Why running this code gives an error as a non-static variable this cannot be referenced from a static context  this.availableTickets=availableTickets; public class Ticket {          private static int availableTickets=0;          public static void setAvailableTickets(int availableTickets){         if(availableTickets>0)             this.availableTickets=availableTickets;     }          public static int getAvailableTickets(){         return availableTickets;     } }

To be specific, I was trying this code:  package hello;  public class Hello {      Clock clock = new Clock();      public static void main(String args[]) {         clock.sayTime();     } }   But it gave the error      Cannot access non-static field in static method main   So I changed the declaration of clock to this:  static Clock clock = new Clock();   And it worked. What does it mean to put that keyword before the declaration? What exactly will it do and/or restrict in terms of what can be done to that object?


I am resident of India (Indian passport). I am travelling from Israel (Tel Aviv) to  Rome (Fiumicino) on El Al Airlines, and from Rome (Fiumicino), I fly to India (Delhi) on Air India Airlines.   The connection time between the two flights is 3 hours.   Do I need to get a transit visa or is it not required?

I found many related questions on this site but I am still not sure about the rules. How can I decide if I need a visa to transit? Schengen members as of May 2021 are as follows:  Austria Belgium Czech Republic Denmark (excluding Greenland and the Faroe Islands - but an open border with the Schengen Area is maintained) Estonia Finland France (excluding overseas departments and collectivities) Germany Greece Hungary Iceland Italy Latvia Liechtenstein Lithuania Luxembourg Malta Netherlands (excluding Aruba, Curaçao, Sint Maarten and the Caribbean Netherlands) Norway (excluding Svalbard) Poland Portugal Slovakia Slovenia Spain (except Ceuta and Melilla) Sweden Switzerland


I aim to print a list of every element inside a user-inputted list. The outputted list identifies symbols as strings, and numbers as floats, to basically compare elements as floats and strings. If the number in the list is already a float, the output is not printed properly.  expression_list = [] expression = "(3.1+2)*5"  for index in expression:     try:          float_index = float(index)         expression_list.append(float_index)     except ValueError:         expression_list.append(index) print(expression_list)         I expect the output to be ['(', 3.1, '+', 2.0, ')', '*', 5.0] instead I get ['(', 3.0, '.', 1.0, '+', 2.0, ')', '*', 5.0]

What is the best possible way to check if a string can be represented as a number in Python?   The function I currently have right now is:  def is_number(s):     try:         float(s)         return True     except ValueError:         return False   Which, not only is ugly and slow, seems clunky. However I haven't found a better method because calling float in the main function is even worse.


I am writing a document in exam class. The exam has several sections. I would like the question numbers in the second section to continue on from the first section.   The code below produces Question 1 and Question 2 in both sections. I would like to have Question 1, Question 2 in Section 1 and Question 3, Question 4 in Section 2. Is there an easy way to do this?   \documentclass[12pt]{exam} \begin{document} \begin{questions} Section 1. \question ...  \question ... \end{questions}  Section 2. \begin{questions} \question ...  \question ... \end{questions} \end{document}

How to get the same feature as resume in the enumitem package for the questionsenv in the exam Latex class?  For instance,  \begin{questions}   \question A?   \question B? \end{questions} Some text. \begin{questions}   \question C? \end{questions}   should give something like  Question 1. A? Question 2. B? Some text. Question 3. C?


Let $P$ be a $p$-group and let $N\triangleleft P$. Prove $N\cap Z(P)\ne e$ .  Here's what I know so far: $P$, being a $p$-group, is nilpotent and therefore is solvable. That means that it has its upper central series: $e=Z_0\triangleleft Z_1\triangleleft Z_2....Z_n...$ where $Z_1=Z(P)$ and that at some point, the series stabilizes at P forever... I also know that $Z_{i+1}=${ $x\in P|\forall y\in P: [x,y]\in Z_i$}. (In my notebook it's been defined that way: $Z_{i+1}=\pi^{-1}(Z(G$\ $Z_i)$ whichc confuses me a little. )  How can I show that the desired intersection is not empty?

I have a finite $p$-group $G$ and a normal subgroup $N$ which is not the trivial subgroup. I am asked to show that $|N \cap Z(G)| > 1$.  There has been a similar question on MSE here:  Unfortunately, I cannot comment on other user's questions yet, so I made my own question.  I know that the trick is to use conjugation but I can't follow the logic. Can someone elaborate? Especially on the last part of the top answer.


Given $s \in (0,1)$, prove $$x^sy^{1-s} \leq sx + (1-s)y$$ for $x,y > 0$  Tried some algebraic manipulations but I'm guessing I need to use some trick.  Any suggestions, hints?

I have no idea how to do this. Any help would be appreciated. The chapter I'm on is about differentiation and the mean value theorem.  Prove $a^\alpha b^{1-\alpha} \le \alpha a + (1 - \alpha)b, \; a,b > 0,\; 0 < \alpha < 1$


I have got a stored procedure which has five parameters. I want to include them in where clause as follows   If parameter is not null then include it in query as an IN clause   That is, parameter value can be like 'Test' or 'Test,Best' etc. I'm converting this comma seperated values into table using function in SQL.  I tried to use COALESCE(@test,test_column) = test_column but i'm unable to include IN clause here (What if @test = 'Test,Best').  So, i want to do something like mentioned below  DECLARE @param varchar(max) = 'Test,Best';  Select * from table where CASE when @param is not null then table.column in (@param)   Any suggestions please.

Is there a graceful way to handle passing a list of ids as a parameter to a stored procedure?   For instance, I want departments 1, 2, 5, 7, 20 returned by my stored procedure. In the past, I have passed in a comma delimited list of ids, like the below code, but feel really dirty doing it.   SQL Server 2005 is my only applicable limitation I think.  create procedure getDepartments   @DepartmentIds varchar(max) as   declare @Sql varchar(max)        select @Sql = 'select [Name] from Department where DepartmentId in (' + @DepartmentIds + ')'   exec(@Sql)


Is the correct usage of the non-taxable or nontaxable? I'm not sure what the correct use is. I want to say that it is with the hyphen however it ha become a debate that this could be incorrect.

Some compound words are written without hyphens (nonaggression, nonbeliever), some with hyphens (well-intentioned), and others with spaces (post office).  Is there a rule or good guide as to which option should be used?


I am working on a video file in Blender. I have saved it as a .blend file already, but I want to save it as an .avi file.  How do I do this? I have watched multiple tutorials and have no idea what to do. I am using Blender 2.74.  Thanks.

Yesterday I was working on a simple animation, an animated logo.   Here is an image of the progress:    I already have the animation working and everything is okay with the project, but I can't figure out how I can render the animation and turn it into an AVI format video.  How do I render an animation in Blender?


I am trying to install chrome in the terminal and this is the error that appears when i try to install it:  E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable) E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?   What can i do to fix this?

I get this error when trying to use apt-get:  E: Could not get lock /var/lib/dpkg/lock - open (11 Resource temporarily unavailable) E: Unable to lock the administration directory (/var/lib/dpkg/) is another process using it?     How can I fix this?


Attempt to invoke virtual method java.lang.String getTest_Series_name() on a null object reference. How i solve this error?

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?


How come when I click on "download the Android app for Stack Exchange" in a mail of Stack Overflow, I arrive on Google Play and it tells me there is no such app? Is there really no app for Stack Exhange Q&A websites? How come?

I'm using the official Stack Exchange mobile app for iOS or Android, and  My app crashed! It doesn't look good on my new smartphone. It won't run after I updated my device. I noticed another bug. I have an idea for a new feature which is currently not in the app.  How do I report bugs with or request features for the iOS and Android apps? Also:  I've used the built-in functionality of the app to report a bug or submit a feature request. Did I do the right thing? The app prompted me to post on Meta after an error occurred. Should I post about it here? I'm wondering why the latest version is from 2017. I've heard rumors that the apps are no longer supported; is that true? I can't find the app on my device's app store anymore! Where did it go?     We get a lot of bug reports from users about the mobile apps, which are unsupported, and at the moment, there is no centralized Q&A pair for those to be closed as duplicates of (the relevant answers are spread across multiple unrelated questions). This question is an FAQ proposal, to serve as a directly-related duplicate target for those questions.


I am trying to drag and drop a video file (like .avi) from desktop But ı can not take it to the my program.But when ı try to drag and drop inside my program it works fine.For ex: I have an edittext and a listbox inside my pro and ı can move text that inside edittext to listbox.I could not get what is the difference ??  I take the video using openDialog.But ı wanna change it with drag and drop.  procedure TForm1.Button1Click(Sender: TObject);    begin      if OpenDialog1.Execute then        begin           MediaPlayer1.DeviceType:=dtAutoSelect;           MediaPlayer1.FileName := OpenDialog1.FileName;           Label1.Caption := ExtractFileExt(MediaPlayer1.FileName);           MediaPlayer1.Open;           MediaPlayer1.Display:=Self;           MediaPlayer1.DisplayRect := Rect(panel1.Left,panel1.Top,panel1.Width,panel1.Height);           panel1.Visible:=false;           MediaPlayer1.Play;        end;     end;

I would like to create a Delphi application for Windows XP which allows dropping of files dragged from Windows Explorer (the Desktop or folder windows) or other applications which support this operation (such as Total Commander). What about vice-versa? When the user drags an icon from my application, I should be able to set the contents of the dragged object to custom data.  My goal is to create a custom application toolbar, onto which I can drop applications and show their icons or drag applications or other entities from it.  How can this be done?


I have occasionally observed that some LaTeX macros behave differently with and without end-of-line comments. My understanding of this is that a macro may leave a space on the stack that for some reason is removed if the macro is ended with a percent sign. I have never quite understood why this happens so I've slowly fallen into the habit of ending all "function calls" in LaTeX with %. In the present case, I discovered that \pstScalePoints and \newpsstyle behaves just like that and took the effort to isolate the problem into the following MWE:   \documentclass{standalone} \usepackage{pstricks} \usepackage{pstricks-add} \usepackage{pst-plot} \listfiles \begin{document} \readdata{\mytable}{table.txt}   \pstScalePoints(1.0,1.0){1.0 div}{1.0 div}%  <-- NB! \newpsstyle{legendstyle}{fillstyle=solid}%   <-- NB! \begin{psgraph}(0,0)(0,0)(1,1){1cm}{1cm} \listplot{\mytable} \end{psgraph} \end{document}   Problem: The output changes if the two end-of-line % signs are removed. My suspicion is that the macros leave behind a space on the stack, but I do not know how to correct it - other than stubbornly adding % to all the macro endings!  The contents of file table.txt is:  0.0, 0.00 0.2, 0.04 0.4, 0.16 0.6, 0.36 0.8, 0.64 1.0, 1.00   I halfway expect that the problem depends on which packages I am using so I therefore include the output from \listfiles:  pstricks.sty      2013/12/12 v0.60 pstricks.tex      2014/10/25 v2.60 pst-xkey.tex      2005/11/25 v1.6 pst-fp.tex        2014/10/25 v2.60 pstricks-add.sty  2010/02/11 v.0.14 pst-plot.sty      2011/04/13 pst-xkey.sty      2005/11/25 v1.6 pst-plot.tex      2014/08/23 1.70 pst-node.sty      2010/04/22 pst-node.tex      2014/08/04 1.35 pstricks-add.tex  2014/12/08 v3.77 pstricks-add.cfg  2005/01/10 v0.1   Finally, I've attached two pictures illustrating the problem:   With end-of-line comment  (source: )   Without end-of-line comment  (source: )

I see that the code in many packages and examples contains percent signs % at the end of (many) lines. What are they used for? Do they affect the parsing of those lines?


