I tested the following python code which reverses a string  &gt;&gt; s = 'abcd' &gt;&gt; s[::-1] &gt;&gt; 'dcba'   But I am confused, what exactly the two comma and negative one does it the code ?
I need a good explanation (references are a plus) on Python's slice notation.   To me, this notation needs a bit of picking up.   It looks extremely powerful, but I haven't quite got my head around it.
How to reset KDE desktop to default on Ubuntu 14.04? KDE and Gnome Desktops were looking awesome on my Ubuntu 14.04 LTS, today everything seemed ugly. Slim long font, arabic letters in Chromium/Firefox are barely readable no matter how big I made them on system font settings. How can I get back to my previous looks settings, without compromising other settings and tweaks?  Here are my versions:  kde4-config -v:  Qt: 4.8.6 KDE Development Platform: 4.13.3 kde4-config: 1.0   kded4 --version:  Qt: 4.8.6 KDE Development Platform: 4.13.3 KDE Daemon: 4.13.3 Why does my grep expression need to use $'string' to match tab characters? cube collider losing shape upon rotation I'm not sure what's going on here. I have a cube which I have turned into a rectangle; it's a child of a plane which is the "ground" so that they share rotation (this is a pinball table).   To create these cubes, I just used the create => 3d shape => cube/plane option. No packages are used.   The issue is when I rotate the rectangle, the collider visibly becomes wrong.  This is before rotation:    This is after rotating on the y axis:    The collider does seem to rotate, but not at the correct amount. Can anyone shed some light as to what's going on here?  Here's the inspector and hierarchy:      I also tried making the plane a cube, it didn't change anything. I am learning P&amp;S's Introduction of quantum field theory. My teacher said that if the mass of neutrino is exactly 0, then we should not observe any right-handed neutrinos and left-handed anti-neutrinos according to Weyl's theory. It is because $$ \left( i\gamma^\mu \partial_\mu - m \right) \psi = \left( \begin{array}{cc} -m &amp;  i\left(\partial_0 + \vec\sigma \cdot \vec\nabla\right) \\ i\left(\partial_0 - \vec\sigma \cdot \vec\nabla\right) &amp; -m \end{array} \right) \left( \begin{array}{c} \psi_L \\ \psi_R \end{array} \right) =0. $$  If we set m=0, then we will have:  \begin{align} i\left(\partial_0 - \vec\sigma \cdot \vec\nabla\right) \psi_L &amp;= 0; \\ i\left(\partial_0 + \vec\sigma \cdot \vec\nabla\right) \psi_R &amp;= 0. \end{align}  And if these formulas can describe neutrinos we must conclude that there are two types of neutrinos.  My confusions are:   It is known that the mass of neutrino is not 0, therefore there are chances (depending on the mass) to find right-handed neutrinos and left-handed anti-neutrinos. But we don't. If I accept that there are only these two types of neutrinos (right-handed anti-neutrinos and left-handed neutrinos), this property of neutrino causes the parity violation, so parity violation must relate to angular momentum and therefore spinor space. Am I write? Are there any reasons why neutrino is so weird that is has mass but still has helicity + Or - 1. This goes against with what I have learned that only when a particle  moves at the speed of light can its spin aligned with its momentum. Coordinate-Free Definition of Trace. $\DeclareMathOperator{\tr}{trace}$ I am reading the  on the trace operator. The section titled Coordinate-Free Definition defines the trace as follows.  Let $V$ be a finite dimensional vector space over a field $F$ and define a bilinear map $f:V\times V^*\to F$ as $f(v, \omega)=\omega(v)$ for all $(v, \omega)\in V\times V^*$. This maps induces a unique linear map $\tr:V\otimes V^*\to F$. Since $\text{End}(V)$ has a canonical isomorphism with $V\otimes V^*$, we have now a notion of trace of a linear operator on $V$.  