know that phrases like "There are no comments" or "He is without friends" are common. It seems illogical to me.   Are the majority of people making a grammar mistake when using such expressions, or else can you explain why this is correct?


Whenever I try and install anything including system updates I get this error: The following packages have unmet dependencies:  gstreamer1.0-plugins-bad : Depends: libgstreamer-plugins-bad1.0-0 (= 1.16.2-2.1+b1) but 1.14.5-0ubuntu1~18.04.1 is installed                             Depends: libgstreamer-plugins-base1.0-0 (>= 1.16.2) but 1.14.5-0ubuntu1~18.04.1 is installed  gstreamer1.0-plugins-good : Depends: libgstreamer-plugins-base1.0-0 (>= 1.16.2) but 1.14.5-0ubuntu1~18.04.1 is installed  gstreamer1.0-plugins-good:i386 : Depends: libgstreamer-plugins-base1.0-0:i386 (>= 1.16.2) but 1.14.5-0ubuntu1~18.04.1 is installed  gstreamer1.0-x : Depends: libgstreamer-plugins-base1.0-0 (>= 1.16.2) but 1.14.5-0ubuntu1~18.04.1 is installed  gstreamer1.0-x:i386 : Depends: libgstreamer-plugins-base1.0-0:i386 (>= 1.16.2) but 1.14.5-0ubuntu1~18.04.1 is installed  and whenever I run apt --fix-broken install this will appear: Reading package lists... Done Building dependency tree        Reading state information... Done Correcting dependencies... failed. The following packages have unmet dependencies:  gstreamer1.0-plugins-bad : Depends: libgstreamer-plugins-bad1.0-0 (= 1.16.2-2.1+b1) but 1.14.5-0ubuntu1~18.04.1 is installed                             Depends: libgstreamer-plugins-base1.0-0 (>= 1.16.2) but 1.14.5-0ubuntu1~18.04.1 is installed  gstreamer1.0-plugins-good : Depends: libgstreamer-plugins-base1.0-0 (>= 1.16.2) but 1.14.5-0ubuntu1~18.04.1 is installed  gstreamer1.0-plugins-good:i386 : Depends: libgstreamer-plugins-base1.0-0:i386 (>= 1.16.2) but 1.14.5-0ubuntu1~18.04.1 is installed  gstreamer1.0-x : Depends: libgstreamer-plugins-base1.0-0 (>= 1.16.2) but 1.14.5-0ubuntu1~18.04.1 is installed  gstreamer1.0-x:i386 : Depends: libgstreamer-plugins-base1.0-0:i386 (>= 1.16.2) but 1.14.5-0ubuntu1~18.04.1 is installed E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages. E: Unable to correct dependencies   I also can't open any system apps like system setting system updater and most of my other software besides google and terminal and wireshark. I've run apt-cache policy gstreamer1.0-plugins-bad and I ended up getting this: $ apt-cache policy gstreamer1.0-plugins-bad gstreamer1.0-plugins-bad:   Installed: 1.16.2-2.1+b1   Candidate: 1.18.0-2+b1   Version table:      1.18.0-2+b1 500         500 http://http.kali.org/kali kali-rolling/main amd64 Packages  *** 1.16.2-2.1+b1 100         100 /var/lib/dpkg/status      1.14.5-0ubuntu1~18.04.1 500         500 http://archive.ubuntu.com/ubuntu bionic-updates/universe amd64 Packages      1.14.0-1ubuntu1 500         500 http://archive.ubuntu.com/ubuntu bionic/universe amd64 Packages

There are now errors when updating and I cannot install most software due to a corrupted  /etc/apt/sources.list   file. Is there a copy I can download to replace it?  The file would be for Ubuntu 12.04 (Final Beta) in the United States.


Determine all prime numbers p such that p^2+2 is also a prime number. I have only found 3, and I think that's the only number but I have trouble writing proof for this. But I know that if p is a prime number other than 3 then p^2+2 will be divisible with 3.

Origin —  Elementary Number Theory — Jones — p35 — Exercise 2.17 — For which primes $p$ is $p^2 + 2$ also prime? Only for $p = 3$. If $p \neq 3$ then $p = 3q ± 1$ for some integer $q$, so $p^2 + 2 = 9q^2 ± 6q + 3$ is divisible by $3$, and is therefore composite. (1) The key here looks like writing $p = 3q ± 1$. Where does this hail from? I know $3q - 1, 3q, 3q + 1$ are consecutive. $p$ is prime therefore $p \neq 3q$? (2) How can you prefigure $p = 3$ is the only solution? Does $p^2 + 2$ expose this? On an exam, I can't calculate $p^2 + 2$ for many primes $p$ with a computer — or make random conjectures.


I'm trying to simplify an expression of the form $\sin(f(t)\cos(\omega t + \phi))$.  The nonlinear ordinary differential equation I'm working on involves terms like this (where the equation is to be solved for the unknown function $f(t)$).  Of course, one way would be to use the first several terms of the Taylor series for the sine.  But I'm curious if there is any analytical expression for an angle product like $\sin(\alpha \beta)$.

Can we express a trigonometric function for the product of two angles as a function of trigonometric functions of its factors?  For example: Is there a formula for $\sin(xy)$ as a function of $\sin x$ and $\sin y$ or other trigonometric functions of $x$ and $y$.


i'm  developing a Facial Rig Panel, And I need to get the reference to an object(in this case the Armature) in a custom panel, similar to this picture.Or Maybe tip the Name of the Armature in a Text Field and get the value. Blender has any operator that allows to do it?

How to add an eyedropper functionality to prop_search in my addon?  col.prop_search(scene, "string_property", context.scene, "objects")   This code will create prop_search just like on the animation below, but without an eyedropper.


I am trying to run a basic select Query in PostgreSQL, but I am having trouble using the column alias.  I tried to create the alias as randomfield As [Space In Name] but it gave an error of     Error: syntax error at or near "[" Line 2: randomfield As [Space In Name]   And I also tried to do the alias w/o the brackets but that presented an error as well.  How do you alias with a space in Postgresql?  Select randomfield As [Space In Name] From saledata

I migrated a database from SQL Server to PostgreSQL.  Most column names contain double words, for example:  SELECT [Column Name] FROM table;   ...which does not work in PostgreSQL.  What is the correct syntax for PostgreSQL?


I am trying to install Lyx via ppa in Ubuntu 18.04. I tried following the instructions  and added the ppa. It is giving the following error message:  arpan@arpan-laptop:~$ sudo add-apt-repository ppa:lyx-devel/release [sudo] password for arpan:   Look here for updated release versions of LyX.   More info: https://launchpad.net/~lyx-devel/+archive/ubuntu/release Press [ENTER] to continue or Ctrl-c to cancel adding it.  'Error reading https://keyserver.ubuntu.com/pks/lookup?op=get&options=mr&exact=on&search=0xEDE9A1109EB3355B591159DCA64833C9F8214ACD: [Errno -2] Name or service not known'   After this when I try doing apt update, I again get a similar error:  W: GPG error: http://ppa.launchpad.net/lyx-devel/release/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A64833C9F8214ACD E: The repository 'http://ppa.launchpad.net/lyx-devel/release/ubuntu bionic InRelease' is not signed. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details.

I added some extra repositories with the Software Sources program. But when I reload the package database, I get an error like the following:     W: GPG error:  trusty InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8BAF9A6F   I know I can fix it using apt-key in a terminal, according to the official Ubuntu documentation. But I would have liked to do it graphically. Is there a way to do this without using a terminal?


That is if a user saves up, for example, 3 my dislikes under his posts, all his posts will be marked for me as undesirable.

Stack Overflow has successfully borrowed at least one XBox feature (Achievements).  I'd like to see another feature borrowed as well. Let's say I'm playing Halo online and another player is being a bigot.  I have the option to add him to a list of ignored users.  After doing that, all the racist things he says will never be heard through my headphones anymore. Now, on Stack Overflow, I'd like the ability to add a user to a list of ignored users.  This would hide all of that user's comments, and maybe his questions and answers as well (not sure if hiding questions/answers is necessary). This serves multiple purposes:  It would make it easy for users to avoid other users' flamebait. It would give users a more appropriate response to flamebait. The ability to start flame wars would be reduced, since fewer users would see those comments. Users would now have an incentive to be more diplomatic, as there is now a negative consequence to the behavior (the silent treatment). Administrators could review which users are the most often ignored, which would be a strong indication that someone should be  or even locked out of their account. Administrators wouldn't have to spend as much time dealing with complaints about abusive users, since users would have a better way to respond.    makes a good point in a comment to an answer, that I thought should get more visibility:  I had a problem, reported it and got the response "not bad enough to do anything about, sorry". Which is kind of true, because the only options available to the mods are the nuclear one (penalty box) and the zero-effect one (do nothing). We need a middle ground option where abuse can be handled for you without also being handled for everyone.


