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XmlInclude : List and array Can grep output only specified groupings that match? Say I have a file:  # file: 'test.txt' foobar bash 1 bash foobar happy foobar   I only want to know what words appear after "foobar", so I can use this regex:  "foobar \(\w\+\)"   The parenthesis indicate that I have a special interest in the word right after foobar.  But when I do a grep "foobar \(\w\+\)" test.txt, I get the entire lines that match the entire regex, rather than just "the word after foobar":  foobar bash 1 foobar happy   I would much prefer that the output of that command looked like this:  bash happy   Is there a way to tell grep to only output the items that match the grouping (or a specific grouping) in a regular expression? How to deal with "java.lang.OutOfMemoryError: Java heap space" error? PWM complementary square output waveforms PWM channels in certain microcontrollers such as the SAM3X8E have two complementary square output waveforms, PWMH and PWML, per channel. What is the purpose of having two waves that are the inverses of each other? How to get the file name and a line number of a function call? Markdown + Mathjax => PDF I've used LaTeX a lot in the past, but now, when comparing with StackExchange's great , I find it tedious, for short documents (&lt; 2 pages), to have to use pure LaTeX. For a short document, instead of having 30 lines as introduction: \begin{document} \documentclass[11pt,a4paper]{article} \usepackage[frenchb]{babel} \usepackage[latin1]{inputenc} \usepackage[T1]{fontenc} \usepackage{amsmath} \usepackage{amsfonts}  + &lt;lots of other things&gt; ...  I'd like to write my short document with MarkDown + Math, like on . Question: Is there an offline compiler such that compilemarkdown exercice.tex  would produce a PDF from this: #Title  Here is a *short document* including Markdown and Math, here is the equation:  $$f(x)=x^2$$  ___  Proof: ...   This is **bold**. Labeling stacked polygons with different records I work in Oil and Gas and trying to label leases is a huge pain.  In most cases there are multiple polygons of the exact same size and shape stacked on each other with records that represent different lessees.    The number of lessees per section is unlimited.  How can i label these polys so that they look like the annotation in the picture below. Optimally the labels would be sorted on the date field as well. This label is also an expression containing the Net Acres and the Expiration Date. Omission of "the" in "elected him president" and "made captain" Why is there no the before president and captain?     They elected him president.       She was made captain of the team. I am trying to understand the Georgi chapter of tensor methods in $SU(3)$ representations, and I don't know how to resolve the tensor product of 2 matrices in a 2 heavy quark + 2 light antiquark system. Namely:  Let the tetraquark system be:           $QQ\bar q\bar{q}$  So, those $Q$ heavy quarks interact and can be understood in the $3\bigotimes 3$ representations for $SU(3)$, and $\bar q\bar q$ can be understood as the $\bar 3\bigotimes\bar 3=3\bigoplus\bar 6$ representations for $SU(3)$.  The interaction diagram for the $Q$ heavy quarks is shown in the following scheme, which is an analogy to the Feynman Diagram where a gluon is understood to be exchanged between upper and lower arrows:  $i'\xrightarrow{(T_{a})^{i'}_{i}}i ,  {}^iQ$  $j'\xrightarrow{(T_{a})^{j'}_{j}}j ,  {}^jQ$  So, as usuall we consider the elements of $3$ representation as $u^i$, and therefore the elements of $\bar 3$ representation as $v_{j}$.  I must understand how does the following expression transform:  $(T_{a})^{i'}_{i}(T_{a})^{j'}_{j}\cdot(1/2)\cdot (w^iv^j+w^jv^i)=\Xi\cdot(1/2)\cdot(w^{i'}v^{j'}+w^{j'}v^{i'})$  In other words, how can one give the correct value of $\Xi$?  Note1: $T_a$ is understood to be the $a-ith$ generator of the associated Lie Algebra, which come from the definition of the Gell-Mann Matrices.  $(T_{a})^{i}_{j}\propto(\lambda)_{ij}$, in matrix notation.  Note2: I understand the Young Tableaux and they are not intended to be used here, so please don't try to explain this situation through the tables.   Note3: I assume this is a purely solvable mathematical problem and doesn't need a deep insight into the physical concepts...  Also requesting information about how to understand the tensor products in these cases, since I have been checking many sources but the definitions seem not clear enough. JavaScript hard refresh of current page What techniques are available for collapsing (or pooling) many categories to a few, for the purpose of using them as an input (predictor) in a statistical model?    Consider a variable like  (discipline chosen by an undergraduate student). It is unordered and categorical, but it can potentially have dozens of distinct levels. Let's say I want to use major as a predictor in a regression model.  Using these levels as-is for modeling leads to all sorts of issues because there are just so many. A lot of statistical precision would be thrown away to use them, and the results are hard to interpret. We're rarely interested in specific majors -- we're much more likely to be interested in broad categories (subgroups) of majors. But it isn't always clear how to divide up the levels into such higher-level categories, or even how many higher-level categories to use.  