The Question: The second paragraph of the section in the article says that  This also clarifies why $\tr(AB)=\tr(BA)$.  I can't see how $\tr(AB)=\tr(BA)$ follows from this definition at all. Can somebody give me a hint? Can I travel to the UK unaccompanied on an accompanied child visa now that I am over 18? I got a visa with my mother when I was 17 years old. On it was stated "Not valid unless accompanied by my mother".    Can I travel to the UK alone now that I am 18? Can Button[] generate output without using Print[]? I am trying to adjust spacing between entries in LoF and LoT. My code is  \documentclass[11pt,a4paper]{book} \usepackage[english,greek]{babel} \setcounter{secnumdepth}{3} \usepackage[iso-8859-7]{inputenc} \usepackage{kerkis} \usepackage[pdftex]{graphicx} \usepackage[margin=2.8cm]{geometry} \usepackage[Glenn]{fncychap} \usepackage{fancyhdr} %!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! \usepackage{tocloft} \setlength\cftparskip{-15pt}%For ToC works great \setlength\cftbeforesecskip{-8pt}%For ToC works great \setlength\cftbeforesubsecskip{-5pt}%For ToC works great \setlength\cftbeforechapskip{-1pt}%For ToC works great \setlength\cftaftertoctitleskip{-50pt}%For ToC works great  % I also tried \renewcommand instead of \setlength \setlength\cftbeforeloftitleskip{-2cm}%It has no effect in LoF \setlength\cftbeforelottitleskip{-5cm}%It has no effect inLoT  \makeatletter \newcommand*{\tocwithouttitle}{\@starttoc{toc}} \makeatother %-------------------------------------------------------------------------------- \makeatletter \newcommand*{\lofwithouttitle}{\@starttoc{lof}} \makeatother %-------------------------------------------------------------------------------- \makeatletter \newcommand*{\lotwithouttitle}{\@starttoc{lot}} \makeatother %-------------------------------------------------------------------------------- %!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! \renewcommand{\cftsecleader}{\cftdotfill{\cftdotsep}}  \begin{document}  %~~~~~~~~~~~~~~~~~~~~~~~Front-Page~~~~~~~~~~~~~~~~~~~~~~~~~~ \begin{titlepage} Εξώφυλλο \end{titlepage}  \chapter*{\contentsname} \markboth{\MakeUppercase{\contentsname}}{\MakeUppercase{\contentsname}} \tocwithouttitle \addcontentsline{toc}{chapter}{Πειρεχόμενα}  %LoF \chapter*{Κατάλογος σχημάτων}%List of Figures \markboth{\MakeUppercase{Κατάλογος Σχημάτων}}{\MakeUppercase{Κατάλογος Σχημάτων}} %\renewcommand\cftbeforeloftitleskip{5pt} %\renewcommand\cftbeforelottitleskip{5pt} \lofwithouttitle %\setlength\cftbeforefigskip{0pt} \addcontentsline{toc}{chapter}{Κατάλογος Σχημάτων}  %LoT \newpage  \chapter*{Κατάλογος Πινάκων} \markboth{\MakeUppercase{Κατάλογος Πινάκων}}{\MakeUppercase{Κατάλογος Πινάκων}} \lotwithouttitle %\renewcommand\cftbeforeloftitleskip{5pt} %\renewcommand\cftbeforelottitleskip{5pt} \addcontentsline{toc}{chapter}{Κατάλογος Πινάκων}  \newpage \end{document}   While some code is working on ToC(See comments in Preamble) I cannot adjust spacing in LoF/LoT. How can this be achieved? Monotonicity in argmin function I have the following equation $$f(a)=\text{argmin}_{t\in\mathbb{R}} \sum_{i=1}^n\frac{1}{2}(1-a)(b_i-t)^2+a| b_i-t |, a\in[0,1]$$  How does one prove that the function is monotone in a? In class we've seen that $a$ (the weights) must satisfy $$X^T (y-Xa) =0$$  Here $X$ is a $(n\times d)$ matrix (so we have $n$ samples in $\mathbb R^d$)  let's denote the residuals $r = y-Xa$. In our class notes, it is written that     The normal equations require the residuals to be orthogonal to each of the columns of $X$.   Why?     Therefore, the solution of the linear regression is a projection of $y$ onto the subspace spanned by $v_1 , \ldots , v_d$ (the columns of $X$)   Can you please explain this? How important is the following in purchasing a laptop that will be used for image editing:   processor speed amount of RAM integrated vs. dedicated graphics card HD speed (SSD; or 5400/7200/10000 rpm) I want to prove that if we have a commutative integral domain $D$ with field of fractions $F\neq D$ then $F$ is not finitely generated as a $D$-module. (In this question it may be the case that $1\not\in D$.)    