I have lived in the US for many years. I renewed my New Zealand passport several years ago (born in NZ).  I have been told I must leave and enter the US on my US passport. I am going to NZ soon. What will happen if I show US Airlines my US passport but on arriving in NZ show my NZ passport?

I am a citizen of two different countries, and have two passports.  How should I use my passports when traveling?


I'm trying to get Postfix to pipe ALL email coming in on a specific domain to a PHP script. So far I've been able to do this via a tutorial I found on the web and also editing the /etc/postfix/virtual file with something like what's below;  @domain.com root   The problem is that Postfix is re-writing the original recipient email address (for example my_fake_email@domain.com) to root@domain.com and the PHP script receiving the email does not get the original recipient (my_fake_email@domain.com). It is important that the PHP script sees my_fake_email@domain.com instead of root@domain.com.   Is it possible for Postfix to direct all incoming mail to the PHP script without modifying the address like in the example above?  Note: There can/will potentially be 10,000's of incoming email addresses.  Any ideas on how I can get Postfix to do what I want?

Using postfix, I'd like all incoming mail, to any address (including those that don't map to local users) to be piped to a script.  I've tried configuring mailbox_command in /etc/postfix/main.cf:  mailbox_command = /path/to/myscript.py   This works great if the user is a local user, but it fails for "unknown" users who don't have aliases.  I tried setting luser_relay to a local user, but this pre-empts mailbox_command, and so the command doesn't get run.  I tried setting local_recipient_maps= (empty string), but the message is still bounced (unknown user).  Is there a magic invocation I can use to get all known and unknown users to go to the script as well?  Full /etc/postfix/main.cf follows -- it's the default Ubuntu 10.04, with the exception of the mailbox_command line:  # See /usr/share/postfix/main.cf.dist for a commented, more complete version   # Debian specific:  Specifying a file name will cause the first # line of that file to be used as the name.  The Debian default # is /etc/mailname. #myorigin = /etc/mailname  smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu) biff = no  # appending .domain is the MUA's job. append_dot_mydomain = no  # Uncomment the next line to generate "delayed mail" warnings #delay_warning_time = 4h  readme_directory = no  # TLS parameters smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key smtpd_use_tls=yes smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache  # See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for # information on enabling SSL in the smtp client.  myhostname = ... snip ... alias_maps = hash:/etc/aliases alias_database = hash:/etc/aliases mydestination = sassafras, ... snip ...,localhost.localdomain, localhost relayhost = mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 mailbox_size_limit = 0 recipient_delimiter = + inet_interfaces = all  mailbox_command = /path/to/my/script.py


I am looking for a workflow that allows multiple artists to work on a project where users can work in parallel and assuming they don't change exactly the same thing the work can be smoothly merged.   I am used to working with a game engine using xml and many separate binary files which works well with a versioning system like git or svn.

I remember there was once a project called Verse, which allowed (or at least was supposed to) collaborative editing in Blender, even using Blender collaboratively with other applications.  Is anything along these lines (I.E. collaborative editing across a network) supported in the current version?


Ubuntu was installed in disk H and windows 8 in disk C. Now, I refreshed windows 8 and I am not able to get the option to boot to ubuntu when I start my laptop.

I installed Windows 7, which ate Ubuntu's boot file. When starting up the computer, it now goes straight to Windows, without giving me the option of booting Ubuntu.   How can I get Ubuntu back?


They said that she lost the will to live, but was there other complications when she gave birth and she just didn't have the will to fight it? And if so, is it possible that Anikan's force choke caused it (physically, obviously it hurt her mentally)? Or did she just decide two children are not reason enough to live and just died of grief?

According to      MEDICAL DROID: Medically, she is completely healthy. For reasons we can't explain, we are losing her.       OBI-WAN: She's dying?       MEDICAL DROID: We don't know why. She has lost the will to live. We need to  operate quickly if we are to save the babies.         Medically healthy humans don't die for no good reason.  So what did Padmé die of, and how did they even know she was dying?


when I try to download a free app it asks for my credit card info, and I don't have one and I say none but it just restarts and wont let me pick none.

Ever since adding an iTunes gift card to my account, I'm getting verification requests like crazy. I can't even download free apps. It takes me to my payment info and when I try to select none, I continually get a message under the payment info that says "you must verify your payment info to continue"  I don't want a credit card on file and would really like the none option to work. My ID shows I still have iTunes credit.


Over the past few years I have often heard people repeat the word "is" unnecessarily, for example, "My concern is, is that by going backwards we will throw a spanner in the works and that momentum will be halted." (Sir Michael Wilshaw, Chief Inspector of Schools, Radio 4 Today Programme, 9th September 2016.)  Sometimes, as in the above example, there is a discernible pause between the two words, and sometimes there is none.  Has this phenomenon been remarked upon and does it have a name? If not, may I suggest "isisism".

I am proofreading a professional, technical text written by someone else. In the text, I encountered, "But, the reality is is a..." My intuition says that this should be rewritten as, "But, the reality is that a..." because it looks like a "double is" or a ""  However, I can't tell for sure if this is a legitimate use of two successive copulae. Does, "But, the reality is..." qualify as a dependent clause? It seems to me that "But,..." does not make the subject dependent. Am I right? Am I wrong?  The sentence with a little more context: "But, the reality is is a company like Spacely Sprockets cannot continue to do old fashioned things..."  (We have already had a discussion about beginning sentences with "but" in professional writing. It appears that the consensus is that it is both appropriate and acceptable here.)  I would like to see a way to clearly identify this statement as something that ought to be changed in the document. Grammar dissection, linking to authoritative works and explanations of grammar mechanics will all help me answer this question. Simple answers like, "it's wrong," don't help me be a better proofreader or editor. I already know it is wrong, but I  don't know why it is wrong.


I am having an issue with proxy configuration in Ubuntu 16.04. I have done these steps but it is still not working.   Added the following lines to /etc/apt/apt.conf:  Acquire::http::proxy "http://10.16.0.2:8080/"; Acquire::ftp::proxy "ftp://10.16.0.2:8080/"; Acquire::https::proxy "https://10.16.0.2:8080/";  Executed these commands in a terminal:  export http_proxy=http://10.16.0.2:8080/ export https_proxy=http://10.16.0.2:8080/    When I run the command env | grep proxy, it shows the proxy settings.  Can you please help me resolve this issue?

I need to configure proxy. There wasn't apt.conf file in etc/apt/ so I've created it using nano.   But I don't understand what I need to write there. I've written  http_proxy = http://lgn:pwd@192.168.1.254:8080/ there and then restarted networking. But when I try to apt-get update - it doesn't work.   Actually I don't understand what port and ip I should write in apt.conf file(there was example with 192.168.1.254 ip and 8080 port so I decided to use them).


When I try to open Software Center, the icon blinks, but nothing happens. When I type sudo software-center in my terminal I get:  2012-05-07 12:57:18,385 - softwarecenter.ui.gtk3.em - INFO - EM's: 17 15 21 Traceback (most recent call last):   File "/usr/bin/software-center", line 151, in <module>     app = SoftwareCenterAppGtk3(datadir, xapian_base_path, options, args)   File "/usr/share/software-center/softwarecenter/ui/gtk3/app.py", line 213, in __init__     self.cache.open()   File "/usr/share/software-center/softwarecenter/db/pkginfo_impl/aptcache.py", line 209, in open     self._cache = apt.Cache(GtkMainIterationProgress())   File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 93, in __init__     self.open(progress)   File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 140, in open     self._list.read_main_list() SystemError: E:Malformed line 54 in source list /etc/apt/sources.list (dist parse)   I have Ubuntu 11.10. I am new to Linux.  Appreciate your help!!!

