Full logistic regression model significant but insignificant predictors

I fit a logistic regression model with about ~10 numerical predictors, and got the following:  Full model is stat significant.  Here are the ANOVA results using ChiSq test.   None of the individual predictors are significant in the full model.  Here is the model summary.   Sample size is respectable (500 observations)  No evidence of collinearity (VIFs < 2, none of the pairwise correlations are >0.5, etc). Here is the VIF output for the model.    And when I drop enough variables (or use stepwise selection to reduce the model), the individual predictors eventually start becoming significant.. What might be operating here that I'm missing? Are there some other issues (besides collinearity or small sample) that might lead to such phenomenon (significant full model, insignificant predictors) in GLM as opposed to classic linear regression?


How to copy ONLY those files that are not in the destination?

Is it possible to use robocopy to copy only the files that do not exist in destination?  robocopy has a /is (include same files) switch. What I am looking for is an /xs switch. If a file exists in both the source and the destination I don't want it to be copied. The criteria is file name only, regardless of modified day, size, etc. For example, even if the source has a newer file (based on modified date) than the same file in the destination, I don't want it to be copied. Possible to do this? Thanks.


Biblatex/Biber replace author name with dash for each author

In the bibliography of authoryear-type bibliography styles, BibLaTeX can replace repeated author lists (with all authors the same) with a dash or similar. Is is possible to change this behaviour so that the replacement is made on a per-author basis? This is found in such journals as .  As an example, the following references:  AUTHOR, A. 2000. First reference. Journal A, 2, 21–22. AUTHOR, A. & BAUTHOR, B. 2001. Second reference. Journal B, 4, 34–46. AUTHOR, A., BAUTHOR, B. & CAUTHOR, C. 2002. Third reference. Journal C, 6, 89–99.  Would be published as:  AUTHOR, A. 2000. First reference. Journal A, 2, 21–22. ——— & BAUTHOR, B. 2001. Second reference. Journal B, 4, 34–46. ——— ——— & CAUTHOR, C. 2002. Third reference. Journal C, 6, 89–99.  With three em dashes replacing each repeated author.  A reply to   describes commands to replace a repeated first author only with Idem/Eadem/Eidem/Eaedem, but can this be applied to several authors in the author list?  Addendum: This image is from Porro, L.B., et al., "Computed Tomography, ...", Palaeontology, 2015, p.16.


Prove: if $n\mid 7^n+6^n$ and $n>1$, then $13\mid n$  Let $p$ be the least prime number such that $p\mid n$.   And I want to show that $p=13$  Let $d$ be the least number such that: $14^d\equiv 0 \pmod {p}$  And by Fermat's little theorem I have: $14^{p-1}\equiv 0 \pmod{p}$  Here I'm stuck


I'm developing a Custom Post Type plugin, which works fine in dev. Now that I've moved it to production, I'm getting a 404 when I try to display the template for the CPT.   So, two questions:  1- Is there some mechanism to determine the path WP took to get through the hierarchy?  2- Why wouldn't it just give me the single or index page?  I've dumped $wp_query and a stacktrace at the end of the 404. Here's part of what I found:  [query] => Array     (         [page] =>          [pagename] => refletters/proximity     )  [request] => SELECT   wp_posts.* FROM wp_posts  WHERE 1=1  AND (wp_posts.ID = '0') AND wp_posts.post_type = 'page'  ORDER BY wp_posts.post_date DESC  [posts] => Array     (     )  [queried_object] =>  [queried_object_id] => 0   And the stack trace:  2013-04-27 22:16:41 - 24.52.197.40 - TRACE - index.php - 404.php[39] -      wordpress/wp-content/themes/notoriousconsultant/404.php[39] - aaLog->logtrace     wordpress/wp-includes/template-loader.php[50] - include     wordpress/wp-blog-header.php[16] - require_once     wordpress/index.php[17] - require   Thanks for your help.


Why was sabotage so easy in the Triwizard Tournament?

Since the Triwizard Tournament is the biggest competition in the wizard world, why would it be so easy for someone to bewitch it?


How do you use Berlin crosswalk signal boxes?

I see these all around town and nobody seems to know how to use them - even my German colleagues. We're engineers, so we feel pretty stupid and inadequate around them...  The majority of people I've seen either ignore them or look at them confusedly and try to slap the three black dots - like a  - to no avail.  Obviously there are a lot of different kinds, ranging from old and busted to some having mini LCD screens - but only a few are actually press-able buttons.  What's the deal with them? How do you use them?


No option to install Ubuntu along side Windows

I have a windows 10 professional 64 bit OS on a PC I've recently built. I want to install Ubuntu along side it so I can boot into Windows for games, Ubuntu for everything else. I have a 1 TB M2 SSD that Windows is installed on that I want to split between the two OS's. When I try and install Ubuntu - I don't get an option to install along side windows and the partition screen confuses me. Can you help?


My registrar tell me that I can't have a CNAME record that doesn't start with www. Is it true?  So I am using amazon ec2 with load balancing. the loadbalancer has a convoluted DNS name, and specifically tells you to use a CNAME to send requests to that DNS name, and not an A record.     myloadbalancer-1234567890.us-west-1.elb.amazonaws.com (A Record)      Note: Because the set of IP addresses associated with a LoadBalancer can change over time, you should never create an "A" record with any specific IP address. If you want to use a friendly DNS name for your load balancer instead of the name generated by the Elastic Load Balancing service, you should create a CNAME record for the LoadBalancer DNS name, or use Amazon Route 53 to create a hosted zone. For more information, see Using Domain Names With Elastic Load Balancing.   I purchased a domain. The registrar doesn't allow you to add records yourself, only by emailing them a request. So they set up a CNAME record  mydomain.org  SOA 111  whatever www.mydomain.org    CNAME   3596    myloadbalancer-1234567890.us-west-1.elb.amazonaws.com      when I asked them why it doesn't work with www, the registrar answered that there is a technical prohibition to make a CNAME record without www. Is it true, or are they incompetent/lying and I should switch registrars?


Testfor command procuding error in 1.11 snapshots?

I've been making a map for 1.10 and it's going great, but 1.11 shows great mobs to use for it. However, most things have channged in command syntax. For example, /kill @e[type=ArmorStand,r=6] is now /kill @e[type=Armor_Stand,r=6]  What about /testfor? I can't find a way to testfor a player to stand on a block and give them an effect.   What's is going on in this image is that a redstone clock is running into this command /testfor @a[1117,20,507,r=1] (if I was to stand on them cords the comparator would turn on and power that command block), but it only works in 1.10... from 1.11 snapshots, I've seen some errors of it, like it now needs to have {} at the beginning and end of it. (e.g. /testfor @a{[1117,20,507,r=1]})   It's still not working, though, so does anyone know how to get it to work?


Recently I stumbled upon a sentence      I have to roll my eyes any time I hear someone say they started or   work for a startup.   I tried to find a grammar rule which explains it but all in vain. Can anybody point me in the right direction on why it is "someone say"?!


What is the symmetry which is responsible for preservation/conservation of electrical charges?

Another Noether's theorem question, this time about electrical charge.  According to Noether's theorem, all conservation laws originate from invariance of a system to shifts in a certain space. For example conservation of energy stems from invariance to time translation.  What kind of symmetry creates the conservation of electrical charge?


We want to have a plain empty sandbox - one without any configuration metadata or data from Production.  Is it possible to have such a sandbox?  Please advise.


The interface for material looks different than the one on tutorial

I am a complete beginner and following a tutorial about how to put a texture on a cube. I think maybe they have a different version of Blender because what I see in a few places is different so it is very hard to follow.  In the video after UV unwrapping the cube they click to create a new material then click this little button next to the colour and then get a menu where they can choose 'Image texture'    But in my Blender which is 2.79b when I click Add material it looks like this:    As you can see it is totally different and I can't find anywhere a Color box with a button like in the video. I can't even see 'Surface' anywhere. So I am stuck.   Did they change Blender so much I need to find a new tutorial for my version? Is there a simple way to do the same thing in the version I have?


Strange characters when the output of `ls` is redirected to a file


What should be Blog page URL if we think regarding SEO friendly

I am going to integrate BLOG to my website. Which is best SEO friendly URL for blog from below :  1 - blog.mysite.com  2 - mysite.com/blog  Please advice me so I can do as per that. I am SEO beginner and want to make everything perfect because My blog will have fresh posts daily , weekly and want to generate traffic by blog.


Passing changing (in a loop) parameters to Pgfplot function

Usually I just use TikZ for plots but was hoping Pgfplots would simplify life (axis, labels, etc...) but I can not find what is the right syntax to pass parameters to the function. Here is the MWE:  \documentclass[12pt]{article} \usepackage{tikz} \usepackage{pgfplots} \begin{document}    \pgfplotsset{compat=1.10}    \begin{tikzpicture}       \begin{axis}[        title=Test,        xlabel=$x$,        ylabel=$f$,        ]           \foreach \y in {0,1,2,3}              {\addplot[              red,              domain=0:1,              samples=4,               ]               {x+\y};              }      \end{axis}   \end{tikzpicture} \end{document}


"All the good girls they go to heaven, but the bad girls they get backstage"   The first sentence is fine, but I don't understand what it mean to go "backstage"   Song name is Backstage.


Derive the centroid of an area from a limiting procedure

I wondered if the centroid of an area could be derived as a limit from the centroid of the solid of revolution built by the same area revolving around an axis of revolution.   e.g.: the  is $C_{V} = \frac{3\pi}{16}r\frac{\sin[\theta]}{\theta}$, where $r$ is the radius of the sphere and $\theta$ is the dihedral angle. The  is $C_{A} = \frac{4r}{3\pi}$  Now I tought it was possible a limit procedure like $\lim\limits_{\theta\to 0} C_{V}$=$C_{A}$, but that's false and I would like to know why (I guess that has something to do with the passage from three-dimension to two-dimension)  Thanks


How can I make something like a?b:c in python?

In java, I usually use  boolean x = a? b : c;   instead  if(a)     boolean x = b; else     boolean x = c;   Is there any possibility for doing that in python?


Determining Affine Transformation Parameters?

