Qusetion: Prove $\phi(G)$ is cyclic if $\phi$ : $G \to H$ is  group homomorphism and $G$ is cyclicDo I do something like this to prove this: Let $G$ be a cyclic group and $G$=$\langle g \rangle$Then $\phi$ : $\mathbb Z \to \langle g \rangle$ by $\phi(n)$= $g^{n}$, $n\in \mathbb Z$ I am not sure of my approach to this. Need some help

Just would like to see if I'm right.  Proof: Let $G$ be generated by $x$ (Let $G=\langle x \rangle$ for some $x$ in $G$.) We wish to show that there exists an $x'$ in $G'$ such that $G'=\langle x' \rangle$. First, we will show that for all $x^n$ in $G$, $f(x^n)=f^n(x)$. We proceed by induction.   Base case: $n=1$. $f(x*e_G)=f(x)f(e_G)=f(x)$. Now, assume that $f(x^k)=f^k(x)$ for some arbitrary positive integer k. We show that $f(x^{k+1})=f^{k+1}(x)$. Observe that $f(x^{k+1})=f(x^kx)=f(x^k)f(x)=f^k(x)f(x)=f^{k+1}(x).$   Next we will show that for all $x^{-n}$ in $G$, $f(x^{-n})=f^{-n}(x)$. We proceed by induction. Base case: $n=-1$. $f(x^{-1}*e_G)=f(x^{-1})f(e_G)=f(x)$. Now, assume that $f(x^{-k})=f^{-k}(x)$ for some arbitrary positive integer k. We show that $f(x^{-k-1})=f^{-k-1}(x)$. Observe that $f(x^{-k-1})=f(x^{-k}x)=f(x^{-k})f(x)=f^{-k}(x)f(x)=f^{-k-1}(x).$ Because $f$ is onto, $Im(f)=G'$ and therefore $Im(f)=(...,f^{-2}(x),f^{-1}(x),e_G,f(x),f^2(x),...)=G'$.  Thus, there exists an $x'$ in $G'$ such that $G'=\langle x' \rangle$ and the proof is complete by the principle of mathematical induction. Q.E.D.  I have a feeling the proof shouldn't be this long. Any suggestions for a shorter, cleaner proof?


i have problem. I Dont know why, but i cant render anything in "CUDA" and "OptiX" but OpenCL work fine. And i cant use Cykle render beacuse it's very laggy. I Have newest  version of Blender and i have RX 590 Red Dragon 8gb. Why something like that happend to me?   Look i have screenshot, how i can "turn on" my gpu?

I don't know why, but I cant render anything in CUDA and OptiX but OpenCL work fine. I cant use Cycles render because it's very laggy. I have newest  version of Blender and an RX 590 Red Dragon 8gb. Why does that happen?  How can I turn on my gpu?


I am very new to Java and would ask you for help. I have this: public class Person {  String name; String gender;  public static void main(String[] args) {     Person person = new Person();     person.name("Max");     person.gender = "male";          Person person2 = new Person();     person2.name = "Lea";     person2.gender = "female"; }  What should be the correct syntax for the following method? Should I convert String to boolean? if (String = male) {     System.out.println("You are man!") } else{     System.out.println("You are woman!")      Thank you!

I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?


When you save a web page in Opera Mini, it must be saved somewhere.  I want to know where can I find these pages, specific path or anything?

I have an Android 2.3 Gingerbread and have installed Opera Mini. I used it to save many useful pages for offline viewing and I want to save the links of the pages in a text file. So I need to find the place where the links of the saved pages are stored.


I don't have the option to change the delay on "require password xx after sleep or screen saver begins.  For security, I would like to change it to "immediately" instead of 5 seconds.  I obviously have admin privilege (I'm also the only user on the Mac) I thought that was due from a restriction in mobile profile, so I removed some of the profiles that could have prevented me to change this setting, but no luck how can I change this?  PS Advanced user : use ID 501 group staff

I am trying to prevent the system to always ask for the password when it wakes up from sleep.    I have a MacbookPro with Yosemite 10.10.5.  User has admin rights and password different than the iCloud one.  FileVault is off.   The System Preferences > Security and Privacy > "Require password [5 seconds] after sleep or screen saver begins" is disabled and there's no way to enable it.   If I execute defaults read com.apple.screensaver i get:  {     askForPassword = 0; }   If I execute defaults -currentHost write com.apple.screensaver askForPasswordDelay -int 3600 the defaults don't change...


Is there a ruler symbol in some LaTeX package?  I would like something similar to the clock symbol in the wasysym package.

How can I produce the codes to get the symbols of pencil, ruler and compass in LATEX? I'm gonna write a sentence I can draw this figure by using simple tools in my presentation. So I prefer to include symbols pencil, ruler and compass instead of the words simple tools. Is it possible?


As we know in the universe there are two types of charges, positive for some elementary particles and negative for other. By inversion charge sign of elementary particles the world be the same this couldn't affect some physical phenomena. If not, so the charge signs just hold the information that only exist two kind of electricity.

For historical reasons, I understand that a proton's charge was assigned the label of "positive", the electron's charge was assigned the label of negative, and, crucially, equations of current in E & M are written with the notion that current is the flow of positive charge despite the rarity of actual flows of protons in real systems (which I understand are mostly biological systems).   If the possibility existed to instantaneously and at no cost, retcon these associations such that protons have a negative charge, electrons have a positive charge, and current remains the flow of positive charge, would there be any beneficial or detrimental outcomes?  For instance, would there be:   new interpretations of physical laws that would provide different or better insights into any relevant subfield of Physics significant simplifications to notation in any field of Physics or Engineering significant increases in understanding in the fields of electricity, electronics, electrical engineering, radiation/radiative transport, etc. a noticeably easier learning curve for any subfield of physics dealing with the concept of charge   Additionally, is there a permutation of positive charge, negative charge, and flow of current definition that would improve upon the one I suggested?


On some sites such as SO, it may happen that for specific review queues there are hundreds (thousands?) of outstanding reviews. For such queues, users may be allowed to perform up to 40 (instead of 20) reviews on a single day. Here is a sample of some of those queues (as shown to me on the /review page today):  ... 2.2k posts (First posts): Thank you for reviewing 40 first posts today; come back in 8 hours to continue reviewing. 139 posts (Late answers): Thank you for reviewing 40 late answers today; come back in 8 hours to continue reviewing. 131 posts (Low quality posts): Thank you for reviewing 20 low quality posts today; come back in 8 hours to continue reviewing. ...  And even though you cannot tell from the above sample, for all these 3 queues, I already performed 40 reviews. So for the low quality posts queue, the number is actually 40, and not 20. At first I thought "hm, this might be some caching issue or something, give it some time and it'll probably show as 40 instead of 20 also". However, that does not appear to be the case. Instead, what seems to happen is:  If the number of outstanding reviews (like the 131) increases enough, e.g. to somewhere around 150 or so, then the 20 will become 40 as well.  If the number of outstanding reviews (like the 131) does not increase anymore that day, i.e. it always remains 131 or less, then the 20 will never become 40.  If the number of outstanding reviews (like the 139 for the Late answers) goes down enough again (say to somewhere below 100 or so), then the 40 (for Late answers) will become 20 again.   My question: what's going on here, is this the intended design? If so: what is the actual design? Or is it some undocumented feature (aka bug)? Update: On Apr 18, 2021 (early morning, before performing any Low quality posts reviews, the number of outstanding reviews was 156. After I completed 40 reviews there were 111 outstanding reviews, and at that point this is what was (correctly) shown:  111 posts (Low quality posts): Thank you for reviewing 40 first posts today; come back in 15 hours to continue reviewing.  However, about 5 hours later, without me performing any additional reviews (since I had reached my daily limit of 40 about 5 hours before), this is what was shown:  109 posts (Low quality posts): Thank you for reviewing 20 first posts today; come back in 15 hours to continue reviewing.  That 20 is wrong, it was already 40 since about 5 hours ago ... Notes:   is not a duplicate question, e.g. because the (accepted) answer to it states “... after 20 reviews in a given queue*, you're done for the day ...”, which is clearly not what my question is about.  is not a duplicate question either, e.g. because the (accepted) answer to it explains (within the reviews part of it) what the maximum number of reviews for a given queue is, while my question is about the mismatch between the number (40 or 20) as shown, as compared to the correct number (it is actually 40 for each of the 3 queues).

I noticed that I can only perform certain actions such as commenting a finite number of times in a given period of time. Obviously, rate limiting is in place to prevent accidental misuse or intentional abuse of certain features.  Where else is rate limiting applied on Stack Exchange sites, and what are the limits?


I'm working with code from , which copies the alt attribute of an img when clicked and pastes the attribute into a textarea when the textarea is clicked.   The code works great on a static textarea that is loaded in on page load, but I'd like to be able to dynamically add in the textarea. I have a button at the top of the HTML that calls a function that loads in a new textarea. The function is at the very bottom of the

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


I'm using Ubuntu 12.04 LTS. I'm trying to install Oracle JDK 7. When I tried to directly download the jdk-7u51-linux-x64.tar.gz from the official website, the download started and after downloading couple of MBs it stopped (you can try it as well, worked the same way for a friend). Using a guide.  led me to   Oracle JDK 7 is NOT installed. dpkg: error processing oracle-java7-installer (--configure):  subprocess installed post-installation script returned error exit status 1 Errors were encountered while processing:  oracle-java7-installer E: Sub-process /usr/bin/dpkg returned an error code (1)   which is normal, as it is downloading from the same link. Exact report   I tried to download and install the .rpm file. I converted it to deb and installed it. It appears as installed in the Software center, but could not find it via terminal (java -version returns suggestions for installing packages). Image from the Software center   I tried everything here.  and could not find anything on the internet.

I want to install Oracle's JRE and to update to the latest version with the Software Updater when they released. Is there a Ubuntu package that is provided by Canonical or Oracle?  Before release Java 7, I followed  to install Java 6.  But it doesn't work for Java 7. There is no package sun-java7-xxx. How can you install Java 7?


