How can one receive android updates?
How do I update Android on my device?
I was reading French's Vibrations &amp; Waves where he discusses Huygens-Frensel Principle.   The principle talks about how secondary sources give rise to secondary wavelets to form the displaced wavefront. However, any secondary source can form two wavelets one moving forward &amp; other towards the original source as pointed by French:     [...] The Huygen's construction would define two subsequent wavefronts , not one. In addition to a new wavefront farther away from the source, there would be another one corresponding to a wavefront back toward the surface, But we know this does not happen.    Then he writes:     If the Huygens way of visualizing wave propagation is to be acceptable, it must introduce the unidirectional property of a traveling wave. This can be achieved by requiring that the disturbance  starting out from a given point in the medium at a given instant is not equal in all directions. Specifically, if $O$ is the true original source ,&amp; $S$ is the origin of Huygens wavelet, &amp; $P$ is the point at which the disturbance is being recorded, then the effect at $P$ due to the region near $S$is a function of $f(\theta)$ of the angle $\theta$ between $OS$ &amp; $SP$.     I am not understanding how his reasoning actually averts the possiblity of formation of back-waves. Can anyone help me visualise what he is talking? How does his reasoning maintain the unidirectional propagation of waves? Can anyone explain his argument? Package incompatibilites: etoolbox, hyperref, and bm, standalone? I am trying to transition to using the etoolbox package, but seem to have run into some difficulties and they appear related to the hyperref and bm packages which to me seem totally unrelated.  The MWE example compiles since \RemoveEToolbox is defined and shows that there is no apparent problem before etoolbox was used.    Commenting out the \def\RemoveEToolbox{} line produces two problems:   With both the \renewcommand, and the usepackage{hyperref} commented, this results in "Runaway argument? Paragraph ended before \bm@test@token was complete". Including the usepackage{hyperref} (with \renewcommand commented) results in "Undefined control  sequence. \Call@AtVeryEndDocument ...cumentHook \@undefined"   But if uncomment the \renewcommand{\bm}{#1} line (effectively doing without any \bm), then this seems to compile.  I have been using this for a while now and things appeared to have been working fine, but now that I attempt to use etoolbox I seem to run into problems.  \documentclass{standalone} \def\RemoveEToolbox{}% Shows that this works fine without {etoolbox}  \usepackage{amsmath} \usepackage{xcolor} \usepackage{bm}  \ifdefined\RemoveEToolbox     \newcommand*{\iftoggle}[3]{#2}% Default to true value of "if" \else     \usepackage{etoolbox}     \newtoggle{paper}     \toggletrue{paper}      %\renewcommand{\bm}[1]{#1}% Why can't I have a normal \bm with {etoolbox}? \fi  % \usepackage{hyperref}  \begin{document}  This document is intended for  \iftoggle{paper}{paper}{electronic} distribution.  \bm{\textcolor{blue}{Solve $x^2-1=0$}}  \begin{align*}     a &amp;= b\\     \iftoggle{paper}{         c &amp;= d\\     }{}     e &amp;= f\\ \end{align*} \end{document} According to , weight decay (regularization) is not usually applied to the bias terms b why?  What is significance (intuition) behind it? Find this integral $$\operatorname I=\int\limits_{0}^{1}\dfrac{\arcsin{\sqrt{x}}}{x^4-2x^3+2x^2-x+1}\operatorname d\!x$$  My try: let $$f(x)=x^4-2x^3+2x^2-x+1$$ I found  $$f(1-x)=(1-x)^4-2(1-x)^3+2(1-x)^2-x+1=x^4-2x^3+2x^2-x+1=f(x)$$ so $$I=\int_{0}^{1}\dfrac{\arcsin{\sqrt{(1-x)}}}{x^4-2x^3+2x^2-x+1}dx$$ so $$2I=\int_{0}^{1}\dfrac{\arcsin{\sqrt{x}}+\arcsin{\sqrt{(1-x)}}}{x^4-2x^3+2x^2-x+1}dx$$ then I can't,Thank you very much bash regex with quotes? The following code  number=1 if [[ $number =~ [0-9] ]] then   echo matched fi   works. If I try to use quotes in the regex, however, it stops:  number=1 if [[ $number =~ "[0-9]" ]] then   echo matched fi   I tried "\[0-9\]", too. What am I missing?  Funnily enough,  suggests this should work.  Bash version 3.2.39. Another homework problem from my Group Theory class.  Let $a,b$ be elements of a group, $G$.  Let $\operatorname{ord}(a)=m$ and $\operatorname{ord}(b)=n$. Let $a$ and $b$ commute. Prove: If $m$ and $n$ are relatively prime, then the $\operatorname{ord}(ab)=mn$.  So I am having trouble starting off on this problem.  Here is what I believe I know:  $a^m=e$ and $b^n=e$ [as defined by the order of the elements] which leads $a^m=b^n$  $\operatorname{ord}(ab)=mn=\operatorname{ord}(ba)=nm$ as defined by commuting.  $\gcd(m,n)=1$ as defined by $m,n$ being relatively prime.    I don't know how to start this proof. Do I want to to go the route of $a^mb^n=e$?  Then $(ab)^{mn}=e$?   Any tips to start this would be greatly appreciated!!! Empty vector menu in QGIS on PC with French as default language Why does the review system disable the "First Posts" and "Late Answers" if I reached daily upvote limit? I was reviewing on , and I faced a weird thing. I can review "Close Votes", "Low Quality Posts", and "Suggested Edits" if I reached my daily vote limit, but I can't for "First Posts" and "Late Answers". Why?    