I am trying to use the qgsAffine plugin to do the transformation but I have no idea in its usage.   How to find the transformation parameters? I found some posts suggest using the OpenJump How to use the plug-in? I found my plug-in UI does not match with my found in Google. Why?   Here is my coordinates:   Original x 0.3704 (EPSG:4326) to Target long 114.2031 Original y 0.52804 (EPSG:4326) to Target lat 22.3249


When dealing with abstract classes in Java it is not possible to create an object of that class.  So this would not work AbstractClassName object = new AbstractClassName();.  Why this is working AbstractClassName object = new NonAbstractClassName(); ?   Can you tell me what am I doing by using a constructor from a non abstract class (that extends the abstract one) and assign the object to a abstract class type?


Each coefficient in the equation $ax^2+bx+c$ is determined by throwing an ordinary dice. Find the probability that the given equation will have real roots? I counted the cases which fulfill D(discriminant) greater than zero, but that turned into a long method.   Is there an elegant short way to do this question?


Oracle SQL - nested subquery throws parenthesis exception

I got the following oracle-sql-statement:  select xxx.a, xxx.b, xxx.c, xxx.d, (SELECT e FROM ghj WHERE f in (SELECT u FROM hgz WHERE ddf = xxx.ddf limit  1)) AS fff from fcv xxx where k = '100';   I get the following error: ORA-00907: missing right parenthesis ORA-06512: at "SYS.DBMS_SQL", line 1185 ORA-06512: at line 1  Why?


If I have only one front door, and only one back door, and they are both red.  Which is correct:         The front and back door are red;   The front and back doors are red.      I feel that (1) looks wrong and that (2) indicates that there are a plurality of both front and back doors.


Q&A Identification of seldom man-made physical objects not being piece of art?

Is SE Q&A format relevant for "identification of seldom physical objects observed in real world"?  Questions like "I do not know function of this object (picture) - which purpose does it have?"  In many cases I suppose these question could have civil engineering or handcraft i.e. cultural/historical background. In second case "SE history" might be okay. For first case, I do not know.


What does "would" actually mean in the following sentence? My friend says that "would" here means "will possible".     Question: Which is a correct way in a dialogue?      1a: Have you seen my book?      2a: Do you see my book?      3a: Where is my book?      B: The book is on the table      Answer: All three work, but technically speaking, the question B is answering 3. Since 1 and 2 are yes-or-no questions, a more precies answer would be "yes, it's on the table". Note that since A already knows he's asking about a book, it would be more natural for B to refer to it as "it" than "the book".


I have Ubuntu 16.04. I cannot see any wifi enabling option. I have selected the Broadcom driver in software and update, and the Wi-Fi switch is enabled in the BIOS.  I've looked through the help pages and run the following:  $ sudo lshw -C network   *-network                       description: Network controller        product: BCM4311 802.11b/g WLAN        vendor: Broadcom Corporation        physical id: 0        bus info: pci@0000:0b:00.0        version: 01        width: 32 bits        clock: 33MHz        capabilities: pm msi pciexpress bus_master cap_list        configuration: driver=b43-pci-bridge latency=0        resources: irq:16 memory:efdfc000-efdfffff   *-network        description: Ethernet interface        product: BCM4401-B0 100Base-TX        vendor: Broadcom Corporation        physical id: 0        bus info: pci@0000:03:00.0        logical name: eth0        version: 02        serial: 00:1d:09:b6:10:83        size: 100Mbit/s        capacity: 100Mbit/s        width: 32 bits        clock: 33MHz        capabilities: pm bus_master cap_list ethernet physical mii 10bt 10bt-fd 100bt 100bt-fd autonegotiation        configuration: autonegotiation=on broadcast=yes driver=b44 driverversion=2.0 duplex=full ip=192.168.1.135 latency=64 link=yes multicast=yes port=twisted pair speed=100Mbit/s        resources: irq:17 memory:ef9fe000-ef9fffff*   What should I do?  $ lspci -knn | grep Net -A3; rfkill list 0b:00.0 Network controller [0280]: Broadcom Limited BCM4311 802.11b/g WLAN [14e4:4311] (rev 01)     Subsystem: Dell Wireless 1390 WLAN Mini-Card [1028:0007]     Kernel driver in use: b43-pci-bridge     Kernel modules: ssb, wl


Intersection of two open dense sets is dense

Let $X$ be a topological space and suppose that $H$ and $G$ are open dense subsets of $X$.Then show that $G \bigcap H$ is also an open dense subset of $X$.  My attempt :  Well since the finite intersection of open sets is open therefore, $G \bigcap H$ is also open.  I was trying to prove the other part by the method of contradiction :  Suppose on the contrary that $G \bigcap H$ is not dense. Then that implies that $Int(Cl(G \bigcap H)) = \phi$ .  Now, $Cl(G \bigcap H) \subset Cl(G) \bigcap Cl(H)$  so, $Int(Cl(G \bigcap H)) \subset Int(Cl(G) \bigcap Cl(H)) = Int(Cl(G)) \bigcap Int(Cl(H)) = X $.  How do i proceed further to get a contradiction ?


Convert a WFS GET request to a WFS POST request

I have a WFS GET Request, created by A WFS Layer in QGIS. However, for my program I need to have a POST Request. How do I convert the WFS GET request to a WFS POST request?


So, we know Harry . By descriptions from the books, it looks like he had enough money to spend during his school years with plenty to spare for later life.  Is there an estimate on how much money he had? How much would that be in muggle money? Was he extremely rich?  I'm thinking here that he could have received more than just an inheritance. For example, anonymous supporters could have given him money through the bank while he was a baby, or when he was about to go to Hogwarts, and he wouldn't have known (not even Dumbledore would have known).


Is there a Google Sheets functions equivalent of mysql_fetch_row?

Is there any way to get the row result in Google just like mysql_fetch_row that returns only the row base on query statement?   I hope there has a formula for this.  Using this formula =Query(IMPORTRANGE("",""),"Select Col1 where Col1='somevalue') i want to get only the counts of row results instead of displaying the data on my sheet.


Can quantum computers be used to solve P = NP

The P versus NP problem is a major unsolved problem in computer science. It asks whether every problem whose solution can be quickly verified can also be solved quickly. It is one of the seven Millennium Prize Problems selected by the Clay Mathematics Institute, each of which carries a US$1,000,000 prize for the first correct solution. My question is, can a quantum computer be used to solve P = NP?


I can't be 100% sure I'm asking this question

I like to believe one can't be 100% sure of anything, for one can't be 100% sure their brain functions correctly (because if it doesn't, it may mistake itself as functioning correctly as a result). Is there a name for and/or existing material on this theory?


I have been facing this issue even when I boot through Gparted LiveCD. My goal is to install Windows dual booting with Ubuntu (My wife is not comfortable with linux)  Don't ask me about the ext2 and fat32 partitions here, I don't have any clue myself as to when and how they got created. Also let me know if it would be safe to remove these.  Suggestions? Advice?


Proving the pairing axiom from the rest of ZF

In , the pairing axiom states that for every $x,y$ there exists the set $\{x, y\}$. Wikipedia also tells us we can dispense this axiom:     This axiom is part of Z, but is redundant in ZF because it follows from the axiom schema of replacement applied to any two-member set. The existence of such a set is assured by either the axiom of infinity, or by the axiom of the power set applied twice to the empty set.   I have a few questions about it:   It seems to me we only need to prove that given $x$, there exists the set $\{x\}$ and use the axiom of union for $\{x\}, \{y\}$. Am I correct? To prove $\{x\}$ exists we can apply separation on $P(x)$ - the power set of $x$ whose existence is guaranteed from the axiom of power set. Am I correct? If both the previous statements were correct, is it correct to say that the axiom of pairing can be proved without the need to assume the existence of any set (i.e. without the axiom of infinity or the axiom of the empty set). How can the axiom of infinity be stated without implicitly relying on the axiom of pairing? After all, the formulation I know of for this axiom literally says "there is an inductive set", and to formulate what "inductive set" means you have to use the expression $x\cup\{x\}$ which assumes $\{x\}$ is really an existing set...


Meaning of congruence (in twin prime criterion)

I'm a programmer, a newbie on math. I'm trying to code to list twin prime.  I've found this:      The pair (m, m + 2) is twin prime, iff 4((m − 1)! + 1) ≡ −m (mod m(m + 2)).   However, if I set m=5 and then,   4((m - 1)! + 1) = 4 * (4! + 1) = 4 * 25 = 100 -m (mod m(m + 2)) = -5 mod 35 = 35 - (5 mod 35) = 30   Well, 100 does not equal to 30, right? But (5, 7) is a twin prime.  Did I do something wrong?


This dreaded issue started at some time after upgrade to OS X (Yosemite) 10.10.3. accountsd uses about 60% CPU constantly, making the laptop hot and noisy.  I'm not using iCloud at all.  Killing it doesn't help, because it starts again quickly.  Probably related question, but it's about iOS:


I used a Brillo pad on my cast iron skillet. It is seasoned, not enameled. I want to know if this could damage my cast iron skillet. Also can it be fixed?


In some situations, it will be very useful to save the state of a process to file and to be able to load the state at a future point in time to continue from exactly the state which was saved. Is it possible to save Windows process state to file and after restarting it to load the same state?


I am a beginner. Can anyone state what it means if anyone says "The aperture of the photo/pic is not correct."? I donot know what actually aperture means.


I am wondering whether there is a general way of passing multiple options to an executable via the shebang line (#!).   I use NixOS, and the first part of the shebang in any script I write is usually /usr/bin/env. The problem I encounter then is that everything that comes after is interpreted as a single file or directory by the system.  Suppose, for example, that I want to write a script to be executed by bash in posix mode. The naive way of writing the shebang would be:  #!/usr/bin/env bash --posix   but trying to execute the resulting script produces the following error:  /usr/bin/env: ‘bash --posix’: No such file or directory   I am aware of , but I was wondering whether there was a more general and cleaner solution.    EDIT: I know that for  scripts, there is a way to achieve what I want, documented in  of the manual:   #!/usr/bin/env sh  exec guile -l fact -e '(@ (fac) main)' -s "$0" "$@"  !#   The trick, here, is that the second line (starting with exec) is interpreted as code by sh but, being in the #! ... !# block, as a comment, and thus ignored, by the Guile interpreter.  Would it not be possible to generalize this method to any interpreter?     Second EDIT: After playing around a little bit, it seems that, for interpreters that can read their input from stdin, the following method would work:  #!/usr/bin/env sh sed '1,2d' "$0" | bash --verbose --posix /dev/stdin; exit;   It's probably not optimal, though, as the sh process lives until the interpreter has finished its job. Any feedback or suggestion would be appreciated.


