Tl;dr: Took a rigorous linear algebra 2 years ago, forgot most of the stuff now. Trying to resharpen my LA skills, so looking for a suitable LA book.  2 Years ago, I took a very rigorous course in Linear Algebra and Abstract Algebra. We covered content such as Groups/homomorphisms, fields, rings, vector spaces, subspaces, linear transformations, rank/nullity, isomorphisms, matrix arithmetic, representation of linear maps by a matrix, computational algorithms, dot product, inner product spaces, determinants, spectral theory, and the Cayley Hamilton theory.   The course was very proof heavy, and I came out of the course with a solid understanding about the theory of linear algebra.  Fast forward 2 years later, I am trying to resharpen my linear algebra skills. I tried reading Strang's book but I got demotivated very quickly because I felt I was benefiting very little (as I remembered most of these stuff). However, at the same time, I have forgot lots of elementary bits and pieces in the middle so I can't say I remember everything!  So I guess what I am trying to ask is, is there a suitable book for my case which still starts with the basics but picks up the pace quickly, while still covering most of the elementary content?

I'm a mathematics undergrad student who finished his first university year succesfully. For this post, it should be interesting to note that I already took a course in group theory.  I also had a course in linear algebra where we treated the following topics:  1) Vector spaces; basis; span; linear dependency; direct sum   2) Linear transformations, matrices, rank  3) Linear varieties, system of linear equations  4) Determinants  5) Eigenvalues and eigenvectors, diagonalisation, triangalisation, cayley-hamilton,  6) Euclidean spaces: inner products, norm, hermitian transformations, orthogonal basis, Gramm-Schmidt, orthogonal transformations  7) Prehilbert spaces  8) Isometries  9) Bilinear forms and quadrics in $2$ and $3$ dimensions  Now, I want to revise these topics, but it would be too boring to reread these books again, so now I look for a book that has all these topics, but also some additional requirements:   Focus on intuition (e.g. connections between linear algebra and geometry). This is a hard requirement for me, since there was no attention given to this in the course I took) Additional topics such as Jordan form of matrices, quotient vector spaces, ... Good exercises (preferred with solutions somewhere) The book must be rigorous   In the course I had, we mainly discussed finite-dimensional vector spaces, but I am also interested in a theory of infinite dimensional vector spaces.  Can someone hint me towards a good book that would suit me? If I have to add any information, please leave a comment and I will edit my post.  Thank you for your time.


I'm experimenting with SimpleXML for PHP and I was wondering about something. The XML document is like this:  <?xml version="1.0" standalone="yes"?> <users>     <user id="1">         <name>Jan</name>         <sex>Male</sex>         <password>fu9f8w9080fd9id9di093r9f9if9if9d0sfu</password>         <avatar type="remote">http://www.avatars.com/av_1.gif</avatar>     </user>      <user id="3">         <name>Piet</name>         <sex>Male</sex>         <password>fu9f8w9080fd9id9di093r9f9if9676674bv</password>         <avatar type="local">html/avatars/Eten%20en%20drinken/cola.png</avatar>     </user>      <user id="4">         <name>Ilse</name>         <sex>Female</sex>         <password>fu9f8w9080fd9id9di4564564564539d0sfu</password>         <avatar type="none"/>     </user>      <user id="5">         <name>Els</name>         <sex>Female</sex>         <password>fu9f8w9080fd9id9di09gi5uy378wrfuih4w</password>         <avatar type="upload">avatar_1.gif</avatar>     </user> </users>   I made a descending for loop to remove all female users, but I was wondering if there were other methods, using foreach to iterate through the users or using xpath to select all records of females and remove them all at once.  Also, I was wondering if you could remove all nodes  without iterating through all users.  So far I have figured out that "removeChild" does not work in simpleXML, or have I missed something.  Thanks,  Coenj

I have several identical elements with different attributes that I'm accessing with SimpleXML:  <data>     <seg id="A1"/>     <seg id="A5"/>     <seg id="A12"/>     <seg id="A29"/>     <seg id="A30"/> </data>   I need to remove a specific seg element, with an id of "A12", how can I do this?  I've tried looping through the seg elements and unsetting the specific one, but this doesn't work, the elements remain.  foreach($doc->seg as $seg) {     if($seg['id'] == 'A12')     {         unset($seg);     } }


Let $n\in\mathbb N$ and consider the sum $$\sum_{d\mid n}\frac{n}{d}.$$ I understand that dividing $n$ by any of it's divisors is also a divisor of $n$ so intuitively it would make sense that $\{\frac n d\ :\ d\mid n \}=\{d\ :\ d\mid n\}$, from which the desired equality in the title is acquired. but I cannot "see" how this can be proven rigorously. Any help or insight would be appreciated! Edit: In many sources, including the question this one is marked as a possible duplicate to, it is not explained why the identity holds, it's just used. If it actually is explained, it's not clear to me, at least. I am interested in an actual explanation, that's why my question differs from the one marked as duplicate.

Show that $\sum\nolimits_{d|n} \frac{1}{d} = \frac{\sigma (n)}{n}$ for every positive integer $n$.   where $\sigma (n)$ is the sum of all the divisors of $n$ and $\sum\nolimits_{d|n} f(d)$ is the summation of $f$ at each $d$ where $d$ is the divisor of $n$.    I have written $n=p_1^{\alpha_1}p_2^{\alpha_2}p_3^{\alpha_3}.......p_k^{\alpha_k}$ then:- $$\begin {align*} \sum\nolimits_{d|n} \frac{1}{d}&=\frac{d_2.d_3......d_m+d_1.d_3......d_m+........+d_1.d_2.d_3......d_{m-1}}{d_1.d_2.d_3......d_m}  \\&=\frac{d_2.d_3......d_m+d_1.d_3......d_m+........+d_1.d_2.d_3......d_{m-1}}{p_1^{1+2+...+\alpha_1}p_2^{1+2+...+\alpha_2}p_3^{1+2+....+\alpha_3}.......p_k^{1+2+....+\alpha_k}}  \\ \end{align*}$$ where $d_i$ is some divisor among the $m$ divisors. Then I cannot comprehend the numerator so that to get the desired result.  Also suggest some other approches to this question.


This issue actually frustrates me for a while, but prior for finding the solution, I would like to know why this happens. In a nutshell: My TeXStudio does recognise ALL my \label, but the output does not recognise some labels.  Problem  I am writing my notes on Physics, however, sometimes I got warnings of:  LaTeX Warning: Reference `eq:pointcd' on page 196 undefined on input line 985.   This is just for example, I have other examples in the document that does not have \label recognised. There are also some weird situation where I have the same format of putting \label, but got recognised by the compiler.  MWE  \documentclass[12pt,a4paper,headinclude,openright]{scrbook} \usepackage{amsmath} \usepackage{amssymb} % ------------here comes the problem part------------ \usepackage[listings,theorems,skins,breakable]{tcolorbox} \tcbuselibrary{breakable} %======================== Ch.4 boxes ========================= \tcbset{exercisestyle04/.style={arc=0.5mm,coltitle=black,fonttitle=\sffamily\bfseries,colback=color04!50!,colframe=color04}}  \newtcolorbox[auto counter,number within=chapter,list inside=eg]% {exercise04}[2][]{exercisestyle04, title={Exercise ~\thetcbcounter: #2}}  \tcbuselibrary{theorems} \usepackage[amsthm,thmmarks,hyperref]{ntheorem} % theorem  \usepackage{regexpatch} \makeatletter \xpatchcmd*{\thm@@thmline@name}{2.3em}{5em}{}{}  \xpatchcmd*{\thm@@thmline@noname}{2.3em}{5em}{}{} \makeatother \makeatletter \renewtheoremstyle{plain}% {\item[\hskip\labelsep \theorem@headerfont ##1\ ##2 \theorem@separator]}% {\item[\hskip\labelsep \theorem@headerfont ##1\ ##2\ \sffamily{##3}  \theorem@separator]} \makeatother \theoremstyle{plain} \theorembodyfont{\normalfont\sffamily} \theoremheaderfont{\bfseries} \newtheorem{theorem}{Theorem}[section] % ------------here ends the problem part------------ \begin{document} \begin{equation} \rho\left(\mathbf{r}\right)\;=\;\sum_{k=1}^{N}\: q_k \delta\left(\mathbf{r}\;-\;\mathbf{r}_k\right) \label{eq:pointcd} \end{equation} However, one should alert for the unphysical divergence in other quantities associated with \eqref{eq:pointcd}. \end{document}   In your answer...  I am not specifying you of how to answer this question, this section is just my suspects on the issue. For example,   The pdf compiler is faulty? (I use Acrobat XI and with PdfLaTeX as compiler and using DVI -> PS -> PDF chain in TeXStudio) My compiling procedures has done wrongly? My format is done wrong (although I fairly think so because I changed my format according to many sources but no luck). TeXStudio is faulty? (Just a suspect, but did happened with other IDEs before and I am using ver. 2.8.0) I haven't read the manual carefully? (smile)   It turns out some code has obstructed the PdfLaTeX to recognise some \label.  Update  While I was omitting the parts that I have some idea why it happens, however, it is neither of the five above.   While I deleted some of the \frontmatter, by delete a section (see MWE above) become fine to recognise the referencing. I suspect the part is obstructing the compiler to recognise some \label.   Solution  See Mico's answer, but I would like to append that it was actually because of  5. I haven't read the manual carefully