I have unistalled and reinstalled the Ubuntu Software Center as per info I found in a similar thread and I got the same response about line 91 or something like that.  I just tried to upload a screen shot but since I'm new it won't allow me to.  I also can not figure out how to cut and paste anything so I have to hand type what the error screen says, both when I attempt to open the software center and nothing happens, when I try to enter commands into the terminal to uninstall, reinstall, whatever I get the same following:  COULD NOT INTITIALIZE THE PACKAGE INFORMATION An unresolvable problem occured while initializing the package information Please report t:his bug against the 'update-manager' package and include the following error message: 'E: Malformed line 91 in source list/etc/apt/sources.list (dist parse)  E: The list of sources could not be read.,  E: The package list of status file could not be parsed or opened.   How do I report bugs?  What can be done about this.  I have searched and everything everyone says to do leads me back to the same line error message.  So, I don't know how to get to line 91 in the source list; to tell you what it says. Sorry, I'm really new to this. That is what I need is to find out how to get there and fix what it says. I would really like to NOT have to re partition my hard drive and start from scratch, so I'm really looking forward to getting this problem solved. I need to be able to install new software.


It can be useful when reading some source code to know that after initialization, a variable will not change. For example in the following code sample:  for (int i = 0; i < Height; ++i) {     for (int j = 0; j < Width; ++j)     {         int index = i * Width + j;  // This variable never changes later. Or will it? [TrollFace]         float myValue = ComputeValue(i, j);         // ...         myArray[index] = myValue;      } }   It would be nice for code reviewers to be able to tell them not to care too much about the index variable because its value will never change. Obviously you can do it in a comment, but comments are not always updated and not necessarily reliable. In some languages, a keyword can be used to ensure the assertion "the value of this local variable will not change after initialization". Is there such a keyword in C#?

Having a friendly debate with a co-worker about this.  We have some thoughts about this, but wondering what the SO crowd thinks about this?


i have a
 element containing multiple lines, each starting with an image, followed by text. I want the text to be next to the vertical center of the image, so i put it inside a div a div and set display:inline-block and vertical-align:middle, but the text is still at the bottom. here is my code:  <!DOCTYPE html>               <meta http-equiv="content-type" content="text/html; charset=UTF-8">         <link rel="stylesheet" href="game.php-Dateien/style.css">

Some describing text

Why won't vertical-align: middle work?  And yet, vertical-align: top does work.   span{   vertical-align: middle; }
      Doesn't work.


When you show the info of a badge by hovering the mouse over it, e.g. for the nice/good/great question it shows:   bronze badge: Question score of 10 or more silver badge:: Question score of 25 or more gold badge:: Question score of 100 or more   The :: is a typo for all silver/gold badges.

I just hovered over the Gold tag-badge on the badges page and this is what I saw*:     4 problems:   The tooltip says it needs 20 answers. The text says 200. The silver is incorrect too. Other tooltips appear correct in their numbers. Bronze badges have a single : all silver and gold badges ::... That's a bit odd. I'd suggest just one : Could we have some title-case for the badge type? What is "score"? Having  (oh the humanity!) it occurs to be that the language should probably be explicit and say it's talking about a vote score.   Taking the above into account, badge tooltips should read like:  Gold Badge: Earned at least 1000 net votes....   And this seems to be network-wide (which makes sense).  * Well that's almost what I saw. On my screen there was a mouse-cursor over the badge but KSnapshot is a massive racist** and won't let my cursor be seen by other users because it's white.  **Maybe it's just misunderstood.


What I want is this:  Having a file called file somewhere in the filesystem with a content something like:  #!/bin/whatever-interpreter-you-want echo 'line1' echo 'line2'   When ANY (almost any since must exist a way to edit the script itself) program opens  file to read it gets:  line1 line2   As its contents instead of:  #!/bin/whatever-interpreter-you-want echo 'line1' echo 'line2'   Something like file contents being executed on the fly by the filesystem or the kernel itself (please, no cron, no inotify, no duct tape).

Is there any way to create a virtual file, such that reading from the file actually reads from the stdout of a command; writing to the file is acually writing to the stdin of a command?  So far I have kludged this with an inotifywait on a file, which calls a command when the file is modified, taking it's input from the file and writing back to it.  I don't like that the inotifywait has to be constantly restarted though (and I have to ensure that it is always running). I only use this file perhaps twice a week.


Before this gets marked as duplicate I have found answers at several sources (, , ) however all of them either use makecert.exe, signtool.exe, or fail to mention proper workflow of the New-SelfSignedCertificate command in PowerShell 4.  Could you describe the certificate signing process to an absolute novice?  The process should be free and understandable for someone who has nothing to work with but an executable they made and a domain (in my case purchased from ).  The end goal of this is to remove the "Unknown Publisher" warning from all of my applications that I have made for other people to use. Usually these are packaged by PyInstaller as single-file applications, however I plan to expand this to full installable applications with one main executable in the future.    The file that I will be testing this on is my  that simply finds the iTunes installer from Apple's website, extracts only Bonjour, and runs only the installer for the system architecture.  I should also mention that I am doing this on Windows 10.

How do I create a self-signed certificate for code signing using tools from the Windows SDK?


I am following a tutorial about how to make a simple stick man. Everything went fine until I reached bones. To follow the tutorial do I need to rotate all the vertical bones.  On the image I selected all the bones I need to rotate. I need them 180 degrees rotated.  (if you don't understand what I mean,  is a screenshot of the video)  Can somebody help me with fixing this?

I spent a lot of time building up my armature for my dragon model and then, after I was all done and started to refine it, I realized that the bones from the pelvis out to the end of the tail were pointing the wrong way - they need to have their heads pointing the other direction:    I don't want to have to delete these bones and start over.  Is there an easy way to switch the direction of the tail bones?


I am trying get information of 2 lowest salary holders from default "scott" table.   This is the query I am trying:  SELECT TOP 2 * FROM emp ORDER BY sal ASC   But I'm getting this error:     ORA-00923: FROM keyword not found where expected   Screenshot:

Is there a way to make an Oracle query behave like it contains a MySQL limit clause? In MySQL, I can do this: select *  from sometable order by name limit 20,10  to get the 21st to the 30th rows (skip the first 20, give the next 10). The rows are selected after the order by, so it really starts on the 20th name alphabetically. In Oracle, the only thing people mention is the rownum pseudo-column, but it is evaluated before order by, which means this: select *  from sometable where rownum <= 10 order by name  will return a random set of ten rows ordered by name, which is not usually what I want. It also doesn't allow for specifying an offset.


A favorite view of Spider-Man (at least in movies and games) is of the hero web-slinging his way through the streets of New York City. But what becomes of all the web ropes that Spider-Man discards as he moves from building to building? We don't see them hanging around the city, so presumably someone removes them.  Do people collect them as souvenirs? Does Spider-Man come back later to clean up after himself? Does the city employ a group of cleaners just to remove the webs?

Especially if he is not using his  but .   Also what happens to the web that he leaves behind? Does it decay after certain time or lose it stickiness and drops off?


As a kid, I never really liked cooked eggs, but fried ones. Naturally, I've always wondered if cooked eggs could be reused to make fried eggs with sunny side up instead of using new raw ones. I thought it was probably a really stupid question, but then I've found these related questions:       Now, obviously, it seems a very tall order to get runny yolk if it's already cooked, but what is the closest thing we can get? How close can we get to dipping bread into yolk?

This is probably a stupid question, but I'm curious now after I opened the refrigerator looking for eggs to make a cake and there was only one and it was cooked. Is there any way to undo that, whether at home or an industrial way?


I'm looking for a way to get a control at where my cursor is pointing to, is there any way to do this in C#?

I need to find the control under the mouse, within an event of another control.  I could start with GetTopLevel and iterate down using GetChildAtPoint, but is there a quicker way?


Ok so I'm trying to install ubuntu onto my laptop that I've just received. The error in the title occurs as soon as I click install ubuntu. Once or twice its let me get further than for example it allowed me to 'Try ubuntu without installing' once and its also gone through the full installation once however on booting on installing the error in the title occurs and there is no clear reason as to why that is on various posts with the same issues (on other websites).  Some people have stated that it has something to do with the power supply and others are stating that its fixed by updating the kernal however I cannot update the kernel without actually managing to load linux and of course its a laptop so changing the power supply is out of the question.  Does anybody have a clear fix as to why it won't install?