If $\lim_{x \rightarrow 1} f'(x)=2015$. Prove that $f$ is differentiable at $x=1$.

Let $f:[0,2] \rightarrow \mathbb R$ be a continuous function such that, $f$ is differentiable everywhere on $[0,2]$ except possibly at $x=1.$ If $\lim_{x \rightarrow 1} f~'(x)=2015$. Prove that $f$ is differentiable at $x=1$.  Attempt:  $f:[0,2] \rightarrow \mathbb R$ be a continuous function $\implies ~\exists~m,M \in \mathbb R$ such that $m \le f(x) \le M~\forall x\in [0,2] $  It is given that $\lim_{x\rightarrow 1} f~'(x) = 2015$. We need to prove that $f~'(1) $ exists or that $$ \lim_{h^+ \rightarrow 0 } \dfrac {f(1-h)-f(1)}{h} =  \lim_{h^+ \rightarrow 0 } \dfrac {f(1+h)-f(1)}{h}$$ Could someone please give me a hint on how to move ahead with this problem?  Thank you for your help in this regard.


How can I merge hundreds of Excel spreadsheet files?

I have hundreds of excel files which are all of the same format (i.e. 4 worksheets per Excel file). I need to combine all the files into 1 all singing and dancing file which must have the same format as the originals (i.e. maintain the four separate worksheets, which are all identically named).  While each file is structured the same, the number of columns (and the heading names) between sheet 1 and 2 (for example) is different. So it can’t be combined into one file with everything in one sheet!  There are two complications:   I need to create an EXTRA column in the merged file (on EACH sheet) to identify the source file (“file name”). The files contain a lot of zero data entries (e.g. 55 rows of useful data followed by hundreds of rows of zeros) which I need to remove from the merged file.   I’ve never used VBA, but everyone has to start somewhere I suppose.


Basic question regarding variance and stdev of a sample

Suppose there is a very big (infinite?) population of normally distributed values with unknown mean and variance.  Suppose also that we have a sample, S, of n values from the entire population. We can calculate mean and standard deviation for this sample (we use n-1 for stdev calculation).  The first and most important question is how is stdev(S) related to the standard deviation of the entire population?  An illustration for this issue is the second question:  Suppose we have an additional number, x, and we would like to test whether it is an vis-a-vis the general population. My intuitive approach is to calculate Z as follows:  $Z = \frac{x - mean(S)}{stdev(S)}$  and then test it against standard distribution if n>30 or against t-distribution if n<30.  However, this approach doesn't account for n, the size of the sample. What is the right way to solve this question provided there is only single sample S?


Is this right way to initialize an array of objects?

public class HelloWorld{   class Student { int marks;  }   public static void main(String []args){  Student studentArray[] = new Student[2]; studentArray[0].marks = 100; studentArray[1].marks = 75;  int m=0; m = studentArray[0].marks;  System.out.println(m);       } }   This compiles with no problem but when I execute it, I am getting null pointer exception error as following:      Exception in thread "main" .lang.NullPointerException at   HelloWorld.main(HelloWorld.java:13)   can somebody help me to locate where the cause is?


How do I embed my icons, and resource files into my EXE while using Visual Studio 2012 and C#

I have created a C# WinForm app.   I would like a single EXE file instead of  appname.exe Resource\file1.ext Resource\file2.ext Resource\file3.ext   How can I embed my resources into my exe and how will my code change?  One line of code is   Help.ShowHelp(this, "Resources\\help.chm");   The other files I have are text files with values for the "About" window.


Here is one definition of a differential equation:  "An equation containing the derivatives of one or more dependent variables, with respect to one of more independent variables, is said to be a differential equation (DE)" (Zill - A First Course in Differential Equations)  Here is another:  "A differential equation is a relationship between a function of time & it's derivatives" (Braun - Differential equations and their applications)  Here is another:  "Equations in which the unknown function or the vector function appears under the sign of the derivative or the differential are called differential equations" (L. Elsgolts - Differential Equations & the Calculus of Variations)  Here is another:  "Let $f(x)$ define a function of $x$ on an interval $I: a < x < b$. By an ordinary differential equation we mean an equation involving $x$, the function $f(x)$ and one of more of it's derivatives" (Tenenbaum/Pollard - Ordinary Differential Equations)  Here is another:  "A differential equation is an equation that relates in a nontrivial way an unknown function & one or more of the derivatives or differentials of an unknown function with respect to one or more independent variables." (Ross - Differential Equations)  Here is another:  "A differential equation is an equation relating some function $f$ to one or more of it's derivatives." (Krantz - Differential equations demystified)  Now, you can see that while there is just some tiny variation between them, calling $f(x)$ the function instead of $f$ or calling it a function instead of an equation but generally they all hint at the same thing. However:  "Let $U$ be an open domain of n-dimensional euclidean space, & let $v$ be a vector field in $U$. Then by the differential equation determined by the vector field $v$ is meant the equation $x' = v(x), x \in U$. Differential equations are sometimes said to be equations containing unknown functions and their derivatives. This is false. For example, the equations $\frac{dx}{dt} = x(x(t))$ is not a differential equation." (Arnold - Ordinary Differential Equations)  This is quite different & the last comment basically says that all of the above definitions, in all of the standard textbooks, are in fact incorrect. Would anyone care to expand upon this point if it is of interest as some of you might know about Arnold's book & perhaps be able to give some clearer examples than $\frac{dx}{dt} = x(x(t))$, I honestly can't even see how to make sense of $\frac{dx}{dt} = x(x(t))$. The more explicit (and with more detail) the better! A second question I would really appreciate an answer to would be - is there any other book that takes the view of differential equations that Arnold does? I can't find any elementary book that starts by defining differential equations in the way Arnol'd does & then goes on to work in phase spaces etc... . Multiple references welcomed.


Nautilus: Visited directory via symlink, now I can't go one level up in the target directory hierarchy

I created a shortcut via "make link" option. When I enter to this shortcut's folder I can't see any folders above it so I can't easily navigate to them.  Is there a way to go one folder up in the GUI? Maybe a hotkey? (Can't do cd .. this time ^__^ ).      In Windows for example I am indeed able to navigate in the way I describe, here is a Win10 image that explains it:


What do indexed mean in 'indexed family' in set theory?  Thanks! :)


How do I make tabs in a JTabbedPane rearrangeable?

I want to be able to move my tabs in my jTabbedPane left or right to change the sorting order. I looked around but I noticed most of what I found is asking how to drag and drop a tab in. I just want to make it resortable so that I can move the rightmost tab to the left of the leftmost tab or any order I want.   I know for table columns in a JTable, there is a method, something along the lines of   JTable table = new JTable(); table.setReordering(false); //disables reordering of columns   which prevents this so this functionality is already enabled with columns in tables but with tabs in JTabbedPanes, I cannot find any method similar to this but I'm thinking it would be something similar like  tab.setReordering(true)    as well but I don't see anything.


Bacteria resistance to natural antibiotics?

It is a known fact that bacteria develop immunity to antibiotics. Why then did not all bacteria develop immunity to natural antibiotics like penicillin in the fungi?  It is for sure that fungi did not care to continue killing all bacteria so that them won't be able to develop immunity (as we're adviced today to use antibiotics carefully, in order not to develop a superinfection)..  Looking at all the time span that bacteria and fungi exist, it seems unlikely that there'd be any bacteria left not yet immune to penicillin at all. However, that's not the case, the antibiotic is still a rather successful one.


systemd: Grant an unprivileged user permission to alter one specific service

I'm running a private game server on a headless linux box. Because I'm not an idiot, said server is running as its own unprivileged user with the bare minimum access rights it needs to download updates and modify the world database.  I also created a systemd unit file to properly start, stop and restart the server when needed (for said updates, for example).   However, in order to actually call systemctl or service <game> start/stop/restart I still need to log in as either root or a sudo capable user.   Is there a way to tell systemd that for the <game> service, unprivileged user gamesrv is permitted to run the start/stop/restart commands?


I have a 120 GB SSD and a 500 GB HDD .  In the SSD I have partitioned 98 GB (usable) as C: to start Windows and 19 GB as E: to start Ubuntu. In the HDD I have partitioned 350 GB as D: for Windows data and 116 GB as F: for Ubuntu data.  I have not yet attempted to install Ubuntu and want to ask, will this work?


I would like to know what are the causes for a chiffon cake to have a caved in centre.  After baking, the cake turns out with a nice dome. The cake is overturned immediately to cool. But after about 15 minutes of cooling, the centre of the cake which was previously a dome became caved in (not too deeply caved in, maybe just about 2cm from the level of the cake height.)  So the result after the cake is cooled, the top of the cake (which was previously the bottom) is light and fluffy and the bottom of the cake (which was previously the top) is dense.   The sides and bottom of the cake are evenly browned. The sides do not shrink as much as the centre.   The cake is baked at 160C-Fan for 45min for a 5-egg recipe. I use cake flour and a very small amount of baking powder.


Is a Maclaurin series in an interval that doesn't include $0$ unique?

In interval q, $0\notin q$, ( e.g.[1,2] ), $   \sum_{n=0}^\infty a_nx^{n} $ converge to $0$. Can there be an $a_i$ that $a_i \ne 0$?  p.s I know the case when $0 \in q$, where you can prove it by derivative.  p.p.s  I asked the question in mathoverflow(now I know it is for mathematicians to ask each other questions about their research.).   it seems it     follows from the uniqueness theorem for holomorphic functions   ?


I have been trying to render a thumbnail for a Roblox game. I have everything ready I just need to render it. When I try to render the final product It only shows the terrain and not the actual people. I think something is wrong with the camera. Not sure though.


Why couldn't Voldemort view the prophecy without Harry's help?