I am running this LaTeX file through pdflatex and getting these warnings:     latex warning: there were undefined references.   latex warning: label(s) may have changed. Rerun to get cross-reference right.   and also some more warnings like this:     latex warning: reference 'lastpage' on page 76 undefined on input line 3200.   on every page end.  My LaTeX file is like this   \documentclass[a4paper,leqno,twoside]{article}  \usepackage[latin1]{inputenc} \usepackage[english]{babel} \usepackage{multirow}  \renewcommand{\familydefault}{\sfdefault}  \usepackage{color} \usepackage[colorlinks=true]{hyperref} \usepackage{draftwatermark} \SetWatermarkText{EXPERIMENTAL}  \SetWatermarkScale{0.6}  \usepackage{parskip}   \graphicspath{{Figure/}}    \let\oldsection\section  \renewcommand{\section}{\clearpage\oldsection}   \begin{document}      % Issued by {Name, acronym, department, phone}  \issuedby{vrebwr}  % Checked by   \checkedby{-}   % Approved by  \approvedby{-}   % Document title. Use \doctitleShort{} to insert a shorter title in the header.   \doctitle{test numbers with id}   \doctitleShort{document for tests}   % Publish date  \publishdate{\today}     % Titlepage  \frontmatter % Should be on first page  \maketitle     \vspace*{08eX}   \begin{center}    \subsection*{Abstract}    \end{center}    \noindent      it contains information about tests.    \newpage     \mainmatter     % Main pages. This command should be on page 2 or later.     \phantom{phantom}    \cleardoublepage     \subsection*{Change Record}    \begin{itemize}   \item R.1: Initial version.    \begin{itemize}   \item  generation of documentation using the vrebwr     \end{itemize}    \end{itemize}      \cleardoublepage    \setcounter{tocdepth}{2}     \tableofcontents      \cleardoublepage     \section{ How to read the tset information}     \begin{enumerate}      \item information how to read     \item information of tests     \end{enumerate}      \section{test numbers}     \subsection*{1, temperature sensor. }    \addcontentsline{toc}{subsection}{ 1, temperature sensor.}    \subsubsection*{data}    some data regarding test where we performed    \subsubsection*{values}    temperature sensor value here three or more.     \subsubsection*{reason}        why we get like this.      \newpage      \subsection*{2, humidity sensor. }     \addcontentsline{toc}{subsection}{ 2, humidity sensor.}    \subsubsection*{data}    some data regarding test where we performed    \subsubsection*{values}    humidity sensor value here three or more.     \subsubsection*{reason}         why we get like this.    \subsection*{3, pressure sensor. }    \addcontentsline{toc}{subsection}{ 3, pressure sensor.}    \subsubsection*{data}    some data regarding test where we performed    \subsubsection*{values}    pressure sensor value here three or more.    \subsubsection*{reason}      why we get like this.    \newpage   \end{document}   In the above LaTeX file I have around 100 tests. I used the * symbol to eliminate numbering in subsections, because I am using test names with number so there is no need to add numbering. It looks bad in the PDF, so I  tried to add that test name and number in table of contents by using this command:  \addcontentsline{toc}{subsection}{1,temperature sensor.}   When I used this command I am getting errors like as I explained above. I searched and I found some reasons why this error occurred, because of \label{} and \ref{} is not used like that. But I don't know how to use that in my file. Can anyone help me with it?


From ancestry.co.uk I know I have an Italian Great-Great Grandmother, name Maude Angelina Georgina Antonio, born 1880 Milano, Italy, father Thomas Antonio, married William Elias Barnett in 1899, Greenhill England.   I would like to find more about her parents, likely to both be Italian. For Uk research Ive found census records invaluable. I know they did censues in Italy but are they publicably available (online)

I need to know if I can find, online of offline, information about the years that census were performed in Italy.  According to the thread  from the forum at the website  it seems that Ancestry.com could have that information, but I don't have those premier plans.


[I believe that this question is very different than the question about arranging magnets into a sphere. Solenoids are ruled by Ampere's Law and magnets are not. Ampere's Law is what could make it work.]  I am wondering if Ampere's Law can be a loophole around Gauss's law of magnetism (Gauss's Law not allowing for magnetic monopoles). With solenoids arranged in a sphere, particularly if you had two of these solenoid-sphere's (one positive and one negative), couldn't the field lines be induced to extend out rather than loop back around on themselves?  Arrange solenoids into a sphere so that the outside of the sphere is made only of the positive ends of the solenoids, and the inside of the sphere only has the negative end of the solenoids (or vice-versa). Doesn't Ampere's Law suggest that there would be no place for the field lines to reconnect? The contour integrals have a maximum capacity that is used up by the field lines moving towards (or away from) the center. Could this not create a magnetic monopole?    Whether or not this would work, surely someone has done the experiment, right? I cannot find evidence of this experiment. I really want to know how this experiment turned out, does anyone know?

Setup: we have a large number of thin magnets shaped such that we can place them side by side and eventually form a hollow ball. The ball we construct will have the north poles of all of the magnets pointing toward the center of the ball, and the south poles pointing away from the center. The magnets in this case are physically formed such that in this hollow ball arrangement they are space filling and there are no gaps between them.  Is such as construction possible? If so, what is the magnetic field (B-field) inside and outside the ball?


As you can see I have 4 table to join below and I've search for the stuff function but it seems to support a single table only.   DECLARE @portal varchar(100) = 'A4E7890F-A188-4663-89EB-176D94DF6774' select       list.[name]     as [Company]     ,list.[address]  as [Address]     ,b.[name]        as [Business]     ,comm.[value]    as [Telephone Number]     ,pp.title + ' ' + pp.first_name + ' ' + pp.last_name as [Contact Person]  from [panpages].[listings] as list     left join panpages.extra_communications as comm         on comm.listing_uuid = list.uuid and comm.type = 'Tel'     left join panpages.listing_people as lp         on lp.listing_uuid = list.uuid     left join panpages.people as pp         on pp.id = lp.person_id     left join panpages.listing_categories as r         on r.listing_uuid = list.uuid     left join panpages.categories as b         on b.uuid = r.category_uuid where     list.[portal_uuid]=@portal and     list.[is_active]=1    This is my sql code and the data shown like below.  My current result appear like this :  Company | Address | Business            | Telephone Number | Contact Person  A&B     | Perak   | Khmer Restaurants   | 012541           | Mr. Yu Lee A&B     | Perak   | F&B                 | 012541           | Mr. Yu Lee King Co.| Ipoh    | Paper Distributors  | 021453           | Mrs. Cheng King Co.| Ipoh    | Paper Distributors  | Null             | Mrs. Cheng DinoX   | Sunway  | Guesthouses         | 0124587          | Mr. Hong Dinox   | Sunway  | Guesthouses         | 0124587          | Mr. Q   My expected result should be like this :  Company |Address| Business              | Telephone Number | Contact Person  A&B     | Perak | Khmer Restaurants, F&B| 012541           | Mr. Yu Lee King Co.| Ipoh  | Paper Distributors    | 021453, Null     | Mrs. Cheng DinoX   | Sunway| Guesthouses           | 0124587          | Mr. Hong, Mr Q   Can somebody help me? I'm stuck around 4 hours because of this shit. Thanks in advance.

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


I read Harry Potter many times and I don't get why they (ministry) suspect Hagrid when the Chamber of Secrets has been opened.  I understand why they suspected him before 50 years ago, in that time people rather believed Tom Riddle than him, but at present they know that Tom Riddle became Lord Voldemort, he was dark wizard, terrible person etc.  Why this acknowledgement didn't show that Hagrid was innocent and there is no reason to imprison him when the Chamber of Secrets has been opened again?

I've just finished re-reading Chamber of Secrets and this stuck with me. Once it becomes clear that the Chamber of Secrets has been opened again and the attacks have resumed, The Ministry of Magic arrive and send Hagrid straight to Azkaban.  I just can't get my head around why. Even if Hagrid had opened the Chamber the first time, what evidence did the Ministry have that he was involved in the latest round of attacks? I can understand why they'd want to question him at least, but sending him straight to Azkaban (without even a trial, as far as I'm aware) seems a little extreme.  Was there some other factor involved that I've missed, or was the Ministry just looking for a scapegoat?  There's a similar question regarding , but the accepted answer doesn't seem to apply to Hagrid's situation.


How can I get a HEX code entry into the Color Chooser for Mavericks?

How can I choose hexadecimal web colours (like #000000 and #fffff) to use in system and third party apps? (e.g. an image editor like GraphicConverter)


How should I evaluate the sum: $\sum_{k=1}^{n}\frac{1}{k}\binom{n}{k}$ ?  I have no relevant observations or partial results so far.  Any kind of help or advice would be truly appreciated!

I got this sum, in some work related to another :  $$S_m=\sum_{k=1}^m  \frac{1}{k}{m \choose k} $$  Are there any known results about this (bounds, asymptotics)?


---- Minecraft Crash Report ---- // There are four lights!    Time: 5/7/16 9:13 AM Description: Initializing game    org.lwjgl.LWJGLException: Pixel format not accelerated     at org.lwjgl.opengl.WindowsPeerInfo.nChoosePixelFormat(Native Method)     at org.lwjgl.opengl.WindowsPeerInfo.choosePixelFormat(WindowsPeerInfo.java:52)     at org.lwjgl.opengl.WindowsDisplay.createWindow(WindowsDisplay.java:247)     at org.lwjgl.opengl.Display.createWindow(Display.java:306)     at org.lwjgl.opengl.Display.create(Display.java:848)     at org.lwjgl.opengl.Display.create(Display.java:757)     at org.lwjgl.opengl.Display.create(Display.java:739)     at bcc.ap(SourceFile:594)     at bcc.an(SourceFile:430)     at bcc.a(SourceFile:377)     at net.minecraft.client.main.Main.main(SourceFile:124)    A detailed walkthrough of the error, its code path and all known details is as follows:  -- Head -- Stacktrace:     at org.lwjgl.opengl.WindowsPeerInfo.nChoosePixelFormat(Native Method)     at org.lwjgl.opengl.WindowsPeerInfo.choosePixelFormat(WindowsPeerInfo.java:52)     at org.lwjgl.opengl.WindowsDisplay.createWindow(WindowsDisplay.java:247)     at org.lwjgl.opengl.Display.createWindow(Display.java:306)     at org.lwjgl.opengl.Display.create(Display.java:848)     at org.lwjgl.opengl.Display.create(Display.java:757)     at org.lwjgl.opengl.Display.create(Display.java:739)     at bcc.ap(SourceFile:594)     at bcc.an(SourceFile:430)    -- Initialization -- Details: Stacktrace:     at bcc.a(SourceFile:377)     at net.minecraft.client.main.Main.main(SourceFile:124)    -- System Details -- Details:     Minecraft Version: 1.9.2     Operating System: Windows 7 (x86) version 6.1     Java Version: 1.8.0_45, Oracle Corporation     Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation     Memory: 82295608 bytes (78 MB) / 148910080 bytes (142 MB) up to 523501568 bytes (499 MB)     JVM Flags: 6 total;   -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode   -XX:-UseAdaptiveSizePolicy -Xmn128M     IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0     Launched Version: 1.9.2     LWJGL: 2.9.4     OpenGL: ~~ERROR~~ RuntimeException: No OpenGL context found in the current thread.     GL Caps:     Using VBOs: No     Is Modded: Probably not. Jar signature remains and client brand is untouched.     Type: Client (map_client.txt)     Resource Packs:     Current Language: ~~ERROR~~ NullPointerException: null     Profiler Position: N/A (disabled)     CPU:

Similar to  on the bugs in Minecraft, I would like a complete list of what error codes exist in Minecraft and how they occur, as well as how they can be resolved.


There is currently  causing vote buttons to move as you scroll up or down.   I have also noticed, () that the voting buttons won't work if the post is your own, or if the post is locked. However, on these posts, the feature causing vote buttons to move isn't enabled.   I understand that I can't vote on those kind of posts, but:   The buttons are there to have a consistent look and feel, so the buttons should also be moved to have a consistent behavior. Even one can't vote,  could want to see vote counts in the middle of the post, with the benefit of the new feature. I guess that probably it will be easier to maintain the code, since there wouldn't be any logic to apply or not the new feature.   Is there a clear reason to disable that feature that I'm missing here? Otherwise, why does the new feature of moving voting buttons not work for our own or locked posts?