I have found the z score by taking the square root of pqr (30).5.5 =sq rt of 7.5.  z score = 1.15 and using tables probability = 23.27% chance of rain more than 20 of the 30 days we checked.  Is this correct?

...2 to 5 questions answered correctly, out of 20 of them? Each question has 5 choices. Probability of getting one right is 1/5. Probability of getting exactly 1 right is ${20 \choose 1} p^1  q^{19}$, with $p=P(\mathrm{right})$ and $q=P(\mathrm{wrong})$  (which I managed to understand and calculate). However how do I calculate for the problem above?


I try to make and INSERT INTO with a variable for table but i can't make it work.  here is my code :      $tb = "mytable" ; $req = $bdd->prepare('INSERT INTO :tb (users, info)                 VALUES(:users, :info)')             or exit(print_r($req->errorInfo())); $req->execute(array(             'tb' => $tb,                 'users' => $name,             'info' => $website,             ));   I get this message : You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''mytable' (users, info' at line 1 )   I really don't know what i should change...  thanks a lot

Why can't I pass the table name to a prepared PDO statement?  $stmt = $dbh->prepare('SELECT * FROM :table WHERE 1'); if ($stmt->execute(array(':table' => 'users'))) {     var_dump($stmt->fetchAll()); }   Is there another safe way to insert a table name into a SQL query? With safe, I mean that I don't want to do  $sql = "SELECT * FROM $table WHERE 1"


I saw a question asked that interests me on one of the Stack Exchange sites. However, I would like a different perspective than that of the site it was posted on.  Is it considered impolite to repost on a separate SE site?

Is it okay to repost a question from another Q&A website/forum that was never answered there? Is that plagiarism?  I came across  that is very similar to a problem I am currently encountering, and would really like to see an answer/response. Would it b e appropriate to copy and paste that question into a question on Stack Overflow?


what is the difference between of this. I am not good in mathematics

In solving differential equation, one encounters with steady-state solution. My textbook says that steady-state solution is the limit of solutions of (ordinary) differential equations when $t \rightarrow \infty$. But the steady-state solution is given as $f(t)$, and this means that the solution is a function of $t$ - so what is this $t$ being in limit?


On steel utensils there are certain colour combination observed, why is so? May be it is due to heating, but how can heating create such kind of colours ?   Description : certain group of blending colours like violet blue etc.

What happens on atomic and molecular level?  Is this true also for non-metals and metalloids?


I have installed Ubuntu os after that I have installed the windows 7 in another partition. But Windows 7 is working fine but Ubuntu grub loader is not there. I tried to installed dual OS in different partitions only. Then why the Ubuntu is not loading.  Can anyone have solution to get the Ubuntu.

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?


I'm looking for a tool or script that will allow me to automate the digitization of polygons by the most outlying points in a cluster of points with the same key attribute. Below is a sample image displaying this done manually.    Selected points are all with the same ID of "MD_1001". I have drawn a polygon around these points, and angled the polygon via the most outlying points in the cluster.  I have thousands of these clusters to digitize polygons over, and need some sort of tool or script to get this done quickly. I am using ArcMap 10.2.2.

I would like to be able to create a convex hull in ArcGIS Desktop 9.x, but I cannot find an appropriate tool.   How does one go about creating one?   I am interested in answers for all license levels: ArcView, ArcEditor and ArcInfo.


I am new to LaTeX, but learnt that it's the best document preparation as researchers. I have downloaded ProTeX, but I do not know anything about coding and programming, how do I ( I am a PhD mechanical engineering student ) start enjoying what the great researchers like you have been enjoying by optimally using it? What other program(s) do I need to download to maximally make the best of this document preparation? How do I collaborate with other researchers of different accent ( speaking a different language )? How can I import or export to MS word? Are there good or even better reference managers like EndNote on this platform? I would appreciate answers from intelligent professional / researchers.  Thank you.

I'm not really a programmer but I'm quite interested in learning how to use LaTeX/TeX. I've looked it up on Wikipedia and scanned through it and the documents created through this way of editing is just  beautiful. Formulas are also available within it too, so writing math thesis or physics papers would be amazing.   Is this system just for programmers, or can normal people use it too? (I'm mainly a designer, so I usually edit it in Word or InDesign.)


If $n$ is an even natural number, then find    $$\sum_{r=0}^n \left(\frac{(-1)^r}{\binom{n}{r}}\right)$$    I tried to solve the question using conventional method, by trying to use calculus, but I don't think that would be applicable here, because no binomial expansion (as far I as know) can give a coefficient in denominator hence I got stuck at it.

Find a closed form expression for $$\sum_{r=0}^n \dfrac{(-1)^r}{\dbinom{n}{r}}$$ where $n$ is an even positive integer.  I tried using binomial identities, but since the binomial coefficient is in the denominator, I can't do much. Also, I'm seeking a non-calculus, elementary solution, if possible. Thanks.


I have been working on a question where I have to decompose this matrix in terms of Pauli Matrices: \begin{bmatrix}1&0&0&1\\0&0&0&0\\0&0&0&0\\1&0&0&1\end{bmatrix} I already have a solution but I don't understand the solution I've been given, this is the solution: First there is a truth table: +------+-----------+ |Input | Output    | +------+-----------+ | |00> | |00>+|11> | = 1/2(|00>+|11>+|11>+|11>) | |01> | 0         | = 1/2(|01>-|01>+|10>-|10>) | |10> | 0         | = 1/2(|10>-|10>+|01>-|01>) | |11> | |11>+|00> | = 1/2(|00>+|00>+|11>+|11>) +------+-----------+  I understand the truth table, but I don't understand the things after the "=" and I also don't understand how the final answer is achieved. This is the final answer: $$ \frac{1}2(I_1 \otimes I_2) + \frac{1}2(Z_1 \otimes Z_2) + \frac{1}2(X_1 \otimes X_2) - \frac{1}2(Y_1 \otimes Y_2) $$ Any help in understanding the solution would be really appreciated. Thank you!

I need to see an example of how Hamiltonian, i.e. any Hermitian matrix, can be decomposed into a linear combination of Pauli matrices. I would prefer an option to do this in larger than 2 dimensions, if that is possible.


I don't want to wear pants in Animal Crossing: New Leaf, but I can't take them off. I tried putting on a dress, but it didn't work.

So I was in my New Leaf house and I accidentally put on a pair of pants instead of displaying them. Then I went and clicked on myself and I have no option to take off my pants. Ever. I swapped them with another pair for the display, but I can't get those off either. And the weird bit is when I put on the pants nothing was swapped back to my inventory.  How do I take off my pants?


I was wondering why we need time dillation . I close my eyes , I take the assumption that the speed of a light beam is constant for every rest frame.The lifht beam is travelling inside a box . I am inside a box and see the beam go upwards and downwards.Now my dog , Wayne , is inside another box . My dog's box travels at some speed related to my rest frame.The beam of light will have the same speed for both boxes , so I will see my dog's box length to be reduced.Why do I need time dillation for a constant speed of light?

Please will someone explain what time dilation really is and how it occurs? There are lots of questions and answers going into how to calculate time dilation, but none that give an intuitive feel for how it happens.


From  I learned that : can be used to get the side effects of a parameter expansion. I stumbled upon this code which uses a parameter expansion that looks new to me:   $ R=32; : $[R--]; echo $R 31   Here  : $[R--] seems to be equivalent to ((R--)). What is $[]? And is it documented in man  bash(1)? I couldn't find it on the man pages.

On the paragraph explaining arithmetic expansion,  uncovers 2 different ways of evaluating an expression, the first one uses $(( EXPRESSION )) and the second one uses $[ EXPRESSION ]. The two ways seem pretty similar as the only difference I have found is:     $[ EXPRESSION ] will only calculate the result of EXPRESSION, and do no tests:   Yet, I am intrigued because the same document recommends using $[ EXPRESSION ] rather than $(( EXPRESSION )).     Wherever possible, Bash users should try to use the syntax with square brackets:   Why would you want that if less tests are being done?


I know that $E[x_i] = \sum X_iP_i= \bar{X}$   But I can't quite figure out the probability in the middle step. I can't find any material online to help clarify this. Any suggestions ?

I'm having a little trouble with the proof that the expected value of $x_i$ is $ \bar{X} $.  What I have is   $E[x_i]=\sum_{j=1}^{N}X_j Pr(x_i=X_j) $  Then,  $Pr(x_i=X_j) = 1/N $  This is the bit I can't understand, how does that probability evaluate to that value.  I know the denominator is how many ways you can choose n out N. I think that the numerator should be how many ways you can choose (n-1) out of (N-1). But I seem to have an extra n.  Any advice ?


Can someone explain to me in a concise way what the difference between these two vars is?   What is the safest way to pass variables to another program?   E.g.   #! /bin/bash  # do stuff  # pass variables onto another program java $@

Which one of $* or $@ is better to use (in array syntax,command line parameters, etc.) to avoid any bugs/problems in code? Or it does not make any difference?


Is there a way to get the overall list of all , together with the categories and history of each bang being introduced or modified?  For example, I've noticed a few months ago that one of my sites, , appears on the bang list.  However, today I've noticed that DuckDuckGo must have recently introduced the categories, as a two-level hierarchy, and I could only find my site on the first level "Tech", not on the second level "Programming" where I think it should belong as well, but I couldn't find out any more info (like whether it belongs to any second-level category at all, maybe even a more relevant one that I may have overlooked; I finally found it's at Sysadmin, but this involved a few too many manual attempts at listing each category individually).  Is there a way to see all DuckDuckGo bang sites, together with their categories?    I'm also curious when each site was added, possibly who added it, and, possibly an unrelated question, what's the procedure to modify it, if necessary?  For example, whoever added my site, appears to have restricted the search on it to symbol references (e.g., identifier search), whereas it is my expectations that most people would instead be interested in a full-text search.  (Also, any chance of getting any sort of search statistics?)  The question  is similar to this one, but while that question only asks for a list of bangs, this question is asking for a list of bangs with history and categories.

Recently I switched from Google to DuckDuckGo and so far I am very pleased with the experience. "The Internet" tells me that one of DuckDuckGo's best features is the possibility to directly search on specific pages using bangs (defined prefixes). E.g. search for "!so [duck-duck-go]" on DuckDuckGo to get duck-duck-go tagged questions on Stackoverflow.  I was searching for a comprehensive list of all available bangs, but the only thing I found was the official  wich offers a search box and categorized lists, but no complete list of all 7,447* bangs.  Is there a possibility to find all bangs without clicking through all the categories on the bang-page?    (*) by time of writing, 2015-12-15


When I upgrade my version from 12.04 to 20.4: Can I use the applications like Evolution and Libre Office Base, flashplayer, kaffein and other in the modern version. I have seen, that this applications are not provided in the software center. Thanks for answers. Kay

I updated Ubuntu last night (sudo apt get update && sudo apt get upgrade) and to  my surprise this morning I didn't find the 'Ubuntu Software' app and there's a new entry called 'Snap Store' which when opened looks just like the old 'Ubuntu Software' app. So has 'Ubunu Software' been renamed to 'Snap Store'? And if yes, why?


I am having problems with laggy mouse pointer movement in Ubuntu 16.10. The problem only occures after graphic intensive activities such as playing 1080p videos, browsing high-res images or playing games. When it appears, it persists until I reboot my computer, even logging off and on doesn't help. Also, the problem only appears when I am using integrated touchpad of my notebook - when I connect a USB mouse the pointer moves as usual (but it still lags when I try to use touchpad). I am using NVIDIA GeForce 940MX card with NVIDIA binary driver 367.57.

Occasionally my laptop will enter a state where the cursor starts lagging so bad that it's unusable.  Oddly during this state, everything other than the cursor is still completely responsive.  I.e. anything that only involves the keyboard (opening a terminal, typing, etc) is unaffected.  Once it enters this state, on successive reboots and shutdowns it re-enters this state within seconds.  However, if I shutdown and leave it alone for a few minutes, it does not immediately re-enter this state.  Based on search results for "acer aspire ubuntu freeze" I have tried setting the intel_idle_max_cstate field in grub to 0, 1, and 2, but this did not seem to help.  To be clear - I am not experiencing any crashes, the system is completely responsive except for the cursor is delayed to the point where it would take several seconds to go from one edge of the screen to the other.


Its getting too difficult to think.if we travel at the speed of light then will light will cross us at same speed or travel with us adjacent (special theory of relativity)

I was told that the Galilean relative velocity rule does not apply to the speed of light. No matter how fast two objects are moving, the speed of light will remain same for both of them.   How and why is this possible?   Also, why can't anything travel faster than light?


The top two tabs won't close. I've tried and can't seem to find out how to get rid of them on my own.

I would like to close some view windows that I opened accidentally.  See the image below:    Edit: another note: I tried searching for the solution, but only found things like "Join Area", which don't seem to work in this situation.


I has idea on abstract algebra, group theory ect. Ihave also check in the test block i have but could not get the solution. And also check the net but also no solution.

This is probably stupid question, but I can't see the difference between the two subgroups:  $$C_G(A)=\{g\in G| gag^{-1}=a,\forall a\in A\}$$ $$Z(G)=\{g\in G| ga=ag,\forall a\in G\}$$  Is the difference that the centralizer takes a subset $A\in G$ and the center always uses the entire group $G$?


I installed ubuntu 14.04 with mysql and the rest of lamp. I created a file called test.php in sublime and when i try to save this file it says unable to safe file in var/www/html  I tried to chown user:user /var/www  but it didnt do anything  I know there are many similir threads to this 1 but id like you to answer it for me so i can understand what i need to do which is not the case with other posts/comments  I had lamp istalled before and i had no problems creating files andsaving them

Having installed the web server is there a simple way to set a user able to use the graphic interface to copy files and directories to the local web server /var/www  I gave myself administrative privileges in Ubuntu but it still doesn't allow copies.


I have installed Ubuntu 17.10 on my machine yesterday.  It had a launch bar/dock at the left of the screen yesterday. But not remembering what I had done yesterday, I somehow realized that I made dock disappear.  It now looks like in the screenshots:      How will I bring Ubuntu dock back to actual desktop?

This is how my desktop looks after the update, the top bar turning grey and the addition of the bottom bar happened after the update.    From my searching of screenshots this does not appear to be how it is supposed to be. Is there any way to fix it?


I've noticed something on multiple different stack sites that confuses me. For some reason, the reputation requirements for certain privileges are different.  For example, you need 50 reputation be able to comment on Stack Overflow questions, but you only need 5 on Meta Stack Exchange.  Another example, you need 1500 reputation on Stack Overflow, 500 on Meta Stack Exchange, and 1000 on Math Stack Exchange for the same privilege; create tags.  Why is that?

So, let's take Skeptics.SE for an example. You can become a trusted user when you acquire 4000 rep., not 20000  I was like, wow, so is it like this because of the lack of users on Skeptics.Se, as in, not so much as Stack Overflow or something?  Why do some sites need less reputation to be a trusted user?


Evaluate  $$\binom{n}{1} + 2\binom{n}{2} + 3 \binom{n}{3}+...+ n \binom{n}{n}$$ My attempt : I know  $(a+b) ^n = \sum\limits_{k=0}^{n} \binom{n}{k} a^{n-k}b^k$ But here Im confuse how to evaluate and im not able to proceed further.

I do as follows  $(1+x)^n= \binom{n}{0}+\binom{n}{1}x+\binom{n}{2}x^2+...+\binom{n}{n}x^n$   differentiating in both sides  $n(1+x)^{n-1}= \binom{n}{1}+2\binom{n}{2}x+3\binom{n}{3}x^2...+n\binom{n}{n}x^{n-1}$  then, for $x=1$  $n \cdot2^{n-1} = \sum_{k=1}^{n}k\binom{n}{k}$  From here, I don't know how to proceed, I have tried to multiply both sides for $(1+x)$ to make $n \cdot2^{n}$ but then the summatory changes, I don't know how to prove the equality.


I just received armor which adds +2 to my charisma. Does it also affect my skills like performance and persuasion? If possible, could you link some source in your answer? I searched and didn't find any conclusive answer.

I'm a new DM. One of the PCs obtained , which raise the Strength score of the creature wearing and attuned to them to 19. Does this increase the modifier or any of the skill checks or damage rolls as well?  I'm not sure how having higher Strength is helpful if it doesn't.


Here is what I did:  1) I divided the mtcars dataset into a training set (80%) and a validation set (20%).  2) I built a simple linear model predicting mileage (mpg) based on displacement (disp).  3) I built a multi-linear model predicting mileage (mpg) based on displacement, horsepower and weight (disp + hp + wt).  Here is the R code I used:  set.seed(123)  trainingRowIndex <- sample(1:nrow(mtcars), 0.8*nrow(mtcars)) trainingSet <- mtcars[trainingRowIndex, ] validationSet  <- mtcars[-trainingRowIndex, ] # Build simple linear model (disp only) lmMtcars <- lm(mpg ~ disp, data=trainingSet)  summary (lmMtcars) # Build multi-linear model (disp + hp + wt) mlmMtcars <- lm(mpg ~ disp + hp + wt , data=trainingSet) summary (mlmMtcars)   In the simple linear model, the disp has a p-value of 2.33e-07 (basically meaning that it is a good predictor). However, in the multi-linear model, disp has a p-value of 0.87220 (meaning that it is not a good predictor). I would expect disp to be a rather good predictor for mgp as there is a strong (negative) correlation between the two (=-0.8475514).  Why is the disp p-value not significant in the case of the multi-linear model? Is there something wrong with my code or do I miss something here?  Thanks,


I can't find an answer to this after searching meta and : how do "typo" tags get killed off? For example, currently there are tags for  and , which are both obviously typos. .  So, how do we get rid of these? My take so far is that it is partly automatic, like "tags that are x days old with no posts are closed automatically," and partly a moderator activity. Is this correct?  Closely related: is there any way for users to suggest destruction of a tag that is obviously irrelevant or a typo other than (1) a meta "burninate" post or (2) marking it as a synonym of a legit tag, which just perpetuates the typo's existence?

During the re-tagging of questions, tags sometimes become orphaned from existing questions.  Are these zombie tags ever removed from the ?  What if a tag is misspelled and needs to be removed? How do we get rid of it?


Given an arbitrary number field $K/\mathbb{Q}$, and let $\alpha$ an arbitrary primitive element, i.e. $K=\mathbb{Q}(\alpha)$.      What is the relation between $\text{Disc}(\text{min}_{\alpha}(x))$ and $\text{Disc}(K/\mathbb{Q})$?    For instance, in the case of quadratic extensions, it would be equal module ${\mathbb{Q}}/{\mathbb{Q}^{\times 2}}$.

Let $f\in\mathbb{Z}[x]$ be monic and irreducible, let $K=$ splitting field of $f$ over $\mathbb{Q}$. What can we say about the relationship between $disc(f)$ and $\Delta_K$? I seem to remember that one differs from the other by a multiple of a square, but I don't know which is which. On a more philosophical note: why are these quantities related at all? Is there an explanation for why they can be different, i.e. some information that one keeps track of that the other doesn't?


I'm running Ubuntu Budgie 18.04 on a 3440x1440 resolution, combine that with bad eyesight and the default mouse pointer size can be hard to see.  Is there a way to increase it's size?

I have recently created an Ubuntu 12.04 partition on my Windows 7 laptop. When installing it, I switched to "high contrast" mode, which has rather large cursors (by large I mean about twice as large and thick as they should normally are).  Now I have successfully installed the partition, the large cursors have stuck around even after exiting this high contrast mode, but only when I am hovering over stuff e.g. hovering over text inputs, links, and when resizing windows. All of these cursors are too large. They cursor is only normally sized when the computer should be displaying the normal mouse pointer.  Does anyone know how I might go about fixing this?


For a few months now, but introduced this year, in Opera (12.x) the timeline of reputation changes looks awkward. See this screenshot:    As you can see the timeline stretches onto two lines and therefore overlaps with the list of rep changes.

Last item in the user reputation chart summary in Opera jumps to new line. I am using Opera Version 12.15 and Windows 7 64-bit operating system, zoom level is 100%.  See the screen shot:


I just used the windows backup utility to store a bootable image (I think..) to a 1TB external hard drive.  Do I have to store the Ubuntu partition (backup) to a different sub directory in the hard drive, or will the computer read both of the partitions in GRUB even if they are stored in the same directory? (Like, the series of files stored when one backs up).  Also, how do I backup my entire Ubuntu partition (including GRUB bootloader) to said external hard drive?   Thank you very much!  I realize these are multiple questions, but they are rather related, so I decided to use a single thread.

No, this is not a , nor is it a solicitation on  to backup or  and only a little bit about Where to backup and When to do it.  This is basically a strategy question: what, where and when all together. "How" is not really relevant: there are tons of back-up programs out there and they all do the same basic thing: make copies of data.  But the real question is: are these back-up programs making copies of the data important to you?  How should you install&run Ubuntu while safeguarding your data?  There is no "one size fits all" when it comes to computers, Ubuntu versions or a backup strategy, therefore I've split this up into 5 basic user types with each their own answer:       (or you're running in UEFI mode!)   And as the above does not fit everyone, one for the impatient:   !    So click one of the above links and go to your user type!  P.S. If you're running a server farm and you've read this question so far, I'm sorry: this is about a single PC, not a network, nor a server farm.


Some questions solicit, by their nature, have many answers. For example  or . Could we have a feature to hide comments, and shorten long answers (to perhaps their first line or so), so you can browse through many answers quickly?

A question with attachments, screenshots and/or long code, makes it vertically long and often difficult to read fast.  It would be nice to have a new kind of format, such as 'hideable', with a graphic button or a '+' / '-' sign, so you can add additional details, visible only on a click.


I want to add some registry using WiX installer. Here's my code:  <DirectoryRef Id="TARGETDIR">   <Component Id="DisableWeakCipherSuites" Guid="7DBE2D50-3C00-4CEF-86CC-897C0C96E7FF" KeyPath="yes">     <RegistryKey Key="SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Ciphers\RC4 40/128" Root="HKLM" Action="createAndRemoveOnUninstall">       <RegistryValue Name="Enabled" Value="0" Type="integer" />     </RegistryKey>     <RegistryKey Key="SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Ciphers\Triple DES 168" Root="HKLM" Action="createAndRemoveOnUninstall">       <RegistryValue Name="Enabled" Value="0" Type="integer" />     </RegistryKey>     <RegistryKey Key="SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Ciphers\RC4 128/128" Root="HKLM" Action="createAndRemoveOnUninstall">       <RegistryValue Name="Enabled" Value="0" Type="integer" />     </RegistryKey>     <RegistryKey Key="SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Ciphers\RC4 56/128" Root="HKLM" Action="createAndRemoveOnUninstall">       <RegistryValue Name="Enabled" Value="0" Type="integer" />     </RegistryKey>   </Component> </DirectoryRef>   But instead of adding these keys into CurrentControlSet, installer adds those keys into ControlSet001.

In the Windows registry, how does CurrentControlSet differ from ControlSet001 and ControlSet002? Which should be set when installing for all users? We are trying to add an environment variable for all users. Is this correct? HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Envinronment


I read the comments on  question and somehow stumbled over this comment:     Downvotes on meta indicate disagreement with the question's premise,       not that you asked a bad question.   as it indicates that if you want to get some reputation (which is for example needed for mod-elections) you actually have to ask questions that are not individual, and maybe controversy but, those which represent the masses opinion and this completely contradicts my opinion of a valuable question, especially if discussions (and therefore different opinions) are ok.  Now I am wondering if this comment can be applied on most meta-users or is just a single opinion.

Meta Stack Exchange seems to have different rules and user behavior than the "regular" Stack Exchange sites.  How is it different?    Individual questions answered below:                Related


Is this allowed to bring on flight as a carry-on luggage? Its size is like an electronic toothbrush.    And this is the instrument (quite long).  I will fly with SAS airline in a business class, normally I'm allowed to bring 2 of 23kg luggages, but I prefer to take my instrument al a carry-on luggage.

How can I travel to another country (by plane) and take my instruments with me?  I live in Greece and I want to go to the USA with my double and electric bass.  I found  question, but it is limited to traveling in the states.


Let's say I execute a query like this:  $assignments = $database->getDataAsArray("SELECT * FROM assignments WHERE userId = '$id'");   The function (getDataAsArray) looks like this:  public function getDataAsArray($myQuery){         $this->connection = mysqli_connect($this->host, $this->dbUsername, $this->dbPassword, 'portal');         $statement = $this->connection->prepare($myQuery);         $statement->execute();         $result = $statement->get_result();         $results = array();         while($line = $result->fetch_array()){             $results[] = $line;         }         return $results;     }   This is unsafe because I do not parameterize the query with items like :ID  Is it safe if I do it like this:   $id = mysqli_real_escape_string($database->getConnection(), $_SESSION['id']);         $assignments = $database->getDataAsArray("SELECT * FROM assignments WHERE userId = $id AND closed = 0 AND completed = 0");   In case this it not safe how can I parameterize my queries with one function. For instance I have this query:   "SELECT * FROM assignments WHERE userId = $id AND closed = 0 AND completed = 0"   and I have this query:   "SELECT * FROM state WHERE id='$stateId'"   Both have different number of parameters which need to be added to the query. How can I handle this in one function?   Thanks in advanced

If user input is inserted without modification into an SQL query, then the application becomes vulnerable to , like in the following example:  $unsafe_variable = $_POST['user_input'];   mysql_query("INSERT INTO `table` (`column`) VALUES ('$unsafe_variable')");   That's because the user can input something like value'); DROP TABLE table;--, and the query becomes:  INSERT INTO `table` (`column`) VALUES('value'); DROP TABLE table;--')   What can be done to prevent this from happening?


I have a file I can't delete as "it is used by System". I tried rebooting, turning off and on, then I tried using Revo Uninstaller forced delete and FileAssassin, but none of them worked. I checked if it was a virus using ESET 9 but the file is not infected, it is just "used by System" and cannot be deleted. Any ideas on removing that file?   EDIT: I'm using Windows 10 64 bit. The file itself is a file I made into a .bin some time ago, nothing important. I did close Daemon of course, still no clue why System uses it.

So I found out that I had a Trojan on my external hard drive. My anti-virus app killed it, but it has created a bunch of random files on my computer which cannot be deleted. These are image files. They cannot be renamed - using any method - nor can they be moved, cut, copied, permanently deleted or even opened (in any program).  How can we rid these files from our system?  I have tried:   Right-click > Delete Shift+Delete (Permanently Delete) Swearing   and then:   FileASSASSIN from MalwareBytes Eraser program sdelete program several commands in cmd   but none of them have been successful. How can I completely obliterate these files?


In a linux terminal I use "cat > file.txt" to make a file one line at a time.  What I find is that per-line the delete key works but the arrow keys insert escape codes rather than moving left and right in the line.  Why is this? Is there a reason that the terminals basic action cannot do left and right arrow keys? I know there are things like GNU readline which do it but my question is not about those.

Whenever I'm at the console login, I press up arrow intentionally to see the previously typed commands. But I see this ^[[A.  But when I press Ctrl Alt Print Screen Scroll Lock Pause Break Page Up Page Down Win keys doesn't echo any characters.  What might be the reason behind?  Does ^[[A sort of characters imply anything?


I have this unicode  xx = u"Merci d'avoir acheté Electricité mobile, votre SPS sera activé prochainement"   when i print it it looks ok when i want to compare this xx the unicode appears like this  u'Merci d\'avoir acheté Electricité mobile, votre SPS sera activé prochainement'   i want to remove this backslash i tried like this but get exception  ddd=xx.decode('string_escape')  EncodeError: 'ascii' codec can't encode character u'\xe9' in position 19: ordinal not in range(128)   any help will be appriciated

I have a string that contains both double-quotes and backslashes that I want to set to a variable in Python. However, whenever I try to set it, the quotes or slashes are either removed or escaped. Here's an example:  >>> foo = 'baz "\"' >>> foo 'baz ""'   So instead of baz "\" like I want I'm getting baz "". If I then try to escape the backslash, it doesn't help either:  >>> foo = 'baz "\\"' >>> foo 'baz "\\"'   Which now matches what I put in but wasn't what I originally wanted. How do you get around this problem?


You have a 2-Dimensional list of numbers like:  x = [[1,2],[3,4],[5,6],[7,8],[9,10],[11,12],[13,14],[15,16],[17,18]]   You need to split it into two lists in such a way that you get the numbers from the first column in one list and the second column in another list:  [1,3,5,7,9,11,13,15,17] [2,4,6,8,10,12,14,16,18]   How can that be done in python?  I am posting this question because I could not find a simple answer to it. I will be answering it later.

I have a list of 2-item tuples and I'd like to convert them to 2 lists where the first contains the first item in each tuple and the second list holds the second item.  For example:  original = [('a', 1), ('b', 2), ('c', 3), ('d', 4)] # and I want to become... result = (['a', 'b', 'c', 'd'], [1, 2, 3, 4])   Is there a builtin function that does that?


I been trying to install adobe reader from Synaptic Package Manager but I keep getting a error message. Are any of you experiencing the same error or bug? I even tried downloading it from the Terminal but no dice! What do you guys think it could be? The website is no help since Linux is not listed as one of the OS to download, what's up with that?

I am new to Ubuntu, but I believe I have Ubuntu 11.10 installed correctly.  I am trying to install Acroread using AdbeRdr9.4.6-1_i386linux_enu.deb that I downloaded from the Adobe web site.  How do I do this?


If X1 X2 are independent Uniform variates on (0,1), Find the distribution of Z=X1/X2.   I tried using the CDF method where P(X1<=zX2) is equal to z/2 when z is in(0,1). However, I am unable to find the CDF when z is greater than 1

Suppose that  $X$ and $Y$ are two i.i.d. uniform random variables on the interval $[0,1]$  Let $Z=X/Y$, I am finding the cdf of $Z$, i.e. $ \Pr(Z\leq z) $.  Now, I came up with two ways of doing this. One produces a correct answer consistent with the pdf here: , the other does not. Why is the second method wrong?  First Method  $\newcommand{\rd}{\mathrm{d}} \Pr(Z\leq z) = \Pr(X/Y\leq z) = \Pr(X\leq zY) = \int^{1}_{0}\int^{\min(1,zy)}_{0} \rd x \rd y = \int^{1}_{0}\min(1,zy)\ \rd y$ $  = \left\{      \begin{array}{lr}        \int^{1/z}_{0}zy\ \rd y + \int^{1}_{1/z} \rd y& : z > 1\\        \int^{1}_{0}zy\ \rd y & : z \leq 1      \end{array}    \right. $ $  = \left\{      \begin{array}{lr}        1 - \frac{1}{2z} & : z > 1\\        \frac{z}{2} & : z \leq 1      \end{array}    \right. $  This appears correct.  Second Method  $\Pr(X/Y\leq z) = \Pr(X \leq zY\ |\ zY \geq 1)\Pr(zY \geq 1) + \Pr(X \leq zY\ |\ zY < 1)\Pr(zY < 1) $ by total probability  $ = \Pr(X \leq zY\ |\ zY \geq 1)\Pr(Y \geq 1/z) + \Pr(X \leq zY\ |\ zY < 1)\Pr(Y < 1/z)$  Taking $z>1$ yields $ (1)(1-\frac{1}{z}) + (\int^{1/z}_{0}\int^{zy}_{0} \rd x \rd y)(\frac{1}{z}) = 1-\frac{1}{z} + (\int^{1/z}_{0}zy\ \rd y)(\frac{1}{z}) = 1-\frac{1}{z} + \frac{1}{2z^{2}}$  This is already different. Why is this wrong?  Thanks!


