I'm planning on buying a Dell with pre-installed Ubuntu image.  In case something goes wrong, how do I reinstall Ubuntu from scratch with the Dell's image containing all of Dell's specific drivers?   I couldn't even find a downloadable image on  :-(
Background  My Lenovo X250 is arriving in two weeks, which according to  will work well only with "a special image of Ubuntu pre-installed by the manufacturer."   points out that the X250 has "Excellent" compatibility to the Linux OSes they install. On the other hand, a quick search on  or  shows that a standard image of Ubuntu on the X250 is rife with hardware problems.  Ubuntu Certified Hardware acknowledges this for the X250: "Standard images of Ubuntu may not work at all on the system or may not work well." This  clearly shows the difference between an Ubuntu standard image installation and the one that comes pre-installed by the manufacturer. Hardware seems to work fully on the OEM version.  Question  Any idea where we may access or download these "special images of Ubuntu"?  (Hopefully not only for the X250, but also for the other systems out there.)
How can i find the python triggered by the GUI? chown as non-root user How do I hide posts matching my ignored tags? Where and how do I go about hiding the posts that match any of the tags on my ignored list? Why is Leia okay with being tracked to Yavin? In A New Hope, after Han and Luke fight off the TIE Fighters while escaping from the Death Star, these exchanges happen:             INT. DEATH STAR - CONTROL ROOM             Darth Vader strides into the control room, where Tarkin is             watching the huge view screen. A sea of stars is before him.                                   TARKIN                      Are they away?                                   VADER                      They have just made the jump into                       hyperspace.                                   TARKIN                      You're sure the homing beacon is                       secure aboard their ship? I'm taking                       an awful risk, Vader. This had better                       work.             INT. MILLENNIUM FALCON - COCKPIT             Han, removes his gloves and smiling, is at the controls of             the ship. Chewie moves into the aft section to check the             damage. Leia is seated near Han.                                   HAN                      Not a bad bit of rescuing, huh? You                       know, sometimes I even amaze myself.                                   LEIA                      That doesn't sound too hard. Besides,                       they let us go. It's the only                       explanation for the ease of our                       escape.                                   HAN                      Easy... you call that easy?                                   LEIA                      They're tracking us!                                   HAN                      Not this ship, sister.             Frustrated, Leia shakes her head.                                   LEIA                      At least the information in Artoo is                       still intact.                                   HAN                      What's so important? What's he                       carrying?                                   LEIA                      The technical readouts of that battle                       station. I only hope that when the                       data is analyzed, a weakness can be                       found. It's not over yet!   Leia doesn't even know if there is a weakness, let alone whether they'll find one. If she (correctly) realizes that they're being tracked, why doesn't she suggest that the Millennium Falcon go somewhere besides Yavin 4 instead of just frustratedly shaking her head? I know the plans , but it seems unlikely that continuing to fly to the secret Rebel base in the ship she's certain is being tracked is the only option. They are already in hyperspace when this conversation happens, but they apparently have time to talk for a little while after, so presumably they'd have time to stop and reroute. How to add appendix in thesis using LyX I want to add an appendix (questionnaire etc.) at the end of my thesis after the references. I use the article class and work with LyX: Document -&gt; Start appendix here. But I am not getting it in the TOC.  \documentclass[12pt,english]{article} \usepackage[T1]{fontenc} \usepackage[latin9]{inputenc} \setlength{\parskip}{\smallskipamount} \setlength{\parindent}{0pt} \usepackage{color} \definecolor{document_fontcolor}{rgb}{0, 0, 0} \color{document_fontcolor} \usepackage{babel} \usepackage{float} \usepackage{textcomp} \usepackage{pdfpages} \usepackage{tipa} \usepackage{amsmath} \usepackage{graphicx} \usepackage{setspace} \PassOptionsToPackage{normalem}{ulem} \usepackage{ulem} \usepackage[unicode=true,  bookmarks=true,bookmarksnumbered=false,bookmarksopen=false,  breaklinks=false,pdfborder={0 0 0},backref=false,colorlinks=false]  {hyperref}  \makeatletter  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%% LyX specific LaTeX commands. %% Because html converters don't know tabularnewline \providecommand{\tabularnewline}{\\} %% A simple dot to overcome graphicx limitations \newcommand{\lyxdot}{.}   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Textclass specific LaTeX commands. \numberwithin{equation}{section}  \@ifundefined{date}{}{\date{}} \@ifundefined{showcaptionsetup}{}{%  \PassOptionsToPackage{caption=false}{subfig}} \usepackage{subfig} \makeatother  \appendix \noindent \begin{center} \textbf{Questionnaire (Case Study 1)} \par\end{center} Find a formula for Taylor series of $\left(\frac{1}{1+z^2}\right)^n$ So the way I think I should approach this is by getting a result for $n=1,2,3...$  and then examine them. I could easily get the Taylor series expansion for $n=1$, but then I don't really know how to proceed, because I can't always break down a power of a polynomial. And a power of a summation doesn't seem as a legit answer either.   Can anyone help? Thanks Given the following groups, what is the maximum possible order for an element for   (a) $S_5$ (b) $S_6$ (c) $S_7$ (d) $S_{10}$ (e) $S_{15}$  My book justifies the answer as          (a) The greatest order is $6$ and comes from a product of disjoint cycles of length 2 and 3          (b) The greatest order is $6$ and comes from a cycle of length $6$      The other answers were justified exactly the same way, that is (c) 12, (d) 30, (e) 105  I do not understand how in (a) we even got the number "6" from $S_5$ and what disjoint cycles they are referring to. Could someone at least justify one for me? Apt/Synaptic needs to reinstall package but can't find the archive for it Running Synaptic I get the following error message:  E: The package hl1440lpr needs to be reinstalled, but I can't find an archive for it. E: Internal error opening cache (1). Please report.   Upon accepting the message, Synaptic quits. verifying an incorrect integrating factor I was doing some practice problems that my professor had sent us and I have not been able to figure out one of them. The given equation is:  $-y^2dx +x^2dy = 0$  He then asks us to verify that:  $ u(x, y) = \frac{1}{(x-y)^2}$  is an integrating factor.   I multiplied through to get:  $\frac{-y^2}{(x-y)^2}dx + \frac{x^2}{(x-y)^2}dy = 0$   However, the partial derivatives of these do not equal each other so I am a bit confused... Detecting start bit in software UART I'm experimenting with writing a software UART on my microcontroller using GPIO pins. This is to temporarily add a UART channel on a project until we get the new design implemented that uses a uC with more UART ports.  What I'm having difficulty with is correctly detecting a start bit in a serial stream. The source of the stream is external and doesn't care when my device powers up. So it's very likely that my device will power on and start seeing data bits in the middle of a byte transmission. Undoubtedly, that will cause my software UART to read erroneous values, as it won't be able to tell the difference between a start bit and any other high-to-low transition.  Is this an inevitable issue with a UART channel? Or is there some clever trick that the uC manufacturers use in their hardware UARTs? Why is Linux's filesystem designed as a single directory tree? Nested List Indices Fourier series identity I need to prove that $\dfrac{a \sin(bx)}{1 - 2a \cos(bx) + a^2} = \sum_{n=1}^\infty a^n \sin(nbx)$ where $|a| &lt; 1$.  It seems that this can be proved by using Euler's formula identities for $\cos(bx)$ and $\sin(bx)$ and substituting $z = e^{ibx}$. From that, I get $$ \dfrac{a \sin(bx)}{1 - 2a \cos(bx) + a^2} = \dfrac{a (z - 1/z)}{2i(1 - a(z + 1/z) + a^2)}$$ $$= \dfrac{a (z^2 -1)}{2i(z - a(z^2 +1) + za^2)}$$ $$= \dfrac{a (z^2 -1)}{-2ai(z^2 - z(1-a^2)/a + 1)}$$  I don't understand what I am supposed to do next. Embedding C++ Objects into QML with Context Properties According to Qt5 documentation:  all public slots of C++ classes that inherit from QObject, are accessible from QML Here what I did:  C++  class MyClass : public QObject {     Q_OBJECT  public slots:     void doStuffFromQmlSlot()     {         qDebug() &lt;&lt; Q_FUNC_INFO;     }  public:     MyClass()     {         qDebug() &lt;&lt; Q_FUNC_INFO;     } };   my main.cpp contains:  MyClass myClass; QQmlEngine engine; engine.rootContext()-&gt;setContextProperty( "myclass", &amp;myClass ); QQmlComponent component( &amp;engine, QUrl::fromLocalFile("qml/qtquick-01/main.qml") ); component.create();   QML  import QtQuick 2.0  Rectangle {     width: 360     height: 360     Text {         text: qsTr("Hello World")         anchors.centerIn: parent     }     MouseArea {         anchors.fill: parent         onClicked: {             myclass.doStuffFromQmlSlot();              Qt.quit();         }     } }   Actually the QtCreator seems to recognixe the exposed myclass object into the QML as it enables auto-completion of both class name (myclass) and the public slot doStuffFromQmlSlot(). When I run the application I unfortunately got the following error:  ReferenceError: myclass is not defined  Any clue on what I'm doing wrong? I'm having a lot of trouble figuring this one out.  Determine if  $\sum_{i=2}^{\infty} \frac{(-1)^n}{n+(-1)^n}$ converges or diverges  Both ratio and root test are inconclusive and I'm at a loss. Can anyone help me? Where are the corrosive weapons at? I'm a Siren and I'm getting almost nothing but Fire elemental guns; about 90% of guns have been fire, most of the rest Explosive and a scare few Shock.  Are the elemental varieties more common at different levels? I've seen zero corrosive/shock guns so far. I'm level 12 at the moment. Should I normalize word2vec's word vectors before using them? After training word vectors with word2vec, is it better to normalize them before using them for some downstream applications? I.e what are the pros/cons of normalizing them? I'm new here. Can anyone give me a hint in this problem? Please.  Let $X$ be a topological space. If $f,g$ are continuous function of $f,g\colon X\to S^n$  which $f(x)\neq -g(x)$ for all $x$ in $X$, show $f$ and $g$ are homotopics. I try to show a homotopy using $$q(x) = \frac{f(x)+g(x)}{\|f(x)+g(x)\|}$$ it's well defined, but i'm stuck. Equivalence Relation problem Let $S$ be the relation on $\mathbb{N} \times \mathbb{N}$ defined by $(a,b)S(c,d)$ if and only if $ad=bc$. Prove this is an equivalence relation on $\mathbb{N} \times \mathbb{N}$.  I think I've found this to be reflexive and symmetric, but I'm stuck on transitivity. Can someone check my work so far and assist with testing transitivity?  Reflexive: Let $(x,y)S(x,y)$. Then $xy = yx$. So $S$ is reflexive. Symmetric: Suppose $(a,b)S(c,d)$. Then, $ad = bc$. Therefore, $da = cb$ and $cb = da$. Therefore, $(c,d)S(a,b)$. Thus, $S$ is symmetric.  Transitive: Suppose $(a,b)S(b,c)$. Then $ac = bb$.   This is where I'm stuck. Any ideas? Let $C_*$ be a chain complex such that each $C_i$ is a torsion-free, finite-range abelian group with $C_i=0$ for all $i&lt;0$. Suppose that $C_i=0$ for all $i$ is large enough. The Euler characteristic of $C_*$ chain complex is defined as $$\chi(C_*)=\sum_{i\geq 0}(-1)^iRank(C_i)$$ Prove that $$\chi(C_*)=\sum_{i\geq 0}(-1)^iRank(H_i(C_*))$$  I have to prove that $\sum_{i\geq 0}(-1)^iRank(C_i)=\sum_{i\geq 0}(-1)^iRank(H_i(C_*))$, I think that one way to do this is by showing that $Rank(C_i)=Rank(H_i(C_*))$ but I do not know if this is true in general, in a nutshell, I want to show that the cardinality of the base of any $C_i$ is the same as the cardinality of the basis of the corresponding homology, how can I do this? Thank you