I've been trying to create a Bash shell script that would create and alter a file called list. Effectively, my goal with the program is to append names to a list, creating the file with a header (if necessary).  However, the script currently fails at one particular point: Whenever I run the script again, the old name disappears and is replaced by the name that was just entered. How can I solve this?  My script:  #!/bin/bash #Please sign your name here.  echo "Hi, what's your name?" read name echo "Hi $name, welcome to the Linux course!"  echo Course Attendees > list echo $name >> list   Example of problem:  $ bash list.sh Hi, what's your name? Test Hi Test, welcome to the Linux course!  $ cat list Course Attendees Test  $ bash list.sh Hi, what's your name? Test2 Hi Test, welcome to the Linux course!  $ cat list Course Attendees Test2

Assuming i have a line that i want to add to a file without opening an editor.  How could i append this line  alias list='ls -cl --group-directories-first'   to this file  config.fish


How do I have to implement the following comparison?  \documentclass{scrartcl} \usepackage{etoolbox} \usepackage{tikz} \begin{document} \begin{tikzpicture}  \pgfmathparse{sin(60)}  \let\x=\pgfmathresult  \ifnumgreater{\x}{0}{}{} \end{tikzpicture} \end{document}

Why does the following test using \ifthenelse not compile:  \documentclass[border=30pt, tikz]{standalone} \usepackage{tikz,tikz-3dplot} \usepackage{ifthen} \usepackage{animate, calc}%%%%%%%%%%%% \usepackage{animate} \usepackage{circuitikz}  \begin{document}  \foreach \x in {0.1,0.2,...,4}{   \begin{tikzpicture}    \begin{circuitikz}  \draw (0,0)       to[V,v=$U_q$] (0,2) % The voltage source       to[short] (2,2)       to[R=$R_1$] (2,0) % The resistor       to[short] (0,0);       \draw (2,2)       to[short] (4,2)       to[R=$R_2$] (4,0)       to[short] (2,0);          \ifthenelse{\x<2}{\fill[color=red] (0,\x) circle (3pt);}{}  \end{circuitikz}  \end{tikzpicture} } \end{document}   On compilation I get the following error:  ! Missing = inserted for \ifnum. <to be read again>


Let $E$ be a commutative monoid with identity $e$, $S\subseteq E$, and let $S'$ be the submonoid of E generated by $S$.   For every invertible element $x$ of E, $x^{*}$ denotes the inverse of $x$.   Let $R(x,y)$ denote the following relation:  $$\text{there exist }a,b\in E\text{ and }p,q,s\in S'\text{ such that }x=(a,p), y=(b,q)\text{ and }aqs=bps;$$  this is an equivalence relation on the product monoid $E\ \times\ S'$, compatible with its law. Denote the quotient monoid $E\times S'/R$ by $E_{S}$.   For $a\in E$ and $p\in S'$, let $a/p$ denote the equivalence class of $(a,p)$ modulo R. Then, mapping  $$\varepsilon: E\longrightarrow E_{S},\ a\mapsto a/e,$$  is a homomorphism.  For every $a\in E$ and $p\in S'$, we have $a/p=(a/e)(e/p)$: i.e., $a/p=\varepsilon(a)\varepsilon(p)^{*}.$   Therefore, $\varepsilon(E) \cup\varepsilon(S)^{*}$ generates $E_{S}$, where $\varepsilon(S)^{*}$ denotes the set of invertible elements of $\varepsilon(S)$.  This construction is taken from Bourbaki's Algebra. Now Bourbaki goes on to say:   Question: Can someone please explain what is going on in this screenshot? (I understand why $\varepsilon$ is injective.) In particular, I don't understand how one can "identify" $E_S$ with the submonoid of $\Phi$ generated by $E\cup S^*$? This whole business of "identification" is unclear to me: I don't understand what I am exactly able to do logically and formally whenever I am to told to "identify" two objects.  Any help will be appreaciated. Thank you.

Let $E$ be a commutative monoid, $\Sigma$ the submonoid of cancellable elements of $E$, $E_{\Sigma}$ the monoid of fractions of $E$ associated with $\Sigma$ and $\varepsilon$ the canonical homomorphism of $E$ into $E_\Sigma$.   Since every element of $\Sigma$ is cancellable, $\varepsilon$ is injective.  Logically speaking, what does "identifying the monoid $E$ with the submonoid $\varepsilon(E)$ of $E_\Sigma$" allow me to do? I mean: w.r.t the set-theoretic formulas, what can I formally replace with what? For example, does it allow me to write $\varepsilon(a)=a$ for $a\in E$ (I hope not...) ? What is gained by this "identification"?   I ask this because I would like to know how one can "identify" $E_{\Sigma}$ with the submonoid generated by $E\cup\Sigma^*$, where $\Sigma^*$ denotes the set of inverses of the elements of $\Sigma$.  EDIT: (You can ignore the details concerning this specific construction of the monoid of fractions)


Take the following example:  class Foo {     public int SomeProperty { get; }     public IEnumerable<Foo> Children { get; }     // .... }   If another class (e.g. Bar) implements Foo, Foo becomes non-recursive and Bar instead becomes recursive.  class Bar {     public Foo { get; } // At this point Foo.Children doesn't make sense anymore     public IEnumerable<Bar> Children { get; } // How can I enforce this part     // ... }   Currently I need to write two versions of every class, one with Children and one without. Inheritance makes this slightly less tedious but I can't statically guarantee that the requirements will be implemented correctly. I was also thinking about some kind of monad pattern with a higher kinded type Recursive but I can't wrap my head around it (especially since I just started learning it).  Any ideas?  Edit: I don't understand how this got marked as a duplicate. While I ended up with writing my own generic tree in the end, I didn't require it in my question and definitely didn't ask for a library. I was asking for general advice on how to approach the problem, where the solution I settled with ended up being a generic tree by chance. The fact that this question got closed after I provided my solution leads me to believe that someone read the answer, searched for trees on SO and then chose the first result, which doesn't help anyone. The "original" question doesn't even provide a solution to my question. This nothing more than laziness paired with the abuse of admin rights.

I was looking for a tree or graph data structure in C# but I guess there isn't one provided.  explains a bit about why.  Is there a convenient library which is commonly used to provide this functionality?  Perhaps through a strategy pattern to solve the issues presented in the article.  I feel a bit silly implementing my own tree, just as I would implementing my own ArrayList.     I just want a generic tree which can be unbalanced.  Think of a directory tree.  C5 looks nifty, but their tree structures seem to be implemented as balanced red-black trees better suited to search than representing a hierarchy of nodes.


the function is very simple:  arcpy.CalculateField_management (fc, "DFDD", "aaa", "PYTHON")   and I want to calculate DHDD field with simple text "aaa", but I get error:   name 'aaa' is not defined. Any solutions?

I am trying to populate a field with corresponding file name. For example, if the file name is Route1.shp then the field value will be Route1 as well. However my code is not working. Can you please suggest a code that works? The code I used is given below, along with the error message             import arcpy, os, sys     from arcpy import env     arcpy.env.overwriteOutput = True     env.workspace = r"C:\ABC\GIS"     fc_tables = arcpy.ListFeatureClasses ("R*")     for fc in fc_tables:         field = "RouteName"         arcpy.AddField_management (fc, field, "TEXT")     for fc in fc_tables:     arcpy.CalculateField_management (fc, field, str(fc), "PYTHON")   And this is the error message     Runtime error  Traceback (most recent call last):   File "",   line 2, in    File "c:\program   files\arcgis\desktop10.1\arcpy\arcpy\management.py", line 3128, in   CalculateField     raise e ExecuteError: ERROR 000539: Error running   expression: Route1.shp  Traceback (most recent call last):   File   "", line 1, in  NameError: name 'Route1' is not   defined  Failed to execute (CalculateField).


When is it correct to use the form "I did want to ..." versus "I wanted to..." (substitute other verb for "want"). I often find myself changing from the former to the latter when I edit early drafts, but sometimes the former seems to better emphasize my "wanting".  EDIT: Part of my curiosity was that this has the feel of a slightly different tense, but it is not. The discussions in the following, which I found rather indirectly via the ELL meta site, are more what I was looking for.

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


For a given object if the input "value" of a property is "" , we want to delete that property from the object .  Ex   {  "Speed": "59 MBPS",  "latitude": "90.2",  "longitude": "" }   As per the example ,since the value of longitude is "" , this should get deleted from the object. Please suggest a javascript code to achieve this .

How do I remove all attributes which are undefined or null in a JavaScript object?  (Question is similar to  for Arrays)


I'm having a problem changing a variable in a function that was initially defined outside a function.     # Define inital bool     x = False          def test():         # Print inital bool         print(x)         if not x:             # Change bool state             x = True          test()  I want to print x at the start of the function but then change the value of x if it is False but when I run this, I get the error local variable 'x' referenced before assignment.. Defining x as a global variable doesn't change anything either:     # Change bool state     global x     x = True  When I run this code (with global x), I get the error: name 'x' is used prior to global declaration Defining global x outside the function doesn't make a difference either. Any way I can fix this or get around it? Thanks.

The following code works as expected in both Python 2.5 and 3.0:  a, b, c = (1, 2, 3)  print(a, b, c)  def test():     print(a)     print(b)     print(c)    # (A)     #c+=1       # (B) test()   However, when I uncomment line (B), I get an UnboundLocalError: 'c' not assigned at line (A). The values of a and b are printed correctly. This has me completely baffled for two reasons:   Why is there a runtime error thrown at line (A) because of a later statement on line (B)? Why are variables a and b printed as expected, while c raises an error?   The only explanation I can come up with is that a local variable c is created by the assignment c+=1, which takes precedent over the "global" variable c even before the local variable is created. Of course, it doesn't make sense for a variable to "steal" scope before it exists.  Could someone please explain this behavior?


Though I'm a while in this field I recognized that I can't say for sure that I understood this basic, very simple equation $ \hat{y} = xw + w_0 $ I know $ w_0 $ denotes the bias term (mostly given as $ b $) which is basically the offset of the function. But how do I understand $ xw $? Does $ x $ represent the feature(s) like speed and acceleration so it would have two dimensions with $ x_i , i=0,1 $ Or does it stand for all the data points of a feature with $ x_i, i=0,..,n $ ? And $ w $ is then exactly, what?

Consider a simple regression (normality not assumed): $$Y_i = a + b X_i + e_i,$$ where $e_i$ is with mean $0$ and standard deviation $\sigma$. Are the Least Square Estimates of $a$ and $b$ uncorrelated?


When writing comments or using chat, users can use "" as markdown shortcuts.   [help] –  [tour] –  [chat] –  [answer] –  [meta.se] –  [something.se] – something.stackexchange.com (if it exists)   Currently, these shortcuts are only available in comments and chat. Using them anywhere else will have no effect.  It would be [helpful] to have access to these shortcuts when writing [questions] and [answers].

I know that most (if not all) SE sites have a shorthand link in comments. For example, [SO] for Stack Overflow, [Math.SE] for math.stackexchange.com, and [SoftwareEngineering.SE] for softwareengineering.stackexchange.com. Apparently these are not supported in questions and answers. Is there any plan to add this feature or is it intended only for comments?