I have added a WordPress blog to my site, added non-canonical URLs, put it through Bing, and Google Webmaster tools added about 100 + backlinks, and I've not had one any of my Wordpress blog pages ran on SEO search engines at all, bing, yahoo, yahoo.co.jp, google.com and other google search pages including google.fr, all of which I want to be ranked for international traffic. The site is a little old, and I hope I am not recovering after old errors and penalities, because from what I have read it could take up to a year, so that's the reason I've been going the extra mile on it, and I have not added too many pages to it, and have recovered some configuration issues where a lot of pages were going to a bad 404 page... However, I have added WordPress to sites many times and can see a transparent issue, wondering if anyone has any tips to get the WordPress pages ranking up soon. Really never seent his issue before. So tried pretty much everything, the Yoast app says there is some conflict with having two sitemaps, but the problem is that the one for my main hosting from the hosting company, is actually important because it comprises the core sitemap for my HTML pages.... So Is there a way to utilize the 'Toggle' sitemaps function? Should matter though because I have even confirmed the site pages exist with an RSS feed in bing webmaster tools, but it won't even rank in bing when I type in site: followed by the domain dot com.... So this RSS feed is also catching data in webmaster tools however there is still nothing.  Any ideas? Anything would help, I lost a lot of ranking on an old blog I used for my business page, that I shut down as I decided to merge everything into one site and forward some of the links between each other, but now it is ranking much worse, and none of my new WordPress pages are ranking after 30 days. And, my apologies if the StackExchange system saw a duplicate memo, this was because the WordPress thread I followed on the site was actually related to WordPress drops... REALLY need help here, my WordPress ranking is fundamental to my site's traffic. Another concern of mine is that someone might be negative backlinking my old broken blog pages, so I keep adding redirects to supplement the negative SEO, it's really bizarre, but I am only happy to at least be ranking on my brand keywords again... Everything else though for external brand related keywords has been quite sabotaged.. And, to think it all use to come from WordPress, I was getting more than 100 clicks a day related to my blogs...

This is a general, community wiki  question and answer pair intended to address any questions   concerning the reasons a site or specific site contents do not appear   in search engine results.      If your question was closed as a duplicate of this question and you   feel that the information provided here does not provide a sufficient   answer, please open a discussion on .   My site (or specific pages on my site) is not appearing in search engine results.  Why isn't my content indexed and what can I do about it?


I would like to know if there is a way to determine where a specific part of my $PATH variable is being set.  About a year and and a half ago I went through the tedious process of setting up a Oracle XE 11.2.0 on my machine for a course I was taking. Somewhere in the process I added the path "/u01/app/oracle/product/11.2.0/xe/bin" to my $PATH variable to get things working. Well now I've deleted the root /u01/ folder that was exclusively used by the Oracle DB and so bash throws the error on startup that the file or directory doesn't exist. So I went manually looking through every possible file I can find listed and nothing.  As far as I can tell, that part of $PATH is not being set in any of these files: /etc/login.defs, ~/.profile, /etc/environment, /etc/profile, ~/.bash_login, ~/.bash_profile or ~/.bashrc.  That was verified first by running cat ~/.bashrc | grep "*oracle*" on every file listed above. I even did the insane thing and ran sudo strings /dev/sdb -n 11 | grep -C100 "/u01/app/oracle/*" to give me a list of every file that contained the string. I got lots of results, but nothing super valuable. My poor SSD didn't deserve that.  So any tips? How can I find out where that part of $PATH is being concatenated onto? Are there any other typical files that I should check? I'm running this on Linux Mint 18.3 if that narrows anything down.

I want to remove ~/bin from my PATH.  I set it up months ago when Linux (Ubuntu) was very new to me, but I don't know how I added it...    Nothing shows up when I search all the files listed below. Where else could it be being set?  It is being pre-pended after $HOME/.profile prefixes PATH with $HOME/bin      If it makes any difference, I get the same PATH from both the command-prompt and a running script.    #!/bin/bash {   echo "first dir of PATH is: '${PATH%%:*}'"   shopt -s nullglob   cat \     /etc/profile \     /etc/bash.bashrc \     /etc/profile.d/*.sh \     $HOME/.bashrc \     $HOME/.bash_aliases \     /etc/bash_completion \     $HOME/.bash_completion* \     $HOME/.profile \     $HOME/.profile_zap \     $HOME/.bash_profile* \     $HOME/.bash_login* \   | sed -rne '/~\/bin/p' }   Output is:  first dir of PATH is: '~/bin'


I want to write a regex to match phone numbers in following format i.e. 1- without country code 9999999999 2 - with 1 digit country code +19999999999 3 - with country code and () +1(999)9999999 4 - with country code () and - +1(999)-999-9999 I wrote a regex which matches condition 2 but failed in 1,3 and 4. ^[\+]?[(]?[0-9]{3}[)]?[-\s\.]?[0-9]{3}[-\s\.]?[0-9]{4,6}$  As soon as I adds country code after + sign along with () and - my regex stops working. How Can I fix it? I am not a regex pro and assembled my regex by trying different patterns that I got by googling. Any help would be appreciated.

I'm trying to put together a comprehensive regex to validate phone numbers. Ideally it would handle international formats, but it must handle US formats, including the following:   1-234-567-8901 1-234-567-8901 x1234 1-234-567-8901 ext1234 1 (234) 567-8901 1.234.567.8901 1/234/567/8901 12345678901   I'll answer with my current attempt, but I'm hoping somebody has something better and/or more elegant.


Working mostly with Linux, I rediscover from time to time Windows and Microsoft's applications such as Internet Explorer/Edge. I also notice that the trend is not limited to Microsoft, although I don't know if other companies mimic Microsoft, or if all those companies, Microsoft included, are following a common trend.  I'm surprised for the past ten years by the evolution in the graphical design which, in turn, has a direct impact on the user experience.  At Windows XP era, a button looked like a button: it had a specific shape with its round corners, a specific background with a gradient—light gray at the top, dark gray at the bottom—and a border. When you clicked on it, the appearance changed to show you that the button is pressed. Similarly, a window looked like a window, icons looked like objects they represent, and so on.  With Windows 10, things are different. No more rounded corners or gradients. All is left are single-color rectangles and circles. A button is no longer a button—you have to guess that the rectangle can be clicked on. Icons are all monochrome now, and in Edge, you can only guess that the rectangles at the top of the browser are tabs. It starts to look a lot like Windows 1.0 and Windows 2.0.  This makes it quite challenging to use those interfaces even for me, an IT professional. Twice, I've seen persons who are unfamiliar with computers, tablets or smartphones, trying to use Windows and Edge, and they were totally lost—“What do you mean click on the button? Oh, I can press a mouse on this rectangle?! I didn't know that!”  I suppose that the choice of Microsoft (and other companies which follow the same shift) to make its products look like they did back in Windows 1.0 is not motivated not by technical considerations (simpler graphics means higher performance). While it could make sense five years ago for low-grade smartphones, I can hardly see how it would make any sense today, especially for desktops, most of which having a powerful GPU.  Therefore, my hypothesis is that this simplification is motivated by factors related to user experience. I remember reading a few years ago a discussion explaining that a bunch of changes in Visual Studio interface, such as a move to monochrome icons, were motivated to enhance the interface for people with disabilities (although I'm not sure how making an icon difficult to understand would make the life easier for those persons).  So:   Is it really a general trend? Is it related to the user experience, or it has something to do with factors which are completely independent, and the user experience is just suffering from it as a neglected side effect? If the shift is done on purpose by user experience specialists, what exactly is the purpose? Who benefits from it?

I've noticed an interesting phenomenon in the user interfaces of many famous applications, they're moving away from the glossy complex to a more dull and bare minimum design.  Why the sudden change? It also appears that most of these companies have adopted this design around the same time, was that linked to some new study?  Examples:


I have a anonymous share setup on my linux box.  I'd like to access it without passwords from my mac.  However, when I try to do that it crashes my Finder.   Here's the samba config:  [global]   workgroup = HOBBIT   dns proxy = no   netbios name srvr1   log file = /var/log/samba/log.%m   max log size = 1000   security = user   map to guest = bad user   name resolve order bcast host  [theshare]   comment = theshare   path = /media/maja/Samba   public = yes   writable = yes   available = yes   browsable = yes   guest ok = yes   create mask = 0777   directory mask = 0777   So I see the PC in the network, and I see the share:   But when I try to click on the folder, Finder crashes and I get this error:   Any ideas?

Just installed Ubuntu 14.10 on my server, replacing 14.04 (not upgrading it). I gave it the same name (ubuntu-server) as before. I installed Samba and redefined the shares previously established, using the same names: sde, sdf, etc.  However, I can no longer access those shares from Mac OS (Yosemite). I've rebooted the server and the Mac OS systems, to no avail. The server and the shares appear on both of the Macs, but my connection to the server is that of Guest, and although I've enabled Guest access, when I try to access one of the shares, I get a dialog "The operation can't be completed because the original item for "" can't be found". If I try to change the connection to be as a registered user, I get "There was a problem connecting to the server "". Check the server name or ip address and then try again . . .".  Does anyone know what the problem is or what I can check to get further details about what the actual problem is?  Regards, David


$\quad$ In group theory class we considered only the group of geometric symmetries(rotation and reflection), but the definition involves that there can be any group and any set as long as the following conditions are met \begin{align} &1. \quad \forall g_1, g_2 \in G, \forall x \in X \quad g_1*(g_2*x) = (g_1*g_2)*x\\ &2. \quad \forall x\in X \quad e*x=x \end{align} $\quad$ Can you provide some more examples with different groups and different sets? In particular, with $\mathbb{Z}_6$ group for instance.

First, a little motivation: I have read the section on Group Actions in Dummit & Foote, the wikipedia page, and (countably many) other references. And seemingly without exception, they only offer rote and/or abstract examples, such as:   Let $ga = a$ for al $ g \in G, a \in A$ The symmetric group $S_N$ acting on $A$ by $\sigma \cdot a = \sigma(a)$ Something about regular n-gons and $D_{2n}$ $g \cdot a = ga$...   I don't mean to undermine the importance of these examples, but I'm left with no hands-on experience with these things. Exercise $\S$ 1.7.8(b) in D&F says: "Describe explicitly how the elements $(1 \  2)$ and $(1 \ 2 \ 3)$ act on the six 2-element subsets of $ \left \{1, 2, 3, 4 \right \}$. How does a three cycle permute two elements?       Furthermore, what are some concrete examples of (computational exercises of) group actions?     Thanks.