The  doesn't seem to be enabled for my own questions and answers.  While this makes sense given the motivation of the feature being to encourage voting and the fact that I can't vote for my own posts, I find the inconsistency a bit disconcerting when scrolling through a page that happens to contain one of my answers, especially when I'm not specifically looking for/expecting one of my answers.  Personally, I would rather accidentally try to vote for a post that I forgot was my own, every once in a while, than have the voting buttons behave in a way that's logically consistent but visually inconsistent.  At least if I try to vote for my own post, there's immediate feedback that explains why my expectation (that I'll be able to vote) is wrong. (I'll wager One (1) Good Beer that the lack of similar feedback regarding the expectation that "vote buttons scroll" explains ).


This is a simple question concerning undefined articles usage. I have a doubt if the an should be used when the next word to it starts with vowel, or it is related to the noun.  I though it was related the the following word, if I used an adjective as the sentence:   undefined article old man   would be:   an old man  not:  a old man  But I saw in this  that the author writes: An RE (which means Regular Expression) what made question it.  How the an and a usage works?

I was reading a comic book and I noticed that the author used "an A" and "an N" in a particular phrase (screenshot below). While I understand the usage of "An A" here (A being a vowel and what not) and "N" having a pronunciation which has a sound similar to "A".  Since most of English alphabets have pronunciations which start with a syllable similar to one of the vowels or semi-vowels; is it OK to prefix the letters using "An"?  For eg. An X, or An Y.        Zenescope's Grimm Fairy Tales - Werewolves: The Hunger, page #8 (Click to enlarge)


I have a dual boot system with ubuntu 13.10 and windows 8.1. At times i can access windows file from ubuntu but not ubuntu files from windows. is there an option to create a shared folder so that i can put the common files in it and access from both ubuntu and windows when necessary

I have a new laptop which I am setting up as dual boot Windows/Linux.    I would like to access files from both Ubuntu and Windows 7.  Should I create a separate NTFS partition?


If possible please add target blank for each link references in question. It's will be nice if we click it, we didn't leave stackoverflow website.

Most of the time when I follow a user's link, I just want to see their site, look it over, then return to answer their question (not leave SO completely and not come back). Could we make the links users post open in a new window please?  EDIT: I originally wanted this implemented because it's what some other sites did, but I now definitely prefer SO's way. If I want to open a new tab, I middle-click/control-click (or whatever); if not, I just click. I'm in control of what happens. Would never want to go back now.


I want something like this foreach (TextBox tb in mainGrid.Children)             {                 tb.Text = "";             }  But this gives me all Elements. Thanks for help

I need to search a WPF control hierarchy for controls that match a given name or type. How can I do this?


I have been using non-www redirect in .htaccess for a couple of years now for my Wordpress site. I want to switch to redirecting to www because, among other reasons, a naked URL does not work with Cloudflare CDN. Will it hurt my SEO score?

After having read various articles on this site about WWW or Non-WWW website setup, ,  and , and after having setup a correct redirection rule in .Htaccess to at least eliminate duplicate contents (currently the non-www solution (e.g. http://example.com) I have a feeling that my site rank less since I changed this.   My confusion was strengthened by these two opponents:     &     Could the change of www.example.com >> http://example.com have a factual impact on ranking?  say either is better or worse. Are they holding information back?  I am confused fellow folks...  As much as I would like to separate facts from fiction, I am aware that not all the good valid information is written. Not on google webmaster site and perhaps not elsewhere. If so it seems out of date!  Does or does not a WWW domain impact SEO/rank better than its NON-WWW version? (Given that you have setup a proper redirect to avoid duplicates and go with one)


"I don't talk about me like a TV show character would to his shrink"  I've heard this alternate usage very rarely, so I couldn't understand what the person means when he/she says it.  I guess this is not the literal meaning of the word 'shrink', which is to reduce in size?  I also read about another usage, where 'shrink' means your psychiatrist or doctor, but the above sentence definitely means something in a different context, not as a doctor but a different meaning. Can someone explain this please?

James Paterson in his novel writes, “she was shrink by trade, a forensic profiler, and Jack Morgan’s number two at Private “.   What does whole sentence mean?


I usually find, after blowing up my pic on the computer, that at one point (where I wished to focus) the image is very sharp, then as I inspect the picture I see that some more parts of the image, either horizontally or vertically, are in focus.  My confusion is that when we lock the focus at a certain point, is it that entire plane (both in the x and y directions) that is in focus? because I see most of the time (in Macro), that focusing is either horizontal or vertical or am I mistaken, because of minute differences in distance? E.g.,                          (In focus)                                |                             |    (Not in focus )  ________|__________ (Not in focus or I have mistaken)                             |                             |                             |                          (In focus)   I understand the general statement that a higher F-number means a greater area of focus.

The title says it pretty much all. I'm asking this because I find myself always using the focus point in the center, and after I focused, I rotate my camera to make the framing right. However, if lenses do create a plane in which everything is sharp, then the focus will be slightly off after rotating the body.  Doing some maths: if I focus at distance x meters, and rotate my camera for alpha radians, then the focus plane would be off for:  ∆f = x*tan(alpha/2)*tan(alpha)   So, let's plug in: x = 2 meters, alpha = 20 degrees = 0.349 radians, we get: ∆f = 0.128 meters. So this means, my optimal focus point is now almost 13 centimeters away from the original focus point.  If they are not spherical, I will experience my focus being off. So is it safe to use other focus points except for the one at the center and immediately put my framing right? This will slow down the process of taking pictures?


I want to download a file in Python shell like files get downloaded into browser. Yes, I know there are multiple ways like curl, wget, url retrieve etc. but here in all the cases, file name is not the same as original file.  Like if I want to download file from this url:    I want to download the file from this url as it get downloaded in browser, with the same name as original.

I have a small utility that I use to download an MP3 file from a website on a schedule and then builds/updates a podcast XML file which I've added to iTunes.  The text processing that creates/updates the XML file is written in Python. However, I use wget inside a Windows .bat file to download the actual MP3 file. I would prefer to have the entire utility written in Python.  I struggled to find a way to actually download the file in Python, thus why I resorted to using wget.  So, how do I download the file using Python?


I tried searching for the answer here but nothing worked. When I run my website, I press the start button and the question appears with multiple choice answers, when I try to click them I get Uncaught ReferenceError: checkAnswer is not defined even though i defined the function in my javascript file. I put an onclick sentence which is supposed to run the function and check if what the user clicks is the right answer this is my html for the quiz

 Start The Quiz!

       and this is my javascript function  function checkAnswer(answer) {   if (answer == questions[runningQuestion].correct) {     // answer is correct     quizScore++;     // change progress color to green     answerIsCorrect();   } else {     // answer is wrong     // change progress color to red     answerIsWrong();   }    if (runningQuestion < lastQuestion) {     runningQuestion++;     renderQuestion();   } else {     // end the quiz and show the score      scoreRender();     } }  note the onclick="checkAnswer('A') this seems to be the problem but i don't know how else to run my function from a user click to check the Answer. any help would be appreciated, i use node js, npm, and parcel 2 to run my website

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


I'm running zulip on a virtual private server, and have created a script backup-zulip on my laptop (with ubuntu 20.04) to back up zulip via ssh. I want to run this script daily, so I put the line @daily  10      backup-zulip    sudo -u username /home/username/bin/backup-zulip  into /etc/anacrontab/. However, now the backup seems to run hourly whenever the laptop is turned on, filling up my drive far too fast. What's going on? I wondered whether the script gets rerun each hour by anacron since it exits on error, but running it by hand returns 0. Is there a log file that I can look into? Searching for cron in /var/log/ gives nothing. My complete /etc/anacrontab looks as follows: # /etc/anacrontab: configuration file for anacron  # See anacron(8) and anacrontab(5) for details.  SHELL=/bin/sh PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin HOME=/root LOGNAME=root  # These replace cron's entries 1       5       cron.daily      run-parts --report /etc/cron.daily 7       10      cron.weekly     run-parts --report /etc/cron.weekly @monthly        15      cron.monthly    run-parts --report /etc/cron.monthly  @daily  10      backup-zulip    sudo -u username /home/username/bin/backup-zulip  (If this is not the correct stack exchange for this question, where should I post it to?)

I have Anacron set up to run a backup daily, weekly and monthly. The monthly seems okay, but the daily and the weekly are running roughly every half hour every day! Here is my /etc/anacrontab # /etc/anacrontab: configuration file for anacron                                                                                # See anacron(8) and anacrontab(5) for details.                                                                                SHELL=/bin/sh                                                                                PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin                                              HOME=/root                                                                                LOGNAME=root                                                                                # These replace cron's entries                                                                                1       5       cron.daily      run-parts --report /etc/cron.daily                                             7       10      cron.weekly     run-parts --report /etc/cron.weekly                                            @monthly        15      cron.monthly    run-parts --report /etc/cron.monthly                                                                                # PERIOD        DELAY   IDENTIFIER      COMMAND                                                                @daily  3       Rsnapshot_daily /root/scripts/rsnapshot_launcher.sh daily                                      @weekly 15      Rsnapshot_weekly        /root/scripts/rsnapshot_launcher.sh weekly                             @monthly        30      Rsnapshot_monthly       /root/scripts/rsnapshot_launcher.sh monthly  I've checked /var/spool/anacron/Rsnapshot_daily and it has todays date in it and was last updated less than 30 minutes ago. It's now 6pm and the daily Rsnapshot task has been run 11 times today and the weekly 10 times so far. What could be going on here? Thanks. (this is on Kubuntu 20.04 LTS)


We know that the $\phi(n)$ function denotes the total numbers which are co-prime to n , but like most of the mathematical concepts , can it be geometrically interpreted  ? Like in terms of graph?  If  yes , would it be like a normal graph of a function? Could we use more geometrical tools like finding it's slope , maximum and minimum etc. ??  Edit : This question doesn't merely imply the possibility of the graph of the function , but to relate to the geometric interpretation and if possible , to use geometric means to find some characteristic properties of the function.

If you look the at  there is a graph of the Euler phi function up to 1000:   Out of the plot you can see various trend lines that appear to be linear.  Q1) Are these lines actually lines? (ie do all the points that appear to be on one line actually all solutions to some linear eqn?)  Q2) Given that they're lines and not just something that looks a bit like lines can they be described? and what points are on them?   Q3) Are the points that don't appear to be on lines actually just the first points on lines that would only be 'visible' if we zoomed out and evaluated the Euler phi up to (say) 10000 or whatever number is large enough.


, I asked if $\mathbb{Q}_p$ is the completion of $\mathbb{Q}$ over some valuation of an prime ideal (and it seems to be true, according to an answer). Now I am asking if this can be generalized for finite extensions of $\mathbb{Q}_p$. To put it in other words: Let $K$ be a finite extension of $\mathbb{Q}_p$. Question: Is there a valuation $v$ of some prime ideal in $\mathcal{O}_k$ on a global field $k$ (i.e. a finite extension of $\mathbb{Q}$) such that the completion $k_v$ of $k$ over $v$ is equal to $K$?