Is it possible to use this formulation?      This quote is so accurate to them.   I'm trying to say it fits them just perfectly. Such as when something fits somebody like it was meant for them: e.g. It fits like ass on the pot!

For example:     The building is accurate to its schematics   Is this invalid use of the word "accurate"?


Actually, this is a markdown question. But I can't find a markdown community.  I want the letter "w" to be bold in the expression y(x, w). $y(x, \boldsymbol{w})$ works. But the following parentheses become bold also. How can I fix it?

To make Latin-letter variables bold I can use e.g. \mathbf{a}, but while putting Greek letters or symbols such as \nabla inside \mathbf doesn't cause any errors or warnings, it also doesn't do anything else.  What is the best way to make bold math symbols, in particular Greek letters and \nabla?


Behavior of below code like this.First declaration gives compiler error while second works fine, even we print result of second line its give output of 1270 not 02366. so is it any specific truncation or shifting in integer in such cases?   public static void main(String[] args) {          int i =01339;//compiler error out of int range          int j= 02366;//works fine         System.out.println(j); //value 1270  }

This prints 83  System.out.println(0123)   However this prints 123  System.out.println(123)   Why does it work that way?


I was searching for a good base to attack this morning and I received two messages.  The first message prompted when I clicked to search for a new base, "Your attacking has been disabled" and then I was kicked from the game.    Now I am receiving a message that says, "You have been playing for too long and your villagers need to rest for a few minutes."  I spoke with a few other people I play clash of clans with and they said they could attack (not a maintenance window).  Why did I get these messages?

What is "playing too long"? How much is too long?    How long is "rest for a few minutes"?  What is the purpose of this feature? Player benefits? Account maintenance?


I gather from the dictionary that pen is pronounced as /pen/ and pence as  /pens/. Is the plural pens pronounced as /pens/ or /penz/?

A general rule of English pronunciation states that the 's' in plural nouns is to be pronounced as /z/ if it is preceded by a 'voiced consonant' such as /n/ or /g/, and as /s/ if it is preceded by a 'voiceless consonant' such as /t/ or /p/.  Therefore, "pens" is pronounced as /penz/ and "cats" is pronounced as /cats/.  Now my question is, do native speakers of English always follow this rule? Secondly, and this is what I really need to understand, does this rule apply also to the 's' in the verbs of 'third person singular subjects'?


I'm looking for a word that simply means something that used to be popular but is no longer.   I do not want the word to denote that it is not as good as it once was  ex:    Obsolete: no longer in use or no longer useful   Whether or not it is still very important, just that the popular attention has shift away, is up for the context.  The closest thing I could find was:   It's so yesterday: something that is out of fashion   But that's slang and (for me, at least) gives a small implication that it's not as good as whatever is the new thing now.  Edit: I found:   Old-School: used, usually approvingly, to refer to someone or something that is old-fashioned or traditional   However, I'm not sure if 'old-school' could be used for some political thought/opinion.   Are there any other single-word adjectives that could describe this?  Sample Sentence:     When I showed my dad a trending music video, he took one look at it and said "My goodness, this is so ______! It's so nice to see this kind of music video again - it really takes me back to my younger days."   Edit:  I've realized that my example give off a positive connotation, so 'old-school' would be closer than any other word I've found - but I'm looking  for a word with a neutral connotation as to why it's no longer popular.

I am looking for an opposite to the word trendy without giving a meaning that those who adopted the trend are old-fashioned in hindsight. For example,     Service Oriented Architecture is the trend as of now. But what is trendy in 2014 can become ______ in 2015.   So in 2015, the trend becomes widespread to the extent that it is no longer trendy, but not necessarily old-fashioned.  Edit: I am currently thinking of using mainstream. But still any other thoughts are welcome!


Ok, I have an odd little question.  I'm sure that I've played a number of video games with this kind of stylized 2D background, though I can't think of an good example for the life of me (I tried, promise):   Instead of a single background image, this kind of background has several 2D images stacked on top of each other. If you move a little left or right, the images shift a just a little bit accordingly. You might see a little more of one image or another, but the overall effect is to create a kind of 2D depth of vision, like a paper diorama.   That isn't the best description, but hopefully gets the memory across.   So, my question: Does this kind of background have a name?

I need to know the term for the kind of projection in games like Cadillacs and Dinosarus (a beat-´em up, shown below). The game uses a kind of pseudo-3D effect with techniques including isometric/axonometric projection, oblique projection, orthographic projection etc  What is the correct term for this behavior? Cavalier, cabinet, isometric, ...?


I'm running a batch script that clears files, in which I need to delete all empty folders. It is identical to the question posted here:   except I am using batch instead of bash (Windows 10).  I tried using rmdir but it would either remove dirs. and files or remove nothing.

I have a directory on my Windows 7 machine that has hundreds if not thousands of sub-directories.  Some of them have files, some do not.  I want to delete all the empty directories.  Looking at the del and rmdir DOS command, it does not look like you can recursively do this without deleting all the files.  Is there a way to do this from the command line?


I am tweaking our current user journey for adding specific items to your 'favourites' list.  The question is: if the user isn't logged in when they add an item to their 'favourites' - should they be prompted to log in at that point?  Or should they be allowed to add more items until they click checkout and then be prompted to log in then?  I feel it would be less disruptive to what the user expects if they need to log in after clicking 'Checkout' then being prompted. But then my concern is if the users don't click checkout and the session ends. They could potentially lose their items.

I believe that signing into a site can be a big barrier to users so prefere e-commerce sites that offer guest access.  The question is should wishlists be a guest feature or do the business advantages enforcing the user to sign up outweigh the potential increases in profits.   Does anyone have any research or views on this?


I recently bought an SSD and installed Windows 7 on it, however it didn't install exactly how I intended - it still requires my HDD to be plugged in to boot onto the SSD.   Hopefully the following image explains my situation a bit better. My SSD is the C: drive, and the old HDD is D: - this drive has a 100MB partition which contains the boot sector that requires the HDD for booting into Windows.    From what I've found out, booting from the Windows 7 install DVD and running startup repair will resolve the issue. However, as every situation is different (and I'm particularly paranoid I'll somehow brick my system), I wanted to be sure this was correct.  So, what's the best way to get my SSD to boot without requiring the HDD to be present?

When I installed Windows 7 on my new SSD it seems I messed some parts up during the partition selection, and now I have my system partition with the boot sector on another harddrive, and the boot partition containing Windows on my SSD.  How can I move the boot sector from my hard drive to my SSD, so that the system and boot partition are both the SSD and I don't need the hard drive to boot anymore?  I'm a bit lost on how to do this, as I don't have any idea how I split them in the first place. When I had to repair the boot sector using BootRec.exe I could only put it back on the hard drive, I saw no option to create one somewhere else.  I also want to keep all content on my SSD, so reinstalling Windows is not an option.   Here's a screenshot of my current disk layout (in german, but most terms should be easily recognizable):


So I got these codes that for printing the statements but I don't get the purpose of the last two lines of the if loop? from random import random  def flip(bias):     """     Flip a coin once.     `bias` is the likelihood of the result being heads, 0. <= bias <= 1.     Returns True for heads or False for tails     """     return random() < bias  def main():     bias = float(input("What bias do your coins have? "))     count = {False: 0, True: 0}     for i in range(1, 4):         toss = flip(bias)         count[toss] += 1         print("Coin flip {} has a value of heads: {}".format(i, toss))     print("Final result: {} heads, {} tails".format(count[True], count[False]))  if __name__ == "__main__":     main()   Thanks in advance.

Given the following code, what does the if __name__ == "__main__": do?  # Threading example import time, thread  def myfunction(string, sleeptime, lock, *args):     while True:         lock.acquire()         time.sleep(sleeptime)         lock.release()         time.sleep(sleeptime)  if __name__ == "__main__":     lock = thread.allocate_lock()     thread.start_new_thread(myfunction, ("Thread #: 1", 2, lock))     thread.start_new_thread(myfunction, ("Thread #: 2", 2, lock))


With a mouse or trackpad, we can double-click in text to select an entire word. If we hold the pressing of that second click, and then drag, we can select a series of entire words in most text editing places in most apps on macOS.   Is there a way do the same effect (selecting a series of whole words) on a trackpad without the physical clicking, using only touches and taps?   (I want to give my thumb a break from that downward-pressure repetitive motion.)  Using Apple Magic Trackpad 2 or MacBook Pro built-in trackpad, with macOS Sierra.   I tried each of the Answers on this . But none of them work. They seem to be outdated, from the Mac OS X era rather than macOS times today.

If you double click a word to select it, and keep the mouse held down, you go it starts word selection mode, meaning it will select whole words as you move the mouse over them.  This only works when using the physical click on the trackpad. The problem is that I want the same behavior using a tap (i.e. the One Finger Tap to Click feature is enabled). When I try to use a tap, though, it goes into character selection mode rather than word selection.  Is there ant way to perform word selection using tap gestures on a trackpad?


I don't know how to disable the Fn key and in the process messed up my keyboard shortcuts, I am mainly looking for a way to return them to default. I use Ubuntu 16.04 LTS and I use a Microsoft All-In-One Media Keyboard (N9Z-00022).

How do I reset the default value of Unity shortcut?   In: "System Settings -▸ Keyboard -▸ Shortcuts ..."  For instances:   I can't put the default Alt L for the HUD.    I can't put the default Alt+Print to capture the active window.   Simply typing it doesn't work.  Solving this in CLI is preferable.


Where can I find the mount point of some network shared folder. For example, I shared folder pac from MachineB. That folder can already be seen/browsed from MachineA via nautilus.  But I need is a way to browse that pac folder from command line from MachineA. How can that be done?

Please note: I am two weeks old in Linux. I have found a lot of answers to this question on the internet, tried many, but all failed one way or another. Therefore I dare to ask once again in the hope that someone here could explain it simply :)  Pre-conditions:  In my institute, we have a Samba server. In Windows, it is accessed by going to \\xyz.220.131.233\ and entering the login abc and the password def.   In Ubuntu, I was able to do exactly the same using Nautilus, pressing Ctrl+L and entering smb://xyz.220.131.233/. It then asks for the login and the password and connects. I can even drag a folder from here to the 'Places' and have a shortcut to the remote location.   So far so good. I've just installed Matlab and want to open this remote location. Trying to cd to smb://xyz.220.131.233/ returns      Cannot CD to smb://xyz.220.131.233 (Name is nonexistent or not a directory).   A Mac user in my group told me I first mount the location, but he didn't know how to do it.   Is it true and how do I do it?