For typical data I would be happy to use factor analysis, matrix factorization, or a discrete latent modeling technique. But majors are mutually exclusive categories, so I'm hesitant to exploit their covariance for anything.  Furthermore I don't care about the major categories on their own. I care about producing higher-level categories that are coherent with respect to my regression outcome. In the binary outcome case, that suggests to me something like linear discriminant analysis (LDA) to generate higher-level categories that maximize discriminative performance. But LDA is a limited technique and that feels like dirty data dredging to me. Moreover any continuous solution will be hard to interpret.  Meanwhile something based on covariances, like multiple correspondence analysis (MCA), seems suspect to me in this case because of the inherent dependence among mutually exclusive dummy variables -- they're better suited for studying multiple categorical variables, rather than multiple categories of the same variable.  edit: to be clear, this is about collapsing categories (not selecting them), and the categories are predictors or independent variables. In hindsight, this problem seems like an appropriate time to "regularize 'em all and let God sort 'em out". Glad to see this question is interesting to so many people! Can Ubuntu run on a Microsoft Surface with Windows RT? My family might be buying a Windows Surface tablet with Windows RT (Nvidia)? I was wondering if I can run Ubuntu or WUBI on it for my homework? If light rays obey to the wave equation, why can they be thought as straight lines? I'm a newbie with physics but I'm wondering how a ray of light can essentially be represented. I have always known that a ray of light proceeds in a straight line until it encounters another object (or material) that refracts/reflects it. But a light ray should be part of an electro-magnetic wave, is this correct? If it is so, it should obey to the  and this doesn't seem to me to describe a straight line ray.  I'm having problems visualizing how light is emitted and how it relates with the wave equation. Can someone with a clear understanding of the problem explain it to me in simple terms? Why do some badges appear white in color and others are dark? I want to resolve merge conflicts in my Git repository. How to do that ? How can I prove these are the adjoint operators? sed command not giving proper output for regular expression used I am trying to fetch data between a range of time intervals from the log file. However, the complete data is not fetched for the end date.  Below is the command used:   sed -n '/26/Nov/2018/,/30/Nov/2018/ p' /path/file.log    The data I am having in the above log file is somewhat like:   192.168.0.123 - - [25/Nov/2018:13:24:59 +0530] "Data 1"  192.168.0.123 - - [26/Nov/2018:13:24:59 +0530] "Data 2"  192.168.0.123 - - [26/Nov/2018:13:25:09 +0530] "Data 3"  192.168.0.123 - - [27/Nov/2018:13:25:09 +0530] "Data 4"  192.168.0.123 - - [27/Nov/2018:13:25:11 +0530] "Data 5"  192.168.0.123 - - [27/Nov/2018:13:25:53 +0530] "Data 6"  192.168.0.123 - - [28/Nov/2018:13:25:53 +0530] "Data 7"  192.168.0.123 - - [29/Nov/2018:13:25:53 +0530] "Data 8"  192.168.0.123 - - [30/Nov/2018:13:25:53 +0530] "Data 9"  192.168.0.123 - - [30/Nov/2018:13:25:53 +0530] "Data 10"  192.168.0.123 - - [01/Dec/2018:13:25:53 +0530] "Data 11"  192.168.0.123 - - [01/Dec/2018:13:25:53 +0530] "Data 12" Detecting and acting on keyboard direction keys in Java How do I suspend a whole process (like the Process Explorer does when I click Suspend) in C#.  I'm starting the Process with Process.Start, and on a certain event, I want to suspend the process to be able to do some investigation on a "snapshot" of it. Continuity and existence of directional derivatives at all directions of a $f:\mathbb{R}^{2} \to \mathbb{R}$ given by $f(x,y)=\frac{2x^2y}{x^2+y^2}$ Let $f(x,y)=     \begin{cases}       \frac{2x^2y}{x^2+y^2} &amp; if &amp; (x,y) \neq (0,0) \\       0       &amp; if &amp; (x,y)=(0,0) .  \end{cases}$  (i) Prove the directional derivatives of $f$ exist in any direction at the point $(0,0)$.  (ii)¿Is $f$ continuous on (0,0)?  For (i) I took $u=(u_{1},u_{2}) \in \mathbb{R^{2}}$ such $\|u\|=1$ and $0=(0,0)$. So $$\lim_{t \to 0} \frac{f(0+ t u)-f(0)}{t}=\lim_{t \to 0}\frac{2(tu_{1})^2 (tu_{2})}{(tu_{1})^4+(tu_{2})^2}=\lim_{t \to 0}\frac{(t^2 u_{1}^2)(t^2 u_{1}^{2}) tu_{2}}{t^{4}u_{1}^{4}+t^{2} u_{2}^{2}}.$$ But I cannot find the limit when $t$ aproaches to $0$. Which by finding them I would prove the directional derivative exist at every direction right?  For (ii) I got the intuition $f$ is not continuous at $(0,0)$ so I took $\lbrace (\frac{1}{k},\frac{1}{k}) \rbrace_{k \in \mathbb{N}}$ and $\lbrace (\frac{1}{k},0) \rbrace_{k \in \mathbb{N}}$ which are two different sequences in $\mathbb{R}^{2}$ converging to $(0,0)$. However, $\lbrace f(\frac{1}{k},\frac{1}{k}) \rbrace_{k \in \mathbb{N}}=\lbrace \frac{1}{k^{2}} \rbrace_{n \in \mathbb{N}} \to 0$ and $\lbrace f(\frac{1}{k},0) \rbrace_{k \in \mathbb{N}} \to 0$. So maybe my intuition was not right? Can anyone help me end the proof of continuity or not continuity , please?