I get this error message   NMI watchdog: BUG: soft lockup - CPU#2 stuck for 23s! [plymouthd:305]    on the startup of my system (even with live-cd).  My PC is a dell inspiron 7559 with intel graphic and nvidia.  UPDATE - this issue also happens when attempting to install ubuntu 18.10 using LiveUSB


Suppose $a_1, \dots, a_n$ are distinct integers and let $$ f(x) = [(x - a_1) \cdots (x - a_n)]^4 + 1. $$ Show that $f(x)$ is irreducible over $\mathbb{Q}$. For the case $f(x) = [(x - a_1) \cdots (x - a_n)]^2 + 1$, I supposed $f(x)$ was reducible ($f(x) = g(x)h(x)$) and got to a contradiction manipulating the degrees of $g(x)$ and $h(x)$, using a result concerning the $n$ values $a_1, \dots, a_n$ for which $f(x) = 1$. However, I tried to adapt this same argument here and it didn't work because now the degree of $f$ is higher ($4n$) and the contradiction doesn't arise immediately. How should I proceed?

I try to solve this problem. I seems to come close to the end but I can't get the conclusion. Can someone help me complete my proof. Thanks          Show that the polynomial $h(x) = (x-1)(x-2)\cdots(x-n) + 1$ is irreducible over $\mathbb Z$ for all $n\ge1$ and $ n\ne4$.      Suppose $h(x) = f(x) g(x)$, then we must have $f(i)g(i) = 1$ for all $i = 1,2,...n$. So both $f(i)$ and $g(i)$ are $1$ or $-1$. In either case, $m(x) = f(x) - g(x)$ has degree smaller than $n$ and have $n$ different roots ($1,2,...,n$). So we must have $m(x) = 0$. Then $h(x) = f(x)^{2}$. So $n$ must be even. Let $n = 2k$. Because $f(x)$ has degree $k$, there are $k$ values from $\{1,2,...,2k\}$ at which $f(x)$ is $1$ and $k$ values at which $f(x)$ is $-1$.  This is where I got stuck. Hope some one can help me solve this. Thanks.


I tried changing my locale and also configured Python 3 alternatives. Nothing worked, but I can access the terminal after getting into file explorer. Error message for Gnome terminal:

After I installed Python 3.5 and ran the commands below, my terminal and many other programs won't launch any more.  cd /usr/bin sudo rm python3 sudo ln -s python3.5 python3    How can I restore the default Python version again to fix these problems?


We are developing an appexchange product and there is a functionality which needs to be different if its a Non profit vs the rest of the licenses.  Is there a way we can identify if the org uses NPSP?  Thanks

I am writing a test class that needs to be instance-agnostic. On some of our instances we have a managed package that affects the outcome of the test, so I need to insert some test data that will be used by that managed package, but I'm worried that if I migrate this test case to instances without that managed package, it will fail when trying to insert this test data for objects that don't exist on that instance.  To make a long question shorter, is there a way to test for the presence or absence of either a specific object or a managed package so I can run this code conditionally?


This sentence is in the context of dinner.     Beans is/are our only option   I'm confused as to whether "is" or "are" is necessary in this construct.

My fish's native habitat is rice fields. My fish's native habitat are rice fields.   Which one is correct? I'm pretty sure it's the first, since 'is' modifies 'habitat,' but it still sounds weird...


How can I create a newcommand that automictically capitalises the first letter, when the command is used after a full stop (or question mark, exclamation mark, etc.)?  \newcommand{\tinycommand}{tiny command}   The desired input:  This is some text and a \tinycommand. This is some text. \tinycommand.   The desired result:  This is some text and a tiny command. This is some text. Tiny command.

Is it possible to make macros give different results at the beginning of a new sentence? Suppose that I want the macro "\secname" to write "Section" at the beginning of a new sentence, and "section" anywhere else. How can I do so?


Why even-numbered elements, with their even proton numbers are more abundant than odd-numbered elements ?

In reading  about the origins of elements, I found the following diagram:    What strikes me about this image is the very consistent zig-zagging of the line that appears to indicate that elements/isotopes with an even number are more abundant.  Am I correct? What's going on here?


I am unable to download the latest version of Ubuntu  I  am getting below error:  The required dependency 'dpkg (>= 1.17.5ubuntu5.6)' is not installed.  i have tried everything about updating and downloading the dpkg package but its still getting the same here.  Can someone please help?

(This question was not resolved. Due to time constraints Computer was restored to factory settings.)  I was attempting to upgrade from 14.04 to 16.04, but apt threw this error:  The required dependency 'apt (>= 1.0.1ubuntu2.13)' is not installed.   What does this mean, and how can I fix it?  When I type in the command apt-cache policy apt  Shageenth@shageenth-Inspiron-3451:~$ apt-cache policy apt apt: Installed: 1.0.1ubuntu2.11 Candidate: 1.0.1ubuntu2.11 Version table: *** 1.0.1ubuntu2.11 0 100 /var/lib/dpkg/status 1.0.1ubuntu2 0 500 http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64  Packages   The error happens when I run the command:   sudo do-release-upgrade -d   and it produces the following:  Checking for a new Ubuntu release Get:1 Upgrade tool signature [198 B] Get:2 Upgrade tool [1,265 kB] Fetched 1,265 kB in 0s (0 B/s) authenticate 'xenial.tar.gz' against 'xenial.tar.gz.gpg' extracting 'xenial.tar.gz'  Reading cache  Checking package manager Reading package lists... Done Building dependency tree Reading state information... Done Building data structures... Done  Required depends is not installed  The required dependency 'apt (>= 1.0.1ubuntu2.13)' is not installed.


I am trying to show that  If X~N(0,1) and Y~N(0,1) then X+Y~N(0,2), where X and Y are independent random variables. Any help will be appreciated.

If $X_i$, $i =1,2$ are independent and have normal distribution with mean $0$ and variance $\sigma_i ^2$. Show that $X_1 + X_2$ has a normal distribution with mean $0$ and variance $\sigma_1^2 + \sigma_2^2$.  Any idea is appreciated.


I am working with the method randomForest for model building. And for a good model performance, it is very important to select the right features. At my example I have 30 variables and I would like to try to build different models with all possible combination with the given features, to choose at the and the best performed model. I am working with R and my question is if someone knows a method which could perform all feature combination as training data for model building thanks

I have a dataset with mostly financial variables (120 features, 4k examples) which are mostly highly correlated and very noisy (technical indicators, for example) so I would like to select about max 20-30 for later use with model training (binary classification - increase / decrease).  I was thinking about using random forests for feature ranking. Is it a good idea to use them recursively? For example, let's say in the first round I drop the worst 20%, second too and so on until I get the desired number of features.  Should I use cross-validation with RF? (It's intuitive for me not to use CV because that's pretty much what RF does already.)  Also if I go with random forests should I use them as classifiers for the binary or regressor for the actual increase / decrease to get feature importances?  By the way, the models I would like to try after feature selection are: SVM, neural nets, locally weighted regressions, and random forest. I'm mainly working in Python.


I understand that students at Hogwarts learn about magic, but what about the core subjects such as Math, English, History, and Science? If they do not wish to pursue a career in magic, they need to know these core subjects!

I always wondered if children who graduate from Hogwarts have an education that is actually worth while in the real world.  Do the children learn math and English?  I can see History of Magic as practical. I know of Arithmancy, but that's the study of the magical properties of numbers, not math.   Since Hogsmead is one of the very last all-magical towns, it's a fair assumption that a majority of the students at Hogwarts will be living in non-magical towns or cities. If practical classes (like math or English) aren't taught, then how do these students function in the non-magical cities?


Can anyone give a proof for the following elementary assertion without use of Bézout's theorem which says that The Greatest Common Divisor of two integers is an integer linear combination of them.  "Every common divisor of two integers divides their greatest common divisor."  I should mention that I do not want to use the definition of GCD with prime factorization.