Assume you have a list A = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].  In a single line of code, cut A in half and assign B to be a copy of A’s last half followed by the first half (i.e. B would be equal to [6, 7, 8, 9, 10, 1, 2, 3, 4, 5]).

I need a good explanation (references are a plus) on Python's slice notation.   To me, this notation needs a bit of picking up.   It looks extremely powerful, but I haven't quite got my head around it.


Assuming I have the abstract Shape class, within I have the method getArea(). As a subclass of the Shape class, I have the Rectangle class, which overrides the getArea() method. As a subclass of the Rectangle class, I have the Square class, but in the Square class, I want to reference the getArea() as implemented in the Shape class. How can I do this without copying the code over?

I read  and thought that would easily be solved (not that it isn't solvable without) if one could write:   @Override public String toString() {     return super.super.toString(); }   I'm not sure if it is useful in many cases, but I wonder why it isn't and if something like this exists in other languages.  What do you guys think?  EDIT: To clarify: yes I know, that's impossible in Java and I don't really miss it. This is nothing I expected to work and was surprised getting a compiler error. I just had the idea and like to discuss it.


c=map(lambda *x:x, range(3)) print(list(c))  c=map(lambda x:x, range(3)) print(list(c))   Can someone tell me how is the output different if we use variable positional args  [(0,), (1,), (2,)] #1st output  [0, 1, 2] #2nd output

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


I am newbie in java but I think I have done well teaching myself in these few weeks. But now I am stuck at this loop.  Here is a method from one of my class. To help me debug, I have added "myString" string and "syntax" list inside this method to demonstrate what is happening and to keep it simple, at least for now.  public void getIndex(){     String myString = "2 2 + 3 5";     String[] syntax = myString.split(" ");      for (int index = 0; index < syntax.length; index++){         System.out.println("current index is: " + index);         System.out.println("It has: " + syntax[index]);         // these print statements are made to help me debug         if (syntax[index] == "+"){             indexNeeded = index;             break;         }     }     System.out.println("Index Needed: " + indexNeeded);      As you can see inside the loop, I want to break the "for loop" when the element of the list, "syntax" is "+". (I am showing "+" here but it can be anything in the actual program.)  Here is the output, when run this method:  current index is: 0 It has: 2 current index is: 1 It has: 2 current index is: 2 It has: + current index is: 3 It has: 3 current index is: 4 It has: 5 Index Needed: 0   The loop should have stopped when it found "+" but it seems that "if statement" is not working at all, and hence "indexNeeded" hasn't changed.  It's a simple method but what am I doing wrong here?

I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?


In p.35 of Miranda's book Algebraic Curves and Riemann Surfaces, the following theorem is stated and is called as Hilbert's Nullstellensatz. Theorem. Let $f\in \Bbb C[x_1,\dots,x_n]$ is an irreducible polynomial, and $h$ is a polynomial vanishing everywhere on the zero set of $f$. Then $f$ divides $h$. But as I remember, the original Nullstellensatz is the following: Theorem. Every maximal ideal of $\Bbb C[x_1,\dots,x_n]$ is of the form $(x_1-a_1,\dots,x_n-a_n)$. How does the original Nullstellensatz imply the new one?

Let $k$ be an algebraically closed field.  Let $I$ be the map that takes algebraic sets in $k^n$ to the ideal generated by them: $I : \{$ algebraic sets $\} \to \{$ ideals of $k[x_1,\dots, x_n] \}$, $I(X) = \{ f \in k[x_1, \dots, x_n] : f(X) = \{0\}\}$.  Similarly let $Z$ be the map that takes ideals in $k[x_1,\dots, x_n]$ to algebraic sets.  Then $I(Z(I)) = \sqrt{I}$.  How does that follow from Hilbert's Nullstellensatz?  This version of Nullstellensatz: If $k$ is an algebraically closed field then, the maximal ideals of $k[x_1,\dots, x_n]$ are of the form $(x_1 - a_1, \dots, x_n - a_n)$ where $a = (a_1, \dots, a_n)$ is a point in $k^n$.


I'm trying to import images as planes to make a diorama in blender, and with Cycles, the images have this strange artifact where you can't see through some of them: The black part in the image below. Right now i have them all as blend mode: Alpha blend, and shadow mode: alpha hashed. Does anybody know what could be going on?  Below is what the same setup looks like in Eevee with a reflection plane, was wanting to use cycles to try to make the reflection they're standing on like water and add some ripples and things. Any idea what could be happening? Thank you!!!

Using v2.73, cycles and a very simple scene: an array of cubes, no big deal.   If I set the shader's material to transparent, the cubes in the foreground do become transparent but those far away in the back do not disappear completely and this strange dark things appear (visible in rendered mode and in final renders)    I've played with the clipping distance on the viewport and camera, but I can't figure out how to make those ghosts go away...


If I made a backup of /usr with:  # cp -r /usr /usrRESERVE1   how can i switch it back after some time:  1# mv usr usrRESERVE2 2# mv usrRESERVE1 usr   second command will not work because mv is inside /usr/bin/mv and it does not exist after first line execution.  //answering to my self...  Solution 1: Using 'mount --bind' as dummy-var  (pointed by comment of user MarkPlotnick):  # mount --bind /usrRESERVE1 /usr  #usr points --to--> usrRES1 from now # mkdir /dummy # mount --bind / /dummy           #contains original root folders # cd /dummy ; mv usr usrRESERVE2 #             mv usrRESERVE1 usr # cd / ; umount dummy ; umount usr ; rmdir dummy    Solution 2: using single process - moving tool  # package manager install mmv # mmv /usr /usrRESERVE1 -- /usrRESERVE2 /usr

I accidentally moved all folders from root to a subfolder. (/bin, /etc, /home, /lib, /usr... all moved) The only ones that were not moved, since they were in use, are  /bak, /boot, /dev, /proc, /sys.  Now, any command that I try to execute will simply not happen. I constantly get "No such file or directory".  I am connected through ssh and through ftp, but I cannot move files through ftp, as direct SU login is disabled. I also have access to the actual server if I need to do something directly from there.  I'm assuming I would need to edit a configuration file in order to tell it where to find the /bin folder and that would help me get access again, but I don't know which file that would be or how to do it (since I can't even run chmod to change permissions).  Is there any way out of this other than re-installing?  I am working on an old version of CentOS.  I'm extremely new to the world of Linux, hence this action and the question...


Let A be a 100 x 100 matrix such that every number from {1, 2, ... 100} shows in A exactly 100 times.  Prove that there's a row or a column with at least 10 different numbers.  The context is the Pigeonhole Principle.  EDIT: theres a solution to this questuion here:   but the problem is that I dont understand how to prove the part which is said to be "clearly  I couldn't solve it by myself, when trying every strategy I know for solving Pigeonhole problems.

On each cell of an $n \times n$ chessboard, we write a number from $1, 2, 3, .  . . , n$ in such a way that each number appears exactly $n$ times. Prove   that there exists a row or a column of the chessboard which contains   at least $\sqrt{n}$ distinct numbers.   This question is dying for a proof by contradiction, but I can't seem to show how. When I searched through the Internet, there is the following hint:     Assume each row and each column has less than $\sqrt{n}$ distinct numbers in   it. For each row or column, consider the number of distinct numbers in   it.   I feel like double counting is involved in the process, but what to count in two different ways? Also I can prove the statement with the probabilistic method but I would really like to learn the double counting approach.  Here is the other proof:  Choose a random row or column ($2n$ choices). Let $\textbf X$ be the number of distinct entries in it. Use the indicator variable $I_i$, for the existence of number $i$ in the block: $\textbf X = \sum I_i.$ Clearly, $E[I_i] = P[I_i = 1]$.  Then $P[I_i = 1] \geq 2\sqrt n / (2n) = 1/\sqrt n$. The lower bound is obtained if all the $i$ happens to be in some $\sqrt n$ edged square sub-matrix. Hence, by linearity $\textbf E[X] \geq \sqrt n$. This proves the existence.


As the title says, I'm toying around with developing a 2D space RTS game. All of my units are spaceships that basically just shoot at one another, but they have to do a variety of other things as well: they have to "discover" (notify, draw, etc) other ships and planets not owned by the owner of this ship and within the arbitrary range of the ship's "scanners" (since they would otherwise be hidden), and if the ship is told to fire on an enemy ship, it needs to find the closest enemy (and fly to it if out of shooting range), and then shoot it obviously.   I've been wondering what efficient data containers could I use for the ships if there is going to be a large number of ships (100s to maybe 1000s) and why them? Also to note, is that ships must be distinguished by their owner (I may go to war with one player, so I obviously do not want my ships to search for ships of other players), where ownership will probably be represented by some integer (1 = player 1, 2 = player 2, etc) or maybe the unique pointer/memory address of a "player" object (0x4ff = player 1, 0x5ea = player 2, etc) or some other simple identifier.   I initially thought about using an array of vectors (C++), with the index of the array representing the player and each vector being the ships belonging to that player; then take all ships belonging to whatever player you are at war with and place them into a priority queue, whose root would be the enemy ship closest to a specific (friendly) ship and decide if its in range or not, but this seemed far too slow and memory-expensive, and didn't really address how to scan for ships/planets.   I then read up a few related posts about quadtrees and this lead me to other such tree data structures, like R-trees, that are also used for optimal spatial queries, but I do not quite understand exactly how they work and whether or not they would be best for me, so here we are.

I'm making a 4 player co-op r-type game, and I'm about to implement the collision detection code. I've read a lot of articles and stuff about how to handle collision detection, but I'm having a hard time figuring out what to go with. It seems the quad tree is the most common way to go, but in some resources they mention the grid based solution. For having used a grid for detections in a previous game, I'm comfortable with that, but is it actually better than a quad tree ? I'm not sure which offers best performance, and I've also ran a little benchmark, there is not much difference between both solutions.  Is one better than the other ? or more elegant ? I'm really not sure which one I should use.  Any advice is welcome. Thanks.


I do not mean that I deserved a Kofia hat, but today I asked and answered questions, all of which have at least one upvote.  Are there another requirement for the hat?     Kofia           first post between 12/26 and 1/1

During Winter Bash, users can earn hats. But sometimes it seems that a hat was awarded even though its requirements weren't (yet) met, or vice versa.  What could be the reason for this?