Voldemort filled Harry's mind with visions of Sirius dying in the Department of Mysteries, to lure Harry there.  This was because the prophecies were enchanted so that only the people referred to could lift them from the shelves. Albus Dumbledore:     ‘Only the people to whom they refer can lift [prophecies] from the shelves without suffering madness ...’   But the prophecy also referred to Voldemort, at least as much as Harry! Why couldn't he just go and take the prophecy off the shelf?    An analysis of the prophecy     The one with the power to vanquish the Dark Lord approaches That's a reference to Voldemort      Born to those who have thrice defied him The 'him' is Voldemort      Born as the seventh month dies      And the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not Clearly referring to Voldemort      And either must die at the hand of the other for neither can live while the other survives and again. This line also means that the prophecy is also about Voldemort as well as Harry, rather than just referring to him.      The one with the power to vanquish the Dark Lord will be born as the seventh month dies and yet again.   Voldemort was referred to on almost every line of the prophecy.  Why did he need Harry to take the prophecy off the shelf?


Easy way to quickly locate the mouse pointer?

I am visually impaired, and find it really difficult to locate the mouse pointer on screen. (I am running Ubuntu 16.04.3 LTS) Other OS's have built-in methods to make the mouse pointer more easily visible. In Windows you can turn on "pointer trails" where moving the pointer will  making it easier to visually track/follow the pointer. (I nicknamed them "mouse droppings" ;-) ) And in MacOS Sierra, Apple added a feature whereby if you jiggle the mouse pointer (move it back and forth rapidly) it will , again to make it easier to see on screen. Is there a similar feature (either built-in or provided by a third-party app) for Ubuntu?


I have below javascript code which is used to convert 15 digit salesforce ID to 18 digit salesforce Id:  document.getElementById("convert").addEventListener("click", myFunction); function myFunction(){     var digit = document.getElementById("15digitId").value;      var suffix = '';     var flags;     var alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ012345",     isUppercase = function(c) {                 return c >= "A" && c < = "Z";             };     alert(digit.length);      for(var i=0;i < 3; i++){         alert(".. 1st loop.. ");         flags=0;         for(var j=0;j < 5; j++){             alert(digit.substring(i*5+j,i*5+j+1));             var c = digit.substring(i*5+j,i*5+j+1);              if(c.toUpperCase().equals(c) && c >= 'A'&& c <= 'Z'){                 flags = flags + (1 << j);             }          if(flags <= 25){             suffix = suffix + 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.substring(flags,flags+1);             }else{             suffix = suffix + '012345'.substring(flags-25,flags-24);          }         }     }     document.getElementById('18digitId').value = digit + suffix; }   This code is working till var c = digit.substring(i*5+j,i*5+j+1); line and after that it stopped working


show that $\int_{0}^{\infty} \frac {\sin^3(x)}{x^3}dx=\frac{3\pi}{8}$

show that  $$\int_{0}^{\infty} \frac {\sin^3(x)}{x^3}dx=\frac{3\pi}{8}$$  using different ways  thanks for all


Why can't we list out the most close voted first at review queue?

Why can't we list out the most close voted questions first in the review queue? While reviewing duplicate questions I noticed that the least close voted questions (1 close vote) and the most close voted questions (4 close votes) get listed in no apparent order.  Why can't we sort the questions, starting from most close voted to least close voted? It would help to close questions sooner.


Is it possible to customize the side panel, when you press N in the 3d view, in 2.92?

Like the title says I want to customize the side panel, mainly I want to remove some of the properties from add-ons that I got. A lot of it is import and export add-ons, but I only use it for that, not the side panel property stuff. I don't want to get rid of the add-ons, as I do use them. I just want to clean up the side panel to make it easier to navigate. This V


How do I deal with a compromised server?

This is a  about Server Security - Responding to Breach Events (Hacking)   See Also:                  Canonical Version I suspect that one or more of my servers is compromised by a hacker, virus, or other mechanism:   What are my first steps? When I arrive on site should I disconnect the server, preserve "evidence", are there other initial considerations? How do I go about getting services back online? How do I prevent the same thing from happening immediately again? Are there best practices or methodologies for learning from this incident? If I wanted to put a Incident Response Plan together, where would I start? Should this be part of my Disaster Recovery or Business Continuity Planning?   Original Version       2011.01.02 - I'm on my way into work at 9.30 p.m. on a Sunday because our server has been compromised somehow and was resulting in a    attack on our provider. The servers access to the Internet   has been shut down which means over 5-600 of our clients sites are now   down. Now this could be an FTP hack, or some weakness in code   somewhere. I'm not sure till I get there.      How can I track this down quickly? We're in for a whole lot of   litigation if I don't get the server back up ASAP. Any help is   appreciated. We are running Open SUSE 11.0.            2011.01.03 - Thanks to everyone for your help. Luckily I WASN'T the only person responsible for this server, just the nearest. We managed   to resolve this problem, although it may not apply to many others in a   different situation. I'll detail what we did.      We unplugged the server from the net. It was performing (attempting to   perform) a Denial Of Service attack on another server in Indonesia,   and the guilty party was also based there.      We firstly tried to identify where on the server this was coming from,   considering we have over 500 sites on the server, we expected to be   moonlighting for some time. However, with SSH access still, we ran a   command to find all files edited or created in the time the attacks   started. Luckily, the offending file was created over the winter   holidays which meant that not many other files were created on the   server at that time.      We were then able to identify the offending file which was inside the   uploaded images folder within a  website.      After a short cigarette break we concluded that, due to the files   location, it must have been uploaded via a file upload facility that   was inadequetly secured. After some googling, we found that there was   a security vulnerability that allowed files to be uploaded, within the   ZenCart admin panel, for a picture for a record company. (The section   that it never really even used), posting this form just uploaded any   file, it did not check the extension of the file, and didn't even   check to see if the user was logged in.      This meant that any files could be uploaded, including a PHP file for   the attack. We secured the vulnerability with ZenCart on the infected   site, and removed the offending files.      The job was done, and I was home for 2 a.m.            The Moral   - Always apply security patches for ZenCart, or any other CMS system for that matter. As when security updates are released, the whole   world is made aware of the vulnerability.   - Always do backups, and backup your backups.   - Employ or arrange for someone that will be there in times like these. To prevent anyone from relying on a panicy post on Server   Fault.


So I'm asked to prove that $$S_{3}\cong D_{3}$$ where $D_3$ is the dihedral group of order $6$. I know how to exhibit the isomorphism and verify every one of the $6^{2}$ pairs, but that seems so long and tedious, I'm not sure my fingers can withstand the brute force. Is there a better way?


Cannot override systemd timer with specific time

I use systemd-cron which creates unit files under /lib/systemd. The unit file for cron-daily.timer has  [Timer] OnCalendar=daily   This triggers the scripts at midnight. I want them to trigger at 3am instead.  If I create override.conf in the cron-daily.timer.d directory under /etc/systemd/system to have  [Timer] OnCalendar=*-*-* 03:00:00   and run daemon-reload, restart the timer and run systemctl list-timers it still wants to run at 00:00:00. However, if I change my override.conf to have  [Timer] OnCalendar=hourly   then it wants to run hourly as expected. Why can I not override the service to run at a specific time?


PCA standard deviations reported by princomp() in R do not match eigenvalues of the covariance matrix

I am using the function princomp in R to run a principal components analysis.  In the summary() of the model, the standard deviations of the components are listed. However, these standard deviations are not the same as the square root of the eigenvalues. Shouldn't these values be the same?  In an attempt to figure out what was wrong, I also tried to take each observation and multiply each term by its respective coefficient in the first component and then summed them. I then took the standard deviation of all of these calculated values. The standard deviation from this method matched the square root of the eigenvalues.  Why is the standard deviation in the summary not matching the standard deviation I calculated by hand and the square root of the eigenvalues? Am I mistaken in believing they should be the same?  Here is the code:  #import Data data <- T8.5 attach(data)  #name variables names(data) <- c("Total Population", "Median School Years", "Total    Employment", "Health Services Employment", "Median Home Value")  #show data data  #PCA pca <- princomp(data, cor=FALSE, scores=TRUE) eigenvalues <- eigen(var(data), symmetric=FALSE, only.values=FALSE)  #The standard deviations are different in the next two lines summary(pca) sqrt(eigenvalues$values)  #Here is where I tried to calculate the first component by hand load <- with(pca, unclass(loadings)) value <- c(0,0,0,0,0,0,0,0,0,0,0,0,0,0) #Testing the standard deviation for component 1 for (i in 1:14){   sum=0   for (j in 1:5){     sum = sum + data[i,j]*(load[j,1])   }    value[i] = sum } sd(value) #This matches the sqrt(eigenvalues)


What is the Corresponding author about in the list of authors of a Journal or Conference paper? As fas as I read, it is the person who confirms results or whom actually is the intellectual mind of the idea behind the published work. Can it be more than 1 author in some cases then?


How to make permanent change to .config/user-dirs.dirs?

Each time I changed and saved .config/user-dirs.dirs, and after restarted the system, the XDG_DOWNLOAD_DIR are reverted:  diff --git a/.config/user-dirs.dirs b/.config/user-dirs.dirs index 8f6e2db..dcff34e 100644 --- a/.config/user-dirs.dirs +++ b/.config/user-dirs.dirs @@ -7,11 +7,9 @@  #   XDG_PUBLICSHARE_DIR="$HOME/public"  XDG_TEMPLATES_DIR="$HOME/public/template" -  XDG_DESKTOP_DIR="$HOME/private/desktop"  XDG_DOCUMENTS_DIR="$HOME/private/doc"  XDG_PICTURES_DIR="$HOME/private/picture"  XDG_MUSIC_DIR="$HOME/private/music"  XDG_VIDEOS_DIR="$HOME/private/video" - -XDG_DOWNLOAD_DIR="$HOME/var/downloads" +XDG_DOWNLOAD_DIR="$HOME/"   How to make my changes permanent?


The notification tray at the top of Stack Exchange sites: what is it called? And are there other good examples of this?

I'm trying to clean up notifications for a client site and was wondering if the notification pattern that Stack Exchange employs has a name that I can use to search for more examples.