I've been wondering about this for a while, is it the case that if $K$ is a finite Galois extension of $\mathbb{Q}_p$, then there exists some field $L$ with $$\mathbb{Q} \subset L \subset K,$$ such that $[L:\mathbb{Q}]<\infty$ and $L\cdot \mathbb{Q}_p = K$. I can see that this is true for $K$ unramified, because we can just attach the appropriate roots of unity to $\mathbb{Q}$ so it remains the case where $K$ totally ramifies. I guess it would be enough to show that there exists some $\alpha \in K$ which is algebraic over $\mathbb{Q}$ but not an element of $\mathbb{Q}$. I have tried to use Hensel's lemma but that fails spectacularly because the uniformizer is the root of some Eisenstein polynomial which reduces to be $x^n$.


I get these text bubbles on all sites that are in the way. See below:   How can I disable them? (And why do I get them now?) I am on  14.1.1. I have very few plugins that I would think could interfere -  for Safari,  and .

As per the image, Safari has been showing the roll-over popups all the time on all Stack Exchange sites. I've tried disabling all ad blockers but to no avail. I'm on MacOS 11.2.3, using Safari 14.0.3. Edit: A stopgap solution was to add .s-popover.s-popover__tooltip to the CSS Hide Elements list in 1Blocker. The downside is that this completely removes the tooltips so that they can't be seen even when hovering over the buttons.


I have an SQL Job which processes minimum amount of rows at a given time. Currently its running every 10 seconds which is the minimum available in Job Scheduler. But because of that the table used processed by the Job gets filled with many records. So I need to run the job every 1 second. How can achieve this? please advice.

I want to run a job every 3 seconds, however in SQL Server 2008 we cannot define an interval of less than 10 seconds.  The job is used to insert/update visitor information, and segmentation information into a database which is tracked by google search.   There are up to about 100 rows inserted in a 2 or 3 seconds. That job inserts and update the table in a database. Is there any way to schedule it using sp job scheduling configuration?


We have 4 PCs connected to each other. We all download our apps through Internet which uses our Internet bandwidth. Is there a way to share downloaded softwares through network to prevent others from downloading the same thing through Internet.

I have setup one computer on our network as the file server. Because Internet here in Tanzania is both slow and expensive I would like that one system to download all the updates and then the other 10 computers on the network to get those update files from the server. I'm a bit of a noobie to Ubuntu, but really want to learn how to get this working smoothly so as to help other NGOs and schools here in Tanzania. Brendon


This image is from scanner. I am using C# WPF to show image.But my problem is that image showing is not unclear. Below is my code( .xaml and .cs) .I found 2 ways to tranfer the file into image source. But both not work well. If you use any image view sofeware to open image, the image is very clear.  .xaml  <Window x:Class="WpfApplication2.MainWindow"     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"     Title="MainWindow" Height="350" Width="525"     Loaded="WindowLoaded">     <Grid>         <Image Name="image"></Image>     </Grid> </Window>   .cs(just part of code)      private void WindowLoaded(object sender, RoutedEventArgs e)     {            string StrImage = @"ImageFilePath";         this.image.Source = FileToImageSource(StrImage);         //this.image.Source = FileToImageSource_2(StrImage);     }     //blurry     public static BitmapImage FileToImageSource(string strFileName)     {         byte[] bytes = File.ReadAllBytes(strFileName);         BitmapImage bitmap = new BitmapImage();         bitmap.BeginInit();         bitmap.StreamSource = new MemoryStream(bytes);         bitmap.EndInit();         return bitmap;     }     //blurry too     public static BitmapImage FileToImageSource_2(string strFileName)     {         BitmapImage logo = new BitmapImage();         logo.BeginInit();         logo.UriSource = new Uri(strFileName);         logo.EndInit();         return logo;     }   Update: i have try but failed image property : RenderOptions.BitmapScalingMode="NearestNeighbor" Stretch="None"   blurry image vs clear image

I'm using some Images in my WPF applcation.  XAML:  <Image Name="ImageOrderedList"        Source="images/OrderedList.png"        ToolTip="Ordered List"        Margin="0,0,5,5"        Width="20"        Height="20"        SnapsToDevicePixels="True"        MouseUp="Image_MouseUp"        MouseEnter="Image_MouseEnter"        MouseLeave="Image_MouseLeave" />   But, they appear fuzzy.  Why doesn't that SnapsToDevicePixels="True" line prevent this problem?


I am working with a set of genes for which I have both methylation values $\beta$ (continuous on unit interval) and gene expression $E$ (non-negative continuous) that I want to test for correlation $\hat\rho(log_2E,\beta)=R$. To filter out only the significant correlations I perform a permutation test where for each site I randomly permute $E$ a large number of times and calculate $R$. This gives me a distribution under the null hypothesis $p(R|H_0)$, i.e. when there is no dependence between $\beta$ and $E$, that I can compare $R$ against.  Now to my question,  I want to test both for positive and negative correlation. Do I make two tests per gene and use double multiple testing correction, where  $p_- = \int\limits_{-\inf}^Rp(x|H_0)dx$  $p_+ = \int\limits_{R}^\inf(x|H_0)dx$  or can and should I calculate a two-tailed p-value directly based on $|R|$ or such, and use normal multiple testing correction? I can only think of the following, but it feels wrong and has lousy power.  $p_2 = \int\limits_{-\inf}^{-|R|}p(x|H_0)dx + \int\limits_{|R|}^\inf(x|H_0)dx$    Edit: Updated the figure and added the missing x-axis label. The y-axis is the same for all panels.

Suppose we have two samples and we wish to determine if they are drawn from the same distribution, the samples A,B being composed of some integers say.  If we test this using a two-sample permutation test, specifically by looking at permutations where the differences in the means of the samples are as extreme as the difference observed: is there any reason to think that we can calculate the two-tailed p-value by looking at one tail and doubling the probability?  This is what it appears to say in my lecture notes, but I don't understand why we could assume that the tails are symmetrical (or why it doesn't entail that assumption). Explanations were not forthcoming.


So our Analysis teacher has given us this homework:  Let $B=\{b_k\}_{k=1}^\infty $ be a sequence of real numbers. Prove that the following are equivalent: a) The sequence is bounded (i.e., $B\in \ell^\infty(\mathbb N))$. b) For every sequence $A =\{a_k\}_{k=1}^\infty \in \ell^1(\mathbb N)$ (i.e., $\sum_{k=1}^{\infty}|a_k|$ convergent) we have $A\cdot B=\{a_kb_k\}_{k=1}^\infty \in \ell^1(\mathbb N)$  And one can easily do the "$ a)\implies b) $" but the backwards implication is the one I'm trying to figure out. Our teacher insists on proving it by contradiction i.e.: Assuming $B\notin \ell^\infty(\mathbb N)$ ($B$ not bounded) then there exists $A \in \ell^1(\mathbb N)$ so that $A\cdot B \notin \ell^1(\mathbb N)$. I imagine such an A sequence is constructed from the B values using that it's unbounded, but no matter how many I try I can't find a general way of constructing A. In addition the second part of the exercise is proving an 'equivalent' result but for continuous functions and I have the same issue...any idea?  Let $g $ be a Lebesgue measurable function defined on $\mathbb R$. Prove that the following are equivalent: a) The function is bounded (i.e., $g\in L^\infty(\mathbb R)$. b) For every function $f \in L^1(\mathbb R)$ we have $f(x) g(x)\in L^1(\mathbb R)$  Anyways thank you very much!!

Let $(k_n)$ be a sequence of scalars. Prove that  $(a)$ if $\sum_{n\geq1} k_n x_n$ converges for every $x \in l_1$, then $\sup_{n\geq1} |k_n| < \infty$.  $(b)$ if $\sum_{n\geq1} k_n x_n$ converges for every $x \in c_0$ then $\sum_{n\geq1} |k_n| < \infty$.  For the second part I have used Uniform Boundedness Theorem. Require help in the first part.  Thank You.


Here Is the Console Log  root@raspberrypi:/home/pi# java -jar /home/pi/keypad.jar Exception in thread "main" java.lang.reflect.InvocationTargetException         at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)         at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)         at java.lang.reflect.Method.invoke(Method.java:483)         at org.eclipse.jdt.internal.jarinjarloader.JarRsrcLoader.main(JarRsrcLoader.java:58) Caused by: java.lang.NullPointerException         at me.Andrew.Keypad.GPIO.GPIOMethords.setupPins(GPIOMethords.java:33)         at me.Andrew.Keypad.Listener.ButtonInput.ButtonListener(ButtonInput.java:45)         at me.Andrew.Keypad.Listener.ButtonInput.start(ButtonInput.java:22)         at me.Andrew.Keypad.Main.main(Main.java:15)         ... 5 more root@raspberrypi:/home/pi#  unavailable)   Here is the code  GPIOMethords  public class GPIOMethords { public Main MA; public Settings settings = new Settings(); final GpioController gpio = GpioFactory.getInstance();  public HashMap<String,GpioPinDigitalInput> ColPins = new HashMap<String,GpioPinDigitalInput>(); public HashMap<String,GpioPinDigitalOutput> RowPins = new HashMap<String,GpioPinDigitalOutput>();  public void setupPins(){     if(ColPins.isEmpty()){         ColPins.put("1",gpio.provisionDigitalInputPin(settings.Col1));         ColPins.put("2",gpio.provisionDigitalInputPin(settings.Col2));         ColPins.put("3",gpio.provisionDigitalInputPin(settings.Col3));         ColPins.put("4",gpio.provisionDigitalInputPin(settings.Col4));     }     if(RowPins.isEmpty()){         RowPins.put("1",gpio.provisionDigitalOutputPin(settings.Row1));         RowPins.put("2",gpio.provisionDigitalOutputPin(settings.Row2));         RowPins.put("3",gpio.provisionDigitalOutputPin(settings.Row3));         RowPins.put("4",gpio.provisionDigitalOutputPin(settings.Row4));     }     MA.store.ColPins = ColPins; // line 33     MA.store.RowPins = RowPins; }   }   Main   public class Main {     private static Main instance = null;      public Settings set = new Settings();     public static Methords Meths = new Methords();     public GPIOMethords GPIOMeths = new GPIOMethords();     public Storage store = new Storage();      public static void main(String[] args) {             Meths.buttonIn.start();      }     public static Main getInstance() {           if(instance == null) {              instance = new Main();           }           return instance;        }  }   Settings  public class Settings { public String Code = "ABCD";  //Define Row Pins! public Pin Row1 = RaspiPin.GPIO_00; public Pin Row2 = RaspiPin.GPIO_01; public Pin Row3 = RaspiPin.GPIO_02; public Pin Row4 = RaspiPin.GPIO_03;  //Define Col Pins! public Pin Col1 = RaspiPin.GPIO_04; public Pin Col2 = RaspiPin.GPIO_05; public Pin Col3 = RaspiPin.GPIO_06; public Pin Col4 = RaspiPin.GPIO_07;  }

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


Test the convergence of the series   $\frac{1}{3}+\left(\frac{1}{3}\right)^{1+\frac{1}{2}}+\left(\frac{1}{3}\right)^{1+\frac{1}{2}+\frac{1}{3}}+\cdots$   The $n$-th term of the series is $t_n=\left( \dfrac{1}{3}\right)^{1+\frac{1}{2}+\frac{1}{3}+\cdots+\frac{1}{n}}$.    Now, $\dfrac{t_{n+1}}{t_n}\to1$ as $n\to \infty$. Thus D'alembert ratio test fails. How can I check convergency?  Added: The given solution is quite complicated. I am looking for a simpler one.

$$x + x^{1+\frac{1}{2}}+x^{1+\frac{1}{2}+ \frac{1}{3}}+\cdots$$  I know that $u_n = \lim_{n \to \infty}   x^{1/n}$   I used root test and ratio test but it isn't working.


Below is my code, goal is to read instructions from a txt file to make java robot preform them. When changing any part of the if statement to != the robot portion works, therefore I have to think that the strings are in some way not equal.  public void interpretGoo() throws AWTException, FileNotFoundException,  InterruptedException{     Scanner scanner = new Scanner( new File("instruct.txt") );     String in;     String instruct = "";     while(scanner.hasNextLine()== true){         in = scanner.nextLine();         instruct+= in;     }     scanner.close();      String[] instructSet= instruct.split("-");     System.out.println("String: " + instruct);      String[] command= new String[10];     for(int i= 0; i< instructSet.length;i++){         command= instructSet[i].split(" ");         System.out.println("Set: " + instructSet[i]);         System.out.println("Word: " + command[0]);         if(command[0].trim()== "key"){             keyboardHandler(command[1].charAt(1));             Thread.sleep(150);         }else if(command[0].trim()== "clickL"){             accuMouse(Integer.parseInt(command[1]),Integer.parseInt(command[2]), 1, false);         }else if(command[0].trim()== "clickR"){             accuMouse(Integer.parseInt(command[1]),Integer.parseInt(command[2]), 0, true);         }else{             System.out.println("FAIL");             continue;         }     } }   OUTPUT:  String: clickL 728 1062-clickL 540 382-key h-key e-key l-key l-key o- Set: clickL 728 1062 Word: clickL FAIL Set: clickL 540 382 Word: clickL FAIL Set: key h Word: key FAIL Set: key e Word: key FAIL Set: key l Word: key FAIL Set: key l Word: key FAIL Set: key o Word: key FAIL   According to the output the strings are identical but fail the checks, any help would be appreciated!

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?


I have 2 tables Transporter and Cars ,    I want to display all cars for a single Transporters in a single row   using joins I am getting cars all but in different row    I tried Group by clause but it is not working    What modifications Can i do in a query ?

Using MySQL, I can do something like:  SELECT hobbies FROM peoples_hobbies WHERE person_id = 5;   My Output:  shopping fishing coding   but instead I just want 1 row, 1 col:  Expected Output:  shopping, fishing, coding   The reason is that I'm selecting multiple values from multiple tables, and after all the joins I've got a lot more rows than I'd like.  I've looked for a function on  and it doesn't look like the CONCAT or CONCAT_WS functions accept result sets.  So does anyone here know how to do this?


I am currently trying to write a regex code for the following rules in my javascript.   E-mail address must be a valid address ( X @ Y . Z ) Allowed characters for the name part is uppercase and lowercase a-z, digits, dash and dot characters Allowed characters for the domain part is only letters and dot (.).   How could I write whole cases in one regular expression?  What I did so far is /^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/  Thanks in advance.

Is there a regular expression to validate an email address in JavaScript?


I am looking at the "Frequently Asked" sidebar mentioned :  I noticed that there is a question there that seems very very localized (and probably not FAQ):    So I click on it to check:    Nope... it is still not FAQ.   So what is it doing in the sidebar?

Ding!  Hello, new feature!  I just noticed a new "Frequently Asked" section on the main page.  I'm guessing it's a test of a new feature, like the recent .  Seems cool so far.  But what is it populated with?  Common dupes?  Topics the viewing user asks about a lot?  Topics the viewing user searches for a lot?  For what it's worth, I'm getting a link to the  tag underneath it.


I have been using blender for about two years. And i am still lagging in molding, sculpting and shading knowledge would any one have some good wholesome and helpful tutorials?

Since asking for tutorials, videos, resources, links to other content or downloads is considered off topic here, this is a specifically created Community Wiki which gathers resources for Blender and it has been approved by the .  Just write in the appropriate answer/section. If you have concerns, questions, post a  question, so we don't clutter the comments, but you can link your meta question from the comments.  Questions regarding such resources are not allowed anymore, except for very specific and on topic requests (ask on  if you're unsure about your question). Follow the instructions made in the question about how to post, what can be posted, etc.  Learning             Assets    (also see: )   Reference Images/Blueprints (also see: )    Tools    (also see: )      Other   Special Interest ()     Also see the .


This question is from a practice workbook for a college entrance exam. Let each corner of a cube is represented by +1 or -1 arbitrarily and on each of the six faces of the cube we write the product of numbers written at four corners of that face. Let $s_1, s_2, s_3,...,s_8$ be the numbers written on the corners and $p_1,p_2,...,p_6$ be the product of numbers written on the faces. Then the total number of ways to make the solution of the equation- $$\Sigma_{i=1}^8s_i + \Sigma_{i=1}^6p_i = 0 $$ So my first thought was to work case by case. $\Sigma_{i=1}^8s_i$ can take values of {-8,-6,-4,-2,0,2,4,6,8} and $\Sigma_{i=1}^6p_i$ can take values {-6,-4,-2,0,2,4,6} even if we ignore possible configurations and just give each $p_i$ a value equal to -1 or 1. Now clearly $\Sigma_{i=1}^8s_i = -8,8$ will not give any solutions to the equation. For the case where $\Sigma_{i=1}^8s_i = 6$. There are 7, +1 vertices and 1, -1 vertex. This will hence give $\Sigma_{i=1}^6p_i = 0$ Because that single (-1) vertex will make three products -1. For the case where $\Sigma_{i=1}^8s_i = 4$. There are 2, (-1)vertices and three ways to place them. If you take body diagonals, the product will be -6, if you take face diagonals, the sum of products will be -2 and for adjacent vertices the sum of products will be +2. Now while this approach of taking cases does work and will get the answer, it is rather long(the $\Sigma_{i=1}^8s_i = 2$ case will have way more possibilities) and also leaves plenty of scope to go wrong or miscount. So I was looking for maybe an organized way to check these cases or an alternate method entirely which utilizes maybe some different intuition. Also I'm unsure what to tag this question under, so if someone would comment some tags or edit this post to include useful tags, I'd appreciate it.

A cube has numbers ±1 placed at each vertex and each center of cube’s six faces (so 14 numbers altogether). Moreover, it is known that each number in the center of a square face equals to the product of the 4 numbers at the vertices of this face. Can the sum of all 14 numbers be equal to zero? My first thoughts were test out some combinations and look for a pattern, but I was not able to notice anything major about it. So, the only progress I was able to really make was breaking it down into $V_1*V_2*V_3*V_4$, and so on for each face. Any help is greatly appreciated.


I try an Edge loop select in the following object. But Blender 2.79 does not select anything, are there any hidden parameters which can influence edge loop select?   (I try this from the Select menu in Edit mode)

Alright so I've seen some postings about loop cuts and done some research. I am very new to blender and modeling overall. I am trying to loop cut this concrete barrier. Now I'm following a tutorial and kind of did my own thing in some areas. I cleaned it up following some instructions in another answer here on stack exchange.  I can't for the life of me figure out why I can loop cut around the whole bottom:   ...but not the whole middle:   I see this marked as answered by another question. That question refers to ngons and inside faces. Now once again I'm totally new to this. I looked on the inside. I don't believe I have inside faces or any ngons by the terms I've read online in my research.  Here is a wireframe picture and the inside view:     Maybe I'm missing something the answers on other posts are saying. If so and you know what it is I'd be very appreciative of what it is.


The company ofutable (pronounced UFO-table) likes to start their movies with a black background, and     An ufotable Production   emblazoned in the middle of the screen.  As a native english speaker, I find this phrase rather jarring.  It seems grammatically incorrect.  I'm confident it should be:      A ufotable Production   Why?

On a Physics specification, it says:     6.7 Know how to use two permanent magnets to produce a uniform magnetic field pattern.   Isn't it "produce an uniform magnetic field", or is the existing "produce a uniform magnetic field pattern" correct?


hello I am working on this dragon and I used a plug-in for blender..well using this set of bones does work but it pulls in places that it shouldn't even after weight painting I was directed here even though the group I asked the same question in.. some how could not help me..here is a snapshot of it..i don't think it should pull in those places when I move that leg  I have learned some of blender on my own the past two years so I really have had no help except watching video's on youtube so if you guys have any idea's id appreciate it

I follow this  which uses rigify and I have run into some issues.    Not every vertex moves along the rig. Any idea what could cause this? I applied the location and rotation for every object.  The entire head is weight painted with blue.


I wanted to use while loop to keep executing my script over and over but there is a problem as my code calls an API that doesn't allow so many calls in small time so I wanted to make the while loop be executed at time interval so I tried this code  from threading import Timer def myfunc():    some code while True:    t = Timer(1.0, myfunc)    t.start()   but it doesn't work, so is there any other way to do it correctly?

I would like to know how to put a time delay in a Python script.


I am trying to install electrum on my Ubuntu live USB. Please forgive me because I am very new to this OS. I have also made a persistence 4GB space for installing software.     How can I get past this error? I tried using   sudo apt-get update   first, but I still get   E: Unable to locate package python-pip   when I try to install.

How do I get to the Universe Repository in supported versions of Ubuntu?


I am an Indian citizen applying for a visitor visa to UK for tourist purpose. I'll be accompanying my husband who will be visiting UK for business work for 1 week and he'll be sponsoring my trip (his trip is sponsored by the company). Do I need to get a letter from my husband stating that he'll be sponsoring my trip or just mentioning this in the Visa application would suffice? Are there any other documents required to support the application? Do I need to attach my bank statements as well?

There seems to be a consistent pattern on TSE, with scores of questions about what documentation best accompanies a visa application, posed not just by those reapplying after a refusal, but by first-time applicants prior to submission (and a few with post-submission anxiety).  What is being overlooked, lost in translation, missed? Why is this question even being asked here, when the UK government publishes its own straightforward information?


I am currently running Ubuntu 12.04 and would like to upgrade/update it to 13.10 without losing my files. I have the Ubuntu One cloud but I have limited space. Is there any way to get a different version of Ubuntu without having to lose my files or upload them to a cloud?

I am currently using Ubuntu 10.04. I know there is a 10.10 release, but can I upgrade directly to 11.04? Could you walk me through the steps please?


I'm trying to create hive table with multi-delimiter (I can't use multi delimiter serde in hive as we need to update the jar file),for example I want to split the following string with a two-character delimiter #$: 1234#$CSI#$MAN # NO#$MANN#$1212#$N  The desired result is: 1234 | CSI | MAN # NO | MANN |1212 | N  When I have tried #$ the result is 1234 | CSI | MAN | NO | MANN |1212 | N  How could I split the string with a two-character delimiter #$?

I am tired of always trying to guess, if I should escape special characters like '()[]{}|' etc. when using many implementations of regexps.  It is different with, for example, Python, sed, grep, awk, Perl, rename, Apache, find and so on. Is there any rule set which tells when I should, and when I should not, escape special characters? Does it depend on the regexp type, like PCRE, POSIX or extended regexps?


When it says Documents received in Our office by July 27, 2020, will be processed by August 7, 2020. Does this include date 27 july. Can we say that documents received on 27 july also processed. Or we have to use “till” 27 july.

I have read the Rules of a competition. The text of the Rules include a sentence as follows:     As per stated in the Rules the entrants will be notified by May 30th 2010.   Does the sentence above mean that May 30th is included in the term of notification or not?


There are a lot of web-sites that use this feature. It is quite a common thing for "long" sites. I see the following scenario for SO:   You open the question and quickly read it You scroll down to look through the all answers to make sure nobody has proposed your answer/solution You scroll up to read the question more detailed for giving a best answer    Thus, at the 3rd phase this button might be extremally usefull.

Can we get Back to Top Button on  and ?   The reason behind this request is sometimes I scroll down the questions to see the available questions that I can answer, when the scroll bar already on the bottom page I want to refresh the page to find the newest questions. When the whole page already load, the page will display on the latest state (in this case my scroll bar on the bottom page). So when I want to go to top page I must scroll back to the top, maybe if this possible added some button in the right corner like in .


The links to Stack Overflow's 'Twitter' and 'Blog' accounts are missing under the Stack Exchange '' listing. If you look at the 'Super User' or 'Server Fault' (and few others), they do link to 'Twitter' and/or 'Blog', if available. For example:    I am aware of the fact that Stack Overflow blog i.e.  is the same as (or combined with the SE blog)  but not sure if that's the reason for not displaying the SO 'Blog' link. Also, Stack Overflow does have it's own dedicated Twitter a/c: . I am curious to know why SO's 'Twitter' link is not displayed as well. As per the Normal Human's comment:  Stack Overflow does have a Twitter account now, so the question of why it isn't linked makes perfect sense. The list does not say that the account has to be a bot...  Can anyone please explain or point me to any documented evidence on the same.

Most (all?) of the Stack Exchange sites have dedicated Twitter accounts that tweet questions, pleas for answers, upcoming events, and so forth (e.g. @stackscifi, @stackcooking, @stackparenting, @stacksuper_user, @serverfault).  Does one of these exist for Stack Overflow? @stackoverflow is someone else, and @stackstackoverflow and @stack_stackoverflow don't exist.  @stackexchange follows all (?) of the individual accounts, and doesn't appear to follow one for Stack Overflow. I've tried searching Twitter, but there's so much Stack Exchange content on Twitter that even if the account did exist, I'm not sure it would be visible in the noise.


The eldritch invocation Shroud of Shadow from the  reads as follows:      You can cast invisibility at will, without expending a spell slot.   Similar abilities such as a wizard's spell mastery specify that the caster can only cast the at-will spells at their lowest spell level:      You can cast those [at will] spells at their lowest level without expending a spell slot when you have them prepared.   Shroud of Shadow has no such clause. So can this invisibility spell be cast at a higher level?

There are ways to cast spells without expending a spell slot such as:  Master Transmuter (PHB 119):     Restore Life. You cast the raise dead spell on a creature you touch   with the transmuter’s stone, without expending a spell slot or needing   to have the spell in your spellbook.   Armor of Shadows (PHB 110):     You can cast mage armor on yourself at will, without expending a spell slot or material components.   Whispers of the Grave (PHB 111):     You can cast speak with dead at will, without expending a spell   slot.   See also: Channel Divinity: Read Thoughts (PHB 59-60), Mystic Arcanum (PHB 108), Beast Speech (PHB 110), Chains of Carceri (PHB 110), Eldritch Sight (PHB 110), Fiendish Vigor (PHB 111), Mask of Many Faces (PHB 111), Master of Myriad Forms (PHB 111), Misty Visions (PHB 111), Otherwordly Leap (PHB 111), Signature Spells (PHB 115), Spell Mastery (PHB 115), Shapechanger (PHB 119), Boon of Spell Mastery (DMG 232) and Boon of Spell Recall (DMG 232).  What level are these spells if you cast them without expending a spell slot?


Sum the series to infinite terms: $$1+\frac14+\frac{1\cdot3}{4\cdot8}+\frac{1\cdot3\cdot5}{4\cdot8\cdot12}+...$$   I couldn't get any clue on how to solve this summation. I tried to solve without any help  and the things I got confused with : [...]  Is how to, do summation on the general term, that's:  $$m=\sum_{n=0}^\infty\frac{(2n+1)!}{2^n\cdot n!\cdot 4\cdot n!}$$

How to find infinite sum How to find infinite sum $$1+\dfrac13+\dfrac{1\cdot3}{3\cdot6}+\dfrac{1\cdot3\cdot5}{3\cdot6\cdot9}+\dfrac{1\cdot3\cdot5\cdot7}{3\cdot6\cdot9\cdot12}+\dots? $$   I can see that 3 cancels out after 1/3, but what next? I can't go further.


I am using the system curl as I cannot get the ruby curl to work. How do I get the output of the curl into my ruby variable? the example below shows that the variable did not get the output of the curl url1="\"https://ca.yahoo.com/\"" a=Kernel.system "curl #{url1}" irb(main):026:0> a => true

If I call a command using  in Ruby, how do I get its output?  system("ls")


I've just answered a question in SO where I had to post four snippets of XML (yes, it was a JavaEE question, how did you guess?)  I made an effort to keep the snippets short and meaningful, but all this code can clutter the visuals of the page, and moves attention away from the rest of the answer.  The site can already detect which parts of the question or answer are code, and paints them in a different font and background. What if it could also add a small toggle button that hides/display each snippet of code?  An example. Displayed:   Hidden:   Please acknowledge my superior Photoshop skillzs.

It would be great to have the option to fold code snippets, entire questions and answer posts on a user basis and allow defining some generic foldable regions within the question/answer editor.  Non generic folding info could be stored in cookies perhaps to move the storage/processing requirement to the client side.  Definable folding can take any free and safe HTML tag or other multi character trick (<>Fold this<>)


What does the "link" () mean in the Wi-Fi network list on iOS?  Example (see red rectangle):

When there is a Personal Hotspot network available, it displays a chain link icon instead of the usual lock icon in the list of available networks on iOS and OS X.    My question is, how does OS X distinguish these networks? Is it specified in 802.11 how hotspots broadcast their SSID's differently?


As a part of one computer algorithm, I want to find sum for $$n+ \frac{n(n+1)}{2!} + \frac{n(n+1)(n+2)}{3!}+....+ \frac{n(n+1)(n+2)...(n+r-1)}{r!} $$. I looked at $$\frac1{(1-x)^n}$$. But it is infinite series. Is there some formula? Please help.

Is there a closed formula for:  $\sum_{i=1}^{N}{\binom{i+k}{i}}$   ( k is a constant whole number )


This is the Theorema Egregium of Gauss.  Gaussian curvature (something defined from derivative of the normal unit vector) depends only from coefficients of the first fundamental form, so it is intrinsic. My question is "Why"?   The first fundamental form is given by these three coefficients $E=(\partial_1,\partial_1), F,G$ defined similarly.   Now, we have that $I(v_1\partial_1+v_2\partial_2)=Ev_1^2+2Fv_1v_2 + Gv_2^2$ is independent from the local chart, but its coefficients change. So, ok that $I$ is intrinsic, but why we call also its coefficients intrinsic if they are actually defined from a local chart and depend from the local chart? Why can I call everything which uses only $E,F,G$ to be intrinsic? Why is $E,F,G$ themselves intrinsic?

I am reading Kuhnel's differential geometry book, and in chapter 4, it says that "intrinsic geometry of a surface" can be considered to be things that can be determined solely from the first fundamental form. But I am unsure on why the first fundamental form itself can be considered to be something intrinsic to the surface. Kuhnel defines the first fundamental form to be the inner product induced from that of $\mathbb{R}^3$ restricted to $T_pM$. So isn't the larger $\mathbb{R}^3$ used?  So my question is: Supposed I have a smooth 2-dimensional manifold (e.g. in the sense defined by Lee's Introduction to Smooth Manifolds), but I didn't put it in any ambient space. Is there a way for me to define the first fundamental form? $T_pM$ is intrinsically defined (as the space of derivations in Lee's book), and so what is the inner product that I should put on $T_pM$?


I recently did a ZAP report on my project, and there was a high alert saying SQL Injection may be possible through Foldable' AND '1'='1' attack on this particular drop-down menu 'bsearch'. I would like to know if it is possible to solve this issue through Prepared Statement and how do I do it? Thank you.  This is my SQL (PHP)          $filter = "";         if(isset($_POST['bsearch']))         {             $mod_selected = $_POST['bsearch'];             $filter = " WHERE catename ='$mod_selected'";         }              $conn = mysqli_connect('localhost','root','','my_db');              $productsql = "SELECT DISTINCT catename FROM catetable";         $model_list = mysqli_query($conn,$productsql);                  mysqli_close($conn);        And this the drop-down menu form.

                     Category
                 <form name = "bikeoption" id = "bikeoption" method = "post">
                         Select Bike Category: &nbsp;
                     <select name="bsearch" id="bsearch">                         <?php while ($one_model= mysqli_fetch_assoc($model_list)  ) { ?>                                                   <option value="<?php echo $one_model['catename']; ?>">                             <?php echo $one_model['catename']; ?>                                                      </option>                     <?php } ?>                     </select>                       &nbsp;&nbsp;&nbsp;                        <input type="submit" value = "Search" id = "bsearchBtn" class = "button">                 </form>

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


Isommorphism that maps identity elements of each group. But how to find the number of such isomorphism.

How many isomorphisms are there from $\Bbb Z_{12}$ to $\Bbb Z_{4} \oplus \Bbb Z_{3}$?  I can see that if $f$ is the isomorphism, the isomorphism is determined by the value of $f(1)$ because $f(1) = (1,1)$ and $f(k) = f(k) + f(1) = f(k) + (1,1)$.  But since $\Bbb Z_{12}$ has $4$ generators, there are $4$ different ways to set $f(1)$ equal to a generator.  Therefore there are $4$ isomorphisms.  Is this correct?


I am trying to initialize the following object:  return new ObjectNaturalPerson             {                 Initials = entity.Initials,                 FirstName = entity.FirstName,                 LastName = entity.LastName,                 Gender = GetGender(entity.Gender),                 BirthPlace = entity.Birthplace             };   So far there is no problem with the code. But focus on the line:  Gender = GetGender(entity.Gender)   What I want to achieve is that I would like to set Gender to null or GetGender(entity.Gender) depending on entity.Gender, which is a string. Moreover, Gender is a nullable property, named indeed Gender and of type Gender, which is an enum.  public Gender? Gender { get; set; }   What I don't understand is that, if during the object initalization I try to set directly Gender = null, there is no problem! Instead, if try to use the operators :? in the following way then I receive an error:  Gender = entity.Gender.IsNullOrEmpty() ? null : GetGender(entity.Gender)   The error is: type of conditional expression cannot be determined because there is no implicit conversion between Null and Gender. But again, if I set Gender directly to null then there is no problem! Thanks in advance.

EmployeeNumber = string.IsNullOrEmpty(employeeNumberTextBox.Text)     ? null     : Convert.ToInt32(employeeNumberTextBox.Text),  I often find myself wanting to do things like this (EmployeeNumber is a Nullable<int> as it's a property on a LINQ-to-SQL dbml object where the column allows NULL values).  Unfortunately, the compiler feels that  There is no implicit conversion between 'null' and 'int'  even though both types would be valid in an assignment operation to a nullable int on their own. Using the null coalescing operator is not an option as far as I can see because of the inline conversion that needs to happen on the .Text string if it's not null. As far as I know the only way to do this is to use an if statement and/or assign it in two steps.  In this particular case I find that very frustrating because I wanted to use the object initializer syntax and this assignment would be in the initialization block... Does anyone know a more elegant solution?


I'm trying to find a general formula for the series and x is a constant: $$\sum\limits_{i=1}^N  \frac{i}{(1+r)^i}$$ I have deduced the general formula for the sum. $$\frac{(1+r)^{N+1}-(1+r)-rN}{r^2(1+r)^N}$$ Will this sum converge to some value when N is very large? Could someone explain how to deal with it?

How can I evaluate $$\sum_{n=1}^\infty\frac{2n}{3^{n+1}}$$? I know the answer thanks to , but I'm more concerned with how I can derive that answer. It cites tests to prove that it is convergent, but my class has never learned these before. So I feel that there must be a simpler method.  In general, how can I evaluate $$\sum_{n=0}^\infty (n+1)x^n?$$


Where does Unity (under 16.04) keep its list of desktop files for the Launcher. Not "where are .desktop files found?" but where are just the ones that Unity has right now in my launcher. One of them is placeholder "?" for an appimage executable, and I want to tweak that entry to point to an appropriate icon. The app doesn't have an existing .desktop entry yet in /usr/share/application or my .local stash, so I want to tweak the placeholder that Unity created for it rather than hand-roll one.

can anyone tell me the name of the file which contains the default icons list for Unity launcher?  I am assuming it will be a .conf file.


I have a fews of songs in a folder which I would like to add the metadata items of artist, title, genre and album to. I would like to take the metadata info for the title and artist from the file name itself.   For Example: I have a song file named Melvv - Glide.mp3. I would like to take the name of the artist Melvv and the title of the song Glide from the file name and add it as MetaData. For the Album and Genre, I'll add this in myself.   Is there a way I can do this in the Linux environment via bash or python? Is there a way this can be done in the Windows environment?

I have a ton of MP3s, but their ID tags are not filled in.  Going in manually to populate them is simply too much work.    I was wondering if there is a way to populate them automatically.  Perhaps by feeding the MP3s to Shazam or Midori or something like.  I am not above writing some code to make it happen, if someone can suggest a way.


I cannot find myself in the Stack Overflow reputation league. I have just got my reputation above 200 on Stack Overflow.  It is written in the top user page of StackOverflow that      users with less than 200 reputation are not tracked in the leagues   So basically  When do users enter the reputation leagues once they reach 200 rep?   If it takes some time like (2-3 hours or days or weeks), then it should be mentioned on the Top user page or some other page. Sorry if it is mentioned in somewhere, but to my knowledge I couldn't find such statement.

While I was perusing  today, I noticed that it stated my all-time rep was 412 when it actually is 453 (as of now). Does this reputation take time to update itself? (I had gotten a few upvotes just before I checked). I'm just curious.


Let $ X, Y \in \mathfrak{X}(M)$ tangent vector fields, $ g,\tilde{g}$ two Riemannian metrics such that $ \tilde{g} = f^{2}g$, being $f$ a function that does not cancel, compare as Levi-Civita of $g$ and $\tilde{g} connections. I think about doing this, since the metric is a function, we have: $\nabla_{Y}gX=g \nabla_YX+Y(g)X$ and so... $\nabla_{Y}f^2gX=f^{2}g\nabla_YX+Y(f^2g)X$ Through these two equations can I conclude something? What conclusions can I draw? Can someone help me? Thank you.

I am doing this problem:  Let $g$ be a Riemannian metric on  manifold $M$ and $\tilde{g}=e^{2f}g$ another metric conformal to $g$, where $f$ is a smooth function on $M$. Give the relation between the Levi-Civita connection $\nabla$ of $g$ and the Levi-Civita connection $\tilde{\nabla}$ of $\tilde{g}$.  I am currently at this step, but don't know how to continue next:  $2\tilde{g}(\tilde{\nabla}_{X}Y,Z)-2e^{2f}g(\nabla_{X}Y,Z)=X(e^{2f}g(Y,Z))+Y(e^{2f}g(Z,X))-Z(e^{2f}g(X,Y))-e^{2f}Xg(Y,Z)-e^{2f}Yg(Z,X)+e^{2f}Zg(X,Y)$  Any help is appreciated!


Just a problem from my old lap - Dell Latitude D430 : 1.3 Ghz Core 2 Duo, 2GB Ram.   I installed Ubuntu 14.04 just last week , but it was very slow when i run any applications.   And I found that Xubuntu is much better performance than Ubuntu on old lap.  So i download Xubuntu 14.04 . will it better performance on my laptop ? or i have to download the older Xubuntu or using Lubuntu ?

For a given hardware configuration, how do I find out if Ubuntu will run on it? What considerations should I take into account when choosing an Ubuntu version and  such as:    with a lighter desktop than the usual Gnome and Unity  with the even lighter LXDE desktop   Obviously Ubuntu does not run on some processor architectures. So how do I go about choosing the right version and derivate. How can I find out the minmal system requirements?


I would like to print a backslash character:  \   But whne I try to use escape characters  print(\"\"\)   I get a syntax error. I have looked into ecape characters, however is their a specific one for backslash ()?

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


If a question asked on this forum does not get an answer because the feature requested does not exist (e.g. [1]), or it is agreed that there is a bug, ... what is the best way to report this to Apple?  This forum does I have found help in phrasing the question and problem, and if enough time has elapsed helps to reveal the limits of the understanding of a knowledgeable community on a topic. A question posed and edited here should therfore be very valuable to Apple.  So can one link to a description here and send it to Apple? And where would one send it? Or do they follow what is going on here so that there is no need to do that?  PS. I think it may be useful to have a tag for issues relating to how to submit issues to apple. Eg. bug-reports or something like that.  [1] For example:

Inspired by  I became curious about what is the current preferred mechanism for submitting bug reports and feature requests to Apple. I'm aware that they have the internal RDAR bug tracking system, and that there is an  project to crowdsource the tracking of issues, but I'm at a loss as to the preferred channel to submit something.    Is there a public-facing portal for submitting issues?


----------------EDIT-----------------------  I was grabbing the wrong value for comparison, the cdcdcdcd was coming from somewhere else.  I still have my methods throwing exceptions before they are even reached, but my problem lies elsewhere, I wish there was a way to just "unpost" my original question.  Thanks for the help.  ----------------EDIT-----------------------  I have a class (MyClass) I have inherited from some third party class (which in turn derives from direct show classes - from CBaseFilter if this matters).  I write this code:  MyClass* val = NULL; val = new MyClass(); // Create an instance of the class.   Attempting to make method calls results in a thrown exception.  With a little sleuthing I found that when I dereference val (val itself seems valid... something like 0x0777fc90), it contains 0xcdcdcdcd.  I looked around and it seems that this might indicate that the memory has been allocated on the heap, but not initialized.  What does that mean?!  How can the call to new succeed (val != NULL) and yet the memory isn't initialized enough to have a pointer to it?  Is it possible that something went wrong with some of the base class initialization?  And if so - what am I looking for?

I know that the compiler will sometimes initialize memory with certain patterns such as 0xCD and 0xDD.  What I want to know is when and why this happens.  When  Is this specific to the compiler used?  Do malloc/new and free/delete work in the same way with regard to this?  Is it platform specific?  Will it occur on other operating systems, such as Linux or VxWorks?  Why  My understanding is this only occurs in Win32 debug configuration, and it is used to detect memory overruns and to help the compiler catch exceptions.  Can you give any practical examples as to how this initialization is useful?  I remember reading something (maybe in Code Complete 2) saying that it is good to initialize memory to a known pattern when allocating it, and certain patterns will trigger interrupts in Win32 which will result in exceptions showing in the debugger.  How portable is this?


How do I typeset multiple authors with the pdfauthor option from the  package?  If I try     pdfauthor={A, B, and C}   the names in the author field (when displayed in Adobe Reader) are surrounded by ";        How do I get rit of the "s.

EDIT: As Bill B. and Caramdir point out in their comments after Bill B. produced his results posted below, more information is needed in order to make a better call. To remedy, my output was produced using MiKTeX 2.8 pdflatex with no special command line flags or switches. My pdf viewer is Adobe Acrobat Pro 9.0. The platform is Windows 7. All software including hyperref is fully up to date against the latest rev levels and patches.  As I'm guessing that this is a pretty normal setup, at least in the Windows world, I'd be very interested (and grateful) in learning whether this problem affects other people or whether it's just some kind of rather weird one-off. My gut feel after seeing Bill B's results (and also after having traversed hyperref's code) is that the culprit is Adobe Acrobat or possibly MiKTeX pdflatex.    Can anyone corroborate? I'd be very grateful to know.    Original question:  I have a problem with hyperref; it "enquotes" Author and Keywords (but not Title or Subject) metadata if the data sent to these contain a comma or semi-colon (but not, say, a full stop or a colon).    I've included some figures and code that show this below.         \documentclass{article}  \newcommand*\metadata{% % uncomment all but one line below %  a  b  c%     <-- no problem    a, b, c%     <-- problem %  a; b; c%     <-- problem %  a: b: c%     <-- no problem %  a* b* c%     <-- no problem }  \usepackage[   pdftitle={\metadata},    % never enquoted   pdfauthor={\metadata},   % enquoted if , or ; is present   pdfsubject={\metadata},  % never enquoted   pdfkeywords={\metadata}, % enquoted if , or ; is present ]{hyperref}  \begin{document}   Press ctl-d (in Acrobat Reader) to see pdf file metadata. \end{document}   Not only is this quite ugly but, more importantly, it interferes with metadata extracting programs used by certain document repositories.   I've worked my way through hyperref's code without much success. Would anyone have a solution for this problem?  Or advice about what I might be doing wrong?


I am trying to include the bibliography in a file I'm writing. The editor I'm using is TeXShop (OS is mac OSX).  I'm following a tutorial where I found that to include the bibliography using Biber I need a .bib file and the following commands:  \usepackage[autostyle]{csquotes}  \usepackage[backend=biber]{biblatex} \addbibresource{bib_file.bib}   and then  \printbibliography   Then it says that, in order to make the bibliography appear in the document, I should:   Compile Run Biber from the editor Re-compile twice   But how do I run Biber from TeXShop?  PS I've already set Biber as my default BibTeX Engine in Preferences/Engine, but I don't know how to run it. If I simply compile the document (i.e. press "Typeset") no bibliography will appear.

Running the minimal example  \documentclass{article} \usepackage{filecontents} \begin{filecontents*}{\jobname.bib} @ARTICLE{example,   author  = {Other, Anthony Norman},   title   = {Some things I did},   year    = {2014},   journal = {J.~Irrep. Res.},   volume  = {1},   number  = {1},   pages   = {1-10} } \end{filecontents*} \usepackage[backend=biber]{biblatex} \addbibresource{\jobname.bib} \begin{document} Hello\cite{example}. \printbibliography \end{document}   I get the warning There were undefined references.  I have read  and know that I need to run:   LaTeX Biber LaTeX   However, my editor is only set up to run BibTeX. How do I go about setting up my editor/IDE to be able to run Biber, and how do I run the LaTeX/Biber/LaTeX cycle?  Answers (sorted alphabetically by editor name)                    Answer guidelines   Each answer should be for one editor. If the editor is cross-platform, if possible give a single answer with notes covering the minor platform variations. Please edit the question to include new answers in the 'link list' Each answer should be 'stand alone', i.e. don't say 'It's almost the same as editor Y but ...' for the editor part Instructions for 'build tools' such as arara or latexmk are welcome but should explain how to set up the editor in question as not all editors allow simple addition of arbitrary tools


look at the white bar at the bottom left of the picture, is there any way to get rid of that?  Notice: I don't want to use chrome theme

I want to turn off the feature where whenever I hover over a hyperlink and in the bottom lefthand corner it shows a light blue hover tooltip about where that link goes.   Why do I want to turn it off? It's annoying to me. I am distracted as I work. None of the other browsers do it. Besides, it serves little purpose because it can be spoofed with the onmousedown event on a link. Take for instance ads on Facebook -- those spoof.   I really don't care where a given link goes and wish I could turn that feature off, even if I have to install a Google Chrome Extension.   So, is there a fix to turn the annoying link hover tooltip feature off?


What book can I find the Yuan-Ti Pureblood race in?  I know its really simple but I just forgot.

There's not a lot of material published by WotC for 5e (relative to previous editions), nor is there planned to be. However, there are playable races for D&D scattered around in a few different locations in published products that people may not even know about. What are all the playable races, and where can one find each?  To be clear, we're talking about first party D&D 5e materials published by Wizards of the Coast.  Both "official" races (sanctioned for Adventurers League Play) and others, like races from Unearthed Arcana or from other WotC sources outside the D&D team that are less canonical, are of interest, but please designate whether they're considered official and sanctioned or not.     Topicality and utility of this question discussed in Meta . Inspired by .


I would like to enable bitlocker on my C: drive, but I dont understand the following message:    If it's the hardware, which part exactly? I have a recent asus motherboard with UEFI. How can I find out if my motherboard supports TPM?

HP Pavilion complains about Bitlocker saying TPM is not found. Is there a setting that I need to enable in the motherboard or is there an update for it?


Ubuntu keeps telling me there is a system error and won't send updater to updates site.  this line keeps comming up:   E:Line 1 too long in source list /etc/apt/sources.list.d/medibuntu.list.    How do I fix this?

I accidentally added this in a terminal:  sudo wget http://www.medibuntu.org/sources.list.d/gutsy.list -0 /etc/apt/sources.list.d/medibuntu.list   after which I get this error:  E:not known on line 1 file /etc/apt/sources.list.d/medibuntu.list E:Could not read source list etc...etc...   I saw that you already 'solved a similar problem ... can you help me  Original (italian):  gestore pacchetti bloccato   Ho inserito per sbaglio questo comando nel terminale:   sudo wget http://www.medibuntu.org/sources.list.d/gutsy.list -0 /etc/apt/sources.list.d/medibuntu.list dopodiche si e'bloccato gestione pacchetto e ricevo questo errore: E:non riconosciuto alla riga 1nel file /etc/apt/sources.list.d/medibuntu.list E:impossibile leggere elenco sorgenti etc...etc...   ho visto che hai gia' risolto un problema simile... mi puoi aiutare


So I haven't used Blender too much in about a week or so. I decided to open up some of the last things I was working on and was horrified at what I saw. At first, it was hard to tell what was going on exactly, and I still don't know what is happening, but it looks like some severe rendering bug related to shaders. I can't even really describe in words what is happening because it's so weird. But basically, when I go into Material Preview or Rendered View, my mesh goes completely broken and gets some weird, warped, transparent property. I've recorded a video with a new file.  I think this might be related to my updating my video card driver a couple days ago. I would revert, but the reason I updated it because otherwise Steam wouldn't launch. Has anyone else seen anything like this before? I've reinstalled already. Is this some severe bug or am I being really stupid here?

I don't know why but now, when i go in material preview or rendered (in solid mode it works fine), my object is entirely gray, or invisible idk, because it has the same color of the background. I've been working for days on this project without having this issue, it suddenly showed up. I tried opening other old projects and suddenly they all do the same so i guess it is some blender program setting that applies for all the projects, but idk how it happened cuz i didn't change anything :/, anyone got any tips?


I'm writing a script in which I need to generate a tree of directories.  How to pass to tree a variable with list of directories to ignore? And those directories are with spaces in name.  I tried something like this:  tree -o /volume1/web/eb.html -T "List" --charset UTF-8 -C -I "$to_ignore" -P '*pdf' --prune --noreport /volume1/docs   Where vaiable to_ignore is a list of directories generated somewhere else by script:  'dir1|dir2|dir with space|dir4'   but that didn't worked. It crashed on dir with space.  Ok, so using quotes around variable helped with crashes but then tree prints even those directories that have required pdf files and are on list to ignore. And what's strange if I write those directories to ignore directly in my tree ... command than it works fine.

Or, an introductory guide to robust filename handling and other string passing in shell scripts.  I wrote a shell script which works well most of the time. But it chokes on some inputs (e.g. on some file names).  I encountered a problem such as the following:   I have a file name containing a space hello world, and it was treated as two separate files hello and world. I have an input line with two consecutive spaces and they shrank to one in the input. Leading and trailing whitespace disappears from input lines. Sometimes, when the input contains one of the characters \[*?, they are replaced by some text which is is actually the name of files. There is an apostrophe ' (or a double quote ") in the input and things got weird after that point. There is a backslash in the input (or: I am using Cygwin and some of my file names have Windows-style \ separators).   What is going on and how do I fix it?


Let $G$ be a finite group, and $K$, $L$ subgroups of $G$ and $H=K \cap L$ such that:     $G = \langle K,L \rangle$.   $\forall g \in G$ : $HgK=KgH$ and $HgL=LgH$   Remark: These assumptions imply that $G=KL=LK$, but the converse is false,  because the example of Jack Schmidt  doesn't check the second assumption.  Let $\Omega = G/K$ and $\pi: G \to S_{\Omega}$ the canonical action on cosets.       Question: Is it true that $\forall g \in G$ $\exists l \in L $ such that $\pi(g)=\pi(l)$ ?      If yes, then $\forall k \in K$ $\exists s \in K \cap L $ such that $\pi(k)=\pi(s)$, because $ker(\pi) \subset K$.

Let $G$ be a finite group, and $K$, $L$ subgroups of $G$ such that $G = KL=LK$. Let $\Omega = G/K$ and $\pi: G \to S_{\Omega}$ the canonical action on cosets.       Question: Is it true that $\forall g \in G$ $\exists l \in L $ such that $\pi(g)=\pi(l)$ ?      If yes, then $\forall k \in K$ $\exists s \in K \cap L $ such that $\pi(k)=\pi(s)$, because $ker(\pi) \subset K$.


iPhone 5 is running iOS7. Macbook Pro is the 15" MacBook Pro Retina on Mavericks.  I have AirDrop enabled on both but the phone and Macbook don't see each other. Both keep searching, searching, searching ...  FYI, I have enabled Bluetooth and WiFi on both devices are also on the same WiFi network. There is also no firewall between them and they are within 2 feet of each other.  Apple tech is supposed to "just work" and it almost always does so intuitively but this one has me scratching my head. What is going on here?

A new MacBook came with something called AirDrop and worked between many MacBooks such as MacBook Pro and MacBook Air. Can I also use AirDrop to exchange data between Macs and iOS devices?


I'm running DHCPD (isc-dhcp-4.2.4) on an Ubuntu 14.04 system.  The var/lib/dhcp/dhcpd.leases file is getting pretty huge (350MB).  Looking in it, there's historical data going back many months about leases that have long since expired.  How do I purge the old info?  Presumably stopping dhcpd and deleting the file is a bad idea because then it will forget recent leases that might still be relevant?  [edit] Apparently dhcpd is supposed to auto-purge the leases file once an hour, but this isn't happening for me.  Apparently this is down to a permissions problem - the /var/lib/dhcp directory and contents are ownwd by root:root but the server runs as dhcpd:dhcpd.  I tried changing the ownership as follows:-  sudo service isc-dhcp-server stop sudo chown -R dhcpd:dhcpd /var/lib/dhcp/ sudo service isc-dhcp-server start   but after this the ownership of the directory, dhcpd.leases and dhcpd.leases~ reverted to root:root.  So how do I sort out directory ownership vs the user:group running the dhcpd process to get auto-purge to work?

When running isc-dhcp the leases file seems to grow indefinitely (several hundred MB). If I restart the isc-dhcp service, the file shrinks to 1.5MB.   How can I have isc-dhcp flush expired records periodically without restarting the full service?