I am confused by this question for a long time. Let's say the initial states are R=1,S=0,Q=1,Q'=0, and both NOR gates are ideal (no propagation delay). Then both gates should change their states simultaneously, and we get R=1,S=0,Q=0,Q'=0.    But as the figure below shows, it contains two steps change, firstly R=1,Q'=0 and we get Q=0. Then S=0,Q=0 and we get Q'=1. This is the result in all contexts. I don't understand why it is two steps change.    Thanks

Ok this is a basic question but i am not able to figure out how does this work  1: This is the representation of the RS Flip-Flop with the truth table given in my  book    I am not able to connect the truth table to the representation as inn my knowledge every time the answer should be same, which i know that i am wrong so please help me.  2: what does Disallowed and no change stands for.  Thanks  Akash


So I was playing with supervised classification with GRASS. The first issue that I ran into was right after the first two steps of classification (v.to.rast and i.gensig) which was:     unable to read signature file   Now that is an issue I've been searching the last 2 days. Is there a practical answer to that?

I'm trying to make a supervised classification in Grass 6.4.3 under Linuxmint 16.  After digitizing the training areas, I transformed them from vector to raster. Then I've done the following: just in case: g.region rast=train_area_2013_03_05_raster@PERMANENT,2013_03_05_toar4@PERMANENT  then  i.group group=group subgroup=sub_group input=2013_03_05_toar4@PERMANENT,2013_03_05_toar5@PERMANENT,2013_03_05_toar3@PERMANENT  and   i.gensig trainingmap=train_area_2013_03_05_raster@PERMANENT group=group@PERMANENT subgroup=sub_group signaturefile=superv_class  but the resulting signature file, only contains one character: "#".  The output of i.gensig in the console is the following:  Finding training classes... 3 classes found Calculating class means... Calculating class covariance matrices... Signature 1 not invertible Signature 2 not invertible Signature 3 not invertible i.gensig complete.   Obviously if I try: i.maxlik group=group@PERMANENT subgroup=sub_group sigfile=superv_class class=results_class  I obtain the following error message:  ERROR: Unable to read signature file <superv_class>   I've been searching, but I couldn't find the solution.   I've tried: this   My problem is similar to this: . But here, there's no solution suggested. As in this case, I also used i.cluster to generate an unsupervised signature file and i.maxlik reads this perfectly well.   there's another similar question, but again, with no solution...  What does Signature X not invertible means?  Any idea? Thanks for your help!


I have one administrator account in my system which named as "admin". One more admin account called "test". I don't want test account to reset "admin" account and root account password in my system.  I have blocked sudo users by following command.  %sudo ALL=(ALL) ALL, !/usr/bin/passwd root,!/usr/bin/passwd admin admin ALL=(ALL:ALL) ALL   It's working on when executing this command as test user.  If test user tries   sudo passwd root or sudo passwd admin  It throws following error called      Sorry, user test is not allowed to execute '/usr/bin/passwd root' as   root on magesh-test.   But it's not working while executing the following command sudo passwd $root  How to block the test user alone in resetting the password?

I don't need an administrator to change my root password. I don't want any sudo user to execute this command:  sudo passwd $root   I have tried it in the sudoers file using the following command:  %sudo ALL=(ALL) ALL, !/usr/bin/passwd $root   How can I block it?


Recently I came across this proof for fact that primes are infinite.  It's a proof by contradiction. The proof assumes that primes are finite and there is a prime M which is larger than any prime out there. Then you basically take the product of all primes up to and including M and you add one to it, which the source where I read this proof claims is a prime obviously larger than M hence a contradiction to our assumption that primes are finite.  So why is it that product of first N primes + 1 another prime?

In Euclid's proof that there are infinitely many primes, the number  $p_1 p_2 ... p_n + 1$ is constructed and proved to be either a prime, or a product of primes greater than $p_n$.  Trivially, we could also use the number $R_n=p_1 p_2 ... p_n - 1$ to prove the theorem, for n>2.  Intuitively, as $n$ grows, the probability that $R_n$ is prime gets smaller. Is there a proof that $R_n$ is not prime for any $n$ greater than some integer $M$ ? Or conversely, that there is an infinite number of prime $R_n$ numbers?  A possibly equivalent question: Is there a prime number greater than $p_n$ and smaller than $R_n$ for any $n$ greater than some integer $M$ ?


I cannot explain the following (using  C++20 rules) //FooTemplate.h template<typename T> class FooTemplate { private:    static std::vector<T> t; //linker error.    //inline static std::vector<T> t; --> will not produce linker error    //static T t; -->this works also with the appropriate changes in the following code public:     static void setT(T t1)     {         t.push_back(t1);     }     static T getT(int i)     {         return t.at(i);     } };  //main.cpp #include"FooTemplate.h" int main() {   FooTemplate<Foo>::setT(Foo{});   FooTemplate<Foo>::getT(0); }  I have to inline the static member t in order for it to work. If I do not use a templated container (e..g define T t instead of vector<T> t it also works. Any idea?

What is the best way to initialize a private, static data member in C++?  I tried this in my header file, but it gives me weird linker errors:  class foo {     private:         static int i; };  int foo::i = 0;   I'm guessing this is because I can't initialize a private member from outside the class.  So what's the best way to do this?


I am behind a corporate proxy and it needs authorization to use it. When I try just to use option -p http://ip.of.my.proxy:3128, it throws error 407. Is there a workaround?

The firewall I'm behind is running Microsoft ISA server in NTLM-only mode. Hash anyone have success getting their Ruby gems to install/update via Ruby SSPI gem or other method?  ... or am I just being lazy?  Note: rubysspi-1.2.4 does not work.  This also works for "igem", part of the IronRuby project


I am to use mathematical induction to prove:     $$\sum_{i=1}^n\frac{1}{i^2}<2 - \frac{1}{n}$$   my base case is n = 3:  LHS: $\frac{1}{1}+\frac{1}{4}+\frac{1}{9}= \frac{49}{36}$  RHS: $2-\frac{1}{3}=\frac{5}{3}$  base case holds true.  assume $n = k$  $$2-\frac{1}{k}$$  now show $k+1$  $$2-\frac{1}{k+1}$$  Inductive Step:  $$2-\frac{1}{k}+ \frac{1}{{k+1}^2}$$  Now I am stuck I have no clue what math I should be doing from here. I thought about trying to FOIL the $\frac{1}{{k+1}^2}$ but that didn't really give me anything I could work with. Any tips? Or general pointers when doing this stuff? Thanks guys!

Let $n$ be a positive natural number, $n\ge 2$. Then $\displaystyle\sum_{k=1}^n \frac{1}{k^2} \lt 2 - \frac{1}{n}.$   The basis step was easy but could someone give me a hint in the right direction as to how to do the induction step?  I tried this:  $\displaystyle\sum_{k=1}^k \frac{1}{k^2} + \frac{1}{(k + 1)^2} \lt 2 - \frac{1}{k + 1}$  But it's getting me nowhere or I am doing something wrong. I am no expert so a clear explanation would be appreciated. Thanks.


I've read several articles regarding the limited supply of helium gas on our planet and one that many scientists/engineers require for their research. I suppose if the government were to issue any mandates limiting the commercial sale of helium it would be bursting balloons leaving behind pouty children in its wake. Now, I know the proceeding observation is probably oversimplified but the article didn't mention the 'life of helium' after earth.   As far as I understand it, untethered helium will float into space leaving us in want once it is all gone. So then, imagining a helium atom floating beyond our atmosphere, where will it ultimately arrive? Does the earths magnetic field prevent the helium atom from escaping too far from our planet? Or, do the solar winds sweep those loose atoms into deeper space?  I know the space vacuum is not perfect and full of different elements and I would imagine the distance between these atoms is great. Will the helium atom eventually bond with other atoms -- given a strong enough electromagnetic attraction -- and form new elements??

Helium is lighter than air, so it should fly off from Earth. Is it possible that in the future we will run out helium?


In few weeks I'll be on a competition for website development.  I can use Emacs from a usb stick. I can't write to system drives anything so all Emacs configs and plugins are needed to be loaded from the usb stick. These are rules so I would rather not break them.   So I think this can be done with setting load-path or recompiling emacs to look config files from the usb but I no idea how this would be done in practice.

Is there a way run Emacs from a USB drive? I am a Windows user and I would like to be able use it on any PC without an Emacs install.


Let $\eta$ be non-negative (a.c.) continuous random variable. How to prove that $\mathbf{E}\eta = \int_{0}^{\infty}\mathbf{P}(\{\eta > z\})dz$ for arbitrary non-negative random variable?  If $\eta$ is discrete random variable it's quite simple. I have an idea that we can prove it easily for random variable $$\xi = \sum_{i=1}^{n}\xi_i\mathbf{1}_{\Delta_i}$$ that can take only finite set of values , where $\mathbf{1}_{\mathbf{X}}$ is an indicator function of a set $\mathbf{X}$. Since for every measurable function $\xi$ there is an approximating sequence $\{\xi_i\}_{i\ge1}$ of the functions of such kind that tends to $\xi$ pointwise, I would like to make a passage to the limit to prove this statement for an arbitrary continuous non-negative random variable? How can one do that rigorously?

Let $X$ be a non-negative random variable and $F_{X}$ the corresponding CDF. Show,   $$E(X) = \int_0^\infty (1-F_X (t)) \, dt$$   when $X$ has : a) a discrete distribution, b) a continuous distribution.   I assumed that for the case of a continuous distribution, since $F_X (t) = \mathbb{P}(X\leq t)$, then $1-F_X (t) = 1- \mathbb{P}(X\leq t) = \mathbb{P}(X>  t)$. Although how useful integrating that is, I really have no idea.


I need to drop a table that is 500 GB in size. It contains historical data that's not needed or used. There are no FK constraints. Any consequences of just dropping the table? I'm also using DB Mirroring. Will there be blocking or some other things that I should be concerned?  Microsoft official statement:     Large tables and indexes that use more than 128 extents are dropped in two separate phases: logical and physical. In the logical phase, the existing allocation units used by the table are marked for deallocation and locked until the transaction commits. In the physical phase, the IAM pages marked for deallocation are physically dropped in batches.

I'm about to delete a large table which is approximately 100GB in size.  I'd like to understand the impact on the mirroring that's in place on this db.  Can anyone confirm?


I am unable to find any feature to make the desktop wallpaper autochange after an interval. If there is, please let me know. If not, then is there any app for the same?