Suppose I have a  and my opponent has a  in play. They attack with the Cavalier, and it becomes tapped. On my turn, I Adapt my Sharktocrab, putting a +1/+1 counter on it and causing its ability to trigger.  Can I target their Cavalier with this ability, preventing it from untapping during their next untap step? Or is it an invalid target, because of rule 701.20a:     To tap a permanent, turn it sideways from an upright position. Only untapped permanents can be tapped.   (Emphasis mine.)  Arena lets me do this, but it seems like it should be forbidden.


Allow user tagging in comments on the app

When you start typing @ on the site, it suggests users who commented before you. This feature doesn't exist in the android app. (which is a shame, because commenting is the easiest action you can do on the app)


I'm writing a program where there is a particular string in a line to be replaced  Below is my sample program.  public class MyFirstJavaProgram {      public static void main(String []args) {         String x="<link rel=\"stylesheet\" type=\"text/css\" href=\"abc.css\" />";         System.out.println(x);      } }    In the above program I want to replace abc.css with xyz.css. I'm aware of general String replacement function like String.replace(oldString, newString), But here the problem is that abc.css changes from file to file. I want to replace anything.css with xyz.css.  Here is a working Example   please let me know how can I do this.  Thanks


I just measured a pair of LEDs "just for fun" and discovered that they're outputting energy. I held one on the LEDs in the sun's direction and the Multimeter went straight up to 10V. I laughed because I had absolutely no clue what's happening inside those things and how...  How is that possible? Are they "solar panels" in a way, because ... how can this be?  Below are two pictures of my "finding":     (I tried plugging an Arduino Mega on the other end to see if it would power on but unfortunately it stayed off)  I also measured the amperage between the two leads, but the only mode that work on my multimeter is the "10A" mode. It stated 0.00(A).  EDIT: The LED has this appareance:


How does one evaluate the "strength" of a hand in Magic the Gathering?

In MTG (or other games), if one player is dealt a strong hand, and the other a weak one, the first player is likely to win. Unless, of course, the first player plays much worse or is unlucky during the course of the game.  How does one evaluate the strength of a hand in MTG? This is NOT a question about when to take a mulligan (which applies only to the weaker hands), but is a general question about all hands, weak, average, strong, and even "come" hands. (An example of a "come" hand, from poker is four to a straight or a flush, that is weaker than one pair, but will be a very strong hand if it "fills.")  I'm using some examples from bridge, which I know better:   One has a disproportionate number of the most powerful cards (three or all four of the aces in the deck). One has a large number of moderately powerful cards (e.g. face cards, not all aces). One has a hand with only average "raw" strength, but that is highly co-ordinated (e.g. seven or eight cards of a single suit for trumps). This can be combined with having few low cards, and hence few weaknesses, in other suits. One has "position", e.g. by playing after an opponent with a slightly weaker hand, so it is easy to "cancel" or "one-up" him.   What are similar, or analogous advantages in MTG? Are there "standard" evaluation methods, as there are in bridge (with its high card point count), or is it more of a situational thing?


I use a LaTeX template which center aligns all section titles. I want to left align these section titles but I do not know how. I tried  \begin{flushleft} \section{\textbf{Introduction and Background}} \end{flushleft}   but it has no effect on the section title (i.e., it is still centered). I tried   \begin{flushleft} \textbf{Introduction and Background} \end{flushleft}   and it is left aligned the word "Introduction and Background" but it is no longer a section title and thus the numbering using section number are all messed up.   I am new to LaTeX so please keep it simple.


16.04 LTS kernel upgrade fails to update

My kernel in my 16.04 LTS installation doesn't seem to be upgrading.  It is  stuck at the 4.4.0-116 kernel I got when I initially upgraded to 16.04.    I thought 16.04.5 ahould have the 4.15 kernel.  Am I not getting the point releases (I thought I was supposed to get the point releases automatically)?  I've seen references to HWE for 16.04 kernel upgrades but I have no clue what this is or what it means.  It apparently has something to do with the X stack, which makes me nervous; kernel upgrades back when I was on 12.04 caused me X server crashes on boot up.  (This got fixed when I upgraded to 16.04.)    aptitude is not showing any kernel upgrades past 4.4.0-116.  What should I do to get kernel upgrades?


So, I started out by trying to find the 100th Fibonacci number using a recursive function and by memoizing the function using the following code.  Function.prototype.memoize = function () {     var originalFunction = this,         slice = Array.prototype.slice;         cache = {};     return function () {         var key = slice.call(arguments);         if (key in cache) {             return cache[key];         } else {             return cache[key] = originalFunction.apply(this, key);         }     }; };  var fibonacci = function (n) {     return n === 0 || n === 1 ? n : fibonacci(n - 1) + fibonacci(n - 2); }.memoize();  console.log(fibonacci(100));   Now, as you can see in  fiddle, JavaScript logs 354224848179262000000 as the result. The hundredth Fibonacci number is actually 354224848179261915075 according to  which is correct.  Now, my question is this. Why does the number compute incorrectly, even though the algorithm is completely sane? My thoughts point to JavaScript because according to 1, the two numbers are equal.  What is it about JavaScript that causes such an error? The number is safely within limits of the maximum value of an IEEE 754 number, which is 1.7976931348623157e+308.  1In case this could be a bug on my platform, I have tested this on both Chromium and Firefox on Ubuntu.


Does LR automatically apply lens profiles?

I am looking at buying a Nikon D810 with 20mm 1.8, 50mm 1.8, and 85mm 1.8. I use LR 5.7.1 and Windows 7.0. I found the files that LR stores its lens profiles in and all three lenses are listed there. My question is: After I upload a picture to LR, will LR automatically find the correct profile from the LR lens profile files and use it for corrections?


Which Ubuntu should I run on my Windows PC

I intend to dual boot Ubuntu 16.04 and Windows 10 but I'm a bit confused about the information on the official Ubuntu website:     64-bit PC (AMD64) desktop imageChoose this to take full advantage of computers based on the AMD64 or EM64T architecture (e.g., Athlon64, Opteron, EM64T Xeon, Core 2). If you have a non-64-bit processor made by AMD, or if you need full support for 32-bit code, use the i386 images instead.32-bit PC (i386) desktop imageFor almost all PCs. This includes most machines with Intel/AMD/etc type processors and almost all computers that run Microsoft Windows, as well as newer Apple Macintosh systems based on Intel processors. Choose this if you are at all unsure.   Now, my Windows machine is 64-bit with Intel processor. Which of the architecture of Ubuntu should I install, 32-bit or 64-bit


Should I capitalise the first letter when a sentence starts with a number?

When starting a sentence with a number, should the first letter be capitalised?  For example,     96% Real meat.   or     96% real meat.


Why is my "pre" HTML tag not working in one specific instance?

I have some html that uses a few "pre" tags to preserve code snippets, using "html" as the lang. For the most part, it works, but in one specific instance, namely:

Images

   Instead of preserving the snippet, it shows a bullet and a hyperlinked "Images" - what the deuce?  The whole shebang can be seen, malformed, beneformed, and/or mutilated at:


How to password protect streaming videos with php

What is the best way to password protect quicktime streaming videos using php/.htaccess. They are being streamed using rtsp, but I can use other formats if necessary.  I know how to do authentication with php, but I'm not sure how to setup authentication so that will protect the streaming files urls so that a user can't just copy the url and share it.  Or am I overthinking this and I can just use a normal authentication scheme and place the files in a protected directory?


Calculating the Riemann sum $\lim_{n \to \infty} { \sum_{k=1}^{n} { (\frac{nk-1}{n^3})\sin(\frac{k}{n}) } }$

We need to calculate this:  $$\lim_{n \to \infty} { \sum_{k=1}^{n} { (\frac{nk-1}{n^3})\sin(\frac{k}{n}) }       }$$  So I know this is Riemann sum. This is what I started doing:     $$\sum_{k=1}^{n} { (\frac{nk-1}{n^3})\sin(\frac{k}{n})}  = \sum_{k=1}^{n} { (\frac{k}{n^2 } - \frac{1}{n^3})\sin(\frac{k}{n})}$$   But then I noticed that we can not get $\frac{1}{n}$ outside. How do we exactly know what is the partition?


getting “ConcurrentModificationException” even though i m using iterator?

I m getting ConcurrentModificationException but i dont really understand why.. When i use an iterator shouldnt it supposed to work fine ?  public void nextDay(){         int range = (10 - 0) + 1;          ListIterator<User> it = this.socialNetwork.getPeopleInNetwork().listIterator();             while(it.hasNext()) {              User user = it.next();                int random = (int)(Math.random() * range) + 0;             if(user.getFriends().size()<=25){                 try {                      this.socialNetwork.getPeopleInNetwork().add(user.addFriend(new UserImpl("new","user")));                     user.addFriend(this.socialNetwork.getPeopleInNetwork().get(random));                 } catch (IllegalArgumentException | UserAlreadyInFriendListException e) {                     logger.error(e.getMessage());                 }             }else{                 try {                     this.socialNetwork.getPeopleInNetwork().add(user.addFriend(new UserImpl("new","user")));                     this.socialNetwork.getPeopleInNetwork().add(user.addFriend(new UserImpl("new","user")));                     this.socialNetwork.getPeopleInNetwork().add(user.addFriend(new UserImpl("new","user")));                     user.addFriend(this.socialNetwork.getPeopleInNetwork().get(random));                 } catch (IllegalArgumentException | UserAlreadyInFriendListException e) {                     logger.error(e.getMessage());                 }              }         }     }


Updated as original was unclear.  I'm setting up postfix on a computer to work with my email's SMTP.  I don't want to enter my credentials in plain text, especially when typing in public.  Is it possible to make bash not show my input for a command or two?  Example: I'm entering a series of commands and then I want to echo a username and password into a config file.  I'd like to quickly go into a mode where my input isn't shown on screen, then easily leave that mode with ctl+c.


What do parameterless constructors mean when explicitly called at declaration

The question sounds a bit odd, but check the code sample  #include <iostream>  using namespace std;  int main() {     string a, b(), c("test");      // No problems     a = c;      // tester.cpp:9:7: error: assignment of function ‘std::string b()’     b = c;      // tester.cpp:10:7: error: invalid conversion from ‘std::string (*)() {aka std::basic_string<char> (*)()}’ to ‘char’     a = b;      // No problems     c = a; }   You can see that it looks like b is created with the default constructor, but in fact it is not. So my question is really is, what does string b() mean?