In the integers, it follows almost immediately from the division theorem and the fact that $a | x,y \implies a | ux + vy$ for any $u, v \in \mathbb{Z}$ that the least common multiple of $a$ and $b$ divides any other common multiple.  In contrast, proving $e|a,b \implies e|gcd(a,b)$ seems to be more difficult. In Elementary Number Theory by Jones & Jones, they do not try to prove this fact until establishing Bezout's identity.  has a proof without Bezout's identity, but it is convoluted to my eyes.  I tried my hand at it, and what I got seems no cleaner:  Proposition: If $e | a,b$, then $e | gcd(a,b)$.  Proof: Let $d = gcd(a,b)$. Then if $e \nmid d$, by the division theorem there's some $q$ and $c$ such that $d = qe + c$ with $0 < c < r$.  We have $a = k_1 d$ and $b = k_2 d$, so by substituting we obtain $a = k_1 (qe + c)$ and $b = k_2 (qe + c)$. Since $e$ divides both $a$ and $b$, it must divide both $k_1 c$ and $k_2 c$ as well. This implies that both $k_1 c$ and $k_2 c$ are common multiples of $c$ and $r$.  Now let $l = lcm(r, c)$. $l$ divides both $k_1 c$ and $k_2 c$. Since $l = \phi c$ for some $\phi$, we have $\phi | k_1, k_2$, so $d \phi | a, b$.  But we must have $\phi > 1$ otherwise $l = c$, implying $r | c$, which could not be the case since $c < r$. So $d \phi$ is a common divisor greater than $d$, which is a contradiction. $\Box$  Question: Is there a cleaner proof I'm missing, or is this seemingly elementary proposition just not very easy to prove without using Bezout's identity?


Given a random sample $X_1, X_2, ..., X_n$  where each $X_i$ has pdf:  $$ f(x; \theta) = 3 \theta^3 x^{-4} $$  and $0 \lt \theta \le x \le \infty$. Show that the distribution function $F$ for $min_{1 \le i \le n}{X_i}$ is:  $$ F(x) = 1 - (\theta/x)^{3n} $$  My calculations:  $$ F(x) = \int_{-\infty}^x{f(u)du} = \int_\theta^x{3 \theta^3 u^{-4}du} = 3 \theta^3 -\frac{1}{3}(x^{-3} - \theta^{-3}) = 1 - (\theta/x)^3 $$  I do not get how $F(x) = 1 - (\theta/x)^{3n}$. Where does the $n$ come from?

Please. I am trying to understand the proof, that cdf of minimum of $n$ random variables is $1-[1-F(x)]^n$  If I have $n$ independent random variables $X_1, \dots, X_n$, all of them have the same CDF $F(x)$, what is the point of searching for the $\min=\{X_1, \dots, X_n\}$? Shouldn't $X_1, \dots, X_n$ have the same value for every x? (In the meaning: $P (\min \{X_1, \dots, X_n\}≤x) = P (\bigcup_{i=1}^n X_i\}≤x) \cdots$)  Thanks.


Show that the equation $\displaystyle 3^x+4^x=5^x$ has exactly one root  I proved it graphically but I am in need of an analytic solution

I would like to prove that the equation $ 3^x+4^x=5^x $ has only one real solution ($x=2$)  I tried to study the function $ f(x)=5^x-4^x-3^x $ (in order to use the intermediate value theorem) but I am not able to find the sign of $ f'(x)= \ln(5)\times5^x-\ln(4)\times4^x-\ln(3)\times3^x $ and I can't see any other method to solve this exercise...


How often does "Data Received" and "Data Sent" reset in the activity monitor pane shown below:    Nothing I can think of (daily, since last restart, all time, etc.) seems correct given the numbers I'm getting, so I'm baffled as to what it could actually be.    I know that I've downloaded more than 24 GB since I've owned the computer, but less than 24GB today.

In the network tab in activity monitor there is a read out of data usage showing sent and received in GB. What this dosnt tell you is over what time period this is, is it from a day, a week and month ?   This is from OSX Yosemite.


I have accidentally deleted all the files in my /usr/share/icons directory by using a wrong command. Do you know a solution to restore the files?

okay, so tyeing to type "icons" in the /usr/share/ directory, hit the delete key as root, now my icons are gone, all of them, the options for play in totem or the ones on the desktop....all of them, any help?


Let $K$ be a field and $n \in \mathbb N$. Show the following: (i) Let $V \subset K^n$ be a subspace and $I_V$ the subset of $M_n(K)$ consisting of all the matrices whose rows belong to $V$. Prove that $I_V$ is a left ideal of $M_n(K)$. (ii) Show that every left ideal of $M_n(K)$ is of the form defined in (i).  I think I could show (i). I am having problems with (ii) For (i), take $M \in M_n(K)$ and $N \in I_V$. Let $P=MN$, I want to show that $P \in I_V$. Let $P_i=(P_{i1} ... P_{in})$ be the i-th row of $P$. Then, by definition of matrix multiplication, $$P_i=(\sum_{k=1}^n M_{ik}N_{k1} ... \sum_{k=1}^n M_{ik}N_{kn})$$ $$=\sum_{k=1}^n M_{ik} (N_{k1} ... N_{kn})$$ $$=M_{i1}(N_{11} ... N_{1n})+...+M_{in}(N_{n1} ... N_{nn})$$ This means that the $i-th$ row  of $P$ is a linear combination of the rows of $N$. From here it follows $P=MN \in I_V$. This proves $I_V$ is a left ideal of $M_n(K)$. I don't know how to show (ii), I would appreciate some help with that part.

What are the left and right ideals of matrix ring? How about the two sided ideals?


Let $f$ be non zero symmetric bilinear form on $\Bbb{R^3}$.  Suppose that there exists linear transformation $T_i:\Bbb{R}^3\to\Bbb{R}$ ,$i=1,2$ such that $\forall a,b \in \Bbb{R}^3$ ,  $$f(a,b)=T_1(a)T_2(b)$$  Then  I) rank $f$=1  II)  dim$\{b\in\Bbb{R}^3 :f(a,b)=0 \forall a\in\Bbb{R}^3\}=2$  III) $f$ is positive semi-definite or negative semi -definite   IV) $\{a:f(a,a)=0\}$ is a linear subspace of dimension $2$

Let $f$ be a non-zero symmetric bilinear form on $\Bbb R^3$. Suppose that there exist linear transformations $T_i:\Bbb R^3\to\Bbb R, i=1,2$ such that for all $\alpha,\beta\in\Bbb R^3,f(\alpha,\beta)=T_1(\alpha)T_2(\beta)$. Then         rank $f=1$   $\dim\{\beta\in\Bbb R^3:f(\alpha,\beta)=0\text{ for all }\alpha\in\Bbb R^3\}=2$   $f$ is a positive semi-definite or negative semi-definite   $\{\alpha:f(\alpha,\alpha)=0\}$ is a linear subspace of dimension $2$         (CSIR December 2014)   My attempt:  (1), (2) and (4) are wrong if $\ker(T_1)=\{0\},\ker(T_2)=\{0\}$  All information I could find about positive/negative semi-definiteness of bilinear form is  about positive definiteness.  Edit: (question has already been answered in comments; "intermediate link" Travis talks about is .   Can someone please guide me?


I just came across the following  $$\nabla x^TAx = 2Ax$$  which seems like as good of a guess as any, but it certainly wasn't discussed in either my linear algebra class or my multivariable calculus class. Is there any intuitive way to see why this should be true?

It's stated that the gradient of:  $$\frac{1}{2}x^TAx - b^Tx +c$$  is   $$\frac{1}{2}A^Tx + \frac{1}{2}Ax - b$$  How do you grind out this equation? Or specifically, how do you get from $x^TAx$ to $A^Tx + Ax$?


How can  2 stock have different  Average return and different standard deviation and Still have the same probability distribution

If two continuous random variables have exactly the same expected value and variance, do they always have the same distribution?


I've read  and curious about polynomial with infinitely many variables. Where I can find the definition of polynomial with infinitely many variables? I have to write this definition in my final assignment, thanks for your help.

How can we prove that (the set of all polynomials in infinitely non commutative indeterminants over $k$) is a ring, where $k$ is a ring with unity?   Adding two polynomials is a polynomial, but for commutativity  How can we show the following: $ax_1+bx_2=bx_2+ax_1$ (commutativity of addition) If we have finite number of variable it is easy to prove it, (we take the $n-1$ variables...), but what about the infinite number of variables?  Can someone give me a hint?


I need help splitting string in javascript.  I have a string with currency. The string depends on the location.   For example: "1,99€" or "$1,99"  I would like to split the string and extract the "amount" and the "currency" out of it.   If this fails, I would like to return an empty string or just null.  Does someone know how to solve that?

I have a text box that will have a currency string in it that I then need to convert that string to a double to perform some operations on it.   "$1,100.00" → 1100.00  This needs to occur all client side. I have no choice but to leave the currency string as a currency string as input but need to cast/convert it to a double to allow some mathematical operations.