How do  I create a desktop wallpaper slideshow with my own set of images?   With the images coming from a pictures folder, or pre-selected With the images displayed in order, or randomly With the images changing every few minutes, or after random periods of time


I need to calculate a composite hash code from an array of object references. (Not an array of bytes.) It looks like there is something tailor-made for this:  So I have written some code to use it: public override int GetHashCode() {     var h = new HashCode();     foreach (var x in data)         h.Add(x);     return h.ToHashCode(); }  And it looks fine in Visual Studio 2019; no red underlines anywhere. But when I try to run an actual build using my build script: call C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvars64.bat csc -debug -out:boot.exe -r:System.Numerics.dll Boot.cs lib\*.cs  I get an error message:  lib\VList.cs(96,21): error CS0246: The type or namespace name 'HashCode' could not be found (are you missing a using directive or an assembly reference?)  What am I missing? CSC was working fine with everything up to now. CSC /version says:  3.5.0-beta4-20153-05 (20b9af91)

In .NET, the  is used in a lot of places throughout the .NET base class libraries. Implementing it properly is especially important to find items quickly in a collection or when determining equality.  Is there a standard algorithm or best practice on how to implement GetHashCode for my custom classes so I don't degrade performance?


I setup a image box of Vista Business to ghost a couple of weeks ago. I turned it on today and I seem to have forgotten the password. I've tried using OPH-Crack to crack it but with no luck. Does anybody have software that they use to crack user account passwords or know of a work-around for Vista?

I got a brand new Windows 7 machine, installed the operating system, created one account and forgot its password. What can I do?  There is no external CD, the operating system is loaded from somewhere inside the machine.  I already tried to remember passwords and tried all candidates with all possible combinations of caps lock, num lock etc.


I'm currently learning the C language and I'm having trouble in the multiplication by negative number. I've tried following code and got 4294966 for value 'a'. Environment: Windows 10 Visual Studio Code gcc version 8.1.0 (x86_64-posix-seh-rev0, Built by MinGW-W64 project) #include <stdio.h> #include <stdlib.h> #include <stdint.h>  #define FACTOR 1000  int main() {     int32_t a;     int32_t b = -1;     uint32_t c = 1000;      a = (b * c) / FACTOR;      printf("%d\n", a);     return 0; }  When I changed int32_t to int16_t and got -1 for value 'a'. Could anyone tell me what's going on with the value 'a'. Greatly appreciated. int main() {     int16_t a;     int16_t b = -1;     uint16_t c = 1000;      a = (b * c) / FACTOR;      printf("%d\n", a);     return 0; }

Suppose I have the following C code.  unsigned int u = 1234; int i = -5678;  unsigned int result = u + i;   What implicit conversions are going on here, and is this code safe for all values of u and i? (Safe, in the sense that even though result in this example will overflow to some huge positive number, I could cast it back to an int and get the real result.)


I have a Dell Windows 8.1 with lost administrative accounts' passwords. I have exhausted the following options:   chntpw: I have tried both booting chntpw and a live CD boot to install and run chntpw. I enable and blank password for the built-in administrator account and also blank the password for the regular administrator account. Upon reboot, I notice no changes. Strangely, chntpw claims that the password is "already blank" when booting chntpw from USB stick. NOTE: I have used chntpw several times in the past on Windows 7 and older OSs. This is, however, the first time I have used it on 8.1. Ophcrack: I am not familiar with this software, so I might have been using it wrong. The software seemed to not even be able to recognize that the accounts had passwords.  Perhaps there is no local password, but rather a Microsoft account password? There seems to be no indication of this. The option on the sign-on screen to "reset password" mentions no Microsoft account, only to insert a recovery USB stick. Trinity Rescue Kit: I could not figure it out. I kept running into issues I couldn't find support for online. I'd rather not go that route. Reset to factory settings: No luck. There is no recovery partition (no option to "reset this PC" from login or from troubleshooting boot screen). Creating a recovery ISO requires an admin password. I tried to create a recovery ISO from Dell's website, but they do not have any images for this device.   At this point, I do not know what to do. The only option left I can think to do is to buy a new Window's license and install, but I naturally do not want to go that route. Fellow technicians, are there any options I have not attempted? What else can I do from the options I have tried? At this point, any destruction of data is fine, save for Windows itself, which I would like to keep!  As described in my question, I have tried the solutions listed in the similar question.

I accidentally disabled my admin account.  After I login to another account I found I can not get admin rights, because all admin accounts on my computer are disabled.  I clicked on 'run as administrator' but only see a smart card choice (all the admin accounts are disabled so no choice provided)    I don't want to re-install my OS, help!    Details:  I have account A on my computer.    I got a new computer so I want to give the old one to my mother.    Creating a new user account B for her and disable account A.    Logout and restart.    Successfully login B, now I found I could not get admin rights because no account choice is provided.    More informations about my machine:  OS is Windows 10 and my admin account is a Microsoft Account.  I have an arch-linux installed on my computer and dual-boot it using GRUB, so maybe I can not use safe mode.


What is a good book on electricity such as generators for someone who is a beginner and want to learn about the generator and such.

I need basic electronics books  (diodes,transistors,current.. etc) as I am just starting out with electronics and want to have something to read over the holiday.  Any suggestions of good beginners' books?


When telling stories in the past tense, I've noticed that Americans will tend to say "I was standing on stage..." or "I was sitting at our table at Friendly's last night when..." while the Brits will tend toward "I was stood on stage..." or "I was sat at our table at Nando's last night when...". It's quite interesting, that the British will generally use this passive past type structure while the Americans will generally use the continuous past for the same situations.  Does this phenomenon have a name? Has it been studied?  Examples of this used in British Speech:

Is "I am sat" bad English? I believe it is incorrect and instead either the present continuous     I am sitting   or the predicate adjective     I am seated   should be used.  I hear this quite often, however, and ultimately usage overrules formality.  Does anybody know where this originated or how to describe it grammatically?


When particle physicists said interaction, I interpreted it as force.  So, when I heard that elementary particles interact with the Higgs field, which confers them with mass, I thought this must be a force as well. But, particle physicists make it clear that there are only four fundamental forces. So is the Higgs force the fifth force?  I checked up on some more information. So, if interaction with Higgs field, flips the chirality of a lepton, then surely this chirality flipping force is the fifth fundamental force, is it not?  Edit: Though the linked question is similar to my question, the answers there are a bit too technical for me. Even the question is worded in a more mature way. There is no way I can understand the answers there.

When I first learned about the four fundamental forces of nature, I assumed that they were just the only four kind of interactions there were. But after learning a little field theory, there are many other kinds of couplings, even in the standard model. So why isn't the Yukawa Higgs coupling considered a fifth fundamental force? To be a fundamental force, does there need to be a gauge boson mediating it?


It's been proven that √7 and √2 are .  However, I am not sure how to go about proving that √7 - √2. Is it an acceptable proof to just solve the equation which would prove/disprove the equation or as should the proof be done as a contrapositive, similar to how √7 and √2 are proven to be irrational.   What would a valid proof/disproof of irrationality look like in this case?

Can the expression $\sqrt{n} + \sqrt{m}$ be rational if neither $n,m \in \mathbb{N}$ are perfect squares? It doesn't seem likely, the only way that could happen is if for example $\sqrt{m} = a-\sqrt{n}, \ \ a \in \mathbb{Q}$, which I don't think is possible, but how to show it?


I was just trying something in javascript and came across this scenario for the javascript equality operator, which baffled me    My questions are,  1) Why ""==0 is true ?  2) If "0"==0 and ""==0 is true then why ""=="0" is false ?  Any explanation and the pointers for more reading will be great.

I'm using  to go through JavaScript, and it's returning many suggestions to replace == (two equals signs) with === (three equals signs) when doing things like comparing idSele_UNVEHtype.value.length == 0 inside of an if statement.  Is there a performance benefit to replacing == with ===?   Any performance improvement would be welcomed as many comparison operators exist.  If no type conversion takes place, would there be a performance gain over ==?


I'm resolving the limit of $\frac{(2x^2).y}{x^4+y^2}$  when $(x,y)\to(0,0)$  We didn't study any special theorem, we did only approach.  I tried first the  changes $y=x^2$ and $y=0$.  In $f(x,x^2)$, operating I get that the $\lim =\frac{2x^4}{2x^4}=1$ So then I test the $f(x,0)$ operating I get $\frac{2x^2.0}{x^4+0}$, that is still $0/0$,but has a zero on the numerator, that is always enough to claim that the limit of $f(x,0)$ is $0$? Assuming that the limit $f(x,x^2)$=1 $f(x,0)$=0 so the limit don't exist.  Is right the procedure? Any way to do it easy? is right the assumption of the 0 on the numerator that the limit will be cero? Thanks.

Please help me in computing the following limit. $$\lim_{(x,y) \to (0,0)}\frac{2x^2y}{x^4 + y^2}.$$ This will be my first attempt in computing a limit involving 2 variables. Is this a part of multivariable calculus as it contains more than one variable? How can I interpret this geometrically?  Thank You


How does on prove $\gcd(a, b) = 1 \wedge a\  |\  b\ c \Rightarrow a \ | \ c $ with as elementary steps as possible (i.e. not using the fundamental theorem of arithmetic (unique prime factorization))?  EDIT:  I saw that this theorem is called Gauss Theorem and is proved formally for integers $\mathbb Z$ in Coq,   EDIT: Clarification:  I forgot to tell that I want to prove this for the natural numbers $\mathbb N \geq 0$.  Is Bezout's lemma applicable for the natural numbers, or is some other method needed?

Well I thought this is obvious. since $\gcd(a,b)=1$,  then we have that $a\not\mid b$ AND $a\mid bc$. This implies that $a$ divides $c$. But apparently this is wrong. Help explain why this way is wrong please.   The question tells you give me two relatively prime numbers $a$ and $b$ such that $a$ divides the product $bc$, prove that $a$ divides $c$. how is this not obvious? Explain to me how my "proof" is not correct.


I would like to learn to make commutative rectangles using Tikz. How can I do that? I have tried \[\begin{tikzcd} A \arrow{r}{\varphi} \arrow[swap]{dd}{g\circ f} & B \arrow{d}{g} \\ & C \end{tikzcd} \]  but it draws only a triangle.

Can anyone help me in giving commands for commutative diagrams in LaTeX ? It doesn't seem to appear properly in the LaTeX guides that I have. A command for a simple triangular diagram with arrows associated to maps would be good enough, or maybe some appropriate reference.


When Gandalf became "the White", did he usurp Saruman's power, or get boosted up, and if so what happened to Saruman's powers? Other than the "gift of voice" he seems to have lost all his.

Saruman was strong enough to defeat Gandalf the Grey, but upon banishment from Orthanc and his taking over of the Shire he seemed like nothing more than a normal old man. He apparently retained his powers of persuasion (somewhat) but his great fighting strength seemed to all be gone.  Why did Saruman lose all or most of his power?