I was looking at  and I didn't realize that Minecraft had some Easter eggs in it. Besides the Christmas chest Easter egg, and the sheep Easter egg, what else is there?


i know this question has been asked a lot on superuser, but i am stuck as i have checked with different applications, windows system information, vmware processor x64 processor utility, cpu-z, securable, registry entry..and i am getting different results. i have windows 8 32-bit.  windows system information  System Type X86-based PC  System Properties    vmware guest64check    cpu-z    Securable    Why am i getting different results in windows system info and vmware processor utility, and what exaclty is my machine type? Will it be able to run windows 8 64-bit?  Thanks.


How to access and use custom class in the form of arrays in Java?

I am trying to create a custom class Student, which contains 2 fields, Name and Marks. I read on the internet that I need Getters & Setters to do so. So, I wrote the following code but it is giving me a NullPointerException. import java.util.*;  class Student {     public String name;     public int marks;     public int getMarks()     {         return this.marks;     }     public void setMarks(int marks)     {         this.marks = marks;     }     public String getName()     {         return this.name;     }     public void setName(String name)     {         this.name = name;     } } public class getterSetter {     public static void main(String[] ab)     {         Scanner s = new Scanner(System.in);         int n = s.nextInt();         int x;         Student[] student = new Student[n];         String[] inputs = new String[n];         s.nextLine();         for(int i = 0; i < n; i++)         {             String xx = s.nextLine();             inputs[i] = xx;         }         for(int i = 0; i < n; i++)         {             String[] words = inputs[i].split("\\s+");             student[i].setName(words[0]);             student[i].setMarks(Integer.parseInt(words[1]) + Integer.parseInt(words[2]) + Integer.parseInt(words[3]));         }         for(int i = 0; i < n; i++)         {             System.out.println(student[i].getName());             System.out.println(student[i].getMarks());         }     } }  The console screen is : java getterSetter 3 abc 10 10 10 def 10 10 10 ghi 10 10 10 Exception in thread "main" java.lang.NullPointerException         at getterSetter.main(getterSetter.java:58)


How to get list of all sobject records modified today in the system?

I need a list of all sobject records that got modified today. this is not just for one object but for all objects in the system. Is there a simpler way to do this?


Return emails from Deleted Items back to their original folders

Someone I know went into the Large Emails "folder" and cleared it out thinking that those were just duplicates. She didn't realize that she was actually deleting the emails from her many folders.  Now, all the emails are in her Deleted Items folder. Since they came from several different folders, reorganizing them back to those folders is going to be a major task.  Is there any way in Outlook 2010 to select all the emails at once and tell it to move them back to the folders they were orginally in?


How the small negative number produced in numpy exactly

I'm seeing many small negative numbers, below is a minimal reproducible example, i.e. -1.77635684e-15 is the small negative number produced. In [1]: import numpy as np  In [2]: np.cumsum(np.array([11.9,  32.6, -32.6, -11.9])) Out[2]: array([ 1.19000000e+01,  4.45000000e+01,  1.19000000e+01, -1.77635684e-15])  However, if I reorder the numbers, -1.77635684e-15 will be gone, e.g. In [3]: np.cumsum(np.array([11.9,  32.6, -11.9, -32.6])) Out[3]: array([11.9, 44.5, 32.6,  0. ])  I understand it likely has something to do with the floating-point arithmetic issue, but I wonder if someone can explain exactly how -1.77635684e-15 is produced in this example or with a more trivial example if one can be found? I'm using python-3.8 and my number version is In [4]: np.__version__ Out[4]: '1.19.1'


Confusion between Voltage gain & Voltage gain in decibels (dB)

The definition of voltage gain is \$V_{\text{out}}/V_{\text{in}}\$.  However, I read some articles about the gain in decibels, and I have a confusion now.  Here is an article about it:   Here, I understand the definition of Power gain in decibels, which is $$ \text{Gain} = 10 \log \left( {P_{\text{out}} \over P_{\text{in}}} \right)\text{ dB} $$  However, I can't understand why Voltage gain in decibels is $$ 20 \log \left( {V_{\text{out}} \over V_{\text{in}}} \right)\text{ dB} $$  If \$ 20 \log \left( {V_{\text{out}} \over V_{\text{in}}} \right)\text{ dB} \$ is derived from $$ 10 \log {\left( {V_{\text{out}}^2 \over R_{\text{out}}}\right) \over \left({V_{\text{in}}^2 \over R_{\text{in}}}\right) }\text{ dB} $$ then this is the power gain, not the voltage gain, isn't it? However, the Wikipedia says it is a formula for the Voltage gain in decibels. I thought the voltage gain in decibels would be \$ 10 \log \left( {V_{\text{out}} \over V_{\text{in}}} \right)\text{ dB} \$. Actually, the example section in that linked page uses voltage gain \$ V_{\text{out}} \over V_{\text{in}} \$.  Why did \$V^2/R\$ suddenly come out from the voltage gain in decibels?


Reduce gap between subfloat and subcaption

How can I reduce the gap between the subfloat and its caption? I tried to use   \captionsetup[subfigure]{aboveskip=0pt}    but it doesnt work for me. Below is the snippet i have and the output  \begin{figure} \captionsetup[subfigure]{labelformat=empty} \captionsetup[subfigure]{aboveskip=0pt}     \centering     \subfloat[Ground Truth]{{\includegraphics[width=\textwidth]{ood-ms/ood-1-gt.png} }}     \\ \vspace{-1\baselineskip}     \subfloat[Recurrent Neural Network]{{\includegraphics[width=\textwidth]{ood-ms/ood-1-rnn.png} }}     \\ \vspace{-1\baselineskip}     \subfloat[]{{\includegraphics[width=\textwidth]{ood-ms/ood-1-vrnn.png} }}     \\ \vspace{-0.5\baselineskip} \noindent\rule{14cm}{0.4pt}     \subfloat[]{{\includegraphics[width=\textwidth]{ood-ms/ood-3-gt.png} }}     \\ \vspace{-1\baselineskip}     \subfloat[]{{\includegraphics[width=\textwidth]{ood-ms/ood-3-rnn.png} }}     \\ \vspace{-1\baselineskip}     \subfloat[]{{\includegraphics[width=\textwidth]{ood-ms/ood-3-vrnn.png} }}     \\ \vspace{-0.5\baselineskip} \noindent\rule{14cm}{0.4pt}         \subfloat[]{{\includegraphics[width=\textwidth]{ood-ms/ood-1-gt.png} }}     \\ \vspace{-1\baselineskip}     \subfloat[]{{\includegraphics[width=\textwidth]{ood-ms/ood-1-rnn.png} }}     \\ \vspace{-1\baselineskip}     \subfloat[]{{\includegraphics[width=\textwidth]{ood-ms/ood-1-vrnn.png} }}     \\ \vspace{-0.5\baselineskip} \noindent\rule{14cm}{0.4pt}     \subfloat[]{{\includegraphics[width=\textwidth]{ood-ms/ood-3-gt.png} }}     \\ \vspace{-1\baselineskip}     \subfloat[]{{\includegraphics[width=\textwidth]{ood-ms/ood-3-rnn.png} }}     \\ \vspace{-1\baselineskip}     \subfloat[]{{\includegraphics[width=\textwidth]{ood-ms/ood-3-vrnn.png} }}     \\ \vspace{-1\baselineskip}     \caption{}     \label{fig:ms} \end{figure}   Here is the output


I'm working on a very large scale project and I want to try to make an object with Smoke Inflow but only from certain faces. How would I select or define those certain faces in Edit Mode?


Can i copy the Question from stack overflow and answer it in my blog?

Can i copy the Question from stack overflow and answer it in my blog and place the blog link in stack overflow?  By doing this, Am I violating any of the terms & conditions?  Please let me know? Thanks


Linker not able to find the template function

I have following scenario .. (sorry for the long (& detailed code presentation), but not sure how to explain this problem otherwise) --- misc.cpp ---  template <typename T> const T& mymax(const T &a, const T &b) {     return a > b ? a : b; }  --- misc.h --- #ifndef __MISC_H__ #define __MISC_H__  template <typename T> const T& mymax(const T &a, const T &b);  #endif /* __MISC_H__ */  --- test.cpp --- include <iostream> #include "A.h" #include "misc.h"  using namespace std;  int main(int argc, char *arg[]) {     A turtle {"Turtle", 70}, hbird{"Humming bird", 47};          turtle.show();     hbird.show();     A animal = mymax<A>(turtle, hbird);     animal.show();      return 0; }  --- A.h --- #ifndef __A_H__ #define __A_H__ #include <iostream> // for std::ostream class A {     friend std::ostream& operator<<(std::ostream &, const A&);     private:         char *str;         int i;     public:         A(const char *, int);   // Overloaded constuctor         A();                    // No-args constructor         ~A();                   // destructor          A(const A&);            // copy constructor         A(A&&);                 // move constructor         A& operator=(const A&); // copy assignment         A& operator=(A&&);      // move assignment         bool operator>(const A&) const;         void setint(int i=0);         void show();            // display };  #endif /* __A_H__ */  A implements operator> like this -- --- A.cpp --- bool A::operator>(const A& rhs) const {     if (i > rhs.i)         return true;     return false; }   Now if I build it, it is giving me below error:  make g++ -g -std=c++14 -Wall -c A.cpp g++ -g -std=c++14 -Wall -c misc.cpp g++ -g -std=c++14 -Wall -c test.cpp g++ -g -std=c++14 -Wall A.o misc.o test.o -o test /usr/bin/ld: test.o: in function `main': /home/onkar/cc/learncpp/stl/test.cpp:23: undefined reference to `A const& mymax<A>(A const&, A const&)' collect2: error: ld returned 1 exit status make: *** [Makefile:5: test] Error 1  Not sure what's wrong. Can anyone, please help me figure this out.