Really struggling with a question on coursera robotics perception:     Find the projective transformation $A$ which will keep the points   $\boldsymbol{p}_{1}=(0,0,1)$ and $\boldsymbol{p}_{2} = (1,1,1)$ fixed and will map point $\boldsymbol{p}_{3} = (1,0,1)$ to $\boldsymbol{p}_{3}'=(1,0,0)$ and point $\boldsymbol{p}_{4} = (0,1,1)$ to $\boldsymbol{p}_{4}' = (0,1,0)$?   The answer is the matrix: \begin{bmatrix}-1&0&0\\0&-1&0\\-1&-1&1\end{bmatrix}  The idea from my lectures is to take 4 points (3 of which are not collinear) and use that to solve the  equation:  $$\alpha \boldsymbol{a} + \beta \boldsymbol{b} + \gamma \boldsymbol{c} = \boldsymbol{d}$$  where $\boldsymbol{a}, \boldsymbol{b}, \boldsymbol{c}$ and $\boldsymbol{d}$ are the vector coordinates of 4 points.   If I pick $\boldsymbol{p}_{1}'$, $\boldsymbol{p}_{3}'$, $\boldsymbol{p}_{4}'$ and $\boldsymbol{p}_{2}'$  as $\boldsymbol{a}, \boldsymbol{b}, \boldsymbol{c}$ and $\boldsymbol{d}$ respectively I get the incorrect matrix. As far as I can see the point $\boldsymbol{p}_{1}'$, $\boldsymbol{p}_{3}'$, and $\boldsymbol{p}_{4}'$ are not collinear.  The actual solution uses $\boldsymbol{p}_{1}$, $\boldsymbol{p}_{3}$, $\boldsymbol{p}_{4}$ and $\boldsymbol{p}_{2}$  as $\boldsymbol{a}, \boldsymbol{b}, \boldsymbol{c}$ and $\boldsymbol{d}$ respectively and calculates the matrix the other way round.   Essentially gets the matrix that maps from $\boldsymbol{p}'$ to $\boldsymbol{p}$ and then inverts it.  I have no idea why that works (Gives a better estimate to exact)  Completely confused as to how one choses the correspondence points.  The answer here gives an estimate that is way off:

I'm working on a project using Chrome - JS and Webkit 3D CSS3 transform matrix. The final goal is to create a tool for artistic projects using projectors and animation - somewhat far away from using maths... I'm using a projector to project several squares over several shapes - as seen in the picture. What I would like to do is for the user to draw 4 points on the screen (2D x and y) and from there extract a matrix object that I could apply to a regular DIV element of a dimension of 100px by 100px. By finding scaleX, scaleY, rotation, rotationX, rotationZ and probably some perspective that I could apply to the div to relatively match the surface. I'm not really familiar with geometry beyond sin and cos, and 3D in general and don't even know if that is something doable. If anyone could help me get started or point me in the right direction, I would greatly appreciate. Here is an animated gif (click to enlarge), hoping it makes it more clear to understand.


I have the following beamer layout. This layout is great but the problem is that when I type math equations, the font is not set to the default font as in the picture. I think some command in the below code makes the font different but I don't know what is that. Please give a way to set math font as default.  \documentclass[11pt]{beamer} \hypersetup{pdfencoding=auto}  \usetheme{Berkeley}  \usepackage{xcolor} \usepackage{amssymb,amsmath,graphicx} \usepackage{kotex} \usepackage{multimedia} \usepackage{setspace} \usepackage{multicol} \usepackage{verbatim} %use   %% Color Setting %% \definecolor{Grey}{rgb}{0.6,0.6,0.6} \definecolor{GSHSred}{RGB}{105,0,0} \definecolor{GSHSRED}{RGB}{80,0,0} \definecolor{gshsred}{RGB}{240,210,210} \setbeamercolor{title}{bg=white,fg=GSHSred} \setbeamercolor{author}{fg=GSHSred} \setbeamercolor{institute}{fg=GSHSred} \setbeamercolor{date}{fg=GSHSred} \setbeamercolor{logo}{bg=GSHSred} \setbeamercolor{sidebar}{bg=GSHSred} \setbeamercolor{frametitle}{bg=white,fg=GSHSred} \setbeamercolor{section in sidebar}{use=sidebar,bg=white,fg=sidebar.bg} \setbeamercolor{subsection in sidebar}{parent=section in sidebar} \setbeamercolor{subsubsection in sidebar}{parent=subsection in sidebar} \setbeamercolor{item}{fg=GSHSred} \setbeamercolor{block title}{bg=GSHSRED,fg=white} \setbeamercolor{block body}{bg=gshsred,fg=black}  %% Frametitle Setting %% %\setbeamerfont{frametitle}{series=\bfseries} \setbeamertemplate{frametitle} { \vspace*{-10mm}   \leavevmode   \hspace*{3pt}   \begin{beamercolorbox}[wd=\paperwidth,ht=1ex,dp=1ex]{frametitle}     \hspace*{7pt}\underline{\makebox[0.6\paperwidth][l]{     \Large{\insertframetitle}}}   \end{beamercolorbox} }   %% Title Page Setting %% \setbeamerfont{title}{series=\bfseries} \setbeamertemplate{title page}{   %% Background Logo   \begin{picture}(0,0)%     \setlength{\unitlength}{1cm}% default     \protect\put(0,0){%     \begin{picture}(6,6)(4,10)%     %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%       %\includegraphics[width=0.4\paperwidth]{./logo/100_01.png}%       \includegraphics[width=0.7\paperwidth]{./logo/gshslogo2.jpg}%     \end{picture}%     }%   \end{picture}%   \vfill   \vspace*{10mm}   \raggedleft   %% Title   \usebeamerfont{title}\usebeamercolor[fg]{title}\inserttitle\par   \vskip 2mm   %% Subtitle   \ifx\insertsubtitle\@empty   \else\usebeamerfont{subtitle}\usebeamercolor[fg]{subtitle}\insertsubtitle   \fi    \vskip 3mm   %% Horizontal line   \usebeamercolor[fg]{title}\hrule height 2pt\hfill   \vskip 10mm   %% Author   \usebeamercolor[fg]{author}\usebeamerfont{author}\insertauthor   \vskip 1cm   %% Institute   \usebeamercolor[fg]{institute}\usebeamerfont{institute}\insertinstitute   \vskip 1cm   %% Date   %\usebeamercolor[fg]{date}\usebeamerfont{date}\insertdate   \vfill }  %% itemize bullet setting %% \setbeamertemplate{itemize items}[ball]  %% block setting %% \setbeamertemplate{blocks}[rounded][shadow=true]

In a LaTeX article, the math characters are more "curvy" than the text characters:  \documentclass[12pt]{article} \begin{document}  $x^2 + y^2 = z^2$ \end{document}     In a beamer presentation, the math characters do not have the same curves:  \documentclass{beamer} \begin{document} \begin{frame}  $x^2 + y^2 = z^2$ \end{frame} \end{document}     Question  How can I get the beamer math to look just like the article math?  I would prefer if the solution was a single line (that I could place at the top of my LaTeX file) as opposed to something that needs to appear next to every piece of math.


Is there some simple way to make ls display the file size number with thousand (and million, billion, ...) separator? A sample output should look like this:  $ ls -lAF /bin/ -rwxr-xr-x 1 root root 975,488 Dec 30  2012 bash* -rwxr-xr-x 3 root root  31,184 Jul 29  2012 bunzip2* -rwxr-xr-x 3 root root  31,184 Jul 29  2012 bzcat*   This would, in my opinion, greatly increase the readability of ls output, especially with large files. Without the thousand (and million, billion..) separator, it is almost impossible to correctly read the magnitude of a big file.

It is possible to make ls -l output the size field with digits grouped by thousands? If so, how?  For instance:  $ ls -l -rw-rw---- 1 dahl dahl 43,210,052 2012-01-01 21:52 test.py   (Note the commas in the size).  Maybe by modifying the LC_NUMERIC setting inside the locale I'm using (en_US.utf8)?  I'm on Kubuntu 12.04 LTS.


When we perform a double slit experiment we receive interference pattern. when we measure in a specific slit the exact location of the photon (or electron) the interference pattern disappears and we receive only 2 light spots with no interference pattern.  Now let's assume that we perform the double slit experiment on two entangled photon (or electrons) far away from each other (Alice & Bob).  If Alice measures the location of the photon in the slits, she doesn't receive interference pattern, but because of entanglement the location of Bob's photon is now known and he also doesn't get an interference pattern. This way he knows instantaneously that Alice performed a measurement even when she is far away.  If she doesn't measure the location of the photon in the slits, they will both receive interference pattern and Bob will know instantaneously that she didn't measure the photons location.  This ideas based on the EPR famous paper enables faster than light communication. What did I miss here?

I understand that faster-than-light communication is impossible when making single measurements, because the outcome of each measurement is random. However, shouldn't measurement on one side collapse the wave function on the other side, such that interference effects would disappear? Making measurements on "bunches" of entangled particles would thus allow FTL communication, by making observed interference effects appear or disappear. How does such an experiment not:  1) Clearly imply that faster-than-light communication is possible?  or  2) (if #1 is rejected) Imply that measurement of one half of an entangled pair does not cause the collapse of the other half's wave function.  Why doesn't this thought experiment clearly show that if we maintain that FTL communication is ruled out, we must also rule out "universal collapse" in the Copenhagen interpretation?  EDIT: Here is an example of an explicit experiment (though I think experts could come up with something better):  You can entangle a photon with an electron such that the angle of the photon is correlated with the electron's position at each slit of a double slit experiment. If the photon is detected (it's outgoing angle measured), then which-path information is known, and there is no interference. If the photon is not detected, the interference remains.   The experiment is designed such that the photon and electron go in roughly opposite directions, apart from the tiny deflection which gives which-path information. You set up a series of photon detectors 100 ly away on one side, and your double slit experiment 100 ly away in the opposite direction. Now you produce the entangled pairs in bunches, say of 100 entangled pairs, each coming every millisecond, with a muon coming between each bunch to serve as a separator.   Then the idea is that someone at the photon detector side can send information to someone watching the double-slit experiment, by selectively detecting all of the photons in some bunches, but not in others. If all of the photons are detected for one bunch, then the corresponding electron bunch 200 ly away should show no interference effects. If all of the photons are not detected for one bunch, then the corresponding electron bunch 200 ly away would show the usual double-slit interference effects (say on a phosphorus screen). (Note that this does not require combining information from the photon-detector-side with the electron-double-slit side in order to get the interference effects. The interference effects would visibly show up as the electron blips populate the phosphorus screen, as is usual in a double-slit experiment when which-path information is not measured.)  In such a way the person at the photon detectors can send '1's and '0's depending on whether they measure the photons in a given bunch. Suppose they send 'SOS' in Morse code. This requires 9 bunches, and so this will take 900 milliseconds, which is less than 200 years. The point is that such an experiment would only work if you assume that the measurement of the photon really does collapse the wave function nonlocally.


I'm currently studying Cambridge A-Levels Based on the definition of electric field strength in the textbook, in which electric field strength at a point is the force per unit charge exerted on a charge at the point, the equation E = F/Q can be derived. However, there is another formula which can be derived: E = -V/d which I don't know how to derive. Any help would be greatly appreciated, Thanks !

I know gradient shows you the direction in which function is increasing most. So does electric field direction show us in which direction potential energy function is decreasing most....  My efforts : we know electric field lines go from positive to negative charge. So that's where value of electric potential energy function is decreasing. As we know electric field lines show us the electric field direction. So electric field points out the direction in which potential energy function is decreasing so it's the negative gradient vector of the potential energy function. Am I right with this reasoning?


Let's imagine a generator that gives you one of the numbers from $[1; n]$, each with probability $1/n$, whenever you push a button. What is the mean amount of button pushes you need to get all numbers from $1$ to $n$?  I've considered using a Markov chain and computing its absorption time, I couldn't compute the fundamental matrix for this chain.

What is the average number of times it would it take to roll a fair 6-sided die and get all numbers on the die?  The order in which the numbers appear does not matter.  I had this questions explained to me by a professor (not math professor), but it was not clear in the explanation.  We were given the answer $(1-(\frac56)^n)^6 = .5$ or $n = 12.152$  Can someone please explain this to me, possibly with a link to a general topic?


Could someone explain, from a high level overview, the difference between ArcPy and the new ArcGIS API package in Python?

Today I found out about the . I was wondering if you could use this to (eventually) replace ArcPy?  Recently I have been doing analyses that require cloud based solutions. When using AWS, Docker and Jupyter it is very convenient to stick with a Unix based OS such as Ubuntu. However, the Unix alternatives for ArcGIS have their own limitations as well such as the always hard to install python bindings for the  GDAL library. ArcGIS for Python operates cross platform.  Perhaps there are the things I should and should not expect from the ArcGIS API for Python.  Perhaps Arcpy is going to disappear altogether.


I'm trying to make a button type to redirect in an external Url and I don't know how to make it.  I already make the simple Form and I need help for make this function. I'm using Drupal 8 Thanks in advance

Drupal 7 has drupal_goto() that would allow redirecting to an external url.  The change record indicated that ControllerBase::redirect is the method to be called in D8.   This seems to work with internal drupal URLs but throws an error with external http urls -   [12-Nov-2014 21:00:22 Asia/Kolkata] Uncaught PHP Exception Symfony\Component\Routing\Exception\RouteNotFoundException: "Route "https://www.facebook.com/dialog/oaut....." does not exist." at /Applications/MAMP/htdocs/d8/core/lib/Drupal/Core/Routing/RouteProvider.php line 147   What would be the ideal equivalent of drupal_goto in D8 to redirect to an external URL?


I scheduled and ran CHKDSK after restart, but it took a long time, so I left it to run all night. In the morning, it had finished and the computer had logged in, but I had no way of knowing if it found bad sectors or anything.  Is there a log file I can look at?  This is what CHKDSK looks like when running before login:

I recently ran the chkdsk in Windows 7 on my local C: drive. After chkdsk completed, the results flashed on the screen for a few seconds and then the computer booted up. I wasn't able to read the results in time. Are the results saved to a text file somewhere?


I have been trying to run analysis and model a ts series of Natural Gas spot prices. With data provided by the Qandl API.   The whole analysis was working fine, however, I experiences issues with the auto.arima function.  1- If I specify the NG series as XTS, the auto.arima function does not take into account the seasonality. It's quite a bummer for Natural Gas, as the consumption of this resources is all about the time of the year.   2- If I specify the NG series as TS, the auto.arima function takes forever to calculate, and I am not even sure it can finish it. As i let it run the calculation for 20 min once, and it couldn't come with an answer. Hence, I am wondering if there is a problem with my code or my specification.  I'm new to data science, it's my first TS project. I really love what I am doing !   Here is my code:   NG1= Quandl("CHRIS/CME_NG1", start_date =start, end_date =end, type =  type)$Settle prices2returns <- function(x) diff(log(x)) spotprice2returns <- function(x,y) log(x) - log(y) nn=300 r_NG1=xts((NG1),frequency = 300)   **tsrng= xts(r_NG1, frequency = 300)**  NG_model1= auto.arima(tsrng,trace = TRUE, test = "kpss", ic="bic") forecast=forecast(NG_model1, h=100) [![Forecast without seasonality][1]][1] ############################################################# Fitting models using approximations to speed things up...   ARIMA(2,1,2) with drift         : -1746.361  ARIMA(0,1,0) with drift         : -1735.83  ARIMA(1,1,0) with drift         : -1771.906  ARIMA(0,1,1) with drift         : -1773.598  ARIMA(0,1,0)                    : -1744.349  ARIMA(1,1,1) with drift         : -1764.14  ARIMA(0,1,2) with drift         : -1765.134  ARIMA(1,1,2) with drift         : -1755.608  ARIMA(0,1,1)                    : -1782.117  ARIMA(1,1,1)                    : -1772.66  ARIMA(0,1,2)                    : -1773.653  ARIMA(1,1,0)                    : -1780.426  ARIMA(1,1,2)                    : -1764.128   Now re-fitting the best model(s) without approximations...   ARIMA(0,1,1)                    : -1785.296   Best model: ARIMA(0,1,1)                      Series: r_NG1  ARIMA(0,1,1)   Coefficients:           ma1       -0.0966 s.e.   0.0141  sigma^2 estimated as 0.04087:  log likelihood=901.17 AIC=-1798.34   AICc=-1798.33   BIC=-1785.3  Training set error measures:                        ME      RMSE       MAE        MPE     MAPE      MASE         ACF1 Training set 3.216548e-06 0.2021306 0.1179395 -0.0660193 2.448464 0.9986513 0.0003003316  Forecast method: ARIMA(0,1,1)  Model Information: Series: r_NG1  ARIMA(0,1,1)   Coefficients:           ma1       -0.0966 s.e.   0.0141  sigma^2 estimated as 0.04087:  log likelihood=901.17 AIC=-1798.34   AICc=-1798.33   BIC=-1785.3  Error measures:                        ME      RMSE       MAE        MPE     MAPE      MASE         ACF1 Training set 3.216548e-06 0.2021306 0.1179395 -0.0660193 2.448464 0.9986513 0.0003003316  ###############################################################  **tsrng= ts(r_NG1, frequency = 300)**  NG_model2 = auto.arima(tsrng, trace=TRUE, test="kpss", ic="aic",                      stepwise=FALSE, approximation=FALSE, D=1)    # It blocks here, and takes a lot of time to compute the model   NG_frct=forecast(NG_model4,h=100) plot(NG_frct, include = 1500)   What do you suggest I do ?  I was thinking about specifying manually the seasonal arima function, but I lack the skills to do so for now, where should I start to learn how to specify the function myself ?  What did I do wrong in my code?

I'm looking for some forecasting advice when dealing with seasonal time series data that has a large number of observations.  By "large" I only mean a few thousand --- I'm used to such sizes in Data Mining being considered pretty small, but it seems that in time series modeling that's pretty unwieldy for many of the tools I've tried.  For example, here's a toy data set that records an observation once per minute, for five days:  set.seed(123) t <- 1:(5*24*60) x <- ts(15 + 0.001*t + 10*sin(2*pi*t/(length(t)/5)) + rnorm(length(t)), freq=length(t)/5) plot(x, type='l')     (In my real operational data set, the values are observed at irregular intervals, but I've regularized them by doing something like x <- approx(d$t, d$x, xout=1:(5*24*60)) first.  Advice on whether that's advisable, or alternative approaches, is welcome too.)  So the seasonality in this data set has a lag of 1,440 observations, which seems to be way outside the range that things like auto.arima() (in the forecast package) will find:  m1 <- auto.arima(x) plot(forecast(m1))     And I'm not quite sure how to interpret the ets() function here, but it doesn't seem to be able to handle this size data, and it didn't seem to pick up on the seasonality:  > m2 <- ets(x, 'MAZ') > plot(forecast(m2)) Error in forecast.ets(m2) : Forecast horizon out of bounds > m2$method [1] "ETS(M,A,N)"   Where to go from here?  Any suggestions?


What is the difference between $\gg$ and $\gt$ ?  Thank you $\infty$ times.

I saw two less than signs on this Wikipedia article and I was wonder what they meant mathematically.    EDIT: It looks like this can use TeX commands. So I think this is the symbol: $\ll$


In English grammar, to my understanding, it is incorrect to say "this does makes," but I'm not sure why (and nor does my mother, who is an editor).  It is acceptable to say "this makes [sense]," and "this does make [sense]," but why is it not allowable to interchange the two?   What English grammar rule does "this does makes sense" violate? It clearly sounds wrong, but I'm having trouble justifying why.

This morning I read this sentence (see ):     On July 24th and again on July 29th,   Egyptian police did shoot dead unarmed   African migrants attempting to cross   that border.   Why "did shoot" and not "shot"?


Let $ABC$ be a triangle with $AB=AC$. If $D$ is the midpoint of $BC$, $E$ is the foot of the perpendicular drawn from $D$ to $AC$ and $F$ the mid-point of $DE$, prove that $AF$ is perpendicular to $BE$.   (JEE-1989)       I have solved it using coordinate geometry (or rather truthfully, seen the solution), but was wondering if it could be solved by geometry. Thanks in advance.

We have given isosceles triangle $ABC$ with baseline $AB$. Point $M$ is midpoint of AB. Draw perpendicular line to side $AC$ through $M$ which intersects $AC$ in point $H$. Let $P$ be midpoint of $MH$. Show that lines $BH$ and $CP$ are perpendicular to each other.  I also have "hint": Construct height $BD$ to side $AC$ and look at the triangles $ABD$ and $MCH$.  Analytically there is no problem but I get stuck in geometrical approach to solution.


From the research I've done the common answer is that you can not remove insignificant dummy variables from a regression. I'm having a hard time finding academic papers or books that back up this thought. If anyone knows of any papers dealing with this issue or a good place to search through statistics papers that would be great!

After seeking clarification about linear model coefficients  I have a follow up question concerning non-signficant (high p value) for coefficients of factor levels.  Example: If my linear model includes a factor with 10 levels, and only 3 of those levels have significant p values associated with them, when using the model to predict Y can I choose to not include the coefficient term if the subject falls in one of the non-signficant level?  More drastically, would it be wrong to lump the 7 non-significant levels into one level and re-analyze?


In my app, I have a table view with a detail view. The detail view loads blog posts from  and the detail view will display the text from that post. I almost have it working but I still need to figure out how I can fix the text (example below). Here is the code I have to pull the text from the website in the detail view:  -(void)viewDidLoad {                                           //self.url is from the table view where the link to the website is     NSURL *myURL = [NSURL URLWithString: [self.url stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding]];     NSURLRequest *request = [NSURLRequest requestWithURL:myURL];      [self.webView loadRequest:request];      timer = [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:@selector(LoadText) userInfo:nil repeats:YES];  }  -(void)webViewDidLoadText {      NSString *textForBlog = [self.webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByClassName('paragraph')[0].innerHTML;"];      self.textView.text = textForBlog;  }

There are a couple of different ways to remove HTML tags from an NSString in Cocoa.   is to render the string into an NSAttributedString and then grab the rendered text.   is to use NSXMLDocument's -objectByApplyingXSLTString method to apply an XSLT transform that does it.  Unfortunately, the iPhone doesn't support NSAttributedString or NSXMLDocument. There are too many edge cases and malformed HTML documents for me to feel comfortable using regex or NSScanner. Does anyone have a solution to this?  One suggestion has been to simply look for opening and closing tag characters, this method won't work except for very trivial cases.   For example these cases (from the Perl Cookbook chapter on the same subject) would break this method:  <IMG SRC = "foo.gif" ALT = "A > B">  <!-- <A comment> -->  <script>if (a<b && a>c)</script>  <![INCLUDE CDATA [ >>>>>>>>>>>> ]]>


What would be the Big-O for the following function? for a in range(n):         for b in range(n - a):             for c in range(n - b):                 if a + b + c == 0:                     break             if a + b == 0:                 break         if a == 0:             break     return n + 1  I was thinking that it would be O(N^3) since there is a triple nested for loop and each of the components of the for loop would have a Big O of O(N). Is my thinking correct or is there possibly a different Big-O for this function?