If they just deserve an upvote/downvote then they should not include in the review system. But if we can improve them through leaving comments and by editing the posts then why can't we access them? How to pronounce "Stannis's"? I know that the &quot;s&quot; becomes &quot;z&quot; when it comes after a voiced sound. And it is pronounced as &quot;s&quot; when it comes after a voiceless sound. I also know rules about possessives but I don't know how natives pronounce a word when it ends in S and &quot;apostrophe S&quot; is added to it. For example: &quot;Stannis's army&quot;. Do you add another syllable to it? Like Stannisiz? or just Stannis and ignore the possessive S? I really have difficulty in pronouncing words that end in S and possessive S is attached to it. It would seem that far-away stars are at such a distance that I should be able to take a step to the side and not have the star's photons hit my eye. How do stars release so many photons to fill in such great angular distances? Most efficient way to concatenate strings? What's the most efficient way to concatenate strings? Then what is the probability that out of $n$ men $A_1,A_2,....,A_n$ each aged $x$ years,$A_1$ will die and will be the first to die Let $p$ be the probability that a man aged $x$ years will die in a year time.Then what is the probability that out of $n$ men $A_1,A_2,....,A_n$ each aged $x$ years,$A_1$ will die and will be the first to die?  The probability that a man aged $x$ years will die in a year time$=p$  The probability that a man aged $x$ years will not die in a year time$=1-p$  But from here on,i got stuck.Some hints and suggestions are welcome. Error :: You must put some 'source' URIs in your sources.list I'm trying to install PIL a python module on ubuntu   I first need to install a package called python-imaging using the following command    sudo apt-get build-dep python-imaging   When I try and do this I get the error   E: You must put some 'source' URIs in your sources.list   I saw  question whihc shows how to fix via the GUI but I'm using the command line. Does anyone know how I can fix this error..?    UPDATE: Based on the below answers I've updated my package list but I now get this error. Not sure if it is related, if not I'll start a new question as I can't find reference to the error anywhere.   E: Build-Depends dependency for python-imaging cannot be satisfied because candidate version of package python-all-dev can't satisfy version requirements ROC vs Precision-recall curves on imbalanced dataset I just finished reading  discussion. They argue that PR AUC is better than ROC AUC on imbalanced dataset.   For example, we have 10 samples in test dataset. 9 samples are positive and 1 is negative. We have a terrible model which predicts everything positive. Thus, we will have a metric that TP = 9, FP = 1, TN = 0, FN = 0.  Then, Precision = 0.9, Recall = 1.0. The precision and recall are both very high, but we have a poor classifier.  On the other hand, TPR = TP/(TP+FN) = 1.0, FPR = FP/(FP+TN) = 1.0. Because the FPR is very high, we can identify that this is not a good classifier.  Clearly, ROC is better than PR on imbalanced datasets. Can somebody explain why PR is better? Why shouldn't the denominator of the covariance estimator be n-2 rather than n-1? How to make specifics apps password protected even after passcode in iPhone? Are there any countable Hausdorff connected spaces? Do countable Hausdorff connected topological spaces exist? Does gravity affects on electrons in a noticeable way? Is there a way to force a free electron move in a low speed in order to observe it actually hitting 'on the floor'? Keeping the time stamp when syncing with Ubuntu One? I would like to keep the original time stamp of a file when synchronizing with Ubuntu One.  Now Ubuntu One is messing with my time stamps, and I no longer know when I last worked on the file.  Ubuntu One also seem to mess up time stamps on the original source host.  This really is a show stopper, and we are just about to implement Ubuntu One across the many users in the organization. When Free shipping is available hide other shipping methods except Local pickup in WooCommerce I currently have WooCommerce setup to allow free shipping on orders over a certain amount. However, I also have local pickup available and would like to allow BOTH if over a certain amount. I have the following code to remove the other rates, however it also doesn't keep the local pickup option. function fd_shipping_rates( $rates, $package ) {           $all_free_rates = array();          foreach ( $rates as $rate_id =&gt; $rate ) {         if ( 'free_shipping' === $rate-&gt;method_id ) {              $all_free_rates[ $rate_id ] = $rate;             break;         }     }          if ( empty( $all_free_rates )) {         return $rates;     } else {         return $all_free_rates;     }  } add_filter( 'woocommerce_package_rates', 'fd_shipping_rates', 10, 2 );  Any help regarding this is much appreciated! I am looking for a code solution only as I am looking to minimise unneeded plugins. EDIT: I recently found this article on  website regarding this exact issue.