So guys I have this improper integral $\int_{0}^{\infty}\frac{x}{x^3+1}dx$. I checked that it converges by $ \int_{0}^{1}\frac{x}{x^3+1}dx + \int_{1}^{\infty}\frac{x}{x^3+1}dx $ and using the $\frac{c}{(x-a)^\lambda}  $ and $\frac{1}{x^\lambda} $ criteria. But for finding the value I have trouble.I tried $ \int_{0}^{\infty}\frac{x}{(x+1)(x^2-x+1)}dx$ and $\int_{0}^{\frac{\pi}{2}}\frac{tg\alpha}{tg\alpha^3+1}dx$ but it gets me nowhere. Any ideas on solving it?


How to hide files with a specific extension

I have set of temp files created in my folder with .bak extensions. How can I make them hide by default in Ubuntu?  I tried adding a .hidden file with *.bak as entry in the file, but that is not working. Any help is very appreciated...


How do I get the font name from a font file?

Say I have a file "foo_whatever.ttf"  Is there a command line tool to get the actual font name from the file?    The below link does contain the answer but I didn't turn it up in my search results, in particular "/fonts name".  Looking back, I could have used a more general search.  What is mod policy on this?    This is in fact the link I found that led me to the correct answer (where I learned of the rest of the fc- commands:


I have actually an enum in c++:  class myClass { public:     enum ExampleType     {        TEST1        TEST2        TEST3        TEST4     } };   I would like to print the enum not as number but as String.. Actually it prints 0 .. 1 .. 2 .. 3 I would like it print TEST1 or TEST2 etc ...  I already try Switch case as :   std::string type;   switch (this->type)     {     case 0:   type = "TEST1";     case 1:   type = "TEST2";     case 2: type = "TEST3";     case 3: type = "TEST4";     }   then print type, but he don't go in the right case ..  How can it be possible ?


$M\otimes A_\mathfrak{p}/\mathfrak{p}A_\mathfrak{p}\neq0$ if and only if $\text{Ann}(M)\subseteq \mathfrak{p}$?

Let $A$ be a Noetherian ring, $M$ be a finitely generated $A$-module, and $\mathfrak{p}$ be a prime ideal in $A$. I want to ask how to prove that $M\otimes A_\mathfrak{p}/\mathfrak{p}A_\mathfrak{p}\neq0$ if and only if $\text{Ann}(M)\subseteq\mathfrak{p}$. Thanks.


In edit mode, if I move a vertex the whole mesh is transformed

Not sure what I've done or pressed, but in edit mode if I select a vertex/edge/face the whole mesh is transformed when I grab, rotate, etc. Also if I add new mesh elements and scale for instance even unselected elements are scaling  What have I pressed?  Thanks John


I need a search icon button icon in my compoonent. I have got the code as well. Below is the link from where i have referred the code.     The problem that i am facing is for the svg.  the error says "Failed to save AddressSearch.cmp: No COMPONENT named markup://svg found : [markup://c:AddressSearch]: Source"  If there is no svg. how i create one for this kind of button???   <button class="slds-button slds-button_icon slds-button_icon-brand" title="Search"> <svg class="slds-button__icon" aria-hidden="true"> <use xlink:href="/assets/icons/utility-sprite/svg/symbols.svg#search"></use> </svg> Search </button>


INotifyPropertyChanged vs. DependencyProperty in ViewModel

When implementing the ViewModel in a Model-View-ViewModel architecture WPF application there seem to be two major choices how to make it databindable. I have seen implementations that use DependencyProperty for properties the View is going to bind against and I have seen the ViewModel implementing INotifyPropertyChanged instead.   My question is when should I prefer one over the other? Are there any performance differences? Is it really a good idea to give the ViewModel dependencies to WPF? What else do I need to consider when make the design decision?


Plural or singular: "The socks in these pictures [are/is] the left one, before and after it was cleaned." Is the correct conjugation "are" or "is"?

"The socks in question [are or is] the left one, before and after it was cleaned." Is the correct conjugation "are" or "is"?  In the above sentence (and this one), a pair of socks is expected, but it is introduced that the two socks are/is in fact the same one. Should the plural or singular form of the verb be used?


Should you unplug the cable once your MBP is fully charged?

With Mavericks is this still needed? Doesn't this eventually cause the battery to die faster because it means it'll have to go through more cycles frequently?


Does one always need some choice to show the existence of nonprincipal ultrafilters?

The last sentence of the section "Types and existence of ultrafilters" of  () says:  In ZF without the axiom of choice, it is possible that every ultrafilter is principal.{see p.316, [Halbeisen, L.J.] "Combinatorial Set Theory", Springer 2012}  This statement is incorrect isn't it? Shouldn't "ultrafilter" here be replaced by "ultrafilter on $\mathscr{P}(\omega)$ (the power set of the set of natural numbers)"? I think that for some Boolean algebras, one can show the existence of a nonprincipal ultrafilter without assuming the axiom of choice (or the ultrafilter lemma or the Boolean prime ideal theorem). Let $B$ be the set of all finite and cofinite subsets of the set of natural numbers, and let $U$ be the set of all cofinite subsets of the set of natural numbers. Then $U$ is a nonprincipal ultrafilter on the Boolean algebra $B$, isn't it? I would also like to ask the following more general question: for what kind of Boolean algebra, can one show the existence of a nonprincipal ultrafilter without assuming some choice? EDIT: I am not asking whether there is an infinite Boolean algebra with a unique ultrafilter (unless "nonprincipal ultrafilter that can be found without choice" and "unique filter" should mean the same thing, which I fail to see). I am first asking whether my example is a counterexample to the statement from Wikipedia. Assuming that I am right about this first point, I am then asking in what cases you can find nonprincipal ultrafilters without using choice. I actually don't know what $\mathcal{P}(\omega)/\text{fin}$ denotes in the suggested question. In any case, the answer given there is only an example and cannot be an answer to my question. I would appreciate if you could explain how my question is a duplicate or reopen my question so that people could provide answers that I would be able to understand.


Here my code:  As you can see on the image, the first space is squeezed; I don't understand why.  \documentclass{article}  \usepackage{datatool} \usepackage{colortbl}  \begin{filecontents*}{bogus_first_char.csv} nom, prenom A la la, toto B lala, titi C yoyo, tutu \end{filecontents*}  \begin{document}  \DTLloaddb{dat}{bogus_first_char.csv} \begin{tabular}{ll}   nom & prenom \\   \DTLforeach{dat}{\nom=nom, \prenom=prenom}{   \\ \nom & \ prenom} \end{tabular}  \end{document}


Error: Counter too large! with \alph{cntr} and cntr>26

I would like to have \alph{counter} for values larger than 26. The following MnWE gives me the error ! LaTeX Error: Counter too large.  \documentclass{article} \begin{document}  \begin{enumerate} \def\theenumi{\alph{enumi}} \setcounter{enumi}{24} \item twenty-five \item twenty-six \item twenty-seven \end{enumerate}  \end{document}   I would like it to behave like one of these:  ..., x, y, z, aa, bb, cc, ..., xx, yy, zz, aaa, bbb, ccc, ... (preferred) ..., x, y, z, aa, ab, ac, ..., ax, ay, az, ba,  bb,  bc,  ... (can be if nothing else works)   A solution without LaTeX3 extensions would be awesome as I cannot run LaTeX3 extensions.


what is the spelling rule that applies to "zeros" and "heroes"?

What is the proper spelling rule that applies to "zeros", "heroes" and the like?


Every prime number divide some sum of the first $k$ primes.


Excel function working like SQL group by + count(distinct *)?

Suppose I have an Excel sheet with below data    CODE (COL A) | VALUE (COL B) ==============================   A01         | 10   A01         | 20   A01         | 30   A01         | 10   B01         | 30   B01         | 30   Is there an Excel function working like ..    SELECT CODE, count (Distinct *) FROM TABLE GROUP BY CODE    CODE    | Distinct Count of Value ===================================   A01    | 3   B01    | 1   or, better yet, can I have an Excel formula pasted in column C to get something like this:     CODE (COL A) | VALUE (COL B) | DISTINCT VALUE COUNT WITH MATCHING CODE (COL C) ===============================================================================   A01         | 10            | 3   A01         | 20            | 3   A01         | 30            | 3   A01         | 10            | 3   B01         | 30            | 1   B01         | 30            | 1   I know I can use pivot table to get this result easily. However due to reporting requirements I have to append the "distinct count" column to the Excel sheet, hence pivot table is not an option.  My last resort is to use Excel macros (which are fine), but before that I would like to learn whether Excel functions can accomplish this kind of task.


How do I enter a directory on a different hard drive using cd in the terminal?

I have Ubuntu 16.04 installed on my SSD and I have a HDD where I keep all of my C++ files and programs. Ubuntu recognizes that I have the HDD. When I am in the terminal and want to access my c++ files on the hdd how do I get the directory? I tried using cd then the name of the drive but that didn't work.  I'd like to make it so that every time I start my terminal I am automatically in the HDD instead of desktop too.


How to List Multiple Figures in One Line of the List of Figures

Is there a way to condense multiple figures into one line for the List of Figures?  For instance, I have an appendix of measurements that are figures, which total about 600 images (multiple measurements made at multiple stations) that I don't necessarily want listed out individually, so can you force the List of Figures to read:  Figure B.1-B.30  Diagnostic Plots for station APZ....................302-310  Figure B.31-B40  Diagnostic Plots for station CRLZ...................311-320  etc.?


Why are extra timelike dimensions seldom considered?

There are a number of models (String theory, Cascading Gravity, Emergent Dimensions) that contain extra space like dimensions. Why do people tend to avoid considering extra timelike dimensions?  The only reason I have heard so far is that you want to avoid close timelike curves (which would violate causality). I would think that if causality is respected in our usual time dimension, we could (at least for the purpose of initial toy models) demand causality be respected in other time dimensions as well.  (The m+n dimensional question linked to was asking about what happens if m and n are be integers.)


Using binary data as a parameter in bash - any way to allow nuls?

So I'd like to pass the first 512 bytes of binaryFile.dd as the second parameter to myProgram but bash strips out all the NUL chars. Is there any way to avoid this in bash or am I on a hiding to nothing?   myProgram parameter1 "$(head -c 512 binaryFile.dd)"


Do I use kinetic energy or momentum to figure out the final velocity?