My original plan was to localize at a maximal ideal and then use Nakayama's lemma but as we don't have a $1$ our localization may not be local (in fact we need not have maximal ideals).  So I'm a bit lost as to where to go?  Thanks for any help. Consistency of an order statistic in exponential distribution In version 5.2 of Apple's Pages app for OS X (Mavericks), how do I change the page layout? T-SQL: Selecting Column Based on MAX(Other Column) How to use an alpha map in Blender Render? I can think of three general ways of explaining why the universe contains more matter than antimatter:  (1) Near the Planck time, the universe had zero baryon asymmetry, but at some later time, determined by some GUT energy scale, the  were satisfied, and the baryon asymmetry became nonzero.  (2) Nonconservation of baryon number occurs only at Planckian energies. Near the Planck time, the baryon asymmetry evolved from zero to some nonzero value.  (3) The Sakharov conditions have never been satisfied. The baryon asymmetry has always been nonzero, and has simply scaled as expected. (Apparently one  $\Delta n=n_B-n_\bar{B}\propto s$, where $n$ is number density and $s$ is entropy density).  It seems like most theorists are interested in #1, but is there any reason why 2 and 3 aren't possible?  2 seems pretty reasonable, since for the reasons given in , we have good reasons to think that baryon number is not conserved under Planckian conditions.  3 also seems reasonable to me, since even if baryon number is nonconserved at Planckian energies, that's only one of the three Sakharov conditions. I don't see any obvious fine-tuning objections to #3, since the scaling of baryon asymmetry with cosmological expansion isn't particularly drastic (not an exponential decay or anything). Is there something unphysical about maintaining $\Delta n\propto s$ all the way back to the Planckian era?   Some people might object to #3 on aesthetic grounds, since we "expect" the initial conditions of the universe to be symmetric, but that seems weak to me. After all, we don't object aesthetically to the fact that homogeneity was an imperfect symmetry of the early universe, and we even accept that the early universe was in a thermodynamically unlikely state. What is this heart in the crimson biome? I found this heart while exploring the crimson biome - what is it? We currently have around 20 apex classes and 5 triggers which are not used in our production org. We want to delete them in our production instance. We dont have ant scripts ready yet to be used for our deployments and so we cannot use destructivechanges file. Currently our production deployments are done by our support team and they need documentation from us to do these deletes. Changesets do not allow to delete apex classes and triggers. So what is the best way to delete these apex classes and triggers from production? How to run 32-bit app in Ubuntu 64-bit? I installed Ubuntu 14.04 and the current Android development SDK, which contains 32-bit executables. I found that I cannot run those 32-bit binaries. Trying to start them from bash gives me an error: $ ./adb bash: ./adb: No such file or directory  It is there though: $ ls -al ./adb -rwxrwxrwx 1 thomas thomas 1231255 Jan 17 13:31 ./adb $ file ./adb ./adb: ELF 32-bit LSB  executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.8, not stripped.   Same symptom for all the other 32-bit tools in the Android SDK. In olden days one could just install 32-bit libraries on 64-bit Ubuntu to get 32-bit support, but that does not seem to work anymore. How do I run 32-bit apps on a 64-bit Ubuntu distribution?