Most people with a degree in CS will certainly know what . It helps us to measure how well an algorithm scales.   But I'm curious, how do you calculate or approximate the complexity of your algorithms?


What modifications do phrasal verbs make  There are two sentences     I shaved my beard.      I shaved off my beard/I shaved my beard off.   What is the difference between these two sentences?

Sometimes I read a verb (or adverb) and I get the complete meaning yet I find "Off" (or some other prepositions) follows the verb or adverb.   For example, In the following sentences why do we need an "Off"? what does "off" add to the meaning?     I will shave my beard off. (shave was enough)      Wendy drank half the bottle straight off. (straight was enough)       Treatment should start off with attention to die. (start was enough)      They ended the meal off with coffee and liquids. (ended was enough)      He will drop me off near the station. (drop was enough)   I need the the meaning of "off" here so as to be able to always use  "off" in similar situations. Thanks all


This is my account earlier today:    I was getting extremely sick of getting "You cannot comment because you haven't earned 50 rep" messages which I saw many many times before getting the association bonus, and would generally cause me to close the SE site I was on immediately.  The association bonus feels like it kicked in way too late for me. As you can see I had at least 600 rep across sites, but none over 200. It was a fairly awful user experience, especially not having "Comment Everywhere" everywhere.  I waited until I actually got it before commenting here so I wouldn't be dismissed as trying to be bend the rules or whatever.  Perhaps the bonus could be given in two stages. Or it could weight rep from all the sites you're associated with. Other suggestions?

The stack exchange umbrella is getting wider and for some of us living just on one site is not ideal.    When questions that used to be housed on one board are now housed on two boards.  For example:  could have been put on the Ubuntu site.  By spreading points around different sites it is possible to earn more than double the 200 point barrier and not have the most basic privileges on new sites.  Why have we limited the 100 point bump to just a single site?  I am wondering if there was some reasoning for this not being implemented or if it just hasn't been proposed yet.


In J.R.R Tolkien's, The Lord of the Rings: The Fellowship of the Ring. Frodo sings a song at Bree, that is supposed to be a precursor to the nursery rhyme, 'Hey Diddle Diddle'.  Is there anything else that exists in Tolkien's Middle-Earth work that is designed to be an earlier version of something that exists/existed?   (For example, are there certain cities or land marks that still exist today?)

If The Lord of the Rings and The Silmarillion took place in different ages than us, but on Earth, is there any suggestion in those works that some elements would or could have been immortal or invincible, and therefore lasted into our age (modern times)?   In works like History of Middle Earth did JRR ever hint at something that carried over into our times, beings or geographical features? Did he ever acknowledge a possible carry-over into modern day, or was it only the old ages he wrote about with no hint of the future (our present)?


I have been experimenting with making whole grain sourdough bread at home. My current recipe is for a loaf that is about 4 cups of flour total, not counting sourdough starter, evenly split between bread flour, whole wheat, and dark rye. After preparation and rising, I cook in a dutch oven, with the dough shaped like a long cylinder stretching from one side of the dutch oven to the other, so that it rises into a loaf shape. Cook time is 30 mins with the lid on, then 5 mins uncovered; at 500 F in a conventional oven. After cook time, I immediately take the loaf out of the dutch oven and let it cool on the counter.   This creates a pretty satisfactory loaf of bread; simple to make, tasty enough,  cooked all the way through with a nice crust on the outside. My only issue is that it "burns" on the bottom where the loaf is in contact with the dutch oven. The loaf is slightly blackened on bottom, though that is mostly a cosmetic issue, there is no burnt toast flavor. However, the bottom 1/4 inch of the loaf is very tough and hard to cut when slicing.   I've tried varying cook times and haven't be able to solve this burning problem. What are some tactics that might allow my loaf to cook the same way on the crust and insides, but not burn the bottom as much?

When I bake bread in my dutch oven, to get the bread crust a darker brown and where it should be, the bottom will burn. I've used several recipes and different ovens with the same problem outcome. The dutch oven is as high as I can put it in the oven, which helps but it's still burned slightly.   The recipes always call for a pre-heat of 475F before the bread goes in, 25-30 top on 15-20 top off. I'm trying to adjust the temperature now, but I don't see how this isn't a more common problem. Any suggestions for this?


I have a MeshRenderer mr public variable in script1. I dragged mesh1 from the assets in the mr place in the inspector of script1. mesh1 has a material mat1, I try to change this material to mat2 using this mr.sharedMaterial = mat2; but the material doesn't change. It only changes the material in the assets but not the one in the hierarchy, so in the runtime nothing changes. Any advice please?

Currently, I have an object on the scene, and one in prefab. I want the prefab's script to reference to the object on the scene through the   public GameObject obj;   code. However, when I tried to add the object in the editor, I cant seem to be able to select any objects from the scene, only ones in prefabs.  I am quite new at unity, so am I missing something really basic here?   Thanks for any help!


Having done a fair bit of contest- type math, I was interested in trying to write similar sorts of problems, only to find myself immediately stumped. How does one write "elegant problems" of the kind that are found in the IMO and comparable national mathematics olympiads? Is it a question of just investigating some simple system, finding an interesting problem and solving it, or does one somehow consciously design the "trick" to solving the problem beforehand?

The problems that appear in difficult math competitions such as the IMO or the Putnam exam are usually very difficult and require some ingenuity to solve. They also usually don't look like they can be solved by simply knowing more advanced theory and the such.  How do people typically come up with these problems? Do they arise naturally from advanced mathematics (the somewhat infamous 'grasshopper problem' from the 2009 IMO comes to mind - to my not exactly knowledgeable mind this problem looks like it popped out of basically nowhere)? What is the perspective that mathematicians take when seemingly "inventing" these problems with no theoretical motivation to them whatsoever?


I'm flying into CPH (Copenhagen Airport) and then need to get to Odense, Denmark via train. How do I navigate through CPH (Copenhagen Airport)to the central station to get the right train to Odense?

My son is traveling for the first time by plane, although he is 24 years old. He will travel by plane from Zagreb to Copenhagen (on 28.2.) and he has to take a train to Odense. I'm wondering is it difficult to find train station at the airport (could he walk from terminal 2 do train station) and how he would manage to get on the right train. He has his train ticket already.


I am having a lot of trouble showing that this set is connected. $$\{(x,y,z) \in \mathbb{R}^3 : x^2 + y^2 + z^2 = 1 \}$$  This set contains all of the points on the boundary of a sphere (or the surface, if you like) with a empty core/inside.   What I have tried doing is proving path connectedness, by picking two arbitrary points a and b and defining a map $ [0, 1] $ that maps on S, but I am not sure how to construct such a path since I need to go around the circle. Though a technique I have also tried is going through the sphere and simply projecting every vector on the line onto the sphere (by dividing every point on the line with its norm resulting in a unit vector) - however I am not looking for "tricks" and a rather more robust solution - something that I can learn from. :)  Any help appreciated!

My homework assignment contains the following question:     Prove that $S^n = \{x \mid x \in \mathbb R^{n+1}, d(x,0)=1\}$ is connected.   Can you give me a hint please?  What I can do is nothing..


Using the iOS app, I was checking my achievements, and it showed the reputation from the same  twice. Once before the edit of the parent post's title, and the other text from after. See the screenshot. I (of course) was awarded just the 50 rep from the 5 upvotes.    Having no issues using the website.

Step to reproduce  Answer a question; Answer gets accepted or upvoted; Receive notification in the app; Change the title of the question; Notification is duplicated with updated title.  Expected behavior When going into notifcations you should see only one entry for that reputation event. Actual behavior You get two notification entries. In the screen notice the two entries for the same question, the one related to EF. After answering I have changed the name to make it more searchable for future questions and i've noticed it.      App Version: 1.6.1.2 Device: iPhone 6s OS Version: Version 10.1.1 (Build 14B100)


I have a question which is based on the question . The question reads:     Show that if A is compact, show that $d(x,A)= d(x,a)$ for some $a \in A$.   What if I change the question to     Show that if X is complete and $A \subset X$ is closed, show that $d(x,A)= d(x,a)$ for some $a \in A$.   I'm at a lost here. Can I get a hint? I can't seem to use to hints at the original post. My initial thoughts are to construct a sequence such that it converges to $inf\{d(x,a) | a \in A\}$. However, I need to show that the set $\{d(x,a)|a \in A\}$ contains its $inf$. I'm not sure how to proceed.

If $(X,d)$ is a complete metric space and $A$ is closed in $(X,d)$ then show that for each $x \in X$ there exists an element $a_0 \in A$ such that $d(x,A)=d(x,a_0).$   I tried this problem several times but always got stuck at some point or another. For instance, I initially thought about showing the existence of a Cauchy sequence $(a_n)$ in A such that $d(x,a_n) \to \operatorname{inf}\{d(x,a):a \in A\}=d(x,A)$ and then by completeness of $A$ and by continuity of the function $f(a)=d(x,a)$, to prove the existence of an element $a_0$ in $A$ such that $a_n \to a_0$ which would imply $d(x,a_n)=f(a_n) \to f(a_0)=d(x,a_0)=d(x,A)$. But the problem was that I could not construct such a Cauchy sequence in $A$. All my other attempts have similarly gone in vain.  If anybody has any answer, please reply. Thank you.


In PHP we can call methods dynamically like this:  class Klass{     function method1(){ ... }     function method2(){ ... }     function method3(){ ... }      function methodN(){ ... } }   And I can call dynamically like this:  Klass k = new Klass(); $i = 0; while($i <= N){     k->method{$i}(); }  //or $i = 'anything';     k->$i();   Can anybody please tell me how can I achieve this in JAVA?

If I have two variables:  Object obj; String methodName = "getName";   Without knowing the class of obj, how can I call the method identified by methodName on it?  The method being called has no parameters, and a String return value. It's a getter for a Java bean.


I've created this code in Java which opens a file if it exists in my pc and read from it the number of words. When trying to execute  NUllPointerException occurs in the line "x.hasNext() " eventhough I've created an object of x. Can someone explain this? Notice that the file already exists in my pc  import java.io.*; import java.util.*;  public class nrFjaleve {     private Scanner x;      public void open(){         try{             x=new Scanner(new File("p.txt"));         }         catch(Exception e){             System.out.println("The file doesnt exist");         }     }      public void read()      {         while(x.hasNext()){             int nr=0;             String a = x.next();             nr++;         }     }      public void close() {         x.close();     }        public static void main(String[] args)     {                    nrFjaleve ob=new nrFjaleve();         //ob.exist();         ob.read();         ob.open();         ob.close();     } }

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?