I would like to handle a change event on elements dynamically created, and selected with each():  $("input[type=date]").each(function() {     $("#myForm").on("change", this, function() {         $(this).css({ color: "#B73132" });     }); });   on() doesn't seem to work.  I tried:  $this= $(this); // and    $this= this;with $("#form_cahier").on("change", $this, function() {   Nothing works, any idea ?

I have a bit of code where I am looping through all the select boxes on a page and binding a .hover event to them to do a bit of twiddling with their width on mouse on/off.  This happens on page ready and works just fine.  The problem I have is that any select boxes I add via Ajax or DOM after the initial loop won't have the event bound.  I have found this plugin (), but before I add another 5k to my pages with a plugin, I want to see if anyone knows a way to do this, either with jQuery directly or by another option.


I am currently using gnome-keyring to manage my ssh passwords. I would like to know if there are any alternatives to this, which I can use in situations when I don't have access to the UI. I am currently running Ubuntu 12.04.

Is there a way to enter the default keyring password using the command line?   For instance:  You have a remote setup of Ubuntu 10.10 thats set to auto login. You don't want to remove  the keyring password.  All right the system boots up and logs in automatically, then asks for the keyring password now at this point you can create ssh connections but you can't remote desktop.   What can you do to enter the keyring password at this point?  Also, to better clarify, this is from a remote connection using the command line.


I have two tables A & B. Table A id | name | num  Table B id | date | roll  id in table B is a foreign key which relates to the id in table A. I want to get the contents of table B where id is given and also along with that data, I need the name whose id is given from table A. NOTE: cannot use multiple queries separated by commas; need to do both the SELECTs in one query.

Table A (users)  id     | name   | ip 52433    Yashas   1.1.1.1 512      Admin    5.6.7.8   Table B (admin_record)  id    | admin | time    | date    | reason | action  52433   512     2312352   1213213   Test     WARN   id is FOREIGN key  Table B keeps a log of all actions an administrator takes on his users. And the table A stores the account information of the users & administrators.  I am trying to display a list of actions taken by a administrators on a user.   I want to write a query which gets me all the rows of table B where id = fixed number.  Here is what I want to display:  "Administrator1 [Name]" took action on "User Name" for "[Note]" on XX/XX/XXXX. "Administrator2 [Name]" took action on "User Name" for "[Note]" on XX/XX/XXXX. "Administrator3 [Name]" took action on "User Name" for "[Note]" on XX/XX/XXXX.   All I have is the user's id using which I need to obtain all the entries in the log along with the administrator names. I need to obtain the admin's name, users name and all the contents of table B related to a particular user in one single query. If possible, I want the to change the field name(not literally change, but want the SQL server to send the data with new field names to separate admin name & user name) of the admin's name to admin_name and user's name as . I mean something like this  SELECT users.name AS admin_name WHERE users.id = %i  AND SELECT users.name AS user_name WHERE users.id = %i   (the query isn't correct,it us just an example to show what I am trying)  Progress so far:   SELECT player.name, player.ip, admin.name, record.date, record.time, record.action, record.reason FROM admin_record AS record JOIN users AS player ON player.id = record.id JOIN users AS admin ON admin.id = record.admin WHERE player.id=%i   where admin_record is table B & users is table A.


I am having very very very frustrating problem here. I am coding my app, dumping to debug logs whatever I need and everything works magically. But at some point apex stops printing my debug logs. So i have system logs, I can read them, but not the logs dumped with system.debug(");  My debug log request limit is not used, I didn't touch or change Debug Log levels in Developer console. It just stops printing debug logs from methods being called.  This is not the first time this happens, it is recurring event unfortunately.   Did anyone experience something similar or does anyone have some idea what to do regarding this issue. Thanks a lot.

Has anyone else noticed that the Debug Logs in the Developer Console are becoming notoriously unreliable? I am finding that often when I run code through Execute Anonymous in the hopes of examining the resulting Debug Log, none is generated there, even if it shows up in Logs > Debug Logs. I have tried switching around my Workspace and some other strategies, but it seems really inconsistent as far as I am able to observe.  UPDATE  From what I can tell, the most reliable fix for this issue is to instantiate a Debug Log for the running User (Setup > Monitor > Logs > Debug Logs).


I dont use this particular computer often (sometimes go a month without use) but recently it keeps randomly rebooting, at ANY time.  Sometimes it will reboot multiple times before it even posts. Sometimes it reboots just after posting. Sometimes I can login (to XP) and it runs fine for a few minutes then just reboots. Occastionally, it doesnt reboot at all. One thing that is consistent, it doesnt turn OFF it, it always reboots.  It's really hard to test since I never know when its going to reboot. I tried moving the DIMMs to a different bank but that hasnt worked. The case fan and lights dont flicker/stop.  Whats the most likely component to be failing?   MoBo: Gigabyte GA-EP43C PSU: EVO Labs 500w Memory: 2x2Gb DDR2 CPU: Intel E7300 GPU: NVIDIA GeForce GTX650

My computer reboots, seemingly completely at random, about once every week to two weeks but has occasionally gone months. It just goes from running fine to the POST with no error messages or anything and doesn't seem to be due to heat or usage as it's happened a couple of times when the computer has booted just a few moments ago and is idling. It's been happening for as long as I've had this computer, almost two years. It's happened in both Vista and Windows7.  I strongly suspect it's a hardware problem. But due to the rareish and random nature of the crashes my normal strategy of just removing hardware until the problem stops isn't really practical. My guess would be Power Supply, Ram, or Motherboard. But I just don't know how to test an issue this random and want to figure out how to confirm which it is before I go replacing things. So is there some software or hardware that can be used to test these sorts of errors? I did run memtest86 for about 8 hours without finding any issues. And the power supply is more than capable of running my system.


My dual boot Ubuntu system has its Ubuntu OS corrupted.  Efforts to fix it via changing source.list and other means proved in vain.  Now I want to re-install Ubuntu on that partition with a USB stick.  Will my files on that partition and other partitions be left intact?  I just wanna fix the OS.  Wanna confirm this as I am using the computer for many things and cant afford to have it screwed up.  Thanks.

Recently I installed Ubuntu 12.10 x64 Server Edition on my PC. Unfortunately, I attempted to install a lightweight desktop but due to the fact that I have an old graphics card, the PC does not perform so well. I am thinking of re-installing an Ubuntu version but I do not want to lose the contents in my home folder. Is there any way to do that with a Live CD?


Here's the thing I own a small business and currently my emails are being managed by some regular hosting using cpanel and that  I bought a small server and installed windows server and exchange   Can you tell what I did wrong here   Installed and configured my current existing domain Configured all email address Installed noip in case my public address change In the cpanel of the domain I've added an MX record to the noip domain of the server with priority 0 so now emails are being received by my own server   Now whenever I send an email to anyone gmail hotmail etc I get a response that cannot be delivered since may be junk  This didn't happen when I sent emails from the hosting   What's missing what did I do wrong  heres the code  mx.google.com rejected your message to the following e-mail addresses: Joan J. Guerra Makaren (joanjgm23@gmail.com) mx.google.com gave this error: [186.88.202.13 12] Our system has detected that this message is likely unsolicited mail. To reduce the amount of spam sent to Gmail, this message has been blocked. Please visit http://support.google.com/mail/bin/answer.py?hl=en&answer=188131 for more information. cn9si815432vcb.71 - gsmtp  Your message wasn't delivered due to a permission or security issue. It may have been rejected by a moderator, the address may only accept e-mail from certain senders, or another restriction may be preventing delivery.  Diagnostic information for administrators: Generating server: SERVERMEGA.megaconstrucciones.com.ve joanjgm23@gmail.com mx.google.com #550-5.7.1 [186.88.202.13 12] Our system has detected that this message is 550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to Gmail, 550-5.7.1 this message has been blocked. Please visit 550-5.7.1 http://support.google.com/mail/bin/answer.py?hl=en&answer=188131 for 550 5.7.1 more information. cn9si815432vcb.71 - gsmtp ## Original message headers: Received: from SERVERMEGA.megaconstrucciones.com.ve  ([fe80::9096:e9c2:405b:6112]) by SERVERMEGA.megaconstrucciones.com.ve  ([fe80::9096:e9c2:405b:6112%10]) with mapi; Thu, 29 May 2014 11:32:19 -0430 From: prueba <prueba@megaconstrucciones.com.ve> To: "Joan J. Guerra Makaren" <joanjgm23@gmail.com> Subject: Probando correos Thread-Topic: Probando correos Thread-Index: Ac97V1eW4OBFmoqJTRGoD7IPTC2azg== Date: Thu, 29 May 2014 16:04:35 +0000 Message-ID: <000f4249.4487966276f7b241@megaconstrucciones.com.ve> Accept-Language: en-US, es-VE Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: Content-Type: multipart/alternative;     boundary="_000_000f42494487966276f7b241megaconstruccionescomve_" MIME-Version: 1.0

This is a  about how to handle email sent from your server being misclassified as spam.  For additional information you may find these similar questions helpful:                    Sometimes I want to send newsletters to my customers. The problem is, that some of the emails get caught as spam messages. Mostly by Outlook at the client (even in my own Outlook 2007).  Now I want to know what should be done to create "good" emails. I know about reverse lookup etc., but (for example), what about a unsubscribe link with an unique ID?  Does that increase a spam rating?


To indicate "a collection of items," do you say "an item collection" or "items collection"? What's the rule?  A quick comparative Google Books search indicates that the  is more common than the , but I don't know if I can trust that as a parameter.

Possible Duplicates:             I'm wondering whether or not I should use a plural form noun with a collection name. For example, which one is correct, bookList or booksList (obviously they are variables in a programming language)?


I want to delete the extra duplicate record  i.e. in the image shown there are two records with corporate_id = 5 and category_id = 19, how to delete any one row which is duplicate (here corporate_sed_id is the primary key)

What is the best way to remove duplicate rows from a fairly large SQL Server table (i.e. 300,000+ rows)?  The rows, of course, will not be perfect duplicates because of the existence of the RowID identity field.  MyTable  RowID int not null identity(1,1) primary key, Col1 varchar(20) not null, Col2 varchar(2048) not null, Col3 tinyint not null


This is NOT a duplicate. The other answers do not apply to this situation.   When trying to boot a 64 bit image in a headless VirtualBox, I get      This kernel requires an x86-64 CPU, but only detected an i686 CPU.   Unable to boot – please use a kernel appropriate for your CPU   My processor is 64 bit.  uname -a     Linux medusa 3.13.0-32-generic #57-Ubuntu SMP Tue Jul 15 03:51:08 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux   It supports VMX  egrep '(vmx|svm)' /proc/cpuinfo  flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat   pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc  arch_perfmon pebs bts rep_good nopl aperfmperf pni dtes64 monitor ds_cpl vmx smx est  tm2 ssse3 cx16 xtpr pdcm lahf_lm dtherm tpr_shadow vnmi flexpriority   And the virtualization options are enabled in BIOS.  I've set the ostype to both Linux_64 and Ubuntu_64 but neither work. I've also tried setting VBoxManage modifyvm <vmname> --longmode on  "use a 32 bit image" isn't a solution, which is why I'm asking the question again. I see it's come up many times, and "your processor is 32 bit" is a very common response.  A potentially relevant piece of information is that the processor was upgraded after the initial installation of Ubuntu. I moved the processor that supports virtualization into this computer. I've had 64 bit VM's running on this machine before, with the same setup; I'm not sure if actually installing on the supported processor matters.

I was trying to install Ubuntu 12.04 in VirtualBox 4.2.12r84980. I see    this kernel requires an x86-64 CPU, but only detects an i686 CPU, unable to boot   But I am using a 64 bit Windows 8, and trying same .iso for trying Ubuntu. Then what is the problem?


On my new tablet I installed the gmail app and also configured the builtin app. Now I get two notifications for each email. How can I get rid of the builtin email app which does not seem as good as the gmail app?

How to disable system apps without root?  My phone model is vivo x5 max+ and android 4.4.4  I have tried Debloater but it failed to connect (I am sure I've allowed USB debugging).


I'm trying to write a simple tip calculator in Python, but I need it to always output two decimal places. With some whole numbers, like 100, it will only give one decimal point, what should I do?  Here is my code:  print("Only input numbers, do not input dollar signs or letters") subtotalprice = eval(input("What is the bill total?: "))    percent10 = subtotalprice * 0.1 percent15 = subtotalprice * 0.15 percent20 = subtotalprice * 0.2  percent10_2 = str(round(percent10, 2)) percent15_2 = str(round(percent15, 2)) percent20_2 = str(round(percent20, 2))   percent10total = subtotalprice * 1.10 percent15total = subtotalprice * 1.15 percent20total = subtotalprice * 1.20   percent10total_2 = str(round(percent10total, 2)) percent15total_2 = str(round(percent15total, 2)) percent20total_2 = str(round(percent20total, 2))  print("If you want to leave a 10% tip, the tip comes to", percent10_2, "With  the  subtotal coming to", percent10total_2,)  print("If you want to leave a 15% tip, the tip comes to", percent15_2, "With  the  subtotal coming to", percent15total_2,)  print("If you want to leave a 20% tip, the tip comes to", percent20_2, "With  the subtotal coming to", percent20total_2,)  input("Press Enter to Close")

I want a to be rounded to 13.95.  >>> a 13.949999999999999 >>> round(a, 2) 13.949999999999999   The  function does not work the way I expected.


How physicists come to the conclusion that the cosmological constant and the other constants are really fine-tuned in a way that if they are changed just a bit, then stars and life won't exist?

Is the fine tuning that cosmologists talk about (that our Universe is fine tuned for intelligent life) is the same as the fine tuning of the squared mass parameter of the Higgs in the Standard Model? And that in SUSY models?  Also, could anyone refer me to a source that explains the fine tuning issue in general?


I have a Canon 400D with the EF-S 18-55mm 1:3.5-5.6 II kit lens and a Nikon D800 with an AF-S NIKKOR 24-120mm 1:4 G ED.  Today I took the same picture with both cameras and I like the Nikon's much better (second image).     However, I love the Canon camera because it's much lighter, I find the controls much more intuitive and I have several flashes for it.  Is there an upgrade I can make to get similar photos from the/a similar Canon camera?

I'm currently using a Canon 700D with a few EF-S lenses, I like the Canon system, the looks, feel and ergonomics but I'm not happy with the files I'm getting. Whenever I come across a photo that appeals to me from a technical point of view it happens to be shot on a full frame camera or some Sony sensor APS-C. The most important thing I miss in my files is sharpness, overall Canon crop sensor cameras lack in focus and / or sharpening ability when compared to Nikon / Sony / Fuji etc. Would you advise me to upgrade to a full frame 6D or to switch brands to Nikon D7100 / D7200 / possibly Nikon D610? I have just 4 basic lenses so the cost wouldn't be very high. I don't want to ask another question which brand is better, just some opinions on the best / the most efficient way to raise technical image quality. I know I can buy a professional lens like Sigma 18-35, but I have just one body which I'm going to upgrade soon, and I think maybe it would be more wise to buy the Sigma lens for a Nikon body to get optimal results.


On October 31st, I earned the Epic badge on SO (woohoo!).  This badge is awarded for getting >=200 daily points score 50 times.  However, if I go to the raw reputation report page† the summary at the bottom tells me that I've only earned >=200 points 49 times.  days represented 1088 rep cap was reached via rep from upvotes *only* on 22 days earned at least 200 reputation on 49 days earned 6 reputation from suggested edits   I understand that these things aren't always in sync or up-to-date, but I thought this raw rep page should be correct. It does show my latest points, so it's clearly got all the data; it just seems to be the summary figures that are off.  I've exceeded 200 points a further 4 times since getting the badge as well, so I don't think it's just an off-by-one counting error either.  Is this a bug, or is it counting different to what the Epic badge counts? Or maybe I really have only done it 49 times, and the badge was awarded prematurely?  I've tried doing a recalc, but that didn't change the stats.  † link is , although don't bother clicking as you'll see your rep report not mine.

There are already many questions about the epic badge and that it was assigned too late, but:  I have just received the  on  after earning 200 rep today (which incl. 2x15 for two accepted answers). However the rep listing under  states for me:  rep cap was reached via rep from upvotes *only* on 41 days rep cap was exceeded on 48 days   I had been keeping an eye on those numbers so the badge came as a surprise. Is this an error? I'd really like to earn the badge ;-).  Also just to clarify: Must the rep cap be hit, i.e. must a limitation have been encountered? By this I mean you got 21 up-votes at one day (20 to get the max 200 rep + 1 to hit the limitation, which is than listed as [0] in the listing). Or is it enough to get 200 (or 200+) rep points in any combination? My listing tells me that both of these values are below 50 times. I've tried hitting the recalculate button, with no change.    Ok, I manually recounted all days where I got 200 or more rep. I actually count 50 of them, however on one I had exactly 200 which might not count for the rep cap was exceeded on number while counting for the badge. This makes 49 days. I thought the last missing one might simply be because the day isn't over, but now it is 5 min after midnight UTC and it is still just 48.    The same -2 offset happened now to me with the Legendary badge:  rep cap was reached via rep from upvotes *only* on 111 days earned at least 200 reputation on 148 days   I don't mind it at this point, but in general there should be an exact display of the days available.


