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Can the effects of a person's mass upon the local gravitational field be detected and measured remotely? Crontab entry executing every hour Solving minimization problem $L_2$ IRLS (Iteration derivation) In the article ''' Chartrand, Rick, and Wotao Yin. "Iteratively reweighted algorithms for compressive sensing." Acoustics, speech and signal processing, 2008. ICASSP 2008. IEEE international conference on. IEEE, 2008. '''  It is given that one iteration of  iterative reweighed least squares problem can be written as $\min \sum_{i=1}^N w_i u_i^2 $ subject to $\Phi u = b  $ which has a closed form solution given as   $u^{(n)} = Q_n \Phi^T (\Phi Q_n \Phi^T)^{-1} b$. where $Q_n$ is the diagonal matrix containing entries $1/(|u_i^{(n-1)}|^2 + \epsilon )^{1/2} $ And the closed form equation can be derived from the Euler Lagrange equation. Can someone please help me to get the derivation of the iteration?\ I understood till $$\min_u u^TWu+λ|| \Phi u−b||_2^2 $$  which can be written as $(\bigtriangledown=0)$ which gives $$ W u + \lambda (\Phi^T \Phi u - \Phi^T b) =0$$ For example, in this text:     Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc eu tellus vel nunc pretium lacinia. Proin sed lorem. Cras sed ipsum. Nunc a libero quis risus sollicitudin imperdiet.   I want to match the word after 'ipsum'. Help to do something or help do something? I wrote:      I will help you to acquire Russian.    A native English speaker corrected me saying that 'to' is unnecessary here. Is it correct to say      "I will help you acquire Russian" Set up a scheduled job? I've been working on a web app using Django, and I'm curious if there is a way to schedule a job to run periodically.   Basically I just want to run through the database and make some calculations/updates on an automatic, regular basis, but I can't seem to find any documentation on doing this.  Does anyone know how to set this up?  To clarify:  I know I can set up a cron job to do this, but I'm curious if there is some feature in Django that provides this functionality.   I'd like people to be able to deploy this app themselves without having to do much config (preferably zero).  I've considered triggering these actions "retroactively" by simply checking if a job should have been run since the last time a request was sent to the site, but I'm hoping for something a bit cleaner. Repeat copies of array elements: Run-length decoding in MATLAB Display the full URL of the home page? Is it possible to display the full, absolute URL of the home page in Drupal 7, like  www.example.com/The-best-example-possible ?  I'd like to display the full URL of the home page, not just the hostname. How to Add Background Images in 2.8 and later 2.81a here. I am trying to add a "background image" similar to how , so that I see a screen that looks something like this:    However I can't figure out how/where to access this screen in 2.81a as the UI is wildly different. Any ideas?  I am new to Blender so if you can provide a click-by-click list of instructions it would be enormously appreciated! TikZ: turning edges into arrows using "child" notation I'm using TikZ for the first time to draw a simple Kripke model, and I'm using the child notation to produce new nodes. How can I turn my edges into arrows?  \begin{tikzpicture}   \node [circle,draw] (q0) {}   child {node [circle,draw] (q1) {$p$}     child {node [circle,draw] (q4) {$p$}       child {node [circle,draw] (q7) {$p\land q$}}       child {node [circle,draw] (q8) {$p\land q$}}       child {node (q9) {} edge from parent[-&gt;, dashed]}}     child {node [circle,draw] (q5) {$q$}}     child {node (q6) {} edge from parent[dashed]}}   child {node [circle,draw] (q2) {$p$}}   child {node (q3) {} edge from parent[dashed]}; \end{tikzpicture}   I know how to change the color or thickness of all edges by passing an option at the beginning of \begin{tikzpicture}, but I can't turn them into arrows.   Also, while we're at it, is there a way to label these edges? Or am I left with simply using node notation for all my nodes?  Thanks for all your help, Piotr I'm trying to determine if there is a best practice for typesetting the "evaluated at" bar for derivatives. The three possibilities I'm thinking of are shown in the code excerpt below:  \begin{gather*} 5 + \frac{df}{dt} \Bigr\rvert_{t = 0} \\ 5 + \frac{df}{dt} \biggr\rvert_{t = 0} \\ 5 + \left. \frac{df}{dt} \right\rvert_{t = 0} \\ \end{gather*}     The \Bigr option doesn't quite reach the top and bottom of the fraction. The \biggr option overshoots the top and bottom of the fraction by a little bit. And the \left...