Let's say hypothetically that a gun fires a bullet which has a mass of 1 gram and a $V_\mathrm{initial}$ of 10 m/s, which becomes lodged in a wooden block that has a mass of 9 grams and is initially at rest. The impact causes the block (with the lodged bullet) to travel at a velocity $V_\mathrm{final}$. What is $V_\mathrm{final}$?  I'm confused. I don't know whether I should use momentum or kinetic energy to figure out the $V_\mathrm{final}$. I plugged in the numbers to both equations, and the resulting values of $V_\mathrm{final}$ didn't agree.


Redirect script output to /dev/tty1 and also capture output to file

I want to display text output on the console that is always displayed on a small screen on my Raspberry Pi.   The following code works for showing that text output:  cd /home/pi/python_test_scripts_linux && sudo nice -n -20 /home/pi/python_test_scripts_linux/test_wrapper.py > /dev/tty1   Now I want to capture the output in parallel with seeing it on the screen - I have tried 'tee' but that does not show text on the screen and also does not capture it to file:  cd /home/pi/python_test_scripts_linux && sudo nice -n -20 /home/pi/python_test_scripts_linux/test_wrapper.py | tee /dev/tty1 /tmp/capture.txt   How can I redirect the output of my script to /dev/tty1 so I can see it on my screen but also capture the output to file?  UPDATE 1:  Per the answer below - I tried using 'script' - unfortunately it did not work:  script -c "cd /home/pi/python_test_scripts_linux && sudo nice -n -20 /home/pi/python_test_scripts_linux/test_wrapper.py > /dev/tty1" /home/pi/python_test_scripts_linux/report.html   UPDATE 2:  I also tried to 'tail' the output of the file that I redirected the output to into /dev/tty1, but it also did not work:  sudo tail -F /home/pi/python_test_scripts_linux/report.html > /dev/tty1 & cd /home/pi/python_test_scripts_linux && sudo nice -n -20 /home/pi/python_test_scripts_linux/test_wrapper.py > /home/pi/python_test_scripts_linux/report.html


I’m learning on how to code in Apex, and I’m trying to figure out how I can bulkify my code in a better way so that I won’t get SOQLExceptions. Scenario: Whenever I upload a lot of records using data loader to a child custom object called Inventory Snapshot, the system should check if there is a product record in the system. If there is a product record, then I should map the value with the Inventory Snapshot record. If not, then I should create a new Product record. This is my apex trigger code: trigger UpdateCreateProducts on Inventory_Snapshot__c (before insert, after insert) {     if(Trigger.isBefore){         FindOrCreateProducts.findProduct(Trigger.new);         FindOrCreateProducts.createProducts(Trigger.new);     } }  This is my apex class: publicclass FindOrCreateProducts {          public static void findProduct(List<Inventory_Snapshot__c> snapshotList){         List<Product2> prds = new List<Product2>();         for (Inventory_Snapshot__c inv: snapshotList){             prds = [Select Id,ProductCode from Product2 where ProductCode =:inv.Item_Number__c Limit 1];                 if (!prds.isEmpty()){                     for(Product2 prd: prds){                         inv.Product__c = prd.Id;                     }                 }         }     }                  public static void createProducts(List<Inventory_Snapshot__c> invList){         String prodDescr, newProdName, descr;         List<Product2> prds = new List<Product2>();         List<Product2> newPrds = new List<Product2>();         for(Inventory_Snapshot__c invt: invList){             prds = [Select Id,ProductCode from Product2 where ProductCode =:invt.Item_Number__c Limit 1];             if (prds.isEmpty()){                 descr = invt.Product_Description__c;                 Integer colonValue = descr.indexOf(':');                 System.debug('colonValue ' + colonValue);                 if (colonValue != -1){                     prodDescr = descr.substringAfter(':');                     newProdName = invt.Item_Number__c + ' : ' + prodDescr;                     System.debug('Product Name: ' + newProdName);                 }                 else{                     newProdName = invt.Item_Number__c + ' : ' + invt.Product_Description__c;                 }                 Product2 newProd = new Product2();                 newProd.Name = newProdName;                 newProd.Description = descr;                 newProd.ProductCode = invt.Item_Number__c;                 newPrds.add(newProd);             }if(!newPrds.isEmpty() && prds.isEmpty()){                 insert newPrds;                 for(Product2 prd: newPrds){                     invt.Product__c = prd.id;                 }             }         }      }        }  The code will work if I manually test, but won’t work if I’m inserting records using Dataloader. Can anyone help me out on how I should bulkify my code?


What is the difference between IComparable and IComparer Interfaces? Is it necessary to use this interface always with Array.Sort() method


As I was going through my dad's college magazine (of 1989), in the mathematics department quiz section, there was a question:     What is $i^i$, where $i=(-1)^{1/2}$, that is, is $i^i$ a real number, an imaginary number, or undefined?   I was suddenly taken aback, I mean how can be $i$ be raised to the power $i$, I thought may be Cartesian representation helps a bit in solving it but it led me nowhere so can anyone help?


binomial coefficient and recurrence relation

any hints on how to solve the recurrence relations for the following binomial coefficient   \begin{equation}   {n \choose k}=\begin{cases}     1, & \text{if $k\in\{0,n\}$}.\\     {n-1 \choose k-1}+{n-1 \choose k}, & \text{otherwise}.   \end{cases} \end{equation} for $ 0\ge k \le n $


Why we draw finite electric field lines passing through a surface when we can draw infinite ? also why electric flux is proportional to the number of lines passing through a surface ? i am confused because it doesnt make sense to calculate lines ...


$(A\times B)\cap (C\times D)=(A\cap C)\times (B\cap D)$: Proof Strategy for Cross Products of Intersected Sets

How can I prove that $$(A\times B)\cap (C\times D)=(A\cap C)\times (B\cap D)?$$


I have read a lot of posts in the past one hour, but I am still not very clear with the concept of using immutable objects as keys in a Hashmap. I have a hashmap that has its key as a String. The value in the hashmap is MyStore, where MyStore represents information regarding stores I own. The String represents address. In my code, the logic I have is, I first look in the map for that key, if present --> get its value, if its not present put it in hashmap. My manager just told me the key will change in the future, that is address of my stores will change in the future. He said in that case, my logic of first checking if the key exists won't work. I don't understand what he means here. I want to understand the below points very clearly -   Difference between mutable and immutable keys for a hashmap. What happens if you use a immutable key that can change? - I know this doesn't make sense, but I want to clearly understand what my manager is talking about here. Some posts talk about Strings if used as keys in a hashmap cache their hashcode -What does this mean? If lets say I used mutable objects as keys in my hashmap that implemented hashcode and equals, then will it work? I am assuming it will because if the key changes, the contains method will look if the key is present. If it is not present, it will put the entry so you can get it in the future.   I don't mean to create a duplicate post if this has been discussed before. If I missed reading the post that has answers to all my questions, please point me to it. If not, please explain in layman terms the above questions I have so it is useful in the future for other readers :). Feel free to edit my post's subject so in future if anyone has a similar question, they land here directly :)


What book would you recommend as a decent 'intro to UX' aimed at non-practitioners?

Via @uxbooks on Twitter I often get asked to recommend books on various subjects. Recently I was asked which book I would recommend to a non-practitioner as an intro to UX. I opened the question up and thought I'd do the same on here to see what people thought.  EDIT: Please up vote the answers you agree with so we can promote the most popular suggestions for future reference.


Doubt on proof showing matrices of certain rank form a submanifold.

I have gone through two proofs to show that matrices of rank $k$, where $0 \leq k \leq \min(m,n)$ form a submanifold of the set $ M(m \times n ,\mathbb{R}) $. Both proofs involve writing down an arbitrary matrix in the set considered, as :  $$ X = \begin{bmatrix} A & B \\ C & D \\ \end{bmatrix}$$  where $A$ is assumed to be of a minor of order $ k \times k$ that has non-zero determinant,(which I understand) and then they ask us to consider either the matrix :  $$ M_X= \begin{bmatrix} A^{-1} & -A^{-1}B \\ 0      &  I_{n-k} \\ \end{bmatrix}$$  or alternatively:  $$M_X= \begin{bmatrix} I & -A^{-1}B\\ 0 &  I \end{bmatrix}$$  This is followed by multiplication of $X$ with $M_X$. I understand what follows next. But this particular choice of matrix seemed to be picked out of the air as I viewed it.Could anyone please help motivate this idea??  Ref: The proof is found in J.Lee's Introduction to Smooth Manifolds, pg 117, ex 5.30.


With a short term C type visa, is the allowed duration a six month stay or the visa expiry date?  Because the duration of stay is 180 days. I entered the UK on September 27; my visa will expire on 12 October. How long I can stay in UK in this case?  If I stay after 12 October is it overstay or I can stay maximum 180 days from the date of entry even if the visa expires. What is over stay in this case please let me know.


In python using string arrays inside class

Hi I am new to Python and have an issue with using arrays in class.  When using array of strings, when I update one of the arrays with a string - all the other array entries get the same value.  Your kind guidance will be appreciated.  I am showing below the working code - without using arrays and then the same using arrays (which is not working). #Working Code:  class sessionData:     num_threads = 0     session_id = []     audio_check_audio_1 = []     audio_check_audio_2 = []     audio_check_audio_3 = []       def __init__(self, id, f1, f2):         self.id = id   #in main function later on:        if (session_id not in sessionData.session_id):             sessionData.audio_check_audio_1.append(wav_file_name1)             sessionData.audio_check_audio_2.append(wav_file_name1)             sessionData.audio_check_audio_3.append(wav_file_name1)             sessionData.session_id.append(session_id)         else:              i = sessionData.session_id.index(session_id)              if (recording_number == '1'):                 sessionData.audio_check_audio_1[i] = wav_file_name1             elif (recording_number == '2'):                 sessionData.audio_check_audio_2[i] = wav_file_name2             else:                 sessionData.audio_check_audio_3[i] = wav_file_name3  #Not working code:  class sessionData:     num_threads = 0     session_id = []     audio_check_audio = [[]*3]       def __init__(self, id, f1, f2):         self.id = id   #in main function later on:      if (session_id not in sessionData.session_id):          sessionData.session_id.append(session_id)         sessionData.audio_check_audio.append([wav_file_name[0],'',''])      else:           i = sessionData.session_id.index(session_id)           for x in range 3:               sessionData.audio_check_audio[i][x] = reg_wav_file[x]


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