I was watching , and came across a sentence in which they form the plural of "no" with an apostrophe:     There are a thousand no's for every yes   But shouldn't it be nos?  Or is this just for the sake of readability? Like,     We need to dot the i's and cross the t's   Edit: Apparently this has been discussed .

When I was in high school back in the 1970s, I was taught that to make a plural of an acronym, a letter, or a number, one should add an apostrophe and "s". Like I would have written this sentence, "... back in the 1970's ..." I would write "one CD, two CD's". Etc. I followed this rule faithfully for years until a co-worker told me it was wrong. Now I can't find any source that agrees with what I was taught.  Is this a rule that has changed over time? Was the convention in the 70s that one should use an apostrophe but this has changed and now we do not? Or were my high school English teachers just confused?


I'm making a map.  I want the player to create a stone button but they are on adventure mode so i need a command that makes it possible to be placed on something so when they make the button it can be replaced with a button that can be placed on dirt.

In a map I'm making the player has to survive while locked in a maze. To stop them from breaking out, they will be in adventure mode. However, I still want them to be able to craft items and use them with specified blocks. I have tried several methods already but they all have a flaw.  One method is to have a scoreboard objective called item and giving certain item entities a specific score using something like:  /scoreboard players set @e[type=Item] item 1 {Item:{id:"minecraft:sapling"}}   Then it is possible to select these items with:  /entitydata @e[type=Item,score_item=1,score_item_min=1] {Item:{tag:{CanPlaceOn:["dirt"],HideFlags:24}}}   This works but it requires the item to be dropped, which isn't a problem for saplings, but for tools and other craftable items, it becomes a hassle.  To fix this, I'm currently clearing tools without damage and giving the player a slightly damaged tool in return:  /clear @a minecraft:stone_axe 0 1   /give @a minecraft:stone_axe 1 1 {CanDestroy:["log","log2","leaves","leaves2"],HideFlags:24}   This doesn't work for items without damage values (e.g. torches), but I don't mind these having to be dropped as there aren't too many of these. However, there is another problem. In the nether, the player will have access to an enchantment table and an anvil. This means they can repair enchanted tools, which will cause them to be cleared and replaced with unenchanted ones as soon as they go back to the overworld.  I also thought about using a stat.craftItem scoreboard objective and giving them the usable item if they craft it. However, this would result in the player having a duplicate of every item they crafted, as I think it is impossible to select an item without NBT-data in the /clear command.  Is there any way to make this work? And if not, would it be better to have the player drop all crafted items or have duplicates of them all?


I'm trying to understand the strategy pattern and enums in java. I've googled this and have found a few articles on the subject, but most of them seemed too complex for my understanding. Could anyone provide a simple example or another link that demonstrates strategy pattern using enums in laymen terms using java?  Thanks you in advance.

I've looked at , specifically the C++ sample, and fail to recognize the difference between just defining 3 classes, creating instances and calling them, and that example. What I saw was just placing two other classes into the process and cannot see where there would be a benefit. Now I'm sure I'm missing something obvious (wood for the trees) - could someone please explain it using a definitive real-world example?    What I can make from the answers so far, it seems to me to be just a more complex way of doing this:  have an abstract class: MoveAlong with a virtual method: DoIt() have class Car inherit from MoveAlong,       implementing DoIt() { ..start-car-and-drive..} have class HorseCart inherit from MoveAlong,       implementing DoIt() { ..hit-horse..} have class Bicycle inherit from MoveAlong,       implementing DoIt() { ..pedal..} now I can call any function taking MoveAlong as parm  passing any of the three classes and call DoIt Isn't this what Strategy intents? (just simpler?)   [Edit-update] The function I refer to above is replaced with another class in which MoveAlong would be attribute which is set according to need based on the algorithm implemented in this new class. (Similar to what is demonstrated in the accepted answer.)    [Edit-update] Conclusion  The Strategy Pattern has it's uses, but I am a strong believer in KISS, and would tend to more straightforward and less obfuscatory techniques. Mostly since I want to pass on easily maintainable code (and 'cos I'll most likely be the one who have to make the changes!).


I need a Clarification about Sql server 2014 developer edition licensing.I came to know that,for a Cheap price(50$ or something) developer edition is available.also it is given that multiple users can be connection only requirement is a developer licence for user.can anyone please explain me what is developer edition and also with one developer edition can i connect 4 client machienes to one server.?(for demonstation purposes only,so no worry about max db size limit).Kindly help me.

Do you use SQL Server Developer Edition on server-class machines in DEV and STAGING environments?  I am working on a large project where (if it passes the proof of concept stage) we will have several large geographically distributed enterprise class database servers running SQL Server 2012 Enterprise Edition.  We will have a production environment will initially have 3 servers, our Staging environment will have a minimum of 3 servers, and our Development environment will have 1 server (hosting three instances).  I was under the impression that we would only need to acquire Enterprise licences for the actual production servers, and we could get by with developer edition in our developer and staging environments because they are not "production".  Other sources have told me that we need to have an enterprise licence on all of the above mentioned machines, and that the developer edition is only meant for a single developer on their workstation.  Since developer edition has all the sexy features of Enterprise, I can't really see the value of it on a workstation class machine, especially for developing and testing the type of high availability system we are building.  If we have to fork out Enterprise licences for a dev server, that will just about kill our proof of concept stage, thus killing the project.  Forcing an enterprise licence on a staging environment will make management just want to skip staging altogether.


I have seen quite a few items raised here about down-voting without comments but somehow can't seem to agree with the resolutions.  Yes, there is a message shown to the user (rep < 2000) every time they down-vote asking them to consider adding a comment. Yes, the reputation points that is lost on a down-vote is very minimal. But just because the amount of reputation points lost is less, down-voting without comments should not be encouraged.   I have seen points on why a comment shouldn't be made mandatory while down-voting. Those are also understandable. It is fine to not mandate a comment.   But can't we have a "raise flag" option (like we have for spam posts) where users with a certain minimum rep can request for moderator review if they feel that a good and credible post is down-voted for no obvious reason?

I just noticed that I lost a bunch of points from my reputation score, and I used the "reputation" tab on my user profile page to try and track down the cause.  During my investigation, I noticed there was an unusual event of type "reversal". In the normal place of a question title, it says "voting corrected".     What does this mean, and what caused it?  Did I do something wrong? Why did I lose all of that reputation? Is the system punishing me for leaving too many good answers?  Is there any way to earn it back?


Free neutrons, as we know them, are unstable and hence undergo a three-body decay into proton, electron and antineutrino with a mean lifetime of just under 15 minutes.   But there are astrophysical objects called neutron stars which are produced at the end of the lives of moderately massive stars. These objects are made entirely of neutrons in order to support the strong gravitational pulls. These are pretty stable objects in cosmological time scales lasting at least for billions of years.  So, why they are simply not decaying into proton stars due to unstable nature of neutrons? How to explain this apparent contradiction?

Free neutrons are known to undergo beta decay with a . Binding with other nucleons stabilizes the neutrons in an atomic nucleus, but only if the fraction of protons is high enough (at least a third or so). But what keeps a neutron star stable against beta decay? Apparently, this is extra pressure due to gravity in contrast to "negative pressure" of proton Coulomb repulsion in a nucleus but how do we know that this is enough to stabilize the degenerate neutronic fluid?  I am aware of a  but not really happy with the answers there. There is lot of dazzling details , but I am a looking for an answer suitable form a 8-year old with enhanced curiosity towards astrophysics.


How do I close a certain web page (in Chrome) with the command line?  I have tried taskkill /f /im (PID).  Also, I am looking for a way to do this without killing the entire Chrome process, e.g. my extensions and apps.  I have searched this on the web but I couldn't find anything.

I want to close one tab of chrome. I tried killing the pid of the tab, but the tab doesn't close instead says "Aw, Snap! Something went wrong while displaying this webpage. To continue, reload or go to another page". How can I get rid of this.