I load the package with:  \usepackage{graphicx}   I use it as follows:  \includegraphics{inc/2 aanbod/inc/doc/Vormingplus/inc/img/2 jpg/p. 04-05.jpg}   This is the error I get:    LaTeX Warning: File `inc/2 aanbod/inc/doc/Vormingplus/inc/img/2 jpg/p. 04-05.jp g' not found on input line 444.   ! LaTeX Error: Unknown graphics extension: . 04-05.jpg.  See the LaTeX manual or LaTeX Companion for explanation. Type  H <return>  for immediate help.  ...                                                l.444 ...c/Vormingplus/inc/img/2 jpg/p. 04-05.jpg}  ?      I think the solution for this problem is clear. graphicx should start seeking at the END of the specified filename, seek to the left for the FIRST APPERANCE OF A DOT.  Could this please be solved?

\includegraphics cannot handle filenames that contain more than the one dot, separating the filename from the extension. Apparently it uses everything after the first dot as extension and then, of course, complains about an unknown graphics extension.  This is annoying as I very often have filenames that contain parameter values, e.g. plot_a0.4_b0.6.pdf.  Is there a way to teach LaTeX to interpret only the string behind the last dot as extension?


Suppose $f$ is a continuous function on $R^1$ with period 1. Prove that $$\lim_{N\to\infty}\frac{1}{N}\sum_{n=1}^Nf(n\alpha)=\int_0^1f(t)dt$$   for every irrational number $\alpha$. Hint: Do it first for $$f(t)=e^{2πikt}$$   How are these two thing connected? Intuitively the left hand side is acting like a Riemann sum but it isn't a Riemann sum. $n\alpha$ is fairly ambiguous and hard to understand. In the long run  I understand that $(n\alpha)$ (the decimal value of $n\alpha$) populates the entire interval $(0,1$ fairly uniformly. I don't understand how that may help. I don't know any assistance

Suppose $f$ is continuous and periodic on the reals with period 1. Prove that if $x\in[0,1]$ is an irrational number, then  $$\lim_{N\rightarrow\infty}\frac{1}{N}\sum_{n=1}^N f(nx)=\int_{0}^1f(t)dt$$   Suggestion: First consider $f(t) = e^{2\pi(ikt)}$ where k is an integer.   I can see that this is a limit of a weighted average, but the suggestion throws me off. I've seen the suggestion in fourier transforms but it's not clicking at the moment. Any help would be welcome.


Problem:     The total number of ways in which 5 balls of different colour can be   distributed among three persons so that each person gets at least one   ball?   Source:  A book on combinatorics. Was asked in an entrance exam.  My try:  To simplify the problem, we can distribute $3$ of the $5$ balls beforehand so we can get rid of the constraint. Let us select 3 balls and permute them within these three persons, so the number of ways of doing so $$ N_1 = C(5,3) + P(3,3) = 60$$  Now that we have done so, we have two balls left. Let them be $B_1$ and $B_2$ These can be distributed as below:   Let both the remaining balls be with one person, so we have  $$(B_1 B_2, 0, 0)$$ and there are $3$ ways of doing so.  Let the remaining balls be distributed one by one, so we have $$(B_1, B_2, 0)$$ and there are $3! = 6$ ways of doing so.  We can take the total number ways ($N$) by: $$N = N_1 \times 3 + N_1 \times 6$$ $$N = 60 \times 3 + 60 \times 6$$ $$N = 540$$  This approach seems correct to me but still it gets the wrong answer...  The right answer is $150$ ways  Please guide me and correct me if I'm wrong. All help appreciated!

5 balls of different colours are to be placed in 3 boxes of different sizes. Each box can hold all 5 balls. The number of ways in which we can place the balls in the boxes so that no box remains empty.  My attempt:-  First choose 3 balls to be placed in 3 boxes so that none of them remain empty in ${{5}\choose{3}}\cdot3! = 60$ ways.  Now remaining 2 balls can go into any of the 3 boxes in $3\cdot3 = 9$ ways.  Total number of ways $= 60\cdot9 = 540$.  Where am I going wrong ?


I am writing the report for my lesson with the details like that. I would like to draw by tikz or anything else?   I really have no idea. I've taken a look but I didn't find out anything that could help me. So I hope you can help me.  \documentclass[answers]{exam} \usepackage{amsmath} \usepackage{amsthm} \usepackage{amsfonts}   \end{document}

i am new to latex. how can i make a hierarchy tree diagram as shown below?


I am getting very slow internet speed in the terminal. Whenever I try to install any software/package with apt-get install or do apt-get update, the internet speed is very slow, like about 20 kB/s (160 kb/s) while my internet speed is 10 Mbps. I have an ASUS FX-553VD-DM483 laptop, and I have Windows 10 and Ubuntu and several Linux distributions multiple booted. Screenshots are attached.  The speed on the terminal:   Actual Speed on browser:   I saw  of the same problem but it suggests to change the server to the best server. I have a personal computer on the same network which gives more than 1 MBPS speed on every terminal operation from the same Indian servers. So the problem lies in my laptop Ubuntu itself. I thought of drivers issue but if it was a drivers issue then browsers might have given slow speed, but browsers giving considerable amount of speed and all other applications like Tixati and torrent. Please help!  Note: I tried with both Wifi and Wired with my laptop; same problems occurs with both. Note:: I have installed kali repositories and some of the kali tools using the tool katoolin from github! I tried finding the best server and still the speed is same.

I just installed a fresh install of 32-bit 12.04 LTS Pangolin today. When I tried to install a few applications, it was really slow. But when I download a .deb or .tar.gz file from on my web browser, it is a lot faster.  Computer specs:  HP Pavilion Slimline s7700n PC  [Memory]         873.7 MiB  [Processor]      AMD Athlon(tm) 64 X2 Dual Core Provessor 3800+ x 2  [Graphics]       GeForce 6105 LE/integrated/SSE2/3DNOW!  [Disk Size] 638.5 GB  I normally get 200-400 kbps.  This is the comparison.


I found that latest version which is determined in Synaptic Package Manager is older than what is on developer web site. It is different from latest stable versions as well, and even after 2 (or sometime 6) months the version in synaptic is not updated. Why this difference occurs? And is there any way that update latest version for all packages in Synaptic?

Why are packages in the official Ubuntu repositories older than the latest (upstream) versions from Debian Sid, PPAs, the authors, etc.?


Let me try to explain this. Sorry for being a newbie. Anyways, I have wine installed to install Evernote, then I realized Evernote version 5.9* is no good that I should go for an older version 5.8* which then I downloaded.  I used the alt+F2 to open up the wine uninstaller to remote my Evernote 5.9* then I go into the ~/.wine folder and deleted the Evernote folder within.  Then I tried installing Evernote 5.8* in terminal with wine which didn't work and so I tried going to the add/remove of wine to install which gives me the error message of   Evernote was already installed by another user. Only one per-user installation is supported...........  I searched up for this error alert, lots threads are saying to remove wine in order to remove things in the wine bottle. Is this a must or else I won't be able to install Evernote again?

I am using Ubuntu 11.10. By using wine software i installed some software like nimbuzz and ibibo messenger. Both the programs are not working and showing the bug as We're sorry, but an unknown error has caused ibibo Messenger to close.  So I wanna uninstall those.   How to uninstall those type of programs which I installed through Wine?


What is the equivalent of the following code in C#?  Dim intValidChars As New List(Of Integer)(New Integer() { Asc("0"), Asc("1"), Asc("2"), Asc("3"), Asc("4"), Asc("5"), Asc("6"), Asc("7"), Asc("8"), Asc("9"), _                                                               Asc("A"), Asc("B"), Asc("C"), Asc("D"), Asc("E"), Asc("F"), Asc("G"), Asc("H"), Asc("I"), Asc("J")})       Thanks in advance.

VB has a couple of native functions for converting a char to an ASCII value and vice versa  - Asc() and Chr().  Now I need to get the equivalent functionality in C#.  What's the best way?


Is there a shortcut key to make a macbook sleep?  Sometimes I want to save time and just use the shortcut key to put it to sleep.

I am looking for a quick way to sleep without closing the lid, or using the mouse.  If it matters, I have Lion version OS and a MacBook Air.


Is there a need to install a C/C++ compiler in Ubuntu 14.04 LTS? Where to write the program? How to compile the same?

I am  new to Linux. I am using Ubuntu 11.04 and do not know how to compile and execute C++ program in it. I need to know the commands to Compile and Execute a C++ program in Linux.


I am a 15 year old Indian. I currently stand at 163 cms but I weigh 75 kg, which is overweight I know. But is there any way I'll grow more? If yes, how much?  My dad's height is 172 cm and my mom is 157.  I've been measuring my height for some time now and I've grown about 5 cms in the last 6-7 months. However, I haven't had a huge growth spurt yet. But one of my grandads is just about 148 cms, I guess. So will I grow taller?  I don't think that this question is a duplicate. Here, I just asked if I could grow taller. But that is a purely scientific question, I believe.  Diet: I eat a mainly vegetarian diet with some chicken at least 2 days a week. I drink a glass of milk about 3 days a week. But I don't eat any other meat than chicken. I also eat some fruits 3 days in a week. However, I'm willing to change my diet if that would help me grow.  Exercise: I usually play sports. But these days I haven't been able to, because of my school work. But I have been thinking of working out to reduce fat.

I am an adult, and I want to be taller. I know about many medicines which claim to treat stunted height.  Is there any truth behind these?


Let $L$ and $K$ number fields, if $p$ is ramified in $LK$ then it's ramified at $L$ or $K$?

If $L_i/K$ are Galois extensions of number fields, $i=1,\ldots,n$, and $L=L_1\cdots L_n$ is the compositum. Then it's true that a prime $\mathfrak{p}$ of $K$ splits in $L$ if and only if it splits in all of $L_i$. Does this also hold if the $L_i$ are not Galois extensions of $K$?  The proof that I know regarding the compositum uses the fact that the $L_i/K$ are Galois, so is this true in the more general setting and how would one prove it?


I am using IBM DB2.  So, I have a SQL query in which I am retrieving a person's SSN from a table. I want to put conditions on that SSN column of the result set, conditions like :  1) It should start with only 9.  2) There should not be 2 consecutive zeros at 4th and 5th positions. (For eg. it cant be 999006667).  3) Max. length of a SSN can be 9.  Thank you.

I am using IBM DB2.  So, I am retrieving a column named SSN from a table. I have to apply the following regex on that column:  ([1-57-8][0-9]{2} |0([1-9][0-9] |[0-9][1-9]) |6([0-57-9][0-9] |[0-9][0-57-9])) ([1-9][0-9]|[0-9][1-9])([1-9]\d{3}|\d[1-9]\d{2}|\d{2}[1-9]\d|\d{3}[1-9])   Someone suggested to me that I have to write a function/procedure in the query to validate that the SSN picked from the db follows this regex else it should not be stored in the result set of the query.  I don't know how to write a function or a procedure in SQL, can you please help me out here?