\right option has the same height as the \biggr option, but it introduces a little extra space between the + and the fraction. I'm having trouble deciding between these options. Is there a best practice for typesetting this? I really enjoying using control+r to recursively search my command history. I've found a few good options I like to use with it: # ignore duplicate commands, ignore commands starting with a space export HISTCONTROL=erasedups:ignorespace  # keep the last 5000 entries export HISTSIZE=5000  # append to the history instead of overwriting (good for multiple connections) shopt -s histappend  The only problem for me is that erasedups only erases sequential duplicates - so that with this string of commands: ls cd ~ ls  The ls command will actually be recorded twice. I've thought about periodically running w/ cron: cat .bash_history | sort | uniq &gt; temp.txt mv temp.txt .bash_history  This would achieve removing the duplicates, but unfortunately the order would not be preserved. If I don't sort the file first I don't believe uniq can work properly. How can I remove duplicates in my .bash_history, preserving order? Extra Credit: Are there any problems with overwriting the .bash_history file via a script? For example, if you remove an apache log file I think you need to send a nohup / reset signal with kill to have it flush it's connection to the file. If that is the case with the .bash_history file, perhaps I could somehow use ps to check and make sure there are no connected sessions before the filtering script is run? Secure an Ubuntu OpenSSH server from Brute force attacks but without a firewall or SSH key pair? I use Ubuntu 16.04 and seek to harden my SSH authentication in a special manner.  The current situation:  I have a machine with a minimal Ubuntu server I use mainly to transfer files to via its local OpenSSH server. Now, I don't have a firewall on that machine from a few reasons and I also avoid using a key pair hence I use only a password. One of the only ways I have left to defend from brute force attacks, and the one I most desire at the moment, is using a mechanism that blocks a user for X amount of hours, after Y amount of connection tries.  The desired situation:  I wish to have a standalone mechanism (that is, not as part of a firewall) that blocks a user for X amount of hours, after Y amount of connection tries as a way to defend from brute force attacks.  My Question:  Do you know a utility (and specific configuration) that will let me achieve the desired situation? Is there a term for grammatical mistakes as a result of trying too hard? How many solutions has the equation $\sin x= \frac{x}{100}$ ? How many solutions has the equation $\sin x= \frac{x}{100}$ ?   Usually when I was asked to solve this type of problem, I would solve it graphically but this one seems to be trickier. It doesn't seem wise to put $f(x)=\sin x$ and $g(x)=\frac{x}{100}$ in the same graph and then counting all the intersection points.  What would be some algebraic methods to solve this? How to understand the LaTeX warning “there were undefined references”? The search parameter isanswered ignores acceptances From , I have tried the using \hspace{0pt} and   \makeatletter \renewcommand{\dddot}[1]{%   {\mathop{\kern\z@#1}\limits^{\vbox to-1.4\ex@{\kern-\tw@\ex@    \hbox{\normalfont ...}\vss}}}} \renewcommand{\ddddot}[1]{%   {\mathop{\kern\z@#1}\limits^{\vbox to-1.4\ex@{\kern-\tw@\ex@    \hbox{\normalfont....}\vss}}}} \makeatother   after loading mathtools but the problem still persists.    \documentclass{article} \usepackage{mathtools} \begin{document} \[ \dot{\mathbf{r}}\times\ddot{\mathbf{r}}\times\dddot{\mathbf{r}} \] \end{document}   In the case the font scheme I am using has any affect as well, the fonts are:  \usepackage[utf8]{inputenx} \renewcommand{\rmdefault}{ppl}                  \linespread{1.05}                   \usepackage[scaled]{helvet} \usepackage{courier}               \usepackage{eulervm} \normalfont       \usepackage[T1]{fontenc}            \usepackage{textcomp} Estimating the most important features in a k-means cluster partition What is the command to open the shutdown dialog? I would like to use a gesture to shutdown/restart my computer and I need to know the command that launches the shutdown dialog: