I started to study a cryptographic course and I got stuck on a question about AES: If we take the AES algorithem and only perform mixColumns and addRoundKey operations as well as only using one key instead of a round key. (so all keys are the initial key) describe a "Known Plaintext Attack" on this circumstance. What I know: -That only by using the same key every bit is connected to the cypher text by the second round, even if we didn't take the first 2 operations of the AES. -I need to find the number of operations required to brute force the code with this weakened algorithm. My question: How "mixColumns" and the key works exactly to conceal the cypher, and how many operations it would take to brute force it if I had a message and a matching cypher.

I understand why s-boxes are needed in general especially when ECB mode is used(because of using the same key for encryption of other blocks)but I wonder if it's still relatively secure if we omit S-boxes substitution step in these circumstances  using AES-CTR mode to make sure the same key with the same blocks will encrypt to different ciphertexts if we select a total random key  I'm asking since this way it seems that it's like we encrypting in a similar manner(not exactly) to one-time pad encryption since the result of encryption(that will get x-ored with plaintext) will be random. I know that using S-boxes will increase the security but is this way fine for non-top-secret documents, so we can get some extra performance for like embedded devices, without sacrificing too much in terms of security, also what kind of attacks can be used.


I've got a nice Win10 Tablet/Netbook, but I hate Win10. I tried Installing Ubuntu casually on it, but It couldnt boot from the installation media. I've found out that this has something to do with Windows tablets having a 32bit EFI, but Ubuntu and Grub only supporting either a Bios or a 64bit UEFI. Also there would be driver problems and all if I managed to install it somehow.  Will I soon/ever be able to install Ubuntu on the Win10 Tablet without problems?

I recently purchased a Dell Venue 8 Pro.  I have read online about what it needs in order to boot into Ubuntu or any other Linux distro.  From what I have gathered, what really needs to happen is 32-bit UEFI support.  I got information from several sites, but where it was really summed up was in this previous post:    "Ubuntu has no 32-Bit Uefi installer, ask them to add support, they may listen."  That thread was specifically about getting the Dell Venue 8/11 Pro to boot Linux.  However, there are a slew of new tablets coming out running 32-bit UEFI, and I think this is a trend that is going to continue to grow:  mjg59.dreamwidth.org/26734.html  "UEFI on IA32 isn't going away. It will show up on more embedded systems as time goes on."  Others have tried this before with mixed success, but haven't gotten things to work quite right:    "It doesn’t really work. But it’s interestingly close."  I'm trying to start a thread dedicated thread on 32-Bit UEFI support, because that is the piece that is missing (from what I understand).  I don't really know how to work with this stuff, but I'm hoping that some people who do will read this and either contact canonical or somehow patch Ubuntu (or any other distro, really) to work this way.  Again, I don't really know how to do any of this...I'm just hoping someone can help!  Dell Venue 8, 11 Pro, Toshiba Encore, Acer w3, w4, Lenovo miix, and the asus transformer a100 are all tablets that will be affected by this...I think these are going to be incredibly popular tablets once their prices go down, and I think people are really going to get interested in putting linux on these.  Any help is appreciated, and thank you all so much!  EDIT 4/1/14:  Just booted into Ubuntu on my DV8Pro!  All you have to do is follow the instructions here:    To summarize, what you need to do is download the latest Ubuntu 14 daily build (AMD 64 is what worked for me) and put that on a USB drive via Rufus.  'For “Partition scheme and target system type”, choose “GPT partition scheme for UEFI computer.”' You can get the latest daily build here:   You will need to put the file found below into your EFI/Boot directory:   Disable Secureboot and such--follow the original instructions link if you don't know how.  Then set the USB to boot first in BIOS.  This should get you to GRUB.  The rest I'll quote the original author, it's real straightforward:  In the GRUB menu, highlight “Try Ubuntu”, and press “e” to edit it. In the editing screen, scroll down to the command line options, where it says “quiet splash”. Delete “splash” and replace it with: video=VGA-1:1368x768e reboot=pci,force [EDIT: For those of us using the Dell Venue 8 Pro, you need to use this line instead: video=VGA-1:800x1280e reboot=pci,force That accounts for the different resolution of screen.]  Then press F10 to boot. You should get all the way to the Desktop.  There you have it!  This got me to the Unity Desktop.  Problems:  Wifi is not working, but I used an Ethernet adapter and that seems to work.  I tried rotating the screen, but it throws your touch input off to one side, so I left it.    Make sure to read the tutorial mentioned earlier, it is more comprehensive, even though it is made for the ASUS T100.  If nothing else, the instructions I have provided should be enough just to get you to the Unity Desktop, which for me was amazing!  Hope you too can have the same success and keep building on it!  For what it's worth, someone else did this and posted a youtube video here:


I'm looking for a short story about a two factions engaged in a space war where scientists of one faction figured out a better weapon, but they decided not to waste effort producing it, because, by the end of designing that weapon, they figured out they can actually build an even better weapon. But, once they finished designing that second weapon, they figured they can make an even better one. This repeated until they came to the ultimate weapon, but by which time the other faction already defeated them using the plain old weapons from the beginning of the war.  The story is told from a perspective of an officer of the losing faction explaining why they lost.

I am looking for help to point me out at a very old novel (likely from the '60s) about two empires at interstellar war. When it comes to starships, one is technologically very advanced, and the other has very low and inefficient technology.  The highly advanced empire has apparently strong chances to win the war, in particular considering a new technology they were developing. I remember the technology to work like this: consider the space as a flat surface, and on this surface, a disk around the spaceship. When the technology was turned on, this disk was stretched out, as made of rubber, so that it produced a cone, with the tip being the spaceship. The spaceship was therefore teleported 10 parsec away (if I remember correctly), but retained all the connections to the original position. If the spaceship moved, the cone moved as well. This allowed to move in position among enemy ships completely unnoticed, by stretching while afar, then moving in the proper position 10 parsecs away, then destretching.  Despite this technology, the empire lost the war because of delays. It's a perfect example of how having a disruptive technology does not guarantee to win against the competitors.  I am trying to find out the author and name of this novel, hopefully with the date of publication and in which journal/magazine.


Ran in to this and I can't find documentation explaining the change- why does .push() change an array when it's applied to a new array that is set equal to that original array?   ex:   var arr = [1, 2, 3, 4, 5] var newarr = arr newarr.push(3) console.log(newarr) //returns [1, 2, 3, 4, 5, 3] as expected console.log(arr) //returns [1, 2, 3, 4, 5, 3] as well   What's happening here? I'm not applying any methods to arr (that I can see). It looks like arr and newarr are still linked in a way that doesn't apply to other variables, or .push() is invoking the newarr assignment line somehow?  For contrast, this is analogous to what I was expecting-  var x=6 var y=x y=y*6  console.log(y)  // now 36 console.log(x)  // still six

The primitive types (number, string, etc.) are passed by value, but objects are unknown, because they can be both passed-by-value (in case we consider that a variable holding an object is in fact a reference to the object) and passed-by-reference (when we consider that the variable to the object holds the object itself).  Although it doesn't really matter at the end, I want to know what is the correct way to present the arguments passing conventions. Is there an excerpt from JavaScript specification, which defines what should be the semantics regarding this?


I stumbled on this really nice blog.    It has mentioned- "the linear regression analysis requires all variables to be multivariate normal".  I think the assumption of normal distribution is for the residuals. I understand that skewed data can distort significance tests and it is desirable to have normally distributed data. But can we say "normal distribution of variables" is one of the assumptions of linear regression?  I am confused with this. Could somebody please shed light on this?

I've got a weird question. Assume that you have a small sample where the dependent variable that you're going to analyze with a simple linear model is highly left skewed. Thus you assume that $u$ is not normally distributed, because this would result in normally distributed $y$. But when you compute the QQ-Normal plot there is evidence, that the residuals are normally distributed. Thus anyone can assume that the error term is normally distributed, although $y$ is not. So what does it mean, when the error term seems to be normally distributed, but $y$ does not?


I understand that the official ubuntu website says:     When an Ubuntu release reaches its “end of life” it receives no further maintenance updates, including critical security upgrades. It is highly recommended that you upgrade to a recent version of Ubuntu at this point.   Does it mean that I cannot install anymore packages?  I am using Ubuntu 12.10 (EOL - May, 2014).  When I tried to install tmux, doing  sudo apt-get install tmux   The terminal read:  Reading package lists... Done Building Dependency Tree Reading state information... Done E: Unable to locate package tmux

Recently I have installed an older version of Ubuntu on my old machine. Whenever I try to install any software, I get an error saying it couldn't be found:  $ sudo apt-get install vlc Reading package lists... Done                Building dependency tree        Reading state information... Done     E: Couldn't find package vlc


So, my problem is that I am trying to make a program that increments a number every millisecond, but when I run the code and press the stop incrementing button, it does not do anything to clear the interval. It just continues incrementing, completely ignoring the clearInterval(). I have tried executing the si function in the oc function, but then I thought how stupid that was. I looked online, and I just found how to run a function from another function, but it would not work. Here is the html: <button onclick="oc()">   Start incrementing number </button> <button onclick="si()">   Stop incrementing number </button> <div id="d1">  </div>  And here is the Javascript: function oc() {   var d1 = document.getElementById("d1")   var incremental = 0   var i = setInterval(function() {     incremental++;     d1.innerHTML = "Number: " + incremental   }, 0.01) }  function si() {   clearInterval(i) }  Please make the answer as simple as you can.

What is the scope of variables in javascript? Do they have the same scope inside as opposed to outside a function? Or does it even matter? Also, where are the variables stored if they are defined globally?


I installed Ubuntu 12.04 on my laptop, but now my wifi doesn't work. I installed the additional driver which was just the software modem.   I don't know what else to do about it except for installing the updates, but any time I try, it gets stuck configuring bcmwl-kernel source.   This is my first experience with Ubuntu and I haven't been working with computers for very long, so please speak in simple terms.

I'm having serious problems installing the Broadcom drivers for Ubuntu. It worked perfectly on my previous version, but now, it is impossible.   What are the steps to install Broadcom wireless drivers for a BCM43xx card?  I'm a user with no advance knowledge in Linux, so I would need clear explanations on how to make, compile, etc.    lspci -vnn | grep Network showed:   Broadcom Corporation BCM4322 802.11a/b/g/n Wireless LAN Controller [14e4:432b]      iwconfig showed:  lo        no wireless extensions. eth0      no wireless extensions.   NOTE: Answer below is updated every time new information is added and confirmed working.


There are small extra towels placed on hotel beds despite the normal bathroom towels. What purpose do they serve?

I stayed at hotels in different places, and each hotel provides different set of towels. But sometimes I don't know what is the purpose of each towel!  For example, attached two photos from a en-suite-bathroom in a businesses-European hotel, with 4 different towels.  I think that 1 is to use after shower (large towel) and 3 is used after washing hands. But what is 2 and 4 used for?!


I want to get the round off value of a decimal number Suppose I am getting 24.86 than i want to get 25 as final value

I want to do this using the Math.Round function


I have a query in MySQL which is using group_concat. I want to convert it into a SQL Server query.  select      apj.package_id,      group_concat(DISTINCT concat(asset.asset_id, '-', asset.name) SEPARATOR '||')'asset_names' from      stg.asset_package_join apj (NOLOCK), stg.asset asset (NOLOCK)  where      asset.id = apj.asset_id  group by      apj.package_id   Could you please help me?

I'm trying to migrate a MySQL-based app over to Microsoft SQL Server 2005 (not by choice, but that's life).  In the original app, we used almost entirely ANSI-SQL compliant statements, with one significant exception -- we used MySQL's group_concat function fairly frequently.  group_concat, by the way, does this: given a table of, say, employee names and projects...  SELECT empName, projID FROM project_members;   returns:  ANDY   |  A100 ANDY   |  B391 ANDY   |  X010 TOM    |  A100 TOM    |  A510   ... and here's what you get with group_concat:  SELECT      empName, group_concat(projID SEPARATOR ' / ')  FROM      project_members  GROUP BY      empName;   returns:  ANDY   |  A100 / B391 / X010 TOM    |  A100 / A510   So what I'd like to know is: Is it possible to write, say, a user-defined function in SQL Server which emulates the functionality of group_concat?   I have almost no experience using UDFs, stored procedures, or anything like that, just straight-up SQL, so please err on the side of too much explanation :)


Does anyone know the word for a question asked with the intent to injure or insult?  I know there is term for it, but I can't find it anywhere.  It's driving me crazy.  Example:  Are you blind, or just stupid?    Oh, and it's not rhetorical.  There is a more specific term.  Edit:  It's not sarcasm.  There is an actual grammatical term to describe this sort of question.

When reading some work of a friend, I noticed the sentence "When in doubt ask me". Instead of simply pointing out that it could use a comma after doubt, I read the sentence aloud with no gaps or punctuation, as it is written.  When I was corrected that there should be a pause, I smiled and remarked that there was no punctuation to indicate this and my friend realised their own mistake.  When asked why I didn't just say that, I remarked that I was just being __ for the sake of amusement.  I used "spurious", but having re-read its definition, that is not the correct word to describe the way I acted, because it means: Not being what it purports to be; false or fake: "spurious claims".  I don't think "sarcastic" covers what I did either and I'm at a loss for the word to use.


I took graphic design in school years ago, but have been out of the loop for quite some time. I recently created a vector logo for a friend for their business. I am wondering how to save the files so they have no background around the logo and so they can put on any form for print and rescale it to whatever size they wish. I also would like to give them one for their website. What would you recommend- and how to save it properly if you have specific instructions? I have saves a successful png for web use withough background... as well as an .ai file.

What files should i put in a logo pack to give to clients? Should I put small, medium and large version of my logo as well as the vector file.


I have contacted so far 5 supervisors for my master program that I want to enroll in ( applications open late September and admission January 2017) .   I emailed various faculty in the most polite way possible. Introduced myself, showed that I am interested in pursuing a research career in their field, talked briefly about my achievements  but only one supervisor replied. I am not sure why is this happening ? I have attached my transcript ( I am not a high GPA student but I received excellent grades for my thesis and seminar courses).     I emailed them this week ( and one hardcore researcher last Friday)   what could be the reason ?  note : I am intending to apply for the biomedical engineering program (one I really want to pursue) , most students have engineering undergrad however , I have a biotechnology degree. Could that be the reason? the department said my biotechnology degree is acceptable for that admission purposes.

Most people in research probably have first-hand experience regarding how difficult it is to get some people to reply to emails, e.g. (but not limited to) some reputed professors. It is also difficult to establish how to interpret a lack of response, because the person can be just busy and miss your email (i.e. "save for later" then forget about it) or might be purposely ignoring the email. I find the lack of response particularly annoying when contacting a listed "corresponding author" about their paper.  I have experienced several extremes: professors who reply within hours (or even minutes!); professors who failed to produce any response at all; even once I sent a job query and didn't get a response until after 2-3 months later, when the professor apologized about forgetting to reply and said he was very interested in my application.  The latter case almost cost me a job (luckily I had already secured a position elsewhere), and as it turned out later I could have resolved the situation by sending the professor a reminder that he had not replied to my earlier email. But how could I have interpreted his lack of response as either forgetfulness or disinterest?  The situation is usually better with postdocs and graduate students, who tend to reply, and when they do their replies tend to come faster.  Hence, my questions are:   How to improve the chances of getting a reply to one's email besides the obvious "be brief and to the point" How to interpret the lack of response When is it appropriate to send a reminder and tips to avoid annoying the recipient with it   Edit upon request:  The typical content of the emails I'm referring to would be regarding the work done by the email's recipient or at their lab (questions about papers published by them, for instance). Non-spam job applications or surveying possible collaboration could also be included here.


On a Linux system a C process is started on boot, which creates a fork of itself. It is not a kernal process or something. In most cases a ps -ef show both processes as expecxted, but sometimes it looks like the following:   1258 root       0:00 myproc  1259 root       0:00 [myproc]   i.e. one of the processes surrounded by brackets. According to ps:  If the arguments cannot be located (usually because it has not been set,  as is the case of system processes and/or kernel threads) the command name  is printed within square brackets.   I do not understand what it means when the 'arguments cannot be located'. The process is started always exactly the same, and the fork is always created in the exact same way. How can it happen, that sometimes 'the arguments cannot be located' and sometimes they can?   In addition, the process is always started without any arguments...  Questions I have:    What do those brackets really mean? Does the process run at all when /proc/{pid}/cmdline is empty? Why do I get those brackets sometimes and not always? How/Where to fix this problem?   Additional information:   The process is always started without any arguments! Just the name of the command myproc. The main process seems to run always correct (no brackets around name, executable in /proc/x/cmdline). The child process sometimes has its name in brackets. The content of /proc/child-pid/cmdline of a correct running child process is myproc. The content of /proc/child-pid/cmdline of an incorrect running child process is empty! Again: same code, different child processes!

$ ps -Awwo pid,comm,args   PID COMMAND         COMMAND     1 init            /sbin/init     2 kthreadd        [kthreadd]     3 ksoftirqd/0     [ksoftirqd/0]     5 kworker/u:0     [kworker/u:0]     6 migration/0     [migration/0]     7 cpuset          [cpuset]     8 khelper         [khelper]     9 netns           [netns]    10 sync_supers     [sync_supers]    11 bdi-default     [bdi-default]    12 kintegrityd     [kintegrityd]    13 kblockd         [kblockd]    14 kacpid          [kacpid]    15 kacpi_notify    [kacpi_notify]    16 kacpi_hotplug   [kacpi_hotplug]    17 ata_sff         [ata_sff]    18 khubd           [khubd]   What do the brackets mean? Does args always return the full path to the process command (e.g. /bin/cat)?


I'd like to start by thanking you for your time reading this question and your passion for mathematics.    It would be a pleasant surprise to me if there were a closed form expression for the sum:  $$\sum _{n=1} ^{\infty} \frac{1}{2^n+1}$$  Knowing well that it converges, as term by term, $\frac{1}{2^n+1}<\frac{1}{2^n}$, I searched for a taylor series expansion, I rewrote the expression as $\frac{1}{2^n}-\frac{1}{2^n \cdot (2^n+1)}=\frac {2^{-n}}{1+2^{-n}}=1-\frac {1}{1+2^{-n}}$ in hopes of something, telescoping, nth partial-sum-exposing, or otherwise, all to no avail.     So I ask more accomplished and brilliant minds their thoughts.   Thank goodness for MSE.

Does the convergent infinite sum $$ \sum_{n=0}^{\infty} \frac{1}{2^n + 1} $$ have a closed form solution? Quickly coding this up, the decimal approximation appears to be $1.26449978\ldots$


Does the SIMPLE Recovery Model perform the same transaction logging as FULL Recovery Model? i.e. keep record of each insert/update/delete transaction?  If this is the case, then why should FULL Recovery model be used? In SIMPLE Recovery, Checkpoints run every minute on a busy database, so the data is written to disk.  Where does the data loss potentially occur on SIMPLE Recovery Model?  Thanks!

When should I use the full recovery model and when should I use the simple recovery model for databases?  I always used the full recovery model because it is the default, but today i encountered this error:     Microsoft OLE DB Provider for SQL Server (0x80040E14) The transaction   log for database 'DATABASE NAME' is full. To find out why space in the   log cannot be reused, see the log_reuse_wait_desc column in   sys.databases   The specific database is actually one of the smallest and most inactive databases on my server, so I have no idea how the log can be full on this database, and not the others.  To shrink the log and making the database accessable again, I changed the recovery model from FULL to SIMPLE and shrinked the logical file log, with the following command  alter database myDbName SET recovery simple go dbcc shrinkfile('LOG FILE LOGICAL NAME', 100) go   It helped, but now I need to understand WHY it helped, HOW this situation started and HOW to prevent this in the future?  EDIT:  Every night at 1 o'clock, we are doing a scripted backup of every database on the server. This is being done by a 31 line script where the most important part is  set @Filename = 'D:\backup\' + convert(varchar, getDate(), 112) + ' - ' + @DBName + '.bak' set @Description = 'Full backup of database ' + @Filename BACKUP DATABASE @DBName TO DISK = @Filename WITH INIT , NOUNLOAD , NAME = @Description, NOSKIP , STATS = 10, NOFORMAT   Is the new recovery model and databaseshrink going to be a conflict with this script?  We are not doing any other kind of backup of the databases, and therefore not the transaction logs, should we?


I know this has been asked but I don't see any answers, just comments on the form of the question or responses that don't seem to speak my language.  I unintentionally (yes, I meant to use that word) installed Windows 10 on a HP desktop.  Since then I can't open web pages, can't print my calendar, some programs don't work while others only function on a part time basis and many other glitches that prevent me from doing my work.    After the install I saw a message that said the old files would remain for 30 days then be deleted.  I presumed that meant I could switch back.  I can't continue to function without a computer.

I joined in the  and I don't like it. However, this question may also be relevant to those who install the full version of Windows 10.  How can I downgrade back to Windows 8/7 from Windows 10 or Windows 10 preview?


I'm new to clustering concepts. I would like to know more parallel processing with multiple DB nodes to have load balancing for the incoming requests. Our main goal is to achieve performance and lot of queries held in queue that come from for BI applications.   Is there any built in mechanism in SQL server to redirect requests to secondary node? We have huge volume of queries that runs on specific day and we need to distribute to secondary node.  We have SQL server 2012 in place and one database server up and running.

Is it possible to scale-out a SQL Server database?  There are some solutions for , but is there a solution for load balancing and horizontal partitioning on SQL Server?  There are some in , but not in a standalone SQL Server instance...


How do I remove the chunky, waste-of-space Google search widget at the top of every home screen? And if I do, can I put apps there instead? I know I can add and remove Google widgets on the main home screen:  Note: I am not willing to root it.

I have been reading for days about how to remove the Google Search Bar from the top of my Nexus 6 since I never use it. I have gotten mixed answers on exactly what file to delete and where it is.  I have heard quicksearchbar.apk but it's not in /system/app like in previous versions. Does anybody know where the file/files are I need to delete in order to get rid of the search bar, or else, how to remove it? Preferably not downloading another launcher, since I don't want to bloat my phone when I could reduce the size.


Hi I am curious to know why dark matter forms a halo? Or why doesn't normal matter form a halo.What is the difference between the two  My level is amateur

I'm a complete layperson. As I understand, dark matter theoretically only interacts with the gravitational force, and doesn't interact with the other three fundamental forces: weak nuclear force, strong nuclear force, and electromagnetism.  Those are my understandings going in. If I'm wrong, please correct me. I've done some googling, and I haven't found anything confirming or denying that dark matter is affected by either of the fundamental nuclear forces.  So since dark matter only interacts with gravity, what causes any dark matter particle to be repelled from another? If they can pass freely through each other, and they are gravitationaly attracted to each other, why don't such particles clump together in a single 'point' in space?   It seems to me that particles occupying a single 'space' are philosophically not distinct particles, but I don't know how actual physics would play into this.  Edit , author's credentials unknown, but implicitly claims to be a physicist or astronomer, says "...[P]hysicists generally take all dark matter to be composed of a single type of particle that essentially interacts only through gravity."  Edit 2 The author is this , "Professor of Science on the physics faculty of Harvard University."


I purchased a laptop which was pre installed with Ubuntu 13.10. With whole drive of 350 GB as a one partition (there is an extended swap partition of 2GB)  I want to install windows 7 with dual boot as well as make one partition for data.  How can I do this.??   Gparted can not unmount the drive so I can repartition it. Live CD not booting so that I used Gparted through it. Why it is not booting? (By the way I'm trying ubuntu 12.04 CD as a live CD)

I have Ubuntu on my laptop. Now I want install Windows 7 in a dual-boot. How can I do this? I can't lose my Ubuntu files, and I'm afraid that I might break . Go  for UEFI only!


Let $X$ be a random variable geometrically distributed. I have known that geometric distribution is memoryless which means  $P(X>i+j|X>i)=P(X>j)$.  Now I want to compute the value of $E(X(X-1)(X-2)...(X-r+1))=\frac{r!p^r}{(1-p)^r}$.  I see the answer from this post below. But I really don't understand what does $U$ in this answer mean. Is there another way to interpret the solution?

How can one use memorylessness and the  and the  to find the expectation and variance of the geometric distribution?  I will post my own answer, but as always, that shouldn't stop anyone else from posting theirs.


Before you guys close this question as duplicate, I did go through  and nothing solves my problem there.  When I try to upgrade my ubuntu 12.10 installation it says      The software on this computer is up to date.      There are no upgrades available for your system. The upgrade will now   be canceled.   Here's a snapshot:    Question: how to fix this issue and upgrade 12.10 to 13.04?  Update  I tried @montazeri's command and cated release file. Here's the output:

I am using Ubuntu 12.10.  Please outline the different ways I can upgrade to 13.04.


$a, b, c$ are natural numbers such that $1/a + 1/b = 1/c$ and $gcd(a,b,c)=1$. Prove $a+b$ is a perfect square.

If $1/a  +  1/b  =  1 /c$   where $a, b, c$ are positive integers with no common factor, $(a + b)$ is the square of an integer.  I found this question in RMO 1992 paper !  Can anyone help me to prove this ?  May be it's too easy and simple . But , I'm just novice in number theory !


I found that the Elasticsearch query doesn't accept a lot of characters due its regular expression processment, and this is messing me up.  On :     Reserved charactersedit If you need to use any of the characters which   function as operators in your query itself (and not as operators),   then you should escape them with a leading backslash. For instance, to   search for (1+1)=2, you would need to write your query as (1+1)\=2.      The reserved characters are: + - = && || > < ! ( ) { } [ ] ^ " ~ * ? :   \ /      Failing to escape these special characters correctly could lead to a   syntax error which prevents your query from running.   I already tried to avoid this error but by pre-processing the test on Python but still didn't solve. I tried the following:  def strip_accents(s):    return ''.join(c for c in unicodedata.normalize('NFD', s)                   if unicodedata.category(c) != 'Mn') ::          eval_file_content = eval_file_content.replace('"', '\\"')         eval_file_content = eval_file_content.replace("'", "\\'")         eval_file_content = eval_file_content.replace("-", "\-")         eval_file_content = eval_file_content.replace("+", "\+")         eval_file_content = eval_file_content.replace("&&", "\&&")         eval_file_content = eval_file_content.replace("||", "\||")         eval_file_content = eval_file_content.replace("<", "\<")         eval_file_content = eval_file_content.replace(">", "\>")         eval_file_content = eval_file_content.replace("!", "\!")         eval_file_content = eval_file_content.replace("(", "\(")         eval_file_content = eval_file_content.replace(")", "\)")         eval_file_content = eval_file_content.replace("{", "\{")         eval_file_content = eval_file_content.replace("}", "\}")         eval_file_content = eval_file_content.replace("[", "\[")         eval_file_content = eval_file_content.replace("]", "\]")         eval_file_content = eval_file_content.replace("^", "\^")         eval_file_content = eval_file_content.replace("~", "\~")         eval_file_content = eval_file_content.replace("*", "\*")         eval_file_content = eval_file_content.replace("?", "\?")         eval_file_content = eval_file_content.replace(":", "\:")         eval_file_content = eval_file_content.replace("\\", "\\\\")         eval_file_content = eval_file_content.replace("/", "\/")         eval_file_content = strip_accents(eval_file_content)         eval_file_content = eval_file_content.encode("ascii", errors="ignore").decode()   How can I solve this? Here's an example of "before and after" pre-processing:    For the query, I'm using the following method:  searchQuery = "http://localhost:9200/metis/ER/_search?q='" + eval_file_content + "'"         res = requests.get(searchQuery).content   The request error:  b'{"error":{"root_cause":[{"type":"query_shard_exception","reason":"Failed to parse query [\'the pmNrOfIpTermsRej of VMGW increasing  \\n1.the VMGW1_LFGS8 of LFGM3 pmNrOfIpT'

I want to use input from a user as a regex pattern for a search over some text.  It works, but how I can handle cases where user puts characters that have meaning in regex? For example, the user wants to search for Word (s): regex engine will take the (s) as a group.  I want it to treat it like a string "(s)" .  I can run replace on user input and replace the ( with \( and the ) with \) but the problem is I will need to do replace for every possible regex symbol. Do you know some better way ?


UPDATING: My version of Mysql is now 5.7.23 , i have followed all the instructions of the link above. The charset of all the database, all the tables and the columns is now utf8mb4.  Before every query there is:  mysqli_set_charset($link, 'utf8mb4');  Despite this, i have still problem displaying in the browser the Spanish chars.  My Question:  I know that this is a very common question on Stackoverflow, but i have already looked for a solution and i have implemented all the strategies to solve this problem without success.  I am developing a Spanish Website, on localhost everything is working fine but when i upload the website, i cant see the Spanish characters like ñ for example. I see instead of them the following question mark: �  I precise that:   After <head> there is <meta charset="UTF-8"> In all the PHP files, in the first line of code there is: header('Content-Type: text/html; charset=utf-8')before any further header is sent. Before every Mysql query there is mysqli_set_charset( $conn,'UTF8') All the database, the tables and also columns are set to utf8 In php.ini there is default_charset = "utf-8"  UPDATING:   The problem seems related to the database, if i put the following file online i can see the charñ without problems, but if the same city come from the database i see �.  <html>  <head>   <meta charset="UTF-8"> </head>   <body>    A Coruña  </body> </html>   More info about my database:  mysql> SELECT default_character_set_name FROM information_schema.SCHEMATA -> WHERE schema_name = "mydb";  +----------------------------+ | default_character_set_name | +----------------------------+ | utf8                       | +----------------------------+   And as i have written, all the tables and also columns are set to utf8. I am querying the DB with the following code:  $chandle = @mysqli_connect($dbhost, $dbuser, $dbpass,$dbname) or die("Connection Failure to Database");  mysqli_set_charset( $chandle,'UTF8');  $result=@mysqli_query($chandle,$q) ;    Anyway, executing Curl on the page that gives the encoding problems, these are the headers:  HTTP/1.1 200 OK Server: nginx Date: Wed, 29 Aug 2018 08:12:31 GMT Content-Type: text/html Transfer-Encoding: chunked Connection: keep-alive X-Powered-By: PHP/5.3.3 Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache X-Powered-By: PleskLin X-Robots-Tag: noindex,nofollow

I'm setting up a new server and want to support UTF-8 fully in my web application. I have tried this in the past on existing servers and always seem to end up having to fall back to ISO-8859-1.  Where exactly do I need to set the encoding/charsets? I'm aware that I need to configure Apache, MySQL, and PHP to do this — is there some standard checklist I can follow, or perhaps troubleshoot where the mismatches occur?  This is for a new Linux server, running MySQL 5, PHP, 5 and Apache 2.


Why are they asking me for this? What is it used for?  EDIT: Some have suggested that this is a recent effort to encrypt all of the iCloud data:

During iPhone update to iOS 10.3.1, I was asked for my password using the correct machine name for my Mac mini. To be clear, the request was not for my iCloud password, my actual local user account password for macOS. This can also happen in the other direction - setting up a Mac may ask for verification for you to enter your iPhone / iPad passcode (and not your iCloud password)  I could not find any information about this kind of access. I was thinking it was security for iCloud and possibly related to two step authorization or two factor authorization. This is the first time I can think of that I entered a desktop password outside of that actual desktop.  I don't have a screen shot but I recall an implication that some files in my Mac are encrypted and need my password. '... need to enter the password for .'   Are there settings I can I control this assuming it's a legitimate part of iCloud setup process or iOS setup process?


What is the difference between framerate independent vs framerate dependent?  Can you please give an example.

Should a game loop be based on fixed or variable time steps?  Is one always superior, or does the right choice vary by game?  Variable time step  Physics updates are passed a "time elapsed since last update" argument and are hence framerate-dependent.  This may mean doing calculations as position += distancePerSecond * timeElapsed.  Pros: smooth, easier to to code  Cons: non-deterministic, unpredictable at very small or large steps   example:  while( game_is_running ) {     prev_frame_tick = curr_frame_tick;     curr_frame_tick = GetTickCount();     update( curr_frame_tick - prev_frame_tick );     render(); }   Fixed time step  Updates might not even accept a "time elapsed", as they assume each update is for a fixed time period.  Calculations may be done as position += distancePerUpdate.  The example includes an interpolation during render.  Pros: predictable, deterministic (easier to network sync?), clearer calculation code  Cons: not synced to monitor v-sync (causes jittery graphics unless you interpolate), limited max frame rate (unless you interpolate), hard to work within frameworks that assume variable time steps (like  or )   example:  while( game_is_running ) {     while( GetTickCount() > next_game_tick ) {         update();         next_game_tick += SKIP_TICKS;     }     interpolation = float( GetTickCount() + SKIP_TICKS - next_game_tick )                     / float( SKIP_TICKS );     render( interpolation ); }   Some resources     —allegedly a reason  is frame-locked to 60fps? Flixel requires a variable timestep (I think this is determined by Flash) whereas  allows both types.  suggests it uses constant time steps.


I had a website that I actively used from about 2/2014 through 10/2014. The site is www.tatumparnell.com. It was a collection of personal stories which mean the world to me, but the site is now down and the website builder can't recover it due to the time lapsed (over 30 days).  I had it backed up to a computer, not the cloud, and that computer is no longer in my possession. My fault, no lecture necessary.  I'm a novice in this area and I'm hoping someone can help. I've contacted some of my followers to check the cached pages from their devices, but most have new devices since then and the others didn't find the content. And I can't find a simple way for iPad users to check for cached pages. I want to start a site again but can't properly recreate the content. Is there any hope?

I have a bit of a problem. My client is running a Joomla 1.0 site and some content (text) was lost. There was no backup configured of the MySQL database. The content was lost approx. around the 16:th of December 2012. I tried finding the old site by using the Web Archive, but no cigar. The site is not even indexed.  I tried to retrieve it via Google cache instead. The cached page itself didn't have the content, but the preview screenshot of the website had the old content. I wrote everything I could read off the screenshot. However, there was content below the screenshot that could not be retrieved.  Here is what I typed into Google Search to find the old page:  site:gerami.se previous ass   Ass = assignments for those wondering ;)  I would really like to get the rest of the text that was below the screenshot when it was taken.  P.S: Whether this thread gets a solution or not, the moral of the story is still the same: Backup is your friend!


Which one is correct and why?   Appropriate management and supervision of tourism centers is essential. Appropriate management and supervision of tourism centers are essential.

I was surfing the internet the other day when I found this phrase: Instead your precious time and attention is wasted. To my ears, it sounds wrong. But I'm not a native English speaker, so I consulted with a number of them, and some of them said that it was "is" because the adjective modifies only the noun "time" and not "attention". Others said it "is" because that's just how it is. But I still believe it should be "are". Any help is appreciated.


So, I have a Windows Laptop - Dell XPS 15 (L502X) and a lot of time I have to work on Linux environment. But the thing is that On Linux i have to have some virtual environments running with Vagrant and Virtualbox. Now, I can't run a Virtual Linux environment under my Windows OS and then have another Virtual environment under the Virtual Linux environment.  The only choice i have is to -    Either remove the Windows OS from my Dell Laptop, but when i tried doing so, the machine went unstable and the drivers were not working. The fan was always running at full speed and my laptop became very hot. Now, the only solution is that i have to buy a new computer and then install Ubuntu on it.   The problem however is that I want to have just one desk for both of the systems.  I want to be able to work with just one KEYBOARD and one MOUSE and i want to be able to switch between systems on two different machines whenever i want.  Is there any way i can do that. Because having two KEYBOARDS and MOUSE on a single desk looks weird and there isn't any space to put them either. Also, if  i have two keyboards and mouse i either have to move myself or move the keyboards and mouse whenever i want to switch machines.  Any help is appreciated.

I love my Filco keyboard, I use it as primary keyboard for my Lenovo thinkpad all time. Now Im moving into the mac world and wonder:  is it possible to split my USB keyboard between two USB ports, ie one at my lenovo and one at my new iMac.   I was thinking that maybe there exists some kind of box with a switch to decide which port should receive the input, or preferable it would be possible to switch between the two via a keyboard shortcut.


I have this following code:      class NumberAdder:         def adder(self, *args):             self.sum = 0             for i in args:                 self.sum += i             return self.sum      class StringAdder:         def adder(self, *args):             self.word = []             for i in list(args):                 self.word.append(i)             print(self.word)      class ThingsAdder:         def __init__(self, *args):             self.box = args         def stringAdder(self):             a = StringAdder()             a.adder(self.box)          def numberAdder(self):             a = NumberAdder()             a.adder(self.box)      c = ThingsAdder(1,2,3,4,5,6,9)     c.numberAdder()   The problem is as you can see i assign *args to another *args. What should i do to make *args in NumberAdder class receive unpacked (not in form of tuple) arguments ?

In the following method definitions, what does the * and ** do for param2?  def foo(param1, *param2): def bar(param1, **param2):


Disclaimer: I don't know anything about graphic desiging.  Hi all, I was going through some web designs on dribbble.com. Most of them had a peculiar type of images in their hero area :          What are these types of images called ?   How can I make them ?

I have seen lots of UI designer nowadays including this kind of illustration i want to know the name of this style so that i can also learn and try this in my designs.


I have nginx running on my CentOS 7 machine. Every day I run a cron job that generates new Diffie-Hellman parameters. They are saved in /etc/ssl/dh/dhparam.pem. But SELinux is preventing nginx from reading this file.  This is the line in the nginx error log:  nginx[3189]: nginx: [emerg] BIO_new_file("/etc/ssl/dh/dhparam.pem") failed (SSL: error:0200100D:system library:fopen:Permission denied:fopen('/etc/ssl/dh/dhparam.pem','r') error:2006D002:BIO routines:BIO_new_file:system lib)  This is the audit log:  type=AVC msg=audit(1473285202.181:334): avc:  denied  { open } for  pid=1393 comm="nginx" path="/etc/ssl/dh/dhparam.pem" dev="dm-1" ino=101646309 scontext=system_u:system_r:httpd_t:s0 tcontext=unconfined_u:object_r:user_tmp_t:s0 tclass=file type=AVC msg=audit(1473285832.647:743): avc:  denied  { open } for  pid=2958 comm="nginx" path="/etc/ssl/dh/dhparam.pem" dev="dm-1" ino=101646309 scontext=system_u:system_r:httpd_t:s0 tcontext=unconfined_u:object_r:user_tmp_t:s0 tclass=file type=AVC msg=audit(1473287010.821:803): avc:  denied  { open } for  pid=3083 comm="nginx" path="/etc/ssl/dh/dhparam.pem" dev="dm-1" ino=101646316 scontext=system_u:system_r:httpd_t:s0 tcontext=unconfined_u:object_r:user_tmp_t:s0 tclass=file type=AVC msg=audit(1473287142.871:826): avc:  denied  { open } for  pid=3118 comm="nginx" path="/etc/ssl/dh/dhparam.pem" dev="dm-1" ino=101646309 scontext=system_u:system_r:httpd_t:s0 tcontext=unconfined_u:object_r:user_tmp_t:s0 tclass=file type=AVC msg=audit(1473287172.480:843): avc:  denied  { open } for  pid=3134 comm="nginx" path="/etc/ssl/dh/dhparam.pem" dev="dm-1" ino=101646309 scontext=system_u:system_r:httpd_t:s0 tcontext=unconfined_u:object_r:user_tmp_t:s0 tclass=file type=AVC msg=audit(1473287681.994:866): avc:  denied  { open } for  pid=3189 comm="nginx" path="/etc/ssl/dh/dhparam.pem" dev="dm-1" ino=101646309 scontext=system_u:system_r:httpd_t:s0 tcontext=unconfined_u:object_r:user_tmp_t:s0 tclass=file   I'm not very familiar with SELinux (I know I should learn that): How can I grant nginx access without disabeling SELinux (or setting it to permissive)?

I've got this one file, favicon.ico. It's actually a large group of nested files, but purely for example, just this one.  If I do cp favicon.ico favicon2.ico, Apache can read the second one just fine.  If I do mv favicon.ico favicon3.ico, Apache throws a 403 on favicon3.ico.  If I su apache, I can read the file as apache.  stat says both files are identical, except for the inode number.  Is there some hidden flag somewhere or something that I'm missing? I've never seen anything like this.  error_log says (13)Permission denied: access to /favicon3.ico denied


On tree structure website there's always the problem of what contents to put in the parent page, you know, the page that exists only as a point to subpages to attach.    Write some general descriptive text of what to expect on the sub pages?  Write "click menu on the left"? Generate/duplicate submenu on the page content area? Leave completely empty? Something else?   And of course there is the functionality of skipping the parent page altogether, just automatically jump to the first subpage.  Number one has been my preferred choice, but no solution seem free of problems.  Is there a patented solution to this problem that I have missed?

OK, here's the situation: A reasonably simple website with a primary navigation menu including drop-down list of sublevels on hover. Each navigation level may have 3 - 6 sublevels below it, none more important than the other. For example see this mockup:    My question is: What should happen if the user Clicks on one of the primary navigation options (such as 'News') instead of just hovering over and choosing a sublevel?  My instinct tells me that I should allow a click of this navigation option; it's expected user behavior to be able to click navigation options. If clicked then a landing page of some sort will be present listing all the sublevels (latest news, blog posts, case studies'). However there is no content to add to this landing page other than presenting a list of links, which is pretty useless. I could pad it out by adding iconography and descriptions of the sublevels, but that's just content for the sake of it; does 'Latest News' really need a description in order to understand what it is?  If I don't include a landing page then clicking this primary navigation will have to open something but if I open the 'Latest News' page that risks the user not knowing about the other sections of the site.  (The landing page will be useful for breadcrumb navigation too, so I don't really want to do away with it).  Is my thinking that a landing page showing the list of sublevels actually useful even though there is no actual content to display, or is there a better alternative to go with?


What elementary number theory methods can I use for solving this type of questions? One of these kind of problems is to find $x$ where $985242x6565 = 172195\cdot 572167$ without multiplying the numbers again. I tried doing, let's call $985242x6565$ $N$, $N\text{mod}10^5$ to somehow get to the $5th$ digit but this is doesn't get me anywhere and in hindsight it doesn't make any sense. How should I proceed?

David Burton Elementary Number Theory Revised Printing question 4.3.5(a) is as follows:  Using the 9-test or 11-test, find the missing digits in the calculations below:  $(52817 * 3212146) = 169655x15282$  I can tell the number of the right isn't divisible by 9 or 11 since 5+2+8+1+7 = 23 and 3+2+1+2+1+4+6=19 are both not a multiple of 9 while 5-2+8-1+7=17 and 3-2+1-2+1-4+6=3 are both not a multiple of 11 so neither of the factors of 169655x15282 have 9 or 11 as factors.  Thus, $1+6+9+6+5+5+x+1+5+2+8+2 \not \equiv 0$ (mod 9) and $1-6+9-6+5-5+x-1+5-2+8-2 \not \equiv 0$ (mod 11)  so $x \ne 4$ and $x \ne 5$  Now, if I simply multiply 52817 by 3212146, I can see that $x = 9$ but I'm not sure how to get there from what I have.    How might I bridge this gap or is this just a typo in the text? Later editions seem to have altered the numbers involved.  Thanks


The Axiom of Specification says that:  For a set $ A$ and objects $x\in A$,for any object $y$ there exists a set: $$ y \in \{x: P(x) \wedge x \in A\} \implies y \in A \text{ and } P(y)$$  Where $P(x)$ is a statement pertaining to $x$.  The Axiom of Replacement says that:  For a set $ A$ and objects $x\in A$,for any object y, suppose we have a statement $P(x,y)$, pertaining to $x$ and $y$ such that for each $x$ there is at most one $y$ for which $P(x,y)$ is  true, then there exists a set, such that for any object  z, $$ z\in \{y:P(x,y) \text{ s.t } x \in A \} \implies P(x,z) \text{ for } x \in A$$  I can see that the AOR is stronger than the AOS. If we let $P(x,y)$ be whether $y$ is in the same set as $x$ then $P(x,y)$ is a true of false statement and hence it will follow that if $P(x,y)$ is true then $ y \in A \text{ and } P(y)$. Does this hold any water?  I have sketched diagrams, to try and motivate a solution but have failed.  I am editing this question simply because I don't understand the answers to the other posts. ( I have tried...) So I am going to add an answer to mine.  MY ATTEMPT:  Let A be a set, then for any object $y$ let $\gamma$ be defined as follows:  $$\gamma(x) = x \text{ if } \theta(x) \text{ for } x \in A$$ $$\gamma(x) = y \text{ if } !\theta(x) \text{ for } x \in A$$  Then by the Axiom of replacement There exists a set $B$ such that  $$B = \{\gamma(x): x \in A, \gamma(x) = x\} = \{x:\theta(x), x \in A\}$$  The last set in the above statement implies the Axiom of separation.

It has come to my attention that the pairing axiom and the separation axiom schema are rarely listed since they follows from the replacement axioms. I see how this works for the pairing axiom, since we can take some set, say $A=\{\emptyset,\{\emptyset\}\}$, which exists by the power set axiom and the existence of the emptyset, and define a nominating formula on $A$ by $$ \phi(u,v)\colon (u=\emptyset\land v=a)\lor(u\neq\emptyset\land v=b) $$ to see that $\{a,b\}$ is a set for any sets $a$ and $b$. However, I don't see it for the separation schema. Could someone enlighten me on how they follow? Thanks.


I'm pretty new to python. And I have a question.    def set_man(self, new_pos):     if new_pos is 'left' or 'right' or 'boat':         self.man = new_pos         return True     else:         return False   will this work? Or do i need to call if new_pos for each or?

My  has failed me.  In Python, are the following two tests for equality equivalent?  n = 5 # Test one. if n == 5:     print 'Yay!'  # Test two. if n is 5:     print 'Yay!'   Does this hold true for objects where you would be comparing instances (a list say)?  Okay, so this kind of answers my question:  L = [] L.append(1) if L == [1]:     print 'Yay!' # Holds true, but...  if L is [1]:     print 'Yay!' # Doesn't.   So == tests value where is tests to see if they are the same object?


I'm running Ubuntu 16 and i want to install libsodium library.  here's what i have tried:  apt-get update apt-get install libsodium   but the libsodium they have is outdated when i do apt-get.  they have the latest libsodium here:   it is called "LATEST.tar.gz". sorry im new to this but how do i install libsodium from the new source rather than the old one from apt-get?

I have downloaded tar.gz files. But I don't know how to install it. How do I install this kind of file?


I am a working on designing a network for a new volunteer ambulance headquarters.  I am trying to decide if I should use Sub nets and how to group them. As of now the network load is going to be made up of, 36 IP based security cameras, around 20 ip phone extensions,  1 server that holds all the call report data, IP camera server, 7 work stations, 2 network printers, WIFI for 3 call  reporting devices to connect to the server, separate WIFI for public usage, access control doors and the HVAC system talks to all of the different parts over the network.

This is a  about IPv4 Subnets.      Related:               How does Subnetting Work, and How do you do it by hand or in your head?  Can someone explain both conceptually and with several examples? Server Fault gets lots of subnetting homework questions, so we could use an answer to point them to on Server Fault itself.   If I have a network, how do I figure out how to split it up? If I am given a netmask, how do I know what the network Range is for it? Sometimes there is a slash followed by a number, what is that number? Sometimes there is a subnet mask, but also a wildcard mask, they seem like the same thing but they are different? Someone mentioned something about knowing binary for this?


I have not yet finished the books, but I have seen the films, and in the final film, I think I saw the trio run past Lavender in the courtyard as someone drank her blood.  Is this correct?    DVK's answer to  states that she died, but what actually happened to Lavender? Is it different in the books?

Which Harry Potter characters appear in all seven books, only to die in book seven? [MAJOR SPOILERS/CHARACTER DEATHS]  I can go either way on       Harry,   depending on your interpretation of the King's Cross chapter in Deathly Hallows.      Some feel he died; other believe it was more along the lines of a near-death experience. I'll accept either interpretation.     I'm not requesting this, but just as an FYI: It's fun to try and answer questions like this from memory before hitting up canon. This is not a list question, as there is a finite number of characters who fit the question's criteria.   ★ I'm looking for a canon-based answer (the seven Harry Potter novels, the three supplemental books, J.K. Rowling interviews, and Pottermore) and do not prefer an answer from either the HP Wikia or the Wikipedia.  NOTE: A few months ago I got an email from a fellow SFF.se user about the Harry Potter questions on the site. Now, I cannot find her email :/ She asked me this question as a personal challenge and I put it onto the back burner, but today I decided I would post it here and see if the user who emailed me will comment so I can fully credit her for the question.


I am having this microcontroller -   I want to use the FIRC and want to see the frequency tolerance of the FIRC. Can someone help to find how to find the frequency tolerances of the internal clocks? Like SIRC, FIRC and the clock that can obtained after the PLL? I couldn't find the frequency tolerances of the internal clocks

I am having this microcontroller -   I am using an 8MHz external clock. I want to calculate the Bit error rate of my LIN Communication. My LIN Communication Baud rate is 19.2kbps. My questions :  Can I use the LPUART Module in the Mirocontroller for the LIN Communication?  How to find the Bit error rate for the LIN Protocol communication for my baud rate of 19.2kbps and external clock of 8MHz.   I found this below from the reference manual. But not sure, how to calculate the Bit error rate from this.   How to calculate the SBR Register value, OSR and the LPUART ASYNCH Module clock?  Please help


I've modified org/gnome/desktop/app-folders/folder-children to be equal to [] and whenever I reboot or log out, it gets reset to ['Utilities', 'Sundry', 'YaST']. This is really annoying because I don't want any folders in my Applications Menu.

I can use the dconf-editor to change my touchpad settings to natural scrolling, but upon system restart the settings get reverted. (But not on sleep or hibernate.) When I open the editor, the option is still orange indicating it has been changed. when I uncheck and recheck the natural scroll option, it is re-enabled. Is there a fix, or am I changing the wrong option? The path is org > gnome > settings-daemon > peripherals > touchpad > natural-scroll.  Currently running 13.10


How can I format ( delete all files ) an USB Flash Drives with the command prompt ?  I have the last version of Windows 10 and my USB Flash Drives is fat32.

I was trying to put the  onto a thumb drive, when I was asked if I was OK with wiping it (I said yes I as it was blank).  I had to sleep my computer during the wiping, and now I can't do anything with my dive.  When I put it into my computer:    When I click format disk:    In short, the disk never reformats (I get an error message letting me know that Windows was unable to format the drive).  Whats going on, and how do I fix it?


I am unable to solve this limit of integral asked in a quiz and so looking for help here.  Question : Let $f:[0,1]\to \mathbb{R}$ be a continuous function. Then what is the following limit: $\lim_{n \to \infty} \int_{0}^{1} n x^n f(x) dx $. Give the reasons.  If $n {x}^n f(x) $ was uniformly convegent then $\lim_{n \to \infty }$ could be taken inside the integral  but there is not enough information regarding the behaviour of $f(x)$ to check for uniform convergence. So, Kindly tell how should I proceed. Thanks!!

$\mathbf{Question}:$ Let $f$ be a continuous function on $[0,1]$. Then prove that the limit $\lim_{n \to \infty} \int_0^1{nx^nf(x)}dx$ is equal to $f(1)$.   $\mathbf{Attempt}$: First, we try to show that the sequence of functions $\{nx^nf(x)\}_{x\in [0,1]}$ is uniformly convergent to $0$ on the restricted domain $[0,1-\epsilon]$, $0<\epsilon<1$.   Let $\sup_{x\in[0,1]}f(x)= \mathcal{M}$. Then $|{nx^nf(x)}|\leq n(1-\epsilon)^n|\mathcal{M}|$ for any $x$ and $n(1-\epsilon)^n \to 0$ as $n\to \infty$.  Thereby, $\lim_{n \to \infty}\int_0^{1-\epsilon}nx^nf(x)dx=\int_0^{1-\epsilon}{\lim_{n \to \infty} }nx^nf(x)dx=0$  Now, denote $\sup_{x\in [1-\epsilon,1]} f(x)=M(\epsilon)$ and $\inf_{x\in[1-\epsilon,1]}f(x)=m(\epsilon)$.  $\int_{1-\epsilon}^1nx^n\ m(\epsilon)dx\leq\int_{1-\epsilon}^{1}nx^nf(x)dx\leq \int_{1-\epsilon}^1 nx^n\ M(\epsilon)dx$.  Now,  $\lim_{n \to \infty}\int_{1-\epsilon}^1 nx^n\ M(\epsilon)dx =\displaystyle \lim_{n\to\infty}\bigg[ \frac{nx^{n+1}}{n+1}M(\epsilon)\bigg]_{1-\epsilon}^1=M(\epsilon)$ [Similarly the other one is $m(\epsilon)$]  Clearly, as $\epsilon \to 0 , \ \ M(\epsilon), m(\epsilon) \to f(1)$, so $\lim_{n \to \infty} \int_0^1{nx^nf(x)}dx=f(1)$.  Is the procedure correct? Kindly verify.


Sometimes when I google something, I notice that some websites are shown with some several pages as results. Like in the picture here :    Does anyone know how to get such results on google search please ? What should I add to my web site to get it appear like this ?  I have been looking on rich snippets but I'm not sure it's this.  Thanks

My website used to have sitelinks and now it doesn't. It's very possible that it's due to changing the website to a sidebar design instead of having an "interstitial" type landing page which limited the number of choices, but I'm not sure.  Here is how sitelinks might look for a site:    What are some things that I can do to improve my chances of getting sitelinks?


Let's say I want to buy a house that costs X, and that I have 20% of X to put as a down payment.  But I could put only 5% of X down and I would have to pay a 3.26% insurance premium on the mortgage amount because that's the law. So I would have an extra cost of X * 0.95 * 0.0326 but, on the other hand I would have 0.15 * X to invest and earn interest on.  The question is: How can I calculate how much the interest rate must be so that it will be more advantageous to put just the 5% down instead of putting 20% down?  Edit: To make it clearer, I am looking for the formula that finds what's the interest rate I would have to make on my investments to break-even with the insurance premium.  I forgot to mention something important, the insurance premium will be added to the mortgage balance.

My fiancee and I are shopping for a house, and very fortunate to have the assets to allow us to make a healthy downpayment.  We both like the idea of a lower monthly mortgage payment, specifically the career flexibility that comes with it.  We are looking at houses in the $1.2-1.4MM range, and can put down ~$800K, which delivers a very affordable monthly. After doing so, we'd have ~1.4MM in equities together outside of the house, though about $550K would be locked in retirement accounts.  Question is - are we misguided to make such a large downpayment, even though it buys us some job choices and peace of mind?


I am using qgis version 1.8.0. My project contains tiff and several "shape" layers. The CRS is WGS 84 (EPSG:4326). I am attempting to measure the areas of the layer polygons. However if I click on the symbol "Measure area", I am getting a message. It keeps telling me the measurements are problably wrong. (Testing this statement by measuring leads to enormous but wrong values) It suggests to define a coordinate system in project properties. I have been trying this serveral times - with no results. Furthermore I read "Working with Projections" and "Measuring" in the User guide (http://docs.qgis.org/user_guide/html/en/user_manual/introduction/general_tools.html and ). Also after adjusting all other CRS settings the problem stays.  What should I do ?  Thank you for your advice

I am playing a bit around with Qgis 2.14.6 to understand how it deals with distance measurement.  I took a line-shapefile that I saved in 3 different coordinate systems (4326, 32642 and a national one that doesn't exist in Qgis yet).  Using 32642 and the national one, the length is quite similar (6442m vs. 6428m)  But using 4326 (unprojected WGS84), I get 8057m  In all cases, I just used the Field Calculator and introduced $length.  I was already positively surprised that the result using 4326 was in meters and not in degrees.  To calculate the distance on the dataset in 4326, I assume that Qgis does some kind of re-projection in the background. Does anyone know which one?   Shapefiles here if anyone wants to play around:   EDIT - adding more info after more tests  As you can see, now both my shapefile and the project are in EPSG:4326, so unprojected:    Here the rough measurement of my shapefile, with the Qgis measure tool:   When I use the field calculator, the preview gives me a value in degrees, while the result seems to be in meters:      This would mean that the function $length, like the measurement tool, always gives a result in meters, but using a very coarse approximation of the degrees => meters transformation:    Is this a bug? or should it really behave like this? I find it at best counter-intuitive (but maybe it's just me) and, at worse, completely misleading (it makes very little sense to use, everywhere on earth, the length of 1 degree at the Equator). Any input or opinion here? Should I open a bug report (at least for the inconsistency between the preview and the actual result)?


I am trying to boot Ubuntu 13.10 from a USB Drive. I was expecting a regulation procedure: BIOS>BOOT-order-tweak>boot-from-USB. But it didn't work. I recently upgraded from a 7 year old laptop, and am not familiar with either UEFI or SecureBoot or how these change anything. From first impressions of what research i could do, the combination of said unfamiliar standards help avoid malware from doing there thing, help Windows to boot super fast and are compatible with newer versions of popular Linux distributions. So ideally one should be able to boot into described Linux distro from USB w/o disabling SecureBoot or enabling Legacy anything. The problem seems quite trivial, as it is not being discussed at all. What am I doing wrong? This also worries me a bit, because I was thinking of moving windows recovery to an external drive and freeing up the valuable space from my tiny SSD (and hopefully installing another OS there), and if I can't boot from USB...!! About Linux, can anyone also let me know if installing software not provided by HP voids my warranty?

I'm trying to replace Win8 with Ubuntu on a new Lenovo IdeaPad S10  with 4gb mem,500gb h/d.  Drilling down, I disable "Secure Boot" on the bios boot tab, but the  only 2 options under UEFI Boot priority order are Windows Boot Mgr  and EFI Network.  No "Boot from USB" option.  Someone here kindly suggested a link which reported they got added options by changing  "Secure Boot Mode" under the "Security" tab to "Legacy" but on my PC,  that option isn't selectable, ie, the selection cursor just bypasses  that selection. The only 2 selectable options are "Reset to Setup Mode"  and "Restore Factory Keys".  Anyone know who/where the usual suspects are hiding? How to flush them out?


Show that $d_1=\min(d(x,y),2)$ is a metric space if it is given that $d(x,y)$ is a metric space.   I am stuck at the triangle inequality part, to show that   $d_1(x,z)\leqslant d_1(x,y)+d_1(y,z)$ i.e to show that:   $$\min(d(x,z),2)\leqslant\min(d(y,z),2)+\min(d(x,y),2)$$  It is not a duplicate of  "brute force" question, maybe it is a duplicate of , can someone please post another answers before you are colsing as duplicate, I promise to vote.

Is the following just a matter of showing the 3 properties that make up a metric??  Define d on $\Bbb R\times\Bbb R$ by $d(x,y)=\min \{1,|x-y|\}$. Show that $d$ is a metric on $\Bbb R$     $d(x,y)=0$ if $x=y$   $d(x,y)=d(y,x)$ for every $x,y \in X$   $d(x,y)\le d(x,z)+d(z,y)$ for every $x,y,z \in X$


We purchased tickets at Air Asia's ticket office in Yangon Myanmar for travel to Australia, with a flight change  to New Zealand. As UK passport holders, we were not informed we needed visa's to transit thru Sydney Airport to board our Air New Zealand flight. Upon arriving in Kuala Lumpur, Malaysia to catch our connecting flight to Sydney, we were refused boarding and given no assistance by Air Asia. We were stranded in KL for 3 days until we could buy new tickets. To date Air Asia has not replied to a single phone call, email, twitter or message. What is the responsibility of the airline in regards to providing visa information? If the Airline refuses to respond and considering, there are several thousand complaints available on the web about Air Asia's lack of customer service, what is one to do?

My daughter bought a ticket for a flight with a layover in Emirates (from Dallas, Texas to India). She had a stop of 48 hours in Dubai. When she was checking in in Dubai for Delhi, she was informed that her visa for India has expired in 2012. Did Emirates not have an obligation to check the visa for India before selling a ticket?


I bought a power adapter to my printer but the lable on it says output voltage is 32V at 1.56A that means it is going to deliver around 50 Watts to my printer. On the other hand the original adapter used to supply 20 Watts at 32V and 0.625A. my question is would the new adapter, supplying 50 Watts, break down my printer? Thank you

One concept of electronics I have a hard time understanding is if things like motors, actuators, solenoids etc. use as much power as they need or what you give them.   If a motor needs 12 volts and 500ma and I supply it with 12 volts and 3000ma will it only consume 500ma? Also, if I supply it with 15volts and 500ma what will happen?   It seems logical that an LED and a DC motor are way different when it comes to requiring/using electric where as an led has to be completely regulated and (I assume) a DC motor doesn't.   Is my understanding wrong?


I have Ubuntu MATE 16.04 and Sony WH-1000 XM2 headphones. They worked with my computer before, but today I noticed that Amazon Video and YouTube don't play videos when the headphones are connected via Bluetooth. I have no idea why / how to investigate the problem.  When I turn them off, the videos start playing immediately.  What is going on / how can I investigate the problem?

I have an Emby media server running on Ubuntu 16.04 on a home server. I like to watch video on my laptop, running Ubuntu 16.10. Playback works as expected but when I try to watch with my Bluetooth headphones connected videos will not play.  If I run top on my server I can see that ffmpeg is maxing out the CPU:  6626 emby      20   0 1094264 348240  27820 R 181.2  4.3  10:46.21 ffmpeg   As soon as I quit trying to playback the video CPU usage drops back to an expected normal level.  If I disconnect the Bluetooth headphones, video playback immediately works OK and audio comes through the laptop built in speakers OK.  I usually use Firefox but I've tried Chrome, Chromium and Opera but they all exhibit the same behaviour when trying to play video with the headphones connected.  It appears the behaviour is not limited to my Emby media server, I've tried to play YouTube videos and they will not play either with the Bluetooth headphones connected.  The headphones and Emby video playback both work OK with my Android phone.  If I play the same video file from my server through VLC on my laptop, the video and audio work fine. This is a workaround but not my preference.  The problem seems to be related to playing video in a web browser with Bluetooth headphones connected. Can anyone help me get this working?


Check whether  the series is conditional converges or absolutely converges$\displaystyle\sum_{n=1}^{\infty}\left(\frac{-n}{n+1}\right)^n$  My try:By using root test ,I got no conclusion .Kindly help.

I have managed to use the root test and get as far as getting the limit to equal to $1$. But, I still need clarification on why the answer for the limit to this questions is $\alpha < 1$. \begin{align} \sum _{n=0}^{\infty }\left( \frac {\alpha n} {n+1}\right) ^{n}\end{align} \begin{align} \lim _{n\rightarrow \infty }\left( \left( \frac {\alpha n} {n+1}\right) ^{n}\right) ^{1/n} =\left| \frac {\alpha n} {n+1}\right| =\alpha \lim _{n\rightarrow \infty }\left| \frac {n} {n+1}\right|=1.\end{align}


I really need to get Itunes on Ubuntu for jailbreaking purposes, but none of the other solutions on this website seem to work. I have Ubuntu 14.04 (64 bit) on my HP Chromebook 14, but I have recently discovered that Itunes only works on 32 bit versions of Ubuntu. I have wine installed and have downloaded the 64 bit version of Itunes but it still doesn't work. I also have playonlinux but when I download it from there it asks me to download the 32 bit version from Apple's website. So I do and when it finishes installing nothing happens and it crashes.  Please show me how to get Itunes on a 64 bit version of Ubuntu.

I've always been an Ubuntu lover, but the only thing that holds me back from installing ubuntu on my laptop is iTunes. I have an iPad and an iPod touch and managing them without itunes is almost next to impossible, mainly because of ios upgrades.  Is there any way out?


In the situation where we have:  It used to be thought that...  We use the past tense with the verb that follows since it's something in the past. But what if the following is meant to be a fact?  I came into a question that says:  It used to be thought that the Earth is flat. It used to be thought that the Earth was flat.  Aside from the piece of information in the sentence, it represents a fact(Earth is flat) which makes the tense simple present. I believe that the correct one is is, am I right or not?  Thanks in advance.

This is the subject that's been bugging me for quite some time now, even though I believe I've managed to grasp the entire reported speech pretty well.  If I want to repeat to someone what I previously said about my opinion on swimming, I could go either with #1:        I said I didn't like to swim.      if I didn't want to emphasize anything, or with #2,        I said I don't like to swim.      if I want to make it clear that my not liking to swim still holds true.     What I can't understand is why I have to switch tenses back if I'm talking about things like:        He didn't know California was on the West Coast.      It's obvious that California hasn't moved a single inch, so why can't I express it by saying:        He didn't know California is on the West Coast.        Similarly, is such shifting required in every utterance of such meaning? For example:        I told you it was impossible to fly.      It's obvious that no matter how hard I tried I still wouldn't be able to fly. So can't I say "is impossible" (#7) in this case?        I told you it is impossible to fly.


Based on this  on Quora, group theory doesn't need set theory to be formulated. But isn't it hardwired into the definition of a group that a group is an ordered pair $(G,\; \cdot\;)$, where G is a set. Furthermore, to even define binary operations, would we not need the notion of sets, since functions are a map from a set to another set. Is it because the term "set" used in the definition of a group is just in the sense of "a collection of objects", rather than a set in ZFC.

In school, I have always seen sets. I was watching a video the other day about functors, and they started talking about a set being a collection, but not vice-versa. I also heard people talking about classes. What is their relation? Some background would be nice.   It has to do with something called Russell's paradox, but I don't know what that is.   I think that the difference between a family and a set is that the former is a function and the latter is a set. Is this right?


I was wondering if I can get the name of a function from a nested function. I have tried with __FUNCTION__ but the way I am doing it I do not get the expected result, I think it is due to a scope problem. Suppose I have the following: public function function_1($arguments) {      if (is_array($arguments)) {          return array_map(function ($argument) {              // Here I would like __FUNCTION__ to return the string functon_1              // to refer to the name of the parent function.              return call_user_func_array([$this, __FUNCTION__], [$argument]);          }, $arguments);      }       return $arguments; }  Thank you very much in advance for any help you can give me. EDIT 1 For now I have managed to get the expected result as follows: public function function_1($arguments) {      $callback = __FUNCTION__;       if (is_array($arguments)) {          return array_map(function ($argument) use ($callback) {              // Here I would like __FUNCTION__ to return the string functon_1              // to refer to the name of the parent function.              return call_user_func_array([$this, $callback], [$argument]);          }, $arguments);      }       return $arguments; }

Is there a PHP function to find out the name of the caller function in a given function?


I'm currently reading Brian Greene's The Elegant Universe and have also picked up his other book - The Fabric of the Cosmos. In The elegant universe Brian makes up an interesting point that empty space is not really empty. This is according to string theory. Now I may be completely wrong, but lets consider the assumption that empty space is not really empty.  Now there are several analogies to explain the composition of an atom. One favorite analogy says that the atomic nucleus can be considered to be the size of a football placed in the center of a football field, with the electrons moving just outside this field. That's a lot of space! Assuming that empty space is not really empty, what does this atomic space consist of?

There is a common analogy about the structure of an atom, such as the nucleus is a fly in the centre of a sports stadium and the electrons are tiny tiny gnats circling the stadium (tip of the hat to 'The Greatest Show on Earth') but what is in the space between the 'fly' and circling 'gnats'?


You open cmd and type (for example) cd C:\dragons  How can you open C:\dragons in the file explorer? Yes, you can use explorer C:\dragons, but that is kinda lame. Let's say I'm in the folder C:\dragons\Red\WhiteCrests\infants, this way just isn't convenient.  Already tried explorer dir and explorer path (both of which opens My Documents for some reason), just explorer (opens the Libraries folder), open which is undefined, explorer dirname which gives me that dirname is undefined, and probably other stuff that I can't remember.  Thanks in advance.  ...Shamelessly adding to the question with a thought I just had, how can you open a file (say C:\dragons\intro.txt) with a specified program? Like, instead of the default one (like Notepad), open it in Notepad++, without using Notepad++'s (if one exists) command line stuff. Something like:  cd C:\dragons intro.txt --Notepad++

When I'm in a particular directory in a Windows command prompt, I sometimes want to open Windows Explorer so it already shows that same directory.  How do I do that?  (I'm looking for the equivalent to open . in a Mac OS X terminal.)


I have read few articles on threading python threads and about GIL.  I wrote a small program to understand some of the concepts  import threading import time   def merge_array1(a1): for x in a1:   print (x)   time.sleep(5)  def merge_array2(a1):   for x in a1: print (x)   def run():   threading.Thread(merge_array1([5, 6, 7])).start()   threading.Thread(merge_array2([8,9,10])).start()   run()   Above program prints something 5,6,7,8,9,10 in sequence  But...i thought when one thread is sleeping, system will automatically run another thread  So output will be something similar to 5,8,9,10,6,7.  Am i missing something here, how to modify this program to give the output expected by me.

In Python for *nix, does time.sleep() block the thread or the process?


How do I solve the following PDE for it's general solution? $$ {\partial u \over \partial t} - k {\partial ^2 u \over \partial x^2} =0$$ How do I determine the general the solution of this equation will be $u(x, t) = X(x)T(t) $? I tried  but couldn't get it. My textbook only deals with particular solution using boundary condition.

What is the general solution to the differential equation:  $$\frac{\partial^2 u}{\partial y^2}=\frac{\partial u}{\partial x}$$  I'm a little stuck because all the techniques I know are unable to solve it.


I have a linkage error with the following example:  In a file named a.h:  namespace n { class A {     ...  public:   template<class Function, class... Args>   void a_member(Function &&f, Args &&...args);  private:   std::thread *t_; }; }   In A.cpp:  #include "A.h"  template<class Function, class... Args> void n::A::a_member(Function &&f, Args &&...args) {     this->t_ = new std::thread(std::forward<Function>(f), std::forward<Args>(args)...); }   In a file named B.h:  #include "a.h" #include "c.h" /* declaration of class C */  class B {  public:   void b_member1();   void b_member2(C c);  private:   A *a_; };   In B.cpp:  #include "B.h"  void B::b_member1() {     C c;     this->a_ = new A();     this->a_->a_member(&B::b_member2, c); }   I'd like to wrap the call to the thread callback with a member function with a parameter of class C.  EDIT:  Since the method has been moved in the header, an error still persist: the call to thread constructor seems to be incorrect (signature of function mismatch):  this->t_ = new std::thread(std::forward<Function>(f), std::forward<Args>(args)...);

Quote from :     The only portable way of using templates at the moment is to implement them in header files by using inline functions.   Why is this?  (Clarification: header files are not the only portable solution. But they are the most convenient portable solution.)


If you go to the Hateno village lab early. You will find out about the upgrades to your Sheikah slate's functions.  You can upgrade your scanner to scan for other things than Shrines by proximity.  I used the feature to scan for some nearly worthless weapon (rusty broadsword). I scanned for other things earlier but I used this one to not make it ping everywhere like it would have with Hylian Mushroom.  I don't see a way to "clear" the targeted item from scanner+ so it can scan only for shrines.  Is there a way to clear your scanner+ targeted item?  To be clear I am NOT asking to turn off the indicator only change it back to search only for shrine and nothing else. Which is not a duplicate of the other question.

The shrine indicator (shrine detector? GPShrine?) has both visual and audio cues, so when I'm near a shrine, it beeps constantly. Unfortunately, I occasionally play the game near other humans who are engaged in their own activities, and my wife is decidedly unimpressed with this feature.   When I got the shrine indicator, I could have sworn that the dialogue said I could press [Y] to disable it... but pressing Y pulls out my weapon.   Ideally, I'd like to just make it stop beeping, but stay on for visual cues. But I'll settle for being able to turn it off entirely at times.


Read before you decide THIS question is off-topic  I don't expext to get much sympathy on this one but....   I posted my question on serverfault thinking it was for networking questions. Gets put on hold as off-topic, my mistake, no big deal, let's move on. (Also I didn't get notified of either hold or response to my subsequent flag for migrate. Not sure about flags but I know holds are supposed to show)   Flag my question to be moved to site holding mod suggested it be moved to: denied with no explanation I politely ask for a suggestion as to where to move and the reply? "Frankly, this is a terrible question.  I won't put it anywhere else."   You could imagine 4 hours for such a helpful response and I was a bit peeved.  I had a specific question about a specific function of a uniquitous networking device and he was telling me, rather rudely, that it didn't belong anywhere on the ENTIRE stack network.  Didn't offer a single word as to why it was so terrible.  I illustrate, in kind, how that's not so helpful and question gets closed as "too many off-topic comments."  There were two comments by me: one about the relevant site and the other about the complaint (which was the only one he deletes, doesn't like being questioned I guess)  Just so my post can have a specific question   I've heard of power-tripping mods here and was wondering just how bad it is.  I haven't had any other issues but I want to avoid it as much as possible. I probably know who it was (no names) because of how the question was closed, but is there a specific way to know who responded to a flag request?  Again just to help avoid future situations. Funny enough person who closed put another question of mine on hold yesterday, but I agreed it was too broad and deleted it.   Relevance of THIS post: If you think discussing moderator behaviour is not a meta topic we can have a separate debate on that.  If you think this belongs on meta.serverfault: this post wasn't about the specific question posted there - it was was about a moderator's behaviour and the context isn't specific to serverfault.  Also I'm new there and can't post to meta.

One or more of the following things happened to me on a Stack Exchange site:   My post(s) were wrongly deleted or locked by a moderator A moderator posted a wrong comment on one of my posts I was suspended, but did not do anything wrong I asked a meta question, but the question was closed and/or deleted A moderator discredited me in public ...   I think a moderator has abused their power, but I feel powerless against them.  What recourse do I have now? What can I do when I feel that a moderator has abused their power, and has been repeatedly unfair in their dealings with me?


Let $M$ be a smooth close $4-$dimensional manifold and let $p\in M$ be a point. Denote by $\hat{M}$ the blow-up of $M$ at $p$ and let $E \cong \mathbb{C}P^{1}$ denote the exceptional sphere which is embedded. How can one show that the self-intersection number of $E$ is $-1$, i.e. $E \cdot E = -1$?

Let $X$ be a projective variety over $\mathbf{C}$ of dimension $n$. Let $\pi: Y \to X$ be the blow-up of a smooth point $x \in X$. Is there a nice formula for the intersection number $E^n$?


When I raise some integer to some imaginary power I obtain a complex number. E.g., $$2^i = 0.7692 + 0.6390i.$$ Why does this happen? What does it mean to raise an integer to an imaginary power?

Greetings!  I am trying to understand what it means to have an imaginary number in an exponent. What does $x^{i}$ where $x$ is real mean?  I've read a    on this issue, and they all seem to boil down to the same thing:   Any real number $x$ can be written as $e^{\ln{x}}$ (seems obvious enough.) Mumble mumble mumble This is equivalent to $e^{\cos{x} + i\sin{x}}$    Clearly I'm missing something in step 2. I understand (at least I think I do) how the complex number $\cos{x} + i\sin{x}$ maps to a point on the unit circle in a complex plane.  What I am missing, I suppose, is how this point is related to the natural log of $x$. Moreover, I don't understand what complex exponentiation is. I can understand integer exponentiation as simple repeated multiplication, and I can understand other things (like fractional or negative exponents) by analogy with the operations that undo them. But what does it mean to repeat something $i$ times?


I have a command which list outs events of "Magento 2", which is working fine in the terminal.  I want it's output to be printed into a file but none of the below code works:  find . -type f -exec grep -n -H -A 2 -T "eventManager->dispatch(" {} \ | tee ~/MAGE2EVENTS.txt   Neither this one:  find . -type f -exec grep -n -H -A 2 -T "eventManager->dispatch(" {} \ >> ~/MAGE2EVENTS.txt   I see 'exec' has been used in this code which shows error:  find: missing argument to `-exec'   So how to print the terminal output of this command to file ?

I use the following command to clear a directory, of files and directories over 30 days old, and move them to an archive directory which I can delete after a few weeks if nobody asks for their files back. The target directory has subdirectories by user name, so will the archive directory.  This is the command I use:  find /path/to/directory/username/ -mtime +30 -exec mv "{}" /path/to/archive/username/ \;   I suggested a modified version of this to answer a question on ask ubuntu, another user edited the code to change the end of line \; for + as it's faster(and more correct?).   However, using + in this way works if the -exec command is ls -lh but not in the actual command that I use. If I try it with + I get an error message:  find: missing argument to '-exec'   I don't understand why it's behaving this way, or what the correct command would be. Please don't just post a command correction, I'd like to understand rather than just follow a suggestion blindly.


I'm trying to change the login url from wp-login.php to simply 'login'. I'd been looking through another plugins source to find ways of doing it.  Some of the applicable parts that I've got so far:  register_activation_hook( __FILE__, 'my_plugin_activate' ); register_deactivation_hook( __FILE__, 'my_plugin_deactivate' );  add_action( 'init', 'my_plugin_rewrite' ); add_action( 'login_init', 'my_plugin_login_init' ); add_action( 'template_redirect', 'my_plugin_display' );  function my_plugin_activate() {     add_rewrite_tag( '%login%', '([^/]+)');     add_permastruct( 'login', '/%login%' );     flush_rewrite_rules(); }  function my_plugin_login_init() {     if ( '/wp-login.php' == $_SERVER['PHP_SELF'] ) {         header( 'HTTP/1.0 404 Not Found' );         global $wp_query;         $wp_query->set_404();         require TEMPLATEPATH . '/404.php';         exit;     } }  function my_plugin_display() {     global $wp_query;     switch( $wp_query->query_vars['pagename'] ) {         case 'login' :             include( ABSPATH . '/wp-login.php' );             exit;             break;     } }   The problem I'm having is in the "my_plugin_display" function.  $wp_query->query_vars['pagename'] happens to be empty. How can I test if the url is at /login? Is this the right hook to use?

How to change wordpress login url without using .htaccess, should be a manual process, so example.com/login will not redirect to example.com/wp-login.php so example.com/login will be the login page?


I am an undergrad in economics and really want to get a helping hand as I get from math and stats from a Stack Exchange site for economics. Where can I post my questions on economics topics?

I was wondering if there is a viable place on Stack Exchange to ask economics-related questions.  Questions I'd have in particular could be equation-based or theoretical.  I suppose the equation-based questions could possibly fit into mathematics but I haven't checked their FAQ.


I am using Windows 8.1 as host and in VirtualBox running Ubuntu 14.04 LTS, how can I make it to see the USB sticks in VirtualBox? I found lots of tutorials but all are for Ubuntu as host and Windows in VirtualBox.

I'm using Ubuntu Maverick and Virtual Box 3+. I have Windows 7 Ultimate. The problem is that it doesn't detect USB drives in Windows 7, but USB peripherals (mouse + keybord) are working.  I followed , but I can't find the user group vboxusers. How can I continue? I would also like to upgrade to the latest version without any risk (without losing my virtual hard disk drive).


I am trying to prove that  $A∆B⊆C$ iff $A∪C=B∪C$. I know that I am going to have to convert them to this form.... $AΔB⊆C$  is equivalent to $∀x:((x∈A∧x∉B)∨(x∉A∧x∈B))→x∈C$  and $A∪C=B∪C$ is equivalent to $∀x:(x∈A∨x∈C)↔(x∈B∨x∈C)$  How do I even go about proving this once I have written them out in set theory notation?

Suppose $A,B,C$ are sets.  Prove that $A\mathbin\triangle B\subseteq C \iff A\cup C=B\cup C$.  I proved that for $x\in A\setminus B$, $x\in A\cup C$ and for $x\in B\setminus A$, $x\in B\cup C$. How do I show that $A\cup C=B\cup C$, and that $A\mathbin\triangle B\subseteq C \iff A\cup C=B\cup C$?


I'm working on game, using LibGDX and have some problems with Input Processor. Wnen I launch my game and press Right button it crashes with NullPointerException  @Override public boolean keyDown(int keycode) {     if (keycode == Input.Keys.RIGHT && player.b2body.getLinearVelocity().x <=0.5) {         player.b2body.applyLinearImpulse(new Vector2(0.1f, 0), player.b2body.getWorldCenter(),true);         return true;     }     return false; }    public  void update (float dt) {           world.step(1/10f,6,2);         player.update(dt);        // handleInput(dt);          MyInputProcessor inputProcessor = new MyInputProcessor();         Gdx.input.setInputProcessor(inputProcessor);         if(player.b2body.getPosition().x>=SonicZP.V_WIDTH/2/SonicZP.PPM)         gamecam.position.x = player.b2body.getPosition().x;          if(player.b2body.getPosition().y>=SonicZP.V_HEIGHT/2/SonicZP.PPM)             gamecam.position.y = player.b2body.getPosition().y;         gamecam.update();                renderer.setView(gamecam);     }

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?


Suppose a body is attached to a spring and a constant force $F$ is applied on the other side (Spring constant = $k$)at maximum extension the body is in equilibrium and so $$F=kx,$$ so we get maximum extension $x=F/k$, but if we take the work energy theorem approach then change in kinetic energy is zero as the body starts from rest and in the point of maximum extension comes to rest,so work done on it by all forces should be zero,work done by $$F=Fx$$ (as $F$ is constant), work done by spring = $$-\frac{k}{2}x^2,$$ since the work done on it must be zero, $$Fx-\frac{k}{2}x^2=0,$$ which gives us $$x=\frac{2F}{k}$$ which is different than the first answer,so which one is correct and which one is wrong?

This was a question my friend found in a book.  A block attached to a spring pulled by a constant horizontal force is kept on a smooth horizontal surface. Initially the spring is in its natural state. Then the maximum work that the applied force F can do is:  (a) $F^2/k$ (b) $2F^2/k$ (c) $4F^2/k$ (d) $F^2/2k$  My friend thought that the answer is (a) since the maximum displacement is $x=F/k$ and $W=Fx=F^2/k$. But he saw that the book's answer is different and he asked this question to me. I at first thought that the answer will be (a), but then I realised that this situation is somewhat similar to a charging capacitor. The final energy of the spring is actually $\frac12kx^2=F^2/2k$. So probably the answer is (d)? But the work done is still (a)? But the book says neither. It's (b). This is the logic in the book:  Method 1: in the book:  $$Fx=\frac12kx^2$$  $$x=2F/k$$  $$W=\frac12kx^2=2F^2/k$$  (since the book is an objective questions book it did not have detailed explanations)  What is wrong in the following methods?  Method 2: by calculating the maximum displacement  $$x=F/k$$  $$W=Fx=F^2/k.$$ Method 3: by calculating the final energy  $$x=F/k$$  $$\frac12kx^2=F^2/2k$$  PS: We both know calculus so don't hesitate to use it in the answers.


I have a method rotateImage that returns an int[][] array, I am having trouble understaing how to display the actual values of the array instead of just the hashcode:  [I@548c4f57 [I@1218025c [I@816f27d   I tried doing this:   Arrays.stream(rotateImage(matrix)).forEach(System.out::println);   but that only returns the hashcode, not the actual numbers themselves. I also tried using to Arrays.toString() method in several ways but always get an error.

In Java, arrays don't override toString(), so if you try to print one directly, you get the className + '@' + the hex of the  of the array, as defined by Object.toString():  int[] intArray = new int[] {1, 2, 3, 4, 5}; System.out.println(intArray);     // prints something like '[I@3343c8b3'   But usually, we'd actually want something more like [1, 2, 3, 4, 5]. What's the simplest way of doing that? Here are some example inputs and outputs:  // Array of primitives: int[] intArray = new int[] {1, 2, 3, 4, 5}; //output: [1, 2, 3, 4, 5]  // Array of object references: String[] strArray = new String[] {"John", "Mary", "Bob"}; //output: [John, Mary, Bob]


What am I doing wrong here?  A_B_NAME="something" X=A Y=B  RESULT=`echo \${X}_\${Y}_NAME` echo ${RESULT}   and I'm always getting A_B_NAME as a result, but want "something"  Thanks! Michael

I need to indirectly reference a variable in the bash shell.  I basically want to what you can do in make by writing $($(var)).  I have tried using ${$var} which would be the most straight forward solution in bash but then I get this error:  bash: ${$var}: bad substitution   Is there a way to do this?  What I am trying to do is to iterate over all the arguments ($1, $2, $3, ...) to a program using an iteration variable and I cannot do this without indirection.