Has anyone come across the problem where you add certain numbers such as 3.2 + 3.6 in python 3 you get an output like "6.800000000000001". This has occurred when I was using Python 3.8. One other set of numbers I added was 2.6 + 2.2 which gave the same result. Does anyone know why this happens, and only on these few numbers? print (3.6 + 3.2) print (2.6 + 2.2)

Consider the following code:   0.1 + 0.2 == 0.3  ->  false   0.1 + 0.2         ->  0.30000000000000004   Why do these inaccuracies happen?


I want to get more RAM for my computer, and I understand that to get the right type of RAM I have to know the memory type and speed (minimum and maximum as far as I understand). So how do I find these things out? And is there anything I need to know about the memory before I can get more RAM which will actually fit with the specifications of my computer? I am running Ubuntu GNOME 16.04 with GNOME 3.20.  Note: I know that there are Terminal commands to find out this information, I just can't remember what they are.

How shall I find out the frequency and type of my current RAM? My OS is Ubuntu 12.04.


I'm a Latex beginner, could you please help me to draw these diagrams? Thank you very much!

Can anyone help me in giving commands for commutative diagrams in LaTeX ? It doesn't seem to appear properly in the LaTeX guides that I have. A command for a simple triangular diagram with arrows associated to maps would be good enough, or maybe some appropriate reference.


Script:  text="//ABC/REC/TLC/SC-prod/1f9/20/00000000957481f9-08d035805a5c94bf"  echo ${text##*/}   Here, what is the meaning of 2nd line in the above 2 line script?

I'm quite confused about the following regular expressions I found in a shell script:  ${0##*/} ${0%/*}   How do they work?


Most sites on Stack Exchange are pretty bright, with a lot of light colors. This causes eye strain and makes SE somewhat painful to use at night, even with F.lux or Redshift installed.  Is there something that will turn SE sites dark, so they're a little less blinding?

Each Stack Exchange site should provide users the option of using a dark mode design/theme.  Why is this feature missing?  The major IDEs are already a letdown regarding dark color schemes.


grep --before-context 5 shows 5 lines before the match.  I want to show everything before the match. Doing grep --before-context 99999999 would work but it is not very... professional.  How to show all the file up to the match?


I followed a guide to create a batch file so I can delay a program from starting up for a few seconds. (I didn't want to use a 3rd party tool)  The thing is I don't want to see that cmd window for X seconds until it launches that program. Any ideas?  Here is the code I am using within the .bat file:  @ECHO OFF TIMEOUT /t 3 > nul START "" "C:\program.exe"

I'm looking for some way to run a batch file (.bat) without anything visible to the user (no window, no taskbar name, .etc..).  I don't want to use some program to do that, I'm looking for something cleaner. I've found  that uses VBScript, but I don't really like using VBS, either.


I've noticed that the pronunciations of "picked" gives its sound like "pick" with final sound "d" but for "Crooked" and "Naked" Why do they pronounce them like "Crook-ked" and "Nake-ked"?   How can I know when i must pronounce the word like "picked" and when I must pronounce the word like "Crooked"?

There are three ways I know to pronounce the -ed at the end of an adjective:   /t/ as in cracked. /d/ as in lined. /ɪd/ as in naked   I realise naked is a special case because, as , it comes for Old English nacod, so the suffix isn't added.   shows the pattern of pronunciation of -ed in all other cases. However it doesn't explain why  ends with /ɪd/ (or /id/ or /əd/ depending on the dialect).   that wicked comes from OE wicca, so the d wasn't already there.  Why do we pronounce wicked as /ˈwɪkɪd/ and not /ˈwɪkt/?


I am asked to determine if a series converges or not:  $$\displaystyle\sum\limits_{n=1}^{\infty} \frac{(2^n)n!}{(n^n)}$$  So I'm using the $n$th root test and came up with $\lim_{n \to {\infty}}\frac{2}{n}\times(\sqrt[n]{n!})$ I know that the limit of $\frac{2}{n}$ goes to $0$ when $n$ goes to infinity but what about the $(\sqrt[n]{n!})$?

Convergent, absolutely convergent or divergent:   $$\sum_{k=1}^{\infty}\frac{2^{k}\cdot k!}{k^{k}}$$   I have used ratio test because we got a fraction here and I think I did alright till the end:  $$\lim_{k\rightarrow \infty}\frac{\frac{2^{k+1}\cdot (k+1)!}{(k+1)^{k+1}}}{\frac{2^{k}\cdot k!}{k^{k}}} = \lim_{k\rightarrow \infty}\frac{2^{k+1}\cdot (k+1)! \cdot k^{k}}{(k+1)^{k+1}\cdot 2^{k}\cdot k!} = \lim_{k\rightarrow \infty}\frac{2^{k}\cdot 2^1\cdot k! \cdot (k+1)\cdot k^{k}}{(k+1)^{k}\cdot (k+1)\cdot 2^{k}\cdot k!} = \lim_{k\rightarrow \infty}\frac{2k^{k}}{(k+1)^{k}}$$ $$=2\lim_{k\rightarrow \infty} \left( \frac{k}{k+1}\right)^{k}$$  Now I don't know (without a calculator) to what this would converge / diverge to... In the exam we are not allowed to use a calculator... So what to do?  The denominator will be greater than the enumerator by 1, so dividing each other we got something $<1$. We take exponent $k$ which is $\geq 1$, so we will end up with $<1$ again. Multiply this with 2 we get something $< 1$ but $> 0$ and thus the series is convergent...?  I hope I have described it well? Would you give me full points to this task? :D  Edit: I haven't described it well in the end. See the accepted answer and its comments! Thanks a lot to everyone - from every question I ask here, I always learn new things :-)


The best part of me is my hands. or The best part of me are my hands.

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


I am a bit at a loss right now as to why a script of mine does not work as I perceived it.  Since id3v2 is a bit complex to use, I tried to simplify its uses by writing a script around it.  The parts which are mine work perfectly fine, but coming to handing the collected information over to id3v2, it fails when any of the switch values have spaces in there, even though I forced quotations inside the variables.  The usage for id3v2 requires each switch to be followed by a value.  Everything else is considered a file.  So, in order to define the title the switch would look like this:  --TIT2 "Beautiful Stranger"   The switch without and the value with quotation marks to cope with whitespace.  To be able to fully omit any switch without building a new command line inside the script, I thought it would be smart to submit the variables without quotations with forced quotations inside the value, which I hoped where unwrapped.  Consider the following:  ... sTitle="--TIT2 \"Beautiful Stranger\"" ... /usr/bin/id3v2 ${sTitle} ${sArtist} ${sAlbum} ${sTrack} ${sYear} ${sGenre} ${sGrouping} "${aFiles[${iFile}]}"   However, while the result looks good using the above line with echo, using id3v2 provides me the message Couldn't stat file 'Stranger"' (basically, the second part of my title plus finalizing quotation cannot be found, which is obviously correct).  Disappointed that id3v2 apparently does not adhere to the unwrapped forced quotations, I modified my script to split the variables from the switches and quoted them on the target command line instead:  ... sTitleHead="--TIT2" sTitle="Beautiful Stranger" ... /usr/bin/id3v2 "${sTitleHead}" "${sTitle}" "${sArtistHead}" "${sArtist}" "${sAlbumHead}" "${sAlbum}" "${sTrackHead}" "${sTrack}" "${sYearHead}" "${sYear}" "${sGenreHead}" "${sGenre}" "${sGroupingHead}" "${sGrouping}" "${aFiles[${iFile}]}"   This works as long as all variables are used, but fails if one (or more) variables are omitted.  The error message there is Couldn't stat file ''.  It seems that it still finds the quotes on the command line and tries them as a file name, even though when I omit a variable, I typically unset or set them as zero-length string (tried both).  I also tried to remove quotations from my ...Head variables, just in case they are not properly detected as parameters, but the result is the same.  Does anyone know how to convince id3v2 on how to take the command line parameters without giving out?  Alternatively, if there is a easier scriptable program around, I am also thankful.

In a Bash script, I'm trying to store the options I'm using for rsync in a separate variable. This works fine for simple options (like --recursive), but I'm running into problems with --exclude='.*':  $ find source source source/.bar source/foo  $ rsync -rnv --exclude='.*' source/ dest sending incremental file list foo  sent 57 bytes  received 19 bytes  152.00 bytes/sec total size is 0  speedup is 0.00 (DRY RUN)  $ RSYNC_OPTIONS="-rnv --exclude='.*'"  $ rsync $RSYNC_OPTIONS source/ dest sending incremental file list .bar foo  sent 78 bytes  received 22 bytes  200.00 bytes/sec total size is 0  speedup is 0.00 (DRY RUN)   As you can see, passing --exclude='.*' to rsync "manually" works fine (.bar isn't copied), it doesn't work when the options are stored in a variable first.  I'm guessing that this is either related to the quotes or the wildcard (or both), but I haven't been able to figure out what exactly is wrong.


I found that the rendering xxx**yyy**zzz as xxx*<i>yyy</i>*zzz is by-design, but for latin letters it works identical both in preview and after posting. But this is not so for cyrillic letters.  In  I marked two letters inside a word using double asterisks:  (this is like sailors say комп**а**с, while non-sailors say к**о**мпас).   In edit preview it is shown as bold:        But in the post itself it is shown as italic between asterisks:        Changing double-asterisks to double-underscore yields the same result both for preview and after posting:        So this looks like a bug with processing the highlighting of cyrillic characters in preview mode.  Note: This is not a duplicate of  post. This post is about bug, linked post is about (1) removing the feature on non-programming sites or (2) different processing of ** and __ highlighting.

The similar case was discussed here: . Though quick help on formatting proposes to use _italic_ and **bold**, in fact you can use *italic* and __bold__ with the same effect. But when double asterisk is used inside the word, one pair of asterisks (or underscores) is not converted to formatting, but is kept as is: it_a_lic, italic, b__ol__d, bold. If I understand correctly the double-asterisk bold highlighting doesn't work inside words to make simpler programming_style_underscore_usage. Actually my question is because of , where I tried to indicate difference in stress between two words: , but after posting I've got: . So, I have two questions here:  On programming-related sites - why underscore-protection should influence asterisks as well? Can this feature be disabled on non-programming-related sites?


I want to search for a specific keyword in a pdf file using linux shell. How I will use the grep command to do that?

Is there a way to search PDF files using grep, without converting to text first in Ubuntu?